A Victim of Halide Ion Segregation. How Light Soaking Affects Solar Cell Performance of Mixed Halide Lead Perovskites

DOE PAGES

Samu, Gergely F.; Janaky, Csaba; Kamat, Prashant V.

2017-07-24

Photoinduced segregation in mixed halide perovskites has a direct influence on decreasing the solar cell efficiency as segregated I-rich domains serve as charge recombination centers. Here, the changes in the external quantum efficiency mirror the spectral loss in the absorption; however, the time scale of the IPCE recovery in the dark is slower than the absorption recovery, showing the intricate nature of the photoinduced halide segregation and charge collection in solar cell devices.

Exploration of parameters influencing the self-absorption losses in luminescent solar concentrators with an experimentally validated combined ray-tracing/Monte-Carlo model

NASA Astrophysics Data System (ADS)

Krumer, Zachar; van Sark, Wilfried G. J. H. M.; de Mello Donegá, Celso; Schropp, Ruud E. I.

2013-09-01

Luminescent solar concentrators (LSCs) are low cost photovoltaic devices, which reduce the amount of necessary semiconductor material per unit area of a photovoltaic solar energy converter by means of concentration. The device is comprised of a thin plastic plate in which luminescent species (fluorophores) have been incorporated.The fluorophores absorb the solar light and radiatively re-emit a part of the energy. Total internal reflection traps most of the emitted light inside the plate and wave-guides it to a narrow side facet with a solar cell attached, where conversion into electricity occurs. The eciency of such devices is as yet rather low, due to several loss mechanisms, of which self-absorption is of high importance. Combined ray-tracing and Monte-Carlosimulations is a widely used tool for efficiency estimations of LSC-devices prior to manufacturing. We have applied this method to a model experiment, in which we analysed the impact of self-absorption onto LSC-efficiency of fluorophores with different absorption/emission-spectral overlap (Stokes-shift): several organic dyes and semiconductor quantum dots (single compound and core/shell of type-II). These results are compared with the ones obtained experimentally demonstrating a good agreement. The validated model is used to investigate systematically the influence of spectral separation and luminescence quantum efficiency on the intensity loss inconsequence of increased self-absorption. The results are used to adopt a quantity called the self-absorption cross-section and establish it as reliable criterion for self-absorption properties of materials that can be obtained from fundamental data and has a more universal scope of application, than the currently used Stokes-shift.

A Silicon–Singlet Fission Tandem Solar Cell Exceeding 100% External Quantum Efficiency with High Spectral Stability

PubMed Central

2017-01-01

After 60 years of research, silicon solar cell efficiency saturated close to the theoretical limit, and radically new approaches are needed to further improve the efficiency. The use of tandem systems raises this theoretical power conversion efficiency limit from 34% to 45%. We present the advantageous spectral stability of using voltage-matched tandem solar cells with respect to their traditional series-connected counterparts and experimentally demonstrate how singlet fission can be used to produce simple voltage-matched tandems. Our singlet fission silicon–pentacene tandem solar cell shows efficient photocurrent addition. This allows the tandem system to benefit from carrier multiplication and to produce an external quantum efficiency exceeding 100% at the main absorption peak of pentacene. PMID:28261671

Multioctave infrared supercontinuum generation in large-core As₂S₃ fibers.

PubMed

Théberge, Francis; Thiré, Nicolas; Daigle, Jean-François; Mathieu, Pierre; Schmidt, Bruno E; Messaddeq, Younès; Vallée, Réal; Légaré, François

2014-11-15

We report on infrared supercontinuum (SC) generation through laser filamentation and subsequent nonlinear propagation in a step-index As2S3 fiber. The 100 μm core and high-purity As2S3 fiber used exhibit zero-dispersion wavelength around 4.5 μm, a mid-infrared background loss of 0.2  dB/m, and a maximum loss of only 0.55  dB/m at the S-H absorption peak around 4.05 μm. When pumping with ultrashort laser pulses slightly above the S-H absorption band, broadband infrared supercontinua were generated with a 20 dB spectral flatness spanning from 1.5 up to 7 μm. The efficiency and spectral shape of the SC produced by ultrashort pulses in large-core As2S3 fiber are mainly determined by its dispersion, the S-H contaminant absorption, and the mid-infrared nonlinear absorption.

Model Order Reduction Algorithm for Estimating the Absorption Spectrum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Beeumen, Roel; Williams-Young, David B.; Kasper, Joseph M.

The ab initio description of the spectral interior of the absorption spectrum poses both a theoretical and computational challenge for modern electronic structure theory. Due to the often spectrally dense character of this domain in the quantum propagator’s eigenspectrum for medium-to-large sized systems, traditional approaches based on the partial diagonalization of the propagator often encounter oscillatory and stagnating convergence. Electronic structure methods which solve the molecular response problem through the solution of spectrally shifted linear systems, such as the complex polarization propagator, offer an alternative approach which is agnostic to the underlying spectral density or domain location. This generality comesmore » at a seemingly high computational cost associated with solving a large linear system for each spectral shift in some discretization of the spectral domain of interest. In this work, we present a novel, adaptive solution to this high computational overhead based on model order reduction techniques via interpolation. Model order reduction reduces the computational complexity of mathematical models and is ubiquitous in the simulation of dynamical systems and control theory. The efficiency and effectiveness of the proposed algorithm in the ab initio prediction of X-ray absorption spectra is demonstrated using a test set of challenging water clusters which are spectrally dense in the neighborhood of the oxygen K-edge. On the basis of a single, user defined tolerance we automatically determine the order of the reduced models and approximate the absorption spectrum up to the given tolerance. We also illustrate that, for the systems studied, the automatically determined model order increases logarithmically with the problem dimension, compared to a linear increase of the number of eigenvalues within the energy window. Furthermore, we observed that the computational cost of the proposed algorithm only scales quadratically with respect to the problem dimension.« less

Metamaterial Receivers for High Efficiency Concentrated Solar Energy Conversion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yellowhair, Julius E.; Kwon, Hoyeong; Alu, Andrea

Operation of concentrated solar power receivers at higher temperatures (>700°C) would enable supercritical carbon dioxide (sCO 2) power cycles for improved power cycle efficiencies (>50%) and cost-effective solar thermal power. Unfortunately, radiative losses at higher temperatures in conventional receivers can negatively impact the system efficiency gains. One approach to improve receiver thermal efficiency is to utilize selective coatings that enhance absorption across the visible solar spectrum while minimizing emission in the infrared to reduce radiative losses. Existing coatings, however, tend to degrade rapidly at elevated temperatures. In this report, we report on the initial designs and fabrication of spectrally selectivemore » metamaterial-based absorbers for high-temperature, high-thermal flux environments important for solarized sCO 2 power cycles. Metamaterials are structured media whose optical properties are determined by sub-wavelength structural features instead of bulk material properties, providing unique solutions by decoupling the optical absorption spectrum from thermal stability requirements. The key enabling innovative concept proposed is the use of structured surfaces with spectral responses that can be tailored to optimize the absorption and retention of solar energy for a given temperature range. In this initial study through the Academic Alliance partnership with University of Texas at Austin, we use Tungsten for its stability in expected harsh environments, compatibility with microfabrication techniques, and required optical performance. Our goal is to tailor the optical properties for high (near unity) absorptivity across the majority of the solar spectrum and over a broad range of incidence angles, and at the same time achieve negligible absorptivity in the near infrared to optimize the energy absorbed and retained. To this goal, we apply the recently developed concept of plasmonic Brewster angle to suitably designed nanostructured Tungsten surfaces. We predict that this will improve the receiver thermal efficiencies by at least 10% over current solar receivers.« less

Volume Bragg grating improves characteristic of resonantly diode-pumped Er:YAG, 1.65-μm DPSSL

NASA Astrophysics Data System (ADS)

Kudryashov, Igor; Garbuzov, Dmitri; Dubinskii, Mark

2007-02-01

Significant performance improvement of the Er(0.5%):YAG diode pumped solid state laser (DPSSL) has been achieved by pump diode spectral narrowing via implementation of external volumetric Bragg grating (VBG). Without spectral narrowing, with a pump path length of 15 mm, only 37% of 1532 nm pump was absorbed. After the VBG spectral narrowing, the absorption of the pumping radiation increased to 62%. As a result, the incident power threshold was reduced by a factor of 2.5; the efficiency increased by a factor of 1.7, resulting in a slope efficiency of ~23%. A maximum of 51 W of CW power was obtained versus 31 W without the pump spectrum narrowing.

Absorption spectrum analysis based on singular value decomposition for photoisomerization and photodegradation in organic dyes

NASA Astrophysics Data System (ADS)

Kawabe, Yutaka; Yoshikawa, Toshio; Chida, Toshifumi; Tada, Kazuhiro; Kawamoto, Masuki; Fujihara, Takashi; Sassa, Takafumi; Tsutsumi, Naoto

2015-10-01

In order to analyze the spectra of inseparable chemical mixtures, many mathematical methods have been developed to decompose them into the components relevant to species from series of spectral data obtained under different conditions. We formulated a method based on singular value decomposition (SVD) of linear algebra, and applied it to two example systems of organic dyes, being successful in reproducing absorption spectra assignable to cis/trans azocarbazole dyes from the spectral data after photoisomerization and to monomer/dimer of cyanine dyes from those during photodegaradation process. For the example of photoisomerization, polymer films containing the azocarbazole dyes were prepared, which have showed updatable holographic stereogram for real images with high performance. We made continuous monitoring of absorption spectrum after optical excitation and found that their spectral shapes varied slightly after the excitation and during recovery process, of which fact suggested the contribution from a generated photoisomer. Application of the method was successful to identify two spectral components due to trans and cis forms of azocarbazoles. Temporal evolution of their weight factors suggested important roles of long lifetimed cis states in azocarbazole derivatives. We also applied the method to the photodegradation of cyanine dyes doped in DNA-lipid complexes which have shown efficient and durable optical amplification and/or lasing under optical pumping. The same SVD method was successful in the extraction of two spectral components presumably due to monomer and H-type dimer. During the photodegradation process, absorption magnitude gradually decreased due to decomposition of molecules and their decaying rates strongly depended on the spectral components, suggesting that the long persistency of the dyes in DNA-complex related to weak tendency of aggregate formation.

Spectral Monte Carlo simulation of collimated solar irradiation transfer in a water-filled prismatic louver.

PubMed

Cai, Yaomin; Guo, Zhixiong

2018-04-20

The Monte Carlo model was developed to simulate the collimated solar irradiation transfer and energy harvest in a hollow louver made of silica glass and filled with water. The full solar spectrum from the air mass 1.5 database was adopted and divided into various discrete bands for spectral calculations. The band-averaged spectral properties for the silica glass and water were obtained. Ray tracing was employed to find the solar energy harvested by the louver. Computational efficiency and accuracy were examined through intensive comparisons of different band partition approaches, various photon numbers, and element divisions. The influence of irradiation direction on the solar energy harvest efficiency was scrutinized. It was found that within a 15° polar angle of incidence, the harvested solar energy in the louver was high, and the total absorption efficiency reached 61.2% under normal incidence for the current louver geometry.

Absorption spectrum of a two-level system subjected to a periodic pulse sequence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fotso, H. F.; Dobrovitski, V. V.

We investigate how the quantum control of a two-level system (TLS) coupled to photons can modify and tune the TLS’s photon absorption spectrum. Tuning and controlling the emission and the absorption is of much interest e.g. for the development of efficient interfaces between stationary and flying qubits in modern architectures for quantum computation and quantum communication. We consider the periodic pulse control, where the TLS is subjected to a periodic sequence of the near-resonant Rabi driving pulses, each pulse implementing a 180° rotation. For small inter-pulse delays, the absorption spectrum features a pronounced peak of stimulated emission at the pulsemore » frequency, as well as equidistant satellite peaks with smaller spectral weights. As long as the detuning between the carrier frequency of the driving and the TLS transition frequency remains moderate, this spectral shape shows little change. Therefore, the quantum control allows shifting the absorption peak to a desired position, and locks the absorption peak to the carrier frequency of the driving pulses. Detailed description of the spectrum, and its evolution as a function time, the inter-pulse spacing and the detuning, is presented.« less

Absorption spectrum of a two-level system subjected to a periodic pulse sequence

DOE PAGES

Fotso, H. F.; Dobrovitski, V. V.

2017-06-01

We investigate how the quantum control of a two-level system (TLS) coupled to photons can modify and tune the TLS’s photon absorption spectrum. Tuning and controlling the emission and the absorption is of much interest e.g. for the development of efficient interfaces between stationary and flying qubits in modern architectures for quantum computation and quantum communication. We consider the periodic pulse control, where the TLS is subjected to a periodic sequence of the near-resonant Rabi driving pulses, each pulse implementing a 180° rotation. For small inter-pulse delays, the absorption spectrum features a pronounced peak of stimulated emission at the pulsemore » frequency, as well as equidistant satellite peaks with smaller spectral weights. As long as the detuning between the carrier frequency of the driving and the TLS transition frequency remains moderate, this spectral shape shows little change. Therefore, the quantum control allows shifting the absorption peak to a desired position, and locks the absorption peak to the carrier frequency of the driving pulses. Detailed description of the spectrum, and its evolution as a function time, the inter-pulse spacing and the detuning, is presented.« less

Tandem luminescent solar concentrators based on engineered quantum dots

NASA Astrophysics Data System (ADS)

Wu, Kaifeng; Li, Hongbo; Klimov, Victor I.

2018-02-01

Luminescent solar concentrators (LSCs) can serve as large-area sunlight collectors for terrestrial and space-based photovoltaics. Due to their high emission efficiencies and readily tunable emission and absorption spectra, colloidal quantum dots have emerged as a new and promising type of LSC fluorophore. Spectral tunability of the quantum dots also facilitates the realization of stacked multilayered LSCs, where enhanced performance is obtained through spectral splitting of incident sunlight, as in multijunction photovoltaics. Here, we demonstrate a large-area (>230 cm2) tandem LSC based on two types of nearly reabsorption-free quantum dots spectrally tuned for optimal solar-spectrum splitting. This prototype device exhibits a high optical quantum efficiency of 6.4% for sunlight illumination and solar-to-electrical power conversion efficiency of 3.1%. The efficiency gains due to the tandem architecture over single-layer devices quickly increase with increasing LSC size and can reach more than 100% in structures with window sizes of more than 2,500 cm2.

UV-Vis-NIR luminescence properties and energy transfer mechanism of LiSrPO4:Eu2+, Pr3+ suitable for solar spectral convertor.

PubMed

Chen, Yan; Wang, Jing; Liu, Chunmeng; Tang, Jinke; Kuang, Xiaojun; Wu, Mingmei; Su, Qiang

2013-02-11

An efficient near-infrared (NIR) phosphor LiSrPO(4):Eu(2+), Pr(3+) is synthesized by solid-state reaction and systematically investigated using x-ray diffraction, diffuse reflection spectrum, photoluminescence spectra at room temperature and 3 K, and the decay curves. The UV-Vis-NIR energy transfer mechanism is proposed based on these results. The results demonstrate Eu(2+) can be an efficient sensitizer for harvesting UV photon and greatly enhancing the NIR emission of Pr(3+) between 960 and 1060 nm through efficient energy feeding by allowed 4f-5d absorption of Eu(2+) with high oscillator strength. Eu(2+)/Pr(3+) may be an efficient donor-acceptor pair as solar spectral converter for Si solar cells.

Absorption and dissociative photoionization cross sections of NH3 from 80 to 1120 A

NASA Technical Reports Server (NTRS)

Samson, James A. R.; Haddad, G. N.; Kilcoyne, L. D.

1987-01-01

The total absorption, photoionization, and dissociative photoionization cross sections of ammonia have been measured from 80 to 1120 A. All possible fragment ions have been observed including doubly ionized ammonia. The absolute ionization efficiencies have also been measured in this spectral range. The appearance potentials of the fragment ions have been measured and are compared with the calculated appearance potentials derived from published heats of formation and ionization potentials of the fragments.

Light Coupling and Trapping in Ultrathin Cu(In,Ga)Se2 Solar Cells Using Dielectric Scattering Patterns.

PubMed

van Lare, Claire; Yin, Guanchao; Polman, Albert; Schmid, Martina

2015-10-27

We experimentally demonstrate photocurrent enhancement in ultrathin Cu(In,Ga)Se2 (CIGSe) solar cells with absorber layers of 460 nm by nanoscale dielectric light scattering patterns printed by substrate conformal imprint lithography. We show that patterning the front side of the device with TiO2 nanoparticle arrays results in a small photocurrent enhancement in almost the entire 400-1200 nm spectral range due to enhanced light coupling into the cell. Three-dimensional finite-difference time-domain simulations are in good agreement with external quantum efficiency measurements. Patterning the Mo/CIGSe back interface using SiO2 nanoparticles leads to strongly enhanced light trapping, increasing the efficiency from 11.1% for a flat to 12.3% for a patterned cell. Simulations show that optimizing the array geometry could further improve light trapping. Including nanoparticles at the Mo/CIGSe interface leads to substantially reduced parasitic absorption in the Mo back contact. Parasitic absorption in the back contact can be further reduced by fabricating CIGSe cells on top of a SiO2-patterned In2O3:Sn (ITO) back contact. Simulations show that these semitransparent cells have similar spectrally averaged reflection and absorption in the CIGSe active layer as a Mo-based patterned cell, demonstrating that the absorption losses in the Mo can be partially turned into transmission through the semitransparent geometry.

Colored dissolved organic matter in Tampa Bay, Florida

USGS Publications Warehouse

Chen, Z.; Hu, C.; Conmy, R.N.; Muller-Karger, F.; Swarzenski, P.

2007-01-01

Absorption and fluorescence of colored dissolved organic matter (CDOM) and concentrations of dissolved organic carbon (DOC), chlorophyll and total suspended solids in Tampa Bay and its adjacent rivers were examined in June and October of 2004. Except in Old Tampa Bay (OTB), the spatial distribution of CDOM showed a conservative relationship with salinity in June, 2004 (aCDOM(400) = − 0.19 × salinity + 6.78, R2 = 0.98, n = 17, salinity range = 1.1–32.5) with little variations in absorption spectral slope and fluorescence efficiency. This indicates that CDOM distribution was dominated by mixing. In October, 2004, CDOM distribution was nonconservative with an average absorption coefficient (aCDOM(400), ∼ 7.76 m-1) about seven times higher than that in June (∼ 1.11 m-1). The nonconservative behavior was caused largely by CDOM removal at intermediate salinities (e.g., aCDOM(400) removal > 15% at salinity ∼ 13.0), which likely resulted from photobleaching due to stronger stratification. The spatial and seasonal distributions of CDOM in Tampa Bay showed that the two largest rivers, the Alafia River (AR) and Hillsborough River (HR) were dominant CDOM sources to most of the bay. In OTB, however, CDOM showed distinctive differences: lower absorption coefficient, higher absorption spectral slopes, and lower ratios of CDOM absorption to DOC and higher fluorescence efficiency. These differences may have stemmed from (1) changes in CDOM composition by more intensive photobleaching due to the longer residence time of water mass in OTB; (2) other sources of CDOM than the HR/AR inputs, such as local creeks, streams, groundwater, and/or bottom re-suspension. Average CDOM absorption in Tampa Bay at 443 nm, aCDOM(443), was about five times higher in June and about ten times higher in October than phytoplankton pigment absorption, aph(443), indicating that blue light attenuation in the water column was dominated by CDOM rather than by phytoplankton absorption throughout the year.

Solar cells based on particulate structure of active layer: Investigation of light absorption by an ordered system of spherical submicron silicon particles

NASA Astrophysics Data System (ADS)

Miskevich, Alexander A.; Loiko, Valery A.

2015-12-01

Enhancement of the performance of photovoltaic cells through increasing light absorption due to optimization of an active layer is considered. The optimization consists in creation of particulate structure of active layer. The ordered monolayers and multilayers of submicron crystalline silicon (c-Si) spherical particles are examined. The quasicrystalline approximation (QCA) and the transfer matrix method (TMM) are used to calculate light absorption in the wavelength range from 0.28 μm to 1.12 μm. The integrated over the terrestial solar spectral irradiance "Global tilt" ASTM G173-03 absorption coefficient is calculated. In the wavelength range of small absorption index of c-Si (0.8-1.12 μm) the integral absorption coefficient of monolayer can be more than 20 times higher than the one of the plane-parallel plate of the equivalent volume of material. In the overall considered range (0.28-1.12 μm) the enhancement factor up to ~1.45 for individual monolayer is observed. Maximum value of the spectral absorption coefficient approaches unity for multilayers consisting of large amount of sparse monolayers of small particles. Multilayers with variable concentration and size of particles in the monolayer sequences are considered. Absorption increasing by such gradient multilayers as compared to the non-gradient ones is illustrated. The considered structures are promising for creation of high efficiency thin-film solar cells.

Spectral matching research for light-emitting diode-based neonatal jaundice therapeutic device light source

NASA Astrophysics Data System (ADS)

Gan, Ruting; Guo, Zhenning; Lin, Jieben

2015-09-01

To decrease the risk of bilirubin encephalopathy and minimize the need for exchange transfusions, we report a novel design for light source of light-emitting diode (LED)-based neonatal jaundice therapeutic device (NJTD). The bilirubin absorption spectrum in vivo was regarded as target. Based on spectral constructing theory, we used commercially available LEDs with different peak wavelengths and full width at half maximum as matching light sources. Simple genetic algorithm was first proposed as the spectral matching method. The required LEDs number at each peak wavelength was calculated, and then, the commercial light source sample model of the device was fabricated to confirm the spectral matching technology. In addition, the corresponding spectrum was measured and the effect was analyzed finally. The results showed that fitted spectrum was very similar to the target spectrum with 98.86 % matching degree, and the actual device model has a spectrum close to the target with 96.02 % matching degree. With higher fitting degree and efficiency, this matching algorithm is very suitable for light source matching technology of LED-based spectral distribution, and bilirubin absorption spectrum in vivo will be auspicious candidate for the target spectrum of new LED-based NJTD light source.

Exciton Hybridisation in Organic-Inorganic Semiconductor Microcavities

DTIC Science & Technology

2002-02-01

hybridizing organic and inorganic semiconductors in microcavities to produce a highly efficient light source that could be either a laser or a very efficient...such process may also have an important effect on the spectral distribution of photoluminescence from the microcavity and can be considered as a...Absorption (solid dots) and photoluminescence emission (open circles) of a thin film of J-aggregated cyanine dyes in a PVA matrix. Note, the chemical

Optoelectronic semiconductor device and method of fabrication

DOEpatents

Cui, Yi; Zhu, Jia; Hsu, Ching-Mei; Fan, Shanhui; Yu, Zongfu

2014-11-25

An optoelectronic device comprising an optically active layer that includes a plurality of domes is presented. The plurality of domes is arrayed in two dimensions having a periodicity in each dimension that is less than or comparable with the shortest wavelength in a spectral range of interest. By virtue of the plurality of domes, the optoelectronic device achieves high performance. A solar cell having high energy-conversion efficiency, improved absorption over the spectral range of interest, and an improved acceptance angle is presented as an exemplary device.

Approach for determining the contributions of phytoplankton, colored organic material, and nonalgal particles to the total spectral absorption in marine waters.

PubMed

Lin, Junfang; Cao, Wenxi; Wang, Guifeng; Hu, Shuibo

2013-06-20

Using a data set of 1333 samples, we assess the spectral absorption relationships of different wave bands for phytoplankton (ph) and particles. We find that a nonlinear model (second-order quadratic equations) delivers good performance in describing their spectral characteristics. Based on these spectral relationships, we develop a method for partitioning the total absorption coefficient into the contributions attributable to phytoplankton [a(ph)(λ)], colored dissolved organic material [CDOM; a(CDOM)(λ)], and nonalgal particles [NAP; a(NAP)(λ)]. This method is validated using a data set that contains 550 simultaneous measurements of phytoplankton, CDOM, and NAP from the NASA bio-Optical Marine Algorithm Dataset. We find that our method is highly efficient and robust, with significant accuracy: the relative root-mean-square errors (RMSEs) are 25.96%, 38.30%, and 19.96% for a(ph)(443), a(CDOM)(443), and the CDOM exponential slope, respectively. The performance is still satisfactory when the method is applied to water samples from the northern South China Sea as a regional case. The computed and measured absorption coefficients (167 samples) agree well with the RMSEs, i.e., 18.50%, 32.82%, and 10.21% for a(ph)(443), a(CDOM)(443), and the CDOM exponential slope, respectively. Finally, the partitioning method is applied directly to an independent data set (1160 samples) derived from the Bermuda Bio-Optics Project that contains relatively low absorption values, and we also obtain good inversion accuracy [RMSEs of 32.37%, 32.57%, and 11.52% for a(ph)(443), a(CDOM)(443), and the CDOM exponential slope, respectively]. Our results indicate that this partitioning method delivers satisfactory performance for the retrieval of a(ph), a(CDOM), and a(NAP). Therefore, this may be a useful tool for extracting absorption coefficients from in situ measurements or remotely sensed ocean-color data.

Opo lidar sounding of trace atmospheric gases in the 3 - 4 μm spectral range

NASA Astrophysics Data System (ADS)

Romanovskii, Oleg A.; Sadovnikov, Sergey A.; Kharchenko, Olga V.; Yakovlev, Semen V.

2018-04-01

The applicability of a KTA crystal-based laser system with optical parametric oscillators (OPO) generation to lidar sounding of the atmosphere in the spectral range 3-4 μm is studied in this work. A technique developed for lidar sounding of trace atmospheric gases (TAG) is based on differential absorption lidar (DIAL) method and differential optical absorption spectroscopy (DOAS). The DIAL-DOAS technique is tested to estimate its efficiency for lidar sounding of atmospheric trace gases. The numerical simulation performed shows that a KTA-based OPO laser is a promising source of radiation for remote DIAL-DOAS sounding of the TAGs under study along surface tropospheric paths. A possibility of using a PD38-03-PR photodiode for the DIAL gas analysis of the atmosphere is shown.

Latest developments in resonantly diode-pumped Er:YAG lasers

NASA Astrophysics Data System (ADS)

Kudryashov, Igor; Garbuzov, Dmitri; Dubinskii, Mark

2007-04-01

Significant performance improvement of the Er(0.5%):YAG diode pumped solid state laser (DPSSL) has been achieved by pump diode spectral narrowing via implementation of an external volumetric Bragg grating (VBG). Without spectral narrowing, with a pump path length of 15 mm, only 37% of 1532 nm pump was absorbed. After the VBG spectral narrowing, the absorption of the pumping radiation increased to 62 - 70%. As a result, the incident power threshold was reduced by a factor of 2.5, and the efficiency increased by a factor of 1.7, resulting in a slope efficiency of ~23 - 30%. A maximum of 51 W of CW power was obtained versus 31 W without the pump spectrum narrowing. More than 180 mJ QCW pulse output energy was obtained in a stable-unstable resonator configuration with a beam quality of M2 = 1.3 in the stable direction and M2 = 1.1 in the unstable direction. The measured slope efficiency was 0.138 J/J with a threshold energy of 0.91 J.

Triplet photosensitizers: from molecular design to applications.

PubMed

Zhao, Jianzhang; Wu, Wanhua; Sun, Jifu; Guo, Song

2013-06-21

Triplet photosensitizers (PSs) are compounds that can be efficiently excited to the triplet excited state which subsequently act as catalysts in photochemical reactions. The name is originally derived from compounds that were used to transfer the triplet energy to other compounds that have only a small intrinsic triplet state yield. Triplet PSs are not only used for triplet energy transfer, but also for photocatalytic organic reactions, photodynamic therapy (PDT), photoinduced hydrogen production from water and triplet-triplet annihilation (TTA) upconversion. A good PS should exhibit strong absorption of the excitation light, a high yield of intersystem crossing (ISC) for efficient production of the triplet state, and a long triplet lifetime to allow for the reaction with a reactant molecule. Most transition metal complexes show efficient ISC, but small molar absorption coefficients in the visible spectral region and short-lived triplet excited states, which make them unsuitable as triplet PSs. One obstacle to the development of new triplet PSs is the difficulty in predicting the ISC of chromophores, especially of organic compounds without any heavy atoms. This review article summarizes some molecular design rationales for triplet PSs, based on the molecular structural factors that facilitate ISC. The design of transition metal complexes with large molar absorption coefficients in the visible spectral region and long-lived triplet excited states is presented. A new method of using a spin converter to construct heavy atom-free organic triplet PSs is discussed, with which ISC becomes predictable, C60 being an example. To enhance the performance of triplet PSs, energy funneling based triplet PSs are proposed, which show broadband absorption in the visible region. Applications of triplet PSs in photocatalytic organic reactions, hydrogen production, triplet-triplet annihilation upconversion and luminescent oxygen sensing are briefly introduced.

Spectral- and size-resolved mass absorption efficiency of mineral dust aerosols in the shortwave spectrum: a simulation chamber study

NASA Astrophysics Data System (ADS)

Caponi, Lorenzo; Formenti, Paola; Massabó, Dario; Di Biagio, Claudia; Cazaunau, Mathieu; Pangui, Edouard; Chevaillier, Servanne; Landrot, Gautier; Andreae, Meinrat O.; Kandler, Konrad; Piketh, Stuart; Saeed, Thuraya; Seibert, Dave; Williams, Earle; Balkanski, Yves; Prati, Paolo; Doussin, Jean-François

2017-06-01

This paper presents new laboratory measurements of the mass absorption efficiency (MAE) between 375 and 850 nm for 12 individual samples of mineral dust from different source areas worldwide and in two size classes: PM10. 6 (mass fraction of particles of aerodynamic diameter lower than 10.6 µm) and PM2. 5 (mass fraction of particles of aerodynamic diameter lower than 2.5 µm). The experiments were performed in the CESAM simulation chamber using mineral dust generated from natural parent soils and included optical and gravimetric analyses. The results show that the MAE values are lower for the PM10. 6 mass fraction (range 37-135 × 10-3 m2 g-1 at 375 nm) than for the PM2. 5 (range 95-711 × 10-3 m2 g-1 at 375 nm) and decrease with increasing wavelength as λ-AAE, where the Ångström absorption exponent (AAE) averages between 3.3 and 3.5, regardless of size. The size independence of AAE suggests that, for a given size distribution, the dust composition did not vary with size for this set of samples. Because of its high atmospheric concentration, light absorption by mineral dust can be competitive with black and brown carbon even during atmospheric transport over heavy polluted regions, when dust concentrations are significantly lower than at emission. The AAE values of mineral dust are higher than for black carbon (˜ 1) but in the same range as light-absorbing organic (brown) carbon. As a result, depending on the environment, there can be some ambiguity in apportioning the aerosol absorption optical depth (AAOD) based on spectral dependence, which is relevant to the development of remote sensing of light-absorbing aerosols and their assimilation in climate models. We suggest that the sample-to-sample variability in our dataset of MAE values is related to regional differences in the mineralogical composition of the parent soils. Particularly in the PM2. 5 fraction, we found a strong linear correlation between the dust light-absorption properties and elemental iron rather than the iron oxide fraction, which could ease the application and the validation of climate models that now start to include the representation of the dust composition, as well as for remote sensing of dust absorption in the UV-vis spectral region.

Large-scale cauliflower-shaped hierarchical copper nanostructures for efficient photothermal conversion.

PubMed

Fan, Peixun; Wu, Hui; Zhong, Minlin; Zhang, Hongjun; Bai, Benfeng; Jin, Guofan

2016-08-14

Efficient solar energy harvesting and photothermal conversion have essential importance for many practical applications. Here, we present a laser-induced cauliflower-shaped hierarchical surface nanostructure on a copper surface, which exhibits extremely high omnidirectional absorption efficiency over a broad electromagnetic spectral range from the UV to the near-infrared region. The measured average hemispherical absorptance is as high as 98% within the wavelength range of 200-800 nm, and the angle dependent specular reflectance stays below 0.1% within the 0-60° incident angle. Such a structured copper surface can exhibit an apparent heating up effect under the sunlight illumination. In the experiment of evaporating water, the structured surface yields an overall photothermal conversion efficiency over 60% under an illuminating solar power density of ∼1 kW m(-2). The presented technology provides a cost-effective, reliable, and simple way for realizing broadband omnidirectional light absorptive metal surfaces for efficient solar energy harvesting and utilization, which is highly demanded in various light harvesting, anti-reflection, and photothermal conversion applications. Since the structure is directly formed by femtosecond laser writing, it is quite suitable for mass production and can be easily extended to a large surface area.

Anti-Hermitian photodetector facilitating efficient subwavelength photon sorting.

PubMed

Kim, Soo Jin; Kang, Ju-Hyung; Mutlu, Mehmet; Park, Joonsuk; Park, Woosung; Goodson, Kenneth E; Sinclair, Robert; Fan, Shanhui; Kik, Pieter G; Brongersma, Mark L

2018-01-22

The ability to split an incident light beam into separate wavelength bands is central to a diverse set of optical applications, including imaging, biosensing, communication, photocatalysis, and photovoltaics. Entirely new opportunities are currently emerging with the recently demonstrated possibility to spectrally split light at a subwavelength scale with optical antennas. Unfortunately, such small structures offer limited spectral control and are hard to exploit in optoelectronic devices. Here, we overcome both challenges and demonstrate how within a single-layer metafilm one can laterally sort photons of different wavelengths below the free-space diffraction limit and extract a useful photocurrent. This chipscale demonstration of anti-Hermitian coupling between resonant photodetector elements also facilitates near-unity photon-sorting efficiencies, near-unity absorption, and a narrow spectral response (∼ 30 nm) for the different wavelength channels. This work opens up entirely new design paradigms for image sensors and energy harvesting systems in which the active elements both sort and detect photons.

Enhanced infrared detectors using resonant structures combined with thin type-II superlattice absorbers

DOE PAGES

Goldflam, Michael D.; Kadlec, Emil Andrew; Olson, Ben V.; ...

2016-12-22

Here we examined the spectral responsivity of a 1.77μm thick type-II superlattice based long-wave infrared detector in combination with metallic nanoantennas. Coupling between the Fabry-Pérot cavity formed by the semiconductor layer and the resonant nanoantennas on its surface enables spectral selectivity, while also increasing peak quantum efficiency to over 50%. Electromagnetic simulations reveal that this high responsivity is a direct result of field-enhancement in the absorber layer, enabling significant absorption in spite of the absorber’s subwavelength thickness. Notably, thinning of the absorbing material could ultimately yield lower photodetector noise through a reduction in dark current while improving photocarrier collection efficiency.more » The temperature- and incident-angle-independent spectral response observed in these devices allows for operation over a wide range of temperatures and optical systems. This detector paradigm demonstrates potential benefits to device performance with applications throughout the infrared.« less

Modeling ocean primary production: Sensitivity to spectral resolution of attenuation and absorption of light

NASA Astrophysics Data System (ADS)

Kettle, Helen; Merchant, Chris J.

2008-08-01

Modeling the vertical penetration of photosynthetically active radiation (PAR) through the ocean, and its utilization by phytoplankton, is fundamental to simulating marine primary production. The variation of attenuation and absorption of light with wavelength suggests that photosynthesis should be modeled at high spectral resolution, but this is computationally expensive. To model primary production in global 3d models, a balance between computer time and accuracy is necessary. We investigate the effects of varying the spectral resolution of the underwater light field and the photosynthetic efficiency of phytoplankton ( α∗), on primary production using a 1d coupled ecosystem ocean turbulence model. The model is applied at three sites in the Atlantic Ocean (CIS (∼60°N), PAP (∼50°N) and ESTOC (∼30°N)) to include the effect of different meteorological forcing and parameter sets. We also investigate three different methods for modeling α∗ - as a fixed constant, varying with both wavelength and chlorophyll concentration [Bricaud, A., Morel, A., Babin, M., Allali, K., Claustre, H., 1998. Variations of light absorption by suspended particles with chlorophyll a concentration in oceanic (case 1) waters. Analysis and implications for bio-optical models. J. Geophys. Res. 103, 31033-31044], and using a non-spectral parameterization [Anderson, T.R., 1993. A spectrally averaged model of light penetration and photosynthesis. Limnol. Oceanogr. 38, 1403-1419]. After selecting the appropriate ecosystem parameters for each of the three sites we vary the spectral resolution of light and α∗ from 1 to 61 wavebands and study the results in conjunction with the three different α∗ estimation methods. The results show modeled estimates of ocean primary productivity are highly sensitive to the degree of spectral resolution and α∗. For accurate simulations of primary production and chlorophyll distribution we recommend a spectral resolution of at least six wavebands if α∗ is a function of wavelength and chlorophyll, and three wavebands if α∗ is a fixed value.

Role of a Helix B Lysine Residue in the Photoactive Site in Channelrhodopsins

PubMed Central

Li, Hai; Govorunova, Elena G.; Sineshchekov, Oleg A.; Spudich, John L.

2014-01-01

In most studied microbial rhodopsins two conserved carboxylic acid residues (the homologs of Asp-85 and Asp-212 in bacteriorhodopsin) and an arginine residue (the homolog of Arg-82) form a complex counterion to the protonated retinylidene Schiff base, and neutralization of the negatively charged carboxylates causes red shifts of the absorption maximum. In contrast, the corresponding neutralizing mutations in some relatively low-efficiency channelrhodopsins (ChRs) result in blue shifts. These ChRs do not contain a lysine residue in the second helix, conserved in higher efficiency ChRs (Lys-132 in the crystallized ChR chimera). By action spectroscopy of photoinduced channel currents in HEK293 cells and absorption spectroscopy of detergent-purified pigments, we found that in tested ChRs the Lys-132 homolog controls the direction of spectral shifts in the mutants of the photoactive site carboxylic acid residues. Analysis of double mutants shows that red spectral shifts occur when this Lys is present, whether naturally or by mutagenesis, and blue shifts occur when it is replaced with a neutral residue. A neutralizing mutation of the Lys-132 homolog alone caused a red spectral shift in high-efficiency ChRs, whereas its introduction into low-efficiency ChR1 from Chlamydomonas augustae (CaChR1) caused a blue shift. Taking into account that the effective charge of the carboxylic acid residues is a key factor in microbial rhodopsin spectral tuning, these findings suggest that the Lys-132 homolog modulates their pKa values. On the other hand, mutation of the Arg-82 homolog that fulfills this role in bacteriorhodopsin caused minimal spectral changes in the tested ChRs. Titration revealed that the pKa of the Asp-85 homolog in CaChR1 lies in the alkaline region unlike in most studied microbial rhodopsins, but is substantially decreased by introduction of a Lys-132 homolog or neutralizing mutation of the Asp-212 homolog. In the three ChRs tested the Lys-132 homolog also alters channel current kinetics. PMID:24739160

Excitation of Terahertz Charge Transfer Plasmons in Metallic Fractal Structures

NASA Astrophysics Data System (ADS)

Ahmadivand, Arash; Gerislioglu, Burak; Sinha, Raju; Vabbina, Phani Kiran; Karabiyik, Mustafa; Pala, Nezih

2017-08-01

There have been extensive researches on terahertz (THz) plasmonic structures supporting resonant modes to demonstrate nano and microscale devices with high efficiency and responsivity as well as frequency selectivity. Here, using antisymmetric plasmonic fractal Y-shaped (FYS) structures as building blocks, we introduce a highly tunable four-member fractal assembly to support charge transfer plasmons (CTPs) and classical dipolar resonant modes with significant absorption cross section in the THz domain. We first present that the unique geometrical nature of the FYS system and corresponding spectral response allow for supporting intensified dipolar plasmonic modes under polarised light exposure in a standalone structure. In addition to classical dipolar mode, for the very first time, we demonstrated CTPs in the THz domain due to the direct shuttling of the charges across the metallic fractal microantenna which led to sharp resonant absorption peaks. Using both numerical and experimental studies, we have investigated and confirmed the excitation of the CTP modes and highly tunable spectral response of the proposed plasmonic fractal structure. This understanding opens new and promising horizons for tightly integrated THz devices with high efficiency and functionality.

Medical applications of VIS/NIR spectroscopy of human tissue surfaces by a novel portable instrumentation

NASA Astrophysics Data System (ADS)

Otto, Thomas; Stock, Volker; Schmidt, Wolf-Dieter; Liebold, Kristin; Fassler, Dieter; Wollina, Uwe; Fritzsch, Uwe; Gessner, Thomas

2001-11-01

In medical diagnostics, non invasive optical techniques will become common at a variety of applications because they contribute to objectivity and precision. The spectral properties of human tissue are an important field of interest. They offer opportunities of detection of skin diseases and of evaluation of chronic wounds. In the visible range, the hemoglobin absorption corresponds to blood microcirculation and the melanin absorption to the skin-type. Two types of diode-array equipment will be described: a combined VIS-NIR spectrometer system from J&M Aalen/Germany (400 nm to 1600 nm) and a stand-alone spectrometer from COLOUR CONTROL Farbmesstechnik Chemnitz/Germany (400 nm to 1000 nm). Non-contacting sensing is essential for investigating chronic wounds (no disturbances of blood microcirculation by contact pressure). The spectroscopic VIS-NIR readings of chronic wounds mainly depend on the absorption of hemoglobin and water. Multivariate analysis was applied for an objective spectral classification of eight different wound scores. Some results regarding spectral measurements of wounds and skin will be discussed. The spectrometer of COLOUR CONTROL was tested in dental surgery. To select dentures, its color has to be determined exactly to meet beauty culture demands. Color determination by dentist is not sufficient enough because of possible metameric effects of illumination. Results of spectral evaluation of denture material and human teeth will be given. Medical examination requires portable and ease equipment suitable for precise measurements. This is solved by a modular measurement system comprising microcomputer, display, light source, fiber probe, and diode-array spectrometer. It is efficient to process primary spectral data to appropriate medical interpretations.

Performance characterization of a pressure-tuned wide-angle Michelson interferometric spectral filter for high spectral resolution lidar

NASA Astrophysics Data System (ADS)

Seaman, Shane T.; Cook, Anthony L.; Scola, Salvatore J.; Hostetler, Chris A.; Miller, Ian; Welch, Wayne

2015-09-01

High Spectral Resolution Lidar (HSRL) is typically realized using an absorption filter to separate molecular returns from particulate returns. NASA Langley Research Center (LaRC) has designed and built a Pressure-Tuned Wide-Angle Michelson Interferometer (PTWAMI) as an alternate means to separate the two types of atmospheric returns. While absorption filters only work at certain wavelengths and suffer from low photon efficiency due to light absorption, an interferometric spectral filter can be designed for any wavelength and transmits nearly all incident photons. The interferometers developed at LaRC employ an air spacer in one arm, and a solid glass spacer in the other. Field widening is achieved by specific design and selection of the lengths and refractive indices of these two arms. The principal challenge in using such an interferometer as a spectral filter for HSRL aboard aircraft is that variations in glass temperature and air pressure cause changes in the interferometer's optical path difference. Therefore, a tuning mechanism is needed to actively accommodate for these changes. The pressure-tuning mechanism employed here relies on changing the pressure in an enclosed, air-filled arm of the interferometer to change the arm's optical path length. However, tuning using pressure will not adjust for tilt, mirror warpage, or thermally induced wavefront error, so the structural, thermal, and optical behavior of the device must be well understood and optimized in the design and manufacturing process. The PTWAMI has been characterized for particulate transmission ratio, wavefront error, and tilt, and shows acceptable performance for use in an HSRL instrument.

Spectral matching technology for light-emitting diode-based jaundice photodynamic therapy device

NASA Astrophysics Data System (ADS)

Gan, Ru-ting; Guo, Zhen-ning; Lin, Jie-ben

2015-02-01

The objective of this paper is to obtain the spectrum of light-emitting diode (LED)-based jaundice photodynamic therapy device (JPTD), the bilirubin absorption spectrum in vivo was regarded as target spectrum. According to the spectral constructing theory, a simple genetic algorithm as the spectral matching algorithm was first proposed in this study. The optimal combination ratios of LEDs were obtained, and the required LEDs number was then calculated. Meanwhile, the algorithm was compared with the existing spectral matching algorithms. The results show that this algorithm runs faster with higher efficiency, the switching time consumed is 2.06 s, and the fitting spectrum is very similar to the target spectrum with 98.15% matching degree. Thus, blue LED-based JPTD can replace traditional blue fluorescent tube, the spectral matching technology that has been put forward can be applied to the light source spectral matching for jaundice photodynamic therapy and other medical phototherapy.

Broadband ultrafast transient absorption of multiple exciton dynamics in lead sulfide nanocrystals

NASA Astrophysics Data System (ADS)

Gesuele, Felice; Wong, Chee Wei; Sfeir, Matthew; Misewich, James; Koh, Weonkyu; Murray, Christopher

2011-03-01

Multiple exciton generation (MEG) is under intense investigation as potential third-generation solar photovoltaics with efficiencies beyond the Shockley-Queisser limit. We examine PbS nanocrystals, dispersed and vigorously stirred in TCE solution, by means of supercontinuum femtosecond transient absorption (TA). TA spectra show the presence of first and second order bleaches for the 1Sh-Se and 1Ph-Pe excitonic transition while photoinduced absorption for the 1Sh,e-Ph,e transitions. We found evidence of carrier multiplication (MEG for single absorbed photon) from the analysis of the first and second order bleaches, in the limit of low number of absorbed photons (Nabs ~ 0.01), for energy three times and four times the Energy gap. The MEG efficiency, derived from the ratio between early-time to long-time TA signal, presents a strongly dispersive behavior with maximum red shifted respect the first absorption peak. Analysis of population dynamics shows that in presence of biexciton, the 1Sh-Se bleach peak is red-shifted indicating a positive binding energy. MEG efficiency estimation will be discussed with regards to spectral integration, correlated higher-order and first excitonic transitions, as well as the nanocrystal morphologies.

Spectral Absorption Properties of Atmospheric Aerosols

NASA Technical Reports Server (NTRS)

Bergstrom, R. W.; Pilewskie, P.; Russell, P. B.; Redemann, J.; Bond, T. C.; Quinn, P. K.; Sierau, B.

2007-01-01

We have determined the solar spectral absorption optical depth of atmospheric aerosols for specific case studies during several field programs (three cases have been reported previously; two are new results). We combined airborne measurements of the solar net radiant flux density and the aerosol optical depth with a detailed radiative transfer model for all but one of the cases. The field programs (SAFARI 2000, ACE Asia, PRIDE, TARFOX, INTEX-A) contained aerosols representing the major absorbing aerosol types: pollution, biomass burning, desert dust and mixtures. In all cases the spectral absorption optical depth decreases with wavelength and can be approximated with a power-law wavelength dependence (Absorption Angstrom Exponent or AAE). We compare our results with other recent spectral absorption measurements and attempt to briefly summarize the state of knowledge of aerosol absorption spectra in the atmosphere. We discuss the limitations in using the AAE for calculating the solar absorption. We also discuss the resulting spectral single scattering albedo for these cases.

Conversion of laser energy to gas kinetic energy

NASA Technical Reports Server (NTRS)

Caledonia, G. E.

1977-01-01

Techniques for the gas-phase absorption of laser energy with ultimate conversion to heat or directed kinetic energy are reviewed. It is shown that the efficiency of resonance absorption by the vibration/rotation bands of the working gas can be enhanced by operating at sufficiently high pressures so that the linewidths of the absorbing transition exceed the line spacing. Within this limit, the gas can absorb continuously over the full spectral region of the band, and bleaching can be minimized since the manifold of molecular vibrational levels can simultaneously absorb the laser radiation.

Large-scale cauliflower-shaped hierarchical copper nanostructures for efficient photothermal conversion

NASA Astrophysics Data System (ADS)

Fan, Peixun; Wu, Hui; Zhong, Minlin; Zhang, Hongjun; Bai, Benfeng; Jin, Guofan

2016-07-01

Efficient solar energy harvesting and photothermal conversion have essential importance for many practical applications. Here, we present a laser-induced cauliflower-shaped hierarchical surface nanostructure on a copper surface, which exhibits extremely high omnidirectional absorption efficiency over a broad electromagnetic spectral range from the UV to the near-infrared region. The measured average hemispherical absorptance is as high as 98% within the wavelength range of 200-800 nm, and the angle dependent specular reflectance stays below 0.1% within the 0-60° incident angle. Such a structured copper surface can exhibit an apparent heating up effect under the sunlight illumination. In the experiment of evaporating water, the structured surface yields an overall photothermal conversion efficiency over 60% under an illuminating solar power density of ~1 kW m-2. The presented technology provides a cost-effective, reliable, and simple way for realizing broadband omnidirectional light absorptive metal surfaces for efficient solar energy harvesting and utilization, which is highly demanded in various light harvesting, anti-reflection, and photothermal conversion applications. Since the structure is directly formed by femtosecond laser writing, it is quite suitable for mass production and can be easily extended to a large surface area.Efficient solar energy harvesting and photothermal conversion have essential importance for many practical applications. Here, we present a laser-induced cauliflower-shaped hierarchical surface nanostructure on a copper surface, which exhibits extremely high omnidirectional absorption efficiency over a broad electromagnetic spectral range from the UV to the near-infrared region. The measured average hemispherical absorptance is as high as 98% within the wavelength range of 200-800 nm, and the angle dependent specular reflectance stays below 0.1% within the 0-60° incident angle. Such a structured copper surface can exhibit an apparent heating up effect under the sunlight illumination. In the experiment of evaporating water, the structured surface yields an overall photothermal conversion efficiency over 60% under an illuminating solar power density of ~1 kW m-2. The presented technology provides a cost-effective, reliable, and simple way for realizing broadband omnidirectional light absorptive metal surfaces for efficient solar energy harvesting and utilization, which is highly demanded in various light harvesting, anti-reflection, and photothermal conversion applications. Since the structure is directly formed by femtosecond laser writing, it is quite suitable for mass production and can be easily extended to a large surface area. Electronic supplementary information (ESI) available: XRD patterns of the fs laser structured Cu surface as produced and after the photothermal conversion test, directly measured temperature values on Cu surfaces, temperature rise on Cu surfaces at varied solar irradiation angles, comparison of the white light and IR images of the structured Cu surface with the polished Cu surface, temperature rise on the peripheral zones of the blue coating surface. See DOI: 10.1039/c6nr03662g

Thermophysical Properties of Matter - The TPRC Data Series. Volume 9. Thermal Radiative Properties - Coatings

DTIC Science & Technology

1972-01-01

Coatings - Normal Spectral Reflectance 67 32 Boron Nitride + Diatomaceous Earth Pigmented Coatings - Normal Spectral Reflectance 69 Notet Figure...Absorptance 106 53* Clay + Titanium Dioxide Plgmented Coatings - Normal Solar Absorptance 107 54 Dlatomaceous Earth ...Plgmented Coatings - Normal Spectral Reflectance 112 55* Dlatomaceous Earth Plgmented Coatings - Normal Solar Absorptance 116 56

Synthesis, structure, DNA/BSA binding and antibacterial studies of NNO tridentate Schiff base metal complexes

NASA Astrophysics Data System (ADS)

Sakthi, Marimuthu; Ramu, Andy

2017-12-01

A new salicylaldehyde derived 2,4-diiodo-6-((2-phenylaminoethylimino)methyl)phenol Schiff base(L) and its transition metal complexes of the type MLCl where, M = Cu(II), Ni(II), Co(II), Mn(II) and Zn(II) have been synthesized. The coordination mode of Schiff base holding NNO donor atoms with metal ions was well investigated by elemental analysis, ESI-mass as well as IR, UV-vis, CV and NMR spectral studies. The binding efficiency and mode of these complexes with biological macromolecules viz., herring sperm DNA (HS- DNA) and bovine serum albumin (BSA) have been explored through various spectroscopic techniques. The characteristic changes in absorption, emission and, circular dichroism spectra of the complexes with DNA indicate the noticeable interaction between them. From the all spectral information complexes could interact with DNA via non-intercalation mode of binding. The hyperchromisim in absorption band and hypochromisim in emission intensity of BSA with different complex concentrations shown significant information, and the binding affinity value has been predicted from Stern-Volmer plots. Further, all the complexes could cleave the circular plasmid pUC19 DNA efficiently by using an activator H2O2. The ligand and all metal(II) complexes showed good antibacterial activities. The molecular docking studies of the complexes with DNA were performed in order to make a comparison and conclusion with spectral technic results.

Spectral Absorption By Particulate Impurities in Snow Determined By Photometric Analysis Of Filters

NASA Astrophysics Data System (ADS)

Grenfell, T. C.; Doherty, S. J.; Clarke, A. D.

2009-12-01

Our work is motivated by the 1983-84 survey by Clarke and Noone (Atmos. Environ., 1985) of soot in Arctic snow. Our objective is to resurvey the original area they covered and to extend the observations around the entire Arctic Basin under the auspices of the IPY program. We use the filtering and integrating sandwich techniques developed by Clarke and Noone to process the snow samples. Among the advantages of this method are that (a) it provides a direct measure of light absorption and the result is closely related to the actual absorption of sunlight in the snow or ice, (b) processing and filtering of the snow samples can be carried out in remote locations and (c) it is not necessary to transport large quantities of snow back to our home laboratory. Here we describe the construction, calibration, and some applications of an integrating sphere spectrophotometer system designed to take advantage of recent advances in instrumentation to improve the accuracy of measurements of absorption by particulate impurities collected on nuclepore filters used in our survey. Filter loading in terms of effective black carbon (BC) amount is determined together with the ratio of non-BC to BC concentrations using a set of reference filters with known loadings of Monarch 71 BC prepared by A. D. Clarke. The new spectrophotometer system has (a) system stability of approximately 0.5%; (b) precision relative to ADC standards of 3-4% for filter loadings greater than about 0.5 microgm Carbon/cm2. (c) We can distinguish BC from non-BC from relative spectral shapes of the energy absorption curves with an accuracy that depends on our knowledge of the spectral absorption curves of the non-BC components; and (d) by-eye estimates are consistent with spectrophotometric results. The major outstanding uncertainty is the appropriate value to use for the mass absorption efficiency for BC.

Absorption Efficiencies of Forsterite. I: DDA Explorations in Grain Shape and Size

NASA Technical Reports Server (NTRS)

Lindsay, Sean S.; Wooden, Diane; Harker, David E.; Kelley, Michael S.; Woodward, Charles E.; Murphy, Jim R.

2013-01-01

We compute the absorption efficiency (Q(sub abs)) of forsterite using the discrete dipole approximation (DDA) in order to identify and describe what characteristics of crystal grain shape and size are important to the shape, peak location, and relative strength of spectral features in the 8 - 40 micron wavelength range. Using the DDSCAT code, we compute Q(sub abs) for non-spherical polyhedral grain shapes with a(sub eff) = 0.1 micron. The shape characteristics identified are: 1) elongation/reduction along one of three crystallographic axes; 2) asymmetry, such that all three crystallographic axes are of different lengths; and 3) the presence of crystalline faces that are not parallel to a specific crystallographic axis, e.g., non-rectangular prisms and (di)pyramids. Elongation/reduction dominates the locations and shapes of spectral features near 10, 11, 16, 23.5, 27, and 33.5 micron, while asymmetry and tips are secondary shape effects. Increasing grain sizes (0.1 - 1.0 micron) shifts the 10, 11 micron features systematically towards longer wavelengths and relative to the 11 micron feature increases the strengths and slightly broadens the longer wavelength features. Seven spectral shape classes are established for crystallographic a-, b-, and c-axes and include columnar and platelet shapes plus non-elongated or equant grain shapes. The spectral shape classes and the effects of grain size have practical application in identifying or excluding columnar, platelet or equant forsterite grain shapes in astrophysical environs. Identification of the shape characteristics of forsterite from 8 - 40 micron spectra provides a potential means to probe the temperatures at which forsterite formed.

[Study of the Detecting System of CH4 and SO2 Based on Spectral Absorption Method and UV Fluorescence Method].

PubMed

Wang, Shu-tao; Wang, Zhi-fang; Liu, Ming-hua; Wei, Meng; Chen, Dong-ying; Wang, Xing-long

2016-01-01

According to the spectral absorption characteristics of polluting gases and fluorescence characteristics, a time-division multiplexing detection system is designed. Through this system we can detect Methane (CH4) and sulfur dioxide (SO2) by using spectral absorption method and the SO2 can be detected by using UV fluorescence method. The system consists of four parts: a combination of a light source which could be switched, the common optical path, the air chamber and the signal processing section. The spectral absorption characteristics and fluorescence characteristics are measured first. Then the experiment of detecting CH4 and SO2 through spectral absorption method and the experiment of detecting SO2 through UV fluorescence method are conducted, respectively. Through measuring characteristics of spectral absorption and fluorescence, we get excitation wavelengths of SO2 and CH4 measured by spectral absorption method at the absorption peak are 280 nm and 1.64 μm, respectively, and the optimal excitation wavelength of SO2 measured by UV fluorescence method is 220 nm. we acquire the linear relation between the concentration of CH4 and relative intensity and the linear relation between the concentration of SO2 and output voltage after conducting the experiment of spectral absorption method, and the linearity are 98.7%, 99.2% respectively. Through the experiment of UV fluorescence method we acquire that the relation between the concentration of SO2 and the voltage is linear, and the linearity is 99.5%. Research shows that the system is able to be applied to detect the polluted gas by absorption spectrum method and UV fluorescence method. Combing these two measurement methods decreases the costing and the volume, and this system can also be used to measure the other gases. Such system has a certain value of application.

Single frequency 1560nm Er:Yb fiber amplifier with 207W output power and 50.5% slope efficiency

NASA Astrophysics Data System (ADS)

Creeden, Daniel; Pretorius, Herman; Limongelli, Julia; Setzler, Scott D.

2016-03-01

High power fiber lasers/amplifiers in the 1550nm spectral region have not scaled as rapidly as Yb-, Tm-, or Ho-doped fibers. This is primarily due to the low gain of the erbium ion. To overcome the low pump absorption, Yb is typically added as a sensitizer. Although this helps the pump absorption, it also creates a problem with parasitic lasing of the Yb ions under strong pumping conditions, which generally limits output power. Other pump schemes have shown high efficiency through resonant pumping of erbium only without the need for Yb as a sensitizer [1-2]. Although this can enable higher power scaling due to a decrease in the thermal loading, resonant pumping methods require long fiber lengths due to pump bleaching, which may limit the power scaling which can be achieved for single frequency output. By using an Er:Yb fiber and pumping in the minima of the Yb pump absorption at 940nm, we have been able to simultaneously generate high power, single frequency output at 1560nm while suppressing the 1-micron ASE and enabling higher efficiency compared to pumping at the absorption peak at 976nm. We have demonstrated single frequency amplification (540Hz linewidth) to 207W average output power with 49.3% optical efficiency (50.5% slope efficiency) in an LMA Er:Yb fiber. We believe this is the highest reported efficiency from a high power 9XXnm pumped Er:Yb-doped fiber amplifier. This is significantly more efficient that the best-reported efficiency for high power Er:Yb doped fibers, which, to-date, has been limited to ~41% slope efficiency [3].

The Optical Emission and Absorption Properties of Silicon-Germanium Superlattice Structures Grown on Non-Conventional Silicon Substrate Orientation

DTIC Science & Technology

1994-08-01

evidence needed to someday design and build a silicon- based infrared detector that can efficiently detect light at normal incidence. I chose to...detector a. spectral response b. dark current c. qutiantuam efficiency MAKE DEVICE Figure 1. A simple schematic diagram describing a basic materials... based . If we can extend the capabilities of silicon into the near infrared (iR), the nation would be well- positioned to exploit our advantage in this

Structural, optical absorption and photoluminescence spectral studies of Sm3+ ions in Alkaline-Earth Boro Tellurite glasses

NASA Astrophysics Data System (ADS)

Siva Rama Krishna Reddy, K.; Swapna, K.; Mahamuda, Sk.; Venkateswarlu, M.; Srinivas Prasad, M. V. V. K.; Rao, A. S.; Prakash, G. Vijaya

2018-05-01

Sm3+ ions doped Alkaline-Earth Boro Tellurite (AEBT) glasses were prepared by using conventional melt quenching technique and characterized using the spectroscopic techniques such as FT-IR, optical absorption, emission and decay spectral measurements to understand their utility in optoelectronic devices. From absorption spectra, the bonding parameters, nephelauxetic ratios were determined to know the nature of bonding between Sm3+ ions and its surrounding ligands. From the measured oscillator strengths, the Judd-Ofelt (J-O) intensity parameters were evaluated and in turn used to estimate various radiative parameters for the fluorescent levels of Sm3+ ions in AEBT glasses. The PL spectra of Sm3+ ions exhibit three emission bands corresponding to the transitions 4G5/2 → 6H5/2, 6H7/2 and 6H9/2 in the visible region for which the emission cross-sections and branching ratios were evaluated. The decay spectral profiles measured for 4G5/2 → 6H7/2 transition showed single exponential for lower concentration and non-exponential for higher concentration of doped rare earth ion in the as prepared glasses. Conversion of decay spectral profiles from single to non-exponential have been analyzed using Inokuti-Hirayama (I-H) model to understand the energy transfer mechanism involved in the decay process. CIE Chromaticity coordinates were measured using emission spectral data to identify the exact region of emission from the as-prepared glasses. From the evaluated radiative parameters, emission cross-sections and quantum efficiencies, it was observed that AEBT glass with 1 mol% of Sm3+ ions is more suitable for designing optoelectronic devices.

All-metal meta-surfaces for narrowband light absorption and high performance sensing

NASA Astrophysics Data System (ADS)

Liu, Zhengqi; Liu, Guiqiang; Fu, Guolan; Liu, Xiaoshan; Huang, Zhenping; Gu, Gang

2016-11-01

We report an experimental scheme for high performance sensing by an all-metal meta-surface (AMMS) platform. A dual-band resonant absorption spectrum with a bandwidth down to a single-digit nanometer level and an absorbance up to 89% is achieved due to the surface lattice resonances supported by the resonators array and their hybridization coupling with the particle plasmon resonances. The sensing application in the analysis of the sodium chloride solution has been demonstrated, where remarkable changes from a spectral ‘dark state’ to ‘bright state’ and vice versa are observed. Sensing performance factors of the figure of merit exceeding 50 and the spectral intensity change related FoM* up to 1075 are simultaneously achieved. The corresponding detection limit is as low as 8.849  ×  10-6 RIU. These features make such an AMMS-based sensor a promising route for efficient bio-chemical sensing, etc.

Narrowband thermal radiation from closed-end microcavities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kohiyama, Asaka; Shimizu, Makoto; Iguchi, Fumitada

2015-10-07

High spectral selectivity of thermal radiation is important for achieving high-efficiency energy systems. In this study, intense, narrowband, and low directional absorption/radiation were observed in closed-end microcavity which is a conventional open-end microcavity covered by a semi-transparent thin metal film. The quality factor (Q factor) of optical absorption band strongly depended on the film electrical conductivity. Asymmetric and narrow absorption band with a Q factor of 25 at 1.28 μm was obtained for a 6-nm-thick Au film. Numerical simulations suggest that the formation of a fixed-end mode at the cavity aperture contributes to the narrowband optical absorption. The closed-end microcavity filledmore » with SiO{sub 2} exhibits intense and isotropic thermal radiation over a wide solid angle according to numerical simulation. The narrow and asymmetric absorption spectrum was experimentally confirmed in a model of closed-end microcavity.« less

Spectral Properties and Dynamics of Gold Nanorods Revealed by EMCCD Based Spectral-Phasor Method

PubMed Central

Chen, Hongtao; Digman, Michelle A.

2015-01-01

Gold nanorods (NRs) with tunable plasmon-resonant absorption in the near-infrared region have considerable advantages over organic fluorophores as imaging agents. However, the luminescence spectral properties of NRs have not been fully explored at the single particle level in bulk due to lack of proper analytic tools. Here we present a global spectral phasor analysis method which allows investigations of NRs' spectra at single particle level with their statistic behavior and spatial information during imaging. The wide phasor distribution obtained by the spectral phasor analysis indicates spectra of NRs are different from particle to particle. NRs with different spectra can be identified graphically in corresponding spatial images with high spectral resolution. Furthermore, spectral behaviors of NRs under different imaging conditions, e.g. different excitation powers and wavelengths, were carefully examined by our laser-scanning multiphoton microscope with spectral imaging capability. Our results prove that the spectral phasor method is an easy and efficient tool in hyper-spectral imaging analysis to unravel subtle changes of the emission spectrum. Moreover, we applied this method to study the spectral dynamics of NRs during direct optical trapping and by optothermal trapping. Interestingly, spectral shifts were observed in both trapping phenomena. PMID:25684346

Multi-hump potentials for efficient wave absorption in the numerical solution of the time-dependent Schrödinger equation

NASA Astrophysics Data System (ADS)

Silaev, A. A.; Romanov, A. A.; Vvedenskii, N. V.

2018-03-01

In the numerical solution of the time-dependent Schrödinger equation by grid methods, an important problem is the reflection and wrap-around of the wave packets at the grid boundaries. Non-optimal absorption of the wave function leads to possible large artifacts in the results of numerical simulations. We propose a new method for the construction of the complex absorbing potentials for wave suppression at the grid boundaries. The method is based on the use of the multi-hump imaginary potential which contains a sequence of smooth and symmetric humps whose widths and amplitudes are optimized for wave absorption in different spectral intervals. We show that this can ensure a high efficiency of absorption in a wide range of de Broglie wavelengths, which includes wavelengths comparable to the width of the absorbing layer. Therefore, this method can be used for high-precision simulations of various phenomena where strong spreading of the wave function takes place, including the phenomena accompanying the interaction of strong fields with atoms and molecules. The efficiency of the proposed method is demonstrated in the calculation of the spectrum of high-order harmonics generated during the interaction of hydrogen atoms with an intense infrared laser pulse.

UV and VUV spectroscopy and photochemistry of small molecules in a supersonic jet

NASA Technical Reports Server (NTRS)

Ruehl, E.; Vaida, V.

1990-01-01

UV and VUV absorption and emission spectroscopy is used to probe jet cooled molecules, free radicals, and clusters in the gas phase. Due to efficient cooling inhomogeneous effects on spectral line widths are eliminated. Therefore from these spectra, both structural and dynamical information is obtained. The photoproducts of these reactions are probed by resonance enhanced multiphoton ionization.

Radiation and Temperature Hard Multi-Pixel Avalanche Photodiodes

NASA Technical Reports Server (NTRS)

Bensaoula, Abdelhak (Inventor); Starikov, David (Inventor); Pillai, Rajeev (Inventor)

2017-01-01

The structure and method of fabricating a radiation and temperature hard avalanche photodiode with integrated radiation and temperature hard readout circuit, comprising a substrate, an avalanche region, an absorption region, and a plurality of Ohmic contacts are presented. The present disclosure provides for tuning of spectral sensitivity and high device efficiency, resulting in photon counting capability with decreased crosstalk and reduced dark current.

Ultrawide Spectral Response of CIGS Solar Cells Integrated with Luminescent Down-Shifting Quantum Dots.

PubMed

Jeong, Ho-Jung; Kim, Ye-Chan; Lee, Soo Kyung; Jeong, Yonkil; Song, Jin-Won; Yun, Ju-Hyung; Jang, Jae-Hyung

2017-08-02

Conventional Cu(In 1-x ,Ga x )Se 2 (CIGS) solar cells exhibit poor spectral response due to parasitic light absorption in the window and buffer layers at the short wavelength range between 300 and 520 nm. In this study, the CdSe/CdZnS core/shell quantum dots (QDs) acting as a luminescent down-shifting (LDS) layer were inserted between the MgF 2 antireflection coating and the window layer of the CIGS solar cell to improve light harvesting in the short wavelength range. The LDS layer absorbs photons in the short wavelength range and re-emits photons in the 609 nm range, which are transmitted through the window and buffer layer and absorbed in the CIGS layer. The average external quantum efficiency in the parasitic light absorption region (300-520 nm) was enhanced by 51%. The resulting short circuit current density of 34.04 mA/cm 2 and power conversion efficiency of 14.29% of the CIGS solar cell with the CdSe/CdZnS QDs were improved by 4.35 and 3.85%, respectively, compared with those of the conventional solar cells without QDs.

[Spectral properties of new photosensitizers for photodynamic diagnosis and therapy].

PubMed

Li, Bu-hong; Xie, Shu-sen; Lu, Zu-kang

2002-12-01

The spectral properties of new photosensitizer ZnPcS2P2, PsD-007 and HMME, as well as traditional photosensitizer HpD have been studied by comparing their spectra in physiological saline and in physiological saline with 10 percent serum. Experimental results show that the maximum absorption peaks for PsD-007, HMME and HpD in the physiological saline with 10 percent serum appear at 400 nm in the soret region, while at 670 nm for ZnPcS2P2. The fluorescence excitation spectra closely resemble the absorption spectra. When excited by the light at the wavelengths of 413 and 514.5 nm, the fluorescence emission peaks for PsD-007, HMME and HpD appear at 625 and 690 nm, respectively. The fluorescent excitation efficiency of the same photosensitizer with the same concentration excited by the light at the wavelength of 413 nm is about three fold higher than that at 514.5 nm. Furthermore, the fluorescent excitation efficiency is the highest for HMME, but is lower for HpD and lowest for PsD-007. These results are significant in the selection of photosensitizers for photodynamic diagnosis and therapy.

Solar spectral conversion for improving the photosynthetic activity in algae reactors.

PubMed

Wondraczek, Lothar; Batentschuk, Miroslaw; Schmidt, Markus A; Borchardt, Rudolf; Scheiner, Simon; Seemann, Benjamin; Schweizer, Peter; Brabec, Christoph J

2013-01-01

Sustainable biomass production is expected to be one of the major supporting pillars for future energy supply, as well as for renewable material provision. Algal beds represent an exciting resource for biomass/biofuel, fine chemicals and CO2 storage. Similar to other solar energy harvesting techniques, the efficiency of algal photosynthesis depends on the spectral overlap between solar irradiation and chloroplast absorption. Here we demonstrate that spectral conversion can be employed to significantly improve biomass growth and oxygen production rate in closed-cycle algae reactors. For this purpose, we adapt a photoluminescent phosphor of the type Ca0.59Sr0.40Eu0.01S, which enables efficient conversion of the green part of the incoming spectrum into red light to better match the Qy peak of chlorophyll b. Integration of a Ca0.59Sr0.40Eu0.01S backlight converter into a flat panel algae reactor filled with Haematococcus pluvialis as a model species results in significantly increased photosynthetic activity and algae reproduction rate.

Temperature and pressure dependence of dichloro-difluoromethane (CF2C12) absorption coefficients for CO2 waveguide laser radiation

NASA Technical Reports Server (NTRS)

Harward, C. N.

1977-01-01

Measurements were performed to determine the pressure and temperature dependence of CFM-12 absorption coefficients for CO2 waveguide laser radiation. The absorption coefficients of CFM-12 for CO2 waveguide laser radiation were found to have no spectral structure within small spectral bandwidths around the CO2 waveguide laser lines in the CO2 spectral band for pressures above 20 torr. All of the absorption coefficients for the CO2 laser lines studied are independent of pressure above 100 torr, except for the P(36) laser CO2 spectral band. The absorption coefficients associated with the P(42) line in the same band showed the greatest change with temperature, and it also has the largest value of all the lines studied.

Photosensitive function of encapsulated dye in carbon nanotubes.

PubMed

Yanagi, Kazuhiro; Iakoubovskii, Konstantin; Matsui, Hiroyuki; Matsuzaki, Hiroyuki; Okamoto, Hiroshi; Miyata, Yasumitsu; Maniwa, Yutaka; Kazaoui, Said; Minami, Nobutsugu; Kataura, Hiromichi

2007-04-25

Single-wall carbon nanotubes (SWCNTs) exhibit resonant absorption localized in specific spectral regions. To expand the light spectrum that can be utilized by SWCNTs, we have encapsulated squarylium dye into SWCNTs and clarified its microscopic structure and photosensitizing function. X-ray diffraction and polarization-resolved optical absorption measurements revealed that the encapsulated dye molecules are located at an off center position inside the tubes and aligned to the nanotube axis. Efficient energy transfer from the encapsulated dye to SWCNTs was clearly observed in the photoluminescence spectra. Enhancement of transient absorption saturation in the S1 state of the semiconducting SWCNTs was detected after the photoexcitation of the encapsulated dye, which indicates that ultrafast (<190 fs) energy transfer occurred from the dye to the SWCNTs.

Balancing the Power-to-Load Ratio for a Novel Variable Geometry Wave Energy Converter with Nonideal Power Take-Off in Regular Waves: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tom, Nathan M; Yu, Yi-Hsiang; Wright, Alan D

This work attempts to balance power absorption against structural loading for a novel variable geometry wave energy converter. The variable geometry consists of four identical flaps that will be opened in ascending order starting with the flap closest to the seafloor and moving to the free surface. The influence of a pitch motion constraint on power absorption when utilizing a nonideal power take-off (PTO) is examined and found to reduce the losses associated with bidirectional energy flow. The power-to-load ratio is evaluated using pseudo-spectral control to determine the optimum PTO torque based on a multiterm objective function. The pseudo-spectral optimalmore » control problem is extended to include load metrics in the objective function, which may now consist of competing terms. Separate penalty weights are attached to the surge-foundation force and PTO control torque to tune the optimizer performance to emphasize either power absorption or load shedding. PTO efficiency is not included in the objective function, but the penalty weights are utilized to limit the force and torque amplitudes, thereby reducing losses associated with bidirectional energy flow. Results from pseudo-spectral control demonstrate that shedding a portion of the available wave energy can provide greater reductions in structural loads and reactive power.« less

Color centers inside crystallic active media

NASA Astrophysics Data System (ADS)

Mierczyk, Zygmunt; Kaczmarek, Slawomir M.; Kopczynski, Krzysztof

1995-03-01

This paper presents research results on color centers induced by radiation of a xenon lamp in non doped crystals of yttrium aluminum garnet Y3Al5O12 (YAG), strontium- lanthanum aluminate SrLaAlO4 (SLAO), strontium-lanthanum gallate SrLaGa3O7 (SLGO), and in doped crystals: Nd:YAG, Cr, Tm, Ho:YAG (CTH:YAG), Nd:SLAO and Nd:SLGO. In all these investigated crystals under the influence of intensive exposure by xenon lamp radiation additional bands connected with centers O-2, O2 and centers F came up near the short-wave absorption edge. In the case of doped crystals the observed processes are much more complicated. In crystals CTH:YAG the greatest perturbations in relation to basic state are present at the short-wave absorption edge, as well as on areas of absorption bands of ions Cr+3 and Tm+3 conditioning the sensibilization process of ions Ho+3. These spectral structure disturbances essentially influence the efficiency of this process, as proven during generating investigations. In the case of SrLaGa3O7:Nd+3 under the influence of exposure substantial changes of absorption spectrum occurred on spectral areas 346 divided by 368 nm, 429 divided by 441 nm and 450 divided by 490 nm. Those changes have an irreversible character. They disappear not before the plate is being held at oxidizing atmosphere. Investigations of laser rods Nd:SLGO, CTH:YAG, and Nd:YAG in a free generation demonstrated that the color centers of these crystals are induced by pomp radiation from the spectral area up to 450 nm.

Broadband, Spectrally Flat, Graphene-based Terahertz Modulators.

PubMed

Shi, Fenghua; Chen, Yihang; Han, Peng; Tassin, Philippe

2015-12-02

Advances in the efficient manipulation of terahertz waves are crucial for the further development of terahertz technology, promising applications in many diverse areas, such as biotechnology and spectroscopy, to name just a few. Due to its exceptional electronic and optical properties, graphene is a good candidate for terahertz electro-absorption modulators. However, graphene-based modulators demonstrated to date are limited in bandwidth due to Fabry-Perot oscillations in the modulators' substrate. Here, a novel method is demonstrated to design electrically controlled graphene-based modulators that can achieve broadband and spectrally flat modulation of terahertz beams. In our design, a graphene layer is sandwiched between a dielectric and a slightly doped substrate on a metal reflector. It is shown that the spectral dependence of the electric field intensity at the graphene layer can be dramatically modified by optimizing the structural parameters of the device. In this way, the electric field intensity can be spectrally flat and even compensate for the dispersion of the graphene conductivity, resulting in almost invariant absorption in a wide frequency range. Modulation depths up to 76% can be achieved within a fractional operational bandwidth of over 55%. It is expected that our modulator designs will enable the use of terahertz technology in applications requiring broadband operation. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High-performance dispersive Raman and absorption spectroscopy as tools for drug identification

NASA Astrophysics Data System (ADS)

Pawluczyk, Olga; Andrey, Sam; Nogas, Paul; Roy, Andrew; Pawluczyk, Romuald

2009-02-01

Due to increasing availability of pharmaceuticals from many sources, a need is growing to quickly and efficiently analyze substances in terms of the consistency and accuracy of their chemical composition. Differences in chemical composition occur at very low concentrations, so that highly sensitive analytical methods become crucial. Recent progress in dispersive spectroscopy with the use of 2-dimensional detector arrays, permits for signal integration along a long (up to 12 mm long) entrance slit of a spectrometer, thereby increasing signal to noise ratio and improving the ability to detect small concentration changes. This is achieved with a non-scanning, non-destructive system. Two different methods using P&P Optica high performance spectrometers were used. High performance optical dispersion Raman and high performance optical absorption spectroscopy were employed to differentiate various acetaminophen-containing drugs, such as Tylenol and other generic brands, which differ in their ingredients. A 785 nm excitation wavelength was used in Raman measurements and strong Raman signals were observed in the spectral range 300-1800 cm-1. Measurements with the absorption spectrometer were performed in the wavelength range 620-1020 nm. Both Raman and absorption techniques used transmission light spectrometers with volume phase holographic gratings and provided sufficient spectral differences, often structural, allowing for drug differentiation.

Spectral and non-spectral interferences in the determination of thallium in environmental materials using electrothermal atomization and vaporization techniques—a case study

NASA Astrophysics Data System (ADS)

Vale, Maria Goreti R.; Welz, Bernhard

2002-12-01

The literature on the determination of Tl in environmental samples using electrothermal atomization (ETA) and vaporization (ETV) techniques has been reviewed with special attention devoted to potential interferences and their control. Chloride interference, which is due to the formation of the volatile monochloride in the condensed phase, is the most frequently observed problem. Due to its high dissociation energy (88 kcal/mol), TlCl is difficult to dissociate in the gas phase and is easily lost. The best means of controlling this interference in ETA is atomization under isothermal conditions according to the stabilized temperature platform furnace concept, and the use of reduced palladium as a modifier. An alternative approach appears to be the 'fast furnace' concept, wherein both the use of a modifier and the pyrolysis stage are omitted. This concept requires an efficient background correction system, and high-resolution continuum-source atomic absorption spectrometry (HR-CS AAS) appears to offer the best results. This chloride interference can also cause significant problems when ETV techniques are used. Among the spectral interferences found in the determination of thallium are those due to Pd, the most efficient modifier, and Fe, which is frequently found at high concentrations in environmental samples. Both interferences are due to nearby atomic lines, and are observed only when deuterium background correction and relatively high atomization temperatures are used. A more serious spectral interference is that due to the molecular absorption spectrum of SO 2, which has a maximum around the Tl line and exhibits a pronounced rotational fine structure. HR-CS AAS again showed the best performance in coping with this interference.

Holographic spectrum-splitting optical systems for solar photovoltaics

NASA Astrophysics Data System (ADS)

Zhang, Deming

Solar energy is the most abundant source of renewable energy available. The relatively high cost prevents solar photovoltaic (PV) from replacing fossil fuel on a larger scale. In solar PV power generation the cost is reduced with more efficient PV technologies. In this dissertation, methods to improve PV conversion efficiency with holographic optical components are discussed. The tandem multiple-junction approach has achieved very high conversion efficiency. However it is impossible to manufacture tandem PV cells at a low cost due to stringent fabrication standards and limited material types that satisfy lattice compatibility. Current produced by the tandem multi-junction PV cell is limited by the lowest junction due to series connection. Spectrum-splitting is a lateral multi-junction concept that is free of lattice and current matching constraints. Each PV cell can be optimized towards full absorption of a spectral band with tailored light-trapping schemes. Holographic optical components are designed to achieve spectrum-splitting PV energy conversion. The incident solar spectrum is separated onto multiple PV cells that are matched to the corresponding spectral band. Holographic spectrum-splitting can take advantage of existing and future low-cost technologies that produces high efficiency thin-film solar cells. Spectrum-splitting optical systems are designed and analyzed with both transmission and reflection holographic optical components. Prototype holograms are fabricated and high optical efficiency is achieved. Light-trapping in PV cells increases the effective optical path-length in the semiconductor material leading to improved absorption and conversion efficiency. It has been shown that the effective optical path length can be increased by a factor of 4n2 using diffusive surfaces. Ultra-light-trapping can be achieved with optical filters that limit the escape angle of the diffused light. Holographic reflection gratings have been shown to act as angle-wavelength selective filters that can function as ultra-light-trapping filters. Results from an experimental reflection hologram are used to model the absorption enhancement factor for a silicon solar cell and light-trapping filter. The result shows a significant improvement in current generation for thin-film silicon solar cells under typical operating conditions.

Effect of phonon-bath dimensionality on the spectral tuning of single-photon emitters in the Purcell regime

NASA Astrophysics Data System (ADS)

Chassagneux, Yannick; Jeantet, Adrien; Claude, Théo; Voisin, Christophe

2018-05-01

We develop a theoretical frame to investigate the spectral dependence of the brightness of a single-photon source made of a solid-state nanoemitter embedded in a high-quality factor microcavity. This study encompasses the cases of localized excitons embedded in a one-, two-, or three-dimensional matrix. The population evolution is calculated based on a spin-boson model, using the noninteracting blip approximation. We find that the spectral dependence of the single-photon source brightness (hereafter called spectral efficiency) can be expressed analytically through the free-space emission and absorption spectra of the emitter, the vacuum Rabi splitting, and the loss rates of the system. In other words, the free-space spectrum of the emitter encodes all the relevant information on the interaction between the exciton and the phonon bath to obtain the dynamics of the cavity-coupled system. We compute numerically the spectral efficiency for several types of localized emitters differing by the phonon bath dimensionality. In particular, in low-dimensional systems where this interaction is enhanced, a pronounced asymmetric energy exchange between the emitter and the cavity on the phonon sidebands yields a considerable extension of the tuning range of the source through phonon-assisted cavity feeding, possibly surpassing that of a purely resonant system.

Spectral and laser properties of Er3+/Yb3+/Ce3+ tri-doped Ca3NbGa3Si2O14 crystal at 1.55 µm

NASA Astrophysics Data System (ADS)

Gong, Guoliang; Chen, Yujin; Lin, Yanfu; Huang, Jianhua; Gong, Xinghong; Luo, Zundu; Huang, Yidong

2018-04-01

An Er3+/Yb3+/Ce3+ tri-doped Ca3NbGa3Si2O14 (CNGS) crystal was grown by the Czochralski method. Spectral properties of the crystal, including the polarized absorption and fluorescence spectra, the fluorescence decay, as well as the energy transfer efficiency from Yb3+ to Er3+ were investigated in detail. End-pumped by a 976 nm diode laser, a 1556 nm continuous-wave laser with a maximum output power of 202 mW and a slope efficiency of 11.4% was achieved in the Er,Yb,Ce:CNGS crystal. The results indicate the Er,Yb,Ce:CNGS crystal is a promising 1.55 µm laser gain medium.

Optical amplification of photothermal therapy with gold nanoparticles and nanoclusters

NASA Astrophysics Data System (ADS)

Khlebtsov, Boris; Zharov, Vladimir; Melnikov, Andrei; Tuchin, Valery; Khlebtsov, Nikolai

2006-10-01

Recently, several groups (Anderson, Halas, Zharov, and their co-workers, 2003; El-Sayed and co-workers, 2006) demonstrated, through pioneering results, the great potential of photothermal (PT) therapy for the selective treatment of cancer cells, bacteria, viruses, and DNA targeted with gold nanospheres, nanoshells, nanorods, and nanosphere clusters. However, the current understanding of the relationship between the nanoparticle/cluster parameters (size, shape, particle/cluster structure, etc) and the efficiency of PT therapy is limited. Here, we report theoretical simulations aimed at finding the optimal single-particle and cluster structures to achieve its maximal absorption, which is crucial for PT therapeutic effects. To characterize the optical amplification in laser-induced thermal effects, we introduce relevant parameters such as the ratio of the absorption cross section to the gold mass of a single-particle structure and absorption amplification, defined as the ratio of cluster absorption to the total absorption of non-interacting particles. We consider the absorption efficiency of single nanoparticles (gold spheres, rods, and silica/gold nanoshells), linear chains, 2D lattice arrays, 3D random volume clusters, and the random aggregated N-particle ensembles on the outer surface of a larger dielectric sphere, which mimic aggregation of nanosphere bioconjugates on or within cancer cells. The cluster particles are bare or biopolymer-coated gold nanospheres. The light absorption of cluster structures is studied by using the generalized multiparticle Mie solution and the T-matrix method. The gold nanoshells with (silica core diameter)/(gold shell thickness) parameters of (50-100)/(3-8) nm and nanorods with minor/major sizes of (15-20)/(50-70) nm are shown to be more efficient PT labels and sensitizers than the equivolume solid single gold spheres. In the case of nanosphere clusters, the interparticle separations and the short linear-chain fragments are the main structural parameters determining the absorption efficiency and its spectral shifting to the red. Although we have not found a noticeable dependence of absorption amplification on the cluster sphere size, 20-40 nm particles are found to be most effective, in accordance with our experimental observations. The long-wavelength absorption efficiency of random clusters increases with the cluster particle number N at small N and reveals a saturation behaviour at N>20.

Broadband dye-sensitized upconverting nanocrystals enabled near-infrared planar perovskite solar cells

NASA Astrophysics Data System (ADS)

Lai, Xuesen; Li, Xitao; Lv, Xinding; Zheng, Yan-Zhen; Meng, Fanli; Tao, Xia

2017-12-01

Extending the spectral absorption of perovskite solar cells (PSCs) from visible into near-infrared (NIR) range is a promising strategy to minimize non-absorption loss of solar photons and enhance the cell photovoltaic performance. Herein, we report on for the first time a viable strategy of incorporating IR806 dye-sensitized upconversion nanocrystals (IR806-UCNCs) into planar PSC for broadband upconversion of NIR light (800-1000 nm) into perovskite absorber-responsive visible emissions. A smart trick is firstly adopted to prepare hydrophilic IR806-UCNCs via a NOBF4 assisted two-step ligand-exchange that allows incorporating with perovskite precursor for in-situ growth of upconverting planar perovskite film. Unlike typically reported upconverting nanoparticles with narrow NIR absorption, the as-prepared IR806-UCNCs are able to harvest NIR light broadly and then transfer the captured energy to the UCNCs for an efficient visible upconversion. The IR806-UCNCs-incorporated cell exhibits a power conversion efficiency of 17.49%, corresponding to 29% increment from that of the pristine cell (13.52%). This strategy provides a feasible way to enable the most efficient harvesting of NIR sunlight for solar cells and other optoelectric devices.

Laser, optical and thermomechanical properties of Yb-doped fluorapatite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Payne, S.A.; Smith, L.K.; DeLoach, L.D.

The laser performance of Yb-doped fluorapatite (Ca[sub 5](PO[sub 4])[sub 3]F or FAP), is assessed by employing a Ti:sapphire laser operating at 905 nm as the pump source. The authors have measured slope efficiencies to be as high as 79%; the residual decrement from the quantum defect-limited efficiency of 87% is accounted for by the presence of passive loss at the 1,043-nm laser wavelength. The important spectral properties of Yb:FAP were evaluated, including the absorption and emission cross sections, excited-state lifetime, and ground-state energy-level splitting. The emission and absorption cross sections of Yb[sup 3+] in FAP are found to be substantiallymore » larger than those of other Yb-doped media. The thermal, physical, and optical properties of the FAP host are reported as well.« less

Energy-Looping Nanoparticles: Harnessing Excited-State Absorption for Deep-Tissue Imaging.

PubMed

Levy, Elizabeth S; Tajon, Cheryl A; Bischof, Thomas S; Iafrati, Jillian; Fernandez-Bravo, Angel; Garfield, David J; Chamanzar, Maysamreza; Maharbiz, Michel M; Sohal, Vikaas S; Schuck, P James; Cohen, Bruce E; Chan, Emory M

2016-09-27

Near infrared (NIR) microscopy enables noninvasive imaging in tissue, particularly in the NIR-II spectral range (1000-1400 nm) where attenuation due to tissue scattering and absorption is minimized. Lanthanide-doped upconverting nanocrystals are promising deep-tissue imaging probes due to their photostable emission in the visible and NIR, but these materials are not efficiently excited at NIR-II wavelengths due to the dearth of lanthanide ground-state absorption transitions in this window. Here, we develop a class of lanthanide-doped imaging probes that harness an energy-looping mechanism that facilitates excitation at NIR-II wavelengths, such as 1064 nm, that are resonant with excited-state absorption transitions but not ground-state absorption. Using computational methods and combinatorial screening, we have identified Tm(3+)-doped NaYF4 nanoparticles as efficient looping systems that emit at 800 nm under continuous-wave excitation at 1064 nm. Using this benign excitation with standard confocal microscopy, energy-looping nanoparticles (ELNPs) are imaged in cultured mammalian cells and through brain tissue without autofluorescence. The 1 mm imaging depths and 2 μm feature sizes are comparable to those demonstrated by state-of-the-art multiphoton techniques, illustrating that ELNPs are a promising class of NIR probes for high-fidelity visualization in cells and tissue.

Rare-earth doped transparent ceramics for spectral filtering and quantum information processing

NASA Astrophysics Data System (ADS)

Kunkel, Nathalie; Ferrier, Alban; Thiel, Charles W.; Ramírez, Mariola O.; Bausá, Luisa E.; Cone, Rufus L.; Ikesue, Akio; Goldner, Philippe

2015-09-01

Homogeneous linewidths below 10 kHz are reported for the first time in high-quality Eu3+ doped Y 2O3 transparent ceramics. This result is obtained on the 7F0→5D0 transition in Eu3+ doped Y 2O3 ceramics and corresponds to an improvement of nearly one order of magnitude compared to previously reported values in transparent ceramics. Furthermore, we observed spectral hole lifetimes of ˜15 min that are long enough to enable efficient optical pumping of the nuclear hyperfine levels. Additionally, different Eu3+ concentrations (up to 1.0%) were studied, resulting in an increase of up to a factor of three in the peak absorption coefficient. These results suggest that transparent ceramics can be useful in applications where narrow and deep spectral holes can be burned into highly absorbing lines, such as quantum information processing and spectral filtering.

Solar EUV Irradiance Measurements by the Auto-Calibrating EUV Spectrometers (SolACES) Aboard the International Space Station (ISS)

NASA Astrophysics Data System (ADS)

Schmidtke, G.; Nikutowski, B.; Jacobi, C.; Brunner, R.; Erhardt, C.; Knecht, S.; Scherle, J.; Schlagenhauf, J.

2014-05-01

SolACES is part of the ESA SOLAR ISS mission that started aboard the shuttle mission STS-122 on 7 February 2008. The instrument has recorded solar extreme ultraviolet (EUV) irradiance from 16 to 150 nm during the extended solar activity minimum and the beginning solar cycle 24 with rising solar activity and increasingly changing spectral composition. The SOLAR mission has been extended from a period of 18 months to > 8 years until the end of 2016. SolACES is operating three grazing incidence planar grating spectrometers and two three-current ionization chambers. The latter ones are considered as primary radiometric detector standards. Re-filling the ionization chambers with three different gases repeatedly and using overlapping band-pass filters, the absolute EUV fluxes are derived in these spectral intervals. This way the serious problem of continuing efficiency changes in space-borne instrumentation is overcome during the mission. Evaluating the three currents of the ionization chambers, the overlapping spectral ranges of the spectrometers and of the filters plus inter-comparing the results from the EUV photon absorption in the gases with different absorption cross sections, there are manifold instrumental possibilities to cross-check the results providing a high degree of reliability to the spectral irradiance derived. During the mission a very strong up-and-down variability of the spectrometric efficiency by orders of magnitude is observed. One of the effects involved is channeltron degradation. However, there are still open questions on other effects contributing to these changes. A survey of the measurements carried out and first results of the solar spectral irradiance (SSI) data are presented. Inter-comparison with EUV data from other space missions shows good agreement such that the international effort has started to elaborate a complete set of EUV-SSI data taking into account all data available from 2008 to 2013.

Efficiency of the intermolecular interaction of salicylic acid neutral form and monoanion with Cd2 + ion studied by methods of absorption and fluorescence

NASA Astrophysics Data System (ADS)

Lavrik, N. L.; Mulloev, N. U.

2018-02-01

The methods of absorption and fluorescence were used to study the efficiency of the interaction between salicylic acid derivatives SAD (neutral SA form and SA monoanion) and Cd2 + ions (in CdBr2 salt) within the range pH = 1.5 ÷ 8. The efficiency was determined from the change in both the absorption band contour and the fluorescence intensity of various SAD forms. It has been established that depending on the SAD form, the addition of CdBr2 to a starting solution leads to the formation of additional absorption for both the shorter wave lengths in the absorption spectrum of the neutral form (at pH < 3) and the longer wave lengths in the absorption spectrum for the HSal- monoanion (at pH > 4). In the fluorescence spectra, the intensity was observed to increase for the neutral SAD form (at pH < 3) and to decrease for the HSal- monoanion (at pH > 4) after addition of CdBr2. The spectral changes were interpreted in the framework of common notions about the effect of three physicochemical factors that determine the interaction between the SAD and the Cd2 + ion and affect the parameters of absorption and fluorescence spectra. These factors are: (1) the decrease in pH after addition of CdBr2 to the SAD solution, (2) the decrease in the efficiency of the H-bonding of SAD molecules to the water ones, and (3) the existence of electrostatic ion-ion interaction between the HSal- monoanion and the Cd2 + ion. The bimolecular fluorescence quenching constants Kq of HSal- monoanion fluorescence quenching by the Cd2 + ion appeared to be substantially less than those of the quenching which would follow either the dynamic (diffusion) or the concentration (static) mechanisms.

Analyte-induced spectral filtering in femtosecond transient absorption spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abraham, Baxter; Nieto-Pescador, Jesus; Gundlach, Lars

Here, we discuss the influence of spectral filtering by samples in femtosecond transient absorption measurements. Commercial instruments for transient absorption spectroscopy (TA) have become increasingly available to scientists in recent years and TA is becoming an established technique to measure the dynamics of photoexcited systems. Furthermore, we show that absorption of the excitation pulse by the sample can severely alter the spectrum and consequently the temporal pulse shape. This “spectral self-filtering” effect can lead to systematic errors and misinterpretation of data, most notably in concentration dependent measurements. Finally, the combination of narrow absorption peaks in the sample with ultrafast broadbandmore » excitation pulses is especially prone to this effect.« less

Analyte-induced spectral filtering in femtosecond transient absorption spectroscopy

DOE PAGES

Abraham, Baxter; Nieto-Pescador, Jesus; Gundlach, Lars

2017-03-06

Here, we discuss the influence of spectral filtering by samples in femtosecond transient absorption measurements. Commercial instruments for transient absorption spectroscopy (TA) have become increasingly available to scientists in recent years and TA is becoming an established technique to measure the dynamics of photoexcited systems. Furthermore, we show that absorption of the excitation pulse by the sample can severely alter the spectrum and consequently the temporal pulse shape. This “spectral self-filtering” effect can lead to systematic errors and misinterpretation of data, most notably in concentration dependent measurements. Finally, the combination of narrow absorption peaks in the sample with ultrafast broadbandmore » excitation pulses is especially prone to this effect.« less

Process development and characterization of centrosymmetric semiorganic nonlinear optical crystal: 4-dimethylaminopyridine potassium chloride

NASA Astrophysics Data System (ADS)

Johnson, J.; Srineevasan, R.; Sivavishnu, D.

2018-06-01

Centrosymmetric semiorganic crystal 4-dimethylaminopyridine potassium chloride (4-DMAPKC) has been grown successfully by using slow evaporation solution growth technique. Powder x-ray diffraction shows the 4-DMAPKC crystal has good crystalline nature. Single crystal XRD shows that the grown 4-DMAPKC is cubic crystal system with cell parameters a = 3.09 Å, b = 3.09 Å, c = 3.09 Å. Investigation has been carried out to assign the Vibrational frequencies of the grown crystal by FTIR spectral studies. UVsbnd Visible NIR optical absorption spectral studies in the range of 200-1100 nm shows low absorption in UVsbnd Visible region with lower cutoff wave length at 261 nm and optical band gap energy was found as Eg = 5.52 eV. Optically transmittance spectral shows 4-DMAPKC crystal is very good transparency in UV-Visible NIR region. Thermogravimetry and differential thermal (TG-DTA) analysis were carried out. Dielectric studies of as grown crystal sample exhibit low dielectric constant and loss at higher frequencies and attests the nonlinear optical activity. Micro hardness studies of as grown crystal were discussed. Second harmonic generation (SHG) efficiency of the 4-DMAPKC is 0.69 times as that of KDP.

Ultraviolet observations of the gas phase abundances in the diffuse clouds toward Zeta Ophiuchi at 3.5 kilometers per second resolution

NASA Technical Reports Server (NTRS)

Savage, Blair D.; Cardelli, Jason A.; Sofia, Ulysses J.

1992-01-01

Goddard High Resolution Spectrograph echelle mode measurements at 3.5 km/s resolution are presented for interstellar absorption produced by C II, O I, Mg I, Mg II, Al III, P II, Cr II, Mn II, Fe II, Ni II, Cu II, Zn II, Ga II, Ge II, and Kr I. The absorption line measurements are converted into representations of apparent column density per unit velocity in order to study the multicomponent nature of the absorption. The high spectral resolution of the measurements allows a comparative study of gas phase abundances for many species in the absorbing clouds near -27 and -15 km/s with a typical precision of about 0.05 dex. The matter absorbing near -27 km/s is situated in the local interstellar medium and has log N(H I) of about 19.74. This absorption provides information about the modest 'base' depletion associated with the lower density interstellar medium. The depletion results suggest that accretion processes are operating interstellar clouds that exhibit similar depletion efficiencies for some elements but much higher depletion efficiencies for others.

Collision broadened resonance localization in tokamaks excited with ICRF waves

NASA Astrophysics Data System (ADS)

Kerbel, G. D.; McCoy, M. G.

1985-08-01

Advanced wave models used to evaluate ICRH in tokamaks typically use warm plasma theory and allow inhomogeneity in one dimension. The authors have developed a bounce-averaged Fokker-Planck quasilinear computational model which evolves the population of particles on more realistic orbits. Each wave-particle resonance has its own specific interaction amplitude within any given volume element. These data need only be generated once, and appropriately stored for efficient retrieval. The wave-particle resonant interaction then serves as a mechanism by which the diffusion of particle populations can proceed among neighboring orbits. Collisions affect the absorption of RF energy by two quite distinct processes: In addition to the usual relaxation towards the Maxwellian distribution creating velocity gradients which drive quasilinear diffusion, collisions also affect the wave-particle resonance through the mechanism of gyro-phase diffusion. The local specific spectral energy absorption rate is directly calculable once the orbit geometry and populations are determined. The code is constructed in such fashion as to accommodate wave propagation models which provide the wave spectral energy density on a poloidal cross-section. Information provided by the calculation includes the local absorption properties of the medium which can then be exploited to evolve the wave field.

Resonance localization in tokamaks excited with ICRF waves

NASA Astrophysics Data System (ADS)

Kerbel, G. D.; McCoy, M. G.

1985-06-01

Advanced wave model used to evaluate ICRH in tokamaks typically used warm plasma theory and allow inhomogeneity in one dimension. The majority of these calculations neglect the fact that gyrocenters experience the inhomogeneity via their motion parallel to the magnetic field. In strongly driven systems, wave damping can distort the particle distribution function supporting the wave and this produces changes in the absorption. A bounce-averaged Fokker-Planck quasilinear computational model which evolves the population of particles on more realistic orbits is presented. Each wave-particle resonance has its own specific interaction amplitude within any given volume element; these data need only be generated once, and appropriately stored for efficient retrieval. The wave-particle resonant interaction then serves as a mechanism by which the diffusion of particle populations can proceed among neighboring orbits. The local specific spectral energy absorption rate is directly calculable once the orbit geometry and populations are determined. The code is constructed in such fashion as to accommodate wave propagation models which provide the wave spectral energy density on a poloidal cross-section. Information provided by the calculation includes the local absorption properties of the medium which can then be exploited to evolve the wave field.

Infrared upconversion for astronomical applications. [laser applications to astronomical spectroscopy of infrared spectra

NASA Technical Reports Server (NTRS)

Abbas, M. M.; Kostiuk, T.; Ogilvie, K. W.

1975-01-01

The performance of an upconversion system is examined for observation of astronomical sources in the low to middle infrared spectral range. Theoretical values for the performance parameters of an upconversion system for astronomical observations are evaluated in view of the conversion efficiencies, spectral resolution, field of view, minimum detectable source brightness and source flux. Experimental results of blackbody measurements and molecular absorption spectrum measurements using a lithium niobate upconverter with an argon-ion laser as the pump are presented. Estimates of the expected optimum sensitivity of an upconversion device which may be built with the presently available components are given.

Nanoscale resonant-cavity-enhanced germanium photodetectors with lithographically defined spectral response for improved performance at telecommunications wavelengths.

PubMed

Balram, Krishna C; Audet, Ross M; Miller, David A B

2013-04-22

We demonstrate the use of a subwavelength planar metal-dielectric resonant cavity to enhance the absorption of germanium photodetectors at wavelengths beyond the material's direct absorption edge, enabling high responsivity across the entire telecommunications C and L bands. The resonant wavelength of the detectors can be tuned linearly by varying the width of the Ge fin, allowing multiple detectors, each resonant at a different wavelength, to be fabricated in a single-step process. This approach is promising for the development of CMOS-compatible devices suitable for integrated, high-speed, and energy-efficient photodetection at telecommunications wavelengths.

System responses to equal doses of photosynthetically usable radiation of blue, green, and red light in the marine diatom Phaeodactylum tricornutum.

PubMed

Valle, Kristin Collier; Nymark, Marianne; Aamot, Inga; Hancke, Kasper; Winge, Per; Andresen, Kjersti; Johnsen, Geir; Brembu, Tore; Bones, Atle M

2014-01-01

Due to the selective attenuation of solar light and the absorption properties of seawater and seawater constituents, free-floating photosynthetic organisms have to cope with rapid and unpredictable changes in both intensity and spectral quality. We have studied the transcriptional, metabolic and photo-physiological responses to light of different spectral quality in the marine diatom Phaeodactylum tricornutum through time-series studies of cultures exposed to equal doses of photosynthetically usable radiation of blue, green and red light. The experiments showed that short-term differences in gene expression and profiles are mainly light quality-dependent. Transcription of photosynthesis-associated nuclear genes was activated mainly through a light quality-independent mechanism likely to rely on chloroplast-to-nucleus signaling. In contrast, genes encoding proteins important for photoprotection and PSII repair were highly dependent on a blue light receptor-mediated signal. Changes in energy transfer efficiency by light-harvesting pigments were spectrally dependent; furthermore, a declining trend in photosynthetic efficiency was observed in red light. The combined results suggest that diatoms possess a light quality-dependent ability to activate photoprotection and efficient repair of photodamaged PSII. In spite of approximately equal numbers of PSII-absorbed quanta in blue, green and red light, the spectral quality of light is important for diatom responses to ambient light conditions.

Systematic determination of absolute absorption cross-section of individual carbon nanotubes

PubMed Central

Liu, Kaihui; Hong, Xiaoping; Choi, Sangkook; Jin, Chenhao; Capaz, Rodrigo B.; Kim, Jihoon; Wang, Wenlong; Bai, Xuedong; Louie, Steven G.; Wang, Enge; Wang, Feng

2014-01-01

Optical absorption is the most fundamental optical property characterizing light–matter interactions in materials and can be most readily compared with theoretical predictions. However, determination of optical absorption cross-section of individual nanostructures is experimentally challenging due to the small extinction signal using conventional transmission measurements. Recently, dramatic increase of optical contrast from individual carbon nanotubes has been successfully achieved with a polarization-based homodyne microscope, where the scattered light wave from the nanostructure interferes with the optimized reference signal (the reflected/transmitted light). Here we demonstrate high-sensitivity absorption spectroscopy for individual single-walled carbon nanotubes by combining the polarization-based homodyne technique with broadband supercontinuum excitation in transmission configuration. To our knowledge, this is the first time that high-throughput and quantitative determination of nanotube absorption cross-section over broad spectral range at the single-tube level was performed for more than 50 individual chirality-defined single-walled nanotubes. Our data reveal chirality-dependent behaviors of exciton resonances in carbon nanotubes, where the exciton oscillator strength exhibits a universal scaling law with the nanotube diameter and the transition order. The exciton linewidth (characterizing the exciton lifetime) varies strongly in different nanotubes, and on average it increases linearly with the transition energy. In addition, we establish an empirical formula by extrapolating our data to predict the absorption cross-section spectrum for any given nanotube. The quantitative information of absorption cross-section in a broad spectral range and all nanotube species not only provides new insight into the unique photophysics in one-dimensional carbon nanotubes, but also enables absolute determination of optical quantum efficiencies in important photoluminescence and photovoltaic processes. PMID:24821815

Systematic determination of absolute absorption cross-section of individual carbon nanotubes.

PubMed

Liu, Kaihui; Hong, Xiaoping; Choi, Sangkook; Jin, Chenhao; Capaz, Rodrigo B; Kim, Jihoon; Wang, Wenlong; Bai, Xuedong; Louie, Steven G; Wang, Enge; Wang, Feng

2014-05-27

Optical absorption is the most fundamental optical property characterizing light-matter interactions in materials and can be most readily compared with theoretical predictions. However, determination of optical absorption cross-section of individual nanostructures is experimentally challenging due to the small extinction signal using conventional transmission measurements. Recently, dramatic increase of optical contrast from individual carbon nanotubes has been successfully achieved with a polarization-based homodyne microscope, where the scattered light wave from the nanostructure interferes with the optimized reference signal (the reflected/transmitted light). Here we demonstrate high-sensitivity absorption spectroscopy for individual single-walled carbon nanotubes by combining the polarization-based homodyne technique with broadband supercontinuum excitation in transmission configuration. To our knowledge, this is the first time that high-throughput and quantitative determination of nanotube absorption cross-section over broad spectral range at the single-tube level was performed for more than 50 individual chirality-defined single-walled nanotubes. Our data reveal chirality-dependent behaviors of exciton resonances in carbon nanotubes, where the exciton oscillator strength exhibits a universal scaling law with the nanotube diameter and the transition order. The exciton linewidth (characterizing the exciton lifetime) varies strongly in different nanotubes, and on average it increases linearly with the transition energy. In addition, we establish an empirical formula by extrapolating our data to predict the absorption cross-section spectrum for any given nanotube. The quantitative information of absorption cross-section in a broad spectral range and all nanotube species not only provides new insight into the unique photophysics in one-dimensional carbon nanotubes, but also enables absolute determination of optical quantum efficiencies in important photoluminescence and photovoltaic processes.

Radiative Properties of Cirrus Clouds in the Infrared (8-13 microns) Spectral Region

NASA Technical Reports Server (NTRS)

Yang, Ping; Gao, Bo-Cai; Baum, Bryan A.; Hu, Yong X.; Wiscombe, Warren J.; Tsay, Si-Chee; Winker, Dave M.; Einaudi, Franco (Technical Monitor)

2000-01-01

Atmospheric radiation in the infrared (IR) 8-13 microns spectral region contains a wealth of information that is very useful for the retrieval of ice cloud properties from aircraft or space-borne measurements. To provide the scattering and absorption properties of nonspherical ice crystals that are fundamental to the IR retrieval implementation, we use the finite-difference time domain (FDTD) method to solve for the extinction efficiency, single-scattering albedo, and the asymmetry parameter of the phase function for ice crystals smaller than 40 microns. For particles larger than this size, the improved geometric optics method (IGOM) can be employed to calculate the asymmetry parameter with an acceptable accuracy, provided that we properly account for the inhomogeneity of the refracted wave due to strong absorption inside the ice particle. A combination of the results computed from the two methods provides the asymmetry parameter for the entire practical range of particle sizes between 1 micron and 10000 microns over wavelengths ranging from 8 microns to 13 microns. For the extinction and absorption efficiency calculations, several methods including the IGOM, Mie solution for equivalent spheres (MSFES), and the anomalous diffraction theory (ADT) can lead to a substantial discontinuity in comparison with the FDTD solutions for particle sizes on the order of 40 microns. To overcome this difficulty, we have developed a novel approach called the stretched scattering potential method (SSPM). For the IR 8-13 microns spectral region, we show that SSPM is a more accurate approximation than ADT, MSFES, and IGOM. The SSPM solution can be further refined numerically. Through a combination of the FDTD and SSPM, we have computed the extinction and absorption efficiency for hexagonal ice crystals with sizes ranging from 1 to 10000 microns at 12 wavelengths between 8 and 13 microns Calculations of the cirrus bulk scattering and absorption properties are performed for 30 size distributions obtained from various field campaigns for midlatitude and tropical cirrus cloud systems. Parameterization of these bulk scattering properties is carried out by using second-order polynomial functions for the extinction efficiency and the single-scattering albedo and the power law expression for the asymmetry parameter. We note that the volume-normalized extinction coefficient can be separated into two parts: one is inversely proportional to effective size and is independent of wavelength, and the other is the wavelength-dependent effective extinction efficiency. Unlike conventional parameterization efforts, the present parameterization scheme is more accurate because only the latter part of the volume-normalized extinction coefficient is approximated in terms of an analytical expression. After averaging over size distribution, the single-scattering albedo is shown to decrease with an increase in effective size for wavelengths shorter than 10.0 microns whereas the opposite behavior is observed for longer wavelengths. The variation of the asymmetry parameter as a function of effective size is substantial when the effective size is smaller than 50 microns. For effective sizes larger than 100 microns, the asymmetry parameter approaches its asymptotic value. The results derived in this study can be useful to remote sensing applications involving IR window bands under cirrus cloud conditions.

Ultrathin Organic Solar Cells with a Power Conversion Efficiency of Over ≈13.0%, Based on the Spatial Corrugation of the Metal Electrode-Cathode Fabry-Perot Cavity.

PubMed

In, Sungjun; Park, Namkyoo

2018-04-01

The application of nanophotonic structures for organic solar cells (OSCs) is quite popular and successful, and has led to increased optical absorption, better spectral overlap with solar irradiances, and improved charge collection. Significant improvements in the power conversion efficiency (PCE) have also been reported, exceeding 11%. Nonetheless, with the given material properties of OSCs with low optical absorption, narrow spectrum, short transport length of carriers, and nonuniform photocarrier generations resulting from the nanophotonic structure, the PCE of single-junction OSCs has been stagnant over the past few years, at a barrier of 12%. Here, an ultrathin inverted OSC structure with the highest efficiency of ≈13.0%, while being made from widely used organic materials, is demonstrated. By introducing a smooth spatial corrugation to the vertical plasmonic cavity enclosing the active layer, in-plane propagation modes and hybridized Fabry-Perot cavity modes inside the corrugated cavity are derived to achieve an ultralow Q , uniform coverage of optical absorption, in addition to uniform photocarrier generation and transport. As the first demonstration of ultra-broadband absorption with the introduction of spatial corrugation to the ultrathin metal film electrode-cathode Fabry-Perot cavity, future applications of the same concept in other light-harvesting devices utilizing different materials and structures are expected.

Effect of water content and organic carbon on remote sensing of crop residue cover

NASA Astrophysics Data System (ADS)

Serbin, G.; Hunt, E. R., Jr.; Daughtry, C. S. T.; McCarty, G. W.; Brown, D. J.; Doraiswamy, P. C.

2009-04-01

Crop residue cover is an important indicator of tillage method. Remote sensing of crop residue cover is an attractive and efficient method when compared with traditional ground-based methods, e.g., the line-point transect or windshield survey. A number of spectral indices have been devised for residue cover estimation. Of these, the most effective are those in the shortwave infrared portion of the spectrum, situated between 1950 and 2500 nm. These indices include the hyperspectral Cellulose Absorption Index (CAI), and advanced multispectral indices, i.e., the Lignin-Cellulose Absorption (LCA) index and the Shortwave Infrared Normalized Difference Residue Index (SINDRI), which were devised for the NASA Terra Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor. Spectra of numerous soils from U.S. Corn Belt (Indiana and Iowa) were acquired under wetness conditions varying from saturation to oven-dry conditions. The behavior of soil reflectance with water content was also dependent on the soil organic carbon content (SOC) of the soils, and the location of the spectral bands relative to significant water absorptions. High-SOC soils showed the least change in spectral index values with increase in soil water content. Low-SOC soils, on the other hand, showed measurable difference. For CAI, low-SOC soils show an initial decrease in index value followed by an increase, due to the way that water content affects CAI spectral bands. Crop residue CAI values decrease with water content. For LCA, water content increases decrease crop residue index values and increase them for soils, resulting in decreased contrast. SINDRI is also affected by SOC and water content. As such, spatial information on the distribution of surface soil water content and SOC, when used in a geographic information system (GIS), will improve the accuracy of remotely-sensed crop residue cover estimates.

Constraining Cometary Crystal Shapes from IR Spectral Features

NASA Technical Reports Server (NTRS)

Wooden, Diane H.; Lindsay, Sean; Harker, David E.; Kelley, Michael S. P.; Woodward, Charles E.; Murphy, James Richard

2013-01-01

A major challenge in deriving the silicate mineralogy of comets is ascertaining how the anisotropic nature of forsterite crystals affects the spectral features' wavelength, relative intensity, and asymmetry. Forsterite features are identified in cometary comae near 10, 11.05-11.2, 16, 19, 23.5, 27.5 and 33 microns [1-10], so accurate models for forsterite's absorption efficiency (Qabs) are a primary requirement to compute IR spectral energy distributions (SEDs, lambdaF lambda vs. lambda) and constrain the silicate mineralogy of comets. Forsterite is an anisotropic crystal, with three crystallographic axes with distinct indices of refraction for the a-, b-, and c-axis. The shape of a forsterite crystal significantly affects its spectral features [13-16]. We need models that account for crystal shape. The IR absorption efficiencies of forsterite are computed using the discrete dipole approximation (DDA) code DDSCAT [11,12]. Starting from a fiducial crystal shape of a cube, we systematically elongate/reduce one of the crystallographic axes. Also, we elongate/reduce one axis while the lengths of the other two axes are slightly asymmetric (0.8:1.2). The most significant grain shape characteristic that affects the crystalline spectral features is the relative lengths of the crystallographic axes. The second significant grain shape characteristic is breaking the symmetry of all three axes [17]. Synthetic spectral energy distributions using seven crystal shape classes [17] are fit to the observed SED of comet C/1995 O1 (Hale-Bopp). The Hale-Bopp crystalline residual better matches equant, b-platelets, c-platelets, and b-columns spectral shape classes, while a-platelets, a-columns and c-columns worsen the spectral fits. Forsterite condensation and partial evaporation experiments demonstrate that environmental temperature and grain shape are connected [18-20]. Thus, grain shape is a potential probe for protoplanetary disk temperatures where the cometary crystalline forsterite formed. The forsterite crystal shapes (equant, b-platelets, c-platelets, b-columns - excluding a- and c-columns) derived from our modeling [17] of comet Hale- Bopp, compared to laboratory synthesis experiments [18], suggests that these crystals are high temperature condensates. By observing and modeling the crystalline features in comet ISON, we may constrain forsterite crystal shape(s) and link to their formation temperature(s) and environment(s).

A Novel Approach to Thermal Design of Solar Modules: Selective-Spectral and Radiative Cooling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Xingshu; Dubey, Rajiv; Chattopadhyay, Shashwata

2016-11-21

For commercial solar modules, up to 80% of the incoming sunlight may be dissipated as heat, potentially raising the temperature 20-30 degrees C higher than the ambient. In the long run, extreme self-heating may erode efficiency and shorten lifetime, thereby, dramatically reducing the total energy output by almost ~10% Therefore, it is critically important to develop effective and practical cooling methods to combat PV self-heating. In this paper, we explore two fundamental sources of PV self-heating, namely, sub-bandgap absorption and imperfect thermal radiation. The analysis suggests that we redesign the optical and thermal properties of the solar module to eliminatemore » the parasitic absorption (selective-spectral cooling) and enhance the thermal emission to the cold cosmos (radiative cooling). The proposed technique should cool the module by ~10 degrees C, to be reflected in significant long-term energy gain (~ 3% to 8% over 25 years) for PV systems under different climatic conditions.« less

Crystal growth, spectral, structural and optical studies of π-conjugated stilbazolium crystal: 4-bromobenzaldehyde-4'-N'-methylstilbazolium tosylate.

PubMed

Krishna Kumar, M; Sudhahar, S; Bhagavannarayana, G; Mohan Kumar, R

2014-05-05

Nonlinear optical (NLO) organic compound, 4-bromobenzaldehyde-4'-N'-methylstilbazolium tosylate was synthesized by reflux method. The formation of molecular complex was confirmed from (1)H NMR, FT-IR and FT-Raman spectral analyses. The single crystals were grown by slow evaporation solution growth method and the crystal structure and atomic packing of grown crystal was identified. The morphology and growth axis of grown crystal were determined. The crystal perfection was analyzed using high resolution X-ray diffraction study on (001) plane. Thermal stability, decomposition stages and melting point of the grown crystal were analyzed. The optical absorption coefficient (α) and energy band gap (E(g)) of the crystal were determined using UV-visible absorption studies. Second harmonic generation efficiency of the grown crystal was examined by Kurtz powder method with different particle size using 1064 nm laser. Laser induced damage threshold study was carried out for the grown crystal using Nd:YAG laser. Copyright © 2014 Elsevier B.V. All rights reserved.

FDTD analysis of the light extraction efficiency of OLEDs with a random scattering layer.

PubMed

Kim, Jun-Whee; Jang, Ji-Hyang; Oh, Min-Cheol; Shin, Jin-Wook; Cho, Doo-Hee; Moon, Jae-Hyun; Lee, Jeong-Ik

2014-01-13

The light extraction efficiency of OLEDs with a nano-sized random scattering layer (RSL-OLEDs) was analyzed using the Finite Difference Time Domain (FDTD) method. In contrast to periodic diffraction patterns, the presence of an RSL suppresses the spectral shift with respect to the viewing angle. For FDTD simulation of RSL-OLEDs, a planar light source with a certain spatial and temporal coherence was incorporated, and the light extraction efficiency with respect to the fill factor of the RSL and the absorption coefficient of the material was investigated. The design results were compared to the experimental results of the RSL-OLEDs in order to confirm the usefulness of FDTD in predicting experimental results. According to our FDTD simulations, the light confined within the ITO-organic waveguide was quickly absorbed, and the absorption coefficients of ITO and RSL materials should be reduced in order to obtain significant improvement in the external quantum efficiency (EQE). When the extinction coefficient of ITO was 0.01, the EQE in the RSL-OLED was simulated to be enhanced by a factor of 1.8.

In vivo imaging of scattering and absorption properties of exposed brain using a digital red-green-blue camera

NASA Astrophysics Data System (ADS)

Nishidate, Izumi; Yoshida, Keiichiro; Kawauchi, Satoko; Sato, Shunichi; Sato, Manabu

2014-03-01

We investigate a method to estimate the spectral images of reduced scattering coefficients and the absorption coefficients of in vivo exposed brain tissues in the range from visible to near-infrared wavelength (500-760 nm) based on diffuse reflectance spectroscopy using a digital RGB camera. In the proposed method, the multi-spectral reflectance images of in vivo exposed brain are reconstructed from the digital red, green blue images using the Wiener estimation algorithm. The Monte Carlo simulation-based multiple regression analysis for the absorbance spectra is then used to specify the absorption and scattering parameters of brain tissue. In this analysis, the concentration of oxygenated hemoglobin and that of deoxygenated hemoglobin are estimated as the absorption parameters whereas the scattering amplitude a and the scattering power b in the expression of μs'=aλ-b as the scattering parameters, respectively. The spectra of absorption and reduced scattering coefficients are reconstructed from the absorption and scattering parameters, and finally, the spectral images of absorption and reduced scattering coefficients are estimated. The estimated images of absorption coefficients were dominated by the spectral characteristics of hemoglobin. The estimated spectral images of reduced scattering coefficients showed a broad scattering spectrum, exhibiting larger magnitude at shorter wavelengths, corresponding to the typical spectrum of brain tissue published in the literature. In vivo experiments with exposed brain of rats during CSD confirmed the possibility of the method to evaluate both hemodynamics and changes in tissue morphology due to electrical depolarization.

Multispectral imaging of absorption and scattering properties of in vivo exposed rat brain using a digital red-green-blue camera.

PubMed

Yoshida, Keiichiro; Nishidate, Izumi; Ishizuka, Tomohiro; Kawauchi, Satoko; Sato, Shunichi; Sato, Manabu

2015-05-01

In order to estimate multispectral images of the absorption and scattering properties in the cerebral cortex of in vivo rat brain, we investigated spectral reflectance images estimated by the Wiener estimation method using a digital RGB camera. A Monte Carlo simulation-based multiple regression analysis for the corresponding spectral absorbance images at nine wavelengths (500, 520, 540, 560, 570, 580, 600, 730, and 760 nm) was then used to specify the absorption and scattering parameters of brain tissue. In this analysis, the concentrations of oxygenated hemoglobin and that of deoxygenated hemoglobin were estimated as the absorption parameters, whereas the coefficient a and the exponent b of the reduced scattering coefficient spectrum approximated by a power law function were estimated as the scattering parameters. The spectra of absorption and reduced scattering coefficients were reconstructed from the absorption and scattering parameters, and the spectral images of absorption and reduced scattering coefficients were then estimated. In order to confirm the feasibility of this method, we performed in vivo experiments on exposed rat brain. The estimated images of the absorption coefficients were dominated by the spectral characteristics of hemoglobin. The estimated spectral images of the reduced scattering coefficients had a broad scattering spectrum, exhibiting a larger magnitude at shorter wavelengths, corresponding to the typical spectrum of brain tissue published in the literature. The changes in the estimated absorption and scattering parameters during normoxia, hyperoxia, and anoxia indicate the potential applicability of the method by which to evaluate the pathophysiological conditions of in vivo brain due to the loss of tissue viability.

Spectroscopic studies of two spectral variants of light-harvesting complex 2 (LH2) from the photosynthetic purple sulfur bacterium Allochromatium vinosum.

PubMed

Niedzwiedzki, Dariusz M; Bina, David; Picken, Nichola; Honkanen, Suvi; Blankenship, Robert E; Holten, Dewey; Cogdell, Richard J

2012-09-01

Two spectral forms of the peripheral light-harvesting complex (LH2) from the purple sulfur photosynthetic bacterium Allochromatium vinosum were purified and their photophysical properties characterized. The complexes contain bacteriochlorophyll a (BChl a) and multiple species of carotenoids. The composition of carotenoids depends on the light conditions applied during growth of the cultures. In addition, LH2 grown under high light has a noticeable split of the B800 absorption band. The influence of the change of carotenoid distribution as well as the spectral change of the excitonic absorption of the bacteriochlorophylls on the light-harvesting ability was studied using steady-state absorption, fluorescence and femtosecond time-resolved absorption at 77K. The results demonstrate that the change of the distribution of the carotenoids when cells were grown at low light adapts the absorptive properties of the complex to the light conditions and maintains maximum photon-capture performance. In addition, an explanation for the origin of the enigmatic split of the B800 absorption band is provided. This spectral splitting is also observed in LH2 complexes from other photosynthetic sulfur purple bacterial species. According to results obtained from transient absorption spectroscopy, the B800 band split originates from two spectral forms of the associated BChl a monomeric molecules bound within the same complex. Copyright © 2012 Elsevier B.V. All rights reserved.

[Near ultraviolet absorption spectral properties of chromophoric dissolved organic matter in the north area of Yellow Sea].

PubMed

Wang, Lin; Zhao, Dong-Zhi; Yang, Jian-Hong; Chen, Yan-Long

2010-12-01

Chromophoric dissolved organic matter (CDOM) near ultraviolet absorption spectra contains CDOM molecular structure, composition and other important physical and chemical information. Based on the measured data of CDOM absorption coefficient in March 2009 in the north area of Yellow Sea, the present paper analyzed near ultraviolet absorption spectral properties of CDOM. The results showed that due to the impact of near-shore terrigenous input, the composition of CDOM is quite different in the north area of Yellow Sea, and this area is a typical case II water; fitted slope with specific range of spectral band and absorption coefficient at specific band can indicate the relative size of CDOM molecular weight, correlation between spectral slope of the Sg,275-300), Sg,300-350, Sg,350-400 and Sg,250-275 and the relative size of CDOM molecular weight indicative parameter M increases in turn and the highest is up to 0.95. Correlation between a(g)(lambda) and M value increases gradually with the increase in wavelength, and the highest is up to 0.92 at 400 nm; being correlated or not between spectral slope and absorption coefficient is decided by the fitting-band wavelength range for the spectra slope and the wavelength for absorption coefficient. Correlation between Sg,275-300 and a(g)(400) is the largest, up to 0.87.

Fluorescent material concentration dependency: Förster resonance energy transfer in quasi-solid state DSSCs

NASA Astrophysics Data System (ADS)

Kim, Dong Woo; Jo, Hyun-Jun; Thogiti, Suresh; Yang, Weon Ki; Cheruku, Rajesh; Kim, Jae Hong

2017-05-01

Förster resonance energy transfer (FRET) is critical for wide spectral absorption, an increased dye loading, and photocurrent generation of dye-sensitized solar cells (DSSCs). This process consists of organic fluorescent materials (as an energy donor), and an organic dye (as an energy acceptor on TiO2 surfaces) with quasi-solid electrolyte. The judicious choice of the energy donor and acceptor facilitates a strong spectral overlap between the emission and absorption regions of the fluorescent materials and dye. This FRET process enhances the light-harvesting characteristics of quasi-solid state DSSCs. In this study, DSSCs containing different concentrations (0, 1, and 1.5 wt%) of a fluorescent material (FM) as the energy donor are investigated using FRET. The power conversion efficiency of DSSCs containing FMs in a quasi-solid electrolyte increased by 33% over a pristine cell. The optimized cell fabricated with the quasi-solid state DSSC containing 1.0 wt% FM shows a maximum efficiency of 3.38%, with a short-circuit current density ( J SC ) of 4.32 mA/cm-2, and an open-circuit voltage ( V OC ) of 0.68 V under illumination of simulated solar light (AM 1.5G, 100 mW/cm-2). [Figure not available: see fulltext.

Luminescent Spectral Conversion to Improve the Performance of Dye-Sensitized Solar Cells.

PubMed

Hosseini, Zahra; Taghavinia, Nima; Wei-Guang Diau, Eric

2017-12-06

Relative to the broadband solar spectrum, a narrow range of spectral absorption of photovoltaic (PV) devices is considered an important determinant that the efficiency of light harvesting of these devices is less than unity. Having the narrowest spectral response to solar radiation among all PV devices, dye-sensitized solar cells (DSSCs) suffer severely from this loss. Luminescent spectral conversion provides a mechanism to manipulate and to adapt the incident solar spectrum by converting, through photoluminescence, the energies of solar photons into those that are more effectively captured by a PV device. This mechanism is particularly helpful for DSSCs because there is much flexibility in both the choice of the light-harvesting materials and the architecture of the DSSC. Here we review and discuss recent advances in the field of luminescent spectral conversion for DSSCs. The focus is on the architectural design of DSSCs, and the complications, advantages and new functionalities offered by each of their configurations are discussed. The loss mechanisms are examined and important parameters governing the spectral conversion mechanism of a DSSC are introduced. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mid-infrared supercontinuum generation in fluoride fiber amplifiers: current status and future perspectives

NASA Astrophysics Data System (ADS)

Gauthier, Jean-Christophe; Robichaud, Louis-Rafaël; Fortin, Vincent; Vallée, Réal; Bernier, Martin

2018-06-01

The quest for a compact and efficient broadband laser source able to probe the numerous fundamental molecular absorption lines in the mid-infrared (3-8 µm) for various applications has been going on for more than a decade. While robust commercial fiber-based supercontinuum (SC) systems have started to appear on the market, they still exhibit poor energy conversion into the mid-infrared (typically under 30%) and are generally not producing wavelengths exceeding 4.7 µm. Here, we present an overview of the results obtained from a novel approach to SC generation based on spectral broadening inside of an erbium-doped fluoride fiber amplifier seeded directly at 2.8 µm, allowing mid-infrared conversion efficiencies reaching up to 95% and spectral coverage approaching the transparency limit of ZrF4 (4.2 µm) and InF3 (5.5 µm) fibers. The general concept of the approach and the physical mechanisms involved are presented alongside the various configurations of the system to adjust the output characteristics in terms of spectral coverage and output power for different applications.

A path to practical Solar Pumped Lasers via Radiative Energy Transfer

DOE PAGES

Reusswig, Philip D.; Nechayev, Sergey; Scherer, Jennifer M.; ...

2015-10-05

The optical conversion of incoherent solar radiation into a bright, coherent laser beam enables the application of nonlinear optics to solar energy conversion and storage. Here, we present an architecture for solar pumped lasers that uses a luminescent solar concentrator to decouple the conventional trade-off between solar absorption efficiency and the mode volume of the optical gain material. We report a 750-μm-thick Nd 3+ -doped YAG planar waveguide sensitized by a luminescent CdSe/CdZnS (core/shell) colloidal nanocrystal, yielding a peak cascade energy transfer of 14%, a broad spectral response in the visible portion of the solar spectrum, and an equivalent quasi-CWmore » solar lasing threshold of 23 W-cm -2, or approximately 230 suns. The efficient coupling of incoherent, spectrally broad sunlight in small gain volumes should allow the generation of coherent laser light from intensities of less than 100 suns.« less

A path to practical Solar Pumped Lasers via Radiative Energy Transfer

PubMed Central

Reusswig, Philip D.; Nechayev, Sergey; Scherer, Jennifer M.; Hwang, Gyu Weon; Bawendi, Moungi G.; Baldo, Marc. A.; Rotschild, Carmel

2015-01-01

The optical conversion of incoherent solar radiation into a bright, coherent laser beam enables the application of nonlinear optics to solar energy conversion and storage. Here, we present an architecture for solar pumped lasers that uses a luminescent solar concentrator to decouple the conventional trade-off between solar absorption efficiency and the mode volume of the optical gain material. We report a 750-μm-thick Nd3+-doped YAG planar waveguide sensitized by a luminescent CdSe/CdZnS (core/shell) colloidal nanocrystal, yielding a peak cascade energy transfer of 14%, a broad spectral response in the visible portion of the solar spectrum, and an equivalent quasi-CW solar lasing threshold of 23 W-cm−2, or approximately 230 suns. The efficient coupling of incoherent, spectrally broad sunlight in small gain volumes should allow the generation of coherent laser light from intensities of less than 100 suns. PMID:26434400

A path to practical Solar Pumped Lasers via Radiative Energy Transfer.

PubMed

Reusswig, Philip D; Nechayev, Sergey; Scherer, Jennifer M; Hwang, Gyu Weon; Bawendi, Moungi G; Baldo, Marc A; Rotschild, Carmel

2015-10-05

The optical conversion of incoherent solar radiation into a bright, coherent laser beam enables the application of nonlinear optics to solar energy conversion and storage. Here, we present an architecture for solar pumped lasers that uses a luminescent solar concentrator to decouple the conventional trade-off between solar absorption efficiency and the mode volume of the optical gain material. We report a 750-μm-thick Nd(3+)-doped YAG planar waveguide sensitized by a luminescent CdSe/CdZnS (core/shell) colloidal nanocrystal, yielding a peak cascade energy transfer of 14%, a broad spectral response in the visible portion of the solar spectrum, and an equivalent quasi-CW solar lasing threshold of 23 W-cm(-2), or approximately 230 suns. The efficient coupling of incoherent, spectrally broad sunlight in small gain volumes should allow the generation of coherent laser light from intensities of less than 100 suns.

Superlattice photonic crystal as broadband solar absorber for high temperature operation.

PubMed

Rinnerbauer, Veronika; Shen, Yichen; Joannopoulos, John D; Soljačić, Marin; Schäffler, Friedrich; Celanovic, Ivan

2014-12-15

A high performance solar absorber using a 2D tantalum superlattice photonic crystal (PhC) is proposed and its design is optimized for high-temperature energy conversion. In contrast to the simple lattice PhC, which is limited by diffraction in the short wavelength range, the superlattice PhC achieves solar absorption over broadband spectral range due to the contribution from two superposed lattices with different cavity radii. The superlattice PhC geometry is tailored to achieve maximum thermal transfer efficiency for a low concentration system of 250 suns at 1500 K reaching 85.0% solar absorptivity. In the high concentration case of 1000 suns, the superlattice PhC absorber achieves a solar absorptivity of 96.2% and a thermal transfer efficiency of 82.9% at 1500 K, amounting to an improvement of 10% and 5%, respectively, versus the simple square lattice PhC absorber. In addition, the performance of the superlattice PhC absorber is studied in a solar thermophotovoltaic system which is optimized to minimize absorber re-emission by reducing the absorber-to-emitter area ratio and using a highly reflective silver aperture.

Cis- and trans-perfluorodecalin: Infrared spectra, radiative efficiency and global warming potential

NASA Astrophysics Data System (ADS)

Le Bris, Karine; DeZeeuw, Jasmine; Godin, Paul J.; Strong, Kimberly

2017-12-01

Perfluorodecalin (PFD) is a molecule used in various medical applications for its capacity to dissolve gases. This potent greenhouse gas was detected for the first time in the atmosphere in 2005. We present infrared absorption cross-section spectra of a pure vapour of cis- and trans-perfluorodecalin at a resolution of 0.1 cm-1. Measurements were performed in the 560-3000 cm-1 spectral range using Fourier transform spectroscopy. The spectra have been compared with previous experimental data and theoretical calculations by density functional theory. The new experimental absorption cross-sections have been used to calculate a lifetime-corrected radiative efficiency at 300 K of 0.62 W m-2 ppb-1 and 0.57 W.m-2.ppb-1 for the cis and trans isomers respectively. This leads to a 100-year time horizon global warming potential of 8030 for cis-PFD and 7440 for trans-PFD.

Optical sensor system for time-resolved quantification of methane concentrations: Validation measurements in a rapid compression machine

NASA Astrophysics Data System (ADS)

Bauke, Stephan; Golibrzuch, Kai; Wackerbarth, Hainer; Fendt, Peter; Zigan, Lars; Seefeldt, Stefan; Thiele, Olaf; Berg, Thomas

2018-05-01

Lowering greenhouse gas emissions is one of the most challenging demands of today's society. Especially, the automotive industry struggles with the development of more efficient internal combustion (IC) engines. As an alternative to conventional fuels, methane has the potential for a significant emission reduction. In methane fuelled engines, the process of mixture formation, which determines the properties of combustion after ignition, differs significantly from gasoline and diesel engines and needs to be understood and controlled in order to develop engines with high efficiency. This work demonstrates the development of a gas sensing system that can serve as a diagnostic tool for measuring crank-angle resolved relative air-fuel ratios in methane-fuelled near-production IC engines. By application of non-dispersive infrared absorption spectroscopy at two distinct spectral regions in the ν3 absorption band of methane around 3.3 μm, the system is able to determine fuel density and temperature simultaneously. A modified spark plug probe allows for straightforward application at engine test stations. Here, the application of the detection system in a rapid compression machine is presented, which enables validation and characterization of the system on well-defined gas mixtures under engine-like dynamic conditions. In extension to a recent proof-of-principle study, a refined data analysis procedure is introduced that allows the correction of artefacts originating from mechanical distortions of the sensor probe. In addition, the measured temperatures are compared to data obtained with a commercially available system based on the spectrally resolved detection of water absorption in the near infrared.

A broadband Tm/Ho-doped fiber laser tunable from 1.8 to 2.09 µm for intracavity absorption spectroscopy

NASA Astrophysics Data System (ADS)

Fjodorow, Peter; Hellmig, Ortwin; Baev, Valery M.

2018-04-01

A broadband tunable Tm/Ho-doped fiber laser is developed for sensitive in situ measurements of intracavity absorption spectra in the spectral range of 4780-5560 cm-1. This spectral range includes an atmospheric transmission window enabling sensitive measurements of various species. The spectral bandwidth of laser emission varies from 20 to 60 cm-1 and is well suitable for multicomponent spectroscopy. The sensitivity achieved in cw operation corresponds to an effective absorption path length of L eff = 20 km, with a spectral noise of less than 1%. The spectroscopic system is applied for measurements of absorption spectra of H2O, NH3 and for simultaneous in situ detection of three isotopes of CO2 in human breath, which is important for medical diagnostics procedures.

Wavelength stabilized multi-kW diode laser systems

NASA Astrophysics Data System (ADS)

Köhler, Bernd; Unger, Andreas; Kindervater, Tobias; Drovs, Simon; Wolf, Paul; Hubrich, Ralf; Beczkowiak, Anna; Auch, Stefan; Müntz, Holger; Biesenbach, Jens

2015-03-01

We report on wavelength stabilized high-power diode laser systems with enhanced spectral brightness by means of Volume Holographic Gratings. High-power diode laser modules typically have a relatively broad spectral width of about 3 to 6 nm. In addition the center wavelength shifts by changing the temperature and the driving current, which is obstructive for pumping applications with small absorption bandwidths. Wavelength stabilization of high-power diode laser systems is an important method to increase the efficiency of diode pumped solid-state lasers. It also enables power scaling by dense wavelength multiplexing. To ensure a wide locking range and efficient wavelength stabilization the parameters of the Volume Holographic Grating and the parameters of the diode laser bar have to be adapted carefully. Important parameters are the reflectivity of the Volume Holographic Grating, the reflectivity of the diode laser bar as well as its angular and spectral emission characteristics. In this paper we present detailed data on wavelength stabilized diode laser systems with and without fiber coupling in the spectral range from 634 nm up to 1533 nm. The maximum output power of 2.7 kW was measured for a fiber coupled system (1000 μm, NA 0.22), which was stabilized at a wavelength of 969 nm with a spectral width of only 0.6 nm (90% value). Another example is a narrow line-width diode laser stack, which was stabilized at a wavelength of 1533 nm with a spectral bandwidth below 1 nm and an output power of 835 W.

Omnidirectional and broadband absorption enhancement from trapezoidal Mie resonators in semiconductor metasurfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pala, Ragip A.; Butun, Serkan; Aydin, Koray

2016-09-19

Light trapping in planar ultrathin-film solar cells is limited due to a small number of optical modes available in the thin-film slab. A nanostructured thin-film design could surpass this limit by providing broadband increase in the local density of states in a subwavelength volume and maintaining efficient coupling of light. Here we report a broadband metasurface design, enabling efficient and broadband absorption enhancement by direct coupling of incoming light to resonant modes of subwavelength scale Mie nanoresonators defined in the thin-film active layer. Absorption was investigated both theoretically and experimentally in prototypes consisting of lithographically patterned, two-dimensional periodic arrays ofmore » silicon nanoresonators on silica substrates. A crossed trapezoid resonator shape of rectangular cross section is used to excite broadband Mie resonances across visible and near-IR spectra. Our numerical simulations, optical absorption measurements and photocurrent spectral response measurements demonstrate that crossed trapezoidal Mie resonant structures enable angle-insensitive, broadband absorption. A short circuit current density of 12.0 mA/cm 2 is achieved in 210 nm thick patterned Si films, yielding a 4-fold increase compared to planar films of the same thickness. As a result, it is suggested that silicon metasurfaces with Mie resonator arrays can provide useful insights to guide future ultrathin-film solar cell designs incorporating nanostructured thin active layers.« less

Gold nanorod reshaping in vitro and in vivo using a continuous wave laser

PubMed Central

Zhou, Yu; Shah, Anant; Ruenraroengsak, Pakatip; Gallina, Maria Elena; Hanna, George B.; Cass, Anthony E. G.; Porter, Alexandra E.; Bamber, Jeffrey; Elson, Daniel S.

2017-01-01

Gold nanorods (GNRs) are increasingly being investigated for cancer theranostics as they possess features which lend themselves in equal measures as contrast agents and catalysts for photothermal therapy. Their optical absorption spectral peak wavelength is determined by their size and shape. Photothermal therapy using GNRs is typically established using near infrared light as this allows sufficient penetration into the tumour matrix. Continuous wave (CW) lasers are the most commonly applied source of near infrared irradiation on GNRs for tumour photothermal therapy. It is perceived that large tumours may require fractionated or prolonged irradiation. However the true efficacy of repeated or protracted CW irradiation on tumour sites using the original sample of GNRs remains unclear. In this study spectroscopy and transmission electron microscopy are used to demonstrate that GNRs reshape both in vitro and in vivo after CW irradiation, which reduces their absorption efficiency. These changes were sustained throughout and beyond the initial period of irradiation, resulting from a spectral blue-shift and a considerable diminution in the absorption peak of GNRs. Solid subcutaneous tumours in immunodeficient BALB/c mice were subjected to GNRs and analysed with electron microscopy pre- and post-CW laser irradiation. This phenomenon of thermally induced GNR reshaping can occur at relatively low bulk temperatures, well below the bulk melting point of gold. Photoacoustic monitoring of GNR reshaping is also evaluated as a potential clinical aid to determine GNR absorption and reshaping during photothermal therapy. Aggregation of particles was coincidentally observed following CW irradiation, which would further diminish the subsequent optical absorption capacity of irradiated GNRs. It is thus established that sequential or prolonged applications of CW laser will not confer any additional photothermal effect on tumours due to significant attenuations in the peak optical absorption properties of GNRs following primary laser irradiation. PMID:29045438

Surface-plasmon-enhanced photoluminescence of quantum dots based on open-ring nanostructure array

NASA Astrophysics Data System (ADS)

Kannegulla, Akash; Liu, Ye; Cheng, Li-Jing

2016-03-01

Enhanced photoluminescence (PL) of quantum dots (QD) in visible range using plasmonic nanostructures has potential to advance several photonic applications. The enhancement effect is, however, limited by the light coupling efficiency to the nanostructures. Here we demonstrate experimentally a new open-ring nanostructure (ORN) array 100 nm engraved into a 200 nm thick silver thin film to maximize light absorption and, hence, PL enhancement at a broadband spectral range. The structure is different from the traditional isolated or through-hole split-ring structures. Theoretical calculations based on FDTD method show that the absorption peak wavelength can be adjusted by their period and dimension. A broadband absorption of about 60% was measured at the peak wavelength of 550 nm. The emission spectrum of CdSe/ZnS core-shell quantum dots was chosen to match the absorption band of the ORN array to enhance its PL. The engraved silver ORN array was fabricated on a silver thin film deposited on a silicon substrate using focus ion beam (FIB) patterning. The device was characterized by using a thin layer of QD water dispersion formed between the ORN substrate and a cover glass. The experimental results show the enhanced PL for the QD with emission spectrum overlapping the absorption band of ORN substrate and quantum efficiency increases from 50% to 70%. The ORN silver substrate with high absorption over a broadband spectrum enables the PL enhancement and will benefit applications in biosensing, wavelength tunable filters, and imaging.

Spectral properties of molecular iodine in absorption cells filled to specified saturation pressure.

PubMed

Hrabina, Jan; Šarbort, Martin; Acef, Ouali; Burck, Frédéric Du; Chiodo, Nicola; Holá, Miroslava; Číp, Ondřej; Lazar, Josef

2014-11-01

We present the results of measurement and evaluation of spectral properties of iodine absorption cells filled at certain saturation pressure. A set of cells made of borosilicate glass instead of common fused silica was tested for their spectral properties in greater detail with special care for the long-term development of the absorption media purity. The results were compared with standard fused silica cells and the high quality of iodine was verified. A measurement method based on an approach relying on measurement of linewidth of the hyperfine transitions is proposed as a novel technique for iodine cell absorption media purity evaluation. A potential application in laser metrology of length is also discussed.

Finite element method for calculating spectral and optical characteristics of axially symmetric quantum dots

NASA Astrophysics Data System (ADS)

Gusev, A. A.; Chuluunbaatar, O.; Vinitsky, S. I.; Derbov, V. L.; Hai, L. L.; Kazaryan, E. M.; Sarkisyan, H. A.

2018-04-01

We present new calculation schemes using high-order finite element method implemented on unstructured grids with triangle elements for solving boundary-value problems that describe axially symmetric quantum dots. The efficiency of the algorithms and software is demonstrated by benchmark calculations of the energy spectrum, the envelope eigenfunctions of electron, hole and exciton states, and the direct interband light absorption in conical and spheroidal impenetrable quantum dots.

The characteristics of brown carbon aerosol during winter in Beijing

NASA Astrophysics Data System (ADS)

Cheng, Yuan; He, Ke-bin; Du, Zhen-yu; Engling, Guenter; Liu, Jiu-meng; Ma, Yong-liang; Zheng, Mei; Weber, Rodney J.

2016-02-01

Brown carbon (i.e., light-absorbing organic carbon, or BrC) exerts important effects on the environment and on climate in particular. Based on spectrophotometric absorption measurements on extracts of bulk aerosol samples, this study investigated the characteristics of BrC during winter in Beijing, China. Organic compounds extractable by methanol contributed approximately 85% to the organic carbon (OC) mass. Light absorption by the methanol extracts exhibited a strong wavelength dependence, with an average absorption Ångström exponent of 7.10 (fitted between 310 and 450 nm). Normalizing the absorption coefficient (babs) measured at 365 nm to the extractable OC mass yielded an average mass absorption efficiency (MAE) of 1.45 m2/g for the methanol extracts. This study suggests that light absorption by BrC could be comparable with black carbon in the spectral range of near-ultraviolet light. Our results also indicate that BrC absorption and thus BrC radiative forcing could be largely underestimated when using water-soluble organic carbon (WSOC) as a surrogate for BrC. Compared to previous work relying only on WSOC, this study provides a more comprehensive understanding of BrC aerosol based on methanol extraction.

Near-infrared spectra of the Martian surface: Reading between the lines

NASA Technical Reports Server (NTRS)

Crisp, D.; Bell, J. F., III

1993-01-01

Moderate-resolution near-infrared (NIR) spectra of Mars have been widely used in studies of the Martian surface because many candidate surface materials have distinctive absorption features at these wavelengths. Recent advances in NIR detector technology and instrumentation have also encouraged studies in this spectral region. The use of moderate spectral resolution has often been justified for NIR surface observations because the spectral features produced by most surface materials are relatively broad, and easily discriminated at this resolution. In spite of this, NIR spectra of Mars are usually very difficult to interpret quantitatively. One problem is that NIR surface absorption features are often only a few percent deep, requiring observations with great signal-to-noise ratios. A more significant problem is that gases in the Martian atmosphere contribute numerous absorption features at these wavelengths. Ground-based observers must also contend with variable absorption by several gases in the Earth's atmosphere (H2O, CO2, O3, N2O, CH4, O2). The strong CO2 bands near 1.4, 1.6, 2.0, 2.7, 4.3, and 4.8 micrometers largely preclude the analysis of surface spectral features at these wavelengths. Martian atmospheric water vapor also contributes significant absorption near 1.33, 1.88, and 2.7 micrometers, but water vapor in the Earth's atmosphere poses a much larger problem to ground-based studies of these spectral regions. The third most important NIR absorber in the Martian atmosphere is CO. This gas absorbs most strongly in the relatively-transparent spectral windows near 4.6 and 2.3 micrometers. It also produces 1-10 percent absorption in the solar spectrum at these NIR wavelengths. This solar CO absorption cannot be adequately removed by dividing the Martian spectrum by that of a star, as is commonly done to calibrate ground-based spectroscopic observations, because most stars do not have identical amounts of CO absorption in their spectra. Here, we describe tow effective methods for eliminating contamination of Martian surface spectra by absorption in the solar, terrestrial, and Martian atmospheres. Both methods involve the use of very-high-resolution spectra that completely resolve the narrow atmospheric absorption lines.

Spectra of Particulate Backscattering in Natural Waters

NASA Technical Reports Server (NTRS)

Gordon, Howard, R.; Lewis, Marlon R.; McLean, Scott D.; Twardowski, Michael S.; Freeman, Scott A.; Voss, Kenneth J.; Boynton, Chris G.

2009-01-01

Hyperspectral profiles of downwelling irradiance and upwelling radiance in natural waters (oligotrophic and mesotrophic) are combined with inverse radiative transfer to obtain high resolution spectra of the absorption coefficient (a) and the backscattering coefficient (bb) of the water and its constituents. The absorption coefficient at the mesotrophic station clearly shows spectral absorption features attributable to several phytoplankton pigments (Chlorophyll a, b, c, and Carotenoids). The backscattering shows only weak spectral features and can be well represented by a power-law variation with wavelength (lambda): b(sub b) approx. Lambda(sup -n), where n is a constant between 0.4 and 1.0. However, the weak spectral features in b(sub b), suggest that it is depressed in spectral regions of strong particle absorption. The applicability of the present inverse radiative transfer algorithm, which omits the influence of Raman scattering, is limited to lambda < 490 nm in oligotrophic waters and lambda < 575 nm in mesotrophic waters.

Using Single-Scattering Albedo Spectral Curvature to Characterize East Asian Aerosol Mixtures

NASA Technical Reports Server (NTRS)

Li, Jing; Carlson, Barbara E.; Lacis, Andrew A.

2015-01-01

Spectral dependence of aerosol single-scattering albedo (SSA) has been used to infer aerosol composition. In particular, aerosol mixtures dominated by dust absorption will have monotonically increasing SSA with wavelength while that dominated by black carbon absorption has monotonically decreasing SSA spectra. However, by analyzing SSA measured at four wavelengths, 440, 675, 870, and 1020 nm from the Aerosol Robotic Network data set, we find that the SSA spectra over East Asia are frequently peaked at 675 nm. In these cases, we suggest that SSA spectral curvature, defined as the negative of the second derivative of SSA as a function of wavelength, can provide additional information on the composition of these aerosol mixtures. Aerosol SSA spectral curvatures for East Asia during fall and winter are considerably larger than those found in places primarily dominated by biomass burning or dust aerosols. SSA curvature is found to increase as the SSA magnitude decreases. The curvature increases with coarse mode fraction (CMF) to a CMF value of about 0.4, then slightly decreases or remains constant at larger CMF. Mie calculations further verify that the strongest SSA curvature occurs at approx. 40% dust fraction, with 10% scattering aerosol fraction. The nonmonotonic SSA spectral dependence is likely associated with enhanced absorption in the shortwave by dust, absorption by black carbon at longer wavelengths, and also the flattened absorption optical depth spectral dependence due to the increased particle size.

Spectroscopy as a tool for geochemical modeling

NASA Astrophysics Data System (ADS)

Kopacková, Veronika; Chevrel, Stephane; Bourguignon, Anna

2011-11-01

This study focused on testing the feasibility of up-scaling ground-spectra-derived parameters to HyMap spectral and spatial resolution and whether they could be further used for a quantitative determination of the following geochemical parameters: As, pH and Clignite content. The study was carried on the Sokolov lignite mine as it represents a site with extreme material heterogeneity and high heavy-metal gradients. A new segmentation method based on the unique spectral properties of acid materials was developed and applied to the multi-line HyMap image data corrected for BRDF and atmospheric effects. The quantitative parameters were calculated for multiple absorption features identified within the VIS/VNIR/SWIR regions (simple band ratios, absorption band depth and quantitative spectral feature parameters calculated dynamically for each spectral measurement (centre of the absorption band (λ), depth of the absorption band (D), width of the absorption band (Width), and asymmetry of the absorption band (S)). The degree of spectral similarity between the ground and image spectra was assessed. The linear models for pH, As and the Clignite content of the whole and segmented images were cross-validated on the selected homogenous areas defined in the HS images using ground truth. For the segmented images, reliable results were achieved as follows: As: R2=0.84, Clignite: R2=0.88 and R2 pH: R2= 0.57.

Absorption Spectra of Gold Nanoparticle Suspensions

NASA Astrophysics Data System (ADS)

Anan'eva, M. V.; Nurmukhametov, D. R.; Zverev, A. S.; Nelyubina, N. V.; Zvekov, A. A.; Russakov, D. M.; Kalenskii, A. V.; Eremenko, A. N.

2018-02-01

Three gold nanoparticle suspensions are obtained, and mean radii in distributions - (6.1 ± 0.2), (11.9 ± 0.3), and (17.3 ± 0.7) nm - are determined by the transmission electron microscopy method. The optical absorption spectra of suspensions are obtained and studied. Calculation of spectral dependences of the absorption index of suspensions at values of the gold complex refractive index taken from the literature showed a significant deviation of experimental and calculated data in the region of 450-800 nm. Spectral dependences of the absorption of suspensions are simulated within the framework of the Mie-Drude theory taking into account the interband absorption in the form of an additional term in the imaginary part of the dielectric permittivity of the Gaussian type. It is shown that to quantify the spectral dependences in the region of the plasmon absorption band of nanoparticles, correction of the parameters of the interband absorption is necessary in addition to the increase of the relaxation parameter of the Drude theory. Spectral dependences of the dielectric permittivity of gold in nanodimensional state are refined from the solution of the inverse problem. The results of the present work are important for predicting the special features of operation of photonic devices and optical detonators based on gold nanoparticles.

Spectral reflectance properties (0.4-2.5 μm) of secondary Fe-oxide, Fe-hydroxide, and Fe-sulphate-hydrate minerals associated with sulphide-bearing mine wastes

USGS Publications Warehouse

Crowley, J.K.; Williams, D.E.; Hammarstrom, J.M.; Piatak, N.; Chou, I.-Ming; Mars, J.C.

2003-01-01

Diffuse reflectance spectra of 15 mineral species commonly associated with sulphide-bearing mine wastes show diagnostic absorption bands related to electronic processes involving ferric and/or ferrous iron, and to vibrational processes involving water and hydroxyl. Many of these absorption bands are relatively broad and overlapping; however, spectral analysis methods, including continuum removal and derivative analysis, permit most of the minerals to be distinguished. Key spectral differences between the minerals are illustrated in a series of plots showing major absorption band centres and other spectral feature positions. Because secondary iron minerals are sensitive indicators of pH, Eh, relative humidity, and other environmental conditions, spectral mapping of mineral distributions promises to have important application to mine waste remediation studies.

Spectral Range Optimization to Enhance the Effectiveness of Phototherapy for Neonatal Hyperbilirubinemia

NASA Astrophysics Data System (ADS)

Plavskii, V. Yu.; Mikulich, A. V.; Leusenko, I. A.; Tretyakova, A. I.; Plavskaya, L. G.; Serdyuchenko, N. S.; Gao, J.; Xiong, D.; Wu, X.

2017-03-01

The effectiveness of phototherapy for hyperbilirubinemia of newborns using narrowband LED sources was found to depend not only on the position of the LED emission spectrum peak within the absorption band of bilirubin but also on the width of the incident radiation spectrum. Extension of the spectral range of radiation by adding a green component with λmax ≈ 505 nm to the blue light band with λmax ≈ 462 nm (provided equal integrated power density) gives a more efficient decrease in the total bilirubin level in the blood of newborns. This effect was attributed to heterogeneity of the spectral characteristics of bilirubin in different microenvironments as well as dependence of the optimal wavelength for photoisomerization of the pigment on the depth of the blood vessels where the bilirubin phototransformation reactions occur. Moreover, extension of the spectral range of the incident radiation by adding a green component increases the irradiated volumes of blood where the photoisomerization reactions with a high lumirubin quantum yield underlying this phototherapy are initiated.

Rare-earth doped transparent ceramics for spectral filtering and quantum information processing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kunkel, Nathalie, E-mail: nathalie.kunkel@chimie-paristech.fr; Goldner, Philippe, E-mail: philippe.goldner@chimie-paristech.fr; Ferrier, Alban

2015-09-01

Homogeneous linewidths below 10 kHz are reported for the first time in high-quality Eu{sup 3+} doped Y {sub 2}O{sub 3} transparent ceramics. This result is obtained on the {sup 7}F{sub 0}→{sup 5}D{sub 0} transition in Eu{sup 3+} doped Y {sub 2}O{sub 3} ceramics and corresponds to an improvement of nearly one order of magnitude compared to previously reported values in transparent ceramics. Furthermore, we observed spectral hole lifetimes of ∼15 min that are long enough to enable efficient optical pumping of the nuclear hyperfine levels. Additionally, different Eu{sup 3+} concentrations (up to 1.0%) were studied, resulting in an increase ofmore » up to a factor of three in the peak absorption coefficient. These results suggest that transparent ceramics can be useful in applications where narrow and deep spectral holes can be burned into highly absorbing lines, such as quantum information processing and spectral filtering.« less

Concentrated Solar Thermoelectric Power

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Gang; Ren, Zhifeng

2015-07-09

The goal of this project is to demonstrate in the lab that solar thermoelectric generators (STEGs) can exceed 10% solar-to-electricity efficiency, and STEGs can be integrated with phase-change materials (PCM) for thermal storage, providing operation beyond daylight hours. This project achieved significant progress in many tasks necessary to achieving the overall project goals. An accurate Themoelectric Generator (TEG) model was developed, which included realistic treatment of contact materials, contact resistances and radiative losses. In terms of fabricating physical TEGs, high performance contact materials for skutterudite TE segments were developed, along with brazing and soldering methods to assemble segmented TEGs. Accuratemore » measurement systems for determining device performance (in addition to just TE material performance) were built for this project and used to characterize our TEGs. From the optical components’ side, a spectrally selective cermet surface was developed with high solar absorptance and low thermal emittance, with thermal stability at high temperature. A measurement technique was also developed to determine absorptance and total hemispherical emittance at high temperature, and was used to characterize the fabricated spectrally selective surfaces. In addition, a novel reflective cavity was designed to reduce radiative absorber losses and achieve high receiver efficiency at low concentration ratios. A prototype cavity demonstrated that large reductions in radiative losses were possible through this technique. For the overall concentrating STEG system, a number of devices were fabricated and tested in a custom built test platform to characterize their efficiency performance. Additionally, testing was performed with integration of PCM thermal storage, and the storage time of the lab scale system was evaluated. Our latest testing results showed a STEG efficiency of 9.6%, indicating promising potential for high performance concentrated STEGs.« less

Optical absorption and emission bands of Tm 3+ ions in calcium niobium gallium garnet crystal

NASA Astrophysics Data System (ADS)

Tsuboi, Taiju; Tanigawa, Masayuki; Shimamura, Kiyoshi

2000-12-01

Absorption spectra of Tm 3+ ions in Ca 3Nb 1.6875Ga 3.1875O 12 (CNGG) crystal have been investigated at various temperatures between 15 and 296 K. Luminescence spectra in a spectral region of 400-1750 nm are investigated under excitation into various excited states of Tm 3+ and the conduction band of CNGG at room temperature. The absorption and emission bands of Tm 3+ in CNGG are observed to be broader than those observed in other Tm 3+-doped crystals such as LiNbO 3. This is due to the disordered structure of CNGG. From the temperature dependence of absorption spectra, five Stark levels are derived for the 3H 6 ground state. The highest Stark level is found to be 351 cm -1 above the ground level. It is suggested that the low efficiency of the 2.02 μm lasing at room temperature is due to the narrow splitting of the Stark levels.

Plasmonic Structure Integrated Single-Photon Detector Configurations to Improve Absorptance and Polarization Contrast

PubMed Central

Csete, Mária; Szekeres, Gábor; Szenes, András; Szalai, Anikó; Szabó, Gábor

2015-01-01

Configurations capable of maximizing both the absorption component of system detection efficiency and the achievable polarization contrast were determined for 1550 nm polarized light illumination of different plasmonic structure integrated superconducting nanowire single-photon detectors (SNSPDs) consisting of p = 264 nm and P = 792 nm periodic niobium nitride (NbN) patterns on silica substrate. Global effective NbN absorptance maxima appear in case of p/s-polarized light illumination in S/P-orientation (γ = 90°/0° azimuthal angle) and the highest polarization contrast is attained in S-orientation of all devices. Common nanophotonical origin of absorptance enhancement is collective resonance on nanocavity gratings with different profiles, which is promoted by coupling between localized modes in quarter-wavelength metal-insulator-metal nanocavities and laterally synchronized Brewster-Zenneck-type surface waves in integrated SNSPDs possessing a three-quarter-wavelength-scaled periodicity. The spectral sensitivity and dispersion characteristics reveal that device design specific optimal configurations exist. PMID:25654724

Brown carbon absorption in the red and near-infrared spectral region

NASA Astrophysics Data System (ADS)

Hoffer, András; Tóth, Ádám; Pósfai, Mihály; Eddy Chung, Chul; Gelencsér, András

2017-06-01

Black carbon (BC) aerosols have often been assumed to be the only light-absorbing carbonaceous particles in the red and near-infrared spectral regions of solar radiation in the atmosphere. Here we report that tar balls (a specific type of organic aerosol particles from biomass burning) do absorb red and near-infrared radiation significantly. Tar balls were produced in a laboratory experiment, and their chemical and optical properties were measured. The absorption of these particles in the range between 470 and 950 nm was measured with an aethalometer, which is widely used to measure atmospheric aerosol absorption. We find that the absorption coefficient of tar balls at 880 nm is more than 10 % of that at 470 nm. The considerable absorption of red and infrared light by tar balls also follows from their relatively low absorption Ångström coefficient (and significant mass absorption coefficient) in the spectral range between 470 and 950 nm. Our results support the previous finding that tar balls may play an important role in global warming. Due to the non-negligible absorption of tar balls in the near-infrared region, the absorption measured in the field at near-infrared wavelengths cannot solely be due to soot particles.

Detection of significant differences between absorption spectra of neutral helium and low temperature photoionized helium plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bartnik, A.; Wachulak, P.; Fiedorowicz, H.

2013-11-15

In this work, spectral investigations of photoionized He plasmas were performed. The photoionized plasmas were created by irradiation of helium stream, with intense pulses from laser-plasma extreme ultraviolet (EUV) source. The EUV source was based on a double-stream Xe/Ne gas-puff target irradiated with 10 ns/10 J Nd:YAG laser pulses. The most intense emission from the source spanned a relatively narrow spectral region below 20 nm, however, spectrally integrated intensity at longer wavelengths was also significant. The EUV radiation was focused onto a gas stream, injected into a vacuum chamber synchronously with the EUV pulse. The long-wavelength part of the EUVmore » radiation was used for backlighting of the photoionized plasmas to obtain absorption spectra. Both emission and absorption spectra in the EUV range were investigated. Significant differences between absorption spectra acquired for neutral helium and low temperature photoionized plasmas were demonstrated for the first time. Strong increase of intensities and spectral widths of absorption lines, together with a red shift of the K-edge, was shown.« less

Resonant Absorption in GaAs-Based Nanowires by Means of Photo-Acoustic Spectroscopy

NASA Astrophysics Data System (ADS)

Petronijevic, E.; Leahu, G.; Belardini, A.; Centini, M.; Li Voti, R.; Hakkarainen, T.; Koivusalo, E.; Guina, M.; Sibilia, C.

2018-03-01

Semiconductor nanowires made of high refractive index materials can couple the incoming light to specific waveguide modes that offer resonant absorption enhancement under the bandgap wavelength, essential for light harvesting, lasing and detection applications. Moreover, the non-trivial ellipticity of such modes can offer near field interactions with chiral molecules, governed by near chiral field. These modes are therefore very important to detect. Here, we present the photo-acoustic spectroscopy as a low-cost, reliable, sensitive and scattering-free tool to measure the spectral position and absorption efficiency of these modes. The investigated samples are hexagonal nanowires with GaAs core; the fabrication by means of lithography-free molecular beam epitaxy provides controllable and uniform dimensions that allow for the excitation of the fundamental resonant mode around 800 nm. We show that the modulation frequency increase leads to the discrimination of the resonant mode absorption from the overall absorption of the substrate. As the experimental data are in great agreement with numerical simulations, the design can be optimized and followed by photo-acoustic characterization for a specific application.

Spectral radiation analyses of the GOES solar illuminated hexagonal cell scan mirror back

NASA Technical Reports Server (NTRS)

Fantano, Louis G.

1993-01-01

A ray tracing analytical tool has been developed for the simulation of spectral radiation exchange in complex systems. Algorithms are used to account for heat source spectral energy, surface directional radiation properties, and surface spectral absorptivity properties. This tool has been used to calculate the effective solar absorptivity of the geostationary operational environmental satellites (GOES) scan mirror in the calibration position. The development and design of Sounder and Imager instruments on board GOES is reviewed and the problem of calculating the effective solar absorptivity associated with the GOES hexagonal cell configuration is presented. The analytical methodology based on the Monte Carlo ray tracing technique is described and results are presented and verified by experimental measurements for selected solar incidence angles.

Dielectric properties of semi-insulating Fe-doped InP in the terahertz spectral region.

PubMed

Alyabyeva, L N; Zhukova, E S; Belkin, M A; Gorshunov, B P

2017-08-04

We report the values and the spectral dependence of the real and imaginary parts of the dielectric permittivity of semi-insulating Fe-doped InP crystalline wafers in the 2-700 cm -1 (0.06-21 THz) spectral region at room temperature. The data shows a number of absorption bands that are assigned to one- and two-phonon and impurity-related absorption processes. Unlike the previous studies of undoped or low-doped InP material, our data unveil the dielectric properties of InP that are not screened by strong free-carrier absorption and will be useful for designing a wide variety of InP-based electronic and photonic devices operating in the terahertz spectral range.

[Spectral absorption properties of the water constituents in the estuary of Zhujiang River].

PubMed

Wang, Shan-shan; Wang, Yong-bo; Fu, Qing-hua; Yin, Bin; Li, Yun-mei

2014-12-01

Spectral absorption properties of the water constituents is the main factor affecting the light field under the surface of the water and the spectrum above the surface of the water. Thus, the study is useful for understanding of the water spectral property and the remote reversing of water quality parameters. Absorption properties of total suspended particles, non-algal particles, phytoplankton and CDOM were analyzed using the 30 samples collected in July 2013 in the estuary of Zhujiang River. The results indicated that: (1) the non-algal particles absorption dominated the absorption of the total suspended particles; (2) the absorption coefficient of the non-algal particles, which mainly came from the terrigenous deposits, decreased exponentially from short to long wavelength. In addition, the average value and spatial variation of the slope S(d) were higher than those in inland case- II waters; (3) the absorption coefficient of phytoplankton in 440 nm showed a better polynomial relationship with chlorophyll a concentration, while the absorption coefficient of phytoplankton in 675 nm linearly related with the chlorophyll a concentration. Moreover, the influence of accessory pigments on phytoplankton absorption coefficient mainly existed in the range of short wavelength, and Chlorophyll a was the main influencing factor for phytoplankton absorption in long wavelength. The specific absorption coefficient of phytoplankton decreased the power exponentially with the increase of the chlorophyll a concentration; (4) CDOM mainly came from the terrigenous sources and its spectral curve had an absorption shoulder between 250-290 nm. Thus, a piecewise S(g) fitting function could effectively express CDOM absorption properties, i.e., M value and S(g) value in period A (240-260 nm) showed a strong positive correlation. The M value was low, and the humic acid had a high proportion in CDOM; (5) the non-algal particles absorption dominated the total absorption in the estuary of Zhujiang River, and the contribution of the phytoplankton absorption to the total absorption was far lower than that of the non-algal particles. While the contribution of the CDOM was the lowest. The contribution of the CDOM absorption to the total absorption was relatively larger when the content of humic acid was higher.

A Fast Hyperspectral Vector Radiative Transfer Model in UV to IR spectral bands

NASA Astrophysics Data System (ADS)

Ding, J.; Yang, P.; Sun, B.; Kattawar, G. W.; Platnick, S. E.; Meyer, K.; Wang, C.

2016-12-01

We develop a fast hyperspectral vector radiative transfer model with a spectral range from UV to IR with 5 nm resolutions. This model can simulate top of the atmosphere (TOA) diffuse radiance and polarized reflectance by considering gas absorption, Rayleigh scattering, and aerosol and cloud scattering. The absorption component considers several major atmospheric absorbers such as water vapor, CO2, O3, and O2 including both line and continuum absorptions. A regression-based method is used to parameterize the layer effective optical thickness for each gas, which substantially increases the computation efficiency for absorption while maintaining high accuracy. This method is over 500 times faster than the existing line-by-line method. The scattering component uses the successive order of scattering (SOS) method. For Rayleigh scattering, convergence is fast due to the small optical thickness of atmospheric gases. For cloud and aerosol layers, a small-angle approximation method is used in SOS calculations. The scattering process is divided into two parts, a forward part and a diffuse part. The scattering in the small-angle range in the forward direction is approximated as forward scattering. A cloud or aerosol layer is divided into thin layers. As the ray propagates through each thin layer, a portion diverges as diffuse radiation, while the remainder continues propagating in forward direction. The computed diffuse radiance is the sum of all of the diffuse parts. The small-angle approximation makes the SOS calculation converge rapidly even in a thick cloud layer.

Efficient Colorful Perovskite Solar Cells Using a Top Polymer Electrode Simultaneously as Spectrally Selective Antireflection Coating.

PubMed

Jiang, Youyu; Luo, Bangwu; Jiang, Fangyuan; Jiang, Fuben; Fuentes-Hernandez, Canek; Liu, Tiefeng; Mao, Lin; Xiong, Sixing; Li, Zaifang; Wang, Tao; Kippelen, Bernard; Zhou, Yinhua

2016-12-14

Organometal halide perovskites have shown excellent optoelectronic properties and have been used to demonstrate a variety of semiconductor devices. Colorful solar cells are desirable for photovoltaic integration in buildings and other aesthetically appealing applications. However, the realization of colorful perovskite solar cells is challenging because of their broad and large absorption coefficient that commonly leads to cells with dark-brown colors. Herein, for the first time, we report a simple and efficient strategy to achieve colorful perovskite solar cells by using the transparent conducting polymer (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS) as a top electrode and simultaneously as an spectrally selective antireflection coating. Vivid colors across the visible spectrum are attained by engineering optical interference effects among the transparent PEDOT:PSS polymer electrode, the hole-transporting layer and the perovskite layer. The colored perovskite solar cells display power conversion efficiency values from 12.8 to 15.1% (from red to blue) when illuminated from the FTO glass side and from 11.6 to 13.8% (from red to blue) when illuminated from the PEDOT:PSS side. The new approach provides an advanced solution for fabricating colorful perovskite solar cells with easy processing and high efficiency.

Toward Improved Modeling of Spectral Solar Irradiance for Solar Energy Applications: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Yu; Sengupta, Manajit

This study introduces the National Renewable Energy Laboratory's (NREL's) recent efforts to extend the capability of the Fast All-sky Radiation Model for Solar applications (FARMS) by computing spectral solar irradiances over both horizontal and inclined surfaces. A new model is developed by computing the optical thickness of the atmosphere using a spectral irradiance model for clear-sky conditions, SMARTS2. A comprehensive lookup table (LUT) of cloud bidirectional transmittance distribution functions (BTDFs) is precomputed for 2002 wavelength bands using an atmospheric radiative transfer model, libRadtran. The solar radiation transmitted through the atmosphere is given by considering all possible paths of photon transmissionmore » and the relevent scattering and absorption attenuation. Our results indicate that this new model has an accuracy that is similar to that of state-of-the-art radiative transfer models, but it is significantly more efficient.« less

Large-scale broadband absorber based on metallic tungsten nanocone structure

NASA Astrophysics Data System (ADS)

Wang, Jiaxing; Liang, Yuzhang; Huo, Pengcheng; Wang, Daopeng; Tan, Jun; Xu, Ting

2017-12-01

We report a broadband tungsten absorber based on a nanocone metallic resonant structure fabricated by self-assembly nanosphere lithography. In experimental demonstration, the fabricated absorber has more than 90% average absorption efficiency and shows superior angular tolerance in the entire visible and near-infrared spectral region. We envision that this large-scale nanostructured broadband optical absorber would find great potential in the applications of high performance optoelectronic platforms and solar-thermal energy harvesting systems.

Near-infrared spectral reflectance of mineral mixtures - Systematic combinations of pyroxenes, olivine, and iron oxides

NASA Technical Reports Server (NTRS)

Singer, R. B.

1981-01-01

Near-infrared spectral reflectance data are presented for systematic variations in weight percent of two component mixtures of ferromagnesium and iron oxide minerals used to study the dark materials on Mars. Olivine spectral features are greatly reduced in contrast by admixture of other phases but remain distinctive even for low olivine contents. Clinopyroxene and orthopyroxene mixtures show resolved pyroxene absorptions near 2 microns. Limonite greatly modifies pyroxene and olivine reflectance, but does not fully eliminate distinctive spectral characteristics. Using only spectral data in the 1 micron region, it is difficult to differentiate orthopyroxene and limonite in a mixture. All composite mineral absorptions were either weaker than or intermediate in strength to the end-member absorptions and have bandwidths greater than or equal to those for the end members. In general, spectral properties in an intimate mixture combine in a complex, nonadditive manner, with features demonstrating a regular but usually nonlinear variation as a function of end-member phase proportions.

Environmentally Clean Mitigation of Undesirable Plant Life Using Lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rubenchik, A M; McGrann, T J; Yamamoto, R M

This concept comprises a method for environmentally clean destruction of undesirable plant life using visible or infrared radiation. We believe that during the blossom stage, plant life is very sensitive to electromagnetic radiation, with an enhanced sensitivity to specific spectral ranges. Small doses of irradiation can arrest further plant growth, cause flower destruction or promote plant death. Surrounding plants, which are not in the blossoming stage, should not be affected. Our proposed mechanism to initiate this effect is radiation produced by a laser. Tender parts of the blossom possess enhanced absorptivity in some spectral ranges. This absorption can increase themore » local tissue temperature by several degrees, which is sufficient to induce bio-tissue damage. In some instances, the radiation may actually stimulate plant growth, as an alternative for use in increased crop production. This would be dependent on factors such as plant type, the wavelength of the laser radiation being used and the amount of the radiation dose. Practical, economically viable realization of this concept is possible today with the advent of high efficiency, compact and powerful laser diodes. The laser diodes provide an efficient, environmentally clean source of radiation at a variety of power levels and radiation wavelengths. Figure 1 shows the overall concept, with the laser diodes mounted on a movable platform, traversing and directing the laser radiation over a field of opium poppies.« less

Efficiency enhancement of hybridized solar cells through co-sensitization and fast charge extraction by up-converted polyethylene glycol modified carbon quantum dots

NASA Astrophysics Data System (ADS)

Zhu, Wanlu; Duan, Jialong; Duan, Yanyan; Zhao, Yuanyuan; Tang, Qunwei

2017-11-01

Photovoltaics are promising solutions to energy crisis and environmental pollution problems. The dye-sensitized solar cells with mesoscopic structures have attracted growing interests because of zero emissions, easy fabrication, scalable materials and techniques, etc. However, the state-of-the-art dye-sensitized solar cells have narrow spectral absorption for photoelectric conversion and high electron-hole recombination rate under sunlight illumination. Therefore, it is a persistent object to make wide-spectral absorption and fast charge extraction solar cells for energy harvest in both solar and dark-light conditions. To address this issue, we present here experimental realization of a category of solar cells converting visible and near-infrared light into electricity by co-sensitizing photoanode with N719 dye and polyethylene glycol (PEG) modified carbon quantum dots (PEG-m-CQDs), arising from up-conversion and hole-transporting behaviors of PEG-m-CQDs as well as photofluorescence of green-emitting long persistence phosphors. The optimized solar cell yields maximized photoelectric conversion efficiencies of 9.89% and 25.81% under simulated sunlight (air mass 1.5, 100 mW cm-2) illumination and dark conditions, respectively. This work is far from optimization, but the physical proof-of-concept hybridized solar cell may markedly increase electricity generation time and total power output of photovoltaic platforms.

Thermal emission and absorption of radiation in finite inverted-opal photonic crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Florescu, Marian; Stimpson, Andrew J.; Lee, Hwang

We study theoretically the optical properties of a finite inverted-opal photonic crystal. The light-matter interaction is strongly affected by the presence of the three-dimensional photonic crystal and the alterations of the light emission and absorption processes can be used to suppress or enhance the thermal emissivity and absorptivity of the dielectric structure. We investigate the influence of the absorption present in the system on the relevant band edge frequencies that control the optical response of the photonic crystal. Our study reveals that the absorption processes cause spectral broadening and shifting of the band edge optical resonances, and determine a strongmore » reduction of the photonic band gap spectral range. Using the angular and spectral dependence of the band edge frequencies for stop bands along different directions, we argue that by matching the blackbody emission spectrum peak with a prescribed maximum of the absorption coefficient, it is possible to achieve an angle-sensitive enhancement of the thermal emission/absorption of radiation. This result opens a way to realize a frequency-sensitive and angle-sensitive photonic crystal absorbers/emitters.« less

Optics-based approach to thermal management of photovoltaics: Selective-spectral and radiative cooling

DOE PAGES

Sun, Xingshu; Silverman, Timothy J.; Zhou, Zhiguang; ...

2017-01-20

For commercial one-sun solar modules, up to 80% of the incoming sunlight may be dissipated as heat, potentially raising the temperature 20-30 °C higher than the ambient. In the long term, extreme self-heating erodes efficiency and shortens lifetime, thereby dramatically reducing the total energy output. Therefore, it is critically important to develop effective and practical (and preferably passive) cooling methods to reduce operating temperature of photovoltaic (PV) modules. In this paper, we explore two fundamental (but often overlooked) origins of PV self-heating, namely, sub-bandgap absorption and imperfect thermal radiation. The analysis suggests that we redesign the optical properties of themore » solar module to eliminate parasitic absorption (selective-spectral cooling) and enhance thermal emission (radiative cooling). Comprehensive opto-electro-thermal simulation shows that the proposed techniques would cool one-sun terrestrial solar modules up to 10 °C. As a result, this self-cooling would substantially extend the lifetime for solar modules, with corresponding increase in energy yields and reduced levelized cost of electricity.« less

Two-photon absorption induced stimulated Rayleigh-Bragg scattering

NASA Astrophysics Data System (ADS)

He, Guang S.; Prasad, Paras N.

2005-01-01

A frequency-unshifted and backward stimulated scattering can be efficiently generated in one-photon-absorption free but two-photon absorbing materials. Using a number of novel two-photon absorbing dye solutions as the scattering media and nanosecond pulsed laser as the pump beams, a highly directional backward stimulated scattering at the exact pump wavelength can be readily observed once the pump intensity is higher than a certain threshold level. The spectral and spatial structures as well as the temporal behavior and optical phase-conjugation property of this new type of backward stimulated scattering have been experimentally studied. This stimulated scattering phenomenon can be explained by using a model of two-photon-excitation enhanced standing-wave Bragg grating initially formed by the strong forward pump beam and much weaker backward Rayleigh scattering beam; the partial reflection of the pump beam from this grating provides an positive feedback to the initial backward Rayleigh scattering beam without suffering linear attenuation influence. Comparing to other known stimulated (Raman, Brillouin, Rayleigh-wing, and Kerr) scattering effects, the stimulated Rayleigh-Bragg scattering exhibits the advantages of no frequency-shift, low pump threshold, and low spectral linewidth requirement.

2-.mu.m fiber amplified spontaneous emission (ASE) source

NASA Technical Reports Server (NTRS)

Jiang, Shibin (Inventor); Wu, Jianfeng (Inventor); Geng, Jihong (Inventor)

2007-01-01

A 2-.mu.m fiber Amplified Spontaneous Emission (ASE) source provides a wide emission bandwidth and improved spectral stability/purity for a given output power. The fiber ASE source is formed from a heavy metal oxide multicomponent glass selected from germanate, tellurite and bismuth oxides and doped with high concentrations, 0.5-15 wt. %, thulium oxides (Tm.sub.2O.sub.3) or 0.1-5 wt% holmium oxides (Ho.sub.2O.sub.3) or mixtures thereof. The high concentration of thulium dopants provide highly efficient pump absorption and high quantum efficiency. Co-doping of Tm and Ho can broaden the ASE spectrum.

Intracellular spectral recompositioning of light enhances algal photosynthetic efficiency

PubMed Central

Fu, Weiqi; Chaiboonchoe, Amphun; Khraiwesh, Basel; Sultana, Mehar; Jaiswal, Ashish; Jijakli, Kenan; Nelson, David R.; Al-Hrout, Ala’a; Baig, Badriya; Amin, Amr; Salehi-Ashtiani, Kourosh

2017-01-01

Diatoms, considered as one of the most diverse and largest groups of algae, can provide the means to reach a sustainable production of petrochemical substitutes and bioactive compounds. However, a prerequisite to achieving this goal is to increase the solar-to-biomass conversion efficiency of photosynthesis, which generally remains less than 5% for most photosynthetic organisms. We have developed and implemented a rapid and effective approach, herein referred to as intracellular spectral recompositioning (ISR) of light, which, through absorption of excess blue light and its intracellular emission in the green spectral band, can improve light utilization. We demonstrate that ISR can be used chemogenically, by using lipophilic fluorophores, or biogenically, through the expression of an enhanced green fluorescent protein (eGFP) in the model diatom Phaeodactylum tricornutum. Engineered P. tricornutum cells expressing eGFP achieved 28% higher efficiency in photosynthesis than the parental strain, along with an increased effective quantum yield and reduced nonphotochemical quenching (NPQ) induction levels under high-light conditions. Further, pond simulator experiments demonstrated that eGFP transformants could outperform their wild-type parental strain by 50% in biomass production rate under simulated outdoor sunlight conditions. Transcriptome analysis identified up-regulation of major photosynthesis genes in the engineered strain in comparison with the wild type, along with down-regulation of NPQ genes involved in light stress response. Our findings provide a proof of concept for a strategy of developing more efficient photosynthetic cell factories to produce algae-based biofuels and bioactive products. PMID:28879232

Relationship between the spectral line based weighted-sum-of-gray-gases model and the full spectrum k-distribution model

NASA Astrophysics Data System (ADS)

Chu, Huaqiang; Liu, Fengshan; Consalvi, Jean-Louis

2014-08-01

The relationship between the spectral line based weighted-sum-of-gray-gases (SLW) model and the full-spectrum k-distribution (FSK) model in isothermal and homogeneous media is investigated in this paper. The SLW transfer equation can be derived from the FSK transfer equation expressed in the k-distribution function without approximation. It confirms that the SLW model is equivalent to the FSK model in the k-distribution function form. The numerical implementation of the SLW relies on a somewhat arbitrary discretization of the absorption cross section whereas the FSK model finds the spectrally integrated intensity by integration over the smoothly varying cumulative-k distribution function using a Gaussian quadrature scheme. The latter is therefore in general more efficient as a fewer number of gray gases is required to achieve a prescribed accuracy. Sample numerical calculations were conducted to demonstrate the different efficiency of these two methods. The FSK model is found more accurate than the SLW model in radiation transfer in H2O; however, the SLW model is more accurate in media containing CO2 as the only radiating gas due to its explicit treatment of ‘clear gas.’

A fully functionalized metamaterial perfect absorber with simple design and implementation.

PubMed

Fu, Sze Ming; Zhong, Yan Kai; Tu, Ming Hsiang; Chen, Bo Ruei; Lin, Albert

2016-10-26

Broadband perfect metamaterial absorbers have been drawing significant attention in recent years. A close-to-unity absorption over a broad spectral range is established and this facilitates many photonic applications. A more challenging goal is to construct a broadband absorber with a tailored spectral absorption. The spectral absorption control and spectral shaping are very critical in many applications, such as thermal-photovoltaic, thermal emitters, spectrum imaging system, biomedical and extraterrestrial sensing, and refractive index sensor. In this work, one-dimensional (1D) planar stacking structure is designed to achieve the ultimate goal of a functionalized absorber with a fully tailorable spectral absorption. The lithography and etching process are totally eliminated in this proposed structure, and the fabrication is fully compatible with the regular silicon IC processing. By using ~2 nm ultra-thin metallic layers with a 10-pair (10X) SiO 2 /Si 3 N 4 integrated dielectric filter, we can achieve decent spectral response shaping. The planar configuration of the ultra-thin-metal metamaterial perfect absorber (MPA) is the key to the easy design/integration of the dielectric filters on top of the MPA. Specifically, band-rejected, high-pass, low-pass and band-pass structure are constructed successfully. Finally, experimental evidence to support our simulation result is also provided, which proves the feasibility of our proposal.

Accurately Measuring the Color of the Ocean on Earth and from Space: Uncertainties Revisited and A Report from the Community-Led Spectral Absorption Workshop to Update and Revise the NASA Inherent Optical Properties Protocol

NASA Technical Reports Server (NTRS)

Neeley, Aimee Renee

2014-01-01

The color of the ocean (apparent optical properties or AOPs) is determined by the spectral scattering and absorption of light by its dissolved and particulate constituents.The absorption and scattering properties of the water column are the so-called inherent optical properties.

Compact characterization of liquid absorption and emission spectra using linear variable filters integrated with a CMOS imaging camera.

PubMed

Wan, Yuhang; Carlson, John A; Kesler, Benjamin A; Peng, Wang; Su, Patrick; Al-Mulla, Saoud A; Lim, Sung Jun; Smith, Andrew M; Dallesasse, John M; Cunningham, Brian T

2016-07-08

A compact analysis platform for detecting liquid absorption and emission spectra using a set of optical linear variable filters atop a CMOS image sensor is presented. The working spectral range of the analysis platform can be extended without a reduction in spectral resolution by utilizing multiple linear variable filters with different wavelength ranges on the same CMOS sensor. With optical setup reconfiguration, its capability to measure both absorption and fluorescence emission is demonstrated. Quantitative detection of fluorescence emission down to 0.28 nM for quantum dot dispersions and 32 ng/mL for near-infrared dyes has been demonstrated on a single platform over a wide spectral range, as well as an absorption-based water quality test, showing the versatility of the system across liquid solutions for different emission and absorption bands. Comparison with a commercially available portable spectrometer and an optical spectrum analyzer shows our system has an improved signal-to-noise ratio and acceptable spectral resolution for discrimination of emission spectra, and characterization of colored liquid's absorption characteristics generated by common biomolecular assays. This simple, compact, and versatile analysis platform demonstrates a path towards an integrated optical device that can be utilized for a wide variety of applications in point-of-use testing and point-of-care diagnostics.

Theoretical model and simulations for a cw exciplex pumped alkali laser.

PubMed

Huang, Wei; Tan, Rongqing; Li, Zhiyong; Lu, Xiaochuan

2015-12-14

The Exciplex Pumped Alkali Laser (XPAL) system, which is similar to DPAL (Diode Pumped Alkali vapor Laser), has been demonstrated in mixtures of Cs vapor, Ar, with and without ethane. Unlike DPAL, it uses the broadband absorption blue satellite of the alkali D₂ line, created by naturally occuring collision pairs. For example, Cs-Ar collision pairs have an absorption width which is as wide as the one of commercial semiconductor diode lasers. A continuous wave XPAL four-level theoretical model is presented in this paper. More factors are considered, such as the spectral dependence of pumped laser absorption for broadband pumping and the longitudinal population variation. Some intra-cavity details, such as longitudinal distributions of pumped laser and alkali laser, can also be solved well. The predictions of optical-to-optical efficiency as a function of temperature and pumped laser intensity are presented. The model predicts that there is an optimum value of temperature or pumped laser intensity. The analysis of the influence of cell length on optical-to-optical efficiency shows that a better performance can be achieved when using longer cell. The prediction of influence of Ar concentration and reflectivity of output coupler shows that higher optical-to-optical efficiency could be achieved if lower reflectivity of output coupler and higher Ar concentration are used. The optical-to-optical efficiency as high as 84% achieved by optimizing configuration with the pumped intensity of 5 × 10⁷ W/cm² presented shows that broadband pumped four-level XPAL system has a potential of high optical-to-optical efficiency.

Aging behavior of near atmospheric N2 ambient sputtered/patterned Au IR absorber thin films

NASA Astrophysics Data System (ADS)

Gaur, Surender P.; Kothari, Prateek; Rangra, Kamaljit; Kumar, Dinesh

2018-03-01

Near atmospheric N2 ambient sputtered Au thin films exhibit significant spectral absorptivity over medium to long wave infrared radiations. Thin films were found adequately robust for micropatterning using conventional photolithography and metal lift off processes. Since long term spectral absorptivity is major practical concern for Au blacks, this paper reports on aging behavior of near atmospheric Ar and Ar + N2 (1:1) ambient sputtered infrared absorber Au thin films. Comparative analysis on electrical, morphological and spectral absorption behavior of twenty-five weeks room temperature/vacuum aged Au infrared absorber thin films is performed. The Ar and Ar + N2 ambient sputtered Au thing films have shown anticipated consistency in their physical, electrical and spectral properties regardless the long term aging in this work.

The influence of the distance between the donor-acceptor groups of polymethine dyes on their photovoltaic properties

NASA Astrophysics Data System (ADS)

Seliverstova, E.; Ibrayev, N.

2018-01-01

Spectral-luminescent and photovoltaic properties of polymethine dyes of various structures are studied. It is shown that an increase in the length of the methylene chain between the active chromophores leads to a red-wave shift of the absorption and fluorescence spectra. Significant changes in the absorptivity and lifetime of fluorescence do not occur in this case. The best photovoltaic parameters have cells sensitized with shorter dye molecules. It is shown, that for a longer dye the resistance associated with electron recombination on the TiO2/electrolyte surface is much higher than the electron transfer resistance in the semiconductor, which reduces the efficiency of electron transfer in the solar cell, sensitized with longer dye molecules.

X-ray source development for EXAFS measurements on the National Ignition Facility.

PubMed

Coppari, F; Thorn, D B; Kemp, G E; Craxton, R S; Garcia, E M; Ping, Y; Eggert, J H; Schneider, M B

2017-08-01

Extended X-ray absorption Fine Structure (EXAFS) measurements require a bright, spectrally smooth, and broad-band x-ray source. In a laser facility, such an x-ray source can be generated by a laser-driven capsule implosion. In order to optimize the x-ray emission, different capsule types and laser irradiations have been tested at the National Ignition Facility (NIF). A crystal spectrometer is used to disperse the x-rays and high efficiency image plate detectors are used to measure the absorption spectra in transmission geometry. EXAFS measurements at the K-edge of iron at ambient conditions have been obtained for the first time on the NIF laser, and the requirements for optimization have been established.

Tunable diode laser measurements of HO2NO2 absorption coefficients near 12.5 microns

NASA Technical Reports Server (NTRS)

May, R. D.; Molina, L. T.; Webster, C. R.

1988-01-01

A tunable diode laser spectrometer has been used to measure absorption coefficients of peroxynitric acid (HO2NO2) near the 803/cm Q branch. HO2NO2 concentrations in a low-pressure flowing gas mixture were determined from chemical titration procedures and UV absorption spectroscopy. The diode laser measured absorption coefficients, at a spectral resolution of better than 0.001/cm, are about 10 percent larger than previous Fourier transform infrared measurements made at a spectral resolution of 0.06/cm.

Explaining Space-Weathering Effects on UV-Vis-NIR Spectra with Light-Scattering Methods

NASA Astrophysics Data System (ADS)

Penttilä, Antti; Väisänen, Timo; Martikainen, Julia; Kohout, Tomas; Muinonen, Karri

2015-11-01

Space-weathering (SW) introduces changes to the asteroid reflectance spectra. In silicate minerals, SW is known to darken the spectra and reduce the silicate absorption band depths. In olivine, the neutral slope in Vis and NIR wavelengths is becoming positive [1]. In pyroxene, the positive slope over the 1 µm absorption band is decreasing, and the negative slope over the 2 µm band is increasing towards positive values with increasing SW [2].The SW process generates small nanophase iron (npFe0) inclusions in the surface layers of mineral grains. The inclusions are some tens of nm in size. This mechanism has been linked to the Moon and to a certain extent also to the silicate-rich S-complex asteroids.We offer two simple explanations from light-scattering theory to explain the SW effects on the spectral slope. First, the npFe0 will introduce a posititive general slope (reddening) to the spectra. The npFe0 inclusions (~10 nm) are in the Rayleigh domain with the wavelength λ in the UV-Vis-NIR range. Their absorption cross-section follows approximately the 1/λ-relation from the Rayleigh theory. Absorption is more efficient in the UV than in the NIR wavelengths, therefore the spectra are reddening.Second, the effect of npFe0 absorption is more efficient for originally brighter reflectance values. Explanation combines the effective medium theory and the exponential attenuation in the medium. When adding a small amount of highly absorbing npFe0, the effective absorption coefficient k will increase approximately the same Δk for the typical values of silicates. This change will increase more effectively the exponential attenuation if the original k was very small, and thus the reflectance high. Therefore, both positive and negative spectral slopes will approach zero with SW.We conclude that the SW will introduce a general reddening, and neutralize local slopes. This is verified using the SIRIS code [3], which combines geometric optics with small internal diffuse scatterers in the radiative transfer domain.[1] Kohout T. et al. (2014), Icarus 237(15), 75-83.[2] Kohout T. et al. (2015), Workshop on Space Weathering of Airless Bodies, Abstract.[3] Muinonen K. et al. (2009), JQSRT 110, 1628-1639.

Probing Exciton and Charge Dynamics in Organic Thin Films and Photovoltaics with Nonlinear Spectroscopy

NASA Astrophysics Data System (ADS)

McDonough, Thomas J.

Emerging organic solar cell technologies offer unique advantages over silicon solar cells, such as solution processability and the use of flexible substrates, but the efficiencies of these devices do not yet match the efficiency of silicon. Ultrafast nonlinear spectroscopies can probe the fates of photoexcited species on timescales in which these species are lost to channels that do not result in electric current. In the first study, I compare the ultrafast dynamics of singlet fission and charge generation in pentacene films grown on glass and graphene. The molecular orientation is different on the two substrates: the long axis of the pentacene molecules are "standing-up" (normal to the surface) on glass and "lying-down" (parallel to the surface) on graphene. By studying the fluence and polarization dependence of the transient absorption of pentacene on these two substrates, I am able to clarify previous spectral assignments. I identify a broad, isotropic absorption at 853 nm as due in significant part to hole absorption, in contrast to this feature's typical assignment to T1-T2 absorption. At high fluence, additional peaks at 614 and 688 (on glass) nm appear, whose kinetics and anisotropies are not explained by heating, which I assign to charge generation. In the second study, I utilize two-dimensional white-light spectroscopy to study the morphology dependence of exciton diffusion in semiconducting carbon nanotubes. I analyze the spectral diffusion of the S 1-S1 2D-WL lineshape via the center line slope method to separate the homogeneous and inhomogeneous contributions to the lineshape in each sample. I determine a morphology independent homogeneous linewidth of 10 meV, but I find that the inhomogeneous linewidth is sensitive to the particular sample environment. I model our experimental spectra with kinetic Monte Carlo simulations of exciton diffusion in a 1D potential. I also present preliminary bias-dependent transient absorption and 2D-WL measurements of carbon nanotube solar cell devices. I observe increasing positive trion absorption with increasing forward bias. The kinetics in the device are much different than the kinetics in the thin film, and there is an interesting change in kinetics with bias voltage that requires further investigation.

Impact of Chromophoric dissolved organic matter on light absorption in lake water on the Tibetan Plateau, China

NASA Astrophysics Data System (ADS)

Nima, Ciren; Hamre, Børge; Frette, Øyvind; Erga, Svein Rune; Chen, Yi-Chun; Zhao, Lu; Sørensen, Kai; Norli, Marit; Stamnes, Jakob J.

2017-02-01

Ground-based measurements of optical properties are rare for water in lakes on the Tibetan Plateau (TP). We analyzed the spectral absorption of Chromophoric Dissolved Organic Matter (CDOM) for water samples from Lake Namtso (LN) on the TP. The mean value of the spectral slope S280-500 for CDOM absorption was found to be 0.036 nm-1, whereas the corresponding mean value for S350-500 was found to be 0.015 nm-1, implying that when comparing spectral slope values with published values, the wavelength range used for deriving them should be considered.

Mid-infrared crystalline supermirrors with ultralow optical absorption (Conference Presentation)

NASA Astrophysics Data System (ADS)

Deutsch, Christoph; Cole, Garrett D.; Follman, David; Heu, Paula; Bjork, Bryce J.; Franz, Chris; Alexandrovski, Alexei L.; Heckl, Oliver H.; Ye, Jun; Aspelmeyer, Markus

2017-02-01

Substrate-transferred crystalline coatings are a groundbreaking new concept for the fabrication of ultralow-loss mirrors. The single-crystal lattice structure of these substrate-transferred GaAs/AlGaAs Bragg mirrors exhibits the lowest mechanical losses and hence unmatched Brownian noise performance, which nowadays limits the stability of precision optical interferometers. Another outstanding feature of these coatings is the wide spectral coverage of the GaAs/AlGaAs material platform. Limited by interband absorption at short wavelengths and the reststrahlen band at long wavelengths, crystalline coatings can be employed as low-loss multilayers from approximately 900 nm up to 5 μm and beyond. Excellent optical performance has been demonstrated in the near-infrared with excess optical losses (scatter + absorption) as low as 3 parts per million (ppm), enabling cavity finesse values up to 360,000 at 1.55 μm. Our first attempts at applying crystalline coatings in the mid-infrared has resulted in mirrors with excess optical losses of 159 and 242 ppm at 3.3 and 3.7 μm, respectively. Remarkably, these results are already on par with current state-of-the-art amorphous mirror coatings. Absorption measurements based on photothermal common-path interferometry (PCI) reveal that the optical losses are largely dominated by optical scatter. Via, PCI, we have confirmed absorption losses below 10 ppm at 3.7 μm, showing the enormous potential of GaAs/AlGaAs Bragg mirrors at mid-infrared wavelengths. An optimized fabrication process, which is currently under development, can efficiently suppress optical scatter due to accumulated growth defects on the surface. Ultimately, we foresee excess losses significantly less than 50 ppm in the mid-infrared spectral region.

In situ phytoplankton absorption, fluorescence emission, and particulate backscattering spectra determined from reflectance

NASA Technical Reports Server (NTRS)

Roesler, Collin S.; Pery, Mary Jane

1995-01-01

An inverse model was developed to extract the absortion and scattering (elastic and inelastic) properties of oceanic constituents from surface spectral reflectance measurements. In particular, phytoplankton spectral absorption coefficients, solar-stimulated chlorophyll a fluorescence spectra, and particle backscattering spectra were modeled. The model was tested on 35 reflectance spectra obtained from irradiance measurements in optically diverse ocean waters (0.07 to 25.35 mg/cu m range in surface chlorophyll a concentrations). The universality of the model was demonstrated by the accurate estimation of the spectral phytoplankton absorption coefficents over a range of 3 orders of magnitude (rho = 0.94 at 500 nm). Under most oceanic conditions (chlorophyll a less than 3 mg/cu m) the percent difference between measured and modeled phytoplankton absorption coefficents was less than 35%. Spectral variations in measured phytoplankton absorption spectra were well predicted by the inverse model. Modeled volume fluorescence was weakly correlated with measured chl a; fluorescence quantum yield varied from 0.008 to 0.09 as a function of environment and incident irradiance. Modeled particle backscattering coefficients were linearly related to total particle cross section over a twentyfold range in backscattering coefficents (rho = 0.996, n = 12).

Iodine absorption cells quality evaluation methods

NASA Astrophysics Data System (ADS)

Hrabina, Jan; Zucco, Massimo; Holá, Miroslava; Šarbort, Martin; Acef, Ouali; Du-Burck, Frédéric; Lazar, Josef; Číp, Ondřej

2016-12-01

The absorption cells represent an unique tool for the laser frequency stabilization. They serve as irreplaceable optical frequency references in realization of high-stable laser standards and laser sources for different brands of optical measurements, including the most precise frequency and dimensional measurement systems. One of the most often used absorption media covering visible and near IR spectral range is molecular iodine. It offers rich atlas of very strong and narrow spectral transitions which allow realization of laser systems with ultimate frequency stabilities in or below 10-14 order level. One of the most often disccussed disadvantage of the iodine cells is iodine's corrosivity and sensitivity to presence of foreign substances. The impurities react with absorption media and cause spectral shifts of absorption spectra, spectral broadening of the transitions and decrease achievable signal-to-noise ratio of the detected spectra. All of these unwanted effects directly influence frequency stability of the realized laser standard and due to this fact, the quality of iodine cells must be precisely controlled. We present a comparison of traditionally used method of laser induced fluorescence (LIF) with novel technique based on hyperfine transitions linewidths measurement. The results summarize advantages and drawbacks of these techniques and give a recommendation for their practical usage.

Second-harmonic generation at angular incidence in a negative-positive index photonic band-gap structure.

PubMed

D'Aguanno, Giuseppe; Mattiucci, Nadia; Scalora, Michael; Bloemer, Mark J

2006-08-01

In the spectral region where the refractive index of the negative index material is approximately zero, at oblique incidence, the linear transmission of a finite structure composed of alternating layers of negative and positive index materials manifests the formation of a new type of band gap with exceptionally narrow band-edge resonances. In particular, for TM-polarized (transverse magnetic) incident waves, field values that can be achieved at the band edge may be much higher compared to field values achievable in standard photonic band-gap structures. We exploit the unique properties of these band-edge resonances for applications to nonlinear frequency conversion, second-harmonic generation, in particular. The simultaneous availability of high field localization and phase matching conditions may be exploited to achieve second-harmonic conversion efficiencies far better than those achievable in conventional photonic band-gap structures. Moreover, we study the role played by absorption within the negative index material, and find that the process remains efficient even for relatively high values of the absorption coefficient.

Improvement of black nickel coatings. [product development for use in solar collectors

NASA Technical Reports Server (NTRS)

Peterson, R. E.; Lin, J. H.

1976-01-01

Selectively absorbing black nickel coatings are among the most optically efficient low cost coatings for use on flat plate solar collectors. However, a current Ni-Zn-S-O coating in use is quite susceptible to a humid environment, degrading badly in less than ten days at 38 C (100 F) at 95 percent relative humidity. Therefore, a black nickel formula was developed which can withstand such exposures with no loss of optical efficiency, solar absorption of 0.92 and an infrared emittance (at 100 C) of 1.00 were still present after 14 days of humidity exposure. This compares to a solar absorptance of only 0.72 for the previous formula after a similar time period. The electroplating bath and conditions were changed to obtain the more stable coating configuration. The effect of bath composition, temperature, pH, and plating current density and time on the coating composition, spectral optical properties and durability were investigated systematically.

Advancing colloidal quantum dot photovoltaic technology

NASA Astrophysics Data System (ADS)

Cheng, Yan; Arinze, Ebuka S.; Palmquist, Nathan; Thon, Susanna M.

2016-06-01

Colloidal quantum dots (CQDs) are attractive materials for solar cells due to their low cost, ease of fabrication and spectral tunability. Progress in CQD photovoltaic technology over the past decade has resulted in power conversion efficiencies approaching 10%. In this review, we give an overview of this progress, and discuss limiting mechanisms and paths for future improvement in CQD solar cell technology.We briefly summarize nanoparticle synthesis and film processing methods and evaluate the optoelectronic properties of CQD films, including the crucial role that surface ligands play in materials performance. We give an overview of device architecture engineering in CQD solar cells. The compromise between carrier extraction and photon absorption in CQD photovoltaics is analyzed along with different strategies for overcoming this trade-off. We then focus on recent advances in absorption enhancement through innovative device design and the use of nanophotonics. Several light-trapping schemes, which have resulted in large increases in cell photocurrent, are described in detail. In particular, integrating plasmonic elements into CQD devices has emerged as a promising approach to enhance photon absorption through both near-field coupling and far-field scattering effects. We also discuss strategies for overcoming the single junction efficiency limits in CQD solar cells, including tandem architectures, multiple exciton generation and hybrid materials schemes. Finally, we offer a perspective on future directions for the field and the most promising paths for achieving higher device efficiencies.

Scanning imaging absorption spectrometer for atmospheric chartography

NASA Technical Reports Server (NTRS)

Burrows, John P.; Chance, Kelly V.

1991-01-01

The SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY is an instrument which measures backscattered, reflected, and transmitted light from the earth's atmosphere and surface. SCIAMACHY has eight spectral channels which observe simultaneously the spectral region between 240 and 1700 nm and selected windows between 1940 and 2400 nm. Each spectral channel contains a grating and linear diode array detector. SCIAMACHY observes the atmosphere in nadir, limb, and solar and lunar occultation viewing geometries.

Atmospheric solar absorption measurements in the 9 to 11 mu m region using a diode laser heterodyne spectrometer

NASA Technical Reports Server (NTRS)

Harward, C. N.; Hoell, J. M., Jr.

1980-01-01

A tunable diode laser heterodyne radiometer was developed for ground-based measurements of atmospheric solar absorption spectra in the 8 to 12 microns spectral range. The performance and operating characteristics of this Tunable Infrared Heterodyne Radiometer (TIHR) are discussed along with atmospheric solar absorption spectra of HNO3, O3, CO2, and H2O in the 9 to 11 microns spectral region.

Diffuse-light absorption spectroscopy by fiber optics for detecting and quantifying the adulteration of extra virgin olive oil

NASA Astrophysics Data System (ADS)

Mignani, A. G.; Ciaccheri, L.; Ottevaere, H.; Thienpont, H.; Conte, L.; Marega, M.; Cichelli, A.; Attilio, C.; Cimato, A.

2010-09-01

A fiber optic setup for diffuse-light absorption spectroscopy in the wide 400-1700 nm spectral range is experimented for detecting and quantifying the adulteration of extra virgin olive oil caused by lower-grade olive oils. Absorption measurements provide spectral fingerprints of authentic and adulterated oils. A multivariate processing of spectroscopic data is applied for discriminating the type of adulterant and for predicting its fraction.

Optimal design of aperiodic, vertical silicon nanowire structures for photovoltaics.

PubMed

Lin, Chenxi; Povinelli, Michelle L

2011-09-12

We design a partially aperiodic, vertically-aligned silicon nanowire array that maximizes photovoltaic absorption. The optimal structure is obtained using a random walk algorithm with transfer matrix method based electromagnetic forward solver. The optimal, aperiodic structure exhibits a 2.35 times enhancement in ultimate efficiency compared to its periodic counterpart. The spectral behavior mimics that of a periodic array with larger lattice constant. For our system, we find that randomly-selected, aperiodic structures invariably outperform the periodic array.

[Research on Oil Sands Spectral Characteristics and Oil Content by Remote Sensing Estimation].

PubMed

You, Jin-feng; Xing, Li-xin; Pan, Jun; Shan, Xuan-long; Liang, Li-heng; Fan, Rui-xue

2015-04-01

Visible and near infrared spectroscopy is a proven technology to be widely used in identification and exploration of hydrocarbon energy sources with high spectral resolution for detail diagnostic absorption characteristics of hydrocarbon groups. The most prominent regions for hydrocarbon absorption bands are 1,740-1,780, 2,300-2,340 and 2,340-2,360 nm by the reflectance of oil sands samples. These spectral ranges are dominated by various C-H overlapping overtones and combination bands. Meanwhile, there is relatively weak even or no absorption characteristics in the region from 1,700 to 1,730 nm in the spectra of oil sands samples with low bitumen content. With the increase in oil content, in the spectral range of 1,700-1,730 nm the obvious hydrocarbon absorption begins to appear. The bitumen content is the critical parameter for oil sands reserves estimation. The absorption depth was used to depict the response intensity of the absorption bands controlled by first-order overtones and combinations of the various C-H stretching and bending fundamentals. According to the Pearson and partial correlation relationships of oil content and absorption depth dominated by hydrocarbon groups in 1,740-1,780, 2,300-2,340 and 2,340-2,360 nm wavelength range, the scheme of association mode was established between the intensity of spectral response and bitumen content, and then unary linear regression(ULR) and partial least squares regression (PLSR) methods were employed to model the equation between absorption depth attributed to various C-H bond and bitumen content. There were two calibration equations in which ULR method was employed to model the relationship between absorption depth near 2,350 nm region and bitumen content and PLSR method was developed to model the relationship between absorption depth of 1,758, 2,310, 2,350 nm regions and oil content. It turned out that the calibration models had good predictive ability and high robustness and they could provide the scientific basis for rapid estimation of oil content in oil sands in future.

Efficiency enhancement of ZnO nanostructure assisted Si solar cell based on fill factor enlargement and UV-blue spectral down-shifting

NASA Astrophysics Data System (ADS)

Gholizadeh, A.; Reyhani, A.; Parvin, P.; Mortazavi, S. Z.

2017-05-01

ZnO nanostructures (including nano-plates and nano-rods (NRs)) are grown in various temperatures and Ar/O2 flow rates using thermal chemical vapor deposition, which affect the structure, nano-plate/NR population, and the quality of ZnO nanostructures. X-ray diffraction (XRD) attests that the peak intensity of the crystallographic plane (1 0 0) is correlated to nano-plate abundance. Moreover, optical properties elucidate that the population of nano-plates in samples strongly affect the band gap, binding energy of the exciton, and UV-visible (UV-vis) absorption and spectral luminescence emissions. In fact, the exciton binding energy reduces from ~100 to 80 meV when the population of nano-plates increases in samples. Photovoltaic characteristics based on the drop-casting on Si solar cells reveals three dominant factors, namely, the equivalent series resistance, decreasing reflectance, and down-shifting, in order to scale up the absolute efficiency by 3%. As a consequence, the oxygen vacancies in ZnO nanostructures give rise to the down-shifting and increase of free-carriers, leading to a reduction in the equivalent series resistance and an enlargement of fill factor. To obtain a larger I sc, reduction of spectral reflectance is essential; however, the down-shifting process is shown to be dominant by lessening the surface electron-hole recombination rate over the UV-blue spectral range.

Impact of pentacene film thickness on the photoresponse spectra: Determination of the photocarrier generation mechanism

NASA Astrophysics Data System (ADS)

Gorgolis, S.; Giannopoulou, A.; Anastassopoulos, D.; Kounavis, P.

2012-07-01

Photocurrent response, optical absorption, and x-ray diffraction (XRD) measurements in pentacene films grown on glass substrates are performed in order to obtain an insight into the mobile photocarriers generation mechanism. For film thickness of the order of 50 nm and lower, the photocurrent response spectra are found to follow the optical absorption spectra demonstrating the so-called symbatic response. Upon increasing the film thickness, the photoresponse demonstrates a transition to the so-called antibatic response, which is characterized by a maximum and minimum photocurrent for photon energies of minimum and maximum optical absorption, respectively. The experimental results are not in accordance with the model of important surface recombination rate. By taking into account the XRD patterns, the experimental photoresponse spectra can be reproduced by model simulations assuming efficient exciton dissociation at a narrow layer of the order of 20 nm near the pentacene-substrate interface. The simulated spectra are found sensitive to the film thickness, the absolute optical absorption coefficient, and the diffusion exciton length. By comparing the experimental with the simulated spectra, it is deduced that the excitons, which are created by optical excitation in the spectral region of 1.7-2.2 eV, diffuse with a diffusion length of the order of 10-80 nm to the pentacene-substrate interface where efficiently dissociate into mobile charge carriers.

Method for Balancing Detector Output to a Desired Level of Balance at a Frequency

NASA Technical Reports Server (NTRS)

Sachse, Glenn W. (Inventor)

2003-01-01

A multi-gas sensor is provided which modulates a polarized light beam over a broadband of wavelengths between two alternating orthogonal polarization components. The two orthogonal polarization components of the polarization modulated beam are directed along two distinct optical paths. At least one optical path contains one or more spectral discrimination elements, with each spectral discrimination element having spectral absorption features of one or more gases of interest being measured. The two optical paths then intersect, and one orthogonal component of the intersected components is transmitted and the other orthogonal component is reflected. The combined polarization modulated beam is partitioned into one or more smaller spectral regions of interest where one or more gases of interest has an absorption band. The difference in intensity between the two orthogonal polarization components is then determined in each partitioned spectral region of interest as an indication of the spectral emission/absorption of the light beam by the gases of interest in the measurement path. The spectral emission/absorption is indicative of the concentration of the one or more gases of interest in the measurement path. More specifically, one embodiment of the present invention is a gas filter correlation radiometer which comprises a polarizer, a polarization modulator, a polarization beam splitter, a beam combiner, wavelength partitioning element, and detection element. The gases of interest are measured simultaneously and, further, can be measured independently or non-independently. Furthermore, optical or electronic element are provided to balance optical intensities between the two optical paths.

Multi-Gas Sensor

NASA Technical Reports Server (NTRS)

Sachse, Glenn W. (Inventor); Wang, Liang-Guo (Inventor); LeBel, Peter J. (Inventor); Steele, Tommy C. (Inventor); Rana, Mauro (Inventor)

1999-01-01

A multi-gas sensor is provided which modulates a polarized light beam over a broadband of wavelengths between two alternating orthogonal polarization components. The two orthogonal polarization components of the polarization modulated beam are directed along two distinct optical paths. At least one optical path contains one or more spectral discrimination element, with each spectral discrimination element having spectral absorption features of one or more gases of interest being measured. The two optical paths then intersect, and one orthogonal component of the intersected components is transmitted and the other orthogonal component is reflected. The combined polarization modulated beam is partitioned into one or more smaller spectral regions of interest where one or more gases of interest has an absorption band. The difference in intensity between the two orthogonal polarization components is then determined in each partitioned spectral region of interest as an indication of the spectral emission/absorption of the light beam by the gases of interest in the measurement path. The spectral emission/absorption is indicative of the concentration of the one or more gases of interest in the measurement path. More specifically, one embodiment of the present invention is a gas filter correlation radiometer which comprises a polarizer, a polarization modulator, a polarization beam splitter, a beam combiner, wavelength partitioning element, and detection element. The gases of interest are measured simultaneously and, further, can be measured independently or non-independently. Furthermore, optical or electronic element are provided to balance optical intensities between the two optical paths.

Quantitative photoacoustic microscopy of optical absorption coefficients from acoustic spectra in the optical diffusive regime

NASA Astrophysics Data System (ADS)

Guo, Zijian; Favazza, Christopher; Garcia-Uribe, Alejandro; Wang, Lihong V.

2012-06-01

Photoacoustic (PA) microscopy (PAM) can image optical absorption contrast with ultrasonic spatial resolution in the optical diffusive regime. Conventionally, accurate quantification in PAM requires knowledge of the optical fluence attenuation, acoustic pressure attenuation, and detection bandwidth. We circumvent this requirement by quantifying the optical absorption coefficients from the acoustic spectra of PA signals acquired at multiple optical wavelengths. With the acoustic spectral method, the absorption coefficients of an oxygenated bovine blood phantom at 560, 565, 570, and 575 nm were quantified with errors of <3%. We also quantified the total hemoglobin concentration and hemoglobin oxygen saturation in a live mouse. Compared with the conventional amplitude method, the acoustic spectral method provides greater quantification accuracy in the optical diffusive regime. The limitations of the acoustic spectral method was also discussed.

Quantitative photoacoustic microscopy of optical absorption coefficients from acoustic spectra in the optical diffusive regime

PubMed Central

Guo, Zijian; Favazza, Christopher; Garcia-Uribe, Alejandro

2012-01-01

Abstract. Photoacoustic (PA) microscopy (PAM) can image optical absorption contrast with ultrasonic spatial resolution in the optical diffusive regime. Conventionally, accurate quantification in PAM requires knowledge of the optical fluence attenuation, acoustic pressure attenuation, and detection bandwidth. We circumvent this requirement by quantifying the optical absorption coefficients from the acoustic spectra of PA signals acquired at multiple optical wavelengths. With the acoustic spectral method, the absorption coefficients of an oxygenated bovine blood phantom at 560, 565, 570, and 575 nm were quantified with errors of <3%. We also quantified the total hemoglobin concentration and hemoglobin oxygen saturation in a live mouse. Compared with the conventional amplitude method, the acoustic spectral method provides greater quantification accuracy in the optical diffusive regime. The limitations of the acoustic spectral method was also discussed. PMID:22734767

Quantitative photoacoustic microscopy of optical absorption coefficients from acoustic spectra in the optical diffusive regime.

PubMed

Guo, Zijian; Favazza, Christopher; Garcia-Uribe, Alejandro; Wang, Lihong V

2012-06-01

Photoacoustic (PA) microscopy (PAM) can image optical absorption contrast with ultrasonic spatial resolution in the optical diffusive regime. Conventionally, accurate quantification in PAM requires knowledge of the optical fluence attenuation, acoustic pressure attenuation, and detection bandwidth. We circumvent this requirement by quantifying the optical absorption coefficients from the acoustic spectra of PA signals acquired at multiple optical wavelengths. With the acoustic spectral method, the absorption coefficients of an oxygenated bovine blood phantom at 560, 565, 570, and 575 nm were quantified with errors of <3%. We also quantified the total hemoglobin concentration and hemoglobin oxygen saturation in a live mouse. Compared with the conventional amplitude method, the acoustic spectral method provides greater quantification accuracy in the optical diffusive regime. The limitations of the acoustic spectral method was also discussed.

Impact of absorption in the top layer of a two layer sample on spectroscopic spectral domain interferometry of the bottom layer

NASA Astrophysics Data System (ADS)

Fleischhauer, F.; Feuchter, T.; Leick, L.; Rajendram, R.; Podoleanu, A.

2018-03-01

Spectroscopic spectral domain interferometry and spectroscopic optical coherence tomography combine depth information with spectrally-resolved localised absorption data. These additional data can improve diagnostics by giving access to functional information of the investigated sample. One possible application is measuring oxygenation levels at the retina for earlier detection of several eye diseases. Here measurements with different hollow glass tube phantoms are shown to measure the impact of a superficial absorbing layer on the precision of reconstructed attenuation spectra of a deeper layer. Measurements show that a superficial absorber has no impact on the reconstructed absorption spectrum of the deeper absorber. Even when diluting the concentration of the deeper absorber so far that an incorrect absorption maximum is obtained, still no influence of the superficially placed absorber is identified.

Active multispectral imaging system for photodiagnosis and personalized phototherapies

NASA Astrophysics Data System (ADS)

Ugarte, M. F.; Chávarri, L.; Briz, S.; Padrón, V. M.; García-Cuesta, E.

2014-10-01

The proposed system has been designed to identify dermatopathologies or to apply personalized phototherapy treatments. The system emits electromagnetic waves in different spectral bands in the range of visible and near infrared to irradiate the target (skin or any other object) to be spectrally characterized. Then, an imaging sensor measures the target response to the stimulus at each spectral band and, after processing, the system displays in real time two images. In one of them the value of each pixel corresponds to the more reflected wavenumber whereas in the other image the pixel value represents the energy absorbed at each band. The diagnosis capability of this system lies in its multispectral design, and the phototherapy treatments are adapted to the patient and his lesion by measuring his absorption capability. This "in situ" absorption measurement allows us to determine the more appropriate duration of the treatment according to the wavelength and recommended dose. The main advantages of this system are its low cost, it does not have moving parts or complex mechanisms, it works in real time, and it is easy to handle. For these reasons its widespread use in dermatologist consultation would facilitate the work of the dermatologist and would improve the efficiency of diagnosis and treatment. In fact the prototype has already been successfully applied to pathologies such as carcinomas, melanomas, keratosis, and nevi.

History of one family of atmospheric radiative transfer codes

NASA Astrophysics Data System (ADS)

Anderson, Gail P.; Wang, Jinxue; Hoke, Michael L.; Kneizys, F. X.; Chetwynd, James H., Jr.; Rothman, Laurence S.; Kimball, L. M.; McClatchey, Robert A.; Shettle, Eric P.; Clough, Shepard (.; Gallery, William O.; Abreu, Leonard W.; Selby, John E. A.

1994-12-01

Beginning in the early 1970's, the then Air Force Cambridge Research Laboratory initiated a program to develop computer-based atmospheric radiative transfer algorithms. The first attempts were translations of graphical procedures described in a 1970 report on The Optical Properties of the Atmosphere, based on empirical transmission functions and effective absorption coefficients derived primarily from controlled laboratory transmittance measurements. The fact that spectrally-averaged atmospheric transmittance (T) does not obey the Beer-Lambert Law (T equals exp(-(sigma) (DOT)(eta) ), where (sigma) is a species absorption cross section, independent of (eta) , the species column amount along the path) at any but the finest spectral resolution was already well known. Band models to describe this gross behavior were developed in the 1950's and 60's. Thus began LOWTRAN, the Low Resolution Transmittance Code, first released in 1972. This limited initial effort has how progressed to a set of codes and related algorithms (including line-of-sight spectral geometry, direct and scattered radiance and irradiance, non-local thermodynamic equilibrium, etc.) that contain thousands of coding lines, hundreds of subroutines, and improved accuracy, efficiency, and, ultimately, accessibility. This review will include LOWTRAN, HITRAN (atlas of high-resolution molecular spectroscopic data), FASCODE (Fast Atmospheric Signature Code), and MODTRAN (Moderate Resolution Transmittance Code), their permutations, validations, and applications, particularly as related to passive remote sensing and energy deposition.

Active multispectral imaging system for photodiagnosis and personalized phototherapies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ugarte, M. F., E-mail: marta.ugarte@uem.es, E-mail: sbriz@fis.uc3m.es; Chávarri, L.; Padrón, V. M.

2014-10-15

The proposed system has been designed to identify dermatopathologies or to apply personalized phototherapy treatments. The system emits electromagnetic waves in different spectral bands in the range of visible and near infrared to irradiate the target (skin or any other object) to be spectrally characterized. Then, an imaging sensor measures the target response to the stimulus at each spectral band and, after processing, the system displays in real time two images. In one of them the value of each pixel corresponds to the more reflected wavenumber whereas in the other image the pixel value represents the energy absorbed at eachmore » band. The diagnosis capability of this system lies in its multispectral design, and the phototherapy treatments are adapted to the patient and his lesion by measuring his absorption capability. This “in situ” absorption measurement allows us to determine the more appropriate duration of the treatment according to the wavelength and recommended dose. The main advantages of this system are its low cost, it does not have moving parts or complex mechanisms, it works in real time, and it is easy to handle. For these reasons its widespread use in dermatologist consultation would facilitate the work of the dermatologist and would improve the efficiency of diagnosis and treatment. In fact the prototype has already been successfully applied to pathologies such as carcinomas, melanomas, keratosis, and nevi.« less

Influence of synchrotron self-absorption on 21-cm experiments

NASA Astrophysics Data System (ADS)

Zheng, Qian; Wu, Xiang-Ping; Gu, Jun-Hua; Wang, Jingying; Xu, Haiguang

2012-08-01

The presence of spectral curvature resulting from the synchrotron self-absorption of extragalactic radio sources could break down the spectral smoothness feature. This leads to the premise that the bright radio foreground can be successfully removed in 21-cm experiments that search for the epoch of reionization (EoR). We present a quantitative estimate of the effect of the spectral curvature resulting from the synchrotron self-absorption of extragalactic radio sources on the measurement of the angular power spectrum of the low-frequency sky. We incorporate a phenomenological model, which is characterized by the fraction (f) of radio sources with turnover frequencies in the range of 100-1000 MHz and by a broken power law for the spectral transition around the turnover frequencies νm, into simulated radio sources over a small sky area of 10° × 10°. We compare statistically the changes in their residual maps with and without the inclusion of the synchrotron self-absorption of extragalactic radio sources after the bright sources of S150 MHz ≥100 mJy are excised. Furthermore, the best-fitting polynomials in the frequency domain on each pixel are subtracted. It has been shown that the effect of synchrotron self-absorption on the detection of the EoR depends sensitively on the spectral profiles of the radio sources around the turnover frequencies νm. A hard transition model, described by the broken power law with the turnover of spectral index at νm, would leave pronounced imprints on the residual background and would therefore cause serious confusion with the cosmic EoR signal. However, the spectral signatures on the angular power spectrum of the extragalactic foreground, generated by a soft transition model in which the rising and falling power laws of the spectral distribution around νm are connected through a smooth transition spanning ≥200 MHz in a characteristic width, can be fitted and consequently subtracted by the use of polynomials to an acceptable degree (δT < 1 mK). As this latter scenario seems to be favoured in both theoretical expectations and radio spectral observations, we conclude that the contamination of extragalactic radio sources by synchrotron self-absorption in 21-cm experiments is probably very minor.

Generalized radiative transfer theory for scattering by particles in an absorbing gas: Addressing both spatial and spectral integration in multi-angle remote sensing of optically thin aerosol layers

NASA Astrophysics Data System (ADS)

Davis, Anthony B.; Xu, Feng; Diner, David J.

2018-01-01

We demonstrate the computational advantage gained by introducing non-exponential transmission laws into radiative transfer theory for two specific situations. One is the problem of spatial integration over a large domain where the scattering particles cluster randomly in a medium uniformly filled with an absorbing gas, and only a probabilistic description of the variability is available. The increasingly important application here is passive atmospheric profiling using oxygen absorption in the visible/near-IR spectrum. The other scenario is spectral integration over a region where the absorption cross-section of a spatially uniform gas varies rapidly and widely and, moreover, there are scattering particles embedded in the gas that are distributed uniformly, or not. This comes up in many applications, O2 A-band profiling being just one instance. We bring a common framework to solve these problems both efficiently and accurately that is grounded in the recently developed theory of Generalized Radiative Transfer (GRT). In GRT, the classic exponential law of transmission is replaced by one with a slower power-law decay that accounts for the unresolved spectral or spatial variability. Analytical results are derived in the single-scattering limit that applies to optically thin aerosol layers. In spectral integration, a modest gain in accuracy is obtained. As for spatial integration of near-monochromatic radiance, we find that, although both continuum and in-band radiances are affected by moderate levels of sub-pixel variability, only extreme variability will affect in-band/continuum ratios.

12W laser amplification at 1427nm on the 4F 3/2 to 4I 13/2 spectral line in an Nd 3+ doped fused silica optical fiber

DOE PAGES

Dawson, Jay W.; Pax, Paul H.; Allen, Graham S.; ...

2016-12-08

A 9.3dB improvement in optical gain and a 100x improvement in total optical power over prior published experimental results from the 4F 3/2 to 4I 13/2 transition in an Nd 3+ doped fused silica optical fiber is demonstrated. This is enabled via an optical fiber waveguide design that creates high spectral attenuation in the 1050-1120nm-wavelength range, a continuous spectral filter for the primary 4F 3/2 to 4I 11/2 optical transition. A maximum output power at 1427nm of 1.2W was attained for 43mW coupled seed laser power and 22.2W of coupled pump diode laser power at 880nm a net optical gainmore » of 14.5dB. Reducing the coupled seed laser power to 2.5mW enabled the system to attain 19.3dB of gain for 16.5W of coupled pump power. Four issues limited results; non-optimal seed laser wavelength, amplified spontaneous emission on the 4F 3/2 to 4I 9/2 optical transition, low absorption of pump light from the cladding and high spectral attenuation in the 1350-1450nm range. Lastly, future fibers that mitigate these issues should lead to significant improvements in the efficiency of the laser amplifier, though the shorter wavelength region of the transition from 1310nm to >1350nm is still expected to be limited by excited state absorption.« less

12W laser amplification at 1427nm on the 4F 3/2 to 4I 13/2 spectral line in an Nd 3+ doped fused silica optical fiber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dawson, Jay W.; Pax, Paul H.; Allen, Graham S.

A 9.3dB improvement in optical gain and a 100x improvement in total optical power over prior published experimental results from the 4F 3/2 to 4I 13/2 transition in an Nd 3+ doped fused silica optical fiber is demonstrated. This is enabled via an optical fiber waveguide design that creates high spectral attenuation in the 1050-1120nm-wavelength range, a continuous spectral filter for the primary 4F 3/2 to 4I 11/2 optical transition. A maximum output power at 1427nm of 1.2W was attained for 43mW coupled seed laser power and 22.2W of coupled pump diode laser power at 880nm a net optical gainmore » of 14.5dB. Reducing the coupled seed laser power to 2.5mW enabled the system to attain 19.3dB of gain for 16.5W of coupled pump power. Four issues limited results; non-optimal seed laser wavelength, amplified spontaneous emission on the 4F 3/2 to 4I 9/2 optical transition, low absorption of pump light from the cladding and high spectral attenuation in the 1350-1450nm range. Lastly, future fibers that mitigate these issues should lead to significant improvements in the efficiency of the laser amplifier, though the shorter wavelength region of the transition from 1310nm to >1350nm is still expected to be limited by excited state absorption.« less

A fully functionalized metamaterial perfect absorber with simple design and implementation

PubMed Central

Fu, Sze Ming; Zhong, Yan Kai; Tu, Ming Hsiang; Chen, Bo Ruei; Lin, Albert

2016-01-01

Broadband perfect metamaterial absorbers have been drawing significant attention in recent years. A close-to-unity absorption over a broad spectral range is established and this facilitates many photonic applications. A more challenging goal is to construct a broadband absorber with a tailored spectral absorption. The spectral absorption control and spectral shaping are very critical in many applications, such as thermal-photovoltaic, thermal emitters, spectrum imaging system, biomedical and extraterrestrial sensing, and refractive index sensor. In this work, one-dimensional (1D) planar stacking structure is designed to achieve the ultimate goal of a functionalized absorber with a fully tailorable spectral absorption. The lithography and etching process are totally eliminated in this proposed structure, and the fabrication is fully compatible with the regular silicon IC processing. By using ~2 nm ultra-thin metallic layers with a 10-pair (10X) SiO2/Si3N4 integrated dielectric filter, we can achieve decent spectral response shaping. The planar configuration of the ultra-thin-metal metamaterial perfect absorber (MPA) is the key to the easy design/integration of the dielectric filters on top of the MPA. Specifically, band-rejected, high-pass, low-pass and band-pass structure are constructed successfully. Finally, experimental evidence to support our simulation result is also provided, which proves the feasibility of our proposal. PMID:27782181

Compact characterization of liquid absorption and emission spectra using linear variable filters integrated with a CMOS imaging camera

PubMed Central

Wan, Yuhang; Carlson, John A.; Kesler, Benjamin A.; Peng, Wang; Su, Patrick; Al-Mulla, Saoud A.; Lim, Sung Jun; Smith, Andrew M.; Dallesasse, John M.; Cunningham, Brian T.

2016-01-01

A compact analysis platform for detecting liquid absorption and emission spectra using a set of optical linear variable filters atop a CMOS image sensor is presented. The working spectral range of the analysis platform can be extended without a reduction in spectral resolution by utilizing multiple linear variable filters with different wavelength ranges on the same CMOS sensor. With optical setup reconfiguration, its capability to measure both absorption and fluorescence emission is demonstrated. Quantitative detection of fluorescence emission down to 0.28 nM for quantum dot dispersions and 32 ng/mL for near-infrared dyes has been demonstrated on a single platform over a wide spectral range, as well as an absorption-based water quality test, showing the versatility of the system across liquid solutions for different emission and absorption bands. Comparison with a commercially available portable spectrometer and an optical spectrum analyzer shows our system has an improved signal-to-noise ratio and acceptable spectral resolution for discrimination of emission spectra, and characterization of colored liquid’s absorption characteristics generated by common biomolecular assays. This simple, compact, and versatile analysis platform demonstrates a path towards an integrated optical device that can be utilized for a wide variety of applications in point-of-use testing and point-of-care diagnostics. PMID:27389070

Compact characterization of liquid absorption and emission spectra using linear variable filters integrated with a CMOS imaging camera

NASA Astrophysics Data System (ADS)

Wan, Yuhang; Carlson, John A.; Kesler, Benjamin A.; Peng, Wang; Su, Patrick; Al-Mulla, Saoud A.; Lim, Sung Jun; Smith, Andrew M.; Dallesasse, John M.; Cunningham, Brian T.

2016-07-01

A compact analysis platform for detecting liquid absorption and emission spectra using a set of optical linear variable filters atop a CMOS image sensor is presented. The working spectral range of the analysis platform can be extended without a reduction in spectral resolution by utilizing multiple linear variable filters with different wavelength ranges on the same CMOS sensor. With optical setup reconfiguration, its capability to measure both absorption and fluorescence emission is demonstrated. Quantitative detection of fluorescence emission down to 0.28 nM for quantum dot dispersions and 32 ng/mL for near-infrared dyes has been demonstrated on a single platform over a wide spectral range, as well as an absorption-based water quality test, showing the versatility of the system across liquid solutions for different emission and absorption bands. Comparison with a commercially available portable spectrometer and an optical spectrum analyzer shows our system has an improved signal-to-noise ratio and acceptable spectral resolution for discrimination of emission spectra, and characterization of colored liquid’s absorption characteristics generated by common biomolecular assays. This simple, compact, and versatile analysis platform demonstrates a path towards an integrated optical device that can be utilized for a wide variety of applications in point-of-use testing and point-of-care diagnostics.

Airborne spectroradiometry: The application of AIS data to detecting subtle mineral absorption features

NASA Technical Reports Server (NTRS)

Cocks, T. D.; Green, A. A.

1986-01-01

Analysis of Airborne Imaging Spectrometer (AIS) data acquired in Australia has revealed a number of operational problems. Horizontal striping in AIS imagery and spectral distortions due to order overlap were investigated. Horizontal striping, caused by grating position errors can be removed with little or no effect on spectral details. Order overlap remains a problem that seriously compromises identification of subtle mineral absorption features within AIS spectra. A spectrometric model of the AIS was developed to assist in identifying spurious spectral features, and will be used in efforts to restore the spectral integrity of the data.

Numerical simulation of infrared radiation absorption for diagnostics of gas-aerosol medium by remote sensing data

NASA Astrophysics Data System (ADS)

Voitsekhovskaya, O. K.; Egorov, O. V.; Kashirskii, D. E.; Shefer, O. V.

2015-11-01

Calculated absorption spectra of the mixture of gases (H2O, CO, CO2, NO, NO2, and SO2) and aerosol (soot and Al2O3), contained in the exhausts of aircraft and rocket engines are demonstrated. Based on the model of gas-aerosol medium, a numerical study of the spectral dependence of the absorptance for different ratios of gas and aerosol components was carried out. The influence of microphysical and optical properties of the components of the mixture on the spectral features of absorption of gas-aerosol medium was established.

Spectral model for clear sky atmospheric longwave radiation

NASA Astrophysics Data System (ADS)

Li, Mengying; Liao, Zhouyi; Coimbra, Carlos F. M.

2018-04-01

An efficient spectrally resolved radiative model is used to calculate surface downwelling longwave (DLW) radiation (0 ∼ 2500 cm-1) under clear sky (cloud free) conditions at the ground level. The wavenumber spectral resolution of the model is 0.01 cm-1 and the atmosphere is represented by 18 non-uniform plane-parallel layers with pressure in each layer determined on a pressure-based coordinate system. The model utilizes the most up-to-date (2016) HITRAN molecular spectral data for 7 atmospheric gases: H2O, CO2, O3, CH4, N2O, O2 and N2. The MT_CKD model is used to calculate water vapor and CO2 continuum absorption coefficients. Longwave absorption and scattering coefficients for aerosols are modeled using Mie theory. For the non-scattering atmosphere (aerosol free), the surface DLW agrees within 2.91% with mean values from the InterComparison of Radiation Codes in Climate Models (ICRCCM) program, with spectral deviations below 0.035 W cm m-2. For a scattering atmosphere with typical aerosol loading, the DLW calculated by the proposed model agrees within 3.08% relative error when compared to measured values at 7 climatologically diverse SURFRAD stations. This relative error is smaller than a calibrated parametric model regressed from data for those same 7 stations, and within the uncertainty (+/- 5 W m-2) of pyrgeometers commonly used for meteorological and climatological applications. The DLW increases by 1.86 ∼ 6.57 W m-2 when compared with aerosol-free conditions, and this increment decreases with increased water vapor content due to overlap with water vapor bands. As expected, the water vapor content at the layers closest to the surface contributes the most to the surface DLW, especially in the spectral region 0 ∼ 700 cm-1. Additional water vapor content (mostly from the lowest 1 km of the atmosphere) contributes to the spectral range of 400 ∼ 650 cm-1. Low altitude aerosols ( ∼ 3.46 km or less) contribute to the surface value of DLW mostly in the spectral range 750 ∼ 1400 cm-1.

Effect of solid-phase amorphization on the spectral characteristics of europium-doped gadolinium molybdate

NASA Astrophysics Data System (ADS)

Shmurak, S. Z.; Kiselev, A. P.; Kurmasheva, D. M.; Red'Kin, B. S.; Sinitsyn, V. V.

2010-05-01

A method is proposed for detecting spectral characteristics of optically inactive molybdates of rare-earth elements by their doping with rare-earth ions whose luminescence lies in the transparency region of all structural modifications of the sample. Gadolinium molybdate is chosen as the object of investigations, while europium ions are used as an optically active and structurally sensitive admixture. It is shown that after the action of a high pressure under which gadolinium molybdate passes to the amorphous state, the spectral characteristics of Gd1.99Eu0.01(MoO4)3 (GMO:Eu) change radically; namely, considerable line broadening is observed in the luminescence spectra and the luminescence excitation spectra, while the long-wave threshold of optical absorption is shifted considerably (by approximately 1.1 eV) towards lower energies. It is found that by changing the structural state of GMO:Eu by solid-state amorphization followed by annealing, the spectral characteristics of the sample can be purposefully changed. This is extremely important for solving the urgent problem of designing high-efficiency light-emitting diodes producing “white” light.

Spectrum recovery method based on sparse representation for segmented multi-Gaussian model

NASA Astrophysics Data System (ADS)

Teng, Yidan; Zhang, Ye; Ti, Chunli; Su, Nan

2016-09-01

Hyperspectral images can realize crackajack features discriminability for supplying diagnostic characteristics with high spectral resolution. However, various degradations may generate negative influence on the spectral information, including water absorption, bands-continuous noise. On the other hand, the huge data volume and strong redundancy among spectrums produced intense demand on compressing HSIs in spectral dimension, which also leads to the loss of spectral information. The reconstruction of spectral diagnostic characteristics has irreplaceable significance for the subsequent application of HSIs. This paper introduces a spectrum restoration method for HSIs making use of segmented multi-Gaussian model (SMGM) and sparse representation. A SMGM is established to indicating the unsymmetrical spectral absorption and reflection characteristics, meanwhile, its rationality and sparse property are discussed. With the application of compressed sensing (CS) theory, we implement sparse representation to the SMGM. Then, the degraded and compressed HSIs can be reconstructed utilizing the uninjured or key bands. Finally, we take low rank matrix recovery (LRMR) algorithm for post processing to restore the spatial details. The proposed method was tested on the spectral data captured on the ground with artificial water absorption condition and an AVIRIS-HSI data set. The experimental results in terms of qualitative and quantitative assessments demonstrate that the effectiveness on recovering the spectral information from both degradations and loss compression. The spectral diagnostic characteristics and the spatial geometry feature are well preserved.

Tunable UV-visible absorption of SnS2 layered quantum dots produced by liquid phase exfoliation.

PubMed

Fu, Xiao; Ilanchezhiyan, P; Mohan Kumar, G; Cho, Hak Dong; Zhang, Lei; Chan, A Sattar; Lee, Dong J; Panin, Gennady N; Kang, Tae Won

2017-02-02

4H-SnS 2 layered crystals synthesized by a hydrothermal method were used to obtain via liquid phase exfoliation quantum dots (QDs), consisting of a single layer (SLQDs) or multiple layers (MLQDs). Systematic downshift of the peaks in the Raman spectra of crystals with a decrease in size was observed. The bandgap of layered QDs, estimated by UV-visible absorption spectroscopy and the tunneling current measurements using graphene probes, increases from 2.25 eV to 3.50 eV with decreasing size. 2-4 nm SLQDs, which are transparent in the visible region, show selective absorption and photosensitivity at wavelengths in the ultraviolet region of the spectrum while larger MLQDs (5-90 nm) exhibit a broad band absorption in the visible spectral region and the photoresponse under white light. The results show that the layered quantum dots obtained by liquid phase exfoliation exhibit well-controlled and regulated bandgap absorption in a wide tunable wavelength range. These novel layered quantum dots prepared using an inexpensive method of exfoliation and deposition from solution onto various substrates at room temperature can be used to create highly efficient visible-blind ultraviolet photodetectors and multiple bandgap solar cells.

Visible and near-IR spectral reflectance of geologically important materials: A short review

NASA Technical Reports Server (NTRS)

Singer, R. B.

1982-01-01

Examples of reflectance spectra are presented and discussed for various mineral groups including pyroxenes, olivene, phylosilicates, amphiboles, feldspars, oxides and hydroxides, carbonates, and mixtures of minerals. The physical sources of some spectral features are also reviewed such as charge transfer and conduction bands, crystal field absorptions, and vibrational absorptions.

Absorption and Emission Spectroscopic Investigation of Thermal Dynamics and Photo-Dynamics of the Rhodopsin Domain of the Rhodopsin-Guanylyl Cyclase from the Nematophagous Fungus Catenaria anguillulae

PubMed Central

Penzkofer, Alfons; Scheib, Ulrike; Stehfest, Katja; Hegemann, Peter

2017-01-01

The rhodopsin-guanylyl cyclase from the nematophagous fungus Catenaria anguillulae belongs to a recently discovered class of enzymerhodopsins and may find application as a tool in optogenetics. Here the rhodopsin domain CaRh of the rhodopsin-guanylyl cyclase from Catenaria anguillulae was studied by absorption and emission spectroscopic methods. The absorption cross-section spectrum and excitation wavelength dependent fluorescence quantum distributions of CaRh samples were determined (first absorption band in the green spectral region). The thermal stability of CaRh was studied by long-time attenuation measurements at room temperature (20.5 °C) and refrigerator temperature of 3.5 °C. The apparent melting temperature of CaRh was determined by stepwise sample heating up and cooling down (obtained apparent melting temperature: 62 ± 2 °C). The photocycle dynamics of CaRh was investigated by sample excitation to the first inhomogeneous absorption band of the CaRhda dark-adapted state around 590 nm (long-wavelength tail), 530 nm (central region) and 470 nm (short-wavelength tail) and following the absorption spectra development during exposure and after exposure (time resolution 0.0125 s). The original protonated retinal Schiff base PRSBall-trans in CaRhda photo-converted reversibly to protonated retinal Schiff base PRSBall-trans,la1 with restructured surroundings (CaRhla1 light-adapted state, slightly blue-shifted and broadened first absorption band, recovery to CaRhda with time constant of 0.8 s) and deprotonated retinal Schiff base RSB13-cis (CaRhla2 light-adapted state, first absorption band in violet to near ultraviolet spectral region, recovery to CaRhda with time constant of 0.35 s). Long-time light exposure of light-adapted CaRhla1 around 590, 530 and 470 nm caused low-efficient irreversible degradation to photoproducts CaRhprod. Schemes of the primary photocycle dynamics of CaRhda and the secondary photocycle dynamics of CaRhla1 are developed. PMID:28981475

The absorption budget of fresh biomass burning aerosol from realistic laboratory fires

NASA Astrophysics Data System (ADS)

Wagner, N. L.; Adler, G. A.; Franchin, A.; Lamb, K.; Manfred, K.; Middlebrook, A. M.; Selimovic, V.; Schwarz, J. P.; Washenfelder, R. A.; Womack, C.; Yokelson, R. J.

2017-12-01

Wildfires are expected to increase globally due to climate change. The smoke from these wildfires has a highly uncertain radiative effect, largely due to the lack of detailed understanding of its optical properties. As part of the NOAA FIREX project, we have measured the optical properties of smoke primarily from laboratory burning of North American fuels at the Missoula Fire Sciences Laboratory. Here, we present a budget of the aerosol absorption from a portion of the laboratory fires. The total aerosol absorption was measured with photoacoustic spectrometers (PAS) at four wavelengths (405 nm, 532 nm, 660 nm, 870 nm) spanning the visible spectral region. The aerosol absorption is attributed to black carbon which absorbs broadly across the visible and ultraviolet (UV) spectral region and brown carbon (BrC) which absorbs in the blue and UV spectral regions. Then aerosol absorption measurements are compared with measurements of refractory black carbon (rBC) concentration by laser induced incandescence (SP2) and measurements of BrC concentration from a particle-into-liquid sampler coupled to a liquid absorption cell (BrC-PILS). Periodically, a thermodenuder was inserted upstream of all of the instruments to constrain the relationship between aerosol volatility and absorption. We synthesize these measurements to constrain the various contributors to total absorption including effects of lensing on rBC absorption, and of BrC that is not volatilized in the thermodenuder.

Effective absorption cross sections and photolysis rates of anthropogenic and biogenic secondary organic aerosols

NASA Astrophysics Data System (ADS)

Romonosky, Dian E.; Ali, Nujhat N.; Saiduddin, Mariyah N.; Wu, Michael; Lee, Hyun Ji (Julie); Aiona, Paige K.; Nizkorodov, Sergey A.

2016-04-01

Mass absorption coefficient (MAC) values were measured for secondary organic aerosol (SOA) samples produced by flow tube ozonolysis and smog chamber photooxidation of a wide range of volatile organic compounds (VOC), specifically: α-pinene, β-pinene, β-myrcene, d-limonene, farnesene, guaiacol, imidazole, isoprene, linalool, ocimene, p-xylene, 1-methylpyrrole, and 2-methylpyrrole. Both low-NOx and high-NOx conditions were employed during the chamber photooxidation experiments. MAC values were converted into effective molecular absorption cross sections assuming an average molecular weight of 300 g/mol for SOA compounds. The upper limits for the effective photolysis rates of SOA compounds were calculated by assuming unity photolysis quantum yields and convoluting the absorption cross sections with a time-dependent solar spectral flux. A more realistic estimate for the photolysis rates relying on the quantum yield of acetone was also obtained. The results show that condensed-phase photolysis of SOA compounds can potentially occur with effective lifetimes ranging from minutes to days, suggesting that photolysis is an efficient and largely overlooked mechanism of SOA aging.

Efficient CW diode-pumped Tm, Ho:YLF laser with tunability near 2.067 microns

NASA Technical Reports Server (NTRS)

Mcguckin, B. T.; Menzies, Robert T.

1992-01-01

A conversion efficiency of 42 percent and slope efficiency of approximately 60 percent relative to absorbed pump power are reported from a continuous wave diode-pumped Tm, Ho:YLF laser at 2 microns with output power of 84 mW at sub-ambient temperatures. The emission spectrum is etalon tunable over a range of 16/cm centered on 2.067 microns, with fine tuning capability of the transition frequency with crystal temperature at a measured rate of about -0.03/cm-K. The effective emission cross section is measured to be 5 x 10 exp -21 sq cm. These and other aspects of the laser performance are discussed in the context of calculated atmospheric absorption characteristics in this spectral region and potential use in remote sensing applications.

FLORIS: phase A status of the fluorescence imaging spectrometer of the Earth Explorer mission candidate FLEX

NASA Astrophysics Data System (ADS)

Kraft, S.; Bézy, J.-L.; Del Bello, U.; Berlich, R.; Drusch, M.; Franco, R.; Gabriele, A.; Harnisch, B.; Meynart, R.; Silvestrin, P.

2013-10-01

The Fluorescence Explorer (FLEX) mission is currently subject to feasibility (Phase A) study as one of the two candidates of ESA's 8th Earth Explorer opportunity mission. The FLuORescence Imaging Spectrometer (FLORIS) will be an imaging grating spectrometer onboard of a medium sized satellite flying in tandem with Sentinel-3 in a Sun synchronous orbit at a height of about 815 km. FLORIS will observe vegetation fluorescence and reflectance within a spectral range between 500 nm and 780 nm. It will thereby cover the photochemical reflection features between 500 nm and 600 nm, the Chlorophyll absorption band between 600 and 677 nm, and the red-edge in the region from 697 nm to 755 nm being located between the Oxygen A and B absorption bands. By this measurement approach, it is expected that the full spectrum and amount of the vegetation fluorescence radiance can be retrieved, and that atmospheric corrections can efficiently be applied. FLORIS will measure Earth reflected spectral radiance at a relatively high spectral resolution of ~0.3 nm around the Oxygen absorption bands. Other spectral band areas with less pronounced absorption features will be measured at medium spectral resolution between 0.5 and 2 nm. FLORIS will provide imagery at 300 m resolution on ground with a swath width of 150 km. This will allow achieving global revisit times of less than one month so as to monitor seasonal variations of the vegetation cycles. The mission life time is expected to be at least 4 years. The fluorescence retrieval will make use of information coming from OLCI and SLSTR, which are onboard of Sentinel-3, to monitor temperature, to detect thin clouds and to derive vegetation reflectance and information on the aerosol content also outside the FLORIS spectral range. In order to mitigate the technological and programmatic risk of this Explorer mission candidate, ESA has initiated two comprehensive bread-boarding activities, in which the most critical technologies and instrument performance shall be investigated and demonstrated. The breadboards will include representative optics and dispersive elements in a configuration, which is expected to be very close to the instrument flight configuration. This approach follows the guideline to reach, before it goes into the implementation phase, a technology readiness level of at least 5. It thereby requires a demonstration of predicted performance in a configuration, where the basic technological components are integrated with reasonably realistic supporting elements such that it can be tested in a simulated environment. We will report, within the limits of the competitive nature of the industrial studies, on the currently running or planned preparatory activities. We will present the mission configuration, the imposed instrument requirements and the identified instrument concepts as derived by the Phase A studies.

TiO2 supported gold nanoparticles: An efficient photocatalyst for oxidation of alcohol to aldehyde and ketone in presence of visible light irradiation

NASA Astrophysics Data System (ADS)

Gogoi, Nibedita; Borah, Geetika; Gogoi, Pradip K.; Chetia, Tridip Ranjan

2018-01-01

An efficient heterogeneous photocatalyst composed of Au nanoparticle supported on TiO2 (anatase) is prepared by sol-gel method. This prepared nanocomposite showed good catalytic activity in the oxidation of various alcohols to aldehyde and ketone under irradiation of visible light. Various spectroscopic techniques including UV-Visible absorption spectral studies and photoluminescence study are employed to characterize the catalyst. It was also characterized by XRD, TEM, BET, XPS and ICP-AES analysis. In contrast to air and H2O2, use of TBHP as oxidant gave good yield. The reaction conditions with respect to solvent and amount of catalyst are optimized.

Tunable random lasing behavior in plasmonic nanostructures

NASA Astrophysics Data System (ADS)

Yadav, Ashish; Zhong, Liubiao; Sun, Jun; Jiang, Lin; Cheng, Gary J.; Chi, Lifeng

2017-01-01

Random lasing is desired in plasmonics nanostructures through surface plasmon amplification. In this study, tunable random lasing behavior was observed in dye molecules attached with Au nanorods (NRs), Au nanoparticles (NPs) and Au@Ag nanorods (NRs) respectively. Our experimental investigations showed that all nanostructures i.e., Au@AgNRs, AuNRs & AuNPs have intensive tunable spectral effects. The random lasing has been observed at excitation wavelength 532 nm and varying pump powers. The best random lasing properties were noticed in Au@AgNRs structure, which exhibits broad absorption spectrum, sufficiently overlapping with that of dye Rhodamine B (RhB). Au@AgNRs significantly enhance the tunable spectral behavior through localized electromagnetic field and scattering. The random lasing in Au@AgNRs provides an efficient coherent feedback for random lasers.

Growth and spectral-luminescent study of SrMoO4 crystals doped with Tm3+ ions

NASA Astrophysics Data System (ADS)

Dunaeva, E. E.; Zverev, P. G.; Doroshenko, M. E.; Nekhoroshikh, A. V.; Ivleva, L. I.; Osiko, V. V.

2016-03-01

SrMoO4 crystals doped with Tm3+ ions have been produced from a melt using the Czochralski method; their spectral-luminescent characteristics have been studied, and laser radiation has been generated at the wavelength of 1.94 μm using laser-diode excitation. The high absorption section at the wavelength of 795 nm, the fairly high luminescence section, the long lifetime at the upper laser level 3F4 of 1.5 ms, and a wide luminescence band allow one to hope for developing efficient tunable Tm3+: SrMoO4 crystal lasers with diode pumping in the range of 1.7-2.0 μm, which are capable of implementing SRS self-transformation of radiation into the middle IR band.

System-level analysis and design for RGB-NIR CMOS camera

NASA Astrophysics Data System (ADS)

Geelen, Bert; Spooren, Nick; Tack, Klaas; Lambrechts, Andy; Jayapala, Murali

2017-02-01

This paper presents system-level analysis of a sensor capable of simultaneously acquiring both standard absorption based RGB color channels (400-700nm, 75nm FWHM), as well as an additional NIR channel (central wavelength: 808 nm, FWHM: 30nm collimated light). Parallel acquisition of RGB and NIR info on the same CMOS image sensor is enabled by monolithic pixel-level integration of both a NIR pass thin film filter and NIR blocking filters for the RGB channels. This overcomes the need for a standard camera-level NIR blocking filter to remove the NIR leakage present in standard RGB absorption filters from 700-1000nm. Such a camera-level NIR blocking filter would inhibit the acquisition of the NIR channel on the same sensor. Thin film filters do not operate in isolation. Rather, their performance is influenced by the system context in which they operate. The spectral distribution of light arriving at the photo diode is shaped a.o. by the illumination spectral profile, optical component transmission characteristics and sensor quantum efficiency. For example, knowledge of a low quantum efficiency (QE) of the CMOS image sensor above 800nm may reduce the filter's blocking requirements and simplify the filter structure. Similarly, knowledge of the incoming light angularity as set by the objective lens' F/# and exit pupil location may be taken into account during the thin film's optimization. This paper demonstrates how knowledge of the application context can facilitate filter design and relax design trade-offs and presents experimental results.

Optical and photoconductivity spectra of novel Ag₂In₂SiS₆ and Ag₂In₂GeS₆ chalcogenide crystals.

PubMed

Chmiel, M; Piasecki, M; Myronchuk, G; Lakshminarayana, G; Reshak, Ali H; Parasyuk, O G; Kogut, Yu; Kityk, I V

2012-06-01

Complex spectral studies of near-band gap and photoconductive spectra for novel Ag(2)In(2)SiS(6) and Ag(2)In(2)GeS(6) single crystals are presented. The spectral dependences of photoconductivity clearly show an existence of spectral maxima within the 450 nm-540 nm and 780 nm-920 nm. The fundamental absorption edge is analyzed by Urbach rule. The origin of the spectral photoconductivity spectral maxima is discussed. Temperature dependences of the spectra were done. The obtained spectral features allow to propose the titled crystals as photosensors. An analysis of the absorption and photoconductivity spectra is given within a framework of oversimplified spectroscopic model of complex chalcogenide crystals. Copyright © 2012 Elsevier B.V. All rights reserved.

X-ray source development for EXAFS measurements on the National Ignition Facility

DOE PAGES

Coppari, F.; Thorn, D. B.; Kemp, G. E.; ...

2017-08-28

We present that extended X-ray absorption Fine Structure (EXAFS) measurements require a bright, spectrally smooth, and broad-band x-ray source. In a laser facility, such an x-ray source can be generated by a laser-driven capsule implosion. In order to optimize the x-ray emission, different capsule types and laser irradiations have been tested at the National Ignition Facility (NIF). A crystal spectrometer is used to disperse the x-rays and high efficiency image plate detectors are used to measure the absorption spectra in transmission geometry. Finally, EXAFS measurements at the K-edge of iron at ambient conditions have been obtained for the first timemore » on the NIF laser, and the requirements for optimization have been established.« less

Quantifying the effect of finite spectral bandwidth on extinction coefficient of species in laser absorption spectroscopy

NASA Astrophysics Data System (ADS)

Singh, Manjeet; Singh, Jaswant; Singh, Baljit; Ghanshyam, C.

2016-11-01

The aim of this study is to quantify the finite spectral bandwidth effect on laser absorption spectroscopy for a wide-band laser source. Experimental analysis reveals that the extinction coefficient of an analyte is affected by the bandwidth of the spectral source, which may result in the erroneous conclusions. An approximate mathematical model has been developed for optical intensities having Gaussian line shape, which includes the impact of source's spectral bandwidth in the equation for spectroscopic absorption. This is done by introducing a suitable first order and second order bandwidth approximation in the Beer-Lambert law equation for finite bandwidth case. The derived expressions were validated using spectroscopic analysis with higher SBW on a test sample, Rhodamine B. The concentrations calculated using proposed approximation, were in significant agreement with the true values when compared with those calculated with conventional approach.

Spectral Changes of Erythrosin B Luminescence Upon Binding to Bovine Serum Albumin

NASA Astrophysics Data System (ADS)

Sablin, N. V.; Gerasimova, M. A.; Nemtseva, E. V.

2016-04-01

Changes in absorption, fluorescence, phosphorescence, and delayed fluorescence spectra of erythrosin B are studied in the presence of bovine serum albumin at room temperature. Spectral and chronoscopic characteristics of the observed photophysical processes are defined. The binding of erythrosin B with the protein followed by spectral changes is demonstrated. Absorption and fluorescence spectra of the dye in the bound state are described, the binding mechanism is analyzed. The binding parameters of the dye-protein complex are estimated.

Convenient determination of luminescence quantum yield using a combined electronic absorption and emission spectrometer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prakash, John; Mishra, Ashok Kumar

2016-01-15

It is possible to measure luminescence quantum yield in a facile way, by designing an optical spectrometer capable of obtaining electronic absorption as well as luminescence spectra, with a setup that uses the same light source and detector for both the spectral measurements. Employment of a single light source and single detector enables use of the same correction factor profile for spectral corrections. A suitable instrumental scaling factor is used for adjusting spectral losses.

UV spectroscopy including ISM line absorption: of the exciting star of Abell 35

NASA Astrophysics Data System (ADS)

Ziegler, M.; Rauch, T.; Werner, K.; Kruk, J. W.

Reliable spectral analysis that is based on high-resolution UV observations requires an adequate, simultaneous modeling of the interstellar line absorption and reddening. In the case of the central star of the planetary nebula Abell 35, BD-22 3467, we demonstrate our current standard spectral-analysis method that is based on the Tübingen NLTE Model-Atmosphere Package (TMAP). We present an on- going spectral analysis of FUSE and HST/STIS observations of BD-22 3467.

THE IMPACT OF ACCURATE EXTINCTION MEASUREMENTS FOR X-RAY SPECTRAL MODELS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Randall K.; Valencic, Lynne A.; Corrales, Lia, E-mail: lynne.a.valencic@nasa.gov

Interstellar extinction includes both absorption and scattering of photons from interstellar gas and dust grains, and it has the effect of altering a source's spectrum and its total observed intensity. However, while multiple absorption models exist, there are no useful scattering models in standard X-ray spectrum fitting tools, such as XSPEC. Nonetheless, X-ray halos, created by scattering from dust grains, are detected around even moderately absorbed sources, and the impact on an observed source spectrum can be significant, if modest, compared to direct absorption. By convolving the scattering cross section with dust models, we have created a spectral model asmore » a function of energy, type of dust, and extraction region that can be used with models of direct absorption. This will ensure that the extinction model is consistent and enable direct connections to be made between a source's X-ray spectral fits and its UV/optical extinction.« less

Spectral reflectance properties of minerals exposed to simulated Mars surface conditions

NASA Astrophysics Data System (ADS)

Cloutis, E. A.; Craig, M. A.; Kruzelecky, R. V.; Jamroz, W. R.; Scott, A.; Hawthorne, F. C.; Mertzman, S. A.

2008-05-01

A number of mineral species were exposed to martian surface conditions of atmospheric pressure and composition, temperature, and UV light regime, and their evolution was monitored using reflectance spectroscopy. The stabilities for different groups varied widely. Phyllosilicate spectra all showed measurable losses of interlayer H 2O, with some structural groups showing more rapid H 2O loss than others. Loss of OH from the phyllosilicates is not always accompanied by a change in metal-OH overtone absorption bands. OH-bearing sulfates, such as jarosite and alunite, show no measurable change in spectral properties, suggesting that they should be spectrally detectable on Mars on the basis of diagnostic absorption bands in the 0.4-2.5 μm region. Fe 3+- and H 2O-bearing sulfates all showed changes in the appearance and/or reduction in depths of hydroxo-bridged Fe 3+ absorption bands, particularly at 0.43 μm. The spectral changes were often accompanied by visible color changes, suggesting that subsurface sulfates exposed to the martian surface environment may undergo measurable changes in reflectance spectra and color over short periods of time (days to weeks). Organic-bearing geological materials showed no measurable change in C sbnd H related absorption bands, while carbonates and hydroxides also showed no systematic changes in spectral properties. The addition of ultraviolet irradiation did not seem to affect mineral stability or rate of spectral change, with one exception (hexahydrite). In some cases, spectral changes could be related to the formation of specific new phases. The data also suggest that hydrated minerals detected on Mars to date retain their diagnostic spectral properties that allow their unique identification.

Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS) with Standard Reference Line for the Analysis of Stainless Steel.

PubMed

Fu, Hongbo; Dong, Fengzhong; Wang, Huadong; Jia, Junwei; Ni, Zhibo

2017-08-01

In this work, calibration-free laser-induced breakdown spectroscopy (CF-LIBS) is used to analyze a certified stainless steel sample. Due to self-absorption of the spectral lines from the major element Fe and the sparse lines of trace elements, it is usually not easy to construct the Boltzmann plots of all species. A standard reference line method is proposed here to solve this difficulty under the assumption of local thermodynamic equilibrium so that the same temperature value for all elements present into the plasma can be considered. Based on the concentration and rich spectral lines of Fe, the Stark broadening of Fe(I) 381.584 nm and Saha-Boltzmann plots of this element are used to calculate the electron density and the plasma temperature, respectively. In order to determine the plasma temperature accurately, which is seriously affected by self-absorption, a pre-selection procedure for eliminating those spectral lines with strong self-absorption is employed. Then, one spectral line of each element is selected to calculate its corresponding concentration. The results from the standard reference lines with and without self-absorption of Fe are compared. This method allows us to measure trace element content and effectively avoid the adverse effects due to self-absorption.

Light manipulation for organic optoelectronics using bio-inspired moth's eye nanostructures.

PubMed

Zhou, Lei; Ou, Qing-Dong; Chen, Jing-De; Shen, Su; Tang, Jian-Xin; Li, Yan-Qing; Lee, Shuit-Tong

2014-02-10

Organic-based optoelectronic devices, including light-emitting diodes (OLEDs) and solar cells (OSCs) hold great promise as low-cost and large-area electro-optical devices and renewable energy sources. However, further improvement in efficiency remains a daunting challenge due to limited light extraction or absorption in conventional device architectures. Here we report a universal method of optical manipulation of light by integrating a dual-side bio-inspired moth's eye nanostructure with broadband anti-reflective and quasi-omnidirectional properties. Light out-coupling efficiency of OLEDs with stacked triple emission units is over 2 times that of a conventional device, resulting in drastic increase in external quantum efficiency and current efficiency to 119.7% and 366 cd A(-1) without introducing spectral distortion and directionality. Similarly, the light in-coupling efficiency of OSCs is increased 20%, yielding an enhanced power conversion efficiency of 9.33%. We anticipate this method would offer a convenient and scalable way for inexpensive and high-efficiency organic optoelectronic designs.

Distinctive effects of allochthonous and autochthonous organic matter on CDOM spectra in a tropical lake

NASA Astrophysics Data System (ADS)

Pena Mello Brandão, Luciana; Silva Brighenti, Ludmila; Staehr, Peter Anton; Asmala, Eero; Massicotte, Philippe; Tonetta, Denise; Antônio Rodrigues Barbosa, Francisco; Pujoni, Diego; Fernandes Bezerra-Neto, José

2018-05-01

Despite the increasing understanding about differences in carbon cycling between temperate and tropical freshwater systems, our knowledge on the importance of organic matter (OM) pools on light absorption properties in tropical lakes is very scarce. We performed a factorial mesocosm experiment in a tropical lake (Minas Gerais, Brazil) to evaluate the effects of increased concentrations of allochthonous and autochthonous OM, and differences in light availability on the light absorption characteristics of chromophoric dissolved organic matter (CDOM). Autochthonous OM deriving from phytoplankton ( ˜ Chl a) was stimulated by addition of nutrients, while OM from degradation of terrestrial leaves increased allochthonous OM, and neutral shading was used to manipulate light availability. Effects of the additions and shading on DOC, Chl a, nutrients, total suspended solid concentrations (TSM) and spectral CDOM absorption were monitored every 3 days. CDOM quality was characterized by spectral indices (S250-450, S275-295, S350-450, SR and SUVA254). Effects of carbon sources and shading on the spectral CDOM absorption was investigated through principal component (PCA) and redundancy (RDA) analyses. The two different OM sources affected CDOM quality very differently and shading had minor effects on OM levels, but significant effects on OM quality, especially in combination with nutrient additions. Spectral indices (S250-450 and SR) were mostly affected by allochthonous OM addition. The PCA showed that enrichment by allochthonous carbon had a strong effect on the CDOM spectra in the range between 300 and 400 nm, while the increase in autochthonous carbon increased absorption at wavelengths below 350 nm. Our study shows that small inputs of allochthonous OM can have large effects on the spectral light absorption compared to large production of autochthonous OM, with important implications for carbon cycling in tropical lakes.

Infrared absorption cross-sections, radiative efficiency and global warming potential of HFC-43-10mee

NASA Astrophysics Data System (ADS)

Le Bris, Karine; DeZeeuw, Jasmine; Godin, Paul J.; Strong, Kimberly

2018-06-01

HFC-43-10mee (C5H2F10) is a substitute for CFC-113, HCFC-141b and methyl chloroform, as well as an alternative to perfluorocarbons with high radiative efficiencies. Recent observations have shown that the global mean tropospheric abundance of HFC-43-10mee has increased steadily from the 1990s to reach 0.211 ppt in 2012. To date, the emission of this compound is not regulated. The radiative efficiency (RE) of HFC-43-10mee has recently been re-evaluated at 0.42 W m-2 ppb-1, giving a 100-year time horizon global warming potential (GWP100) of 1650. However, the initial RE, from which the new values were derived, originated from an unpublished source. We calculated a new RE of 0.36 W m-2 ppb-1 and a GWP100 of 1410 from laboratory absorption cross-section spectra of a pure vapour of HFC-43-10mee. Acquisitions were performed in the 550-3500 cm-1 spectral range using Fourier transform spectroscopy. The results were compared with the broadened spectra from the Pacific Northwest National Laboratory (PNNL) database and with theoretical calculations using density functional theory.

Spectral control of an alexandrite laser for an airborne water-vapor differential absorption lidar system

NASA Technical Reports Server (NTRS)

Ponsardin, Patrick; Grossmann, Benoist E.; Browell, Edward V.

1994-01-01

A narrow-linewidth pulsed alexandrite laser has been greatly modified for improved spectral stability in an aircraft environment, and its operation has been evaluated in the laboratory for making water-vapor differential absorption lidar measurements. An alignment technique is described to achieve the optimum free spectral range ratio for the two etalons inserted in the alexandrite laser cavity, and the sensitivity of this ratio is analyzed. This technique drastically decreases the occurrence of mode hopping, which is commonly observed in a tunable, two-intracavity-etalon laser system. High spectral purity (greater than 99.85%) at 730 nm is demonstrated by the use of a water-vapor absorption line as a notch filter. The effective cross sections of 760-nm oxygen and 730-nm water-vapor absorption lines are measured at different pressures by using this laser, which has a finite linewidth of 0.02 cm(exp -1) (FWHM). It is found that for water-vapor absorption linewidths greater than 0.04 cm(exp -1) (HWHM), or for altitudes below 10 km, the laser line can be considered monochromatic because the measured effective absorption cross section is within 1% of the calculated monochromatic cross section. An analysis of the environmental sensitivity of the two intracavity etalons is presented, and a closed-loop computer control for active stabilization of the two intracavity etalons in the alexandrite laser is described. Using a water-vapor absorption line as a wavelength reference, we measure a long-term frequency drift (approximately 1.5 h) of less than 0.7 pm in the laboratory.

Changes in the Far UV Spectrum of Eta Carinae Near the 2003 Minimum

NASA Technical Reports Server (NTRS)

Iping, R. C.; Gull, T. R.; Sonneborn, G.; Massa, D.; Vieira, G. L.; Nielsen, K. E.

2004-01-01

High resolution 905-1180 spectra of \\eta Carinae have been obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite at nine epochs between February 2000 and June 2003 . This period of time extends from the broad maximum up to the very beginning of the minimum of the 5.52-year period initially discovered by A. Damineli. The flux levels were unchanged between February 2000 through February 2003 with minor spectral differences. The X-Ray minimum started on June 29, 2003 . Three observations were accomplished on June 10, June 17 and June 27 leading up to the minimum. Substantial changes were present in the June 10 and June 17 spectra, but a very significant change occurred by June 27, 2003. Longward of 1100A, the overall flux dropped 10 to 30 %. Shortward of 1100A, there are spectral intervals with NO decrease in flux even down to the shortest wavelengths (920--950 ). This indicates that dust absorption has a negligible role in the observed spectral changes and that line absorptions play a major role. Throughout the spectrum there are intervals ranging in width of 3-10A with strong increased absorption. Significant absorptions may be associated with the red portion of the following stellar wind lines: C III 977, O VI 1031,1037, P V 1117, while other absorption features are much broader, more extended and not clearly associated with well-known spectral transitions. Given the complexity of the STIS echelle spectra taken in this period of time, many of these absorption features are likely due to multiple absorption lines

In Situ Measurements of Aerosol Mass Concentration and Spectral Absorption at Three Location in and Around Mexico City

NASA Astrophysics Data System (ADS)

Chaudhry, Z.; Martins, V.; Li, Z.

2006-12-01

As a result of population growth and increasing industrialization, air pollution in heavily populated urban areas is one of the central environmental problems of the century. As a part of the MILAGRO (Megacity Initiative: Local and Global Research Observations) study, Nuclepore filters were collected in two size ranges (PM10 and PM2.5) at 12 hour intervals at three location in Mexico during March, 2006. Sampling stations were located at the Instituto Mexicano del Petroleo (T0), at the Rancho La Bisnago in the State of Hidalgo (T2) and along the Gulf Coast in Tampico (Tam). Each filter was analyzed for mass concentration, aerosol scattering and absorption efficiencies. Mass concentrations at T0 ranged from 47 to 179 μg/m3 for PM10 with an average concentration of 96 μg/m3, and from 20 to 93 μg/m3 for PM2.5 with an average concentration of 41 μg/m3. Mass concentrations at T2 ranged from 12 to 154 μg/m3 for PM10 with an average concentration of 51 μg/m3, and from 7 to 50 μg/m3 for PM2.5 with an average concentration of 25 μg/m3. Mass concentrations at Tam ranged from 34 to 80 μg/m3 for PM10 with an average concentration of 52 μg/m3, and from 8 to 23 μg/m3 for PM2.5 with an average concentration of 13 μg/m3. While some of the extreme values are likely linked to local emissions, regional air pollution episodes also played important roles. Each of the sampling stations experienced a unique atmospheric condition. The site at T0 was influenced by urban air pollution and dust storms, the site at T2 was significantly less affected by air pollution but more affected by regional dust storms and local dust devils while Tam was influenced by air pollution, dust storms and the natural marine environment. The spectral mass absorption efficiency was measured from 350 to 2500 nm and shows large differences between the absorption properties of soil dust, black carbon, and organic aerosols. The strong spectral differences observed can be related to differences in refractive indices from the several collected species and particle size effects.

Understanding the Theory and Practice of Molecular Spectroscopy: The Effects of Spectral Bandwidth

ERIC Educational Resources Information Center

Hirayama, Satoshi; Steer, Ronald P.

2010-01-01

The near-UV spectrum of benzene is used to illustrate the effects of variations in instrument spectral bandwidth on absorbance and molar absorptivity measurements and on the independence of values of quantities such as the oscillator strength that are based on integrated absorptivity. Excel-based computer simulations are provided that help develop…

Bio-Inspired Photon Absorption and Energy Transfer for Next Generation Photovoltaic Devices

NASA Astrophysics Data System (ADS)

Magsi, Komal

Nature's solar energy harvesting system, photosynthesis, serves as a model for photon absorption, spectra broadening, and energy transfer. Photosynthesis harvests light far differently than photovoltaic cells. These differences offer both engineering opportunity and scientific challenges since not all of the natural photon absorption mechanisms have been understood. In return, solar cells can be a very sensitive probe for the absorption characteristics of molecules capable of transferring charge to a conductive interface. The objective of this scientific work is the advancement of next generation photovoltaics through the development and application of natural photo-energy transfer processes. Two scientific methods were used in the development and application of enhancing photon absorption and transfer. First, a detailed analysis of photovoltaic front surface fluorescent spectral modification and light scattering by hetero-structure was conducted. Phosphor based spectral down-conversion is a well-known laser technology. The theoretical calculations presented here indicate that parasitic losses and light scattering within the spectral range are large enough to offset any expected gains. The second approach for enhancing photon absorption is based on bio-inspired mechanisms. Key to the utilization of these natural processes is the development of a detailed scientific understanding and the application of these processes to cost effective systems and devices. In this work both aspects are investigated. Dye type solar cells were prepared and tested as a function of Chlorophyll (or Sodium-Copper Chlorophyllin) and accessory dyes. Forster has shown that the fluorescence ratio of Chlorophyll is modified and broadened by separate photon absorption (sensitized absorption) through interaction with nearby accessory pigments. This work used the dye type solar cell as a diagnostic tool by which to investigate photon absorption and photon energy transfer. These experiments shed some doubt on the Foster Resonant Energy Transfer mechanism since energy relay dye architecture-photosensitizer mixtures do not broaden the response of solar cells. Spectral absorption characterization of chromophore-Chlorophyll solutions in varying solvent polarity confirm the lack of cooperative absorption via a Foster-like mechanism and point the way to new concepts of cooperative absorption in natural systems and the development of a new photovoltaic paradigm.

The tilt effect in DOAS observations

NASA Astrophysics Data System (ADS)

Lampel, Johannes; Wang, Yang; Hilboll, Andreas; Beirle, Steffen; Sihler, Holger; Puķīte, Janis; Platt, Ulrich; Wagner, Thomas

2017-12-01

Experience of differential atmospheric absorption spectroscopy (DOAS) shows that a spectral shift between measurement spectra and reference spectra is frequently required in order to achieve optimal fit results, while the straightforward calculation of the optical density proves inferior. The shift is often attributed to temporal instabilities of the instrument but implicitly solved the problem of the tilt effect discussed/explained in this paper. Spectral positions of Fraunhofer and molecular absorption lines are systematically shifted for different measurement geometries due to an overall slope - or tilt - of the intensity spectrum. The phenomenon has become known as the tilt effect for limb satellite observations, where it is corrected for in a first-order approximation, whereas the remaining community is less aware of its cause and consequences. It is caused by the measurement process, because atmospheric absorption and convolution in the spectrometer do not commute. Highly resolved spectral structures in the spectrum will first be modified by absorption and scattering processes in the atmosphere before they are recorded with a spectrometer, which convolves them with a specific instrument function. In the DOAS spectral evaluation process, however, the polynomial (or other function used for this purpose) accounting for broadband absorption is applied after the convolution is performed. In this paper, we derive that changing the order of the two modifications of the spectra leads to different results. Assuming typical geometries for the observations of scattered sunlight and a spectral resolution of 0.6 nm, this effect can be interpreted as a spectral shift of up to 1.5 pm, which is confirmed in the actual analysis of the ground-based measurements of scattered sunlight as well as in numerical radiative transfer simulations. If no spectral shift is allowed by the fitting routine, residual structures of up to 2.5 × 10-3 peak-to-peak are observed. Thus, this effect needs to be considered for DOAS applications aiming at an rms of the residual of 10-3 and below.

Spectral K-edge subtraction imaging

NASA Astrophysics Data System (ADS)

Zhu, Y.; Samadi, N.; Martinson, M.; Bassey, B.; Wei, Z.; Belev, G.; Chapman, D.

2014-05-01

We describe a spectral x-ray transmission method to provide images of independent material components of an object using a synchrotron x-ray source. The imaging system and process is similar to K-edge subtraction (KES) imaging where two imaging energies are prepared above and below the K-absorption edge of a contrast element and a quantifiable image of the contrast element and a water equivalent image are obtained. The spectral method, termed ‘spectral-KES’ employs a continuous spectrum encompassing an absorption edge of an element within the object. The spectrum is prepared by a bent Laue monochromator with good focal and energy dispersive properties. The monochromator focuses the spectral beam at the object location, which then diverges onto an area detector such that one dimension in the detector is an energy axis. A least-squares method is used to interpret the transmitted spectral data with fits to either measured and/or calculated absorption of the contrast and matrix material-water. The spectral-KES system is very simple to implement and is comprised of a bent Laue monochromator, a stage for sample manipulation for projection and computed tomography imaging, and a pixelated area detector. The imaging system and examples of its applications to biological imaging are presented. The system is particularly well suited for a synchrotron bend magnet beamline with white beam access.

The OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS): Spectral Maps of the Asteroid Bennu

NASA Astrophysics Data System (ADS)

Reuter, D. C.; Simon, A. A.; Hair, J.; Lunsford, A.; Manthripragada, S.; Bly, V.; Bos, B.; Brambora, C.; Caldwell, E.; Casto, G.; Dolch, Z.; Finneran, P.; Jennings, D.; Jhabvala, M.; Matson, E.; McLelland, M.; Roher, W.; Sullivan, T.; Weigle, E.; Wen, Y.; Wilson, D.; Lauretta, D. S.

2018-03-01

The OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) is a point spectrometer covering the spectral range of 0.4 to 4.3 microns (25,000-2300 cm-1). Its primary purpose is to map the surface composition of the asteroid Bennu, the target asteroid of the OSIRIS-REx asteroid sample return mission. The information it returns will help guide the selection of the sample site. It will also provide global context for the sample and high spatial resolution spectra that can be related to spatially unresolved terrestrial observations of asteroids. It is a compact, low-mass (17.8 kg), power efficient (8.8 W average), and robust instrument with the sensitivity needed to detect a 5% spectral absorption feature on a very dark surface (3% reflectance) in the inner solar system (0.89-1.35 AU). It, in combination with the other instruments on the OSIRIS-REx Mission, will provide an unprecedented view of an asteroid's surface.

Development and performance of a laser heterodyne spectrometer using tunable semiconductor lasers as local oscillators

NASA Technical Reports Server (NTRS)

Glenar, D.; Kostiuk, T.; Jennings, D. E.; Mumma, M. J.

1980-01-01

A diode laser based IR heterodyne spectrometer for laboratory and field use was developed for high efficiency operation between 7.5 and 8.5 microns. The local oscillator is a PbSSe tunable diode laser kept continuously at operating temperatures of 12-60 K using a closed cycle cooler. The laser output frequency is controlled and stabilized using a high precision diode current supply, constant temperature controller, and a shock isolator mounted between the refrigerator cold tip and the diode mount. Single laser modes are selected by a grating placed in the local oscillator beam. The system employs reflecting optics throughout to minimize losses from internal reflection and absorption, and to eliminate chromatic effects. Spectral analysis of the diode laser output between 0 and 1 GHz reveals excess noise at many diode current settings, which limits the infrared spectral regions over which useful heterodyne operation can be achieved. System performance has been studied by making heterodyne measurements of etalon fringes and several Freon 13 (CF3Cl) absorption lines against a laboratory blackbody source. Preliminary field tests have also been performed using the Sun as a source.

Assessment of the performance of a compact concentric spectrometer system for Atmospheric Differential Optical Absorption Spectroscopy

NASA Astrophysics Data System (ADS)

Whyte, C.; Leigh, R. J.; Lobb, D.; Williams, T.; Remedios, J. J.; Cutter, M.; Monks, P. S.

2009-12-01

A breadboard demonstrator of a novel UV/VIS grating spectrometer has been developed based upon a concentric arrangement of a spherical meniscus lens, concave spherical mirror and curved diffraction grating suitable for a range of atmospheric remote sensing applications from the ground or space. The spectrometer is compact and provides high optical efficiency and performance benefits over traditional instruments. The concentric design is capable of handling high relative apertures, owing to spherical aberration and comma being near zero at all surfaces. The design also provides correction for transverse chromatic aberration and distortion, in addition to correcting for the distortion called "smile", the curvature of the slit image formed at each wavelength. These properties render this design capable of superior spectral and spatial performance with size and weight budgets significantly lower than standard configurations. This form of spectrometer design offers the potential for exceptionally compact instrument for differential optical absorption spectroscopy (DOAS) applications from LEO, GEO, HAP or ground-based platforms. The breadboard demonstrator has been shown to offer high throughput and a stable Gaussian line shape with a spectral range from 300 to 450 nm at 0.5 nm resolution, suitable for a number of typical DOAS applications.

Optimization of laser energy deposition for single-shot high aspect-ratio microstructuring of thick BK7 glass

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garzillo, Valerio; Grigutis, Robertas; Jukna, Vytautas

We investigate the generation of high aspect ratio microstructures across 0.7 mm thick glass by means of single shot Bessel beam laser direct writing. We study the effect on the photoinscription of the cone angle, as well as of the energy and duration of the ultrashort laser pulse. The aim of the study is to optimize the parameters for the writing of a regular microstructure due to index modification along the whole sample thickness. By using a spectrally resolved single pulse transmission diagnostics at the output surface of the glass, we correlate the single shot material modification with observations of themore » absorption in different portions of the retrieved spectra, and with the absence or presence of spectral modulation. Numerical simulations of the evolution of the Bessel pulse intensity and of the energy deposition inside the sample help us interpret the experimental results that suggest to use picosecond pulses for an efficient and more regular energy deposition. Picosecond pulses take advantage of nonlinear plasma absorption and avoid temporal dynamics effects which can compromise the stationarity of the Bessel beam propagation.« less

The Colorado Ultraviolet Transit Experiment (CUTE): a dedicated cubesat mission for the study of exoplanetary mass loss and magnetic fields

NASA Astrophysics Data System (ADS)

Fleming, Brian T.; France, Kevin; Nell, Nicholas; Kohnert, Richard; Pool, Kelsey; Egan, Arika; Fossati, Luca; Koskinen, Tommi; Vidotto, Aline A.; Hoadley, Keri; Desert, Jean-Michel; Beasley, Matthew; Petit, Pascal

2017-08-01

The Colorado Ultraviolet Transit Experiment (CUTE) is a near-UV (2550 - 3300 Å) 6U cubesat mission designed to monitor transiting hot Jupiters to quantify their atmospheric mass loss and magnetic fields. CUTE will probe both atomic (Mg and Fe) and molecular (OH) lines for evidence of enhanced transit absorption, and to search for evidence of early ingress due to bow shocks ahead of the planet's orbital motion. As a dedicated mission, CUTE will observe > 60 spectroscopic transits of hot Jupiters over a nominal seven month mission. This represents the equivalent of > 700 orbits of the only other instrument capable of these measurements, the Hubble Space Telescope. CUTE efficiently utilizes the available cubesat volume by means of an innovative optical design to achieve a projected effective area of ˜ 22 cm2 , low instrumental background, and a spectral resolving power of R ˜ 3000 over the entire science bandpass. These performance characteristics enable CUTE to discern a transit depth of < 1% in individual spectral absorption lines. We present the CUTE optical and mechanical design, a summary of the science motivation and expected results, and an overview of the projected fabrication, calibration and launch timeline.

Statistically Optimized Inversion Algorithm for Enhanced Retrieval of Aerosol Properties from Spectral Multi-Angle Polarimetric Satellite Observations

NASA Technical Reports Server (NTRS)

Dubovik, O; Herman, M.; Holdak, A.; Lapyonok, T.; Taure, D.; Deuze, J. L.; Ducos, F.; Sinyuk, A.

2011-01-01

The proposed development is an attempt to enhance aerosol retrieval by emphasizing statistical optimization in inversion of advanced satellite observations. This optimization concept improves retrieval accuracy relying on the knowledge of measurement error distribution. Efficient application of such optimization requires pronounced data redundancy (excess of the measurements number over number of unknowns) that is not common in satellite observations. The POLDER imager on board the PARASOL microsatellite registers spectral polarimetric characteristics of the reflected atmospheric radiation at up to 16 viewing directions over each observed pixel. The completeness of such observations is notably higher than for most currently operating passive satellite aerosol sensors. This provides an opportunity for profound utilization of statistical optimization principles in satellite data inversion. The proposed retrieval scheme is designed as statistically optimized multi-variable fitting of all available angular observations obtained by the POLDER sensor in the window spectral channels where absorption by gas is minimal. The total number of such observations by PARASOL always exceeds a hundred over each pixel and the statistical optimization concept promises to be efficient even if the algorithm retrieves several tens of aerosol parameters. Based on this idea, the proposed algorithm uses a large number of unknowns and is aimed at retrieval of extended set of parameters affecting measured radiation.

Absorption coefficients and frequency shifts measurement in the spectral range of 1071.88-1084.62 cm-1 vs. pressure for chlorodifluoromethane (CHClF2) using tunable CW CO2 laser

NASA Astrophysics Data System (ADS)

Al-Hawat, Sharif

2013-02-01

Infrared (IR) absorption in the spectral range of (1071.88-1084.62 cm-1) vs. pressure in chlorodifluoromethane (CFC-22, F-22, and CHClF2) was studied using a tunable continuous wave (CW) CO2 laser radiation on 9R branch lines with a maximum output power of about 2.12 W, provided with an absorber cell located outside the laser cavity. The absorption coefficients were determined vs. the gas pressure between 0.2 mbar and 170 mbar at lines from 9R branch for CFC-22. The frequency shifts of the absorption lines of CFC-22 in relative to the central frequencies of laser lines were calculated vs. the pressure on the basis of these absorption coefficients. The chosen lines were selected according to IR spectrum of the studied gas given by HITRAN cross section database. So the absorption was achieved for CFC-22 at the spectral lines of 9R branch situated from 9R (10) to 9R (30) emitted by a tunable CW CO2 laser. The absorption cross sections of CFC-22 determined in this work were compared with the relevant data given by HITRAN cross section database and a reasonable agreement was observed.

Io's Thermal Regions and Non-SO2 Spectral Features

NASA Technical Reports Server (NTRS)

Smythe, W. D.; Soderblom, L. A.; Lopes, R. M. C.

2003-01-01

Several absorptions have been identified in the Galileo NIMS spectra of Io that are not related to SO2. [1,2]. These absorptions have band centers at 2.97, 3.15, 3.85, and 3.91 microns. There are also broad absorptions in the regions 1-1.3 and 3- 3.4 microns. Patterning noise in wavelength registration, arising from the pushbroom imaging and grating motion of the NIMS instrument have previously inhibited reliable mapping of weak absorptions. Recent improvements in techniques to remove the coherent pattern noise from the NIMS dataset have been made by Soderblom. This greatly improves the signal to noise ratio and enables mapping of weak spectral signatures such as the 3.15 micron absorption on Io.

Using high spectral resolution spectrophotometry to study broad mineral absorption features on Mars

NASA Technical Reports Server (NTRS)

Blaney, D. L.; Crisp, D.

1993-01-01

Traditionally telescopic measurements of mineralogic absorption features have been made using relatively low to moderate (R=30-300) spectral resolution. Mineralogic absorption features tend to be broad so high resolution spectroscopy (R greater than 10,000) does not provide significant additional compositional information. Low to moderate resolution spectroscopy allows an observer to obtain data over a wide wavelength range (hundreds to thousands of wavenumbers) compared to the several wavenumber intervals that are collected using high resolution spectrometers. However, spectrophotometry at high resolution has major advantages over lower resolution spectroscopy in situations that are applicable to studies of the Martian surface, i.e., at wavelengths where relatively weak surface absorption features and atmospheric gas absorption features both occur.

A new on-axis micro-spectrophotometer for combining Raman, fluorescence and UV/Vis absorption spectroscopy with macromolecular crystallography at the Swiss Light Source

PubMed Central

Pompidor, Guillaume; Dworkowski, Florian S. N.; Thominet, Vincent; Schulze-Briese, Clemens; Fuchs, Martin R.

2013-01-01

The combination of X-ray diffraction experiments with optical methods such as Raman, UV/Vis absorption and fluorescence spectroscopy greatly enhances and complements the specificity of the obtained information. The upgraded version of the in situ on-axis micro-spectrophotometer, MS2, at the macromolecular crystallography beamline X10SA of the Swiss Light Source is presented. The instrument newly supports Raman and resonance Raman spectroscopy, in addition to the previously available UV/Vis absorption and fluorescence modes. With the recent upgrades of the spectral bandwidth, instrument stability, detection efficiency and control software, the application range of the instrument and its ease of operation were greatly improved. Its on-axis geometry with collinear X-ray and optical axes to ensure optimal control of the overlap of sample volumes probed by each technique is still unique amongst comparable facilities worldwide and the instrument has now been in general user operation for over two years. PMID:23955041

Plasmon resonance and perfect light absorption in subwavelength trench arrays etched in gallium-doped zinc oxide film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hendrickson, Joshua R., E-mail: joshua.hendrickson.4@us.af.mil; Leedy, Kevin; Cleary, Justin W.

Near-perfect light absorption in subwavelength trench arrays etched in highly conductive gallium-doped zinc oxide films was experimentally observed in the mid infrared regime. At wavelengths corresponding to the resonant excitation of surface plasmons, up to 99% of impinging light is efficiently trapped and absorbed in the periodic trenches. Scattering cross sectional calculations reveal that each individual trench acts like a vertical split ring resonator with a broad plasmon resonance spectrum. The coupling of these individual plasmon resonators in the grating structure leads to enhanced photon absorption and significant resonant spectral linewidth narrowing. Ellipsometry measurements taken before and after device fabricationmore » result in different permittivity values for the doped zinc oxide material, indicating that localized annealing occurred during the plasma etching process due to surface heating. Simulations, which incorporate a 50 nm annealed region at the zinc oxide surface, are in a good agreement with the experimental results.« less

A new on-axis micro-spectrophotometer for combining Raman, fluorescence and UV/Vis absorption spectroscopy with macromolecular crystallography at the Swiss Light Source.

PubMed

Pompidor, Guillaume; Dworkowski, Florian S N; Thominet, Vincent; Schulze-Briese, Clemens; Fuchs, Martin R

2013-09-01

The combination of X-ray diffraction experiments with optical methods such as Raman, UV/Vis absorption and fluorescence spectroscopy greatly enhances and complements the specificity of the obtained information. The upgraded version of the in situ on-axis micro-spectrophotometer, MS2, at the macromolecular crystallography beamline X10SA of the Swiss Light Source is presented. The instrument newly supports Raman and resonance Raman spectroscopy, in addition to the previously available UV/Vis absorption and fluorescence modes. With the recent upgrades of the spectral bandwidth, instrument stability, detection efficiency and control software, the application range of the instrument and its ease of operation were greatly improved. Its on-axis geometry with collinear X-ray and optical axes to ensure optimal control of the overlap of sample volumes probed by each technique is still unique amongst comparable facilities worldwide and the instrument has now been in general user operation for over two years.

Thermal tuning of infrared resonant absorbers based on hybrid gold-VO{sub 2} nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kocer, Hasan; Department of Electrical Engineering, Turkish Military Academy, 06654 Ankara; Butun, Serkan

2015-04-20

Resonant absorbers based on plasmonic materials, metamaterials, and thin films enable spectrally selective absorption filters, where absorption is maximized at the resonance wavelength. By controlling the geometrical parameters of nano/microstructures and materials' refractive indices, resonant absorbers are designed to operate at wide range of wavelengths for applications including absorption filters, thermal emitters, thermophotovoltaic devices, and sensors. However, once resonant absorbers are fabricated, it is rather challenging to control and tune the spectral absorption response. Here, we propose and demonstrate thermally tunable infrared resonant absorbers using hybrid gold-vanadium dioxide (VO{sub 2}) nanostructure arrays. Absorption intensity is tuned from 90% to 20%more » and 96% to 32% using hybrid gold-VO{sub 2} nanowire and nanodisc arrays, respectively, by heating up the absorbers above the phase transition temperature of VO{sub 2} (68 °C). Phase change materials such as VO{sub 2} deliver useful means of altering optical properties as a function of temperature. Absorbers with tunable spectral response can find applications in sensor and detector applications, in which external stimulus such as heat, electrical signal, or light results in a change in the absorption spectrum and intensity.« less

M3 spectral analysis of lunar swirls and the link between optical maturation and surface hydroxyl formation at magnetic anomalies

USGS Publications Warehouse

Kramer, G.Y.; Besse, S.; Dhingra, D.; Nettles, J.; Klima, R.; Garrick-Bethell, I.; Clark, Roger N.; Combe, J.-P.; Head, J. W.; Taylor, L.A.; Pieters, C.M.; Boardman, J.; McCord, T.B.

2011-01-01

We examined the lunar swirls using data from the Moon Mineralogy Mapper (M3). The improved spectral and spatial resolution of M3 over previous spectral imaging data facilitates distinction of subtle spectral differences, and provides new information about the nature of these enigmatic features. We characterized spectral features of the swirls, interswirl regions (dark lanes), and surrounding terrain for each of three focus regions: Reiner Gamma, Gerasimovich, and Mare Ingenii. We used Principle Component Analysis to identify spectrally distinct surfaces at each focus region, and characterize the spectral features that distinguish them. We compared spectra from small, recent impact craters with the mature soils into which they penetrated to examine differences in maturation trends on- and off-swirl. Fresh, on-swirl crater spectra are higher albedo, exhibit a wider range in albedos and have well-preserved mafic absorption features compared with fresh off-swirl craters. Albedoand mafic absorptions are still evident in undisturbed, on-swirl surface soils, suggesting the maturation process is retarded. The spectral continuum is more concave compared with off-swirl spectra; a result of the limited spectral reddening being mostly constrained to wavelengths less than ∼1500 nm. Off-swirl spectra show very little reddening or change in continuum shape across the entire M3 spectral range. Off-swirl spectra are dark, have attenuated absorption features, and the narrow range in off-swirl albedos suggests off-swirl regions mature rapidly. Spectral parameter maps depicting the relative OH surface abundance for each of our three swirl focus regions were created using the depth of the hydroxyl absorption feature at 2.82 μm. For each of the studied regions, the 2.82 μm absorption feature is significantly weaker on-swirl than off-swirl, indicating the swirls are depleted in OH relative to their surroundings. The spectral characteristics of the swirls and adjacent terrains from all three focus regions support the hypothesis that the magnetic anomalies deflect solar wind ions away from the swirls and onto off-swirl surfaces. Nanophase iron (npFe0) is largely responsible for the spectral characteristics we attribute to space weathering and maturation, and is created by vaporization/deposition by micrometeorite impacts and sputtering/reduction by solar wind ions. On the swirls, the decreased proton flux slows the spectral effects of space weathering (relative to nonswirl regions) by limiting the npFe0 production mechanism almost exclusively to micrometeoroid impact vaporization/deposition. Immediately adjacent to the swirls, maturation is accelerated by the increased flux of protons deflected from the swirls.

Fibre-coupled red diode-pumped Alexandrite TEM00 laser with single and double-pass end-pumping

NASA Astrophysics Data System (ADS)

Arbabzadah, E. A.; Damzen, M. J.

2016-06-01

We report the investigation of an Alexandrite laser end-pumped by a fibre-coupled red diode laser module. Power, efficiency, spatial, spectral, and wavelength tuning performance are studied as a function of pump and laser cavity parameters. It is the first demonstration, to our knowledge, of greater than 1 W power and also highest laser slope efficiency (44.2%) in a diode-pumped Alexandrite laser with diffraction-limited TEM00 mode operation. Spatial quality was excellent with beam propagation parameter M 2 ~ 1.05. Wavelength tuning from 737-796 nm was demonstrated using an intracavity birefringent tuning filter. Using a novel double pass end-pumping scheme to get efficient absorption of both polarisation states of the scrambled fibre-delivered diode pump, a total output coupled power of 1.66 W is produced in TEM00 mode with 40% slope efficiency.

Improved predictive modeling of white LEDs with accurate luminescence simulation and practical inputs with TracePro opto-mechanical design software

NASA Astrophysics Data System (ADS)

Tsao, Chao-hsi; Freniere, Edward R.; Smith, Linda

2009-02-01

The use of white LEDs for solid-state lighting to address applications in the automotive, architectural and general illumination markets is just emerging. LEDs promise greater energy efficiency and lower maintenance costs. However, there is a significant amount of design and cost optimization to be done while companies continue to improve semiconductor manufacturing processes and begin to apply more efficient and better color rendering luminescent materials such as phosphor and quantum dot nanomaterials. In the last decade, accurate and predictive opto-mechanical software modeling has enabled adherence to performance, consistency, cost, and aesthetic criteria without the cost and time associated with iterative hardware prototyping. More sophisticated models that include simulation of optical phenomenon, such as luminescence, promise to yield designs that are more predictive - giving design engineers and materials scientists more control over the design process to quickly reach optimum performance, manufacturability, and cost criteria. A design case study is presented where first, a phosphor formulation and excitation source are optimized for a white light. The phosphor formulation, the excitation source and other LED components are optically and mechanically modeled and ray traced. Finally, its performance is analyzed. A blue LED source is characterized by its relative spectral power distribution and angular intensity distribution. YAG:Ce phosphor is characterized by relative absorption, excitation and emission spectra, quantum efficiency and bulk absorption coefficient. Bulk scatter properties are characterized by wavelength dependent scatter coefficients, anisotropy and bulk absorption coefficient.

Spectral properties of gaseous uranium hexafluoride at high temperature

NASA Technical Reports Server (NTRS)

Krascella, N. L.

1980-01-01

A study to determine relative spectral emission and spectral absorption data for UF6-argon mixtures at elevated temperatures is discussed. These spectral data are required to assist in the theoretical analysis of radiation transport in the nuclear fuel-buffer gas region of a plasma core reactor. Relative emission measurements were made for UF6-argon mixtures over a range of temperatures from 650 to 1900 K and in the wavelength range from 600 to 5000 nanometers. All emission results were determined for a total pressure of 1.0 atm. Uranium hexafluoride partial pressures varied from about 3.5 to 12.7 mm Hg. Absorption measurements were attempted at 600, 625, 650 and 675 nanometers for a temperature of 1000 K. The uranium partial pressure for these determinations was 25 mm Hg. The results exhibit appreciable emission for hot UF6-argon mixtures at wavelengths between 600 and 1800 nanometers and no measurable absorption. The equipment used to evaluate the spectral properties of the UF6-argon mixtures included a plasma torch-optical plenum assembly, the monochromator, and the UF6 transfer system. Each is described.

Underresolved absorption spectroscopy of OH radicals in flames using broadband UV LEDs

NASA Astrophysics Data System (ADS)

White, Logan; Gamba, Mirko

2018-04-01

A broadband absorption spectroscopy diagnostic based on underresolution of the spectral absorption lines is evaluated for the inference of species mole fraction and temperature in combustion systems from spectral fitting. The approach uses spectrally broadband UV light emitting diodes and leverages low resolution, small form factor spectrometers. Through this combination, the method can be used to develop high precision measurement sensors. The challenges of underresolved spectroscopy are explored and addressed using spectral derivative fitting, which is found to generate measurements with high precision and accuracy. The diagnostic is demonstrated with experimental measurements of gas temperature and OH mole fraction in atmospheric air/methane premixed laminar flat flames. Measurements exhibit high precision, good agreement with 1-D flame simulations, and high repeatability. A newly developed model of uncertainty in underresolved spectroscopy is applied to estimate two-dimensional confidence regions for the measurements. The results of the uncertainty analysis indicate that the errors in the outputs of the spectral fitting procedure are correlated. The implications of the correlation between uncertainties for measurement interpretation are discussed.

Fiber-Coupled Planar Light-Wave Circuit for Seed Laser Control in High Spectral Resolution Lidar Systems

NASA Technical Reports Server (NTRS)

Cook, Anthony; McNeil, Shirley; Switzer, Gregg; Battle, Philip

2010-01-01

Precise laser remote sensing of aerosol extinction and backscatter in the atmosphere requires a high-power, pulsed, frequency doubled Nd:YAG laser that is wavelength- stabilized to a narrow absorption line such as found in iodine vapor. One method for precise wavelength control is to injection seed the Nd:YAG laser with a low-power CW laser that is stabilized by frequency converting a fraction of the beam to 532 nm, and to actively frequency-lock it to an iodine vapor absorption line. While the feasibility of this approach has been demonstrated using bulk optics in NASA Langley s Airborne High Spectral Resolution Lidar (HSRL) program, an ideal, lower cost solution is to develop an all-waveguide, frequency-locked seed laser in a compact, robust package that will withstand the temperature, shock, and vibration levels associated with airborne and space-based remote sensing platforms. A key technology leading to this miniaturization is the integration of an efficient waveguide frequency doubling element, and a low-voltage phase modulation element into a single, monolithic, planar light-wave circuit (PLC). The PLC concept advances NASA's future lidar systems due to its compact, efficient and reliable design, thus enabling use on small aircraft and satellites. The immediate application for this technology is targeted for NASA Langley's HSRL system for aerosol and cloud characterization. This Phase I effort proposes the development of a potassium titanyl phosphate (KTP) waveguide phase modulator for future integration into a PLC. For this innovation, the proposed device is the integration of a waveguide-based frequency doubler and phase modulator in a single, fiber pigtail device that will be capable of efficient second harmonic generation of 1,064-nm light and subsequent phase modulation of the 532 nm light at 250 MHz, providing a properly spectrally formatted beam for HSRL s seed laser locking system. Fabrication of the integrated PLC chip for NASA Langley, planned for the Phase II effort, will require full integration and optimization of the waveguide components (SHG waveguide, splitters, and phase modulator) onto a single, monolithic device. The PLC will greatly reduce the size and weight, improve electrical- to-optical efficiency, and significantly reduce the cost of NASA Langley s current stabilized HSRL seed laser system built around a commercial off-the-shelf seed laser that is free-space coupled to a bulk doubler and bulk phase modulator.

Flat-plate solar array project. Volume 4: High-efficiency solar cells

NASA Technical Reports Server (NTRS)

Leipold, M.; Cheng, L.; Daud, T.; Mokashi, A.; Burger, D.; Christensen, E. (Editor); Murry, J. (Editor); Bengelsdorf, I. (Editor)

1986-01-01

The High Efficiency Solar Cell Task was assigned the objective of understanding and developing high efficiency solar cell devices that would meet the cost and performance goals of the Flat Plate Solar Array (FSA) Project. The need for research dealing with high efficiency devices was considered important because of the role efficiency plays in reducing price per watt of generated energy. The R&D efforts conducted during the 1982 to 1986 period are summarized to provide understanding and control of energy conversion losses associated with crystalline silicon solar cells. New levels of conversion efficiency were demonstrated. Major contributions were made both to the understanding and reduction of bulk and surface losses in solar cells. For example, oxides, nitrides, and polysilicon were all shown to be potentially useful surface passivants. Improvements in measurement techniques were made and Auger coefficients and spectral absorption data were obtained for unique types of silicon sheets. New modelling software was developed including a program to optimize a device design based on input characteristics of a cell.

Performance of the Fourier transform spectrometer (FTS) for FIS onboard ASTRO-F

NASA Astrophysics Data System (ADS)

Murakami, Noriko; Kawada, Mitsunobu; Takahashi, Hidenori; Ozawa, Keita; Imamura, Tetsuo; Shibai, Hiroshi; Nakagawa, Takao

2004-10-01

We have developed the imaging Fourier Transform Spectrometer (FTS) for the FIS (Far-Infrared Surveyor) onboard the ASTRO-F satellite. A Martin-Puplett interferometer is adopted to achieve high optical efficiency in a wide wavelength range. The total optical efficiency of this spectrometer is achieved 40-80% of the ideal value which is 25% of the incident flux. The wavelength range of 50-200μm is covered with two kinds of detector; the monolithic Ge:Ga photoconductor array for short wavelength (50-110μm) and the stressed Ge:Ga photoconductor array for long wavelength (110-200μm). The spectral resolution expected from the maximum optical path difference is 0.18cm-1. In order to evaluate the spectral resolution of the FTS, we measured absorption lines of H2O in atmosphere using the optics of the FTS with a bolometer at the room temperature. The measured line widths are consistent with the expected instrumental resolution of 0.18 cm-1. Some spectral measurements at the cryogenic temperature were carried out by using cold blackbody sources whose temperatures are controlled in a range from 20 to 50 K. The derived spectra considering with the spectral response of the system are consistent with expected ones. Spectroscopic observations with the FTS will provide a lot of astronomical information; SED of galaxies detected in the all sky survey and the physical diagnostics of the interstellar matter by using the excited atomic or molecular lines.

Supercontinuum generation in silicon waveguides relying on wave-breaking.

PubMed

Castelló-Lurbe, David; Silvestre, Enrique

2015-10-05

Four-wave-mixing processes enabled during optical wave-breaking (OWB) are exploited in this paper for supercontinuum generation. Unlike conventional approaches based on OWB, phase-matching is achieved here for these nonlinear interactions, and, consequently, new frequency production becomes more efficient. We take advantage of this kind of pulse propagation to obtain numerically a coherent octave-spanning mid-infrared supercontinuum generation in a silicon waveguide pumping at telecom wavelengths in the normal dispersion regime. This scheme shows a feasible path to overcome limits imposed by two-photon absorption on spectral broadening in silicon waveguides.

Spectral and multi-wavelength continuous-wave laser properties of Yb3+:BaLaGa3O7

NASA Astrophysics Data System (ADS)

Gao, Shufang; Xu, Shan

2018-05-01

Yb3+ doped BaLaGa3O7 crystal has been successfully grown by Czochralski method. The polarized absorption spectra, the fluorescence spectra and the fluorescence decay lifetime of Yb3+:BaLaGa3O7 crystal were measured at room temperature. The spectroscopic parameters of Yb3+:BaLaGa3O7 crystal are calculated. A continuous wave output power of 1.32W was obtained with four-wavelength emission corresponding to an optical-optical slope efficiency of 55%.

Optical characterization of Nd (3+):AgBr.

PubMed

Bunimovich, D; Nagli, L; Katzir, A

1997-10-20

The luminescence of silver bromide crystals, doped with neodymium, was investigated over the visible and near-infrared spectral ranges. The emission, excitation, and absorption spectra were measured over a broad temperature range. The absolute luminescence quantum yield was estimated by comparing the luminescence with that of a neodymium-doped phosphate glass, for which the manufacturer gives a value of 0.4. The Judd-Ofelt analysis was applied to both materials, and transition rates, branching ratios, and quantum efficiencies were calculated for all the observed bands. Good agreement was obtained between theory and experiment.

Metallic Iron and Iron Oxide as an Explanation for the Dark Material Observed on Saturn's Icy Satellites and Rings with Cassini VIMS

NASA Astrophysics Data System (ADS)

Clark, Roger Nelson; Cruikshank, D. P.; Jaumann, R.; Brown, R. H.; Dalle Ore, C.; Stephan, K.; Hoefen, T. M.; Curchin, J. M.; Buratti, B. J.; Filacchione, G.; Baines, K. H.; Nicholson, P. D.

2010-10-01

The Visual and Infrared Mapping Spectrometer (VIMS) on Cassini has obtained spatially resolved spectra on satellites of Saturn. The Cassini Rev 49 Iapetus fly-by on September 10, 2007, provided data on both the dark material and the transition zone between the dark material and the visually bright ice. The dark material has low albedo with a linear increase in reflectance with wavelength, 3-micron water, and CO2 absorptions. The transition between bright and dark regions shows mixing with unusual optical properties including increased blue scattering and increasing strength of a UV absorber in areas with stronger ice absorptions. Similar spectral effects are observed on other Saturnian satellites and in the rings. We have been unable to match these spectral properties and trends using tholins and carbon compounds. However, the dark material is spectrally matched by fine-grained metallic iron plus nano-phase hematite and adsorbed water which contribute UV and 3-micron absorption, respectively. The blue scattering peak and UV absorption can be explained by Rayleigh scattering from sub-micron particles with a UV absorption, or a combination of Rayleigh scattering and Rayleigh absorption as has been attributed to spectral properties of the Moon. A new radiative transfer model that includes Rayleigh scattering and Rayleigh absorption has been constructed. Models of ice, sub-micron metallic iron, hydrated iron oxide, and trace CO2 explain the observed spectra. Rayleigh absorption requires high absorption coefficient nano-sized particles, which is also consistent with metallic iron. The UV absorber appears to have increased strength on satellite surfaces close to Saturn, with a corresponding decrease in metallic iron signature. A possible explanation is that the iron is oxidized closer to Saturn by oxygen in the extended atmosphere of Saturn's rings, or the dark material is simply covered by clean fine-grained ice particles, for example, from the E-ring.

A lidar system for measuring atmospheric pressure and temperature profiles

NASA Technical Reports Server (NTRS)

Schwemmer, Geary K.; Dombrowski, Mark; Korb, C. Laurence; Milrod, Jeffry; Walden, Harvey

1987-01-01

The design and operation of a differential absorption lidar system capable of remotely measuring the vertical structure of tropospheric pressure and temperature are described. The measurements are based on the absorption by atmospheric oxygen of the spectrally narrowband output of two pulsed alexandrite lasers. Detailed laser output spectral characteristics, which are critical to successful lidar measurements, are presented. Spectral linewidths of 0.026 and 0.018 per cm for the lasers were measured with over 99.99 percent of the energy contained in three longitudinal modes.

Measurement of wavelength-dependent extinction to distinguish between absorbing and nonabsorbing aerosol particulates

NASA Technical Reports Server (NTRS)

Portscht, R.

1977-01-01

Measurements of spectral transmission factors in smoky optical transmission paths reveal a difference between wavelength exponents of the extinction cross section of high absorption capacity and those of low absorption capacity. A theoretical explanation of this behavior is presented. In certain cases, it is possible to obtain data on the absorption index of aerosol particles in the optical path by measuring the spectral decadic extinction coefficient at, at least, two wavelengths. In this manner it is possible, for instance, to distinguish smoke containing soot from water vapor.

Estimating soil zinc concentrations using reflectance spectroscopy

NASA Astrophysics Data System (ADS)

Sun, Weichao; Zhang, Xia

2017-06-01

Soil contamination by heavy metals has been an increasingly severe threat to nature environment and human health. Efficiently investigation of contamination status is essential to soil protection and remediation. Visible and near-infrared reflectance spectroscopy (VNIRS) has been regarded as an alternative for monitoring soil contamination by heavy metals. Generally, the entire VNIR spectral bands are employed to estimate heavy metal concentration, which lacks interpretability and requires much calculation. In this study, 74 soil samples were collected from Hunan Province, China and their reflectance spectra were used to estimate zinc (Zn) concentration in soil. Organic matter and clay minerals have strong adsorption for Zn in soil. Spectral bands associated with organic matter and clay minerals were used for estimation with genetic algorithm based partial least square regression (GA-PLSR). The entire VNIR spectral bands, the bands associated with organic matter and the bands associated with clay minerals were incorporated as comparisons. Root mean square error of prediction, residual prediction deviation, and coefficient of determination (R2) for the model developed using combined bands of organic matter and clay minerals were 329.65 mg kg-1, 1.96 and 0.73, which is better than 341.88 mg kg-1, 1.89 and 0.71 for the entire VNIR spectral bands, 492.65 mg kg-1, 1.31 and 0.40 for the organic matter, and 430.26 mg kg-1, 1.50 and 0.54 for the clay minerals. Additionally, in consideration of atmospheric water vapor absorption in field spectra measurement, combined bands of organic matter and absorption around 2200 nm were used for estimation and achieved high prediction accuracy with R2 reached 0.640. The results indicate huge potential of soil reflectance spectroscopy in estimating Zn concentrations in soil.

O2 on ganymede: Spectral characteristics and plasma formation mechanisms

USGS Publications Warehouse

Calvin, W.M.; Johnson, R.E.; Spencer, J.R.

1996-01-01

Weak absorption features in the visible reflectance spectrum of Jupiter's satellite Ganymede have been correlated to those observed in the spectrum of molecular oxygen. We examine the spectral characteristics of these absorption features in all phases of O2 and conclude that the molecular oxygen is most likely present at densities similar to the liquid or solid ??-phase. The contribution of O2 to spectral features observed on Ganymede in the near-infrared wavelength region affects the previous estimates of photon pathlength in ice. The concentration of the visible absorption features on the trailing hemisphere of Ganymede suggests an origin due to bombardment by magneto-spheric ions. We derive an approximate O2 formation rate from this mechanism and consider the state of O2 within the surface.

Three-dimensional photonic crystals as intermediate filter for thin-film tandem solar cells

NASA Astrophysics Data System (ADS)

Bielawny, Andreas; Miclea, Paul T.; Wehrspohn, Ralf B.; Lee, Seung-Mo; Knez, Mato; Rockstuhl, Carsten; Lisca, Marian; Lederer, Falk L.; Carius, Reinhard

2008-04-01

The concept of a 3D photonic crystal structure as diffractive and spectrally selective intermediate filter within 'micromorphous' (a-Si/μc-Si) tandem solar cells has been investigated numerically and experimentally. Our device aims for the enhancement of the optical pathway of incident light within the amorphous silicon top cell in its spectral region of low absorption. From our previous simulations, we expect a significant improvement of the tandem cell efficiency of about absolutely 1.3%. This increases the efficiency for a typical a-Si / μc-Si tandem cell from 11.1% to 12.4%, as a result of the optical current-matching of the two junctions. We suggest as wavelength-selective optical element a 3D-structured optical thin-film, prepared by self-organized artificial opal templates and replicated with atomic layer deposition. The resulting samples are highly periodic thin-film inverted opals made of conducting and transparent zinc-oxide. We describe the fabrication processes and compare experimental data on the optical properties in reflection and transmission with our simulations and photonic band structure calculations.

Liquid-phase and solid-phase microwave irradiations for reduction of graphite oxide

NASA Astrophysics Data System (ADS)

Zhao, Na; Wen, Chen-Yu; Zhang, David Wei; Wu, Dong-Ping; Zhang, Zhi-Bin; Zhang, Shi-Li

2014-12-01

In this paper, two microwave irradiation methods: (i) liquid-phase microwave irradiation (MWI) reduction of graphite oxide suspension dissolved in de-ionized water and N, N-dimethylformamide, respectively, and (ii) solid-phase MWI reduction of graphite oxide powder have been successfully carried out to reduce graphite oxide. The reduced graphene oxide products are thoroughly characterized by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectral analysis, Raman spectroscopy, UV-Vis absorption spectral analysis, and four-point probe conductivity measurements. The results show that both methods can efficiently remove the oxygen-containing functional groups attached to the graphite layers, though the solid-phase MWI reduction method can obtain far more efficiently a higher quality-reduced graphene oxide with fewer defects. The I(D)/I(G) ratio of the solid-phase MWI sample is as low as 0.46, which is only half of that of the liquid-phase MWI samples. The electrical conductivity of the reduced graphene oxide by the solid method reaches 747.9 S/m, which is about 25 times higher than that made by the liquid-phase method.

Interacting dark resonances with plasmonic meta-molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jha, Pankaj K.; Mrejen, Michael; Kim, Jeongmin

2014-09-15

Dark state physics has led to a variety of remarkable phenomena in atomic physics, quantum optics, and information theory. Here, we investigate interacting dark resonance type physics in multi-layered plasmonic meta-molecules. We theoretically demonstrate that these plasmonic meta-molecules exhibit sub-natural spectral response, analogous to conventional atomic four-level configuration, by manipulating the evanescent coupling between the bright and dark elements (plasmonic atoms). Using cascaded coupling, we show nearly 4-fold reduction in linewidth of the hybridized resonance compared to a resonantly excited single bright plasmonic atom with same absorbance. In addition, we engineered the geometry of the meta-molecules to realize efficient intramolecularmore » excitation transfer with nearly 80%, on resonant excitation, of the total absorption being localized at the second dark plasmonic atom. An analytical description of the spectral response of the structure is presented with full electrodynamics simulations to corroborate our results. Such multilayered meta-molecules can bring a new dimension to higher quality factor plasmonic resonance, efficient excitation transfer, wavelength demultiplexing, and enhanced non-linearity at nanoscale.« less

Nanophotonic photon echo memory based on rare-earth-doped crystals

NASA Astrophysics Data System (ADS)

Zhong, Tian; Kindem, Jonathan; Miyazono, Evan; Faraon, Andrei; Caltech nano quantum optics Team

2015-03-01

Rare earth ions (REIs) are promising candidates for implementing solid-state quantum memories and quantum repeater devices. Their high spectral stability and long coherence times make REIs a good choice for integration in an on-chip quantum nano-photonic platform. We report the coupling of the 883 nm transition of Neodymium (Nd) to a Yttrium orthosilicate (YSO) photonic crystal nano-beam resonator, achieving Purcell enhanced spontaneous emission by 21 times and increased optical absorption. Photon echoes were observed in nano-beams of different doping concentrations, yielding optical coherence times T2 up to 80 μs that are comparable to unprocessed bulk samples. This indicates the remarkable coherence properties of Nd are preserved during nanofabrication, therefore opening the possibility of efficient on-chip optical quantum memories. The nano-resonator with mode volume of 1 . 6(λ / n) 3 was fabricated using focused ion beam, and a quality factor of 3200 was measured. Purcell enhanced absorption of 80% by an ensemble of ~ 1 × 106 ions in the resonator was measured, which fulfills the cavity impedance matching condition that is necessary to achieve quantum storage of photons with unity efficiency.

Zero-reabsorption doped-nanocrystal luminescent solar concentrators.

PubMed

Erickson, Christian S; Bradshaw, Liam R; McDowall, Stephen; Gilbertson, John D; Gamelin, Daniel R; Patrick, David L

2014-04-22

Optical concentration can lower the cost of solar energy conversion by reducing photovoltaic cell area and increasing photovoltaic efficiency. Luminescent solar concentrators offer an attractive approach to combined spectral and spatial concentration of both specular and diffuse light without tracking, but they have been plagued by luminophore self-absorption losses when employed on practical size scales. Here, we introduce doped semiconductor nanocrystals as a new class of phosphors for use in luminescent solar concentrators. In proof-of-concept experiments, visibly transparent, ultraviolet-selective luminescent solar concentrators have been prepared using colloidal Mn(2+)-doped ZnSe nanocrystals that show no luminescence reabsorption. Optical quantum efficiencies of 37% are measured, yielding a maximum projected energy concentration of ∼6× and flux gain for a-Si photovoltaics of 15.6 in the large-area limit, for the first time bounded not by luminophore self-absorption but by the transparency of the waveguide itself. Future directions in the use of colloidal doped nanocrystals as robust, processable spectrum-shifting phosphors for luminescent solar concentration on the large scales required for practical application of this technology are discussed.

Fully suspended slot waveguide platform

NASA Astrophysics Data System (ADS)

Zhou, Wen; Cheng, Zhenzhou; Wu, Xinru; Sun, Xiankai; Tsang, Hon Ki

2018-02-01

A fully suspended slot waveguide (FSSWG) platform, including straight slot waveguides, 90° bends, high-Q racetrack resonators, and strip-to-slot mode converters, is demonstrated for broadband and low-loss operation in the mid-infrared spectral region. The proposed FSSWG platform has inherent merits of a broad spectral range of transparency which is limited only by the absorption of silicon, strong light-analyte interaction, good mechanical stability, and single lithography step fabrication process. By using asymmetric FSSWGs, the propagation loss, bending loss, and intrinsic optical Q factor are demonstrated to be 2.8 dB/cm, 0.15 dB/90°, and 12 600, respectively. The average conversion efficiency of a mode converter is 95.4% over a bandwidth of 170 nm and 97.0% at 2231 nm. The FSSWG platform would be promising for a long-range and cavity-enhanced light-analyte interaction.

Rational Molecular Engineering of Indoline-Based D-A-π-A Organic Sensitizers for Long-Wavelength-Responsive Dye-Sensitized Solar Cells.

PubMed

Zhang, Weiwei; Wu, Yongzhen; Zhu, Haibo; Chai, Qipeng; Liu, Jingchuan; Li, Hui; Song, Xiongrong; Zhu, Wei-Hong

2015-12-09

Indoline-based D-A-π-A organic sensitizers are promising candidates for highly efficient and long-term stable dye-sensitized solar cells (DSSCs). In order to further broaden the spectral response of the known indoline dye WS-2, we rationally engineer the molecular structure through enhancing the electron donor and extending the π-bridge, resulting in two novel indoline-based D-A-π-A organic sensitizers WS-92 and WS-95. By replacing the 4-methylphenyl group on the indoline donor of WS-2 with a more electron-rich carbazole unit, the intramolecular charge transfer (ICT) absorption band of dye WS-92 is slightly red-shifted from 550 nm (WS-2) to 554 nm (WS-92). In comparison, the incorporation of a larger π-bridge of cyclopentadithiophene (CPDT) unit in dye WS-95 not only greatly bathochromatically tunes the absorption band to 574 nm but also largely enhances the molar extinction coefficients (ε), thus dramatically improving the light-harvesting capability. Under the standard global AM 1.5 solar light condition, the photovoltaic performances of both organic dyes have been evaluated in DSSCs on the basis of the iodide/triiodide electrolyte without any coadsorbent or cosensitizer. The DSSCs based on WS-95 display better device performance with power conversion efficiency (η) of 7.69%. The additional coadsorbent in the dye bath of WS-95 does not improve the photovoltaic performance, indicative of its negligible dye aggregation, which can be rationalized by the grafted dioctyl chains on the CPDT unit. The cosensitization of WS-95 with a short absorption wavelength dye S2 enhances the IPCE and improves the η to 9.18%. Our results indicate that extending the π-spacer is more rational than enhancing the electron donor in terms of broadening the spectral response of indoline-based D-A-π-A organic sensitizers.

Initiation of air ionization by ultrashort laser pulses: evidence for a role of metastable-state air molecules

NASA Astrophysics Data System (ADS)

Bulgakov, A. V.; Mirza, I.; Bulgakova, N. M.; Zhukov, V. P.; Machulka, R.; Haderka, O.; Campbell, E. E. B.; Mocek, T.

2018-06-01

Transmission measurements for femtosecond laser pulses focused in air with spectral analysis of emission from the focal region have been carried out for various pulse energies and air pressures. The air breakdown threshold and pulse attenuation due to plasma absorption are evaluated and compared with calculations based on the multiphoton ionization model. The plasma absorption is found to depend on the pulse repetition rate and is considerably stronger at 1 kHz than at 1–10 Hz. This suggests that accumulation of metastable states of air molecules plays an important role in initiation of air breakdown, enhancing the ionization efficiency at high repetition rates. Possible channels of metastable-state-assisted air ionization and the role of the observed accumulation effect in laser material processing are discussed.

Dynamics of defects in Ce³⁺ doped silica affecting its performance as protective filter in ultraviolet high-power lasers.

PubMed

Demos, Stavros G; Ehrmann, Paul R; Qiu, S Roger; Schaffers, Kathleen I; Suratwala, Tayyab I

2014-11-17

We investigate defects forming in Ce³⁺-doped fused silica samples following exposure to nanosecond ultraviolet laser pulses and their relaxation as a function of time and exposure to low intensity light at different wavelengths. A subset of these defects are responsible for inducing absorption in the visible and near infrared spectral range, which is of critical importance for the use of this material as ultraviolet light absorbing filter in high power laser systems. The dependence of the induced absorption as a function of laser fluence and methods to most efficiently mitigate this effect are presented. Experiments simulating the operation of the material as a UV protection filter for high power laser systems were performed in order to determine limitations and practical operational conditions.

An Intense Slit Discharge Source of Jet-Cooled Molecular Ions and Radicals (T(sub rot) less than 30 K)

NASA Technical Reports Server (NTRS)

Anderson, David T.; Davis, Scott; Zwier, Timothy S.; Nesbitt, David J.

1996-01-01

A novel pulsed, slit supersonic discharge source is described for generating intense jet-cooled densities of radicals (greater than 10(exp 12)/cu cm) and molecular ions (greater than 10(exp 10)/cu cm) under long absorption path (80 cm), supersonically cooled conditions. The design confines the discharge region upstream of the supersonic expansion orifice to achieve efficient rotational cooling down to 30 K or less. The collisionally collimated velocity distribution in the slit discharge geometry yields sub-Doppler spectral linewidths, which for open-shell radicals reveals spin-rotation splittings and broadening due to nuclear hyperfine structure. Application of the slit source for high-resolution, direct IR laser absorption spectroscopy in discharges is demonstrated on species such as OH, H3O(+) and N2H(+).

A new nano-enhanced technology proposed to quantify intracellular detection of radiation-induced metabolic processes.

PubMed

Malak, Henryk; Richmond, Robert; Dicello, J F

2011-02-01

A new approach to intracellular detection and imaging of metabolic processes and pathways is presented that uses surface plasmon resonance to enhance interactions between photon-absorbing metabolites and metal nanoparticles in contact with cells in vitro or in vivo. Photon absorption in the nanoparticles creates plasmon fields, enhancing intrinsic metabolite fluorescence, thereby increasing absorption and emission rates, creating new spectral emission bands, shortening fluorescence lifetimes, becoming more photo-stable and increasing fluorescent resonance energy transfer efficiency. Because the cells remain viable, it is proposed that the method may be used to interrogate cells prior to and after irradiation, with the potential for automated analyses of intracellular interactive pathways associated with radiation exposures at lower doses than existing technologies. The design and concepts of the instrument are presented along with data for unexposed cells.

Performance of special radiation-hardened optical fibers intended for use in the telecom spectral windows at a megagray level

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tomashuk, A.L.; Dianov, E.M.; Golant, K.M.

Gamma-radiation-induced absorption spectra (2.15 MGy(Si)) are compared in N-doped and pure silica fibers fabricated by surface plasma CVD-process under different regimes with the aim to reveal the chief absorption mechanisms in the telecom spectral windows and to work out an optimum fiber design. The long wavelength absorption edge is shown to be the main absorption mechanism at megagray doses. Its value increases with increasing bonded hydrogen concentration in the fiber glass network and is slightly greater in N-doped fibers. No nitrogen-related color centers have been revealed in the short wavelength loss edge, which is determined by chlorine impurity in silica.

Prediction of meat spectral patterns based on optical properties and concentrations of the major constituents.

PubMed

ElMasry, Gamal; Nakauchi, Shigeki

2016-03-01

A simulation method for approximating spectral signatures of minced meat samples was developed depending on concentrations and optical properties of the major chemical constituents. Minced beef samples of different compositions scanned on a near-infrared spectroscopy and on a hyperspectral imaging system were examined. Chemical composition determined heuristically and optical properties collected from authenticated references were simulated to approximate samples' spectral signatures. In short-wave infrared range, the resulting spectrum equals the sum of the absorption of three individual absorbers, that is, water, protein, and fat. By assuming homogeneous distributions of the main chromophores in the mince samples, the obtained absorption spectra are found to be a linear combination of the absorption spectra of the major chromophores present in the sample. Results revealed that developed models were good enough to derive spectral signatures of minced meat samples with a reasonable level of robustness of a high agreement index value more than 0.90 and ratio of performance to deviation more than 1.4.

Refractive index measurements in absorbing media with white light spectral interferometry.

PubMed

Arosa, Yago; Lago, Elena López; de la Fuente, Raúl

2018-03-19

White light spectral interferometry is applied to measure the refractive index in absorbing liquids in the spectral range of 400-1000 nm. We analyze the influence of absorption on the visibility of interferometric fringes and, accordingly, on the measurement of the refractive index. Further, we show that the refractive index in the absorption band can be retrieved by a two-step process. The procedure requires the use of two samples of different thickness, the thicker one to retrieve the refractive index in the transparent region and the thinnest to obtain the data in the absorption region. First, the refractive index values are retrieved with good accuracy in the transparent region of the material for 1-mm-thick samples. Second, these refractive index values serve also to precisely calculate the thickness of a thinner sample (~150 µm) since the accuracy of the methods depends strongly on the thickness of the sample. Finally, the refractive index is recovered for the entire spectral range.

Online Spectral Fit Tool for Analyzing Reflectance Spectra

NASA Astrophysics Data System (ADS)

Penttilä, A.; Kohout, T.

2015-11-01

The Online Spectral Fit Tool is developed for analyzing Vis-NIR spectral behavior of asteroids and meteorites. Implementation is done using JavaScript/HTML. Fitted spectra consist of spline continuum and gamma distributions for absorption bands.

Tailoring Eigenmodes at Spectral Singularities in Graphene-based PT Systems.

PubMed

Zhang, Weixuan; Wu, Tong; Zhang, Xiangdong

2017-09-12

The spectral singularity existing in PT-synthetic plasmonic system has been widely investigated. Only lasing-mode can be excited resulting from the passive characteristic of metallic materials. Here, we investigated the spectral singularity in the hybrid structure composed of the photoexcited graphene and one-dimensional PT-diffractive grating. In this system, both lasing- and absorption-modes can be excited with the surface conductivity of photoexcited graphene being loss and gain, respectively. Remarkably, the spectral singularity will disappear with the optically pumped graphene to be lossless. In particular, we find that spectral singularities can exhibit symmetry-modes, when the loss and gain of the grating is unbalanced. Meanwhile, by tuning the loss (gain) of graphene and non-PT diffraction grating, lasing- and absorption-modes can also be excited. We hope that tunable optical modes at spectral singularities can have some applications in designing novel surface-enhanced spectroscopies and plasmon lasers.

Retrieving marine inherent optical properties from satellites using temperature and salinity-dependent backscattering by seawater.

PubMed

Werdell, P Jeremy; Franz, Bryan A; Lefler, Jason T; Robinson, Wayne D; Boss, Emmanuel

2013-12-30

Time-series of marine inherent optical properties (IOPs) from ocean color satellite instruments provide valuable data records for studying long-term time changes in ocean ecosystems. Semi-analytical algorithms (SAAs) provide a common method for estimating IOPs from radiometric measurements of the marine light field. Most SAAs assign constant spectral values for seawater absorption and backscattering, assume spectral shape functions of the remaining constituent absorption and scattering components (e.g., phytoplankton, non-algal particles, and colored dissolved organic matter), and retrieve the magnitudes of each remaining constituent required to match the spectral distribution of measured radiances. Here, we explore the use of temperature- and salinity-dependent values for seawater backscattering in lieu of the constant spectrum currently employed by most SAAs. Our results suggest that use of temperature- and salinity-dependent seawater spectra elevate the SAA-derived particle backscattering, reduce the non-algal particles plus colored dissolved organic matter absorption, and leave the derived absorption by phytoplankton unchanged.

Spectral line shapes of collision-induced light scattering (CILS) and collision-induced absorption (CIA) using isotropic intermolecular potential for H2-Ar

NASA Astrophysics Data System (ADS)

El-Kader, M. S. A.; Godet, J.-L.; El-Sadek, A. A.; Maroulis, G.

2017-10-01

Quantum mechanical line shapes of collision-induced light scattering at room temperature (295 K) and collision-induced absorption at T = 195 K are computed for gaseous mixtures of molecular hydrogen and argon using theoretical values for pair-polarisability trace and anisotropy and induced dipole moments as input. Comparison with other theoretical spectra of isotropic and anisotropic light scattering and measured spectra of absorption shows satisfactory agreement, for which the uncertainty in measurement of its spectral moments is seen to be large. Ab initio models of the trace and anisotropy polarisability which reproduce the recent spectra of scattering are given. Empirical model of the dipole moment which reproduce the experimental spectra and the first three spectral moments more closely than the fundamental theory are also given. Good agreement between computed and/or experimental line shapes of both absorption and scattering is obtained when the potential model which is constructed from the transport and thermo-physical properties is used.

Retrieving Marine Inherent Optical Properties from Satellites Using Temperature and Salinity-dependent Backscattering by Seawater

NASA Technical Reports Server (NTRS)

Werdell, Paul J.; Franz, Bryan Alden; Lefler, Jason Travis; Robinson, Wayne D.; Boss, Emmanuel

2013-01-01

Time-series of marine inherent optical properties (IOPs) from ocean color satellite instruments provide valuable data records for studying long-term time changes in ocean ecosystems. Semi-analytical algorithms (SAAs) provide a common method for estimating IOPs from radiometric measurements of the marine light field. Most SAAs assign constant spectral values for seawater absorption and backscattering, assume spectral shape functions of the remaining constituent absorption and scattering components (e.g., phytoplankton, non-algal particles, and colored dissolved organic matter), and retrieve the magnitudes of each remaining constituent required to match the spectral distribution of measured radiances. Here, we explore the use of temperature- and salinity-dependent values for seawater backscattering in lieu of the constant spectrum currently employed by most SAAs. Our results suggest that use of temperature- and salinity-dependent seawater spectra elevate the SAA-derived particle backscattering, reduce the non-algal particles plus colored dissolved organic matter absorption, and leave the derived absorption by phytoplankton unchanged.

Acceleration of Singlet Fission in an Aza-Derivative of TIPS-Pentacene.

PubMed

Herz, Julia; Buckup, Tiago; Paulus, Fabian; Engelhart, Jens; Bunz, Uwe H F; Motzkus, Marcus

2014-07-17

The influence of the carbon to nitrogen substitution on the photoinduced dynamics of TIPS-pentacene was investigated by ultrafast transient absorption measurements on spin-coated thin films in the visible and in the near-infrared spectral region. A global target analysis was performed to provide a detailed picture of the excited-state dynamics. We found that the chemical modification has a high impact on the triplet formation and leads to shorter dynamics; hence it speeds up the singlet fission process. A faster relaxation from the singlet into the triplet manifold implies a higher efficiency because other relaxation channels are avoided. The air-stable aza-derivatives have the potential to exceed the energy conversion efficiency of TIPS-pentacene.

Composition and structure of fresh ammonia clouds on Jupiter based on quantitative analysis of Galileo/NIMS and New Horizons/LEISA spectra

NASA Astrophysics Data System (ADS)

Sromovsky, L. A.; Fry, P. M.

2018-06-01

Ammonia gas has long been assumed to be the main source of condensables for the upper cloud layer on Jupiter, but distinctive spectral features associated with ammonia have been seen only rarely. Since both ammonia and NH4SH absorb in the 3 μm region, and widespread absorption in the 3 μm region was present (Sromovsky and Fry, 2010), identification of the 2 μm absorption feature of NH3 provided an opportunity to clearly establish its presence in Jovian clouds. Baines et al. (2002) succeeded in finding in Near Infrared Mapping Spectrometer (NIMS) observations one feature that had both 2 μm and 3 μm absorption, and many which were known to have absorption at 2.73 μm. They named these Spectrally Identifiable Ammonia Clouds (SIACs). They also argued that these were fresh ammonia clouds that would eventually succumb to some process that would obscure their absorption features. Detection of many more of the 2 μm features was later achieved by New Horizon's Linear Etalon Imaging Spectral Array (LEISA) instrument, which provided both the spatial and spectral resolution needed to identify these features. Here we report on the first quantitative modeling that uses NIMS spectra over a broad (1-5.2 μm) spectral range and LEISA spectra over a much narrower (1.25-2.5 μm) spectral range to constrain the cloud structure and composition of these rare cloud features and compare them to background clouds. We find that the absorption signature at 2 μm, which is well characterized in LEISA spectra, is relatively subtle and easily matched by model clouds containing spherical particles of ammonia ice with radii of 2-4 μm. The NIMS spectra, which cover both reflected sunlight as well as thermal emission regions are more difficult to model with cloud materials plausibly present in Jupiter's atmosphere. The best signal/noise spectra obtained from NIMS provide a relatively sparse sampling of the spectrum, which does not establish the detailed shape of the 3 μm absorption region. NIMS SIAC spectra with much denser spectral sampling are limited by much higher noise levels that degrade the features that are key to identifying cloud composition. The structure which best matches the wide range NIMS SIAC spectra contains two overlapping NH3 clouds with a bi-modal size distribution over an optically thick NH4SH cloud. The bi-modal distribution may be a result of modeling non-spherical, possibly fractal aggregate, particles with spheres.

Near-infrared light absorption by brown carbon in the ambient atmosphere

NASA Astrophysics Data System (ADS)

Chung, C.; Hoffer, A.; Beres, N. D.; Moosmüller, H.; Liu, C.; Green, M.; Kim, S. W.; Engelbrecht, J. P.; Gelencser, A.

2017-12-01

Organic aerosols have been assumed to have little-to-no absorption in the red and near-infrared spectral regions of solar radiation, even though a class of organic aerosols were shown to absorb significantly in these spectral regions. Here, we show that ambient atmospheric data from commonly-used 7-wavelength aethalometers contain evidence of abundant near-infrared light absorption by organic aerosol. This evidence comes from the absorption Ångström exponent over 880 950 nm, which often exceeds values explainable by fresh or coated black carbon, or mineral dust. This evidence is not due to an artifact from the instrument random errors or biases, either. The best explanation for these large 880/950 nm absorption Ångström exponent values in the aethalometer data is near-infrared light absorption by tar balls. Tar balls are among common particles from forest fire.

Inner filter effect and the onset of concentration dependent red shift of synchronous fluorescence spectra.

PubMed

Tarai, Madhumita; Mishra, Ashok Kumar

2016-10-12

The phenomenon of concentration dependent red shift, often observed in synchronous fluorescence spectra (SFS) of monofluorophoric as well as multifluorophoric systems at high chromophore concentrations, is known to have good analytical advantages. This was previously understood in terms of large inner filter effect (IFE) through the introduction of a derived absorption spectral profile that closely corresponds to the SFS profile. Using representative monofluorophoric and multifluorophoric systems, it is now explained how the SF spectral maximum changes with concentration of the fluorophore. For dilute solutions of monofluorophores the maximum is unchanged as expected. It is shown here that the onset of red shift of SFS maximum of both the mono as well as the multifluorophoric systems must occur at the derived absorption spectral parameter value of 0.32 that corresponds to the absorbance value of 0.87. This value is unique irrespective of the nature of the fluorophore under study. For monofluorophoric systems, the wavelength of derived absorption spectral maximum and the wavelength of synchronous fluorescence spectral maximum closely correspond with each other in the entire concentration range. In contrast, for multifluorophoric systems like diesel and aqueous humic acid, large deviations were noted that could be explained as to be due to the presence of non-fluorescing chromophores in the system. This work bridges the entire fluorophore concentration range over which the red shift of SFS maximum sets in; and in the process it establishes the importance of the derived absorption spectral parameter in understanding the phenomenon of concentration dependent red shift of SFS maximum. Copyright © 2016 Elsevier B.V. All rights reserved.

Theoretical extension and experimental demonstration of spectral compression in second-harmonic generation by Fresnel-inspired binary phase shaping

NASA Astrophysics Data System (ADS)

Li, Baihong; Dong, Ruifang; Zhou, Conghua; Xiang, Xiao; Li, Yongfang; Zhang, Shougang

2018-05-01

Selective two-photon microscopy and high-precision nonlinear spectroscopy rely on efficient spectral compression at the desired frequency. Previously, a Fresnel-inspired binary phase shaping (FIBPS) method was theoretically proposed for spectral compression of two-photon absorption and second-harmonic generation (SHG) with a square-chirped pulse. Here, we theoretically show that the FIBPS can introduce a negative quadratic frequency phase (negative chirp) by analogy with the spatial-domain phase function of Fresnel zone plate. Thus, the previous theoretical model can be extended to the case where the pulse can be transformed limited and in any symmetrical spectral shape. As an example, we experimentally demonstrate spectral compression in SHG by FIBPS for a Gaussian transform-limited pulse and show good agreement with the theory. Given the fundamental pulse bandwidth, a narrower SHG bandwidth with relatively high intensity can be obtained by simply increasing the number of binary phases. The experimental results also verify that our method is superior to that proposed in [Phys. Rev. A 46, 2749 (1992), 10.1103/PhysRevA.46.2749]. This method will significantly facilitate the applications of selective two-photon microscopy and spectroscopy. Moreover, as it can introduce negative dispersion, hence it can also be generalized to other applications in the field of dispersion compensation.

Visualization of hemodynamics and light scattering in exposed brain of rat using multispectral image reconstruction based on Wiener estimation method

NASA Astrophysics Data System (ADS)

Nishidate, Izumi; Ishizuka, Tomohiro; Yoshida, Keiichiro; Kawauchi, Satoko; Sato, Shunichi; Sato, Manabu

2015-07-01

We investigate a method to estimate the spectral images of reduced scattering coefficients and the absorption coefficients of in vivo exposed brain tissues in the range from visible to near-infrared wavelength (500-760 nm) based on diffuse reflectance spectroscopy using a digital RGB camera. In the proposed method, the multi-spectral reflectance images of in vivo exposed brain are reconstructed from the digital red, green, blue images using the Wiener estimation algorithm. The Monte Carlo simulation-based multiple regression analysis for the absorbance spectra is then used to specify the absorption and scattering parameters of brain tissue. In this analysis, the concentration of oxygenated hemoglobin and that of deoxygenated hemoglobin are estimated as the absorption parameters whereas the scattering amplitude a and the scattering power b in the expression of μs'=aλ-b as the scattering parameters, respectively. The spectra of absorption and reduced scattering coefficients are reconstructed from the absorption and scattering parameters, and finally, the spectral images of absorption and reduced scattering coefficients are estimated. We performed simultaneous recordings of spectral diffuse reflectance images and of the electrophysiological signals for in vivo exposed rat brain during the cortical spreading depression evoked by the topical application of KCl. Changes in the total hemoglobin concentration and the tissue oxygen saturation imply the temporary change in cerebral blood flow during CSD. Change in the reduced scattering coefficient was observed before the profound increase in the total hemoglobin concentration, and its occurrence was synchronized with the negative dc shift of the local field potential.

Subgap Absorption in Conjugated Polymers

DOE R&D Accomplishments Database

Sinclair, M.; Seager, C. H.; McBranch, D.; Heeger, A. J; Baker, G. L.

1991-01-01

Along with X{sup (3)}, the magnitude of the optical absorption in the transparent window below the principal absorption edge is an important parameter which will ultimately determine the utility of conjugated polymers in active integrated optical devices. With an absorptance sensitivity of < 10{sup {minus}5}, Photothermal Deflection Spectroscopy (PDS) is ideal for determining the absorption coefficients of thin films of transparent'' materials. We have used PDS to measure the optical absorption spectra of the conjugated polymers poly(1,4-phenylene-vinylene) (and derivitives) and polydiacetylene-4BCMU in the spectral region from 0.55 eV to 3 eV. Our spectra show that the shape of the absorption edge varies considerably from polymer to polymer, with polydiacetylene-4BCMU having the steepest absorption edge. The minimum absorption coefficients measured varied somewhat with sample age and quality, but were typically in the range 1 cm{sup {minus}1} to 10 cm{sup {minus}1}. In the region below 1 eV, overtones of C-H stretching modes were observed, indicating that further improvements in transparency in this spectral region might be achieved via deuteration of fluorination.

Identifying Aerosol Type/Mixture from Aerosol Absorption Properties Using AERONET

NASA Technical Reports Server (NTRS)

Giles, D. M.; Holben, B. N.; Eck, T. F.; Sinyuk, A.; Dickerson, R. R.; Thompson, A. M.; Slutsker, I.; Li, Z.; Tripathi, S. N.; Singh, R. P.;

Prostate Cancer Detection Using Near Infrared Spectral Polarization Imaging

DTIC Science & Technology

2005-07-01

position. This indicates the polarization preservation nature of Cybesin. Time Resolved Fluorescence Intensity of Cybesin 60000 Perpendicular 3000 0...absorption than that of normal tissue at water absorption peaks indicating cancer tissue has less water content than that of normal tissue; (5) preliminary...rectum-and-membrane tissues.’ This indicates that our proposed approach of imaging a prostate gland through rectum using spectral polarization imaging

Hyperspectral analysis of the ultramafic complex and adjacent lithologies at Mordor, NT, Australia

USGS Publications Warehouse

Rowan, L.C.; Simpson, C.J.; Mars, J.C.

2004-01-01

The Mordor Complex consists of a series of potassic ultramafic rocks which were intruded into Proterozoic felsic gneisses and amphibolite and are overlain by quartzite and unconsolidated deposits. In situ and laboratory 0.4 to 2.5 ??m reflectance spectra show Al-OH absorption features caused by absorption in muscovite, kaolinite, and illite/smectite in syenite, granitic gneiss, quartzite and unconsolidated sedimentary deposits, and Fe,Mg-OH features due to phlogopite, biotite, epidote, and hornblende in the mafic and ultramafic rocks. Ferrous-iron absorption positioned near 1.05 ??m is most intense in peridotite reflectance spectra. Ferric-iron absorption is intense in most of the felsic lithologies. HyMap data were recorded in 126 narrow bands from 0.43 to 2.5 ??m along a 7-km-wide swath with approximately 6-m spatial resolution. Correction of the data to spectral reflectance was accomplished by reference to in situ measurements of an extensive, alluvial plain. Spectral classes for matched filter processing were selected by using the pixel purity index procedure and analysis of in situ and laboratory spectra. Considering the spatial distribution of the resulting 14 classes, some classes were combined, which produced eight classes characterized by Al-OH absorption features, and three Fe,Mg-OH absorption-feature classes. Comparison of the distribution of these 11 spectral classes to a generalized lithologic map of the study area shows that the spectral distinction among the eight Al-OH classes is related to variations in primary lithology, weathering products, and vegetation density. Quartzite is represented in three classes, syenite corresponds to a single scattered class, quartz-muscovite-biotite schist defines a single very coherent class, and unconsolidated sediments are portrayed in four classes. The three mafic-ultramafic classes are distinguished on the basis of generally intense Fe,Mg-OH and ferrous-iron absorption features. A single class represents the main Mordor ultramafic mass. Epidote-bearing rocks define another class, which corresponds to biotite gneiss and, in the southern part of the area, to fracture zones. The third class, which exhibits Al-OH, as well as Fe,Mg-OH features, represents hornblende gneiss and other mafic gneisses. These results indicate the importance of analyzing the VNIR and SWIR spectral shape and albedo, as well as analyzing specific spectral features, for mapping lithologic units in this weathered terrain. ?? 2004 Elsevier Inc. All rights reserved.

Plasmonic near-touching titanium oxide nanoparticles to realize solar energy harvesting and effective local heating.

PubMed

Yan, Jiahao; Liu, Pu; Ma, Churong; Lin, Zhaoyong; Yang, Guowei

2016-04-28

Through the excitation of plasmon resonance, the energy of plasmonic nanoparticles either reradiates through light scattering or decays into energetic electrons (absorption). The plasmon-induced absorption can greatly enhance the efficiency of solar energy harvesting, local heating, photodetection and photocatalysis. Here, we demonstrate that heavily self-doped titanium oxide nanoparticles (TiO1.67 analogue arising from oxygen vacancies in rutile TiO2) with the plasmon resonance dominated by an interband transition shows strong absorption to build a broadband perfect absorber in the wavelength range from 300 to 2000 nm covering the solar irradiation spectrum completely. The absorptivity of the fabricated array is greater than 90% in the whole spectral range. And the broadband and strong absorption is due to the plasmon hybridization and hot spot generation from near-touching TiO1.67 nanoparticles with different sizes. What is more, the local heating of a TiO1.67 nanoparticle layer is fast and effective. The temperature increases quickly from 30 °C to 80 °C within 200 seconds. This local heating can realize rapid solar-enabled evaporation which can find applications in large-scale distillation and seawater desalination. These findings actually open a pathway for applications of these newly developed plasmonic materials in the energy and environment fields.

Laser excitation dynamics of argon metastables generated in atmospheric pressure flows by microwave frequency microplasma arrays

NASA Astrophysics Data System (ADS)

Rawlins, W. T.; Galbally-Kinney, K. L.; Davis, S. J.; Hoskinson, A. R.; Hopwood, J. A.

2014-03-01

The optically pumped rare-gas metastable laser is a chemically inert analogue to diode-pumped alkali (DPAL) and alkali-exciplex (XPAL) laser systems. Scaling of these devices requires efficient generation of electronically excited metastable atoms in a continuous-wave electric discharge in flowing gas mixtures at atmospheric pressure. This paper describes initial investigations of the use of linear microwave micro-discharge arrays to generate metastable rare-gas atoms at atmospheric pressure in optical pump-and-probe experiments for laser development. Power requirements to ignite and sustain the plasma at 1 atm are low, <30 W. We report on the laser excitation dynamics of argon metastables, Ar (4s, 1s5) (Paschen notation), generated in flowing mixtures of Ar and He at 1 atm. Tunable diode laser absorption measurements indicate Ar(1s5) concentrations near 3 × 1012 cm-3 at 1 atm. The metastables are optically pumped by absorption of a focused beam from a continuous-wave Ti:S laser, and spectrally selected fluorescence is observed with an InGaAs camera and an InGaAs array spectrometer. We observe the optical excitation of the 1s5-->2p9 transition at 811.5 nm and the corresponding laser-induced fluorescence on the 2p10-->1s5 transition at 912.3 nm; the 2p10 state is efficiently populated by collisional energy transfer from 2p9. Using tunable diode laser absorption/gain spectroscopy, we observe small-signal gains of ~1 cm-1 over a 1.9 cm path. We also observe stable, continuous-wave laser oscillation at 912.3 nm, with preliminary optical efficiency ~55%. These results are consistent with efficient collisional coupling within the Ar(4s) manifold.

Constraining the variability of optical properties in the Santa Barbara Channel, CA: A phytoplankton story

NASA Astrophysics Data System (ADS)

Barron, Rebecca Katherine

The research presented in this dissertation evaluates the direct relationships of phytoplankton community composition and inherent optical properties (IOP); that is, the absorption and scattering of light in the ocean. Phytoplankton community composition affect IOPs in both direct and indirect ways, thus creating challenges for optical measurements of biological and biogeochemical properties in aquatic systems. Studies were performed in the Santa Barbara Channel (SBC), CA where an array of optical and biogeochemical measurements were made. Phytoplankton community structure was characterized by an empirical orthogonal functional analysis (EOF) using phytoplankton accessory pigments. The results showed that phytoplankton community significantly correlated to all IOPs, e.g. phytoplankton specific absorption, detrital absorption, CDOM absorption and particle backscattering coefficients. Furthermore, the EOF analysis was unique in splitting the microphytoplankton size class into separate diatom and dinoflagellate regimes allowing for assessment optical property differences within the same size class, a technique previously not systematically achievable. The phytoplankton functional group dinoflagellates were particularly influential to IOPs in surprising ways. Dinoflagellates showed higher backscattering efficiencies than would be predicted based on Mie theory, and significantly influenced CDOM absorption via direct association with dissolved mycosproine-like amino acid absorption (MAA) peaks in CDOM spectra. A new index was developed in this work to quantify MAA absorption peaks in CDOM spectra, and was named the MAA Index. Prior to this research dissolved MAA absorption in natural waters was never quantified, and CDOM data containing these peaks were often disregarded and discarded from analysis. CDOM dynamics in the SBC were assessed for a 15-year study period, and this work shows that significantly large MAA Index values, e.g. MAA Index > 1, were present in approximately 16% of surface water data. Variability in CDOM spectral shape was quantified using the EOF technique, and regression analysis with EOF outputs showed that CDOM absorption intensity and spectral shape were well correlated dinoflagellate presence. Furthermore, results showed that phytoplankton biomass played a secondary role in relation to CDOM absorption, and that variability in CDOM absorption coefficients were primarily driven by community composition. CDOM quality in the SBC was also assessed using CDOM fluorescence properties via excitation emission matrix spectroscopy (EEMS). The EEMS data was analyzed using a multivariate statistical procedure, again, an EOF analysis, to identify three dominant CDOM source regimes: the surface pelagic regime, deep-water (up to 300 m) regime and kelp forest pelagic regime. This work also found that while CDOM absorption coefficient was strongly influence by which phytoplankton groups were present, DOM quality was characterized more so by the amount of phytoplankton biomass, hence indicating strong microbial component to DOM production. Lastly, with the use of the EEMS data, and characterization of CDOM absorption properties, e.g. spectral slope, S, slope ratio, SR, specific UV-absorbance, SUVA and MAA Index, we found that terrestrial sources of CDOM were very limited in the SBC. Based on this research, mineral particle concentrations that significantly correlated with IOPs were thought to be associated with suspended sediments from shoaling of the continental shelf rather than from stream/river influence. Thus, the SBC is a unique, optically complex ocean system where IOP dynamics, thus remote sensing reflectance, are strongly influenced by shifts in phytoplankton community structure.

Photosensitivity of layered semiconductor propolis heterocontact

NASA Astrophysics Data System (ADS)

Drapak, Stepan I.; Orletskii, Volodymyr B.; Bahtinov, Anatolii P.; Kovalyuk, Zakhar D.; Fotiy, Vasyl D.

2003-03-01

Room temperature photosensitivity and its spectral distribution are investigated for a hetercontact between a layered semiconductor (p-InSe) and a biological entity (propolis). The obtained heterocontacts has a maximum photosensitivity >= 10^4 V/W. It is shown that the form of spectral sensitivity curve depends on the way of the heterocontact preparation. The long-wave edge of relative quantum efficiency varies from hν =1.2 eV (the energy gap for InSe at T=300 K) to 1.6 eV depending on a state of aggregation of propolis. The maximum photosensitivity in the long-wave spectral range takes place when the propolis layer is under illumination. The obtained peculiarities of the photoelectrical properties cannot be explained in the framework of the classical description of photosensitivity spectral description (the window effect) what follows from the optical absorption measurements for InSe and propolis in the range hν <= 1.2 eV. Impurity states in the energy gap of InSe and states at the heterocontact interface (a classical case of isotype p-p heterojunction) also do not give an appropriate explanation. To interpret the obtained results the complexity of the chemical composition of propolis, a product from honey bee, must be taken into account.

Wet-chemistry based selective coatings for concentrating solar power

NASA Astrophysics Data System (ADS)

Maimon, Eran; Kribus, Abraham; Flitsanov, Yuri; Shkolnik, Oleg; Feuermann, Daniel; Zwicker, Camille; Larush, Liraz; Mandler, Daniel; Magdassi, Shlomo

2013-09-01

Spectrally selective coatings are common in low and medium temperature solar applications from solar water heating collectors to parabolic trough absorber tubes. They are also an essential element for high efficiency in higher temperature Concentrating Solar Power (CSP) systems. Selective coatings for CSP are usually prepared using advanced expensive methods such as sputtering and vapor deposition. In this work, coatings were prepared using low-cost wet-chemistry methods. Solutions based on Alumina and Silica sol gel were prepared and then dispersed with black spinel pigments. The black dispersions were applied by spray/roll coating methods on stainless steel plates. The spectral emissivity of sample coatings was measured in the temperature range between 200 and 500°C, while the spectral absorptivity was measured at room temperature and 500°C. Emissivity at wavelengths of 0.4-1.7 μm was evaluated indirectly using multiple measurements of directional reflectivity. Emissivity at wavelengths 2-14 μm was measured directly using a broadband IR camera that acquires the radiation emitted from the sample, and a range of spectral filters. Emissivity measurement results for a range of coated samples will be presented, and the impact of coating thickness, pigment loading, and surface preparation will be discussed.

Investigation of the optical properties of novel organic macromolecules for solar cell applications

NASA Astrophysics Data System (ADS)

Adegoke, Oluwasegun Oluwasina

The search for renewable energy sources to replace fossil fuel has been a major research focus in the energy sector. The sun, with its vast amount of energy, remains the most abundant and ubiquitous energy source that far exceeds the world energy demand. The ability to effectively capture and convert energy from the sun in the form of photons will be the key to its effective utilization. Organic macromolecules have tremendous potentials to replace and out-perform existing materials, due to their low-cost, ease of tunability, high absorption coefficient and "green" nature. In this dissertation, spectroscopic techniques of steady state absorption and time-resolved fluorescence spectroscopy were used to show the improved absorption of the oligothiophene-functionalized ZnPc through ultrafast energy transfer. ZnPc is known for its chemical and thermal stability. The power conversion efficiency (PCE) in ZnPc-based solar devices is however, very low because of the poor absorption of ZnPc in the 300 - 550 nm region of the solar spectrum. Oligothiophenes have good absorption in the spectral region where the absorption of ZnPc is poor. Other groups of organic compounds that have gained prominence in the study for the design of efficient active materials for photovoltaic cells are the polymers. In the dissertation, different factors which can affect the performance of organic polymers in photovoltaics systems were investigated and analyzed. The effects of the alteration of conjugation, donor-acceptor groups, heteroatoms and alkyl side chains on the photophysical properties and ultimately the performance of organic polymers in organic photovoltaics were investigated. The different effects were investigated using ultrafast spectroscopic techniques which are capable of providing insight of fluorescence decay dynamics at very short times in a time scale of femtosecond. The electronic structure calculations of the polymers were carried out to provide further evidence to the experimental findings. PTB7, which has one of the best power conversion efficiency in organic photovoltaics, was one of the investigated polymers. Other novel organic polymers based on thiophene and furan framework were also considered.

Synthesis, growth, structural, spectral, thermal, chemical etching, linear and nonlinear optical and mechanical studies of an organic single crystal 4-chloro 4-nitrostilbene (CONS): a potential NLO material.

PubMed

Dinakaran, Paul M; Kalainathan, S

2013-07-01

4-Chloro 4-nitrostilbene (CONS) a new organic nonlinear optical material has been synthesized. Employing slow evaporation method, good optical quality single crystals (dimensions up to 6×2×3 mm(3)) have been grown using ethyl methyl ketone (EMK) as a solvent. The grown crystals have been subjected to various characterizations such as single crystal X-ray diffraction, powder XRD, Fourier Transform Infrared spectroscopy (FTIR), proton NMR, solid UV absorption, SHG studies. Single crystal X-ray diffraction reveals that the crystal system belongs to monoclinic with noncentrosymmetric space group P21. The UV-Vis absorption spectrum has been recorded and found that the cut off wavelength is 380 nm. Functional groups and the structure of the title compound have been confirmed by FTIR and (1)H NMR spectroscopic analyses respectively. Molecular mass of the CONS confirmed by the high resolution mass spectral analysis .The thermal behavior of the grown crystal has been studied by TG/DTA analysis and it shows the melting point is at 188.66 °C. Dislocations and growth pattern present in the grown crystal revealed by the etching study. The mechanical strength of the CONS crystal has been studied by Vicker's hardness measurement. The SHG efficiency of the grown crystal has been determined by Kurtz and Perry powder test which revealed that the CONS crystal (327 mV) has 15 times greater efficiency than that of KDP (21.7 mV). Copyright © 2013 Elsevier B.V. All rights reserved.

Eco-friendly luminescent solar concentrators with low reabsorption losses and resistance to concentration quenching based on aqueous-solution-processed thiolate-gold nanoclusters

NASA Astrophysics Data System (ADS)

Huang, H. Y.; Cai, K. B.; Chang, L. Y.; Chen, P. W.; Lin, T. N.; Lin, C. A. J.; Shen, J. L.; Talite, M. J.; Chou, W. C.; Yuan, C. T.

2017-09-01

Heavy-metal-containing quantum dots (QDs) with engineered electronic states have been served as luminophores in luminescent solar concentrators (LSCs) with impressive optical efficiency. Unfortunately, those QDs involve toxic elements and need to be synthesized in a hazardous solvent. Recently, biocompatible, eco-friendly gold nanoclusters (AuNCs), which can be directly synthesized in an aqueous solution, have gained much attention for promising applications in ‘green photonics’. Here, we explored the solid-state photophysical properties of aqueous-solution-processed, glutathione-stabilized gold nanoclusters (GSH-AuNCs) with a ligand-to-metal charge-transfer (LMCT) state for developing ‘green’ LSCs. We found that such GSH-AuNCs exhibit a large Stokes shift with almost no spectral overlap between the optical absorption and PL emission due to the LMCT states, thus, suppressing reabsorption losses. Compared with GSH-AuNCs in solution, the photoluminescence quantum yields (PL-QYs) of the LSCs can be enhanced, accompanied with a lengthened PL lifetime owing to the suppression of non-radiative recombination rates. In addition, the LSCs do not suffer from severe concentration-induced PL quenching, which is a common weakness for conventional luminophores. As a result, a common trade-off between light-harvesting efficiency and solid-state PL-QYs can be bypassed due to nearly-zero spectral overlap integral between the optical absorption and PL emission. We expect that GSH-AuNCs hold great promise for serving as luminophores for ‘green’ LSCs by further enhancing solid-state PL-QYs.

Eco-friendly luminescent solar concentrators with low reabsorption losses and resistance to concentration quenching based on aqueous-solution-processed thiolate-gold nanoclusters.

PubMed

Huang, H Y; Cai, K B; Chang, L Y; Chen, P W; Lin, T N; Lin, C A J; Shen, J L; Talite, M J; Chou, W C; Yuan, C T

2017-09-15

Heavy-metal-containing quantum dots (QDs) with engineered electronic states have been served as luminophores in luminescent solar concentrators (LSCs) with impressive optical efficiency. Unfortunately, those QDs involve toxic elements and need to be synthesized in a hazardous solvent. Recently, biocompatible, eco-friendly gold nanoclusters (AuNCs), which can be directly synthesized in an aqueous solution, have gained much attention for promising applications in 'green photonics'. Here, we explored the solid-state photophysical properties of aqueous-solution-processed, glutathione-stabilized gold nanoclusters (GSH-AuNCs) with a ligand-to-metal charge-transfer (LMCT) state for developing 'green' LSCs. We found that such GSH-AuNCs exhibit a large Stokes shift with almost no spectral overlap between the optical absorption and PL emission due to the LMCT states, thus, suppressing reabsorption losses. Compared with GSH-AuNCs in solution, the photoluminescence quantum yields (PL-QYs) of the LSCs can be enhanced, accompanied with a lengthened PL lifetime owing to the suppression of non-radiative recombination rates. In addition, the LSCs do not suffer from severe concentration-induced PL quenching, which is a common weakness for conventional luminophores. As a result, a common trade-off between light-harvesting efficiency and solid-state PL-QYs can be bypassed due to nearly-zero spectral overlap integral between the optical absorption and PL emission. We expect that GSH-AuNCs hold great promise for serving as luminophores for 'green' LSCs by further enhancing solid-state PL-QYs.

Single-photon absorption by single photosynthetic light-harvesting complexes

NASA Astrophysics Data System (ADS)

Chan, Herman C. H.; Gamel, Omar E.; Fleming, Graham R.; Whaley, K. Birgitta

2018-03-01

We provide a unified theoretical approach to the quantum dynamics of absorption of single photons and subsequent excitonic energy transfer in photosynthetic light-harvesting complexes. Our analysis combines a continuous mode < n > -photon quantum optical master equation for the chromophoric system with the hierarchy of equations of motion describing excitonic dynamics in presence of non-Markovian coupling to vibrations of the chromophores and surrounding protein. We apply the approach to simulation of absorption of single-photon coherent states by pigment-protein complexes containing between one and seven chromophores, and compare with results obtained by excitation using a thermal radiation field. We show that the values of excitation probability obtained under single-photon absorption conditions can be consistently related to bulk absorption cross-sections. Analysis of the timescale and efficiency of single-photon absorption by light-harvesting systems within this full quantum description of pigment-protein dynamics coupled to a quantum radiation field reveals a non-trivial dependence of the excitation probability and the excited state dynamics induced by exciton-phonon coupling during and subsequent to the pulse, on the bandwidth of the incident photon pulse. For bandwidths equal to the spectral bandwidth of Chlorophyll a, our results yield an estimation of an average time of ˜0.09 s for a single chlorophyll chromophore to absorb the energy equivalent of one (single-polarization) photon under irradiation by single-photon states at the intensity of sunlight.

Excitation spectra of retinal by multiconfiguration pair-density functional theory.

PubMed

Dong, Sijia S; Gagliardi, Laura; Truhlar, Donald G

2018-03-07

Retinal is the chromophore in proteins responsible for vision. The absorption maximum of retinal is sensitive to mutations of the protein. However, it is not easy to predict the absorption spectrum of retinal accurately, and questions remain even after intensive investigation. Retinal poses a challenge for Kohn-Sham density functional theory (KS-DFT) because of the charge transfer character in its excitations, and it poses a challenge for wave function theory because the large size of the molecule makes multiconfigurational perturbation theory methods expensive. In this study, we demonstrate that multiconfiguration pair-density functional theory (MC-PDFT) provides an efficient way to predict the vertical excitation energies of 11-Z retinal, and it reproduces the experimentally determined absorption band widths and peak positions better than complete active space second-order perturbation theory (CASPT2). The consistency between complete active space self-consistent field (CASSCF) and KS-DFT dipole moments is demonstrated to be a useful criterion in selecting the active space. We also found that the nature of the terminal groups and the conformations of retinal play a significant role in the absorption spectrum. By considering a thermal distribution of conformations, we predict an absorption spectrum of retinal that is consistent with the experimental gas-phase spectrum. The location of the absorption peak and the spectral broadening based on MC-PDFT calculations agree better with experiments than those of CASPT2.

Er-doped sesquioxides for 1.5-micron lasers - spectroscopic comparisons

NASA Astrophysics Data System (ADS)

Merkle, Larry D.; Ter-Gabrielyan, Nikolay

2013-05-01

Due to the favorable thermal properties of sesquioxides as hosts for rare earth laser ions, we have recently studied the spectroscopy of Er:Lu2O3 in the 1400-1700 nm wavelength range, and here report its comparison with our earlier results on Er:Y2O3 and Er:Sc2O3. These studies include absorption and fluorescence spectra, fluorescence lifetimes, and inference of absorption and stimulated emission cross sections, all as a function of temperature. At room temperature, optical absorption limits practical laser operation to wavelengths longer than about 1620 nm. In that spectral range, the strongest stimulated emission peak is that at 1665 nm in Er:Sc2O3, with an effective cross section considerably larger than those of Er:Y2O3 and Er:Lu2O3. At 77K, the absorption is weak enough for efficient laser operation at considerably shorter wavelengths, where there are peaks with much larger stimulated emission cross sections. The three hosts all have peaks near 1575-1580 nm with comparably strong cross sections. As we have reported earlier, it is possible to lase even shorter wavelengths efficiently at this temperature, in particular the line at 1558 nm in Er:Sc2O3. Our new spectroscopic studies of Er:Lu2O3 indicate that its corresponding peak, like that of Er:Sc2O3, has a less favorable ratio of stimulated emission to absorption cross sections. Reasons for the differences will be discussed. We conclude that for most operating scenarios, Er:Sc2O3 is the most promising of the Er-doped sesquioxides studied for laser operation around 1.5-1.6 microns.

Comparison of the Optical Properties of Graphene and Alkyl-terminated Si and Ge Quantum Dots.

PubMed

de Weerd, Chris; Shin, Yonghun; Marino, Emanuele; Kim, Joosung; Lee, Hyoyoung; Saeed, Saba; Gregorkiewicz, Tom

2017-10-31

Semiconductor quantum dots are widely investigated due to their size dependent energy structure. In particular, colloidal quantum dots represent a promising nanomaterial for optoelectronic devices, such as photodetectors and solar cells, but also luminescent markers for biotechnology, among other applications. Ideal materials for these applications should feature efficient radiative recombination and absorption transitions, altogether with spectral tunability over a wide range. Group IV semiconductor quantum dots can fulfill these requirements and serve as an alternative to the commonly used direct bandgap materials containing toxic and/or rare elements. Here, we present optical properties of butyl-terminated Si and Ge quantum dots and compare them to those of graphene quantum dots, finding them remarkably similar. We investigate their time-resolved photoluminescence emission as well as the photoluminescence excitation and linear absorption spectra. We contemplate that their emission characteristics indicate a (semi-) resonant activation of the emitting channel; the photoluminescence excitation shows characteristics similar to those of a molecule. The optical density is consistent with band-to-band absorption processes originating from core-related states. Hence, these observations strongly indicate a different microscopic origin for absorption and radiative recombination in the three investigated quantum dot systems.

Effect of doping on the intersubband absorption in Si- and Ge-doped GaN/AlN heterostructures

NASA Astrophysics Data System (ADS)

Ajay, A.; Lim, C. B.; Browne, D. A.; Polaczyński, J.; Bellet-Amalric, E.; Bleuse, J.; den Hertog, M. I.; Monroy, E.

2017-10-01

In this paper, we study band-to-band and intersubband (ISB) characteristics of Si- and Ge-doped GaN/AlN heterostructures (planar and nanowires) structurally designed to absorb in the short-wavelength infrared region, particularly at 1.55 μm. Regarding the band-to-band properties, we discuss the variation of the screening of the internal electric field by free carriers, as a function of the doping density and well/nanodisk size. We observe that nanowire heterostructures consistently present longer photoluminescence decay times than their planar counterparts, which supports the existence of an in-plane piezoelectric field associated to the shear component of the strain tensor in the nanowire geometry. Regarding the ISB characteristics, we report absorption covering 1.45-1.75 μm using Ge-doped quantum wells, with comparable performance to Si-doped planar heterostructures. We also report similar ISB absorption in Si- and Ge-doped nanowire heterostructures indicating that the choice of dopant is not an intrinsic barrier for observing ISB phenomena. The spectral shift of the ISB absorption as a function of the doping concentration due to many body effects confirms that Si and Ge efficiently dope GaN/AlN nanowire heterostructures.

Distribution of hydrothermally altered rocks in the Reko Diq, Pakistan mineralized area based on spectral analysis of ASTER data

USGS Publications Warehouse

Rowan, L.C.; Schmidt, R.G.; Mars, J.C.

2006-01-01

The Reko Diq, Pakistan mineralized study area, approximately 10??km in diameter, is underlain by a central zone of hydrothermally altered rocks associated with Cu-Au mineralization. The surrounding country rocks are a variable mixture of unaltered volcanic rocks, fluvial deposits, and eolian quartz sand. Analysis of 15-band Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data of the study area, aided by laboratory spectral reflectance and spectral emittance measurements of field samples, shows that phyllically altered rocks are laterally extensive, and contain localized areas of argillically altered rocks. In the visible through shortwave-infrared (VNIR + SWIR) phyllically altered rocks are characterized by Al-OH absorption in ASTER band 6 because of molecular vibrations in muscovite, whereas argillically altered rocks have an absorption feature in band 5 resulting from alunite. Propylitically altered rocks form a peripheral zone and are present in scattered exposures within the main altered area. Chlorite and muscovite cause distinctive absorption features at 2.33 and 2.20????m, respectively, although less intense 2.33????m absorption is also present in image spectra of country rocks. Important complementary lithologic information was derived by analysis of the spectral emittance data in the 5 thermal-infrared (TIR) bands. Silicified rocks were not distinguished in the 9 VNIR + SWIR bands because of the lack of diagnostic spectral absorption features in quartz in this wavelength region. Quartz-bearing surficial deposits, as well as hydrothermally silicified rocks, were mapped in the TIR bands by using a band 13/band 12 ratio image, which is sensitive to the intensity of the quartz reststrahlen feature. Improved distinction between the quartzose surficial deposits and silicified bedrock was achieved by using matched-filter processing with TIR image spectra for reference. ?? 2006 Elsevier Inc. All rights reserved.

Deconstructing the Spectrum of the Soft X-ray Background

NASA Technical Reports Server (NTRS)

Kuntz, K. D.; Snowden, S. L.

2000-01-01

The soft X-ray background in the 0.1-1.0 keV band is known to be produced by at least three sources; the Local Hot Bubble (LHB), the extragalactic power law (EPL), and a seemingly galactic component that lies outside the bulk of the absorption that is due to the ISM of the galactic disk. This last component, which we call the Trans-Absorption Emission (TAE), has been modeled by a number of groups who have derived disparate measures of its temperature. The differences have arisen from differing assumptions about the structure of the emitting gas and unrecognized methodological difficulties. In particular, spectral fitting methods do not uniquely separate the TAE from the foreground emission that is due the LHB. This "degeneracy" can be resolved using the angular variation of the absorption of the TAE. We show that the TAE cannot be characterized by a single thermal component; no single-component model can be consistent with both the spectral energy distribution of the TAE emission and the angular variation due to absorption by the galactic disk. We use the angular anticorrelation of the ROSAT All-Sky Survey with the galactic absorption to separate local from distant emission components, and to fit the spectral energy distribution of the resulting distant emission. We find that the emission is best described by a two-thermal-component model with logT(sub S) = 6.06(sup +0.14, sub -0.12) and log T(sub H) = 6.42(sup +0.14, sub -0.12). This two-thermal-component TAE fits the ROSAT spectral energy distribution significantly better than single-component models, and is consistent with both angular variation and spectral constraints.

Absorption spectral change of peripheral-light harvesting complexes 2 induced by magnesium protoporphyrin IX monomethyl ester association

NASA Astrophysics Data System (ADS)

Yue, Huiying; Zhao, Chungui; Li, Kai; Yang, Suping

2015-02-01

Several spectrally different types of peripheral light harvesting complexes (LH) have been reported in anoxygenic phototrophic bacteria in response to environmental changes. In this study, two spectral forms of LH2 (T-LH2 and U-LH2) were isolated from Rhodobacter azotoformans. The absorption of T-LH2 was extremely similar to the LH2 isolated from Rhodobacter sphaeroides. U-LH2 showed an extra peak at ∼423 nm in the carotenoid region. To explore the spectral origin of this absorption peak, the difference in pigment compositions of two LH2 was analyzed. Spheroidene and bacteriochlorophyll aP were both contained in the two LH2. And magnesium protoporphyrin IX monomethyl ester (MPE) was only contained in U-LH2. It is known that spheroidene and bacteriochlorophyll aP do not produce ∼423 nm absorption peak either in vivo or in vitro. Whether MPE accumulation was mainly responsible for the formation of the ∼423 nm peak? The interactions between MPE and different proteins were further studied. The results showed that the maximum absorption of MPE was red-shifted from ∼415 nm to ∼423 nm when it was mixed with T-LH2 and its apoproteins, nevertheless, the Qy transitions of the bound bacteriochlorophylls in LH2 were almost unaffected, which indicated that the formation of the ∼423 nm peak was related to MPE-LH2 protein interaction. MPE did not bind to sites involved in the spectral tuning of BChls, but the conformation of integral LH2 was affected by MPE association, the alkaline stability of U-LH2 was lower than T-LH2, and the fluorescence intensity at 860 nm was decreased after MPE combination.

Absorption spectral change of peripheral-light harvesting complexes 2 induced by magnesium protoporphyrin IX monomethyl ester association.

PubMed

Yue, Huiying; Zhao, Chungui; Li, Kai; Yang, Suping

2015-02-25

Several spectrally different types of peripheral light harvesting complexes (LH) have been reported in anoxygenic phototrophic bacteria in response to environmental changes. In this study, two spectral forms of LH2 (T-LH2 and U-LH2) were isolated from Rhodobacter azotoformans. The absorption of T-LH2 was extremely similar to the LH2 isolated from Rhodobacter sphaeroides. U-LH2 showed an extra peak at ∼423 nm in the carotenoid region. To explore the spectral origin of this absorption peak, the difference in pigment compositions of two LH2 was analyzed. Spheroidene and bacteriochlorophyll aP were both contained in the two LH2. And magnesium protoporphyrin IX monomethyl ester (MPE) was only contained in U-LH2. It is known that spheroidene and bacteriochlorophyll aP do not produce ∼423 nm absorption peak either in vivo or in vitro. Whether MPE accumulation was mainly responsible for the formation of the ∼423 nm peak? The interactions between MPE and different proteins were further studied. The results showed that the maximum absorption of MPE was red-shifted from ∼415 nm to ∼423 nm when it was mixed with T-LH2 and its apoproteins, nevertheless, the Qy transitions of the bound bacteriochlorophylls in LH2 were almost unaffected, which indicated that the formation of the ∼423 nm peak was related to MPE-LH2 protein interaction. MPE did not bind to sites involved in the spectral tuning of BChls, but the conformation of integral LH2 was affected by MPE association, the alkaline stability of U-LH2 was lower than T-LH2, and the fluorescence intensity at 860 nm was decreased after MPE combination. Copyright © 2014 Elsevier B.V. All rights reserved.

Water vapor self-continuum absorption measurements in the 4.0 and 2.1 μm transparency windows

NASA Astrophysics Data System (ADS)

Richard, L.; Vasilchenko, S.; Mondelain, D.; Ventrillard, I.; Romanini, D.; Campargue, A.

2017-11-01

In a recent contribution [A. Campargue, S. Kassi, D. Mondelain, S. Vasilchenko, D. Romanini, Accurate laboratory determination of the near infrared water vapor self-continuum: A test of the MT_CKD model. J. Geophys. Res. Atmos., 121,13,180-13,203, doi:10.1002/2016JD025531], we reported accurate water vapor absorption continuum measurements by Cavity Ring-down Spectroscopy (CRDS) and Optical-Feedback-Cavity Enhanced Absorption Spectroscopy (OF-CEAS) at selected spectral points of 4 near infrared transparency windows. In the present work, the self-continuum cross-sections, CS, are determined for two new spectral points. The 2491 cm-1 spectral point in the region of maximum transparency of the 4.0 μm window was measured by OF-CEAS in the 23-52 °C temperature range. The 4435 cm-1 spectral point of the 2.1 μm window was measured by CRDS at room temperature. The self-continuum cross-sections were determined from the pressure squared dependence of the continuum absorption. Comparison to the literature shows a reasonable agreement with 1970 s and 1980 s measurements using a grating spectrograph in the 4.0 μm window and a very good consistency with our previous laser measurements in the 2.1 μm window. For both studied spectral points, our values are much smaller than previous room temperature measurements by Fourier Transform Spectroscopy. Significant deviations (up to about a factor 4) are noted compared to the widely used semi empirical MT_CKD model of the absorption continuum. The measured temperature dependence at 2491 cm-1 is consistent with previous high temperature measurements in the 4.0 μm window and follows an exp(D0/kT) law, D0 being the dissociation energy of the water dimer.

Submillimeter Spectroscopic Study of Semiconductor Processing Plasmas

NASA Astrophysics Data System (ADS)

Helal, Yaser H.

Plasmas used for manufacturing processes of semiconductor devices are complex and challenging to characterize. The development and improvement of plasma processes and models rely on feedback from experimental measurements. Current diagnostic methods are not capable of measuring absolute densities of plasma species with high resolution without altering the plasma, or without input from other measurements. At pressures below 100 mTorr, spectroscopic measurements of rotational transitions in the submillimeter/terahertz (SMM) spectral region are narrow enough in relation to the sparsity of spectral lines that absolute specificity of measurement is possible. The frequency resolution of SMM sources is such that spectral absorption features can be fully resolved. Processing plasmas are a similar pressure and temperature to the environment used to study astrophysical species in the SMM spectral region. Many of the molecular neutrals, radicals, and ions present in processing plasmas have been studied in the laboratory and their absorption spectra have been cataloged or are in the literature for the purpose of astrophysical study. Recent developments in SMM devices have made its technology commercially available for applications outside of specialized laboratories. The methods developed over several decades in the SMM spectral region for these laboratory studies are directly applicable for diagnostic measurements in the semiconductor manufacturing industry. In this work, a continuous wave, intensity calibrated SMM absorption spectrometer was developed as a remote sensor of gas and plasma species. A major advantage of intensity calibrated rotational absorption spectroscopy is its ability to determine absolute concentrations and temperatures of plasma species from first principles without altering the plasma environment. An important part of this work was the design of the optical components which couple 500 - 750 GHz radiation through a commercial inductively coupled plasma chamber. The measurement of transmission spectra was simultaneously fit for background and absorption signal. The measured absorption signal was used to calculate absolute densities and temperatures of polar species. Measurements of molecular species were demonstrated for inductively coupled plasmas.

HIghZ: A search for HI absorption in high-redshift radio galaxies

NASA Astrophysics Data System (ADS)

Allison, J.; Callingham, J.; Sadler, E.; Wayth, R.; Curran, S.; Mahoney, E.

2017-01-01

We will use the unique low-frequency spectral capability of the MWA to carry out a pilot survey for neutral gas in the interstellar medium of the most distant (z>5) radio galaxies in the Universe. Through detection of the HI 21-cm line in absorption we aim to place stringent lower limits on the source redshift, confirming its location in the early Universe. Our sample makes use of the excellent wide-band spectral information available from the recently completed MWA GLEAM survey, from which we have selected a sample of ultra-steep peaked-spectrum radio sources that have a spectral turnover below 300 MHz. These sources should be ideal candidates for high-redshift compact radio galaxies since they have (a) spectral peaks that turnover below 1GHz and (b) very steep (alpha < -1.0) spectral indices that are consistent with the high density environments expected for radio galaxies in the early Universe. Using the MWA, we aim to verify this hypothesis through the detection of significant column densities of cold HI. This pathfinder project will provide important technical information that will inform future absorption surveys both with the MWA and, ultimately, the SKA-LOW telescope.

Optical constants of ammonium sulfate in the infrared. [stratospheric aerosol refractive and absorption indices

NASA Technical Reports Server (NTRS)

Downing, H. D.; Pinkley, L. W.; Sethna, P. P.; Williams, D.

1977-01-01

The infrared spectral reflectance at near normal incidence has been measured for 3.2 M, 2.4 M, and 1.6 M solutions of ammonium sulfate, an aerosol abundant in the stratosphere and also present in the troposphere. Kramers-Kronig analysis was used to determine values of the refractive and absorption indices from the measured spectral reflectance. A synthetic spectrum of crystalline ammonium sulfate was obtained by extrapolation of the absorption index obtained for the solution to the absorber number densities of the NH4 and SO4 ions characteristic of the crystal.

Terahertz spectral detection of potassium sorbate in milk powder

NASA Astrophysics Data System (ADS)

Li, Pengpeng; Zhang, Yuan; Ge, Hongyi

2017-02-01

The spectral characteristics of potassium sorbate in milk powder in the range of 0.2 2.0 THz have been measured with THz time-domain spectroscopy(THz-TDS). Its absorption and refraction spectra are obtained at room temperature in the nitrogen atmosphere. The results showed that potassium sorbate at 0.98 THz obvious characteristic absorption peak. The simple linear regression(SLR) model was taken to analyze the content of potassium sorbate in milk powder. The results showed that the absorption coefficient increases as the mixture potassium sorbate increases. The research is important to food quality and safety testing.

Calibrating Laser Gas Measurements by Use of Natural CO2

NASA Technical Reports Server (NTRS)

Webster, Chris

2003-01-01

An improved method of calibration has been devised for instruments that utilize tunable lasers to measure the absorption spectra of atmospheric gases in order to determine the relative abundances of the gases. In this method, CO2 in the atmosphere is used as a natural calibration standard. Unlike in one prior calibration method, it is not necessary to perform calibration measurements in advance of use of the instrument and to risk deterioration of accuracy with time during use. Unlike in another prior calibration method, it is not necessary to include a calibration gas standard (and the attendant additional hardware) in the instrument and to interrupt the acquisition of atmospheric data to perform calibration measurements. In the operation of an instrument of this type, the beam from a tunable diode laser or a tunable quantum-cascade laser is directed along a path through the atmosphere, the laser is made to scan in wavelength over an infrared spectral region that contains one or two absorption spectral lines of a gas of interest, and the transmission (and, thereby, the absorption) of the beam is measured. The concentration of the gas of interest can then be calculated from the observed depth of the absorption line(s), given the temperature, pressure, and path length. CO2 is nearly ideal as a natural calibration gas for the following reasons: CO2 has numerous rotation/vibration infrared spectral lines, many of which are near absorption lines of other gases. The concentration of CO2 relative to the concentrations of the major constituents of the atmosphere is well known and varies slowly and by a small enough amount to be considered constant for calibration in the present context. Hence, absorption-spectral measurements of the concentrations of gases of interest can be normalized to the concentrations of CO2. Because at least one CO2 calibration line is present in every spectral scan of the laser during absorption measurements, the atmospheric CO2 serves continuously as a calibration standard for every measurement point. Figure 1 depicts simulated spectral transmission measurements in a wavenumber range that contains two absorption lines of N2O and one of CO2. The simulations were performed for two different upper-atmospheric pressures for an airborne instrument that has a path length of 80 m. The relative abundance of CO2 in air was assumed to be 360 parts per million by volume (approximately its natural level in terrestrial air). In applying the present method to measurements like these, one could average the signals from the two N2O absorption lines and normalize their magnitudes to that of the CO2 absorption line. Other gases with which this calibration method can be used include H2O, CH4, CO, NO, NO2, HOCl, C2H2, NH3, O3, and HCN. One can also take advantage of this method to eliminate an atmospheric-pressure gauge and thereby reduce the mass of the instrument: The atmospheric pressure can be calculated from the temperature, the known relative abundance of CO2, and the concentration of CO2 as measured by spectral absorption. Natural CO2 levels on Mars provide an ideal calibration standard. Figure 2 shows a second example of the application of this method to Mars atmospheric gas measurements. For sticky gases like H2O, the method is particularly powerful, since water is notoriously difficult to handle at low concentrations in pre-flight calibration procedures.

Development of a Near-Ir Cavity Enhanced Absorption Spectrometer for the Detection of Atmospheric Oxidation Products and Organoamines

NASA Astrophysics Data System (ADS)

Eddingsaas, Nathan C.; Jewell, Breanna; Thurnherr, Emily

2014-06-01

An estimated 10,000 to 100,000 different compounds have been measured in the atmosphere, each one undergoes many oxidation reactions that may or may not degrade air quality. To date, the fate of even some of the most abundant hydrocarbons in the atmosphere is poorly understood. One difficulty is the detection of atmospheric oxidation products that are very labile and decompose during analysis. To study labile species under atmospheric conditions, a highly sensitive, non-destructive technique is needed. Here we describe a near-IR incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS) setup that we are developing to meet this end. We have chosen to utilize the near-IR, where vibrational overtone absorptions are observed, due to the clean spectral windows and better spectral separation of absorption features. In one spectral window we can simultaneously and continuously monitor the composition of alcohols, hydroperoxides, and carboxylic acids in an air mass. In addition, we have used our CEAS setup to detect organoamines. The long effective path length of CEAS allows for low detection limits, even of the overtone absorption features, at ppb and ppt levels.

Comparison of temporal and spectral scattering methods using acoustically large breast models derived from magnetic resonance images.

PubMed

Hesford, Andrew J; Tillett, Jason C; Astheimer, Jeffrey P; Waag, Robert C

2014-08-01

Accurate and efficient modeling of ultrasound propagation through realistic tissue models is important to many aspects of clinical ultrasound imaging. Simplified problems with known solutions are often used to study and validate numerical methods. Greater confidence in a time-domain k-space method and a frequency-domain fast multipole method is established in this paper by analyzing results for realistic models of the human breast. Models of breast tissue were produced by segmenting magnetic resonance images of ex vivo specimens into seven distinct tissue types. After confirming with histologic analysis by pathologists that the model structures mimicked in vivo breast, the tissue types were mapped to variations in sound speed and acoustic absorption. Calculations of acoustic scattering by the resulting model were performed on massively parallel supercomputer clusters using parallel implementations of the k-space method and the fast multipole method. The efficient use of these resources was confirmed by parallel efficiency and scalability studies using large-scale, realistic tissue models. Comparisons between the temporal and spectral results were performed in representative planes by Fourier transforming the temporal results. An RMS field error less than 3% throughout the model volume confirms the accuracy of the methods for modeling ultrasound propagation through human breast.

Orienting the Microstructure Evolution of Copper Phthalocyanine as an Anode Interlayer in Inverted Polymer Solar Cells for High Performance.

PubMed

Li, Zhiqi; Liu, Chunyu; Zhang, Xinyuan; Li, Shujun; Zhang, Xulin; Guo, Jiaxin; Guo, Wenbin; Zhang, Liu; Ruan, Shengping

2017-09-20

Recent advances in the interfacial modification of inverted-type polymer solar cells (PSCs) have resulted from controlling the surface energy of the cathode-modified layer (TiO 2 or ZnO) to enhance the short-circuit current (J sc ) or optimizing the contact morphology of the cathode (indium tin oxide or fluorine-doped tin oxide) and active layer to increase the fill factor. Herein, we report that the performance enhancement of PSCs is achieved by incorporating a donor macromolecule copper phthalocyanine (CuPc) as an anode modification layer. Using the approach based on orienting the microstructure evolution, uniformly dispersed island-shaped CuPc spot accumulations are built on the top of PTB7:PC 71 BM blend film, leading to an efficient spectral absorption and photogenerated exciton splitting. The best power conversion efficiency of PSCs is increased up to 9.726%. In addition to the enhanced light absorption, the tailored anode energy level alignment and optimized boundary morphology by incorporating the CuPc interlayer boost charge extraction efficiency and suppress the interfacial molecular recombination. These results demonstrate that surface morphology induction through molecular deposition is an effective method to improve the performance of PSCs, which reveals the potential implications of the interlayer between the organic active layer and the electrode buffer layer.

Extremely Black Vertically Aligned Carbon Nanotube Arrays for Solar Steam Generation.

PubMed

Yin, Zhe; Wang, Huimin; Jian, Muqiang; Li, Yanshen; Xia, Kailun; Zhang, Mingchao; Wang, Chunya; Wang, Qi; Ma, Ming; Zheng, Quan-Shui; Zhang, Yingying

2017-08-30

The unique structure of a vertically aligned carbon nanotube (VACNT) array makes it behave most similarly to a blackbody. It is reported that the optical absorptivity of an extremely black VACNT array is about 0.98-0.99 over a large spectral range of 200 nm-200 μm, inspiring us to explore the performance of VACNT arrays in solar energy harvesting. In this work, we report the highly efficient steam generation simply by laminating a layer of VACNT array on the surface of water to harvest solar energy. It is found that under solar illumination the temperature of upper water can significantly increase with obvious water steam generated, indicating the efficient solar energy harvesting and local temperature rise by the thin layer of VACNTs. We found that the evaporation rate of water assisted by VACNT arrays is 10 times that of bare water, which is the highest ratio for solar-thermal-steam generation ever reported. Remarkably, the solar thermal conversion efficiency reached 90%. The excellent performance could be ascribed to the strong optical absorption and local temperature rise induced by the VACNT layer, as well as the ultrafast water transport through the VACNT layer due to the frictionless wall of CNTs. Based on the above, we further demonstrated the application of VACNT arrays in solar-driven desalination.

Singlet and triplet excitation management in a bichromophoric near-infrared-phosphorescent BODIPY-benzoporphyrin platinum complex

DOE Office of Scientific and Technical Information (OSTI.GOV)

Whited, M. T.; Djurovich, P. I.; Roberts, Sean T.

2011-01-12

Multichromophoric arrays provide one strategy for assembling molecules with intense absorptions across the visible spectrum but are generally focused on systems that efficiently produce and manipulate singlet excitations and therefore are burdened by the restrictions of (a) unidirectional energy transfer and (b) limited tunability of the lowest molecular excited state. In contrast, we present here a multichromophoric array based on four boron dipyrrins (BODIPY) bound to a platinum benzoporphyrin scaffold that exhibits intense panchromatic absorption and efficiently generates triplets. The spectral complementarity of the BODIPY and porphryin units allows the direct observation of fast bidirectional singlet and triplet energy transfermore » processes (k ST( 1BDP→ 1Por) = 7.8 × 10 11 s -1, k TT( 3Por→ 3BDP) = 1.0 × 10 10 s -1, k TT( 3BDP→ 3Por) = 1.6 × 10 10 s -1), leading to a long-lived equilibrated [ 3BDP][Por]⇌[BDP][ 3Por] state. This equilibrated state contains approximately isoenergetic porphyrin and BODIPY triplets and exhibits efficient near-infrared phosphorescence (λ em = 772 nm, Φ = 0.26). Taken together, these studies show that appropriately designed triplet-utilizing arrays may overcome fundamental limitations typically associated with core-shell chromophores by tunable redistribution of energy from the core back onto the antennae.« less

Energy-Cascaded Upconversion in an Organic Dye-Sensitized Core/Shell Fluoride Nanocrystal.

PubMed

Chen, Guanying; Damasco, Jossana; Qiu, Hailong; Shao, Wei; Ohulchanskyy, Tymish Y; Valiev, Rashid R; Wu, Xiang; Han, Gang; Wang, Yan; Yang, Chunhui; Ågren, Hans; Prasad, Paras N

2015-11-11

Lanthanide-doped upconversion nanoparticles hold promises for bioimaging, solar cells, and volumetric displays. However, their emission brightness and excitation wavelength range are limited by the weak and narrowband absorption of lanthanide ions. Here, we introduce a concept of multistep cascade energy transfer, from broadly infrared-harvesting organic dyes to sensitizer ions in the shell of an epitaxially designed core/shell inorganic nanostructure, with a sequential nonradiative energy transfer to upconverting ion pairs in the core. We show that this concept, when implemented in a core-shell architecture with suppressed surface-related luminescence quenching, yields multiphoton (three-, four-, and five-photon) upconversion quantum efficiency as high as 19% (upconversion energy conversion efficiency of 9.3%, upconversion quantum yield of 4.8%), which is about ~100 times higher than typically reported efficiency of upconversion at 800 nm in lanthanide-based nanostructures, along with a broad spectral range (over 150 nm) of infrared excitation and a large absorption cross-section of 1.47 × 10(-14) cm(2) per single nanoparticle. These features enable unprecedented three-photon upconversion (visible by naked eye as blue light) of an incoherent infrared light excitation with a power density comparable to that of solar irradiation at the Earth surface, having implications for broad applications of these organic-inorganic core/shell nanostructures with energy-cascaded upconversion.

Quantum Yields of Soluble and Particulate Material in the Ocean

DTIC Science & Technology

1999-09-30

and prospects. IEEE Transactions, 46(5): 825-829 In Press Moisan, T.A. & B.G. Mitchell UV Absorption by Mycosporine - like Amino Acids in Phaeocystis...were grown to evaluate the spectral quantum yield of in vivo chlorophyll a fluorescence. We determined that mycosporine amino acids with UV absorption...evaluate the role of photoprotective pigments, including mycosporine amino acids and the xanthophyll pigments in Phaeocystis, on the spectral quantum yield

Single-tone and two-tone AM-FM spectral calculations for tunable diode laser absorption spectroscopy

NASA Technical Reports Server (NTRS)

Chou, Nee-Yin; Sachse, Glen W.

1987-01-01

A generalized theory for optical heterodyne spectroscopy with phase modulated laser radiation is used which allows the calculation of signal line shapes for frequency modulation spectroscopy of Lorentzian gas absorption lines. In particular, synthetic spectral line shapes for both single-tone and two-tone modulation of lead-salt diode lasers are presented in which the contributions from both amplitude and frequency modulations are included.

Spectral-optical-electrical-thermal properties of deposited thin films of nano-sized calcium(II)-8-hydroxy-5,7-dinitroquinolate complex.

PubMed

Farag, A A M; Haggag, Sawsan M S; Mahmoud, Mohamed E

2011-11-01

Spectral-optical-electrical-thermal properties of deposited thin films of nano-sized calcium(II)-8-hydroxy-5,7-dinitroquinolate complex, Ca[((NO(2))(2)-8HQ)(2)], were explored, studied and evaluated in this work. Thin films of Ca[((NO(2))(2)-8HQ)(2)] were assembled by using a direct, simple and efficient layer-by-layer (LBL) chemical deposition technique. The optical properties of thin films were investigated by using spectrophotometric measurements of transmittance and reflectance at normal incidence in the wavelength range 200-2500 nm. The refractive index, n, and the absorption index, k, of Ca[((NO(2))(2)-8HQ)(2)] films were determined from the measured transmittance and reflectance. The real and imaginary dielectric constants were also determined. The analysis of the spectral behavior of the absorption coefficient in the intrinsic absorption region reveals a direct allowed transition with band gaps of 1.1 eV and 2.4 eV for the optical and transport energy gaps, respectively. The current-voltage characteristics of Ca[((NO(2))(2)-8HQ)(2)] showed a trap-charge limited conduction in determining the current at the intermediate and high bias regimes. Graphical representation of the current-voltage characteristics yields three distinct linear parts indicating the existence of three conduction mechanisms. Structural characterization and identification were confirmed by using Fourier transform infrared spectroscopy (FT-IR). Scanning electron microscopy (SEM) was also used to image the surface morphology of the deposited nano-sized metal complex and such study revealed a high homogeneity in surface spherical particle distribution with average particles size in the range 20-40 nm. Thermal gravimetric analysis (TGA) was also studied for [(NO(2))(2)-8HQ] and Ca[((NO(2))(2)-8HQ)(2)] to evaluate and confirm the thermal stability characteristics incorporated into the synthesized nano-sized Ca[((NO(2))(2)-8HQ)(2)] complex. Copyright © 2011 Elsevier B.V. All rights reserved.

Improved reference standards for femtosecond three-photon excitation of fluorescence in the wavelength range 950 - 1750 nm

NASA Astrophysics Data System (ADS)

Rebane, Aleksander; Mikhaylov, Alexander

2018-02-01

Fluorescence excited by instantaneous three-photon absorption (3PA) in organic fluorophores is gaining importance as a versatile modality for deep-tissue microscopy and imaging. However, due to technical difficulty of quantifying the higher-order nonlinear absorption cross-section, reliable 3PA cross section values, σ3PA, covering a broad spectral range have been so far not available. This lack of experimental data hinders us from gaining quantitative understanding of relevant structure-property relationships as well as impedes progress towards developing 3-photon fluorophores optimized for various applications. We report on measurement of the absolute 3PA cross section spectra in the 950 - 1750 nm range in a series of common organic fluorophores in various solvents: (a) Rhodamine 6G in deuterated methanol, (b) Coumarin 153 in DMSO and toluene, (c) Prodan in DMSO and toluene, (d) Fluorescein in pH11 buffer, (e) AF455 in toluene, (f) BDPAS in deuterated methylene chloride. In these experiments, we employ femtosecond wavelength-tunable optical parametric amplifier to excite fluorescence signal that has cubic dependence on the incident photon flux. Absolute values of σ3PA are determined using two complementary methods: (i) calibrating the fluorescence signal relative to one-photon (linear) excitation combined with accurate measurement of the pulse temporal- and spatial profile to determine the excitation photon flux and (ii) calibration of the cubic fluorescence signal relative to quadratic florescence excited in fluorophores with known two-photon absorption cross section. Depending on the method utilized, the peak σ3PA values have estimated accuracy 50% and vary in the range, σ3PA = 10-81 - 10-79 cm6 s2 photon-2 , depending on the system studied, with AF455 showing the most enhanced 3PA efficiency. The 3PA spectral shapes have estimated accuracy of 20% and show some unexpected deviations from corresponding one-photon spectral profiles.

Global Monitoring of Terrestrial Chlorophyll Fluorescence from Moderate-spectral-resolution Near-infrared Satellite Measurements: Methodology, Simulations, and Application to GOME-2

NASA Technical Reports Server (NTRS)

Joiner, J.; Gaunter, L.; Lindstrot, R.; Voigt, M.; Vasilkov, A. P.; Middleton, E. M.; Huemmrich, K. F.; Yoshida, Y.; Frankenberg, C.

2013-01-01

Globally mapped terrestrial chlorophyll fluorescence retrievals are of high interest because they can provide information on the functional status of vegetation including light-use efficiency and global primary productivity that can be used for global carbon cycle modeling and agricultural applications. Previous satellite retrievals of fluorescence have relied solely upon the filling-in of solar Fraunhofer lines that are not significantly affected by atmospheric absorption. Although these measurements provide near-global coverage on a monthly basis, they suffer from relatively low precision and sparse spatial sampling. Here, we describe a new methodology to retrieve global far-red fluorescence information; we use hyperspectral data with a simplified radiative transfer model to disentangle the spectral signatures of three basic components: atmospheric absorption, surface reflectance, and fluorescence radiance. An empirically based principal component analysis approach is employed, primarily using cloudy data over ocean, to model and solve for the atmospheric absorption. Through detailed simulations, we demonstrate the feasibility of the approach and show that moderate-spectral-resolution measurements with a relatively high signal-to-noise ratio can be used to retrieve far-red fluorescence information with good precision and accuracy. The method is then applied to data from the Global Ozone Monitoring Instrument 2 (GOME-2). The GOME-2 fluorescence retrievals display similar spatial structure as compared with those from a simpler technique applied to the Greenhouse gases Observing SATellite (GOSAT). GOME-2 enables global mapping of far-red fluorescence with higher precision over smaller spatial and temporal scales than is possible with GOSAT. Near-global coverage is provided within a few days. We are able to show clearly for the first time physically plausible variations in fluorescence over the course of a single month at a spatial resolution of 0.5 deg × 0.5 deg. We also show some significant differences between fluorescence and coincident normalized difference vegetation indices (NDVI) retrievals.

Global Monitoring of Terrestrial Chlorophyll Fluorescence from Moderate-Spectral-Resolution Near-Infrared Satellite Measurements: Methodology, Simulations, and Application to GOME-2

NASA Technical Reports Server (NTRS)

Joiner, J.; Guanter, L.; Lindstrot, R.; Voigt, M.; Vasilkov, A. P.; Middleton, E. M.; Huemmrich, K. F.; Yoshida, Y.; Frankenberg, C.

2013-01-01

Globally mapped terrestrial chlorophyll fluorescence retrievals are of high interest because they can provide information on the functional status of vegetation including light-use efficiency and global primary productivity that can be used for global carbon cycle modeling and agricultural applications. Previous satellite retrievals of fluorescence have relied solely upon the filling-in of solar Fraunhofer lines that are not significantly affected by atmospheric absorption. Although these measurements provide near-global coverage on a monthly basis, they suffer from relatively low precision and sparse spatial sampling. Here, we describe a new methodology to retrieve global far-red fluorescence information; we use hyperspectral data with a simplified radiative transfer model to disentangle the spectral signatures of three basic components: atmospheric absorption, surface reflectance, and fluorescence radiance. An empirically based principal component analysis approach is employed, primarily using cloudy data over ocean, to model and solve for the atmospheric absorption. Through detailed simulations, we demonstrate the feasibility of the approach and show that moderate-spectral-resolution measurements with a relatively high signal-to-noise ratio can be used to retrieve far-red fluorescence information with good precision and accuracy. The method is then applied to data from the Global Ozone Monitoring Instrument 2 (GOME-2). The GOME-2 fluorescence retrievals display similar spatial structure as compared with those from a simpler technique applied to the Greenhouse gases Observing SATellite (GOSAT). GOME-2 enables global mapping of far-red fluorescence with higher precision over smaller spatial and temporal scales than is possible with GOSAT. Near-global coverage is provided within a few days. We are able to show clearly for the first time physically plausible variations in fluorescence over the course of a single month at a spatial resolution of 0.5 0.5. We also show some significant differences between fluorescence and coincident normalized difference vegetation indices (NDVI) retrievals.

UV laser long-path absorption spectroscopy

NASA Technical Reports Server (NTRS)

Dorn, Hans-Peter; Brauers, Theo; Neuroth, Rudolf

1994-01-01

Long path Differential Optical Absorption Spectroscopy (DOAS) using a picosecond UV laser as a light source was developed in our institute. Tropospheric OH radicals are measured by their rotational absorption lines around 308 nm. The spectra are obtained using a high resolution spectrograph. The detection system has been improved over the formerly used optomechanical scanning device by application of a photodiode array which increased the observed spectral range by a factor of 6 and which utilizes the light much more effectively leading to a considerable reduction of the measurement time. This technique provides direct measurements of OH because the signal is given by the product of the absorption coefficient and the OH concentration along the light path according to Lambert-Beers law. No calibration is needed. Since the integrated absorption coefficient is well known the accuracy of the measurement essentially depends on the extent to which the OH absorption pattern can be detected in the spectra. No interference by self generated OH radicals in the detection lightpath has been observed. The large bandwidth (greater than 0.15 nm) and the high spectral resolution (1.5 pm) allows absolute determination of interferences by other trace gas absorptions. The measurement error is directly accessible from the absorption-signal to baseline-noise ratio in the spectra. The applicability of the method strongly depends on visibility. Elevated concentrations of aerosols lead to considerable attenuation of the laser light which reduces the S/N-ratio. In the moderately polluted air of Julich, where we performed a number of OH measurement spectra. In addition absorption features of unidentified species were frequently detected. A quantitative deconvolution even of the known species is not easy to achieve and can leave residual structures in the spectra. Thus interferences usually increase the noise and deteriorate the OH detection sensitivity. Using diode arrays for sensitive absorption measurements some specific problems of those detectors have to be solved experimentally (i.e. fixed pattern noise, dark signal noise, nonuniform efficiency of individual elements, spatial sensitivity variations). In order to improve the low spatial resolution we performed laboratory studies using a multiple reflection cell to convert the long path technique to a real in situ point measurement. Under the conditions of field experiments in Julich residual absorbance signals at present are about 1.5x10(exp -4) corresponding to an OH detection sensitivity of 2x10(exp 6) OH/cm(exp 3) using a light path of 5.8 km. Total integration times for one measurement point vary between a few minutes and an hour.

ASTER spectral sensitivity of carbonate rocks - Study in Sultanate of Oman

NASA Astrophysics Data System (ADS)

Rajendran, Sankaran; Nasir, Sobhi

2014-02-01

Remote sensing satellite data plays a vital role and capable in detecting minerals and discriminating rock types for explorations of mineral resources and geological studies. Study of spectral absorption characters of remotely sensed data are under consideration by the exploration and mining companies, and demonstrating the spectral absorption characters of carbonates on the cost-effective multispectral image (rather than the hyperspectral, Lidar image) for easy understanding of all geologists and exploration communities of carbonates is very much important. The present work is an integrated study and an outcome of recently published works on the economic important carbonate rocks, includes limestone, marl, listwaenites and carbonatites occurred in parts of the Sultanate of Oman. It demonstrates the spectral sensitivity of such rocks for simple interpretation over satellite data and describes and distinguishes them based on the absorptions of carbonate minerals in the spectral bands of advanced spaceborne thermal emission and reflection radiometer (ASTER) for mapping and exploration studies. The study results that the ASTER spectral band 8 discriminates the carbonate rocks due to the presence of predominantly occurred carbonate minerals; the ASTER band 5 distinguishes the limestones and marls (more hydroxyl clay minerals) from listwaenite (hydrothermally altered rock) due to the presence of altered minerals and the ASTER band 4 detects carbonatites (ultramafic intrusive alkaline rocks) which contain relatively more silicates. The study on the intensity of the total absorptions against the reflections of these rocks shows that the limestones and marls have low intensity in absorptions (and high reflection values) due to the presence of carbonate minerals (calcite and dolomite) occurred in different proportions. The listwaenites and carbonatites have high intensity of absorptions (low reflection values) due to the occurrence of Mn-oxide in listwaenites and carbonates in carbonatites apart the influence of major carbonate minerals that occurred predominantly in these rocks. The study of ASTER thermal infrared (TIR) spectral bands distinguished the marls have low emissivity of energy due to the presence of hydroxyl bearing alumina-silicate minerals from the other rocks such as limestones, listwaenites and carbonatites which have high emissivity due to the absence of hydroxyl bearing alumina-silicate minerals and the presence of carbonate minerals and carbonates. Further, the study demonstrates and confirms the spectral sensitivity of marls and carbonatites. Marls have high reflectivity in ASTER visible near infrared (VNIR) and shortwave infrared (SWIR) spectral bands and low emissivity of energy in ASTER TIR spectral bands due to the presence of hydroxyl bearing alumina-silicate minerals. Carbonatites have low reflectivity in ASTER VNIR-SWIR spectral bands and high emissivity in ASTER TIR spectral bands due to the absence of hydroxyl bearing alumina-silicate minerals and the presence of the carbonate minerals and carbonates. These have been discussed by providing the grey scale color image of 14 ASTER spectral bands of the study sites. The study is based on the interpretation of image spectra of multispectral image conducted to map such economic valuable carbonate rocks. It provides a simple methods and basic knowledge, which are of great help to the geology and exploration communities. It is recommended to the geologists, industrialists, exploration communities of carbonates and mine owners to take up the knowledge for economic exploration of such deposits. Further, the study has proved that the technique is time and cost effective in mapping of such deposits and can be used to the areas which have extremely rugged topography occurred in similar arid region, where difficult to do exhaustive sampling and not reachable for conventional geological mapping.

IR CMOS: near infrared enhanced digital imaging (Presentation Recording)

NASA Astrophysics Data System (ADS)

Pralle, Martin U.; Carey, James E.; Joy, Thomas; Vineis, Chris J.; Palsule, Chintamani

2015-08-01

SiOnyx has demonstrated imaging at light levels below 1 mLux (moonless starlight) at video frame rates with a 720P CMOS image sensor in a compact, low latency camera. Low light imaging is enabled by the combination of enhanced quantum efficiency in the near infrared together with state of the art low noise image sensor design. The quantum efficiency enhancements are achieved by applying Black Silicon, SiOnyx's proprietary ultrafast laser semiconductor processing technology. In the near infrared, silicon's native indirect bandgap results in low absorption coefficients and long absorption lengths. The Black Silicon nanostructured layer fundamentally disrupts this paradigm by enhancing the absorption of light within a thin pixel layer making 5 microns of silicon equivalent to over 300 microns of standard silicon. This results in a demonstrate 10 fold improvements in near infrared sensitivity over incumbent imaging technology while maintaining complete compatibility with standard CMOS image sensor process flows. Applications include surveillance, nightvision, and 1064nm laser see spot. Imaging performance metrics will be discussed. Demonstrated performance characteristics: Pixel size : 5.6 and 10 um Array size: 720P/1.3Mpix Frame rate: 60 Hz Read noise: 2 ele/pixel Spectral sensitivity: 400 to 1200 nm (with 10x QE at 1064nm) Daytime imaging: color (Bayer pattern) Nighttime imaging: moonless starlight conditions 1064nm laser imaging: daytime imaging out to 2Km

New in situ Aerosol Spectral Optical Measurements over 300-700 nm, Extinction and Total Absorption, Paired with Absorption from Water- and Methanol-soluble Aerosol Extracts

NASA Astrophysics Data System (ADS)

Jordan, C. E.; Stauffer, R. M.; Lamb, B.; Novak, M. G.; Mannino, A.; Hudgins, C.; Thornhill, K. L., II; Crosbie, E.; Winstead, E.; Anderson, B.; Martin, R.; Shook, M.; Ziemba, L. D.; Beyersdorf, A. J.; Corr, C.

2017-12-01

A new in situ spectral aerosol extinction instrument (custom built, SpEx) built to cover the 300-700 nm range at 1 nm spectral resolution and temporal resolution of 4 minutes was deployed on the top deck ( 10 m above the water surface) of the R/V Onnuri during the KORUS-OC research cruise around South Korea in spring 2016. This new instrument was one component of a suite of in situ aerosol optical measurements that included 3-visible-wavelength scattering (Airphoton IN101 Nephelometer, at 450, 532, & 632 nm) and absorption (Brechtel Tricolor Absorption Photometer Model 2901, at 467, 528, & 652 nm) with sub-minute temporal resolution; two sets of filters (Teflon and glass fiber, both collected over 3 hour daytime and 12 hour overnight intervals) to provide aerosol absorption spectra over the same wavelength range as SpEx. The glass fiber filters were placed in the center of an integrating sphere (Labsphere DRA-CA-30) attached to a dual beam spectrophotometer (Cary 100 Bio UV-Visible Spectrophotometer) to measure total aerosol absorption spectra via an established method used by the ocean color community to obtain absorption spectra from particles suspended in sea water. Adapting this methodology for atmospheric aerosol measurements provides a new avenue to obtain spectral total aerosol absorption, particularly useful for expanding in situ measurement capabilities into the UV range. The Teflon filters were cut in half with one half extracted in deionized water and the other half extracted in methanol. The solutions were filtered and injected into a liquid waveguide capillary cell (World Precision Instruments LWCC-3100, 100 cm pathlength) to measure the absorption spectra for each solution. In addition, the water extracts were measured via ion chromatography (Dionex ICS-3000 Ion Chromatography System) to obtain water-soluble inorganic ion concentrations, as well as via aerosol mass spectrometry (Aerodyne Research, Inc. HR-ToF High Resolution Aerosol Mass Spectrometer) to obtain organic aerosol concentrations. Results from the KORUS-OC data set will be discussed. In particular, the relationships between the optical information and chemical information will be examined.

Mapping Surface Water DOC in the Northern Gulf of Mexico Using CDOM Absorption Coefficients and Remote Sensing Imagery

NASA Astrophysics Data System (ADS)

Kelly, B.; Chelsky, A.; Bulygina, E.; Roberts, B. J.

2017-12-01

Remote sensing techniques have become valuable tools to researchers, providing the capability to measure and visualize important parameters without the need for time or resource intensive sampling trips. Relationships between dissolved organic carbon (DOC), colored dissolved organic matter (CDOM) and spectral data have been used to remotely sense DOC concentrations in riverine systems, however, this approach has not been applied to the northern Gulf of Mexico (GoM) and needs to be tested to determine how accurate these relationships are in riverine-dominated shelf systems. In April, July, and October 2017 we sampled surface water from 80+ sites over an area of 100,000 km2 along the Louisiana-Texas shelf in the northern GoM. DOC concentrations were measured on filtered water samples using a Shimadzu TOC-VCSH analyzer using standard techniques. Additionally, DOC concentrations were estimated from CDOM absorption coefficients of filtered water samples on a UV-Vis spectrophotometer using a modification of the methods of Fichot and Benner (2011). These values were regressed against Landsat visible band spectral data for those same locations to establish a relationship between the spectral data, CDOM absorption coefficients. This allowed us to spatially map CDOM absorption coefficients in the Gulf of Mexico using the Landsat spectral data in GIS. We then used a multiple linear regressions model to derive DOC concentrations from the CDOM absorption coefficients and applied those to our map. This study provides an evaluation of the viability of scaling up CDOM absorption coefficient and remote-sensing derived estimates of DOC concentrations to the scale of the LA-TX shelf ecosystem.

10.6% Certified Colloidal Quantum Dot Solar Cells via Solvent-Polarity-Engineered Halide Passivation.

PubMed

Lan, Xinzheng; Voznyy, Oleksandr; García de Arquer, F Pelayo; Liu, Mengxia; Xu, Jixian; Proppe, Andrew H; Walters, Grant; Fan, Fengjia; Tan, Hairen; Liu, Min; Yang, Zhenyu; Hoogland, Sjoerd; Sargent, Edward H

2016-07-13

Colloidal quantum dot (CQD) solar cells are solution-processed photovoltaics with broad spectral absorption tunability. Major advances in their efficiency have been made via improved CQD surface passivation and device architectures with enhanced charge carrier collection. Herein, we demonstrate a new strategy to improve further the passivation of CQDs starting from the solution phase. A cosolvent system is employed to tune the solvent polarity in order to achieve the solvation of methylammonium iodide (MAI) and the dispersion of hydrophobic PbS CQDs simultaneously in a homogeneous phase, otherwise not achieved in a single solvent. This process enables MAI to access the CQDs to confer improved passivation. This, in turn, allows for efficient charge extraction from a thicker photoactive layer device, leading to a certified solar cell power conversion efficiency of 10.6%, a new certified record in CQD photovoltaics.

Monodisperse Dual-Functional Upconversion Nanoparticles Enabled Near-Infrared Organolead Halide Perovskite Solar Cells.

PubMed

He, Ming; Pang, Xinchang; Liu, Xueqin; Jiang, Beibei; He, Yanjie; Snaith, Henry; Lin, Zhiqun

2016-03-18

Extending the spectral absorption of organolead halide perovskite solar cells from visible into near-infrared (NIR) range renders the minimization of non-absorption loss of solar photons with improved energy alignment. Herein, we report on, for the first time, a viable strategy of capitalizing on judiciously synthesized monodisperse NaYF4 :Yb/Er upconversion nanoparticles (UCNPs) as the mesoporous electrode for CH3 NH3 PbI3 perovskite solar cells and more importantly confer perovskite solar cells to be operative under NIR light. Uniform NaYF4 :Yb/Er UCNPs are first crafted by employing rationally designed double hydrophilic star-like poly(acrylic acid)-block-poly(ethylene oxide) (PAA-b-PEO) diblock copolymer as nanoreactor, imparting the solubility of UCNPs and the tunability of film porosity during the manufacturing process. The subsequent incorporation of NaYF4 :Yb/Er UCNPs as the mesoporous electrode led to a high efficiency of 17.8 %, which was further increased to 18.1 % upon NIR irradiation. The in situ integration of upconversion materials as functional components of perovskite solar cells offers the expanded flexibility for engineering the device architecture and broadening the solar spectral use. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Assessment of the performance of a compact concentric spectrometer system for Atmospheric Differential Optical Absorption Spectroscopy

NASA Astrophysics Data System (ADS)

Whyte, C.; Leigh, R. J.; Lobb, D.; Williams, T.; Remedios, J. J.; Cutter, M.; Monks, P. S.

2009-08-01

A breadboard demonstrator of a novel UV/VIS grating spectrometer for atmospheric research has been developed based upon a concentric arrangement of a spherical meniscus lens, concave spherical mirror and curved diffraction grating suitable for a range of remote sensing applications from the ground or space. The spectrometer is compact and provides high optical efficiency and performance benefits over traditional instruments. The concentric design is capable of handling high relative apertures, owing to spherical aberration and coma being near zero at all surfaces. The design also provides correction for transverse chromatic aberration and distortion, in addition to correcting for the distortion called "smile", the curvature of the slit image formed at each wavelength. These properties render this design capable of superior spectral and spatial performance with size and weight budgets significantly lower than standard configurations. This form of spectrometer design offers the potential for an exceptionally compact instrument for differential optical absorption spectroscopy (DOAS) applications particularly from space (LEO, GEO orbits) and from HAPs or ground-based platforms. The breadboard demonstrator has been shown to offer high throughput and a stable Gaussian line shape with a spectral range from 300 to 450 nm at better than 0.5 nm resolution, suitable for a number of typical DOAS applications.

Colorado Ultraviolet Transit Experiment: a dedicated CubeSat mission to study exoplanetary mass loss and magnetic fields

NASA Astrophysics Data System (ADS)

Fleming, Brian T.; France, Kevin; Nell, Nicholas; Kohnert, Richard; Pool, Kelsey; Egan, Arika; Fossati, Luca; Koskinen, Tommi; Vidotto, Aline A.; Hoadley, Keri; Desert, Jean-Michel; Beasley, Matthew; Petit, Pascal M.

2018-01-01

The Colorado Ultraviolet Transit Experiment (CUTE) is a near-UV (2550 to 3300 Å) 6U CubeSat mission designed to monitor transiting hot Jupiters to quantify their atmospheric mass loss and magnetic fields. CUTE will probe both atomic (Mg and Fe) and molecular (OH) lines for evidence of enhanced transit absorption, and to search for evidence of early ingress due to bow shocks ahead of the planet's orbital motion. As a dedicated mission, CUTE will observe ≳100 spectroscopic transits of hot Jupiters over a nominal 7-month mission. This represents the equivalent of >700 orbits of the only other instrument capable of these measurements, the Hubble Space Telescope. CUTE efficiently utilizes the available CubeSat volume by means of an innovative optical design to achieve a projected effective area of ˜28 cm2, low instrumental background, and a spectral resolving power of R˜3000 over the primary science bandpass. These performance characteristics enable CUTE to discern transit depths between 0.1% and 1% in individual spectral absorption lines. We present the CUTE optical and mechanical design, a summary of the science motivation and expected results, and an overview of the projected fabrication, calibration, and launch timeline.

Photosystem Trap Energies and Spectrally-Dependent Energy-Storage Efficiencies in the Chl d-Utilizing Cyanobacterium, Acaryochloris Marina

NASA Technical Reports Server (NTRS)

Mielke, Steven P.; Kiang, Nancy Y.; Blankenship, Robert E.; Mauzerall, David

2012-01-01

Acaryochloris marina is the only species known to utilize chlorophyll (Chl) d as a principal photopigment. The peak absorption wavelength of Chl d is redshifted approx. 40 nm in vivo relative to Chl a, enabling this cyanobacterium to perform oxygenic phototrophy in niche environments enhanced in far-red light. We present measurements of the in vivo energy-storage (E-S) efficiency of photosynthesis in A. marina, obtained using pulsed photoacoustics (PA) over a 90-nm range of excitation wavelengths in the red and far-red. Together with modeling results, these measurements provide the first direct observation of the trap energies of PSI and PSII, and also the photosystem-specific contributions to the total E-S efficiency. We find the maximum observed efficiency in A. marina (40+/-1% at 735 nm) is higher than in the Chl a cyanobacterium Synechococcus leopoliensis (35+/-1% at 690 nm). The efficiency at peak absorption wavelength is also higher in A. marina (36+/-1% at 710 nm vs. 31+/-1% at 670 nm). In both species, the trap efficiencies are approx. 40% (PSI) and approx. 30% (PSII). The PSI trap in A. marina is found to lie at 740+/-5 nm, in agreement with the value inferred from spectroscopic methods. The best fit of the model to the PA data identifies the PSII trap at 723+/-3 nm, supporting the view that the primary electron-donor is Chl d, probably at the accessory (ChlD1) site. A decrease in efficiency beyond the trap wavelength, consistent with uphill energy transfer, is clearly observed and fit by the model. These results demonstrate that the E-S efficiency in A. marina is not thermodynamically limited, suggesting that oxygenic photosynthesis is viable in even redder light environments.

Classification of river water pollution using Hyperion data

NASA Astrophysics Data System (ADS)

Kar, Soumyashree; Rathore, V. S.; Champati ray, P. K.; Sharma, Richa; Swain, S. K.

2016-06-01

A novel attempt is made to use hyperspectral remote sensing to identify the spatial variability of metal pollutants present in river water. It was also attempted to classify the hyperspectral image - Earth Observation-1 (EO-1) Hyperion data of an 8 km stretch of the river Yamuna, near Allahabad city in India depending on its chemical composition. For validating image analysis results, a total of 10 water samples were collected and chemically analyzed using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). Two different spectral libraries from field and image data were generated for the 10 sample locations. Advanced per-pixel supervised classifications such as Spectral Angle Mapper (SAM), SAM target finder using BandMax and Support Vector Machine (SVM) were carried out along with the unsupervised clustering procedure - Iterative Self-Organizing Data Analysis Technique (ISODATA). The results were compared and assessed with respect to ground data. Analytical Spectral Devices (ASD), Inc. spectroradiometer, FieldSpec 4 was used to generate the spectra of the water samples which were compiled into a spectral library and used for Spectral Absorption Depth (SAD) analysis. The spectral depth pattern of image and field spectral libraries was found to be highly correlated (correlation coefficient, R2 = 0.99) which validated the image analysis results with respect to the ground data. Further, we carried out a multivariate regression analysis to assess the varying concentrations of metal ions present in water based on the spectral depth of the corresponding absorption feature. Spectral Absorption Depth (SAD) analysis along with metal analysis of field data revealed the order in which the metals affected the river pollution, which was in conformity with the findings of Central Pollution Control Board (CPCB). Therefore, it is concluded that hyperspectral imaging provides opportunity that can be used for satellite based remote monitoring of water quality from space.

The XMM-Newton Wide Angle Survey (XWAS): the X-ray spectrum of type-1 AGN

NASA Astrophysics Data System (ADS)

Mateos, S.; Carrera, F. J.; Page, M. J.; Watson, M. G.; Corral, A.; Tedds, J. A.; Ebrero, J.; Krumpe, M.; Schwope, A.; Ceballos, M. T.

2010-02-01

Aims: We discuss the broad band X-ray properties of one of the largest samples of X-ray selected type-1 AGN to date (487 objects in total), drawn from the XMM-Newton Wide Angle Survey (XWAS). The objects presented in this work cover 2-10 keV (rest-frame) luminosities from 1042-1045 erg s-1 and are detected up to redshift 4. We constrain the overall properties of the broad band continuum, soft excess and X-ray absorption, along with their dependence on the X-ray luminosity and redshift. We discuss the implications for models of AGN emission. Methods: We fitted the observed 0.2-12 keV broad band spectra with various models to search for X-ray absorption and soft excess. The F-test was used with a significance threshold of 99% to statistically accept the detection of additional spectral components. Results: We constrained the mean spectral index of the broad band X-ray continuum to <Γ> = 1.96 ± 0.02 with intrinsic dispersion {σ< Γ >} = 0.27-0.02+0.01. The continuum becomes harder at faint fluxes and at higher redshifts and hard (2-10 keV) luminosities. The dependence of Γ with flux is likely due to undetected absorption rather than to spectral variation. We found a strong dependence of the detection efficiency of objects on the spectral shape. We expect this effect to have an impact on the measured mean continuum shapes of sources at different redshifts and luminosities. We detected excess absorption in ⪆3% of our objects, with rest-frame column densities a few ×1022 cm-2. The apparent mismatch between the optical classification and X-ray properties of these objects is a challenge for the standard orientation-based AGN unification model. We found that the fraction of objects with detected soft excess is 36%. Using a thermal model, we constrained the soft excess mean rest-frame temperature and intrinsic dispersion to kT 100 eV and σkT 34 eV. The origin of the soft excess as thermal emission from the accretion disk or Compton scattered disk emission is ruled out on the basis of the temperatures detected and the lack of correlation of the soft excess temperature with the hard X-ray luminosity over more than 2 orders of magnitude in luminosity. Furthermore, the high luminosities of the soft excess rule out an origin in the host galaxy.

Propagation of spectral characterization errors of imaging spectrometers at level-1 and its correction within a level-2 recalibration scheme

NASA Astrophysics Data System (ADS)

Vicent, Jorge; Alonso, Luis; Sabater, Neus; Miesch, Christophe; Kraft, Stefan; Moreno, Jose

2015-09-01

The uncertainties in the knowledge of the Instrument Spectral Response Function (ISRF), barycenter of the spectral channels and bandwidth / spectral sampling (spectral resolution) are important error sources in the processing of satellite imaging spectrometers within narrow atmospheric absorption bands. The exhaustive laboratory spectral characterization is a costly engineering process that differs from the instrument configuration in-flight given the harsh space environment and harmful launching phase. The retrieval schemes at Level-2 commonly assume a Gaussian ISRF, leading to uncorrected spectral stray-light effects and wrong characterization and correction of the spectral shift and smile. These effects produce inaccurate atmospherically corrected data and are propagated to the final Level-2 mission products. Within ESA's FLEX satellite mission activities, the impact of the ISRF knowledge error and spectral calibration at Level-1 products and its propagation to Level-2 retrieved chlorophyll fluorescence has been analyzed. A spectral recalibration scheme has been implemented at Level-2 reducing the errors in Level-1 products below the 10% error in retrieved fluorescence within the oxygen absorption bands enhancing the quality of the retrieved products. The work presented here shows how the minimization of the spectral calibration errors requires an effort both for the laboratory characterization and for the implementation of specific algorithms at Level-2.

Proclus crater: what a fresh, small crater can tell about the composition of lunar Highlands

NASA Astrophysics Data System (ADS)

Serventi, Giovanna; Carli, Cristian; Giacomini, Lorenza; Sgavetti, Maria

2016-04-01

Proclus crater is a Copernican age (Apollo 15 PSR), simple and fresh crater, with a diameter of 28 km. It is located on the northwest rim of Crisium basin and east of Palus Somni (16.1° N, 47.0° E). Here, we have analyzed a M3 (onboard Chandrayaan-1 mission) image (m3g20090202t024131 image) to study the composition of Proclus crater. We first classified the crater in different spectral regions applying the Spectral Angle Mapper (Kruse et al., 1993) method and using image-driven end-members; subsequently, the spectra representative of each region have been deconvolved applying the Modified Gaussian Model (Sunshine et al., 1990) algorithm and compared to spectral libraries consisting of well characterized terrestrial analogues, both mafic (olivine, OL, and pyroxenes, PX) and plagioclase (PL)-bearing. We recognized 5 spectral units into the crater: 1) spectral unit A, characterized by an absorption band at 1250 nm, is interpreted as dominated by PL; 2) spectral unit B, with three absorption bands at ca. 900, 1250 and 1800 nm, where the band depth ratio between the 900 and 1250 nm bands decreases from spectral sub-unit B5 to B1, can be compared with mixtures composed with high PL content (>90%) and PX; 3) spectral unit C, characterized by two absorption bands at 900 and 1800 nm, can be interpreted as PX affected from space weathering (the band depth is less deep than band depth in PX analyzed in the laboratory) or as a mixture of 90% PL and 10% PX; 4) spectral unit D shows a broad absorption centered at 1050 nm with a shoulder at ca. 1600 nm and can be compared with OL affected from space weathering or with a mixture of 90% PL and 10% OL; 5) spectral unit E, characterized by a broad absorption with a shoulder at shorter wavelengths than in the previous unit, can be compared to the spectrum of a mixture composed of PL, OL, PX and Mg-spinel (from Gross et al., 2104). Moreover, spectral unit F has been recognized widespread into the crater; this unit shows flat, red spectra with a shallow absorption at ca. 2000 nm, but will not be discussed here. Concluding, Proclus crater evidenced a PL-rich mineralogy comparable with what expected for lunar Highland materials. Anorthositic regions, with very high abundance of PL, have been discovered on N-NW crater walls, whereas outcrops enriched with mafic mineralogy, PX (associated with PL), have been observed on the east side walls and in a delimited, west region. Few outcrops of OL-bearing material are present on wall and floor. A unit with mafic mineralogy and spinel-like phase was also detected in a S-E area on the crater floor. Proclus could therefore evidence the presence of a PL-rich crust crystallized during the Magma Ocean, with the possible formation of pockets with more mafic composition entrapped into the PL floating material.

Combination of carbon dot and polymer dot phosphors for white light-emitting diodes.

PubMed

Sun, Chun; Zhang, Yu; Sun, Kai; Reckmeier, Claas; Zhang, Tieqiang; Zhang, XiaoYu; Zhao, Jun; Wu, Changfeng; Yu, William W; Rogach, Andrey L

2015-07-28

We realized white light-emitting diodes with high color rendering index (85-96) and widely variable color temperatures (2805-7786 K) by combining three phosphors based on carbon dots and polymer dots, whose solid-state photoluminescence self-quenching was efficiently suppressed within a polyvinyl pyrrolidone matrix. All three phosphors exhibited dominant absorption in the UV spectral region, which ensured the weak reabsorption and no energy transfer crosstalk. The WLEDs showed excellent color stability against the increasing current because of the similar response of the tricolor phosphors to the UV light variation.

Biosynthesis of Chlorophyll a in a Purple Bacterial Phototroph and Assembly into a Plant Chlorophyll-Protein Complex.

PubMed

Hitchcock, Andrew; Jackson, Philip J; Chidgey, Jack W; Dickman, Mark J; Hunter, C Neil; Canniffe, Daniel P

2016-09-16

Improvements to photosynthetic efficiency could be achieved by manipulating pigment biosynthetic pathways of photosynthetic organisms in order to increase the spectral coverage for light absorption. The development of organisms that can produce both bacteriochlorophylls and chlorophylls is one way to achieve this aim, and accordingly we have engineered the bacteriochlorophyll-utilizing anoxygenic phototroph Rhodobacter sphaeroides to make chlorophyll a. Bacteriochlorophyll and chlorophyll share a common biosynthetic pathway up to the precursor chlorophyllide. Deletion of genes responsible for the bacteriochlorophyll-specific modifications of chlorophyllide and replacement of the native bacteriochlorophyll synthase with a cyanobacterial chlorophyll synthase resulted in the production of chlorophyll a. This pigment could be assembled in vivo into the plant water-soluble chlorophyll protein, heterologously produced in Rhodobacter sphaeroides, which represents a proof-of-principle for the engineering of novel antenna complexes that enhance the spectral range of photosynthesis.

Lasing from lead halide perovskite semiconductor microcavity system.

PubMed

Wang, Jun; Da, Peimei; Zhang, Zhe; Luo, Song; Liao, Liming; Sun, Zeyuan; Shen, Xuechu; Wu, Shiwei; Zheng, Gengfeng; Chen, Zhanghai

2018-06-07

Organic-inorganic halide perovskite semiconductors are ideal gain media for fabricating laser and photonic devices due to high absorption, photoluminescence (PL) efficiency and low nonradiative recombination losses. Herein, organic-inorganic halide perovskite CH3NH3PbI3 is embedded in the Fabry-Perot (FP) microcavity, and a wavelength-tunable excitonic lasing with a threshold of 12.9 μJ cm-2 and the spectral coherence of 0.76 nm are realized. The lasing threshold decreases and the spectral coherence enhances as the temperature decreases; these results are ascribed to the suppression of exciton irradiative recombination caused by thermal fluctuation. Moreover, both lasing and light emission below threshold from the perovskite microcavity (PM) system demonstrate a redshift with the decreasing temperature. These results provide a feasible platform based on the PM system for the study of light-matter interaction for quantum optics and the development of optoelectronic devices such as polariton lasers.

Near-infrared luminescence from Y2O3:Eu3+, Yb3+ prepared by sol-gel method.

PubMed

Xie, Ying; Xiao, Lin J; Yan, Feng Q; Chen, Yong J; Li, Wen Z; Geng, Xiu J

2014-06-01

Eu3+ and Yb3+ codoped Y2O3 phosphors were synthesized by the sol-gel method. The phosphors possess absorption in the region of 300-550 nm, exhibiting an intense NIR emission of Yb3+ around 1000 nm, which is suitable for matching the maximum spectral response of c-Si solar cells. The optimum composition of Eu3+ and Yb3+ codoped Y2O3 was (Y1.94Yb0.04Eu0.02)2O3. It is observed that two-step energy transfer occurs from the 5D2 level of Eu3+ situated around (466 nm) exciting two neighboring Yb3+ ions to the 2F5/2 level (1000 nm). The down-conversion material based on Eu(3+)- Yb3+ couple may have great potential applications in c-Si solar cells to enhance their photovoltaic conversion efficiency via spectral modification.

Cavity-enhanced Raman microscopy of individual carbon nanotubes

PubMed Central

Hümmer, Thomas; Noe, Jonathan; Hofmann, Matthias S.; Hänsch, Theodor W.; Högele, Alexander; Hunger, David

2016-01-01

Raman spectroscopy reveals chemically specific information and provides label-free insight into the molecular world. However, the signals are intrinsically weak and call for enhancement techniques. Here, we demonstrate Purcell enhancement of Raman scattering in a tunable high-finesse microcavity, and utilize it for molecular diagnostics by combined Raman and absorption imaging. Studying individual single-wall carbon nanotubes, we identify crucial structural parameters such as nanotube radius, electronic structure and extinction cross-section. We observe a 320-times enhanced Raman scattering spectral density and an effective Purcell factor of 6.2, together with a collection efficiency of 60%. Potential for significantly higher enhancement, quantitative signals, inherent spectral filtering and absence of intrinsic background in cavity-vacuum stimulated Raman scattering render the technique a promising tool for molecular imaging. Furthermore, cavity-enhanced Raman transitions involving localized excitons could potentially be used for gaining quantum control over nanomechanical motion and open a route for molecular cavity optomechanics. PMID:27402165

Unravelling radiative energy transfer in solid-state lighting

NASA Astrophysics Data System (ADS)

Melikov, Rustamzhon; Press, Daniel Aaron; Ganesh Kumar, Baskaran; Sadeghi, Sadra; Nizamoglu, Sedat

2018-01-01

Today, a wide variety of organic and inorganic luminescent materials (e.g., phosphors, quantum dots, etc.) are being used for lighting and new materials (e.g., graphene, perovskite, etc.) are currently under investigation. However, the understanding of radiative energy transfer is limited, even though it is critical to understand and improve the performance levels of solid-state lighting devices. In this study, we derived a matrix approach that includes absorption, reabsorption, inter-absorption and their iterative and combinatorial interactions for one and multiple types of fluorophores, which is simplified to an analytical matrix. This mathematical approach gives results that agree well with the measured spectral and efficiency characteristics of color-conversion light-emitting diodes. Moreover, it also provides a deep physical insight by uncovering the entire radiative interactions and their contribution to the output optical spectrum. The model is universal and applicable for all kinds of fluorophores.

Wavelength-switchable passively mode-locked fiber laser with mechanically exfoliated molybdenum ditelluride on side-polished fiber

NASA Astrophysics Data System (ADS)

Wang, Guomei

2017-11-01

We experimentally investigated the nonlinear saturable absorption characteristics of molybdenum ditelluride (MoTe2) and demonstrated a wavelength-switchable mode-locked erbium-doped fiber laser (EDFL) by using MoTe2 thin film on side-polished fiber (SPF) as saturable absorber. Here, the MoTe2 thin film was efficiently fabricated via mechanical exfoliation method and transferred onto the SPF with the assistance of polydimethylsiloxane (PDMS). MoTe2-covered SPF (MSPF) exhibits the nonlinear saturable absorption for pulses with different polarization states. Optical solitons with spectral bandwidth of 1.06 (1.31) nm centered at ∼1559 (∼1528) nm and pulse duration of 2.46 (2.04) ps can be obtained from the EDFL by adjusting the polarization controller (PC) properly. The time-bandwidth product (TBP) of the pulses was calculated as 0.322 (0.344).

Spectral slopes of the absorption coefficient of colored dissolved and detrital material inverted from UV-visible remote sensing reflectance

PubMed Central

Wei, Jianwei; Lee, Zhongping; Ondrusek, Michael; Mannino, Antonio; Tzortziou, Maria; Armstrong, Roy

2017-01-01

The spectral slope of the absorption coefficient of colored dissolved and detrital material (CDM), Scdm (units: nm−1), is an important optical parameter for characterizing the absorption spectral shape of CDM. Although highly variable in natural waters, in most remote sensing algorithms, this slope is either kept as a constant or empirically modeled with multiband ocean color in the visible domain. In this study, we explore the potential of semianalytically retrieving Scdm with added ocean color information in the ultraviolet (UV) range between 360 and 400 nm. Unique features of hyperspectral remote sensing reflectance in the UV-visible wavelengths (360–500 nm) have been observed in various waters across a range of coastal and open ocean environments. Our data and analyses indicate that ocean color in the UV domain is particularly sensitive to the variation of the CDM spectral slope. Here, we used a synthesized data set to show that adding UV wavelengths to the ocean color measurements will improve the retrieval of Scdm from remote sensing reflectance considerably, while the spectral band settings of past and current satellite ocean color sensors cannot fully account for the spectral variation of remote sensing reflectance. Results of this effort support the concept to include UV wavelengths in the next generation of satellite ocean color sensors. PMID:29201583

Spectral slopes of the absorption coefficient of colored dissolved and detrital material inverted from UV-visible remote sensing reflectance.

PubMed

Wei, Jianwei; Lee, Zhongping; Ondrusek, Michael; Mannino, Antonio; Tzortziou, Maria; Armstrong, Roy

2016-03-01

The spectral slope of the absorption coefficient of colored dissolved and detrital material (CDM), S cdm (units: nm -1 ), is an important optical parameter for characterizing the absorption spectral shape of CDM. Although highly variable in natural waters, in most remote sensing algorithms, this slope is either kept as a constant or empirically modeled with multiband ocean color in the visible domain. In this study, we explore the potential of semianalytically retrieving S cdm with added ocean color information in the ultraviolet (UV) range between 360 and 400 nm. Unique features of hyperspectral remote sensing reflectance in the UV-visible wavelengths (360-500 nm) have been observed in various waters across a range of coastal and open ocean environments. Our data and analyses indicate that ocean color in the UV domain is particularly sensitive to the variation of the CDM spectral slope. Here, we used a synthesized data set to show that adding UV wavelengths to the ocean color measurements will improve the retrieval of S cdm from remote sensing reflectance considerably, while the spectral band settings of past and current satellite ocean color sensors cannot fully account for the spectral variation of remote sensing reflectance. Results of this effort support the concept to include UV wavelengths in the next generation of satellite ocean color sensors.

Interference between extrinsic and intrinsic losses in x-ray absorption fine structure

NASA Astrophysics Data System (ADS)

Campbell, L.; Hedin, L.; Rehr, J. J.; Bardyszewski, W.

2002-02-01

The interference between extrinsic and intrinsic losses in x-ray absorption fine structure (XAFS) is treated within a Green's-function formalism, without explicit reference to final states. The approach makes use of a quasiboson representation of excitations and perturbation theory in the interaction potential between electrons and quasibosons. These losses lead to an asymmetric broadening of the main quasiparticle peak plus an energy-dependent satellite in the spectral function. The x-ray absorption spectra (XAS) is then given by a convolution of an effective spectral function over a one-electron cross section. It is shown that extrinsic and intrinsic losses tend to cancel near excitation thresholds, and correspondingly, the strength in the main peak increases. At high energies, the theory crosses over to the sudden approximation. These results thus explain the observed weakness of multielectron excitations in XAS. The approach is applied to estimate the many-body corrections to XAFS, beyond the usual mean-free path, using a phasor summation over the spectral function. The asymmetry of the spectral function gives rise to an additional many-body phase shift in the XAFS formula.

Hyperspectral analysis of clay minerals

NASA Astrophysics Data System (ADS)

Janaki Rama Suresh, G.; Sreenivas, K.; Sivasamy, R.

2014-11-01

A study was carried out by collecting soil samples from parts of Gwalior and Shivpuri district, Madhya Pradesh in order to assess the dominant clay mineral of these soils using hyperspectral data, as 0.4 to 2.5 μm spectral range provides abundant and unique information about many important earth-surface minerals. Understanding the spectral response along with the soil chemical properties can provide important clues for retrieval of mineralogical soil properties. The soil samples were collected based on stratified random sampling approach and dominant clay minerals were identified through XRD analysis. The absorption feature parameters like depth, width, area and asymmetry of the absorption peaks were derived from spectral profile of soil samples through DISPEC tool. The derived absorption feature parameters were used as inputs for modelling the dominant soil clay mineral present in the unknown samples using Random forest approach which resulted in kappa accuracy of 0.795. Besides, an attempt was made to classify the Hyperion data using Spectral Angle Mapper (SAM) algorithm with an overall accuracy of 68.43 %. Results showed that kaolinite was the dominant mineral present in the soils followed by montmorillonite in the study area.

Preliminary results from an investigation of AIS-1 data over an area of epithermal alteration: Plateau, Northern Queensland, Australia

NASA Technical Reports Server (NTRS)

Mackin, Steve; Munday, Tim; Hook, Simon

1987-01-01

Airborne Imaging Spectrometer-1 (AIS-1) data were flown over undifferentiated sequences of acid to intermediate volcanics and intrusives; meta-sediments; and a series of partially lateritized sedimentary rocks. The area exhibits a considerable spectral variability, after the suppression of striping effects. Log residual, and Internal Average Relative Reflectance (IARR) analytical techniques were used to enhance mineralogically related spectral features. Both methods produce similar results, but did not visually highlight mineral absorption features due to processing artifacts in areas of significant vegetation cover. The enhancement of mineral related absorption features was achieved using a hybrid processing approach based on the relative reflectance differences between vegetated and non-vegetated surfaces at 1.2 and 2.1 micron. The result is an image with little overall contrast, but which enhances the more subtle spectral features believed to be associated with clays and epidote. The AIS data was subject to interactive analysis using SPAM. Clear separation of clay and epidote related absorption features was apparent, and the identification of kaolinite was possible despite detrimental spectral effects.

Improved spectral absorption coefficient grouping strategy of wide band k-distribution model used for calculation of infrared remote sensing signal of hot exhaust systems

NASA Astrophysics Data System (ADS)

Hu, Haiyang; Wang, Qiang

2018-07-01

A new strategy for grouping spectral absorption coefficients, considering the influences of both temperature and species mole ratio inhomogeneities on correlated-k characteristics of the spectra of gas mixtures, has been deduced to match the calculation method of spectral overlap parameter used in multiscale multigroup wide band k-distribution model. By comparison with current spectral absorption coefficient grouping strategies, for which only the influence of temperature inhomogeneity on the correlated-k characteristics of spectra of single species was considered, the improvements in calculation accuracies resulting from the new grouping strategy were evaluated using a series of 0D cases in which radiance under 3-5-μm wave band emitted by hot combustion gas of hydrocarbon fuel was attenuated by atmosphere with quite different temperature and mole ratios of water vapor and carbon monoxide to carbon dioxide. Finally, evaluations are presented on the calculation of remote sensing thermal images of transonic hot jet exhausted from a chevron ejecting nozzle with solid wall cooling system.

Study of gain and photoresponse characteristics for back-illuminated separate absorption and multiplication GaN avalanche photodiodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xiaodong; Pan, Ming; Hou, Liwei

2014-01-07

The gain and photoresponse characteristics have been numerically studied for back-illuminated separate absorption and multiplication (SAM) GaN avalanche photodiodes (APDs). The parameters of fundamental models are calibrated by simultaneously comparing the simulated dark and light current characteristics with the experimental results. Effects of environmental temperatures and device dimensions on gain characteristics have been investigated, and a method to achieve the optimum thickness of charge layer is obtained. The dependence of gain characteristics and breakdown voltage on the doping concentration of the charge layer is also studied in detail to get the optimal charge layer. The bias-dependent spectral responsivity and quantummore » efficiency are then presented to study the photoresponse mechanisms inside SAM GaN APDs. It is found the responsivity peak red-shifts at first due to the Franz-Keldysh effect and then blue-shifts due to the reach-through effect of the absorption layer. Finally, a new SAM GaN/AlGaN heterojunction APD structure is proposed for optimizing SAM GaN APDs.« less

Confocal absorption spectral imaging of MoS2: optical transitions depending on the atomic thickness of intrinsic and chemically doped MoS2.

PubMed

Dhakal, Krishna P; Duong, Dinh Loc; Lee, Jubok; Nam, Honggi; Kim, Minsu; Kan, Min; Lee, Young Hee; Kim, Jeongyong

2014-11-07

We performed a nanoscale confocal absorption spectral imaging to obtain the full absorption spectra (over the range 1.5-3.2 eV) within regions having different numbers of layers and studied the variation of optical transition depending on the atomic thickness of the MoS2 film. Three distinct absorption bands corresponding to A and B excitons and a high-energy background (BG) peak at 2.84 eV displayed a gradual redshift as the MoS2 film thickness increased from the monolayer, to the bilayer, to the bulk MoS2 and this shift was attributed to the reduction of the gap energy in the Brillouin zone at the K-point as the atomic thickness increased. We also performed n-type chemical doping of MoS2 films using reduced benzyl viologen (BV) and the confocal absorption spectra modified by the doping showed a strong dependence on the atomic thickness: A and B exciton peaks were greatly quenched in the monolayer MoS2 while much less effect was shown in larger thickness and the BG peak either showed very small quenching for 1 L MoS2 or remained constant for larger thicknesses. Our results indicate that confocal absorption spectral imaging can provide comprehensive information on optical transitions of microscopic size intrinsic and doped two-dimensional layered materials.

Near infrared cavity enhanced absorption spectra of atmospherically relevant ether-1, 4-Dioxane.

PubMed

Chandran, Satheesh; Varma, Ravi

2016-01-15

1, 4-Dioxane (DX) is a commonly found ether in industrially polluted atmosphere. The near infrared absorption spectra of this compound has been recorded in the region 5900-8230 cm(-1) with a resolution of 0.08 cm(-1) using a novel Fourier transform incoherent broadband cavity-enhanced absorption spectrometer (FT-IBBCEAS). All recorded spectra were found to contain regions that are only weakly perturbed. The possible combinations of fundamental modes and their overtone bands corresponding to selected regions in the measured spectra are tabulated. Two interesting spectral regions were identified as 5900-6400 cm(-1) and 8100-8230 cm(-1). No significant spectral interference due to presence of water vapor was observed suggesting the suitability of these spectral signatures for spectroscopic in situ detection of DX. The technique employed here is much more sensitive than standard Fourier transform spectrometer measurements on account of long effective path length achieved. Hence significant enhancement of weaker absorption lines above the noise level was observed as demonstrated by comparison with an available measurement from database. Copyright © 2015 Elsevier B.V. All rights reserved.

Absorption and fluorescence properties of colored dissolved organic matter in the Ross Sea during austral summer

NASA Astrophysics Data System (ADS)

D'Sa, E. J.; Kim, H. C.; Ha, S. Y.

2016-12-01

Colored dissolved organic matter (CDOM) spectral absorption and excitation-emission matrix (EEMs) fluorescence with parallel factor analysis (PARAFAC) were examined in the Ross Sea during a survey conducted on board the R/V Araon in the austral summer of 14/15. CDOM absorption at 355 nm ranged from 0.06 to 1.14 m-1 while spectral slope S calculated between 275-295 nm wavelength ranged from 18.83 to 33.32 µm-1 with water masses playing an important role in its variability. Spectral slope S decreased with increasing CDOM absorption indicating the strong role of photo-oxidation on CDOM abundance during the summer. PARAFAC analysis of EEM data identified two humic-like (terrestrial and marine-like) and a protein-like (tryptophan-like) component. The two humic-like components were well correlated with little variability spatially and across the water column ( 0-100 m) likely indicating more refractory material. The protein-like fluorescent component was relatively quite variable supporting the autochthonous production of this fluorescent component in the highly productive Ross Sea waters.

Multivariate Analysis of Solar Spectral Irradiance Measurements

NASA Technical Reports Server (NTRS)

Pilewskie, P.; Rabbette, M.

2001-01-01

Principal component analysis is used to characterize approximately 7000 downwelling solar irradiance spectra retrieved at the Southern Great Plains site during an Atmospheric Radiation Measurement (ARM) shortwave intensive operating period. This analysis technique has proven to be very effective in reducing a large set of variables into a much smaller set of independent variables while retaining the information content. It is used to determine the minimum number of parameters necessary to characterize atmospheric spectral irradiance or the dimensionality of atmospheric variability. It was found that well over 99% of the spectral information was contained in the first six mutually orthogonal linear combinations of the observed variables (flux at various wavelengths). Rotation of the principal components was effective in separating various components by their independent physical influences. The majority of the variability in the downwelling solar irradiance (380-1000 nm) was explained by the following fundamental atmospheric parameters (in order of their importance): cloud scattering, water vapor absorption, molecular scattering, and ozone absorption. In contrast to what has been proposed as a resolution to a clear-sky absorption anomaly, no unexpected gaseous absorption signature was found in any of the significant components.

Two-dimensional imaging of gas temperature and concentration based on hyperspectral tomography

NASA Astrophysics Data System (ADS)

Xin, Ming-yuan; Jin, Xing; Wang, Guang-yu; Song, Junling

2016-10-01

Two-dimensional imaging of gas temperature and concentration is realized by hyperspectral tomography, which has the characteristics of using multi-wavelengths absorption spectral information, so that the imaging could be accomplished in a small number of projections and viewing angles. A temperature and concentration model is established to simulate the combustion conditions and a total number of 10 near-infrared absorption spectral information of H2O is used. An improved simulated annealing algorithm by adjusting search step is performed the main search algorithm for the tomography. By adding random errors into the absorption area information, the stability of the algorithm is tested, and the results are compared with the reconstructions provided by algebraic reconstruction technique which takes advantage of 2 spectral information contents in imaging. The results show that the two methods perform equivalent in low-level noise environment, but at high-level, hyperspectral tomography turns out to be more stable.

Molecular detection with terahertz waves based on absorption-induced transparency metamaterials

NASA Astrophysics Data System (ADS)

G. Rodrigo, Sergio; Martín-Moreno, L.

2016-10-01

A system for the detection of spectral signatures of chemical compounds at the Terahertz regime is presented. The system consists on a holey metal film whereby the presence of a given substance provokes the appearance of spectral features in transmission and reflection induced by the molecular specimen. These induced effects can be regarded as an extraordinary optical transmission phenomenon called absorption-induced transparency (AIT). The phenomenon consist precisely in the appearance of peaks in transmission and dips in reflection after sputtering of a chemical compound onto an initially opaque holey metal film. The spectral signatures due to AIT occur unexpectedly close to the absorption energies of the molecules. The presence of a target, a chemical compound, would be thus revealed as a strong drop in reflectivity measurements. We theoretically predict the AIT based system would serve to detect amounts of hydrocyanic acid (HCN) at low rate concentrations.

Hyperpolarized 13C pyruvate mouse brain metabolism with absorptive-mode EPSI at 1 T

NASA Astrophysics Data System (ADS)

Miloushev, Vesselin Z.; Di Gialleonardo, Valentina; Salamanca-Cardona, Lucia; Correa, Fabian; Granlund, Kristin L.; Keshari, Kayvan R.

2017-02-01

The expected signal in echo-planar spectroscopic imaging experiments was explicitly modeled jointly in spatial and spectral dimensions. Using this as a basis, absorptive-mode type detection can be achieved by appropriate choice of spectral delays and post-processing techniques. We discuss the effects of gradient imperfections and demonstrate the implementation of this sequence at low field (1.05 T), with application to hyperpolarized [1-13C] pyruvate imaging of the mouse brain. The sequence achieves sufficient signal-to-noise to monitor the conversion of hyperpolarized [1-13C] pyruvate to lactate in the mouse brain. Hyperpolarized pyruvate imaging of mouse brain metabolism using an absorptive-mode EPSI sequence can be applied to more sophisticated murine disease and treatment models. The simple modifications presented in this work, which permit absorptive-mode detection, are directly translatable to human clinical imaging and generate improved absorptive-mode spectra without the need for refocusing pulses.

Absolute ozone absorption cross section in the Huggins Chappuis minimum (350-470 nm) at 296 K

NASA Astrophysics Data System (ADS)

Axson, J. L.; Washenfelder, R. A.; Kahan, T. F.; Young, C. J.; Vaida, V.; Brown, S. S.

2011-11-01

We report the ozone absolute absorption cross section between 350-470 nm, the minimum between the Huggins and Chappuis bands, where the ozone cross section is less than 10-22 cm2. Ozone spectra were acquired using an incoherent broadband cavity enhanced absorption spectrometer, with three channels centered at 365, 405, and 455 nm. The accuracy of the measured cross section is 4-30%, with the greatest uncertainty near the minimum absorption at 375-390 nm. Previous measurements vary by more than an order of magnitude in this spectral region. The measurements reported here provide much greater spectral coverage than the most recent measurements. The effect of O3 concentration and water vapor partial pressure were investigated, however there were no observable changes in the absorption spectrum most likely due to the low optical density of the complex.

Light absorption of organic aerosol from pyrolysis of corn stalk

NASA Astrophysics Data System (ADS)

Li, Xinghua; Chen, Yanju; Bond, Tami C.

2016-11-01

Organic aerosol (OA) can absorb solar radiation in the low-visible and ultra-violet wavelengths thereby modifying radiative forcing. Agricultural waste burning emits a large quantity of organic carbon in many developing countries. In this work, we improved the extraction and analysis method developed by Chen and Bond, and extended the spectral range of OC absorption. We examined light absorbing properties of primary OA from pyrolysis of corn stalk, which is a major type of agricultural wastes. Light absorption of bulk liquid extracts of OA was measured using a UV-vis recording spectrophotometer. OA can be extracted by methanol at 95%, close to full extent, and shows polar character. Light absorption of organic aerosol has strong spectral dependence (Absorption Ångström exponent = 7.7) and is not negligible at ultra-violet and low-visible regions. Higher pyrolysis temperature produced OA with higher absorption. Imaginary refractive index of organic aerosol (kOA) is 0.041 at 400 nm wavelength and 0.005 at 550 nm wavelength, respectively.

Two-dimensional layered semiconductor/graphene heterostructures for solar photovoltaic applications.

PubMed

Shanmugam, Mariyappan; Jacobs-Gedrim, Robin; Song, Eui Sang; Yu, Bin

2014-11-07

Schottky barriers formed by graphene (monolayer, bilayer, and multilayer) on 2D layered semiconductor tungsten disulfide (WS2) nanosheets are explored for solar energy harvesting. The characteristics of the graphene-WS2 Schottky junction vary significantly with the number of graphene layers on WS2, resulting in differences in solar cell performance. Compared with monolayer or stacked bilayer graphene, multilayer graphene helps in achieving improved solar cell performance due to superior electrical conductivity. The all-layered-material Schottky barrier solar cell employing WS2 as a photoactive semiconductor exhibits efficient photon absorption in the visible spectral range, yielding 3.3% photoelectric conversion efficiency with multilayer graphene as the Schottky contact. Carrier transport at the graphene/WS2 interface and the interfacial recombination process in the Schottky barrier solar cells are examined.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hagglund, Carl; Zeltzer, Gabriel; Ruiz, Ricardo

In this study, when optical resonances interact strongly, hybridized modes are formed with mixed properties inherited from the basic modes. Strong coupling therefore tends to equalize properties such as damping and oscillator strength of the spectrally separate resonance modes. This effect is here shown to be very useful for the realization of near-perfect dual-band absorption with ultrathin (~10 nm) layers in a simple geometry. Absorber layers are constructed by atomic layer deposition of the heavy-damping semiconductor tin monosulfide (SnS) onto a two-dimensional gold nanodot array. In combination with a thin (55 nm) SiO 2 spacer layer and a highly reflectivemore » Al film on the back, a semiopen nanocavity is formed. The SnS-coated array supports a localized surface plasmon resonance in the vicinity of the lowest order antisymmetric Fabry–Perot resonance of the nanocavity. Very strong coupling of the two resonances is evident through anticrossing behavior with a minimum peak splitting of 400 meV, amounting to 24% of the plasmon resonance energy. The mode equalization resulting from this strong interaction enables simultaneous optical impedance matching of the system at both resonances and thereby two near-perfect absorption peaks, which together cover a broad spectral range. When paired with the heavy damping from SnS band-to-band transitions, this further enables approximately 60% of normal incident solar photons with energies exceeding the band gap to be absorbed in the 10 nm SnS coating. Thereby, these results establish a distinct relevance of strong coupling phenomena to efficient, nanoscale photovoltaic absorbers and more generally for fulfilling a specific optical condition at multiple spectral positions.« less

Efficiency enhancement of semitransparent organic solar cells by using printed dielectric mirrors (Presentation Recording)

NASA Astrophysics Data System (ADS)

Bronnbauer, Carina; Forberich, Karen K.; Guo, Fei; Gasparini, Nicola; Brabec, Christoph J.

2015-09-01

Building integrated thin film solar cells are a strategy for future eco-friendly power generation. Such solar cells have to be semi-transparent, long-term stable and show the potential to be fabricated by a low-cost production process. Organic photovoltaics are a potential candidate because an absorber material with its main absorption in the infrared spectral region where the human eye is not sensitive can be chosen. We can increase the number of absorbed photons, at the same time, keep the transparency almost constant by using a dielectric, wavelength-selective mirror. The mirror reflects only in the absorption regime of the active layer material and shows high transparencies in the spectral region around 550 nm where the human eye is most sensitive. We doctor bladed a fully solution processed dielectric mirror at low temperatures below 80 °C. Both inks, which are printed alternatingly are based on nanoparticles and have a refractive index of 1.29 or 1.98, respectively, at 500 nm. The position and the intensity of the main reflection peak can be easily shifted and thus adjusted to the solar cell absorption spectrum. Eventually, the dielectric mirror was combined with different organic solar cells. For instance, the current increases by 20.6 % while the transparency decreases by 23.7 % for the low band gap absorber DPP and silver nanowires as top electrode. Moreover we proved via experiment and optical simulations, that a variation of the active layer thickness and the position of the main reflection peak affect the transparency and the increase in current.

Infrared spectroscopic measurements relevant to atmospheric remote sensing

NASA Technical Reports Server (NTRS)

Varanasi, Prasad; Gopalan, Arun

1993-01-01

SF6 is a synthetic chemical which is used in many industrial applications and as a meteorological tracer. This paper describes determinations of spectral absorption coefficients k-nu of SF6 measured in the central Q-branches of the nu(3)-fundamental at 947/cm at various temperature-pressure combinations representing tangent heights in solar-occultation experiments or layers in the atmosphere. Spectral data were also obtained for C2H4 and NH3 fundamental bands. Measurements were made with the Doppler-limited spectral resolution of a tunable diode laser spectrometer with a cryogenically cooled absorption cell, described by Varanasi and Chudamani (1992).

High-efficiency and air-stable P3HT-based polymer solar cells with a new non-fullerene acceptor

PubMed Central

Holliday, Sarah; Ashraf, Raja Shahid; Wadsworth, Andrew; Baran, Derya; Yousaf, Syeda Amber; Nielsen, Christian B.; Tan, Ching-Hong; Dimitrov, Stoichko D.; Shang, Zhengrong; Gasparini, Nicola; Alamoudi, Maha; Laquai, Frédéric; Brabec, Christoph J.; Salleo, Alberto; Durrant, James R.; McCulloch, Iain

2016-01-01

Solution-processed organic photovoltaics (OPV) offer the attractive prospect of low-cost, light-weight and environmentally benign solar energy production. The highest efficiency OPV at present use low-bandgap donor polymers, many of which suffer from problems with stability and synthetic scalability. They also rely on fullerene-based acceptors, which themselves have issues with cost, stability and limited spectral absorption. Here we present a new non-fullerene acceptor that has been specifically designed to give improved performance alongside the wide bandgap donor poly(3-hexylthiophene), a polymer with significantly better prospects for commercial OPV due to its relative scalability and stability. Thanks to the well-matched optoelectronic and morphological properties of these materials, efficiencies of 6.4% are achieved which is the highest reported for fullerene-free P3HT devices. In addition, dramatically improved air stability is demonstrated relative to other high-efficiency OPV, showing the excellent potential of this new material combination for future technological applications. PMID:27279376

GaAs nanopillar-array solar cells employing in situ surface passivation

PubMed Central

Mariani, Giacomo; Scofield, Adam C.; Hung, Chung-Hong; Huffaker, Diana L.

2013-01-01

Arrays of III–V direct-bandgap semiconductor nanopillars represent promising photovoltaic candidates due to their inherent high optical absorption coefficients and minimized reflection arising from light trapping, efficient charge collection in the radial direction and the ability to synthesize them on low-cost platforms. However, the increased surface area results in surface states that hamper the power conversion efficiency. Here, we report the first demonstration of GaAs nanopillar-array photovoltaics employing epitaxial passivation with air mass 1.5 global power conversion efficiencies of 6.63%. High-bandgap epitaxial InGaP shells are grown in situ and cap the radial p–n junctions to alleviate surface-state effects. Under light, the photovoltaic devices exhibit open-circuit voltages of 0.44 V, short-circuit current densities of 24.3 mA cm−2 and fill factors of 62% with high external quantum efficiencies >70% across the spectral regime of interest. A novel titanium/indium tin oxide annealed alloy is exploited as transparent ohmic anode. PMID:23422665

Water vapor absorption coefficients in the 8-13-micron spectral region - A critical review

NASA Technical Reports Server (NTRS)

Grant, William B.

1990-01-01

Measurements of water vapor absorption coefficients in the thermal IR atmospheric window (8-13 microns) during the past 20 years obtained by a variety of techniques are reviewed for consistency and compared with computed values based on the AFGL spectral data tapes. The methods of data collection considered were atmospheric long path absorption with a CO2 laser or a broadband source and filters, a White cell and a CO2 laser or a broadband source and a spectrometer, and a spectrophone with a CO2 laser. Advantages and disadvantages of each measurement approach are given as a guide to further research. Continuum absorption has apparently been measured accurately to about the 5-10 percent level in five of the measurements reported.

Coloured Dissolved Organic Matter (CDOM) dynamics in small surface reservoirs in semiarid Brazil

NASA Astrophysics Data System (ADS)

Coelho, Christine; Foerster, Saskia; Heim, Birgit; de Araujo, Jose Carlos

2016-04-01

Coloured Dissolved Organic Matter (CDOM) is one of the major light absorbing constituents in freshwaters. Supplied from degradation of components of the aquatic environment, it consists mainly of humic substances and its concentration is strongly related to primary production, often associated to macrophytes. It plays a central role in several biological and chemical processes affecting the bioavailability of nutrients in aquatic ecosystems. Therefore CDOM can be regarded as a water quality indicator. We used the spectral absorption and spectral slope for understanding CDOM dynamics in surface reservoirs in the Brazilian semiarid region. The analysis was based on water samples collected in three reservoirs in a total of ten sampling locations in the period June 2014 to November 2015 with monthly to bi-monthly intervals totaling 120 samples. The collected water samples were filtered through cellulose acetate membrane filters. Subsequently, spectral absorbance was measured in a Lambda 950 UV-VIS spectrometer in the spectral range 250 to 800 nm using a quartz cuvette with 5 cm optical path. From the absorbance measurement, we obtained CDOM content using the specific absorption coefficient at 440nm as well as spectral slope. The average slope for the entire period for all reservoirs is 0,018, but we found a considerable increase in spectral slope values after the wet period (between February 2014 and June 2014) for the reservoirs São Nicolau and Paus Branco while Marengo reservoir showed only slight variations during this period, but exhibited an increase only in the dry period. Regarding aCDOM(440), the average was equal to 2,55 for Marengo, 5,70 for São Nicolau, and 3,53 for Paus Branco reservoir indicating different characteristics of these reservoirs. We noticed a decrease in the absorption coefficient for São Nicolau and Paus Branco reservoirs at the end of the wet period whereas for Marengo reservoir this value showed a different behavior. Spectral slope and spectral absorption seem consistent and, among other possible factors, its dynamics were affected by high evaporation and low precipitation, typical conditions for semiarid regions in the tropics. The results show also evidence of the hysteresis phenomenon related to humic substance properties. However, it is important to consider also other water quality parameters in order to assess the whole interaction occurring in the reservoirs under eutrophic conditions. This is a first study of the application of spectral absorption and spectral slope of CDOM for small reservoirs in semiarid Brazil providing additional information to the traditional water quality measurements. In the future, we plan to relate the in-situ measurements to satellite imagery to study spatio-temporal water quality dynamics and relate them to land use changes.

Wavelength calibration of imaging spectrometer using atmospheric absorption features

NASA Astrophysics Data System (ADS)

Zhou, Jiankang; Chen, Yuheng; Chen, Xinhua; Ji, Yiqun; Shen, Weimin

2012-11-01

Imaging spectrometer is a promising remote sensing instrument widely used in many filed, such as hazard forecasting, environmental monitoring and so on. The reliability of the spectral data is the determination to the scientific communities. The wavelength position at the focal plane of the imaging spectrometer will change as the pressure and temperature vary, or the mechanical vibration. It is difficult for the onboard calibration instrument itself to keep the spectrum reference accuracy and it also occupies weight and the volume of the remote sensing platform. Because the spectral images suffer from the atmospheric effects, the carbon oxide, water vapor, oxygen and solar Fraunhofer line, the onboard wavelength calibration can be processed by the spectral images themselves. In this paper, wavelength calibration is based on the modeled and measured atmospheric absorption spectra. The modeled spectra constructed by the atmospheric radiative transfer code. The spectral angle is used to determine the best spectral similarity between the modeled spectra and measured spectra and estimates the wavelength position. The smile shape can be obtained when the matching process across all columns of the data. The present method is successful applied on the Hyperion data. The value of the wavelength shift is obtained by shape matching of oxygen absorption feature and the characteristics are comparable to that of the prelaunch measurements.

Measurements of near-IR water vapor absorption at high pressure and temperature

NASA Astrophysics Data System (ADS)

Rieker, G. B.; Liu, X.; Li, H.; Jeffries, J. B.; Hanson, R. K.

2007-03-01

Tunable diode lasers (TDLs) are used to measure high resolution (0.1 cm-1), near-infrared (NIR) water vapor absorption spectra at 700 K and pressures up to 30 atm within a high-pressure and -temperature optical cell in a high-uniformity tube furnace. Both direct absorption and wavelength modulation with second harmonic detection (WMS-2f) spectra are obtained for 6 cm-1 regions near 7204 cm-1 and 7435 cm-1. Direct absorption measurements at 700 K and 10 atm are compared with simulations using spectral parameters from HITRAN and a hybrid database combining HITRAN with measured spectral constants for transitions in the two target spectral regions. The hybrid database reduces RMS error between the simulation and the measurements by 45% for the 7204 cm-1 region and 28% for the 7435 cm-1 region. At pressures above 10 atm, the breakdown of the impact approximation inherent to the Lorentzian line shape model becomes apparent in the direct absorption spectra, and measured results are in agreement with model results and trends at elevated temperatures reported in the literature. The wavelength-modulation spectra are shown to be less affected by the breakdown of the impact approximation and measurements agree well with the hybrid database predictions to higher pressures (30 atm).

Can Infrared Spectroscopy Be Used to Measure Change in Potassium Nitrate Concentration as a Proxy for Soil Particle Movement?

PubMed Central

Luleva, Mila Ivanova; van der Werff, Harald; Jetten, Victor; van der Meer, Freek

2011-01-01

Displacement of soil particles caused by erosion influences soil condition and fertility. To date, the cesium 137 isotope (137Cs) technique is most commonly used for soil particle tracing. However when large areas are considered, the expensive soil sampling and analysis present an obstacle. Infrared spectral measurements would provide a solution, however the small concentrations of the isotope do not influence the spectral signal sufficiently. Potassium (K) has similar electrical, chemical and physical properties as Cs. Our hypothesis is that it can be used as possible replacement in soil particle tracing. Soils differing in texture were sampled for the study. Laboratory soil chemical analyses and spectral sensitivity analyses were carried out to identify the wavelength range related to K concentration. Different concentrations of K fertilizer were added to soils with varying texture properties in order to establish spectral characteristics of the absorption feature associated with the element. Changes in position of absorption feature center were observed at wavelengths between 2,450 and 2,470 nm, depending on the amount of fertilizer applied. Other absorption feature parameters (absorption band depth, width and area) were also found to change with K concentration with coefficient of determination between 0.85 and 0.99. Tracing soil particles using K fertilizer and infrared spectral response is considered suitable for soils with sandy and sandy silt texture. It is a new approach that can potentially grow to a technique for rapid monitoring of soil particle movement over large areas. PMID:22163843

Retrieval of Aerosol Absorption Properties from Satellite Observations

NASA Technical Reports Server (NTRS)

Torres, Omar; Bhartia, Pawan K.; Jethva, H.; Ahn, Chang-Woo

2012-01-01

The Angstrom Absorption Exponent (AAE) is a parameter commonly used to characterize the wavelength-dependence of aerosol absorption optical depth (AAOD). It is closely related to aerosol composition. Black carbon (BC) containing aerosols yield AAE values near unity whereas Organic carbon (OC) aerosol particles are associated with values larger than 2. Even larger AAE values have been reported for desert dust aerosol particles. Knowledge of spectral AAOD is necessary for the calculation of direct radiative forcing effect of aerosols and for inferring aerosol composition. We have developed a satellitebased method of determining the spectral AAOD of absorbing aerosols. The technique uses multi-spectral measurements of upwelling radiation from scenes where absorbing aerosols lie above clouds as indicated by the UV Aerosol Index. For those conditions, the satellite measurement can be explained, using an approximations of Beer's Law (BL), as the upwelling reflectance at the cloud top attenuated by the absorption effects of the overlying aerosol layer. The upwelling reflectance at the cloud-top in an aerosol-free atmospheric column is mainly a function of cloud optical depth (COD). In the proposed method of AAE derivation, the first step is determining COD which is retrieved using a previously developed color-ratio based approach. In the second step, corrections for molecular scattering effects are applied to both the observed ad the calculated cloud reflectance terms, and the spectral AAOD is then derived by an inversion of the BL approximation. The proposed technique will be discussed in detail and application results making use of OMI multi-spectral measurements in the UV-Vis. will be presented.

Improving the accuracy of S02 column densities and emission rates obtained from upward-looking UV-spectroscopic measurements of volcanic plumes by taking realistic radiative transfer into account

USGS Publications Warehouse

Kern, Christoph; Deutschmann, Tim; Werner, Cynthia; Sutton, A. Jeff; Elias, Tamar; Kelly, Peter J.

2012-01-01

Sulfur dioxide (SO2) is monitored using ultraviolet (UV) absorption spectroscopy at numerous volcanoes around the world due to its importance as a measure of volcanic activity and a tracer for other gaseous species. Recent studies have shown that failure to take realistic radiative transfer into account during the spectral retrieval of the collected data often leads to large errors in the calculated emission rates. Here, the framework for a new evaluation method which couples a radiative transfer model to the spectral retrieval is described. In it, absorption spectra are simulated, and atmospheric parameters are iteratively updated in the model until a best match to the measurement data is achieved. The evaluation algorithm is applied to two example Differential Optical Absorption Spectroscopy (DOAS) measurements conducted at Kilauea volcano (Hawaii). The resulting emission rates were 20 and 90% higher than those obtained with a conventional DOAS retrieval performed between 305 and 315 nm, respectively, depending on the different SO2 and aerosol loads present in the volcanic plume. The internal consistency of the method was validated by measuring and modeling SO2 absorption features in a separate wavelength region around 375 nm and comparing the results. Although additional information about the measurement geometry and atmospheric conditions is needed in addition to the acquired spectral data, this method for the first time provides a means of taking realistic three-dimensional radiative transfer into account when analyzing UV-spectral absorption measurements of volcanic SO2 plumes.

Light backscattering efficiency and related properties of some phytoplankters

NASA Astrophysics Data System (ADS)

Ahn, Yu-Hwan; Bricaud, Annick; Morel, André

1992-11-01

By using a set-up that combines an integrating sphere with a spectroradiometer LI-1800 UW, the backscattering properties of nine different phytoplankters grown in culture have been determined experimentally for the wavelengths domain ν = 400 up to 850 nm. Simultaneously, the absorption and attenuation properties, as well as the size distribution function, have been measured. This set of measurements allowed the spectral values of refractive index, and subsequently the volume scattering functions (VSF) of the cells, to be derived, by operating a scattering model previously developed for spherical and homogeneous cells. The backscattering properties, measured within a restricted angular domain (approximately between 132 and 174°), have been compared to theoretical predictions. Although there appear some discrepancies between experimental and predicted values (probably due to experimental errors as well as deviations of actual cells from computational hypotheses), the overall agreement is good; in particular the observed interspecific variations of backscattering values, as well as the backscattering spectral variation typical of each species, are well accounted for by theory. Using the computed VSF, the measured backscattering properties can be converted (assuming spherical and homogeneous cells) into efficiency factors for backscattering ( overlineQbb) . Thhe spectral behavior of overlineQbb appears to be radically different from that for total scattering overlineQb. For small cells, overlineQ (λ) is practically constant over the spectrum, whereas overlineQb(λ) varies approximately according to a power law (λ -2). As the cell size increases, overlineQbb conversely, becomes increasingly featured, whilst overlineQb becomes spectrally flat. The chlorophyll-specific backscattering coefficients ( b b∗ appear highly variable and span nearly two orders of magnitude. The chlorophyll-specific absorption and scattering coefficients, a ∗ and b ∗, are mainly ruled by the interspecific variations in cellssize ( D) and intracellular pigment concentration ( Ci) (actually by the variations of the product DCi). Though b b∗ is involved in the modelling of the diffuse reflectance of waters, the impact of its actual variation is greatly limited because typical b b∗ values, even at their maximum (10 -3 m 2 mg -1), are very low. This result confirms that living algae have a negligible influence on the backscattering process by oceanic waters; other particles (bacteria, detritus, etc.) associated with algae are mainly responsible for this process.

Infrared absorption-coefficient data on SF6 applicable to atmospheric remote sensing

NASA Technical Reports Server (NTRS)

Varanasi, P.; Gopalan, A.; Brannon, J. F., Jr.

1992-01-01

Spectral absorption coefficients, k(nu)/cm per atm, of SF6 have been measured in the central Q-branches of the nu(3)-fundamental at 947/cm at various temperature-pressure combinations representing tangent heights in solar-occultation experiments or layers in the atmosphere. The data obtained with the Doppler-limited spectral resolution (about 0.0001/cm) of a tunable-diode laser spectrometer are useful in the atmospheric remote sensing of this trace gas.

The complex refractive index of atmospheric and model humic-like substances (HULIS) retrieved by a cavity ring down aerosol spectrometer (CRD-AS).

PubMed

Dinar, E; Riziq, A Abo; Spindler, C; Erlick, C; Kiss, G; Rudich, Y

2008-01-01

Atmospheric aerosols absorb and reflect solar radiation causing surface cooling and heating of the atmosphere. The interaction between aerosols and radiation depends on their complex index of refraction, which is related to the particles' chemical composition. The contribution of light absorbing organic compounds, such as HUmic-LIke Substances (HULIS) to aerosol scattering and absorption is among the largest uncertainties in assessing the direct effect of aerosols on climate. Using a Cavity Ring Down Aerosol Spectrometer (CRD-AS), the complex index of refraction of aerosols containing HULIS extracted from pollution, smoke, and rural continental aerosols, and molecular weight-fractionated fulvic acid was measured at 390 nm and 532 nm. The imaginary part of the refractive index (absorption) substantially increases towards the UV range with increasing molecular weight and aromaticity. At both wavelengths, HULIS extracted from pollution and smoke particles absorb more than HULIS from the rural aerosol. Sensitivity calculations for a pollution-type aerosol containing ammonium sulfate, organic carbon (HULIS), and soot suggests that accounting for absorption by HULIS leads in most cases to a significant decrease in the single scattering albedo and to a significant increase in aerosol radiative forcing efficiency, towards more atmospheric absorption and heating. This indicates that HULIS in biomass smoke and pollution aerosols, in addition to black carbon, can contribute significantly to light absorption in the ultraviolet and visible spectral regions.

Broadband Spectral Modeling of the Extreme Gigahertz-peaked Spectrum Radio Source PKS B0008-421

NASA Astrophysics Data System (ADS)

Callingham, J. R.; Gaensler, B. M.; Ekers, R. D.; Tingay, S. J.; Wayth, R. B.; Morgan, J.; Bernardi, G.; Bell, M. E.; Bhat, R.; Bowman, J. D.; Briggs, F.; Cappallo, R. J.; Deshpande, A. A.; Ewall-Wice, A.; Feng, L.; Greenhill, L. J.; Hazelton, B. J.; Hindson, L.; Hurley-Walker, N.; Jacobs, D. C.; Johnston-Hollitt, M.; Kaplan, D. L.; Kudrayvtseva, N.; Lenc, E.; Lonsdale, C. J.; McKinley, B.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.; Oberoi, D.; Offringa, A. R.; Ord, S. M.; Pindor, B.; Prabu, T.; Procopio, P.; Riding, J.; Srivani, K. S.; Subrahmanyan, R.; Udaya Shankar, N.; Webster, R. L.; Williams, A.; Williams, C. L.

2015-08-01

We present broadband observations and spectral modeling of PKS B0008-421 and identify it as an extreme gigahertz-peaked spectrum (GPS) source. PKS B0008-421 is characterized by the steepest known spectral slope below the turnover, close to the theoretical limit of synchrotron self-absorption, and the smallest known spectral width of any GPS source. Spectral coverage of the source spans from 0.118 to 22 GHz, which includes data from the Murchison Widefield Array and the wide bandpass receivers on the Australia Telescope Compact Array. We have implemented a Bayesian inference model fitting routine to fit the data with internal free-free absorption (FFA), single- and double-component FFA in an external homogeneous medium, FFA in an external inhomogeneous medium, or single- and double-component synchrotron self-absorption models, all with and without a high-frequency exponential break. We find that without the inclusion of a high-frequency break these models cannot accurately fit the data, with significant deviations above and below the peak in the radio spectrum. The addition of a high-frequency break provides acceptable spectral fits for the inhomogeneous FFA and double-component synchrotron self-absorption models, with the inhomogeneous FFA model statistically favored. The requirement of a high-frequency spectral break implies that the source has ceased injecting fresh particles. Additional support for the inhomogeneous FFA model as being responsible for the turnover in the spectrum is given by the consistency between the physical parameters derived from the model fit and the implications of the exponential spectral break, such as the necessity of the source being surrounded by a dense ambient medium to maintain the peak frequency near the gigahertz region. This implies that PKS B0008-421 should display an internal H i column density greater than 1020 cm-2. The discovery of PKS B0008-421 suggests that the next generation of low radio frequency surveys could reveal a large population of GPS sources that have ceased activity, and that a portion of the ultra-steep-spectrum source population could be composed of these GPS sources in a relic phase.

Thermal Pressure in Diffuse H2 Gas Measured by Herschel [C II] Emission and FUSE UV H2 Absorption

NASA Astrophysics Data System (ADS)

Velusamy, T.; Langer, W. D.; Goldsmith, P. F.; Pineda, J. L.

2017-04-01

UV absorption studies with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite have made important observations of H2 molecular gas in Galactic interstellar translucent and diffuse clouds. Observations of the 158 μm [C II] fine-structure line with Herschel trace the same H2 molecular gas in emission. We present [C II] observations along 27 lines of sight (LOSs) toward target stars of which 25 have FUSE H2 UV absorption. Two stars have only HST STIS C II λ2325 absorption data. We detect [C II] 158 μm emission features in all but one target LOS. For three target LOSs that are close to the Galactic plane, | {\\text{}}b| < 1°, we also present position-velocity maps of [C II] emission observed by Herschel Heterodyne Instrument in the Far Infrared (HIFI) in on-the-fly spectral-line mapping. We use the velocity-resolved [C II] spectra observed by the HIFI instrument toward the target LOSs observed by FUSE to identify [C II] velocity components associated with the H2 clouds. We analyze the observed velocity integrated [C II] spectral-line intensities in terms of the densities and thermal pressures in the H2 gas using the H2 column densities and temperatures measured by the UV absorption data. We present the H2 gas densities and thermal pressures for 26 target LOSs and from the [C II] intensities derive a mean thermal pressure in the range of ˜6100-7700 K cm-3 in diffuse H2 clouds. We discuss the thermal pressures and densities toward 14 targets, comparing them to results obtained using the UV absorption data for two other tracers C I and CO. Our results demonstrate the richness of the far-IR [C II] spectral data which is a valuable complement to the UV H2 absorption data for studying diffuse H2 molecular clouds. While the UV absorption is restricted to the directions of the target star, far-IR [C II] line emission offers an opportunity to employ velocity-resolved spectral-line mapping capability to study in detail the clouds’ spatial and velocity structures.

In-flight spectral performance monitoring of the Airborne Prism Experiment.

PubMed

D'Odorico, Petra; Alberti, Edoardo; Schaepman, Michael E

2010-06-01

Spectral performance of an airborne dispersive pushbroom imaging spectrometer cannot be assumed to be stable over a whole flight season given the environmental stresses present during flight. Spectral performance monitoring during flight is commonly accomplished by looking at selected absorption features present in the Sun, atmosphere, or ground, and their stability. The assessment of instrument performance in two different environments, e.g., laboratory and airborne, using precisely the same calibration reference, has not been possible so far. The Airborne Prism Experiment (APEX), an airborne dispersive pushbroom imaging spectrometer, uses an onboard in-flight characterization (IFC) facility, which makes it possible to monitor the sensor's performance in terms of spectral, radiometric, and geometric stability in flight and in the laboratory. We discuss in detail a new method for the monitoring of spectral instrument performance. The method relies on the monitoring of spectral shifts by comparing instrument-induced movements of absorption features on ground and in flight. Absorption lines originate from spectral filters, which intercept the full field of view (FOV) illuminated using an internal light source. A feature-fitting algorithm is used for the shift estimation based on Pearson's correlation coefficient. Environmental parameter monitoring, coregistered on board with the image and calibration data, revealed that differential pressure and temperature in the baffle compartment are the main driving parameters explaining the trend in spectral performance deviations in the time and the space (across-track) domains, respectively. The results presented in this paper show that the system in its current setup needs further improvements to reach a stable performance. Findings provided useful guidelines for the instrument revision currently under way. The main aim of the revision is the stabilization of the instrument for a range of temperature and pressure conditions to be encountered during operation.

Single-crystalline germanium nanomembrane photodetectors on foreign nanocavities

DOE PAGES

Xia, Zhenyang; Song, Haomin; Kim, Munho; ...

2017-07-07

Miniaturization of optoelectronic devices offers tremendous performance gain. As the volume of photoactive material decreases, optoelectronic performance improves, including the operation speed, the signal-to-noise ratio, and the internal quantum efficiency. Over the past decades, researchers have managed to reduce the volume of photoactive materials in solar cells and photodetectors by orders of magnitude. However, two issues arise when one continues to thin down the photoactive layers to the nanometer scale (for example, <50 nm). First, light-matter interaction becomes weak, resulting in incomplete photon absorption and low quantum efficiency. Second, it is difficult to obtain ultrathin materials with single-crystalline quality. Wemore » introduce a method to overcome these two challenges simultaneously. It uses conventional bulk semiconductor wafers, such as Si, Ge, and GaAs, to realize single-crystalline films on foreign substrates that are designed for enhanced light-matter interaction. We use a high-yield and high-throughput method to demonstrate nanometer-thin photodetectors with significantly enhanced light absorption based on nanocavity interference mechanism. As a result, these single-crystalline nanomembrane photodetectors also exhibit unique optoelectronic properties, such as the strong field effect and spectral selectivity.« less

Improving Assessments of Chlorophyll Concentration From In Situ Optical Measurements

NASA Astrophysics Data System (ADS)

Nardelli, S.; Twardowski, M.

2016-02-01

Florescence as a chlorophyll proxy has poor accuracy because it is dependent on specific absorption (effective molar absorptivity of packaged chlorophyll in living cells) and fluorescence quantum yield, both of which are highly variable. Absorption is a better proxy, as it is only dependent on specific absorption for packaged chlorophyll, although excepted accuracy in using a nominal specific absorption for all phytoplankton is still about 50%. Bricaud et al. (1995), Ciotti et al. (2002), Mouw et al. (2010), etc. have shown, however, that specific absorption is closely related to the average size of phytoplankton due to the relative packaging effect. Through other methods that have been developed over the years (Morel 1973; Diehl and Haart 1980; Boss et al. 2001; Slade and Boss 2015), it has been shown that measurements of spectral particulate attenuation (i.e., light transmission), and perhaps spectral particulate backscattering, can be used as simple proxies for the average size of the particle field. We therefore test the hypothesis that information on average particle size may be used to better estimate specific absorption for packaged chlorophyll, possibly enabling more accurate retrievals of chlorophyll concentration from optical measurements. The required optical measurements can be made with compact commercial off-the-shelf sensors with high sampling frequency that can be operated from autonomous vehicles; as a result, derived chlorophyll concentration could be resolved at far higher temporal and spatial frequency than is currently possible through extracting chlorophyll from discretely collected samples. This study examines the relationship between specific absorption and the attenuation spectral slope in extensive datasets from Case I and Case II waters found globally in an attempt to assess the link between pigment packaging and phytoplankton size dynamics and the impact on improving the derivation of chlorophyll from in situ optical measurements.

Compton scattering of self-absorbed synchrotron emission

NASA Astrophysics Data System (ADS)

Gao, He; Lei, Wei-Hua; Wu, Xue-Feng; Zhang, Bing

2013-11-01

Synchrotron self-Compton (SSC) scattering is an important emission mechanism in many astronomical sources, such as gamma-ray bursts (GRBs) and active galactic nuclei. We give a complete presentation of the analytical approximations for the Compton scattering of synchrotron emission with both weak and strong synchrotron self-absorption. All possible orders of the characteristic synchrotron spectral breaks (νa, νm and νc) are studied. In the weak self-absorption regime, i.e. νa < νc, the electron energy distribution is not modified by the self-absorption process. The shape of the SSC component broadly resembles that of synchrotron, but with the following features: The SSC flux increases linearly with frequency up to the SSC break frequency corresponding to the self-absorption frequency νa; and the presence of a logarithmic term in the high-frequency range of the SSC spectra makes it harder than the power-law approximation. In the strong absorption regime, i.e. νa > νc, heating of low-energy electrons due to synchrotron absorption leads to pile-up of electrons, and form a thermal component besides the broken power-law component. This leads to two-component (thermal + non-thermal) spectra for both the synchrotron and SSC spectral components. For νc < νa < νm, the spectrum is thermal (non-thermal) dominated if ν _a > √{ν _m ν _c} (ν _a < √{ν _m ν _c}). Similar to the weak-absorption regime, the SSC spectral component is broader than the simple broken power-law approximation. We derive the critical condition for strong absorption (electron pile-up), and discuss a case of GRB reverse shock emission in a wind medium, which invokes νa > max(νm, νc).

Non-invasive measurement of frog skin reflectivity in high spatial resolution using a dual hyperspectral approach.

PubMed

Pinto, Francisco; Mielewczik, Michael; Liebisch, Frank; Walter, Achim; Greven, Hartmut; Rascher, Uwe

2013-01-01

Most spectral data for the amphibian integument are limited to the visible spectrum of light and have been collected using point measurements with low spatial resolution. In the present study a dual camera setup consisting of two push broom hyperspectral imaging systems was employed, which produces reflectance images between 400 and 2500 nm with high spectral and spatial resolution and a high dynamic range. We briefly introduce the system and document the high efficiency of this technique analyzing exemplarily the spectral reflectivity of the integument of three arboreal anuran species (Litoria caerulea, Agalychnis callidryas and Hyla arborea), all of which appear green to the human eye. The imaging setup generates a high number of spectral bands within seconds and allows non-invasive characterization of spectral characteristics with relatively high working distance. Despite the comparatively uniform coloration, spectral reflectivity between 700 and 1100 nm differed markedly among the species. In contrast to H. arborea, L. caerulea and A. callidryas showed reflection in this range. For all three species, reflectivity above 1100 nm is primarily defined by water absorption. Furthermore, the high resolution allowed examining even small structures such as fingers and toes, which in A. callidryas showed an increased reflectivity in the near infrared part of the spectrum. Hyperspectral imaging was found to be a very useful alternative technique combining the spectral resolution of spectrometric measurements with a higher spatial resolution. In addition, we used Digital Infrared/Red-Edge Photography as new simple method to roughly determine the near infrared reflectivity of frog specimens in field, where hyperspectral imaging is typically difficult.

Synthetic Absorption Lines for a Clumpy Medium: A Spectral Signature for Cloud Acceleration in AGN?

NASA Technical Reports Server (NTRS)

Waters, Tim; Proga, Daniel; Dannen, Randall; Kallman, Timothy R.

2017-01-01

There is increasing evidence that the highly ionized multiphase components of AGN disc winds may be due to thermal instability. The ions responsible for forming the observed X-ray absorption lines may only exist in relatively cool clumps that can be identified with the so-called warm absorbers. Here we calculate synthetic absorption lines for such warm absorbers from first principles by combining 2D hydrodynamic solutions of a two-phase medium with a dense grid of photoionization models to determine the detailed ionization structure of the gas. Our calculations reveal that cloud disruption, which leads to a highly complicated velocity field (i.e. a clumpy flow), will only mildly affect line shapes and strengths when the warm gas becomes highly mixed but not depleted. Prior to complete disruption, clouds that are optically thin to the driving UV resonance lines will cause absorption at an increasingly blueshifted line-of-sight velocity as they are accelerated. This behavior will imprint an identifiable signature on the line profile if warm absorbers are enshrouded in an even broader absorption line produced by a high column of intercloud gas. Interestingly, we show that it is possible to develop a spectral diagnostic for cloud acceleration by differencing the absorption components of a doublet line, a result that can be qualitatively understood using a simple partial covering model. Our calculations also permit us to comment on the spectral differences between cloud disruption and ionization changes driven by flux variability. Notably, cloud disruption offers another possibility for explaining absorption line variability.

CdS/CdSe quantum dots and ZnPc dye co-sensitized solar cells with Au nanoparticles/graphene oxide as efficient modified layer.

PubMed

Chen, Cong; Cheng, Yu; Jin, Junjie; Dai, Qilin; Song, Hongwei

2016-10-15

Co-sensitization by using two or more sensitizers with complementary absorption spectra to expand the spectral response range is an effective approach to enhance device performance of quantum dot sensitized solar cells (QDSSCs). To improve the light-harvesting in the visible/near-infrared (NIR) region, organic dye zinc phthalocyanine (ZnPc) was combined with CdS/CdSe quantum dots (QDs) for co-sensitized solar cells based on ZnO inverse opals (IOs) as photoanode. The resulting co-sensitized device shows an efficient panchromatic spectral response feature to ∼750nm and presents an overall conversion efficiency of 4.01%, which is superior to that of the individual ZnPc-sensitized solar cells and CdS/CdSe-sensitized solar cells. Meanwhile, an Au nanoparticles/graphene oxide (Au NPs/GO) composite layer was successfully prepared to modify Cu2S counter electrode for the co-sensitized solar cells. Reducing the carrier recombination process by GO and catalytic process of Au NPs leads to increased power conversion efficiency(PCE) from 4.01 to 4.60% and sustainable stability remains ∼85% of its original value after 60min light exposure. In this paper, introduction of the organic dyes as co-sensitizer and Au NPs/GO as counter electrode modified layer has been proved to be an effective route to improve the performance of QDSSCs. Copyright © 2016 Elsevier Inc. All rights reserved.

Achieving high performance polymer tandem solar cells via novel materials design

NASA Astrophysics Data System (ADS)

Dou, Letian

Organic photovoltaic (OPV) devices show great promise in low-cost, flexible, lightweight, and large-area energy-generation applications. Nonetheless, most of the materials designed today always suffer from the inherent disadvantage of not having a broad absorption range, and relatively low mobility, which limit the utilization of the full solar spectrum. Tandem solar cells provide an effective way to harvest a broader spectrum of solar radiation by combining two or more solar cells with different absorption bands. However, for polymer solar cells, the performance of tandem devices lags behind single-layer solar cells mainly due to the lack of suitable low-bandgap polymers (near-IR absorbing polymers). In this dissertation, in order to achieve high performance, we focus on design and synthesis of novel low bandgap polymers specifically for tandem solar cells. In Chapter 3, I demonstrate highly efficient single junction and tandem polymer solar cells featuring a spectrally matched low-bandgap conjugated polymer (PBDTT-DPP: bandgap, ˜1.44 eV). The polymer has a backbone based on alternating benzodithiophene and diketopyrrolopyrrole units. A single-layer device based on the polymer provides a power conversion efficiency of ˜6%. When the polymer is applied to tandem solar cells, a power conversion efficiency of 8.62% is achieved, which was the highest certified efficiency for a polymer solar cell. To further improve this material system, in Chapter 4, I show that the reduction of the bandgap and the enhancement of the charge transport properties of the low bandgap polymer PBDTT-DPP can be accomplished simultaneously by substituting the sulfur atoms on the DPP unit with selenium atoms. The newly designed polymer PBDTT-SeDPP (Eg = 1.38 eV) shows excellent photovoltaic performance in single junction devices with PCEs over 7% and photo-response up to 900 nm. Tandem polymer solar cells based on PBDTT-SeDPP are also demonstrated with a 9.5% PCE, which are more than 10% enhancement over those based on PBDTT-DPP. Finally, in Chapter 5, I demonstrate a new polymer system based on alternating dithienopyran and benzothiadiazole units with a bandgap of 1.38 eV, high mobility, deep highest occupied molecular orbital. As a result, a single-junction device shows high external quantum efficiency of >60% and spectral response that extends to 900 nm, with a power conversion efficiency of 7.9%. The polymer enables a solution processed tandem solar cell with certified 10.6% power conversion efficiency under standard reporting conditions, which is the first certified polymer solar cell efficiency over 10%.

Identifying and classifying water hyacinth (Eichhornia crassipes) using the HyMap sensor

NASA Astrophysics Data System (ADS)

Rajapakse, Sepalika S.; Khanna, Shruti; Andrew, Margaret E.; Ustin, Susan L.; Lay, Mui

2006-08-01

In recent years, the impact of aquatic invasive species on biodiversity has become a major global concern. In the Sacramento-San Joaquin Delta region in the Central Valley of California, USA, dense infestations of the invasive aquatic emergent weed, water hyacinth (Eichhornia crassipes) interfere with ecosystem functioning. This silent invader constantly encroaches into waterways, eventually making them unusable by people and uninhabitable to aquatic fauna. Quantifying and mapping invasive plant species in aquatic ecosystems is important for efficient management and implementation of mitigation measures. This paper evaluates the ability of hyperspectral imagery, acquired using the HyMap sensor, for mapping water hyacinth in the Sacramento-San Joaquin Delta region. Classification was performed on sixty-four flightlines acquired over the study site using a decision tree which incorporated Spectral Angle Mapper (SAM) algorithm, absorption feature parameters in the spectral region between 0.4 and 2.5μm, and spectral endmembers. The total image dataset was 130GB. Spectral signatures of other emergent aquatic species like pennywort (Hydrocotyle ranunculoides) and water primrose (Ludwigia peploides) showed close similarity with the water hyacinth spectrum, however, the decision tree successfully discriminated water hyacinth from other emergent aquatic vegetation species. The classification algorithm showed high accuracy (κ value = 0.8) in discriminating water hyacinth.

A Fourier transform spectrometer without a beam splitter for the vacuum ultraviolet range: From the optical design to the first UV spectrum.

PubMed

de Oliveira, N; Joyeux, D; Phalippou, D; Rodier, J C; Polack, F; Vervloet, M; Nahon, L

2009-04-01

We describe a Fourier transform (FT) spectrometer designed to operate down to 60 nm (20 eV) on a synchrotron radiation beamline for high resolution absorption spectrometry. As far as we know, such an instrument is not available below 140 nm mainly because manufacturing accurate and efficient beam splitters remains a major problem at these wavelengths, especially if a wide bandwidth operation is desired. In order to overcome this difficulty, we developed an interferometer based on wave front division instead of amplitude division. It relies on a modified Fresnel bimirror configuration that requires only flat mirrors. The instrument provides path difference scanning through the translation of one reflector. During the scanning, the moving reflector is controlled by an optical system that keeps its direction constant within a tolerable value and provides an accurate interferometric measurement of the path difference variation. Therefore, a regular interferogram sampling is obtained, producing a nominal spectral impulse response and an accurate spectral calibration. The first results presented in this paper show a measured spectral resolution of delta(sigma)=0.33 cm-1 (interval between spectral samples). This was obtained with a sampling interval of 29 nm (path difference) and 512 K samples from a one-sided interferogram using a cosine FT. Such a sampling interval should allow the recording of large bandwidth spectra down to lambda=58 nm with an ultimate resolving power of 500,000 at this wavelength. In order to check the instrument performances, we first recorded an interferogram from a He-Ne stabilized laser. This provided the actual spectral impulse function, which was found to be fully satisfactory. The determination of the impulse response distortion and of the noise on the vacuum ultraviolet (VUV) spectral range provided accurate information in the sampling error profile over a typical scan. Finally, the instrument has been moved to the SU5 undulator-based synchrotron radiation beamline (Super-ACO facility, LURE, Orsay, France). A high resolution spectrum of O2 (the Schumann-Runge absorption bands, 185-200 nm) was computed from recorded interferograms using the beamline monochromator at the zeroth order to feed the instrument with an 11% relative bandwidth "white" beam (2003). These UV measurements are very close to those found in the literature, showing nominal performances of the FT spectrometer that should translate into an unprecedented resolving power at shortest VUV wavelengths. A recent upgrade (2007) and future developments will be discussed in light of the current installation of the upgraded FT spectrometer as a permanent endstation for ultrahigh resolution absorption spectrometry on the VUV beamline DESIRS at SOLEIL, the new French third generation synchrotron facility.

Modelling the light absorption coefficients of oceanic waters: Implications for underwater optical applications

NASA Astrophysics Data System (ADS)

Prabhakaran, Sai Shri; Sahu, Sanjay Kumar; Dev, Pravin Jeba; Shanmugam, Palanisamy

2018-05-01

Spectral absorption coefficients of particulate (algal and non-algal components) and dissolved substances are modelled and combined with the pure seawater component to determine the total light absorption coefficients of seawater in the Bay of Bengal. Two parameters namely chlorophyll-a (Chl) concentration and turbidity were measured using commercially available instruments with high sampling rates. For modelling the light absorption coefficients of oceanic waters, the measured data are classified into two broad groups - algal dominant and non-algal particle (NAP) dominant. With these criteria the individual absorption coefficients of phytoplankton and NAP were established based on their concentrations using an iterative method. To account for the spectral dependence of absorption by phytoplankton, the wavelength-dependent coefficients were introduced into the model. The CDOM absorption was determined by subtracting the individual absorption coefficients of phytoplankton and NAP from the measured total absorption data and then related to the Chl concentration. Validity of the model is assessed based on independent in-situ data from certain discrete locations in the Bay of Bengal. The total absorption coefficients estimated using the new model by considering the contributions of algal, non-algal and CDOM have good agreement with the measured total absorption data with the error range of 6.9 to 28.3%. Results obtained by the present model are important for predicting the propagation of the radiant energy within the ocean and interpreting remote sensing observation data.

Simulations of absorption spectra of conjugated oligomers: role of planar conformation and aggregation in condensed phase

NASA Astrophysics Data System (ADS)

Yuan, Xiang-Ai; Wen, Jin; Zheng, Dong; Ma, Jing

2018-04-01

This Review highlights the structure/property relationship underlying the morphology modulation through various factors towards the exploration of light-absorbing materials for efficient utilisation of solar power. Theoretical study using a combination of molecular dynamics imulations and the time-dependent density functional theory demonstrated that the planarity plays an important role in tuning spectral properties of oligomer aggregates. The aggregation-induced blue-shift in absorption spectra of oligothiophenes and the red-shift for oligofluorenols were rationalised in a unified way from the reduced (and increased) content of planar conformations in molecular aggregates. The planarity versus non-planarity of oligomers can be modulated by introduction of alkyl side chain or steric bulky substituents. The substitution with various groups in the ortho-position of azobenzene leads to the distorted backbone, breaking symmetry, and hence the red-shift in spectra, expanding the application in biological systems with visible light absorption. The donor-acceptor substituent groups in conjugated oligomers can increase the degree of planarity, electron delocalisation and polarisation, and charge separation, giving rise to the red-shift in spectra and enhancement in polarisability and charge mobility for device applications. The solvent dependent and pH-sensitive properties and intramolecular hydrogen bonds also caused the shift of absorption spectra with the appearance of planar conformers.

Mapping minerals, amorphous materials, environmental materials, vegetation, water, ice and snow, and other materials: The USGS tricorder algorithm

NASA Technical Reports Server (NTRS)

Clark, Roger N.; Swayze, Gregg A.

1995-01-01

One of the challenges of Imaging Spectroscopy is the identification, mapping and abundance determination of materials, whether mineral, vegetable, or liquid, given enough spectral range, spectral resolution, signal to noise, and spatial resolution. Many materials show diagnostic absorption features in the visual and near infrared region (0.4 to 2.5 micrometers) of the spectrum. This region is covered by the modern imaging spectrometers such as AVIRIS. The challenge is to identify the materials from absorption bands in their spectra, and determine what specific analyses must be done to derive particular parameters of interest, ranging from simply identifying its presence to deriving its abundance, or determining specific chemistry of the material. Recently, a new analysis algorithm was developed that uses a digital spectral library of known materials and a fast, modified-least-squares method of determining if a single spectral feature for a given material is present. Clark et al. made another advance in the mapping algorithm: simultaneously mapping multiple minerals using multiple spectral features. This was done by a modified-least-squares fit of spectral features, from data in a digital spectral library, to corresponding spectral features in the image data. This version has now been superseded by a more comprehensive spectral analysis system called Tricorder.

Spectral Classification of Heavily Reddened Stars by CO Absorption Strength

NASA Astrophysics Data System (ADS)

Garling, Christopher; Bary, Jeffrey S.; Huard, Tracy L.

2017-01-01

The nature of dust grains in dense molecular clouds can be explored by obtaining spectra of giant stars located behind the clouds and examining the wavelength-dependent attentuation of their light. This approach requires the intrinsic spectra of the background stars to be known, which can be achieved by determining their spectral types. In the K-band spectra of cool giant stars, several temperature-sensitive CO absorption bands serve as good spectral type indicators. Taking advantage of the SpeX Infrared Telescope Facility Spectral Library, near-infrared spectra collected with TripleSpec and the 3.5-meter ARC Telescope at Apache Point Observatory, and a previously constructed CO spectral index, we make precise spectral determinations of 20 giant stars located behind two dense cloud cores: CB188 and L429C. With spectral types in hand, we then utilize Markov Chain Monte Carlo techniques to constrain extinctions along these lines of sight. The spectral typing method will be described and assessed as well as its success at finding a couple of incorrectly spectral typed stars in the SpeX Library. Funding for this program was provided by a NSF REU grant to the Keck Northeast Astronomy Consortium and a grant from the NASA Astrophysics Data Analysis Program.

Solar Spectral Irradiance and Climate

NASA Technical Reports Server (NTRS)

Pilewskie, P.; Woods, T.; Cahalan, R.

2012-01-01

Spectrally resolved solar irradiance is recognized as being increasingly important to improving our understanding of the manner in which the Sun influences climate. There is strong empirical evidence linking total solar irradiance to surface temperature trends - even though the Sun has likely made only a small contribution to the last half-century's global temperature anomaly - but the amplitudes cannot be explained by direct solar heating alone. The wavelength and height dependence of solar radiation deposition, for example, ozone absorption in the stratosphere, absorption in the ocean mixed layer, and water vapor absorption in the lower troposphere, contribute to the "top-down" and "bottom-up" mechanisms that have been proposed as possible amplifiers of the solar signal. New observations and models of solar spectral irradiance are needed to study these processes and to quantify their impacts on climate. Some of the most recent observations of solar spectral variability from the mid-ultraviolet to the near-infrared have revealed some unexpected behavior that was not anticipated prior to their measurement, based on an understanding from model reconstructions. The atmospheric response to the observed spectral variability, as quantified in climate model simulations, have revealed similarly surprising and in some cases, conflicting results. This talk will provide an overview on the state of our understanding of the spectrally resolved solar irradiance, its variability over many time scales, potential climate impacts, and finally, a discussion on what is required for improving our understanding of Sun-climate connections, including a look forward to future observations.

Contrast-enhanced spectral mammography with a photon-counting detector.

PubMed

Fredenberg, Erik; Hemmendorff, Magnus; Cederström, Björn; Aslund, Magnus; Danielsson, Mats

2010-05-01

Spectral imaging is a method in medical x-ray imaging to extract information about the object constituents by the material-specific energy dependence of x-ray attenuation. The authors have investigated a photon-counting spectral imaging system with two energy bins for contrast-enhanced mammography. System optimization and the potential benefit compared to conventional non-energy-resolved absorption imaging was studied. A framework for system characterization was set up that included quantum and anatomical noise and a theoretical model of the system was benchmarked to phantom measurements. Optimal combination of the energy-resolved images corresponded approximately to minimization of the anatomical noise, which is commonly referred to as energy subtraction. In that case, an ideal-observer detectability index could be improved close to 50% compared to absorption imaging in the phantom study. Optimization with respect to the signal-to-quantum-noise ratio, commonly referred to as energy weighting, yielded only a minute improvement. In a simulation of a clinically more realistic case, spectral imaging was predicted to perform approximately 30% better than absorption imaging for an average glandularity breast with an average level of anatomical noise. For dense breast tissue and a high level of anatomical noise, however, a rise in detectability by a factor of 6 was predicted. Another approximately 70%-90% improvement was found to be within reach for an optimized system. Contrast-enhanced spectral mammography is feasible and beneficial with the current system, and there is room for additional improvements. Inclusion of anatomical noise is essential for optimizing spectral imaging systems.

Absorption spectroscopy setup for determination of whole human blood and blood-derived materials spectral characteristics

NASA Astrophysics Data System (ADS)

Wróbel, M. S.; Gnyba, M.; Milewska, D.; Mitura, K.; Karpienko, K.

2015-09-01

A dedicated absorption spectroscopy system was set up using tungsten-halogen broadband source, optical fibers, sample holder, and a commercial spectrometer with CCD array. Analysis of noise present in the setup was carried out. Data processing was applied to the absorption spectra to reduce spectral noise, and improve the quality of the spectra and to remove the baseline level. The absorption spectra were measured for whole blood samples, separated components: plasma, saline, washed erythrocytes in saline and human whole blood with biomarkers - biocompatible nanodiamonds (ND). Blood samples had been derived from a number of healthy donors. The results prove a correct setup arrangement, with adequate preprocessing of the data. The results of blood-ND mixtures measurements show no toxic effect on blood cells, which proves the NDs as a potential biocompatible biomarkers.

Quantitative Measurement of Protease-Activity with Correction of Probe Delivery and Tissue Absorption Effects

PubMed Central

Salthouse, Christopher D.; Reynolds, Fred; Tam, Jenny M.; Josephson, Lee; Mahmood, Umar

2009-01-01

Proteases play important roles in a variety of pathologies from heart disease to cancer. Quantitative measurement of protease activity is possible using a novel spectrally matched dual fluorophore probe and a small animal lifetime imager. The recorded fluorescence from an activatable fluorophore, one that changes its fluorescent amplitude after biological target interaction, is also influenced by other factors including imaging probe delivery and optical tissue absorption of excitation and emission light. Fluorescence from a second spectrally matched constant (non-activatable) fluorophore on each nanoparticle platform can be used to correct for both probe delivery and tissue absorption. The fluorescence from each fluorophore is separated using fluorescence lifetime methods. PMID:20161242

High Spectral Resolution Lidar Measurements Using an I2 Absorption Filter

NASA Technical Reports Server (NTRS)

Eloranta, E. W.; Piironen, P.

1996-01-01

The University of Wisconsin high spectral resolution lidar (HSRL) measures optical properties of the atmosphere by separating the Doppler-broadened molecular backscatter return from the unbroadened aerosol return. The HSRL was modified to use an I2 absorption cell The modified HSRL transmitter uses a continuously pumped, Q-switched, injection seeded, frequency doubled Nd:YAG laser operating at a 4 kHz pulse repetition rate. This laser is tunable over a 124 GHz frequency range by temperature tuning the seed laser under computer control.

Isothermal crystallization of poly(3-hydroxybutyrate) studied by terahertz two-dimensional correlation spectroscopy

NASA Astrophysics Data System (ADS)

Hoshina, Hiromichi; Ishii, Shinya; Morisawa, Yusuke; Sato, Harumi; Noda, Isao; Ozaki, Yukihiro; Otani, Chiko

2012-01-01

The isothermal crystallization of poly(3-hydroxybutylate) (PHB) was studied by monitoring the temporal evolution of terahertz absorption spectra in conjunction with spectral analysis using two-dimensional correlation spectroscopy. Correlation between the absorption peaks and the sequential order of the changes in spectral intensity extracted from synchronous and asynchronous plots indicated that crystallization of PHB at 90 °C is a two step process, in which C-H...O=C hydrogen bonds are initially formed before well-defined crystal structures are established.

Apparatus And Methods For Launching And Receiving A Broad Wavelength Range Source

DOEpatents

Von Drasek, William A.; Sonnenfroh, David; Allen, Mark G.; Stafford-Evans, Joy

2006-02-28

An apparatus and method for simultaneous detection of N gas species through laser radiation attenuation techniques is disclosed. Each of the N species has a spectral absorption band. N laser sources operate at a wavelength ?N in a spectral absorption band separated by the cutoff wavelength for single-mode transmission. Each laser source corresponds to a gas species and transmits radiation through an optical fiber constructed and arranged to provide single-mode transmission with minimal power loss.

Coupling of Luminescent Solar Concentrators to Plasmonic Solar Cells

NASA Astrophysics Data System (ADS)

Wang, Shu-Yi

To make inexpensive solar cells is a continuous goal for solar photovoltaic (PV) energy industry. Thin film solar cells of various materials have been developed and continue to emerge in order to replace bulk silicon solar cells. A thin film solar cell not only uses less material but also requires a less expensive refinery process. In addition, other advantages coming along with small thickness are higher open circuit voltage and higher conversion efficiency. However, thin film solar cells, especially those made of silicon, have significant optical losses. In order to address this problem, this thesis investigates the spectral coupling of thin films PV to luminescent solar concentrators (LSC). LSC are passive devices, consisting of plastic sheets embedded with fluorescent dyes which absorb part of the incoming radiation spectrum and emit at specific wavelength. The emitted light is concentrated by total internal reflection to the edge of the sheet, where the PVs are placed. Since the light emitted from the LSC edge is usually in a narrow spectral range, it is possible to employ diverse strategies to enhance PV absorption at the peak of the emission wavelength. Employing plasmonic nanostructures has been shown to enhance absorption of thin films via forward scattering, diffraction and localized surface plasmon. These two strategies are theoretically investigated here for improving the absorption and elevating the output power of a thin film solar cell. First, the idea of spectral coupling of luminescent solar concentrators to plasmonic solar cells is introduced to assess its potential for increasing the power output. This study is carried out employing P3HT/PC60BM organic solar cells and LSC with Lumogen Red dyes. A simplified spectral coupling analysis is employed to predict the power density, considering the output spectrum of the LSC equivalent to the emission spectrum of the dye and neglecting any angular dependence. Plasmonic tuning is conducted to enhance absorption at the emission peak of the dye. A factorial increase in the output power density of coupled PV as compared to PV exposed directly to solar spectrum is observed for high light concentration on the edge. These initial results motivated a more in-depth study of coupled LSC-PV system, which took into account the radiative transport inside the realistic LSC. These investigations were carried out on LSCs using Lumogen Red305 and Rhodamine 6G dyes coupled to pristine and plasmonic ultra-thin film silicon solar cells. Prediction based on detailed balance shows that the coupled LSC-plasmonic solar cell can generate 63.7 mW/cm2 with a photocurrent density of 71.3 mA/cm2 which is higher than that of cSi solar cells available on current market. The second part of the thesis focuses on PV absorption enhancement techniques. First, the effect of vertical positioning of plasmonic nanostructures on absorption enhancement was theoretically investigated to understand which one of the three mechanisms usually responsible for the enhancement (forward scattering, diffraction and localized surface plamson) plays the dominant role. Simulation results suggested that the maximum enhancement occurred when placing the nanostructures in the rear side of the cell because of longer path length due to scattering. The experimental effort then switched focus on substrate patterning, which is a less expensive alternative to plasmonic absorption enhancement. Specifically, a nanostructured substrate was prepared by a simple electrochemical process based on two-step aluminum anodization technique. The absorption of thin film silicon deposited on these substrates showed a broadband enhancement. The overall photocurrent density was up to 40% higher than that of films deposited on flat substrates. In conclusion, the studies carried out in this thesis indicate that spectral coupling of LSCs to thin film solar cells could lead to significant improvements in PV output power density. Moreover, while the absorption of thin film solar cells can be enhanced by plasmonic nanostructures, it is shown that alternative methods, such as direct deposition of the films on inexpensively nanostructured substrates could also be employed to obtain significant enhancements. Combining these strategies may lead to inexpensive solar power harvesting systems with significant economic benefits. These strategies are not material-specific but applicable to a wide range of thin film solar cells.

Attenuated total reflectance spectroscopy of plant leaves: A tool for ecological and botanical studies

USGS Publications Warehouse

Ribeiro da Luz, B.

2006-01-01

??? Attenuated total reflectance (ATR) spectra of plant leaves display complex absorption features related to organic constituents of leaf surfaces. The spectra can be recorded rapidly, both in the field and in the laboratory, without special sample preparation. ??? This paper explores sources of ATR spectral variation in leaves, including compositional, positional and temporal variations. Interspecific variations are also examined, including the use of ATR spectra as a tool for species identification. ??? Positional spectral variations generally reflected the abundance of cutin and the epicuticular wax thickness and composition. For example, leaves exposed to full sunlight commonly showed more prominent cutin- and wax-related absorption features compared with shaded leaves. Adaxial vs. abaxial leaf surfaces displayed spectral variations reflecting differences in trichome abundance and wax composition. Mature vs. young leaves showed changes in absorption band position and intensity related to cutin, polysaccharide, and possibly amorphous silica development on and near the leaf surfaces. ??? Provided that similar samples are compared (e.g. adaxial surfaces of mature, sun-exposed leaves) same-species individuals display practically identical ATR spectra. Using spectral matching procedures to analyze an ATR database containing 117 individuals, including 32 different tree species, 83% of the individuals were correctly identified. ?? The Authors (2006).

The New MODIS-Terra, and the Proposed COBRA Mission: First Global Aerosol Distribution and Properties Over Land and Ocean, and Plans to Measure Global Black Carbon Absorption Over the Ocean Glint

NASA Technical Reports Server (NTRS)

Kaufman, Yoram J.; Tanre, Didier; Remer, Lorraine; Martins, Vanderlei; Schoeberl, Mark; Lau, William K. M. (Technical Monitor)

2001-01-01

The MODIS instrument was launched on the NASA Terra satellite in Dec. 1999. Since last Oct, the sensor and the aerosol algorithm reached maturity and provide global daily retrievals of aerosol optical thickness and properties. MODIS has 36 spectral channels in the visible to IR with resolution down to 250 m. This allows accurate cloud screening and multi-spectral aerosol retrievals. We derive the aerosol optical thickness over the ocean and most of the land areas, distinguishing between fine (mainly man-made aerosol) and coarse (mainly natural) aerosol particles. New methods to derive the aerosol absorption of sunlight are also being developed. These measurements are use to track different aerosol sources, transport and the radiative forcing at the top and bottom of the atmosphere. However MODIS or any present satellite sensor cannot measure absorption by Black Carbon over the oceans, a critical component in studying climate change and human health. For this purpose we propose the COBRA mission that observes the ocean at glint and off glint simultaneously measuring the spectral polarized light and deriving precisely the aerosol absorption.

Highly vibrationally excited O2 molecules in low-pressure inductively-coupled plasmas detected by high sensitivity ultra-broad-band optical absorption spectroscopy

NASA Astrophysics Data System (ADS)

Foucher, Mickaël; Marinov, Daniil; Carbone, Emile; Chabert, Pascal; Booth, Jean-Paul

2015-08-01

Inductively-coupled plasmas in pure O2 (at pressures of 5-80 mTorr and radiofrequency power up to 500 W) were studied by optical absorption spectroscopy over the spectral range 200-450 nm, showing the presence of highly vibrationally excited O2 molecules (up to vʺ = 18) by Schumann-Runge band absorption. Analysis of the relative band intensities indicates a vibrational temperature up to 10,000 K, but these hot molecules only represent a fraction of the total O2 density. By analysing the (11-0) band at higher spectral resolution the O2 rotational temperature was also determined, and was found to increase with both pressure and power, reaching 900 K at 80 mTorr 500 W. These measurements were achieved using a new high-sensitivity ultra-broad-band absorption spectroscopy setup, based on a laser-plasma light source, achromatic optics and an aberration-corrected spectrograph. This setup allows the measurement of weak broadband absorbances due to a baseline variability lower than 2   ×   10-5 across a spectral range of 250 nm.

High-resolution UV-visible spectroscopy of lunar red spots

NASA Technical Reports Server (NTRS)

Bruno, B. C.; Lucey, P. G.; Hawke, B. R.

1991-01-01

A spectral reflectance study of selected lunar 'red spots', highland areas characterized by an absorption in the ultraviolet relative to the visible was conducted. Some red spots were suggested to be the sites of ancient highland volcanism. High-resolution spectral data of eight red spots on the western portion of the moon over the wavelength region 0.39-0.82 micron were obtained. Much spectral variation among these red spots in the magnitude as well as the wavelength position of the ultraviolet absorption were found. Spectral structure at visible and near-infrared wavelength were also identified. These spectral differences indicate that red spots do not have a single mineralogical composition, which in turn suggests that red spots may have multiple origins. Additional imaging spectroscopic observations were taken of the Herigonius red spot, a morphologically complex region northeast of Mare Humorum. These data reveal significant spectral differences among the various morphological units within the Herigonius red spot. Although some of these are likely due to the effects of the maturation process, others appear to reflect differences in mineral abundances and composition.

Remote Sensing of Non-Aerosol (anomalous) Absorption in Cloud Free Atmosphere

NASA Technical Reports Server (NTRS)

Kaufman, Yoram J.; Dubovik, Oleg; Smirnov, Alexander; Holben, Brent N.; Lau, William K. M. (Technical Monitor)

2001-01-01

The interaction of sunlight with atmospheric gases, aerosols and clouds is fundamental to the understanding of climate and its variation. Several studies questioned our understanding of atmospheric absorption of sunlight in cloudy or in cloud free atmospheres. Uncertainty in instruments' accuracy and in the analysis methods makes this problem difficult to resolve. Here we use several years of measurements of sky and sun spectral brightness by selected instruments of the Aerosol Robotic Network (AERONET), that have known and high measurement accuracy. The measurements taken in several locations around the world show that in the atmospheric windows 0.44, 0.06, 0.86 and 1.02 microns the only significant absorbers in cloud free atmosphere is aerosol and ozone. This conclusions is reached using a method developed to distinguish between absorption associated with the presence of aerosol and absorption that is not related to the presence of aerosol. Non-aerosol absorption, defined as spectrally independent or smoothly variable, was found to have an optical thickness smaller than 0.002 corresponding to absorption of sunlight less than 1W/sq m, or essentially zero.

Smile effect detection for dispersive hypersepctral imager based on the doped reflectance panel

NASA Astrophysics Data System (ADS)

Zhou, Jiankang; Liu, Xiaoli; Ji, Yiqun; Chen, Yuheng; Shen, Weimin

2012-11-01

Hyperspectral imager is now widely used in many regions, such as resource development, environmental monitoring and so on. The reliability of spectral data is based on the instrument calibration. The smile, wavelengths at the center pixels of imaging spectrometer detector array are different from the marginal pixels, is a main factor in the spectral calibration because it can deteriorate the spectral data accuracy. When the spectral resolution is high, little smile can result in obvious signal deviation near weak atmospheric absorption peak. The traditional method of detecting smile is monochromator wavelength scanning which is time consuming and complex and can not be used in the field or at the flying platform. We present a new smile detection method based on the holmium oxide panel which has the rich of absorbed spectral features. The higher spectral resolution spectrometer and the under-test imaging spectrometer acquired the optical signal from the Spectralon panel and the holmium oxide panel respectively. The wavelength absorption peak positions of column pixels are determined by curve fitting method which includes spectral response function sequence model and spectral resampling. The iteration strategy and Pearson coefficient together are used to confirm the correlation between the measured and modeled spectral curve. The present smile detection method is posed on our designed imaging spectrometer and the result shows that it can satisfy precise smile detection requirement of high spectral resolution imaging spectrometer.

Conversion efficiency versus sensitizer for electrospun TiO2 nanorod electrodes in dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Jose, R.; Kumar, A.; Thavasi, V.; Ramakrishna, S.

2008-10-01

The electrochemical and optical properties of three indoline dyes, namely C35H28N2O2 (D131), C37H30N2O3S2 (D102), and C42H35N3O4S3 (D149), were studied and compared with that of the N3 dye. D131 has the largest bandgap and lowest unoccupied molecular orbital (LUMO) energies compared to the other dyes. A size-dependent variation in the absorptivity of the indoline dyes was observed—the absorptivity increased with increase in the molecular size. The dyes were anchored onto TiO2 nanorods. The TiO2 nanorods were obtained by electrospinning a polymeric solution containing titanium isopropoxide and polyvinylpyrrolidone and subsequent sintering of the as-spun composite fibers. Absorption spectral measurements of the dye-anchored TiO2 showed blue shifts in the excitonic transition of the indoline dyes, the magnitude of which increased with decrease in the molecular size. Dye-sensitized solar cells (DSSCs) were fabricated using the indoline dyes, TiO2 nanorods, and iodide/triiodide electrolyte. The D131 dye showed comparable energy conversion efficiency (η) to that of the N3 dye. A systematic change in the short circuit current density (JSC) and η of the indoline DSSCs was observed. The observed variation in JC is most likely originated from the difference in the electronic coupling strengths between the dye and the TiO2.

High-efficiency near-infrared enabled planar perovskite solar cells by embedding upconversion nanocrystals.

PubMed

Meng, Fan-Li; Wu, Jiao-Jiao; Zhao, Er-Fei; Zheng, Yan-Zhen; Huang, Mei-Lan; Dai, Li-Ming; Tao, Xia; Chen, Jian-Feng

2017-11-30

Integration of the upconversion effect in perovskite solar cells (PSCs) is a facile approach towards extending the spectral absorption from the visible to the near infrared (NIR) range and reducing the non-absorption loss of solar photons. However, the big challenge for practical application of UCNCs in planar PSCs is the poor compatibility between UCNCs and the perovskite precursor. Herein, we have subtly overcome the tough compatibility issue using a ligand-exchange strategy. For the first time, β-NaYF 4 :Yb,Er UCNCs have been embedded in situ into a CH 3 NH 3 PbI 3 layer to fabricate NIR-enabled planar PSCs. The CH 3 NH 3 I-capped UCNCs generated from the ligand-exchange were mixed with the perovskite precursor and served as nucleation sites for the UCNC-mediated heteroepitaxial growth of perovskite; moreover, the in situ embedding of UCNCs into the perovskite layer was realized during a spin-coating process. The resulting UCNC-embedded perovskite layer attained a uniform pinhole-free morphology with enlarged crystal grains and enabled NIR absorption. It also contributed to the energy transfer from the UCNCs to the perovskite and electron transport to the collecting electrode surface. The device fabricated using the UCNC-embedded perovskite film achieved an average power-conversion efficiency of 18.60% (19.70% for the best) under AM 1.5G and 0.37% under 980 nm laser, corresponding to 54% and 740-fold increase as compared to that of its counterpart without UCNCs.

Absolute ozone absorption cross section in the Huggins Chappuis minimum (350-470 nm) at 296 K

NASA Astrophysics Data System (ADS)

Axson, J. L.; Washenfelder, R. A.; Kahan, T. F.; Young, C. J.; Vaida, V.; Brown, S. S.

2011-08-01

We report the ozone absolute absorption cross section between 350-470 nm, the minimum between the Huggins and Chappuis bands, where the ozone cross section is less than 10-22 cm2. Ozone spectra were acquired using an incoherent broadband cavity enhanced absorption spectrometer, with three channels centered at 365, 405, and 455 nm. The accuracy of the measured cross section is 2 %. Previous measurements vary by more than an order of magnitude in this spectral region. The measurements reported here provide much greater spectral coverage than the most recent measurements. We report a minimum absorption cross section of 3.4×10-24 cm2 at 381.8 nm, which is 22 % lower than the previously reported value. The effect of O3 concentration and water vapor partial pressure were investigated, however there were no observable changes in the absorption spectrum most likely due to the low optical density of the complex.

Characterization of aerosol scattering and spectral absorption by unique methods: a polar/imaging nephelometer and spectral reflectance measurements of aerosol samples collected on filters

NASA Astrophysics Data System (ADS)

Dolgos, Gergely; Martins, J. Vanderlei; Remer, Lorraine A.; Correia, Alexandre L.; Tabacniks, Manfredo; Lima, Adriana R.

2010-02-01

Characterization of aerosol scattering and absorption properties is essential to accurate radiative transfer calculations in the atmosphere. Applications of this work include remote sensing of aerosols, corrections for aerosol distortions in satellite imagery of the surface, global climate models, and atmospheric beam propagation. Here we demonstrate successful instrument development at the Laboratory for Aerosols, Clouds and Optics at UMBC that better characterizes aerosol scattering phase matrix using an imaging polar nephelometer (LACO-I-Neph) and enables measurement of spectral aerosol absorption from 200 nm to 2500 nm. The LACO-I-Neph measures the scattering phase function from 1.5° to 178.5° scattering angle with sufficient sensitivity to match theoretical expectations of Rayleigh scattering of various gases. Previous measurements either lack a sufficiently wide range of measured scattering angles or their sensitivity is too low and therefore the required sample amount is prohibitively high for in situ measurements. The LACO-I-Neph also returns expected characterization of the linear polarization signal of Rayleigh scattering. Previous work demonstrated the ability of measuring spectral absorption of aerosol particles using a reflectance technique characterization of aerosol samples collected on Nuclepore filters. This first generation methodology yielded absorption measurements from 350 nm to 2500 nm. Here we demonstrate the possibility of extending this wavelength range into the deep UV, to 200 nm. This extended UV region holds much promise in identifying and characterizing aerosol types and species. The second generation, deep UV, procedure requires careful choice of filter substrates. Here the choice of substrates is explored and preliminary results are provided.

Evaluation of the in vivo and ex vivo optical properties in a mouse ear model

NASA Astrophysics Data System (ADS)

Salomatina, E.; Yaroslavsky, A. N.

2008-06-01

Determination of in vivo optical properties is a challenging problem. Absorption and scattering measured ex vivo are often used for in vivo applications. To investigate the validity of this approach, we have obtained and compared the optical properties of mouse ears in vivo and ex vivo in the spectral range from 370 to 1650 nm. Integrating sphere spectrophotometry in combination with the inverse Monte Carlo technique was employed to determine absorption coefficients, μa, scattering coefficients, μs, and anisotropy factors, g. Two groups of mice were used for the study. The first group was measured in vivo and ex vivo within 5-10 min post mortem. The second group was measured in vivo and ex vivo every 24 h for up to 72 h after sacrifice. Between the measurements the tissues were kept at 4 °C wrapped in a gauze moistened with saline solution. Then the specimens were frozen at -25 °C for 40 min, thawed and measured again. The results indicate that the absorption coefficients determined in vivo and ex vivo within 5-10 min post mortem differed considerably only in the spectral range dominated by hemoglobin. These changes can be attributed to rapid deoxygenation of tissue and blood post mortem. Absorption coefficients determined ex vivo up to 72 h post mortem decreased gradually with time in the spectral regions dominated by hemoglobin and water, which can be explained by the continuing loss of blood. Absorption properties of the frozen-thawed ex vivo tissues showed increase in oxygenation, which is likely caused by the release of hemoglobin from hemolyzed erythrocytes. Scattering of the ex vivo tissues decreased gradually with time in the entire spectral range due to the continuing loss of blood and partial cell damage. Anisotropy factors did not change considerably.

Evaluation of the in vivo and ex vivo optical properties in a mouse ear model.

PubMed

Salomatina, E; Yaroslavsky, A N

2008-06-07

Determination of in vivo optical properties is a challenging problem. Absorption and scattering measured ex vivo are often used for in vivo applications. To investigate the validity of this approach, we have obtained and compared the optical properties of mouse ears in vivo and ex vivo in the spectral range from 370 to 1650 nm. Integrating sphere spectrophotometry in combination with the inverse Monte Carlo technique was employed to determine absorption coefficients, mu(a), scattering coefficients, mu(s), and anisotropy factors, g. Two groups of mice were used for the study. The first group was measured in vivo and ex vivo within 5-10 min post mortem. The second group was measured in vivo and ex vivo every 24 h for up to 72 h after sacrifice. Between the measurements the tissues were kept at 4 degrees C wrapped in a gauze moistened with saline solution. Then the specimens were frozen at -25 degrees C for 40 min, thawed and measured again. The results indicate that the absorption coefficients determined in vivo and ex vivo within 5-10 min post mortem differed considerably only in the spectral range dominated by hemoglobin. These changes can be attributed to rapid deoxygenation of tissue and blood post mortem. Absorption coefficients determined ex vivo up to 72 h post mortem decreased gradually with time in the spectral regions dominated by hemoglobin and water, which can be explained by the continuing loss of blood. Absorption properties of the frozen-thawed ex vivo tissues showed increase in oxygenation, which is likely caused by the release of hemoglobin from hemolyzed erythrocytes. Scattering of the ex vivo tissues decreased gradually with time in the entire spectral range due to the continuing loss of blood and partial cell damage. Anisotropy factors did not change considerably.

Improving confocal microscopy with solid-state semiconductor excitation sources

NASA Astrophysics Data System (ADS)

Sivers, Nelson L.

To efficiently excite the fluorescent dyes used in imaging biological samples with a confocal microscope, the wavelengths of the exciting laser must be near the fluorochrome absorption peak. However, this causes imaging problems when the fluorochrome absorption and emission spectra overlap significantly, i.e. have small Stokes shifts, which is the case for most fluorochromes that emit in the red to infrared. As a result, the reflected laser excitation cannot be distinguished from the information-containing fluorescence signal. However, cryogenically cooling the exciting laser diode enabled the laser emission wavelengths to be tuned to shorter wavelengths, decreasing the interference between the laser and the fluorochrome's fluorescence. This reduced the amount of reflected laser light in the confocal image. However, the cooled laser diode's shorter wavelength signal resulted in slightly less efficient fluorochrome excitation. Spectrophotometric analysis showed that as the laser diodes were cooled, their output power increased, which more than compensated for the lower fluorochrome excitation and resulted in significantly more intense fluorescence. Thus, by tuning the laser diode emission wavelengths away from the fluorescence signal, less reflected laser light and more fluorescence information reached the detector, creating images with better signal to noise ratios. Additionally, new, high, luminous flux, light-emitting diodes (LEDs) are now powerful enough to create confocal fluorescence signals comparable to those produced by the traditional laser excitation sources in fluorescence confocal microscopes. The broader LED spectral response effectively excited the fluorochrome, yet was spectrally limited enough for standard filter sets to separate the LED excitation from the fluorochrome fluorescence signal. Spectrophotometric analysis of the excitation and fluorescence spectra of several fluorochromes showed that high-powered, LED-induced fluorescence contained the same spectral information and could be more intense than that produced by lasers. An alternative, LED-based, confocal microscope is proposed in this thesis that would be capable of exciting multiple fluorochromes in a single specimen, producing images of several distinct cellular components simultaneously. The inexpensive, LED-based, confocal microscope would require lower peak excitation intensities to produce fluorescence signals equal to those produced by laser excitation, reducing cellular damage and slowing fluorochrome photobleaching.

Superconducting nanowire single-photon detectors with non-periodic dielectric multilayers.

PubMed

Yamashita, Taro; Waki, Kentaro; Miki, Shigehito; Kirkwood, Robert A; Hadfield, Robert H; Terai, Hirotaka

2016-10-24

We present superconducting nanowire single-photon detectors (SSPDs) on non-periodic dielectric multilayers, which enable us to design a variety of wavelength dependences of optical absorptance by optimizing the dielectric multilayer. By adopting a robust simulation to optimize the dielectric multilayer, we designed three types of SSPDs with target wavelengths of 500 nm, 800 nm, and telecom range respectively. We fabricated SSPDs based on the optimized designs for 500 and 800 nm, and evaluated the system detection efficiency at various wavelengths. The results obtained confirm that the designed SSPDs with non-periodic dielectric multilayers worked well. This versatile device structure can be effective for multidisciplinary applications in fields such as the life sciences and remote sensing that require high efficiency over a precise spectral range and strong signal rejection at other wavelengths.

Spectral interferometric microscopy reveals absorption by individual optical nanoantennas from extinction phase

PubMed Central

Gennaro, Sylvain D.; Sonnefraud, Yannick; Verellen, Niels; Van Dorpe, Pol; Moshchalkov, Victor V.; Maier, Stefan A.; Oulton, Rupert F.

2014-01-01

Optical antennas transform light from freely propagating waves into highly localized excitations that interact strongly with matter. Unlike their radio frequency counterparts, optical antennas are nanoscopic and high frequency, making amplitude and phase measurements challenging and leaving some information hidden. Here we report a novel spectral interferometric microscopy technique to expose the amplitude and phase response of individual optical antennas across an octave of the visible to near-infrared spectrum. Although it is a far-field technique, we show that knowledge of the extinction phase allows quantitative estimation of nanoantenna absorption, which is a near-field quantity. To verify our method we characterize gold ring-disk dimers exhibiting Fano interference. Our results reveal that Fano interference only cancels a bright mode’s scattering, leaving residual extinction dominated by absorption. Spectral interference microscopy has the potential for real-time and single-shot phase and amplitude investigations of isolated quantum and classical antennas with applications across the physical and life sciences. PMID:24781663

Airborne remote sensing of ultraviolet-absorbing aerosols during the NASA ATom, SEAC4RS and DC3 campaigns

NASA Astrophysics Data System (ADS)

Hall, S. R.; Ullmann, K.; Commane, R.; Crounse, J. D.; Daube, B. C.; Diskin, G. S.; Dollner, M.; Froyd, K. D.; Katich, J. M.; Kim, M. J.; Madronich, S.; Murphy, D. M.; Podolske, J. R.; Schwarz, J. P.; Teng, A.; Weber, R. J.; Weinzierl, B.; Wennberg, P. O.; Sachse, G.; Wofsy, S.

2017-12-01

Spectrally resolved up and down-welling actinic flux was measured from the NASA DC-8 aircraft by the Charged-coupled device Actinic Flux Spectroradiometers (CAFS) during recent campaigns including ATom, DC3 and SEAC4RS. The primary purpose is retrieval of 40 photolysis frequencies to complement the in situ chemistry. However, the spectra also provide the opportunity to examine absorption trends in the UV where few other measurements exist. In particular, absorption by brown (BrC) and black (BC) carbon aerosols result in characteristic UV signatures. A new technique exploits the spectral changes to detect the presence of these aerosols for qualitative, real-time, remote sensing of biomass burning (BB). The data may prove useful for examination of the evolution of BrC, including chemical processing and hygroscopic growth. The induced UV changes also feed back to the photolysis frequencies affecting the chemistry. Further work will determine the robustness of the technique and if quantitative spectral absorption retrievals are possible.

Constraints on the Compositions of Phobos and Deimos from Mineral Absorptions

NASA Technical Reports Server (NTRS)

Fraeman, A. A.; Murchie, S. L.; Arvidson, R. E.; Rivkin, A. S.; Morris, R. V.

2013-01-01

The compositions of Phobos and Deimos have remained controversial despite multiple Earth- and space-based observations acquired during the last 40 years. Phobos is composed of at least two spectral units that are both dark yet distinct at visible to near infrared wavelenghts; a spectrally red-sloped "red" unit covers most of the moon and a less red-sloped "blue" unit is present in the ejecta of the approximately 9-km diameter impact crater Stickney [1,2]. Deimos is similar spectrally to Phobos' "red" unit [2]. Here we report results from mapping mineral absorptions on Phobos and Deimos using visible/near infrared observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). We find evidence for an absorption feature at 0.65 m in the Phobos red unit and Deimos that is reproducible in observations from other instruments. The phase responsible is uncertain but may be a Fe-bearing phyllosilicate and/or graphite, consistent with the notion that Phobos and Deimos have compositions similar to CM carbonaceous chondrites [3].

Atmospheric correction for JPSS-2 VIIRS response versus scan angle measurements

NASA Astrophysics Data System (ADS)

McIntire, Jeffrey; Moeller, Chris; Oudrari, Hassan; Xiong, Xiaoxiong

2017-09-01

The Joint Polar Satellite System 2 (JPSS-2) Visible Infrared Imaging Radiometer Suite (VIIRS) includes one spectral band centered in a strong atmospheric absorption region. As much of the pre-launch calibration is performed under laboratory ambient conditions, accurately accounting for the absorption, and thereby ensuring the transfer of the sensor calibration to on-orbit operations, is necessary to generate science quality data products. This work is focused on the response versus scan angle (RVS) measurements, which characterize the relative scan angle dependent reflectance of the JPSS-2 VIIRS instrument optics. The spectral band of interest, centered around 1378 nm, is within a spectral region strongly effected by water vapor absorption. The methodology used to model the absolute humidity and the atmospheric transmittance under the laboratory conditions is detailed. The application of this transmittance to the RVS determination is then described including an uncertainty estimate; a comparison to the pre-launch measurements from earlier sensor builds is also performed.

Photoluminescence spectral reliance on aggregation order of 1,1-Bis(2'-thienyl)-2,3,4,5-tetraphenylsilole.

PubMed

Chen, Junwu; Xu, Bin; Yang, Kaixia; Cao, Yong; Sung, Herman H Y; Williams, Ian D; Tang, Ben Zhong

2005-09-15

1,1-Bis(2'-thienyl)-2,3,4,5-tetraphenylsilole (1) was prepared and characterized crystallographically. Silole 1 exhibited aggregation-induced emission (AIE) behavior like other 2,3,4,5-tetraphenylsiloles. Unexpectedly, aggregates formed in water/acetone (6:4 by volume) mixture emitted a blue light that peaked at 474 nm, while aggregates formed in the mixtures with higher water fractions emitted green light that peaked at 500 nm. Transmission electron microscopy demonstrated that the aggregates formed in the mixture with water fraction of 60% were single crystals, while aggregates that formed in the mixture with water fraction of 90% were irregular and poorly ordered particles. The unusual PL spectral reliance on aggregation order was further confirmed by PL emissions of macroscopic crystal powders and amorphous powders of the silole in the dry state. PL spectral blue shifting was observed upon aging of the poorly ordered aggregates formed in mixtures with water fractions of 70-90%, and they finally exhibited the same blue emission as the crystalline aggregates. The as-deposited thin solid film was amorphous and it could be transformed to a transparent crystalline film upon treatment in the vapor of an ethanol/water (1:1 by volume) mixture, along with PL spectral blue shifting due to changing of aggregation order. It was also found that the crystalline film showed a blue-shifted absorption spectrum relative to the amorphous film and the shift of the absorption edge of the spectra could match that of corresponding PL spectra. The FT-IR spectrum of crystal powders of 1 displayed more vibration modes compared with that of amorphous powders, suggesting the existence of different pi-overlaps or different molecular conformations. The crystals of 1-methyl-1,2,3,4,5-pentaphenylsilole and hexaphenylsilole also showed blue-shifted PL emissions of their amorphous solids, with a comparable PL spectral shift of 1. Developing of a silole solution on a TLC plate readily brought about an amorphous thin layer. Our results suggest that crystalline films of AIE-active siloles are potential emissive layers for efficient blue OLEDs with stable color and long lifetime.

Solar energy conversion with tunable plasmonic nanostructures for thermoelectric devices.

PubMed

Xiong, Yujie; Long, Ran; Liu, Dong; Zhong, Xiaolan; Wang, Chengming; Li, Zhi-Yuan; Xie, Yi

2012-08-07

The photothermal effect in localized surface plasmon resonance (LSPR) should be fully utilized when integrating plasmonics into solar technologies for improved light absorption. In this communication, we demonstrate that the photothermal effect of silver nanostructures can provide a heat source for thermoelectric devices for the first time. The plasmonic band of silver nanostructures can be facilely manoeuvred by tailoring their shapes, enabling them to interact with photons in different spectral ranges for the efficient utilization of solar light. It is anticipated that this concept can be extended to design a photovoltaic-thermoelectric tandem cell structure with plasmonics as mediation for light harvesting.

The multi-mode polarization modulation spectrometer: part 1: simultaneous detection of absorption, turbidity, and optical activity.

PubMed

Arvinte, Tudor; Bui, Tam T T; Dahab, Ali A; Demeule, Barthélemy; Drake, Alex F; Elhag, Dhia; King, Peter

2004-09-01

Circular dichroism (CD) is an important spectroscopic technique for monitoring chirality and biological macromolecule conformation. However, during a CD measurement, absorbance, light scattering/turbidity, and fluorescence can also be detected. The simultaneous measurement of these different spectral features for a single sample is the basis of a multi-mode optical spectrometer. This allows time-efficient gathering of complementary information and provides a scheme to ensure that CD measurements are reliable. Aspects of circular polarization differential light scattering, pH, and temperature variation of a protein (antibody) solution are described. A procedure to help ensure that CD measurements are reliable is described.

Re{sup 3+} : YAG laser ceramics: synthesis, optical properties and laser characteristics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bagayev, S N; Vatnik, S M; Vedin, I A

2015-05-31

Highly transparent yttrium aluminium garnet ceramics doped with holmium or ytterbium or neodymium are synthesised. The ceramics were made of a mixture of nanopowders synthesised by laser ablation. The structural and spectral characteristics of ceramics are studied. In the samples with holmium Ho{sup 3+} and neodymium Nd{sup 3+} ions, lasing was achieved with a slope efficiency of 40% and 35.3%, respectively; the maximum laser power exceeded 4 W. The internal absorption and scattering losses for 1% Nd : YAG ceramics are estimated to be 1.6 × 10{sup -2} cm{sup -1}. (extreme light fields and their applications)

An Analysis of AERONET Aerosol Absorption Properties and Classifications Representative of Aerosol Source Regions

NASA Technical Reports Server (NTRS)

Giles, David M.; Holben, Brent N.; Eck, Thomas F.; Sinyuk, Aliaksandr; Smirnov, Alexander; Slutsker, Ilya; Dickerson, R. R.; Thompson, A. M.; Schafer, J. S.

2012-01-01

Partitioning of mineral dust, pollution, smoke, and mixtures using remote sensing techniques can help improve accuracy of satellite retrievals and assessments of the aerosol radiative impact on climate. Spectral aerosol optical depth (tau) and single scattering albedo (omega (sub 0) ) from Aerosol Robotic Network (AERONET) measurements are used to form absorption [i.e., omega (sub 0) and absorption Angstrom exponent (alpha(sub abs))] and size [i.e., extinction Angstrom exponent (alpha(sub ext)) and fine mode fraction of tau] relationships to infer dominant aerosol types. Using the long-term AERONET data set (1999-2010), 19 sites are grouped by aerosol type based on known source regions to: (1) determine the average omega (sub 0) and alpha(sub abs) at each site (expanding upon previous work); (2) perform a sensitivity study on alpha(sub abs) by varying the spectral omega (sub 0); and (3) test the ability of each absorption and size relationship to distinguish aerosol types. The spectral omega (sub 0) averages indicate slightly more aerosol absorption (i.e., a 0.0 < delta omega (sub 0) <= 0.02 decrease) than in previous work and optical mixtures of pollution and smoke with dust show stronger absorption than dust alone. Frequency distributions of alpha(sub abs) show significant overlap among aerosol type categories and at least 10% of the alpha(sub abs) retrievals in each category are below 1.0. Perturbing the spectral omega (sub 0) by +/- 0.03 induces significant alpha(sub abs) changes from the unperturbed value by at least approx. +/- 0.6 for Dust, approx. +/-0.2 for Mixed, and approx. +/-0.1 for Urban/Industrial and Biomass Burning. The omega (sub 0)440nm and alpha(sub ext) 440-870nm relationship shows the best separation among aerosol type clusters, providing a simple technique for determining aerosol type from surface- and future space-based instrumentation.

Dynamic terahertz spectroscopy of gas molecules mixed with unwanted aerosol under atmospheric pressure using fibre-based asynchronous-optical-sampling terahertz time-domain spectroscopy

PubMed Central

Hsieh, Yi-Da; Nakamura, Shota; Abdelsalam, Dahi Ghareab; Minamikawa, Takeo; Mizutani, Yasuhiro; Yamamoto, Hirotsugu; Iwata, Tetsuo; Hindle, Francis; Yasui, Takeshi

2016-01-01

Terahertz (THz) spectroscopy is a promising method for analysing polar gas molecules mixed with unwanted aerosols due to its ability to obtain spectral fingerprints of rotational transition and immunity to aerosol scattering. In this article, dynamic THz spectroscopy of acetonitrile (CH3CN) gas was performed in the presence of smoke under the atmospheric pressure using a fibre-based, asynchronous-optical-sampling THz time-domain spectrometer. To match THz spectral signatures of gas molecules at atmospheric pressure, the spectral resolution was optimized to 1 GHz with a measurement rate of 1 Hz. The spectral overlapping of closely packed absorption lines significantly boosted the detection limit to 200 ppm when considering all the spectral contributions of the numerous absorption lines from 0.2 THz to 1 THz. Temporal changes of the CH3CN gas concentration were monitored under the smoky condition at the atmospheric pressure during volatilization of CH3CN droplets and the following diffusion of the volatilized CH3CN gas without the influence of scattering or absorption by the smoke. This system will be a powerful tool for real-time monitoring of target gases in practical applications of gas analysis in the atmospheric pressure, such as combustion processes or fire accident. PMID:27301319

Dynamic terahertz spectroscopy of gas molecules mixed with unwanted aerosol under atmospheric pressure using fibre-based asynchronous-optical-sampling terahertz time-domain spectroscopy

NASA Astrophysics Data System (ADS)

Hsieh, Yi-Da; Nakamura, Shota; Abdelsalam, Dahi Ghareab; Minamikawa, Takeo; Mizutani, Yasuhiro; Yamamoto, Hirotsugu; Iwata, Tetsuo; Hindle, Francis; Yasui, Takeshi

2016-06-01

Terahertz (THz) spectroscopy is a promising method for analysing polar gas molecules mixed with unwanted aerosols due to its ability to obtain spectral fingerprints of rotational transition and immunity to aerosol scattering. In this article, dynamic THz spectroscopy of acetonitrile (CH3CN) gas was performed in the presence of smoke under the atmospheric pressure using a fibre-based, asynchronous-optical-sampling THz time-domain spectrometer. To match THz spectral signatures of gas molecules at atmospheric pressure, the spectral resolution was optimized to 1 GHz with a measurement rate of 1 Hz. The spectral overlapping of closely packed absorption lines significantly boosted the detection limit to 200 ppm when considering all the spectral contributions of the numerous absorption lines from 0.2 THz to 1 THz. Temporal changes of the CH3CN gas concentration were monitored under the smoky condition at the atmospheric pressure during volatilization of CH3CN droplets and the following diffusion of the volatilized CH3CN gas without the influence of scattering or absorption by the smoke. This system will be a powerful tool for real-time monitoring of target gases in practical applications of gas analysis in the atmospheric pressure, such as combustion processes or fire accident.

Dynamic terahertz spectroscopy of gas molecules mixed with unwanted aerosol under atmospheric pressure using fibre-based asynchronous-optical-sampling terahertz time-domain spectroscopy.

PubMed

Hsieh, Yi-Da; Nakamura, Shota; Abdelsalam, Dahi Ghareab; Minamikawa, Takeo; Mizutani, Yasuhiro; Yamamoto, Hirotsugu; Iwata, Tetsuo; Hindle, Francis; Yasui, Takeshi

2016-06-15

Terahertz (THz) spectroscopy is a promising method for analysing polar gas molecules mixed with unwanted aerosols due to its ability to obtain spectral fingerprints of rotational transition and immunity to aerosol scattering. In this article, dynamic THz spectroscopy of acetonitrile (CH3CN) gas was performed in the presence of smoke under the atmospheric pressure using a fibre-based, asynchronous-optical-sampling THz time-domain spectrometer. To match THz spectral signatures of gas molecules at atmospheric pressure, the spectral resolution was optimized to 1 GHz with a measurement rate of 1 Hz. The spectral overlapping of closely packed absorption lines significantly boosted the detection limit to 200 ppm when considering all the spectral contributions of the numerous absorption lines from 0.2 THz to 1 THz. Temporal changes of the CH3CN gas concentration were monitored under the smoky condition at the atmospheric pressure during volatilization of CH3CN droplets and the following diffusion of the volatilized CH3CN gas without the influence of scattering or absorption by the smoke. This system will be a powerful tool for real-time monitoring of target gases in practical applications of gas analysis in the atmospheric pressure, such as combustion processes or fire accident.

Use of spectral analogy to evaluate canopy reflectance sensitivity to leaf optical property

NASA Technical Reports Server (NTRS)

Baret, Frederic; Vanderbilt, Vern C.; Steven, Michael D.; Jacquemoud, Stephane

1993-01-01

The spectral variation of canopy reflectance is mostly governed by the absorption properties of the elements, hence the leaves, since their intrinsic scattering properties show very little spectral variation. The relationship between canopy reflectance and leaf reflectance measured at the red edge over sugar beet canopies was used to simulate canopy reflectance from leaf reflectance spectra measured over the whole spectral domain. The results show that the spectral analogies found allows accurate reconstruction of canopy reflectance spectra. Explicit assumptions about the very low spectral variation of leaf intrinsic scattering properties are thus indirectly justified. The sensitivity of canopy reflectance (rho(sub c)) to leaf optical properties can then be investigated from concurrent spectral variations of canopy (delta rho(sub c)/delta lambda) and leaf reflectance (delta rho(sub l)/delta lambda): (delta rho(sub c))/(delta rho(sub l)) = ((delta rho(sub c))/(delta lambda) ((delta rho( sub l))/(delta lambda))(sup -1)). This expression is strictly valid only when the optical properties of the soil background or the other vegetation elements such as bark are either spectrally flat or do not contribute significantly to canopy reflectance. Simulations using the SAIL and PROSPECT models demonstrate that the sensitivity of canopy reflectance to leaf reflectance is significant for large vegetation cover fractions in spectral domains where absorption is low. In these conditions, multiple, scattering enhances the leaf absorption features by a factor that can be greater than 2.0. To override the limitations of the SAIL model for the description of the canopy architecture, we tested the previous findings on experimental data. Concurrent canopy and leaf reflectance spectra were measured for a range of sugar beet canopies. The results show good agreement with the theoretical findings. Conclusions are drawn about the applicability of these findings, with particular attention to the potential detectability of leaf biochemical composition from canopy reflectance sensed from space.

Satellite-Based Evidence of Wavelength-Dependent Aerosol Absorption in Biomass Burning Smoke Inferred from Ozone Monitoring Instrument

NASA Technical Reports Server (NTRS)

Jethva, H.; Torres, O.

2012-01-01

We provide satellite-based evidence of the spectral dependence of absorption in biomass burning aerosols over South America using near-UV measurements made by the Ozone Monitoring Instrument (OMI) during 2005-2007. In the current near-UV OMI aerosol algorithm (OMAERUV), it is implicitly assumed that the only absorbing component in carbonaceous aerosols is black carbon whose imaginary component of the refractive index is wavelength independent. With this assumption, OMI-derived aerosol optical depth (AOD) is found to be significantly over-estimated compared to that of AERONET at several sites during intense biomass burning events (August-September). Other well-known sources of error affecting the near-UV method of aerosol retrieval do not explain the large observed AOD discrepancies between the satellite and the ground-based observations. A number of studies have revealed strong spectral dependence in carbonaceous aerosol absorption in the near-UV region suggesting the presence of organic carbon in biomass burning generated aerosols. A sensitivity analysis examining the importance of accounting for the presence of wavelength-dependent aerosol absorption in carbonaceous particles in satellite-based remote sensing was carried out in this work. The results convincingly show that the inclusion of spectrally-dependent aerosol absorption in the radiative transfer calculations leads to a more accurate characterization of the atmospheric load of carbonaceous aerosols.

Quantitative filter technique measurements of spectral light absorption by aquatic particles using a portable integrating cavity absorption meter (QFT-ICAM).

PubMed

Röttgers, Rüdiger; Doxaran, David; Dupouy, Cecile

2016-01-25

The accurate determination of light absorption coefficients of particles in water, especially in very oligotrophic oceanic areas, is still a challenging task. Concentrating aquatic particles on a glass fiber filter and using the Quantitative Filter Technique (QFT) is a common practice. Its routine application is limited by the necessary use of high performance spectrophotometers, distinct problems induced by the strong scattering of the filters and artifacts induced by freezing and storing samples. Measurements of the sample inside a large integrating sphere reduce scattering effects and direct field measurements avoid artifacts due to sample preservation. A small, portable, Integrating Cavity Absorption Meter setup (QFT-ICAM) is presented, that allows rapid measurements of a sample filter. The measurement technique takes into account artifacts due to chlorophyll-a fluorescence. The QFT-ICAM is shown to be highly comparable to similar measurements in laboratory spectrophotometers, in terms of accuracy, precision, and path length amplification effects. No spectral artifacts were observed when compared to measurement of samples in suspension, whereas freezing and storing of sample filters induced small losses of water-soluble pigments (probably phycoerythrins). Remaining problems in determining the particulate absorption coefficient with the QFT-ICAM are strong sample-to-sample variations of the path length amplification, as well as fluorescence by pigments that is emitted in a different spectral region than that of chlorophyll-a.

Lens-Aided Multi-Angle Spectroscopy (LAMAS) Reveals Small-Scale Outflow Structure in Quasars

NASA Astrophysics Data System (ADS)

Green, Paul J.

2006-06-01

Spectral differences between lensed quasar image components are common. Since lensing is intrinsically achromatic, these differences are typically explained as the effect of either microlensing, or as light path time delays sampling intrinsic quasar spectral variability. Here we advance a novel third hypothesis: some spectral differences are due to small line-of-sight differences through quasar disk wind outflows. In particular, we propose that variable spectral differences seen only in component A of the widest separation lens SDSS J1004+4112 are due to differential absorption along the sight lines. The absorber properties required by this hypothesis are akin to known broad absorption line (BAL) outflows but must have a broader, smoother velocity profile. We interpret the observed C IV emission-line variability as further evidence for spatial fine structure transverse to the line of sight. Since outflows are likely to be rotating, such absorber fine structure can consistently explain some of the UV and X-ray variability seen in AGNs. The implications are many: (1) Spectroscopic differences in other lensed objects may be due to this ``lens-aided multi-angle spectroscopy'' (LAMAS). (2) Outflows have fine structure on size scales of arcseconds, as seen from the nucleus. (3) Assuming either broad absorption line region sizes proposed in recent wind models, or typically assumed continuum emission region sizes, LAMAS and/or variability provide broadly consistent absorber size scale estimates of ~1015 cm. (4) Very broad smooth absorption may be ubiquitous in quasar spectra, even when no obvious troughs are seen.

[A Terahertz Spectral Database Based on Browser/Server Technique].

PubMed

Zhang, Zhuo-yong; Song, Yue

2015-09-01

With the solution of key scientific and technical problems and development of instrumentation, the application of terahertz technology in various fields has been paid more and more attention. Owing to the unique characteristic advantages, terahertz technology has been showing a broad future in the fields of fast, non-damaging detections, as well as many other fields. Terahertz technology combined with other complementary methods can be used to cope with many difficult practical problems which could not be solved before. One of the critical points for further development of practical terahertz detection methods depends on a good and reliable terahertz spectral database. We developed a BS (browser/server) -based terahertz spectral database recently. We designed the main structure and main functions to fulfill practical requirements. The terahertz spectral database now includes more than 240 items, and the spectral information was collected based on three sources: (1) collection and citation from some other abroad terahertz spectral databases; (2) collected from published literatures; and (3) spectral data measured in our laboratory. The present paper introduced the basic structure and fundament functions of the terahertz spectral database developed in our laboratory. One of the key functions of this THz database is calculation of optical parameters. Some optical parameters including absorption coefficient, refractive index, etc. can be calculated based on the input THz time domain spectra. The other main functions and searching methods of the browser/server-based terahertz spectral database have been discussed. The database search system can provide users convenient functions including user registration, inquiry, displaying spectral figures and molecular structures, spectral matching, etc. The THz database system provides an on-line searching function for registered users. Registered users can compare the input THz spectrum with the spectra of database, according to the obtained correlation coefficient one can perform the searching task very fast and conveniently. Our terahertz spectral database can be accessed at http://www.teralibrary.com. The proposed terahertz spectral database is based on spectral information so far, and will be improved in the future. We hope this terahertz spectral database can provide users powerful, convenient, and high efficient functions, and could promote the broader applications of terahertz technology.

Model-independent Exoplanet Transit Spectroscopy

NASA Astrophysics Data System (ADS)

Aronson, Erik; Piskunov, Nikolai

2018-05-01

We propose a new data analysis method for obtaining transmission spectra of exoplanet atmospheres and brightness variation across the stellar disk from transit observations. The new method is capable of recovering exoplanet atmosphere absorption spectra and stellar specific intensities without relying on theoretical models of stars and planets. We simultaneously fit both stellar specific intensity and planetary radius directly to transit light curves. This allows stellar models to be removed from the data analysis. Furthermore, we use a data quality weighted filtering technique to achieve an optimal trade-off between spectral resolution and reconstruction fidelity homogenizing the signal-to-noise ratio across the wavelength range. Such an approach is more efficient than conventional data binning onto a low-resolution wavelength grid. We demonstrate that our analysis is capable of reproducing results achieved by using an explicit quadratic limb-darkening equation and that the filtering technique helps eliminate spurious spectral features in regions with strong telluric absorption. The method is applied to the VLT FORS2 observations of the exoplanets GJ 1214 b and WASP-49 b, and our results are in agreement with previous studies. Comparisons between obtained stellar specific intensity and numerical models indicates that the method is capable of accurately reconstructing the specific intensity. The proposed method enables more robust characterization of exoplanetary atmospheres by separating derivation of planetary transmission and stellar specific intensity spectra (that is model-independent) from chemical and physical interpretation.

Strong coupling of plasmon and nanocavity modes for dual-band, near-perfect absorbers and ultrathin photovoltaics

DOE PAGES

Hagglund, Carl; Zeltzer, Gabriel; Ruiz, Ricardo; ...

2016-01-29

In this study, when optical resonances interact strongly, hybridized modes are formed with mixed properties inherited from the basic modes. Strong coupling therefore tends to equalize properties such as damping and oscillator strength of the spectrally separate resonance modes. This effect is here shown to be very useful for the realization of near-perfect dual-band absorption with ultrathin (~10 nm) layers in a simple geometry. Absorber layers are constructed by atomic layer deposition of the heavy-damping semiconductor tin monosulfide (SnS) onto a two-dimensional gold nanodot array. In combination with a thin (55 nm) SiO 2 spacer layer and a highly reflectivemore » Al film on the back, a semiopen nanocavity is formed. The SnS-coated array supports a localized surface plasmon resonance in the vicinity of the lowest order antisymmetric Fabry–Perot resonance of the nanocavity. Very strong coupling of the two resonances is evident through anticrossing behavior with a minimum peak splitting of 400 meV, amounting to 24% of the plasmon resonance energy. The mode equalization resulting from this strong interaction enables simultaneous optical impedance matching of the system at both resonances and thereby two near-perfect absorption peaks, which together cover a broad spectral range. When paired with the heavy damping from SnS band-to-band transitions, this further enables approximately 60% of normal incident solar photons with energies exceeding the band gap to be absorbed in the 10 nm SnS coating. Thereby, these results establish a distinct relevance of strong coupling phenomena to efficient, nanoscale photovoltaic absorbers and more generally for fulfilling a specific optical condition at multiple spectral positions.« less

Modified thermal-optical analysis using spectral absorption selectivity to distinguish black carbon from pyrolized organic carbon.

PubMed

Hadley, Odelle L; Corrigan, Craig E; Kirchstetter, Thomas W

2008-11-15

This study presents a method for analyzing the black carbon (BC) mass loading on a quartz fiber filter using a modified thermal-optical analysis method, wherein light transmitted through the sample is measured over a spectral region instead of at a single wavelength. Evolution of the spectral light transmission signal depends on the relative amounts of light-absorbing BC and char, the latter of which forms when organic carbon in the sample pyrolyzes during heating. Absorption selectivities of BC and char are found to be distinct and are used to apportion the amount of light attenuated by each component in the sample. Light attenuation is converted to mass concentration on the basis of derived mass attenuation efficiencies (MAEs) of BC and char. The fractions of attenuation due to each component are scaled by their individual MAE values and added together as the total mass of light absorbing carbon (LAC). An iterative algorithm is used to find the MAE values for both BC and char that provide the best fit to the carbon mass remaining on the filter (derived from direct measurements of thermally evolved CO2) at temperatures higher than 480 degrees C. This method was applied to measure the BC concentration in precipitation samples collected in northern California. The uncertainty in the measured BC concentration of samples that contained a high concentration of organics susceptible to char ranged from 12% to 100%, depending on the mass loading of BC on the filter. The lower detection limit for this method was approximately 0.35 microg of BC, and the uncertainty approached 20% for BC mass loading greater than 1.0 microg of BC.

Deciphering Galactic Hydrogen with 21-SPONGE

NASA Astrophysics Data System (ADS)

Murray, Claire; Stanimirovic, Snezana; Goss, Miller; Heiles, Carl E.; Miller Dickey, John; Lindner, Robert; Babler, Brian L.

2017-01-01

Neutral hydrogen (HI) in the interstellar medium (ISM) is crucial to the life cycles of galaxies. The balance between disparate phases of HI -- including the cold neutral (CNM) and warm neutral (WNM) medium -- governs the formation of dense, star-forming material, and reflects the nature of feedback in galaxies. To probe the multi-phase structure of HI, we present results from 21-SPONGE: the largest and most sensitive survey for Galactic HI absorption ever at the Karl G. Jansky Very Large Array (VLA). Complemented by HI emission from the Arecibo Observatory, 21-SPONGE is uniquely sensitive to CNM and WNM temperatures from 10-104 K and column densities from 1018-1022 cm-2. Despite our unprecedented sensitivity, the maximum temperature we detect for individual spectral lines is Ts~1500 K, although stacking analysis of 21-SPONGE absorption lines indicates the presence of pervasive, high-Ts WNM population with Ts~7000 K. To understand the physics underlying these results, we developed Autonomous Gaussian Decomposition (AGD), a Python-based tool for efficiently and objectively analyzing spectral lines. By applying AGD to 21-SPONGE and 1000s of synthetic HI spectra from 3D numerical simulations, we correct our measurements for completeness and observational biases. We further prove that we can successfully recover the temperatures and densities of real clouds along simulated lines of sight. In addition, we show that absorption line shapes are sensitive to the strength and topology of the Lyman alpha radiation field and its role in HI excitation, which are poorly-constrained yet important for understanding the energy balance of the ISM. Our results are among the first to statistically quantify the success of observational methods at reproducing true HI properties, and represent crucial steps towards understanding the role of HI in star formation.

Influence of environmental factors on spectral characteristic of chromophoric dissolved organic matter (CDOM) in Inner Mongolia Plateau, China

NASA Astrophysics Data System (ADS)

Wen, Z. D.; Song, K. S.; Zhao, Y.; Du, J.; Ma, J. H.

2015-06-01

Spectral characteristics of chromophoric dissolved organic matter (CDOM) were examined in conjunction with environmental factors in the waters of 22 rivers and 26 terminal waters in Hulun Buir plateau, northeast China. Dissolved organic carbon (DOC), total nitrogen (TN), and total phosphorous (TP) were significantly higher in terminal waters than rivers waters (p < 0.01). Principal component analysis (PCA) indicated that non-water light absorption and anthropogenic nutrient disturbances might be the causes of the diversity of water quality parameters in Hulun Buir plateau. CDOM absorption in river waters was significantly lower than terminal waters (p < 0.01). Analysis of ratio of absorption at 250-365 nm (E250 : 365), specific UV absorbance (SUVA254), and spectral slope ratio (Sr) indicated that CDOM in river waters had higher aromaticity, molecular weight, and vascular plant contribution than in terminal waters. Furthermore, results showed that DOC concentration, CDOM light absorption, and the proportion of autochthonous sources of CDOM in plateau waters were all higher than in other freshwater rivers reported in the literature. The strong evapoconcentration, intense ultraviolet irradiance and landscape features of Hulun Buir plateau may be responsible for the above phenomenon. Redundancy analysis (RDA) indicated that the environmental variables TSM, TN, and EC had a strong correlation with light absorption characteristics, followed by TDS and chlorophyll a. In most sampling locations, CDOM was the dominant non-water light-absorbing substance. Light absorption by non-algal particles often exceeded that by phytoplankton in the plateau waters. Study of these optical-physicochemical correlations is helpful in the evaluation of the potential influence of water quality factors on non-water light absorption in cold plateau water environments. And the study on organic carbon in plateau lakes had a vital contribution to global carbon balance estimation.

Stochastic parameterization for light absorption by internally mixed BC/dust in snow grains for application to climate models

NASA Astrophysics Data System (ADS)

Liou, K. N.; Takano, Y.; He, C.; Yang, P.; Leung, L. R.; Gu, Y.; Lee, W. L.

2014-06-01

A stochastic approach has been developed to model the positions of BC (black carbon)/dust internally mixed with two snow grain types: hexagonal plate/column (convex) and Koch snowflake (concave). Subsequently, light absorption and scattering analysis can be followed by means of an improved geometric-optics approach coupled with Monte Carlo photon tracing to determine BC/dust single-scattering properties. For a given shape (plate, Koch snowflake, spheroid, or sphere), the action of internal mixing absorbs substantially more light than external mixing. The snow grain shape effect on absorption is relatively small, but its effect on asymmetry factor is substantial. Due to a greater probability of intercepting photons, multiple inclusions of BC/dust exhibit a larger absorption than an equal-volume single inclusion. The spectral absorption (0.2-5 µm) for snow grains internally mixed with BC/dust is confined to wavelengths shorter than about 1.4 µm, beyond which ice absorption predominates. Based on the single-scattering properties determined from stochastic and light absorption parameterizations and using the adding/doubling method for spectral radiative transfer, we find that internal mixing reduces snow albedo substantially more than external mixing and that the snow grain shape plays a critical role in snow albedo calculations through its forward scattering strength. Also, multiple inclusion of BC/dust significantly reduces snow albedo as compared to an equal-volume single sphere. For application to land/snow models, we propose a two-layer spectral snow parameterization involving contaminated fresh snow on top of old snow for investigating and understanding the climatic impact of multiple BC/dust internal mixing associated with snow grain metamorphism, particularly over mountain/snow topography.

Stochastic Parameterization for Light Absorption by Internally Mixed BC/dust in Snow Grains for Application to Climate Models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liou, K. N.; Takano, Y.; He, Cenlin

2014-06-27

A stochastic approach to model the positions of BC/dust internally mixed with two snow-grain types has been developed, including hexagonal plate/column (convex) and Koch snowflake (concave). Subsequently, light absorption and scattering analysis can be followed by means of an improved geometric-optics approach coupled with Monte Carlo photon tracing to determine their single-scattering properties. For a given shape (plate, Koch snowflake, spheroid, or sphere), internal mixing absorbs more light than external mixing. The snow-grain shape effect on absorption is relatively small, but its effect on the asymmetry factor is substantial. Due to a greater probability of intercepting photons, multiple inclusions ofmore » BC/dust exhibit a larger absorption than an equal-volume single inclusion. The spectral absorption (0.2 – 5 um) for snow grains internally mixed with BC/dust is confined to wavelengths shorter than about 1.4 um, beyond which ice absorption predominates. Based on the single-scattering properties determined from stochastic and light absorption parameterizations and using the adding/doubling method for spectral radiative transfer, we find that internal mixing reduces snow albedo more than external mixing and that the snow-grain shape plays a critical role in snow albedo calculations through the asymmetry factor. Also, snow albedo reduces more in the case of multiple inclusion of BC/dust compared to that of an equal-volume single sphere. For application to land/snow models, we propose a two-layer spectral snow parameterization containing contaminated fresh snow on top of old snow for investigating and understanding the climatic impact of multiple BC/dust internal mixing associated with snow grain metamorphism, particularly over mountains/snow topography.« less

Polarizers tuned at key far-UV spectral lines for space instrumentation

NASA Astrophysics Data System (ADS)

Larruquert, Juan I.; Malvezzi, A. Marco; Rodríguez-de Marcos, Luis; Giglia, Angelo; Gutiérrez-Luna, Nuria; Espinosa-Yáñez, Lucía.; Honrado-Benítez, Carlos; Aznárez, José A.; Massone, Giuseppe; Capobianco, Gerardo; Fineschi, Silvano; Nannarone, Stefano

2017-05-01

Polarimetry is a valuable technique to help us understand the role played by the magnetic field of the coronal plasma in the energy transfer processes from the inner parts of the Sun to the outer space. Polarimetry in the far ultraviolet (FUV: 100-200 nm), which must be performed from space due to absorption in terrestrial atmosphere, supplies fundamental data of processes that are governed by the Doppler and Hanle effects on resonantly scattered line-emission. To observe these processes there are various key spectral lines in the FUV, from which H I Lyman α (121.6 nm) is the strongest one. Hence some solar physics missions that have been proposed or are under development plan to perform polarimetry at 121.6 nm, like the suborbital missions CLASP I (2015) and CLASP II (2018), and the proposed solar missions SolmeX and COMPASS and stellar mission Arago. Therefore, the development of efficient FUV linear polarizers may benefit these and other possible future missions. C IV (155 nm) and Mg II (280 nm) are other spectral lines relevant for studies of solar and stellar magnetized atmospheres. High performance polarizers can be obtained with optimized coatings. Interference coatings can tune polarizers at the spectral line(s) of interest for solar and stellar physics. Polarizing beamsplitters consist in polarizers that separate one polarization component by reflection and the other by transmission, which enables observing the two polarization components simultaneously with a single polarizer. They involve the benefit of a higher efficiency in collection of polarization data due to the use of a single polarizer for the two polarization components and they may also facilitate a simplified design for a space polarimeter. We present results on polarizing beamsplitters tuned either at 121.6 nm or at the pair of 155 and 280 nm spectral lines.

The MPI-Mainz UV/VIS Spectral Atlas of Gaseous Molecules of Atmospheric Interest

NASA Astrophysics Data System (ADS)

Sander, Rolf; Keller-Rudek, Hannelore; Moortgat, Geert; Sörensen, Rüdiger

2014-05-01

Measurements from satellites can be used to obtain global concentration maps of atmospheric trace constituents. Critical parameters needed in the analysis of the satellite data are the absorption cross sections of the observed molecules. Here, we present the MPI-Mainz UV/VIS Spectral Atlas, which is a large collection of more than 5000 absorption cross section and quantum yield data files in the ultraviolet and visible (UV/VIS) wavelength region for gaseous molecules and radicals primarily of atmospheric interest. The data files contain results of individual measurements, covering research of almost a whole century. To compare and visualize the data sets, multicoloured graphical representations have been created. The Spectral Atlas is available on the internet at http://www.uv-vis-spectral-atlas-mainz.org. It has been completely overhauled and now appears with improved browse and search options, based on PostgreSQL, Django and Python database software. The web pages are continuously updated.

Compton thick AGN in Chandra sureys

NASA Astrophysics Data System (ADS)

Brightman, Murray; Nandra, Kirpal

2014-07-01

We present the results from the X-ray spectral analysis of active galactic nuclei (AGN) in the Chandra Deep Field-South, AEGIS-XD and Chandra-COSMOS surveys, focussing on the identification and characterisation of the most heavily obscured, Compton thick (CT, N H > 104 cm-2) sources. Our sample is comprised of 3088 X-ray selected sources, which has a high rate of redshift completeness (97%). The aim is to produce the largest and cleanest uniform sample of these sources from the data as possible. We identify these sources through X-ray spectral fitting, utilising torus spectral models designed for heavily obscured AGN which self consistently include the spectral signatures of heavy absorption, being Compton scattering, photoelectric absorption and iron Kα fluorescence. We identify a total of 163 CT AGN covering an intrinsic 2-10 keV X-ray luminosity range of 102 -3 × 105 erg s-1 and from z = 0.1-7.

Absolute determination of the cross sections of ozone in the wavelength region 339-355 nm at temperatures 220-293 K

NASA Astrophysics Data System (ADS)

Cacciani, Marco; di Sarra, Alcide; Fiocco, Giorgio; Amoruso, Antonella

1989-06-01

Absolute measurements of the ozone absorption coefficient in the Huggins bands at different temperatures have been carried out. Ozone is produced by an electrical discharge and stored cryogenically; differential absorption measurements are subsequently obtained in a slowly evolving mixture of ozone and molecular oxygen. High resolution (to 0.012 nm) measurements cover a spectral range (339-355 nm) where the ozone absorption shows a strong dependence on temperature. Results at 293 and 220 K are reported; they are particularly interesting in view of the utilization of this spectral region as a low-absorption reference channel for the observation of atmospheric ozone profiles by active probing techniques. Coherent radiation at two wavelengths, around 355 and 353 nm, respectively, can be obtained as third harmonic of the fundamental output of an Nd:YAG laser and by H2 Raman shifting of an XeCl excimer laser output.

Effect of Sequential Exposition to Short- and Long-Wavelength Radiation on the Optical Absorption in the Bismuth Titanium Oxide Crystal Doped by Aluminum

NASA Astrophysics Data System (ADS)

Dyu, V. G.; Kisteneva, M. G.; Shandarov, S. M.; Khudyakova, E. S.; Smirnov, S. V.; Kargin, Yu. F.

Changes in the spectral dependences of the optical absorption induced in the bismuth titanium oxide crystal doped by aluminum as a result of sequential exposition to cw laser radiation first with the wavelength λi = 532 nm and then with the longer wavelength λn = 633, 655, 663, 780, 871, or 1064 nm are investigated. Our experiments show that after the short-wavelength exposition to radiation with λi = 532 nm, the optical absorption in the crystal increases, and in the range 470-1000 nm, yields the spectrum whose form is independent of the initial crystal state. The subsequent exposition to longer-wavelength radiation leads to enhanced transmittance of the crystal in the examined spectral range. A maximum decrease of the optical absorption in the crystal is observed upon exposure to radiation with the wavelength λn = 663 nm.

Understanding the features in the ultrafast transient absorption spectra of CdSe quantum dots

NASA Astrophysics Data System (ADS)

Zhang, Cheng; Do, Thanh Nhut; Ong, Xuanwei; Chan, Yinthai; Tan, Howe-Siang

2016-12-01

We describe a model to explain the features of the ultrafast transient absorption (TA) spectra of CdSe core type quantum dots (QDs). The measured TA spectrum consists of contributions by the ground state bleach (GSB), stimulated emission (SE) and excited state absorption (ESA) processes associated with the three lowest energy transition of the QDs. We model the shapes of the GSB, SE and ESA spectral components after fits to the linear absorption. The spectral positions of the ESA components take into account the biexcitonic binding energy. In order to obtain the correct weightage of the GSB, SE and ESA components to the TA spectrum, we enumerate the set of coherence transfer pathways associated with these processes. From our fits of the experimental TA spectra of 65 Å diameter QDs, biexcitonic binding energies for the three lowest energy transitions are obtained.

Design of near-infrared dyes for nonlinear optics: toward optical limiting applications at telecommunication wavelengths

NASA Astrophysics Data System (ADS)

Bellier, Quentin; Bouit, Pierre-Antoine; Kamada, Kenji; Feneyrou, Patrick; Malmström, E.; Maury, Olivier; Andraud, Chantal

2009-09-01

The rapid development of frequency-tunable pulsed lasers up to telecommunication wavelengths (1400-1600 nm) led to the design of new materials for nonlinear absorption in this spectral range. In this context, two families of near infra-red (NIR) chromophores, namely heptamethine cyanine and aza-borondipyrromethene (aza-bodipy) dyes were studied. In both cases, they show significant two-photon absorption (TPA) cross-sections in the 1400-1600 nm spectral range and display good optical power limiting (OPL) properties. OPL curves were interpreted on the basis of TPA followed by excited state absorption (ESA) phenomena. Finally these systems have several relevant properties like nonlinear absorption properties, gram scale synthesis and high solubility. In addition, they could be functionalized on several sites which open the way to numerous practical applications in biology, solid-state optical limiting and signal processing.

Synthesis, spectral and third-order nonlinear optical properties of terpyridine Zn(II) complexes based on carbazole derivative with polyether group

NASA Astrophysics Data System (ADS)

Kong, Ming; Liu, Yanqiu; Wang, Hui; Luo, Junshan; Li, Dandan; Zhang, Shengyi; Li, Shengli; Wu, Jieying; Tian, Yupeng

2015-01-01

Four novel Zn(II) terpyridine complexes (ZnLCl2, ZnLBr2, ZnLI2, ZnL(SCN)2) based on carbazole derivative group were designed, synthesized and fully characterized. Their photophysical properties including absorption and one-photon excited fluorescence, two-photon absorption (TPA) and optical power limiting (OPL) were further investigated systematically and interpreted on the basis of theoretical calculations (TD-DFT). The influences of different solvents on the absorption and One-Photon Excited Fluorescence (OPEF) spectral behavior, quantum yields and the lifetime of the chromophores have been investigated in detail. The third-order nonlinear optical (NLO) properties were investigated by open/closed aperture Z-scan measurements using femtosecond pulse laser in the range from 680 to 1080 nm. These results revealed that ZnLCl2 and ZnLBr2 exhibited strong two-photon absorption and ZnLCl2 showed superior optical power limiting property.

Cross-phase modulation-induced spectral broadening in silicon waveguides.

PubMed

Zhang, Yanbing; Husko, Chad; Lefrancois, Simon; Rey, Isabella H; Krauss, Thomas F; Schröder, Jochen; Eggleton, Benjamin J

2016-01-11

We analytically and experimentally investigate cross-phase modulation (XPM) in silicon waveguides. In contrast to the well known result in pure Kerr media, the spectral broadening ratio of XPM to self-phase modulation is not two in the presence of either two-photon absorption (TPA) or free carriers. The physical origin of this change is different for each effect. In the case of TPA, this nonlinear absorption attenuates and slightly modifies the pulse shape due to differential absorption in the pulse peak and wings. When free carriers are present two different mechanisms modify the dynamics. First, free-carrier absorption performs a similar role to TPA, but is additionally asymmetric due to the delayed free-carrier response. Second, free-carrier dispersion induces an asymmetric blue phase shift which competes directly with the symmetric Kerr-induced XPM red shift. We confirm this analysis with pump-probe experiments in a silicon photonic crystal waveguide.

Theoretical studies on absorption, emission, and resonance Raman spectra of Coumarin 343 isomers

NASA Astrophysics Data System (ADS)

Wu, Wenpeng; Cao, Zexing; Zhao, Yi

2012-03-01

The vibrationally resolved spectral method and quantum chemical calculations are employed to reveal the structural and spectral properties of Coumarin 343 (C343), an ideal candidate for organic dye photosensitizers, in vacuum and solution. The results manifest that the ground-state energies are dominantly determined by different placements of hydrogen atom in carboxylic group of C343 conformations. Compared to those in vacuum, the electronic absorption spectra in methanol solvent show a hyperchromic property together with the redshift and blueshift for the neutral C343 isomers and their deprotonated anions, respectively. From the absorption, emission, and resonance Raman spectra, it is found that the maximal absorption and emission come from low-frequency modes whereas the high-frequency modes have high Raman activities. The detailed spectra are further analyzed for the identification of the conformers and understanding the potential charge transfer mechanism in their photovoltaic applications.

Accurate predictions of iron redox state in silicate glasses: A multivariate approach using X-ray absorption spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dyar, M. Darby; McCanta, Molly; Breves, Elly

2016-03-01

Pre-edge features in the K absorption edge of X-ray absorption spectra are commonly used to predict Fe3+ valence state in silicate glasses. However, this study shows that using the entire spectral region from the pre-edge into the extended X-ray absorption fine-structure region provides more accurate results when combined with multivariate analysis techniques. The least absolute shrinkage and selection operator (lasso) regression technique yields %Fe3+ values that are accurate to ±3.6% absolute when the full spectral region is employed. This method can be used across a broad range of glass compositions, is easily automated, and is demonstrated to yield accurate resultsmore » from different synchrotrons. It will enable future studies involving X-ray mapping of redox gradients on standard thin sections at 1 × 1 μm pixel sizes.« less

Accurate predictions of iron redox state in silicate glasses: A multivariate approach using X-ray absorption spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dyar, M. Darby; McCanta, Molly; Breves, Elly

2016-03-01

Pre-edge features in the K absorption edge of X-ray absorption spectra are commonly used to predict Fe 3+ valence state in silicate glasses. However, this study shows that using the entire spectral region from the pre-edge into the extended X-ray absorption fine-structure region provides more accurate results when combined with multivariate analysis techniques. The least absolute shrinkage and selection operator (lasso) regression technique yields %Fe 3+ values that are accurate to ±3.6% absolute when the full spectral region is employed. This method can be used across a broad range of glass compositions, is easily automated, and is demonstrated to yieldmore » accurate results from different synchrotrons. It will enable future studies involving X-ray mapping of redox gradients on standard thin sections at 1 × 1 μm pixel sizes.« less

Color representation and interpretation of special effect coatings.

PubMed

Ferrero, A; Perales, E; Rabal, A M; Campos, J; Martínez-Verdú, F M; Chorro, E; Pons, A

2014-02-01

A representation of the color gamut of special effect coatings is proposed and shown for six different samples, whose colors were calculated from spectral bidirectional reflectance distribution function (BRDF) measurements at different geometries. The most important characteristic of the proposed representation is that it allows a straightforward understanding of the color shift to be done both in terms of conventional irradiation and viewing angles and in terms of flake-based parameters. A different line was proposed to assess the color shift of special effect coatings on a*,b*-diagrams: the absorption line. Similar to interference and aspecular lines (constant aspecular and irradiation angles, respectively), an absorption line is the locus of calculated color coordinates from measurement geometries with a fixed bistatic angle. The advantages of using the absorption lines to characterize the contributions to the spectral BRDF of the scattering at the absorption pigments and the reflection at interference pigments for different geometries are shown.

Broadband Epsilon-near-Zero Reflectors Enhance the Quantum Efficiency of Thin Solar Cells at Visible and Infrared Wavelengths.

PubMed

Labelle, A J; Bonifazi, M; Tian, Y; Wong, C; Hoogland, S; Favraud, G; Walters, G; Sutherland, B; Liu, M; Li, Jun; Zhang, Xixiang; Kelley, S O; Sargent, E H; Fratalocchi, A

2017-02-15

The engineering of broadband absorbers to harvest white light in thin-film semiconductors is a major challenge in developing renewable materials for energy harvesting. Many solution-processed materials with high manufacturability and low cost, such as semiconductor quantum dots, require the use of film structures with thicknesses on the order of 1 μm to absorb incoming photons completely. The electron transport lengths in these media, however, are 1 order of magnitude smaller than this length, hampering further progress with this platform. Herein, we show that, by engineering suitably disordered nanoplasmonic structures, we have created a new class of dispersionless epsilon-near-zero composite materials that efficiently harness white light. Our nanostructures localize light in the dielectric region outside the epsilon-near-zero material with characteristic lengths of 10-100 nm, resulting in an efficient system for harvesting broadband light when a thin absorptive film is deposited on top of the structure. By using a combination of theory and experiments, we demonstrate that ultrathin layers down to 50 nm of colloidal quantum dots deposited atop the epsilon-near-zero material show an increase in broadband absorption ranging from 200% to 500% compared to a planar structure of the same colloidal quantum-dot-absorber average thickness. When the epsilon-near-zero nanostructures were used in an energy-harvesting module, we observed a spectrally averaged 170% broadband increase in the external quantum efficiency of the device, measured at wavelengths between 400 and 1200 nm. Atomic force microscopy and photoluminescence excitation measurements demonstrate that the properties of these epsilon-near-zero structures apply to general metals and could be used to enhance the near-field absorption of semiconductor structures more widely. We have developed an inexpensive electrochemical deposition process that enables scaled-up production of this nanomaterial for large-scale energy-harvesting applications.

Highly efficient visible-light driven photochromism: developments towards a solid-state molecular switch operating through a triplet-sensitised pathway.

PubMed

Brayshaw, Simon K; Schiffers, Stephanie; Stevenson, Anna J; Teat, Simon J; Warren, Mark R; Bennett, Robert D; Sazanovich, Igor V; Buckley, Alastair R; Weinstein, Julia A; Raithby, Paul R

2011-04-11

We introduce a new highly efficient photochromic organometallic dithienylethene (DTE) complex, the first instance of a DTE core symmetrically modified by two Pt(II) chromophores [Pt(PEt(3))(2)(C≡C)(DTE)(C≡C)Pt(PEt(3))(2)Ph] (1), which undergoes ring-closure when activated by visible light in solvents of different polarity, in thin films and even in the solid state. Complex 1 has been synthesised and fully photophysically characterised by (resonance) Raman and transient absorption spectroscopy complemented by calculations. The ring-closing photoconversion in a single crystal of 1 has been followed by X-ray crystallography. This process occurs with the extremely high yield of 80%--considerably outperforming the other DTE derivatives. Remarkably, the photocyclisation of 1 occurs even under visible light (>400 nm), which is not absorbed by the non-metallated DTE core HC≡C(DTE)C≡CH (2) itself. This unusual behaviour and the high photocyclisation yields in solution are attributed to the presence of a heavy atom in 1 that enables a triplet-sensitised photocyclisation pathway, elucidated by transient absorption spectroscopy and DFT calculations. The results of resonance Raman investigation confirm the involvement of the alkynyl unit in the frontier orbitals of both closed and open forms of 1 in the photocyclisation process. The changes in the Raman spectra upon cyclisation have permitted the identification of Raman marker bands, which include the acetylide stretching vibration. Importantly, these bands occur in the spectral region unobstructed by other vibrations and can be used for non-destructive monitoring of photocyclisation/photoreversion processes and for optical readout in this type of efficiently photochromic thermally stable systems. This study indicates a strategy for generating efficient solid-state photoswitches in which modification of the Pt(II) units has the potential to tune absorption properties and hence operational wavelength across the visible range. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Midinfrared absorption measured at a lambda/400 resolution with an atomic force microscope.

PubMed

Houel, Julien; Homeyer, Estelle; Sauvage, Sébastien; Boucaud, Philippe; Dazzi, Alexandre; Prazeres, Rui; Ortéga, Jean-Michel

2009-06-22

Midinfrared absorption can be locally measured using a detection combining an atomic force microscope and a pulsed excitation. This is illustrated for the midinfrared bulk GaAs phonon absorption and for the midinfrared absorption of thin SiO(2) microdisks. We show that the signal given by the cantilever oscillation amplitude of the atomic force microscope follows the spectral dependence of the bulk material absorption. The absorption spatial resolution achieved with microdisks is around 50 nanometer for an optical excitation around 22 micrometer wavelength.

Solar absorptance and thermal emittance of some common spacecraft thermal-control coatings

NASA Technical Reports Server (NTRS)

Henninger, J. H.

1984-01-01

Solar absorptance and thermal emittance of spacecraft materials are critical parameters in determining spacecraft temperature control. Because thickness, surface preparation, coatings formulation, manufacturing techniques, etc. affect these parameters, it is usually necessary to measure the absorptance and emittance of materials before they are used. Absorptance and emittance data for many common types of thermal control coatings, are together with some sample spectral data curves of absorptance. In some cases for which ultraviolet and particle radiation data are available, the degraded absorptance and emittance values are also listed.

Spectral properties of ice-particulate mixtures and implications for remote sensing. 1. Intimate mixtures.

USGS Publications Warehouse

Clark, R.N.; Lucey, P.G.

1984-01-01

The spectral properties of water ice-partitioning mixtures are studied for the purpose of deriving the ice and particulate abundances from remotely obtained spectra (particulates referring to non-icy materials in the form of grains). Reflectance levels and ice absorption band depths are a complex function of the single scattering albedo of the particulates embedded in the ice. The ice absorption band depths are related to the mean optical path length of photons in ice through Beers law, Fresnel reflection from the ice-crystal faces on the surface, and ice absorption coefficient as a function of wavelength. Laboratory spectra of many ice- particulate mixtures are studied with high-, medium-, and low-albedo particulates.-from Authors

A High Spectral Resolution Lidar Based on Absorption Filter

NASA Technical Reports Server (NTRS)

Piironen, Paivi

1996-01-01

A High Spectral Resolution Lidar (HSRL) that uses an iodine absorption filter and a tunable, narrow bandwidth Nd:YAG laser is demonstrated. The iodine absorption filter provides better performance than the Fabry-Perot etalon that it replaces. This study presents an instrument design that can be used a the basis for a design of a simple and robust lidar for the measurement of the optical properties of the atmosphere. The HSRL provides calibrated measurements of the optical properties of the atmospheric aerosols. These observations include measurements of aerosol backscatter cross sections, optical depth, backscatter phase function depolarization, and multiple scattering. The errors in the HSRL data are discussed and the effects of different errors on the measured optical parameters are shown.

Temperature and emissivity measurements at the sapphire single crystal fiber growth process

NASA Astrophysics Data System (ADS)

Bufetova, G. A.; Rusanov, S. Ya.; Seregin, V. F.; Pyrkov, Yu. N.; Tsvetkov, V. B.

2017-12-01

We present a new method for evaluation the absorption coefficient of the crystal melt around the phase transition zone for the spectral range of semitransparency. The emissivity distribution across the crystallization front of the sapphire crystal fiber was measured at the quasi-stationary laser heated pedestal growth (LHPG) process (Fejer et al., 1984; Feigelson, 1986) and the data for solid state, melt and phase transition zone (melt-solid interface) were obtained. The sapphire melt absorption coefficient was estimated to be 14 ± 2 cm-1 in the spectral range 1-1.4 μm around the melt point. It is consistent with data, obtained by different other methods. This method can be applied to determine the absorption coefficient for other materials.

Successive ion layer adsorption and reaction (SILAR) technique synthesis of Al(III)-8-hydroxy-5-nitrosoquinolate nano-sized thin films: characterization and factors optimization.

PubMed

Haggag, Sawsan M S; Farag, A A M; Abdel Refea, M

2013-02-01

Nano Al(III)-8-hydroxy-5-nitrosoquinolate [Al(III)-(HNOQ)(3)] thin films were synthesized by the rapid, direct, simple and efficient successive ion layer adsorption and reaction (SILAR) technique. Thin film formation optimized factors were evaluated. Stoichiometry and structure were confirmed by elemental analysis and FT-IR. The particle size (27-71 nm) was determined using scanning electron microscope (SEM). Thermal stability and thermal parameters were determined by thermal gravimetric analysis (TGA). Optical properties were investigated using spectrophotometric measurements of transmittance and reflectance at normal incidence. Refractive index, n, and absorption index, k, were determined. Spectral behavior of the absorption coefficient in the intrinsic absorption region revealed a direct allowed transition with 2.45 eV band gap. The current-voltage (I-V) characteristics of [Al(III)-(HNOQ)(3)]/p-Si heterojunction was measured at room temperature. The forward and reverse I-V characteristics were analyzed. The calculated zero-bias barrier height (Φ(b)) and ideality factor (n) showed strong bias dependence. Energy distribution of interface states (N(ss)) was obtained. Copyright © 2012 Elsevier B.V. All rights reserved.

Polarization, excited states, trans-cis properties and anisotropy of thermal and electrical conductivity of the 4-(phenyldiazenyl)aniline in PVA matrix

NASA Astrophysics Data System (ADS)

Shahab, Siyamak; Filippovich, Liudmila; Sheikhi, Masoome; Kumar, Rakesh; Dikusar, Evgenij; Yahyaei, Hooriye; Muravsky, Alexander

2017-08-01

In the present work, Polarization, Excited States, Trans-Cis (E → Z) Isomerization Properties and Anisotropy of Thermal and Electrical Conductivity of the 4-(phenyldiazenyl)aniline in the presence of polyvinyl alcohol (PVA) matrix were studied. DFT, UV/Vis, IR-Spectroscopies and Indicator Method were used for Determination of Thermal Conductivity of polymer films. The absorption spectra of the 4-(phenyldiazenyl)aniline in dimethylformamide (DMF) solvent and in aqueous medium were calculated. The nature of absorption peaks of the 4-(phenyldiazenyl)aniline in the UV/Vis spectral regions were interpreted. The solvent effect on the absorption spectrum of the 4-(phenyldiazenyl)aniline has established. The molecular HOMO-LUMO, excitation energies and oscillator strengths for E and Z isomers of the 4-(phenyldiazenyl)aniline have also been calculated and presented. Optical Properties of the PVA-films containing 4-(phenyldiazenyl)aniline have been also investigated. Polarizing Efficiency (PE) of obtained PVA-film is 98-99% at Stretching Degree (Rs) 3.5. Anisotropy of thermal and electrical conductivity of PVA-films containing E and Z isomers of the 4-(phenyldiazenyl)aniline was also measured and discussed.

Sulfur determination in coal using molecular absorption in graphite filter vaporizer.

PubMed

Jim, Gibson; Katskov, Dmitri; Tittarelli, Paolo

2011-02-15

The vaporization of sulfur containing samples in graphite vaporizers for atomic absorption spectrometry is accompanied by modification of sulfur by carbon and, respectively, appearance at high temperature of structured molecular absorption in 200-210 nm wavelength range. It has been proposed to employ the spectrum for direct determination of sulfur in coal; soundness of the suggestion is evaluated by analysis of coal slurry using low resolution CCD spectrometer with continuum light source coupled to platform or filter furnace vaporizers. For coal in platform furnace losses of the analyte at low temperature and strong spectral background from the coal matrix hinder the determination. Both negative effects are significantly reduced in filter furnace, in which sample vapor efficiently interacts with carbon when transferred through the heated graphite filter. The method is verified by analysis of coals with sulfur content within 0.13-1.5% (m/m) range. The use of coal certified reference material for sulfur analyte addition to coal slurry permitted determination with random error 5-12%. Absolute and relative detection limits for sulfur in coal are 0.16 μg and 0.02 mass%, respectively. Copyright © 2010 Elsevier B.V. All rights reserved.

Radiation characteristics and effective optical properties of dumbbell-shaped cyanobacterium Synechocystis sp.

NASA Astrophysics Data System (ADS)

Heng, Ri-Liang; Pilon, Laurent

2016-05-01

This study presents experimental measurements of the radiation characteristics of unicellular freshwater cyanobacterium Synechocystis sp. during their exponential growth in F medium. Their scattering phase function at 633 nm average spectral absorption and scattering cross-sections between 400 and 750 nm were measured. In addition, an inverse method was used for retrieving the spectral effective complex index of refraction of overlapping or touching bispheres and quadspheres from their absorption and scattering cross-sections. The inverse method combines a genetic algorithm and a forward model based on Lorenz-Mie theory, treating bispheres and quadspheres as projected area and volume-equivalent coated spheres. The inverse method was successfully validated with numerically predicted average absorption and scattering cross-sections of suspensions consisting of bispheres and quadspheres, with realistic size distributions, using the T-matrix method. It was able to retrieve the monomers' complex index of refraction with size parameter up to 11, relative refraction index less than 1.3, and absorption index less than 0.1. Then, the inverse method was applied to retrieve the effective spectral complex index of refraction of Synechocystis sp. approximated as randomly oriented aggregates consisting of two overlapping homogeneous spheres. Both the measured absorption cross-section and the retrieved absorption index featured peaks at 435 and 676 nm corresponding to chlorophyll a, a peak at 625 nm corresponding to phycocyanin, and a shoulder around 485 nm corresponding to carotenoids. These results can be used to optimize and control light transfer in photobioreactors. The inverse method and the equivalent coated sphere model could be applied to other optically soft particles of similar morphologies.

Study on the mechanism of human blood glucose concentration measuring using mid-infrared spectral analysis technology

NASA Astrophysics Data System (ADS)

Li, Xiang

2016-10-01

All forms of diabetes increase the risk of long-term complications. Blood glucose monitoring is of great importance for controlling diabetes procedure, preventing the complications and improving the patient's life quality. At present, the clinical blood glucose concentration measurement is invasive and could be replaced by noninvasive spectroscopy analytical techniques. The mid-infrared spectral region contains strong characteristic and well-defined absorption bands. Therefore, mid-infrared provides an opportunity for monitoring blood glucose invasively with only a few discrete bonds. Although the blood glucose concentration measurement using mid-infrared spectroscopy has a lot of advantages, the disadvantage is also obvious. The absorption in this infrared region is fundamental molecular group vibration. Absorption intensity is very strong, especially for biological molecules. In this paper, it figures out that the osmosis rate of glucose has a certain relationship with the blood glucose concentration. Therefore, blood glucose concentration could be measured indirectly by measuring the glucose exudate in epidermis layer. Human oral glucose tolerance tests were carried out to verify the correlation of glucose exudation in shallow layer of epidermis layer and blood glucose concentration. As it has been explained above, the mid-infrared spectral region contains well-defined absorption bands, the intensity of absorption peak around 1123 cm-1 was selected to measure the glucose and that around 1170 cm-1 was selected as reference. Ratio of absorption peak intensity was recorded for each set of measurement. The effect and importance of the cleaning the finger to be measured before spectrum measuring are discussed and also verified by experiment.

Effects of alkyl spacer group length on Vis-NIR absorption behavior in FTC-like guest-host EO polymers

NASA Astrophysics Data System (ADS)

Barto, Richard R., Jr.; Bedworth, Peter V.; Epstein, Joseph A.; Ermer, Susan P.; Taylor, Rebecca E.; Frank, Curtis W.

2003-07-01

Spectral absorption behavior of a series of FTC-like dyes of varying shape incorporated into amorphous polycarbonate (APC) is characterized by photothermal deflection spectroscopy. Previous Monte Carlo calculations by Dalton and Robinson predict a strong dependence of the macroscopic nonlinear optical susceptibility on the chromophore waist:length aspect ratio in electric field-poled films. This dependence arises from London interactions between chromophores, which are expected to influence the absorption characteristics of the composite both by changing the local polarity of the medium and through dipole interactions. It is expected that these interactions will play a role in the absorption characteristics of unpoled films as well. Of particular interest are the spectral characteristics of the red edge of the main dye electronic absorption peak, and the fine structure in the near-IR, dominated by overtones of fundamental C-H stretching and bending modes. The spectral structure in these key regions can be influenced by inter- and intramolecular interactions and conformational changes in the dye. The near-IR structure, in turn, will dictate absorption loss in optical devices prepared from these materials at key transmission wavelengths (1.3 and 1.55 um). In this study, a homologous series of spacer lengths, ranging from ethyl to hexyl, attached to an FTC-like NLO chromophore, LMCO-46M, is characterized by a combination of photothermal deflection spectroscopy (PDS) and UV-Vis spectroscopy to examine the effects of the molecular environment on near-IR loss at 1090 nm, 1300 nm and 1550 nm.

Modeling the reflectance of CO2 frost with new optical constants: Application to Martian south polar cap spectra

NASA Technical Reports Server (NTRS)

Hansen, Gary B.; Martin, Terry Z.

1993-01-01

New measurements of the absorption coefficients of CO2 ice, in most of the spectral range 0.2 to 3.9 microns where absorption coefficients are below 1.5 per cm, have recently been made. Although these measurements are preliminary, they contain spectral detail not seen previously in the literature. Therefore, it is useful to combine these new data with older data from spectral regions of stronger absorption and reformulate models of the albedo or reflectance of CO2 frost. These models can then be adjusted in an attempt to match measurements of Martian polar deposits, such as the set of spectra returned by the IRS instrument on Mariner 7 (1969). The new absorption coefficients of CO2 ice were measured on several samples of 41-mm thickness at 150-155 K. A portion of the spectrum from 1.9 to 3.9 microns wavelength is shown in the form of imaginary coefficient of refraction ( = linear absorption x wavelength / 4 pi). The data above 3x10(exp -5) are obtained from, except for the absorption line at 3.32 micrometers, which is extrapolated in a way that is consistent with laboratory frost measurements, but the peak level is still highly uncertain. This new imagary coefficient, combined with the real coefficient, can be immediately applied to the models for hemispherical albedo, resulting in markedly different results from those in that study. The results for an infinite optical depth layer and solar incidence of 60 degrees are plotted for a range of mean particle radii from 0.03 to 3 mm.

Non-Invasive Measurement of Frog Skin Reflectivity in High Spatial Resolution Using a Dual Hyperspectral Approach

PubMed Central

Liebisch, Frank; Walter, Achim; Greven, Hartmut; Rascher, Uwe

2013-01-01

Background Most spectral data for the amphibian integument are limited to the visible spectrum of light and have been collected using point measurements with low spatial resolution. In the present study a dual camera setup consisting of two push broom hyperspectral imaging systems was employed, which produces reflectance images between 400 and 2500 nm with high spectral and spatial resolution and a high dynamic range. Methodology/Principal Findings We briefly introduce the system and document the high efficiency of this technique analyzing exemplarily the spectral reflectivity of the integument of three arboreal anuran species (Litoria caerulea, Agalychnis callidryas and Hyla arborea), all of which appear green to the human eye. The imaging setup generates a high number of spectral bands within seconds and allows non-invasive characterization of spectral characteristics with relatively high working distance. Despite the comparatively uniform coloration, spectral reflectivity between 700 and 1100 nm differed markedly among the species. In contrast to H. arborea, L. caerulea and A. callidryas showed reflection in this range. For all three species, reflectivity above 1100 nm is primarily defined by water absorption. Furthermore, the high resolution allowed examining even small structures such as fingers and toes, which in A. callidryas showed an increased reflectivity in the near infrared part of the spectrum. Conclusion/Significance Hyperspectral imaging was found to be a very useful alternative technique combining the spectral resolution of spectrometric measurements with a higher spatial resolution. In addition, we used Digital Infrared/Red-Edge Photography as new simple method to roughly determine the near infrared reflectivity of frog specimens in field, where hyperspectral imaging is typically difficult. PMID:24058464

Thermodynamic limits to the efficiency of solar energy conversion by quantum devices

NASA Technical Reports Server (NTRS)

Buoncristiani, A. M.; Byvik, C. E.; Smith, B. T.

1981-01-01

The second law of thermodynamics imposes a strict limitation to the energy converted from direct solar radiation to useful work by a quantum device. This limitation requires that the amount of energy converted to useful work (energy in any form other than heat) can be no greater than the change in free energy of the radiation fields. Futhermore, in any real energy conversion device, not all of this available free energy in the radiation field can be converted to work because of basic limitations inherent in the device itself. A thermodynamic analysis of solar energy conversion by a completely general prototypical quantum device is presented. This device is completely described by two parameters, its operating temperature T sub R and the energy threshold of its absorption spectrum. An expression for the maximum thermodynamic efficiency of a quantum solar converter was derived in terms of these two parameters and the incident radiation spectrum. Efficiency curves for assumed solar spectral irradiance corresponding to air mass zero and air mass 1.5 are presented.

Polarization-independent triangular-groove fused-silica gratings with high efficiency at a wavelength of 1550 nm

NASA Astrophysics Data System (ADS)

Cao, Hongchao; Zhou, Changhe; Feng, Jijun; Lv, Peng; Ma, Jianyong

2010-11-01

We describe polarization-independent triangular-groove fused-silica gratings illuminated by incident lights in the C + L bands as (de)multiplexers for dense wavelength division multiplexing (DWDM) application. The physical mechanisms of the grating can be shown clearly by using the simplified modal method with consideration of the corresponding accumulated average phase difference of two excited propagating grating modes, which illustrates that the grating structure depends mainly on the ratio of the average effective indices difference to the incident wavelength. Exact grating profile is optimized by using the rigorous coupled-wave analysis (RCWA). With the optimized grating parameters, the grating exhibits diffraction efficiencies of greater than 90% under TE- and TM-polarized incident lights for 101 nm spectral bandwidths (1500-1601 nm) and it can reach an efficiency of more than 99% for both polarizations at a wavelength of 1550 nm. Without loss of metal absorption, coating of dielectric film layers, the designed triangular-groove fused-silica grating should be of great interest for DWDM application.

Resonant energy transfer and trace-level sensing using branched Ag-rod-supported carbon dots

NASA Astrophysics Data System (ADS)

Nair, Radhika V.; Arya, M.; Vijayan, C.

2018-05-01

We report on the resonant energy transfer in branched Ag rod-supported carbon dots (C-dots) and its applications for the trace-level sensing of highly reactive oxygen species and organic pollutants based on surface plasmon enhanced energy transfer (SPEET) and surface enhanced Raman spectroscopy (SERS). The branched morphology of Ag is found to significantly enhance visible light absorption and thus increases the spectral overlap with C-dot emission. In addition, branched morphology results in the formation of a large number of plasmonic hotspots and efficient propagation of plasmons through the interconnections, as also supported by finite-difference time-domain simulations. Branched Ag-rod—C-dot composite is found to be able to detect 0.02 µM of hydrogen peroxide based on SPEET. The efficient transfer of electrons from C-dots to the Ag rod enhances the SERS efficiency of Ag resulting in an enhancement factor of the order of 108 and enables the composite to detect 10‑10 M of the organic pollutant Rhodamine 6G.

Effects of boundary conditions on the cleaning efficiency of riverbank filtration and artificial groundwater recharge systems regarding bulk parameters and trace pollutants.

PubMed

Storck, Florian R; Schmidt, Carsten K; Wülser, Richard; Brauch, Heinz-Jürgen

2012-01-01

Drinking water is often produced from surface water by riverbank filtration (RBF) or artificial groundwater recharge (AGR). In this study, an AGR system was exemplarily investigated and results were compared with those of RBF systems, in which the effects of redox milieu, temperature and surface water discharge on the cleaning efficiency were evaluated. Besides bulk parameters such as DOC (dissolved organic carbon), organic trace pollutants including iodinated X-ray contrast media, personal care products, complexing agents, and pharmaceuticals were investigated. At all studied sites, levels of TOC (total organic carbon), DOC, AOX (adsorbable organic halides), SAC (spectral absorption coefficient at 254 nm), and turbidity were reduced significantly. DOC removal was stimulated at higher groundwater temperatures during AGR. Several substances were generally easily removable during both AGR and RBF, regardless of the site, season, discharge or redox regime. For some more refractory substances, however, removal efficiency turned out to be significantly influenced by redox conditions.

Development of an analytical-numerical model to predict radiant emission or absorption

NASA Technical Reports Server (NTRS)

Wallace, Tim L.

1994-01-01

The development of an analytical-numerical model to predict radiant emission or absorption is discussed. A voigt profile is assumed to predict the spectral qualities of a singlet atomic transition line for atomic species of interest to the OPAD program. The present state of this model is described in each progress report required under contract. Model and code development is guided by experimental data where available. When completed, the model will be used to provide estimates of specie erosion rates from spectral data collected from rocket exhaust plumes or other sources.

Absorption spectroscopy and multi-angle scattering measurements in the visible spectral range for the geographic classification of Italian exravirgin olive oils

NASA Astrophysics Data System (ADS)

Mignani, Anna G.; Ciaccheri, Leonardo; Cimato, Antonio; Sani, Graziano; Smith, Peter R.

2004-03-01

Absorption spectroscopy and multi-angle scattering measurements in the visible spectral range are innovately used to analyze samples of extra virgin olive oils coming from selected areas of Tuscany, a famous Italian region for the production of extra virgin olive oil. The measured spectra are processed by means of the Principal Component Analysis method, so as to create a 3D map capable of clustering the Tuscan oils within the wider area of Italian extra virgin olive oils.

Apparatus for experimental investigation of aerodynamic radiation with absorption by ablation products

NASA Technical Reports Server (NTRS)

Wells, W. L.; Snow, W. L.

1977-01-01

A description is given and calibration procedures are presented for an apparatus that is used to simulate aerodynamic radiant heating during planetary entry. The primary function of the apparatus is to simulate the spectral distribution of shock layer radiation and to determine absorption effects of simulated ablation products which are injected into the stagnation region flow field. An electric arc heater is used to heat gas mixtures that represent the planetary atmospheres of interest. Spectral measurements are made with a vacuum ultraviolet scanning monochromator.

Metal-core/semiconductor-shell nanocones for broadband solar absorption enhancement.

PubMed

Zhou, Lin; Yu, Xiaoqiang; Zhu, Jia

2014-02-12

Nanostructure-based photovoltaic devices have exhibited several advantages, such as reduced reflection, extraordinary light trapping, and so forth. In particular, semiconductor nanostructures provide optical modes that have strong dependence on the size and geometry. Metallic nanostructures also attract a lot of attention because of the appealing plasmonic effect on the near-field enhancement. In this study, we propose a novel design, the metal-core/semiconductor-shell nanocones with the core radius varying in a linearly gradient style. With a thin layer of semiconductor absorber coated on a metallic cone, such a design can lead to significant and broadband absorption enhancement across the entire visible and near-infrared solar spectrum. As an example of demonstration, a layer of 16 nm thick crystalline silicon (c-Si) coated on a silver nanocone can absorb 27% of standard solar radiation across a broad spectral range of 300-1100 nm, which is equivalent to a 700 nm thick flat c-Si film. Therefore, the absorption enhancement factor approaching the Yablonovitch limit is achieved with this design. The significant absorption enhancement can be ascribed to three types of optical modes, that is, Fabry-Perot modes, plasmonic modes, and hybrid modes that combine the features of the previous two. In addition, the unique nanocone geometry enables the linearly gradient radius of the semiconductor shell, which can support multiple optical resonances, critical for the broadband absorption. Our design may find general usage as elements for the low cost, high efficiency solar conversion and water-splitting devices.

An Accurate Absorption-Based Net Primary Production Model for the Global Ocean

NASA Astrophysics Data System (ADS)

Silsbe, G.; Westberry, T. K.; Behrenfeld, M. J.; Halsey, K.; Milligan, A.

2016-02-01

As a vital living link in the global carbon cycle, understanding how net primary production (NPP) varies through space, time, and across climatic oscillations (e.g. ENSO) is a key objective in oceanographic research. The continual improvement of ocean observing satellites and data analytics now present greater opportunities for advanced understanding and characterization of the factors regulating NPP. In particular, the emergence of spectral inversion algorithms now permits accurate retrievals of the phytoplankton absorption coefficient (aΦ) from space. As NPP is the efficiency in which absorbed energy is converted into carbon biomass, aΦ measurements circumvents chlorophyll-based empirical approaches by permitting direct and accurate measurements of phytoplankton energy absorption. It has long been recognized, and perhaps underappreciated, that NPP and phytoplankton growth rates display muted variability when normalized to aΦ rather than chlorophyll. Here we present a novel absorption-based NPP model that parameterizes the underlying physiological mechanisms behind this muted variability, and apply this physiological model to the global ocean. Through a comparison against field data from the Hawaii and Bermuda Ocean Time Series, we demonstrate how this approach yields more accurate NPP measurements than other published NPP models. By normalizing NPP to satellite estimates of phytoplankton carbon biomass, this presentation also explores the seasonality of phytoplankton growth rates across several oceanic regions. Finally, we discuss how future advances in remote-sensing (e.g. hyperspectral satellites, LIDAR, autonomous profilers) can be exploited to further improve absorption-based NPP models.

Navy Calibration/Validation Protocols and Procedures for Visible and Thermal Satellites: Preparing for NPOESS

DTIC Science & Technology

2007-05-01

difficult but it determines the long-term stability of the sensor. This step includes sensor drift ( spectral response) and spectral (channel...and Navy products using high spectral resolution satellites. This program (Hyperspectral 34 Characterization of the Coastal Zone) is a core NRLSSC...absorption and total attenuation) the standard accepted instrument is the WetLab’s Inc., ac-9, with a higher resolution spectral instrument in final

Mirror coatings for large aperture UV optical infrared telescope optics

NASA Astrophysics Data System (ADS)

Balasubramanian, Kunjithapatham; Hennessy, John; Raouf, Nasrat; Nikzad, Shouleh; Del Hoyo, Javier; Quijada, Manuel

2017-09-01

Large space telescope concepts such as LUVOIR and HabEx aiming for observations from far UV to near IR require advanced coating technologies to enable efficient gathering of light with important spectral signatures including those in far UV region down to 90nm. Typical Aluminum mirrors protected with MgF2 fall short of the requirements below 120nm. New and improved coatings are sought to protect aluminum from oxidizing readily in normal environment causing severe absorption and reduction of reflectance in the deep UV. Choice of materials and the process of applying coatings present challenges. Here we present the progress achieved to date with experimental investigations of coatings at JPL and at GSFC and discuss the path forward to achieve high reflectance in the spectral region from 90 to 300nm without degrading performance in the visible and NIR regions taking into account durability concerns when the mirrors are exposed to normal laboratory environment as well as high humidity conditions. Reflectivity uniformity required on these mirrors is also discussed.

NIR emitting K2SrCl4:Eu2+, Nd3+ phosphor as a spectral converter for CIGS solar cell

NASA Astrophysics Data System (ADS)

Tawalare, P. K.; Bhatkar, V. B.; Omanwar, S. K.; Moharil, S. V.

2018-05-01

Intense near-infrared emitting phosphor K2SrCl4:Eu2+,Nd3+ with various concentrations of Nd3+ were synthesized. These are characterized with X-ray diffraction, reflectance, photoluminescence emission and photoluminescence excitation spectroscopy, PL lifetime measurements. The emission can be excited by a broad band in near ultra violet region as a consequence of Eu2+→Nd3+ energy transfer. The efficiency of Eu2+→Nd3+ energy transfer is as high as 95%. Fluorescence decay curves for Eu2+ doped samples are almost exponential and described by τ = 500 ns. Eu2+ lifetimes are shortened after Nd3+ doping. Near infrared Emission intensity is limited by Nd3+→Nd3+ energy transfer and the consequent concentration quenching. Nd3+ emission matches well with the spectral response of CIGS and CIS solar cells. Absorption of near ultra violet radiations followed by conversion to near infrared indicates the potential application in solar photovoltaics.

Effect of the spectral emission energy of various UV sources on photochemical curing of unsaturated oligomeric ester coatings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Skubin, V.K.; Sazonov, A.P.; Torgonenko, V.A.

1988-11-10

In this paper, using the example of unsaturated oligomeric esters, the effect of UV radiation of various domestic sources on the rate of curing of coatings is investigated. For the investigations a 60% styrene solution of PN-15 grade unsaturated oligomeric ester based on an equimolar ratio of maleic anhydride and oxypropylated diphenylenepropene was used. Isobutyl ether of benzoin served as the photoinitiator. The following lamps were used as radiation sources: electrodeless high-frequency lamps of continuous action with additions of mercury, cadmium, and phosphorus; a DRKS-500 mercury-xenon-arc lamp; and a DRT-1000 tubular mercury-arc lamp. When choosing UV sources to increase themore » efficiency of photochemical decay of the initiator and the rate of curing of the coating it is necessary first of all to be guided by the distribution of the spectral energy of the lamp radiation and the UV absorption spectrum of the photoinitiator.« less

Benzimidazole derivative vs. different phases of TiO2-physico-chemical approach.

PubMed

Karunakaran, C; Jayabharathi, J; Jayamoorthy, K

2013-10-01

1-Benzyl-2-phenyl-1H-benzo[d]imidazole (BPBI) has been synthesized by simple steps and characterized by spectral studies. Absorption and fluorescence spectral studies have been employed to investigate the interaction of BPBI with the anatase, hombikat, P25 and rutile phases of TiO2. The emission of the BPBI is efficiently quenched by anatase, hombikat and P25 TiO2 nanoparticles owing to charge injection from the excited singlet state of BPBI to the conduction band of the TiO2 nanoparticles. Surprisingly, rutile phase enhances the fluorescence which is likely due to lowering of LUMO and HOMO levels of the ligand on ducking of the benzimidazole moiety of the BPBI molecule into the void space of rutile TiO2. Electron injection from photoexcited BPBI to the TiO2 conduction band (S*→S(+)+e(-)(CB)) is likely to enhance the fluorescence. Copyright © 2013 Elsevier B.V. All rights reserved.

Imaging trace gases in volcanic plumes with Fabry Perot Interferometers

NASA Astrophysics Data System (ADS)

Kuhn, Jonas; Platt, Ulrich; Bobrowski, Nicole; Lübcke, Peter; Wagner, Thomas

2017-04-01

Within the last decades, progress in remote sensing of atmospheric trace gases revealed many important insights into physical and chemical processes in volcanic plumes. In particular, their evolution could be studied in more detail than by traditional in-situ techniques. A major limitation of standard techniques for volcanic trace gas remote sensing (e.g. Differential Optical Absorption Spectroscopy, DOAS) is the constraint of the measurement to a single viewing direction since they use dispersive spectroscopy with a high spectral resolution. Imaging DOAS-type approaches can overcome this limitation, but become very time consuming (of the order of minutes to record a single image) and often cannot match the timescales of the processes of interest for volcanic gas measurements (occurring at the order of seconds). Spatially resolved imaging observations with high time resolution for volcanic sulfur dioxide (SO2) emissions became possible with the introduction of the SO2-Camera. Reducing the spectral resolution to two spectral channels (using interference filters) that are matched to the SO2 absorption spectrum, the SO2-Camera is able to record full frame SO2 slant column density distributions at a temporal resolution on the order of < 1s. This for instance allows for studying variations in SO2 fluxes on very short time scales and applying them in magma dynamics models. However, the currently employed SO2-Camera technique is limited to SO2 detection and, due to its coarse spectral resolution, has a limited spectral selectivity. This limits its application to very specific, infrequently found measurement conditions. Here we present a new approach, based on matching the transmission profile of Fabry Perot Interferometers (FPIs) to periodic spectral absorption features of trace gases. The FPI's transmission spectrum is chosen to achieve a high correlation with the spectral absorption of the trace gas, allowing a high selectivity and sensitivity with still using only a few spectral channels. This would not only improve SO2 imaging, but also allow for the application of the technique to further gases of interest in volcanology (and other areas of atmospheric research). Imaging halogen species would be particularly interesting for volcanic trace gas studies. Bromine monoxide (BrO) and chlorine dioxide (OClO) both yield absorption features that allow their detection with the FPI correlation technique. From BrO and OClO data, ClO levels in the plume could be calculated. We present an outline of applications of the FPI technique to imaging a series of trace gases in volcanic plumes. Sample calculations on the sensitivity and selectivity of the technique, first proof of concept studies and proposals for technical implementations are presented.

Remote Sensing of Aerosol and Non-Aerosol Absorption

NASA Technical Reports Server (NTRS)

Kaufman, Y. J.; Dubovik, O.; Holben, B. N.; Remer, L. A.; Tanre, D.; Lau, William K. M. (Technical Monitor)

2001-01-01

Remote sensing of aerosol from the new satellite instruments (e.g. MODIS from Terra) and ground based radiometers (e.g. the AERONET) provides the opportunity to measure the absorption characteristics of the ambient undisturbed aerosol in the entire atmospheric column. For example Landsat and AERONET data are used to measure spectral absorption of sunlight by dust from West Africa. Both Application of the Landsat and AERONET data demonstrate that Saharan dust absorption of solar radiation is several times smaller than the current international standards. This is due to difficulties of measuring dust absorption in situ, and due to the often contamination of dust properties by the presence of air pollution or smoke. We use the remotely sensed aerosol absorption properties described by the spectral sin le scattering albedo, together with statistics of the monthly optical thickness for the fine and coarse aerosol derived from the MODIS data. The result is an estimate of the flux of solar radiation absorbed by the aerosol layer in different regions around the globe where aerosol is prevalent. If this aerosol forcing through absorption is not included in global circulation models, it may be interpreted as anomalous absorption in these regions. In a preliminary exercise we also use the absorption measurements by AERONET, to derive the non-aerosol absorption of the atmosphere in cloud free conditions. The results are obtained for the atmospheric windows: 0.44 microns, 0.66 microns, 0.86 microns and 1.05 microns. In all the locations over the land and ocean that were tested no anomalous absorption in these wavelengths, was found within absorption optical thickness of +/- 0.005.

Direct and simultaneous observation of ultrafast electron and hole dynamics in germanium

DOE PAGES

Zurch, Michael; Chang, Hung -Tzu; Borja, Lauren J.; ...

2017-06-01

Understanding excited carrier dynamics in semiconductors is crucial for the development of photovoltaics and efficient photonic devices. However, overlapping spectral features in optical pump-probe spectroscopy often render assignments of separate electron and hole carrier dynamics ambiguous. Here, ultrafast electron and hole dynamics in germanium nanocrystalline thin films are directly and simultaneously observed by ultrafast transient absorption spectroscopy in the extreme ultraviolet at the germanium M 4,5 edge. We decompose the spectra into contributions of electronic state blocking and photo-induced band shifts at a carrier density of 8 × 10 20 cm –3. Separate electron and hole relaxation times are observedmore » as a function of hot carrier energies. A first-order electron and hole decay of ~1 ps suggests a Shockley–Read–Hall recombination mechanism. Furthermore, the simultaneous observation of electrons and holes with extreme ultraviolet transient absorption spectroscopy paves the way for investigating few- to sub-femtosecond dynamics of both holes and electrons in complex semiconductor materials and across junctions.« less

Green synthesis, characterization and some physico-chemical studies on a novel intermolecular compound; 4-nitro-o-phenylenediamine-N, N-dimethylaminobenzaldehyde system

NASA Astrophysics Data System (ADS)

Rai, U. S.; Singh, Manjeet; Rai, R. N.

2017-09-01

An inter-molecular compound (IMC) L1 was synthesized by taking 1:1 molar ratio of p-nitro-o-phenylenediamine (NOPDA) and N, N-dimethylaminobenzaldehyde (DMAB) via thermally initiated solid state reaction. It was characterized by X-ray diffraction, spectral and optical studies. The single crystal of the (L1) was grown from saturated solution of ethanol using slow evaporation technique at 29 °C. From the single crystal X-ray diffraction analysis, it can be inferred that it crystallizes in triclinic unit cell with P-1 space group (CCDC No 1422765). Absorption spectrum of IMC (L1) shows a band at 318 nm attributed to the intra-molecular charge-transfer (ICT) excited state absorption and the other band at 376 nm is due to n→π* transition. The IMC (L1) shows a strong fluorescence at 418 nm with a Stokes shift (≈100 nm) and quantum efficiency (0.22) upon excitation in methyl alcohol at 318 nm.

a-Si:H/SiNW shell/core for SiNW solar cell applications

PubMed Central

2013-01-01

Vertically aligned silicon nanowires have been synthesized by the chemical etching of silicon wafers. The influence of a hydrogenated amorphous silicon (a-Si:H) layer (shell) on top of a silicon nanowire (SiNW) solar cell has been investigated. The optical properties of a-Si:H/SiNWs and SiNWs are examined in terms of optical reflection and absorption properties. In the presence of the a-Si:H shell, 5.2% reflection ratio in the spectral range (250 to 1,000 nm) is achieved with a superior absorption property with an average over 87% of the incident light. In addition, the characteristics of the solar cell have been significantly improved, which exhibits higher open-circuit voltage, short-circuit current, and efficiency by more than 15%, 12%, and 37%, respectively, compared with planar SiNW solar cells. Based on the current–voltage measurements and morphology results, we show that the a-Si:H shell can passivate the defects generated by wet etching processes. PMID:24195734

Utilization of hydroxypropyl carboxymethyl cellulose in synthesis of silver nanoparticles.

PubMed

Abdel-Halim, E S; Alanazi, Humaid H; Al-Deyab, Salem S

2015-04-01

Hydroxypropyl carboxymethyl cellulose samples having varying degrees of substitution and varying degrees of polymerization were used to reduce silver nitrate to silver nanoparticles. UV spectral analysis of silver nanoparticles colloidal solution reveal that increasing the pH of the reduction solution leads to improvement in the intensity of the absorption band for silver nanoparticles, to be maximum at pH 11. The absorption peak intensity also enhanced upon prolonging the reaction duration up to 60 min. The conversion of silver ions to metallic silver nanoparticles was found to be temperature-dependent and maximum transformation occurs at 60 °C. The reduction efficiency of hydroxypropyl carboxymethyl cellulose was found to be affected by its degree of polymerization. Colloidal solutions of silver nanoparticles having concentration up to 1000 ppm can be prepared upon fixing the ratio between silver nitrate and hydroxypropyl carboxymethyl cellulose at 0.017-0.3g per each 100ml of the reduction solution. Copyright © 2015 Elsevier B.V. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Xingshu; Silverman, Timothy J.; Zhou, Zhiguang

For commercial one-sun solar modules, up to 80% of the incoming sunlight may be dissipated as heat, potentially raising the temperature 20-30 °C higher than the ambient. In the long term, extreme self-heating erodes efficiency and shortens lifetime, thereby dramatically reducing the total energy output. Therefore, it is critically important to develop effective and practical (and preferably passive) cooling methods to reduce operating temperature of photovoltaic (PV) modules. In this paper, we explore two fundamental (but often overlooked) origins of PV self-heating, namely, sub-bandgap absorption and imperfect thermal radiation. The analysis suggests that we redesign the optical properties of themore » solar module to eliminate parasitic absorption (selective-spectral cooling) and enhance thermal emission (radiative cooling). Comprehensive opto-electro-thermal simulation shows that the proposed techniques would cool one-sun terrestrial solar modules up to 10 °C. As a result, this self-cooling would substantially extend the lifetime for solar modules, with corresponding increase in energy yields and reduced levelized cost of electricity.« less

Real-time spectroscopic sensing using a widely tunable external cavity-QCL with MOEMS diffraction grating

NASA Astrophysics Data System (ADS)

Ostendorf, Ralf; Butschek, Lorenz; Merten, André; Grahmann, Jan; Jarvis, Jan; Hugger, Stefan; Fuchs, Frank; Wagner, Joachim

2016-02-01

We present spectroscopic measurements performed with an EC-QCL combining a broadly tunable quantum cascade laser chip with a tuning range of more than 300 cm-1 and a resonantly driven MOEMS scanner with an integrated diffraction grating for wavelength selection in Littrow configuration. The grating geometry was optimized to provide high diffraction efficiency over the wide tuning range of the QCL, thus assuring high power density and high spectral resolution in the MIR range. The MOEMS scanner has a resonance frequency of 1 kHz, hence allowing for two full wavelength scans, one up and the other downwards, within 1 ms. The capability for real-time spectroscopic sensing based on MOEMS EC-QCLs is demonstrated by transmission measurements performed on polystyrene reference absorber sheets as well as on gaseous samples of carbon monoxide. For the latter one, a large portion of the characteristic CO absorption band containing several absorption lines in the range of 2070 cm-1 to 2280 cm-1 can be monitored in real-time.

The integrated radio continuum spectrum of M33 - Evidence for free-free absorption by cool ionized gas

NASA Technical Reports Server (NTRS)

Israel, F. P.; Mahoney, M. J.; Howarth, N.

1992-01-01

We present measurements of the integrated radio continuum flux density of M33 at frequencies between 22 and 610 MHz and discuss the radio continuum spectrum of M33 between 22 MHz and 10 GHz. This spectrum has a turnover between 500 and 900 MHz, depending on the steepness of the high frequency radio spectrum of M33. Below 500 MHz the spectrum is relatively flat. We discuss possible mechanisms to explain this spectral shape and consider efficient free-free absorption of nonthermal emission by a cool (not greater than 1000 K) ionized gas to be a very likely possibility. The surface filling factor of both the nonthermal and the thermal material appears to be small (of order 0.001), which could be explained by magnetic field/density fluctuations in the M 33 interstellar medium. We briefly speculate on the possible presence of a nuclear radio source with a steep spectrum.

Low power consumption lasers for next generation miniature optical spectrometers for trace gas analysis

NASA Astrophysics Data System (ADS)

Forouhar, S.; Frez, C.; Franz, K. J.; Ksendzov, A.; Qiu, Y.; Soibel, K. A.; Chen, J.; Hosoda, T.; Kipshidze, G.; Shterengas, L.; Belenky, G.

2011-01-01

The air quality of any manned spacecraft needs to be continuously monitored in order to safeguard the health of the crew. Air quality monitoring grows in importance as mission duration increases. Due to the small size, low power draw, and performance reliability, semiconductor laser-based instruments are viable candidates for this purpose. Achieving a minimum instrument size requires lasers with emission wavelength coinciding with the absorption of the fundamental absorption lines of the target gases, which are mostly in the 3.0-5.0 μm wavelength range. In this paper we report on our progress developing high wall plug efficiency type-I quantum-well GaSb-based diode lasers operating at room temperatures in the spectral region near 3.0-3.5 μm and quantum cascade (QC) lasers in the 4.0-5.0 μm range. These lasers will enable the development of miniature, low-power laser spectrometers for environmental monitoring of the spacecraft.

Direct and simultaneous observation of ultrafast electron and hole dynamics in germanium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zurch, Michael; Chang, Hung -Tzu; Borja, Lauren J.

Understanding excited carrier dynamics in semiconductors is crucial for the development of photovoltaics and efficient photonic devices. However, overlapping spectral features in optical pump-probe spectroscopy often render assignments of separate electron and hole carrier dynamics ambiguous. Here, ultrafast electron and hole dynamics in germanium nanocrystalline thin films are directly and simultaneously observed by ultrafast transient absorption spectroscopy in the extreme ultraviolet at the germanium M 4,5 edge. We decompose the spectra into contributions of electronic state blocking and photo-induced band shifts at a carrier density of 8 × 10 20 cm –3. Separate electron and hole relaxation times are observedmore » as a function of hot carrier energies. A first-order electron and hole decay of ~1 ps suggests a Shockley–Read–Hall recombination mechanism. Furthermore, the simultaneous observation of electrons and holes with extreme ultraviolet transient absorption spectroscopy paves the way for investigating few- to sub-femtosecond dynamics of both holes and electrons in complex semiconductor materials and across junctions.« less

Direct and simultaneous observation of ultrafast electron and hole dynamics in germanium.

PubMed

Zürch, Michael; Chang, Hung-Tzu; Borja, Lauren J; Kraus, Peter M; Cushing, Scott K; Gandman, Andrey; Kaplan, Christopher J; Oh, Myoung Hwan; Prell, James S; Prendergast, David; Pemmaraju, Chaitanya D; Neumark, Daniel M; Leone, Stephen R

2017-06-01

Understanding excited carrier dynamics in semiconductors is crucial for the development of photovoltaics and efficient photonic devices. However, overlapping spectral features in optical pump-probe spectroscopy often render assignments of separate electron and hole carrier dynamics ambiguous. Here, ultrafast electron and hole dynamics in germanium nanocrystalline thin films are directly and simultaneously observed by ultrafast transient absorption spectroscopy in the extreme ultraviolet at the germanium M 4,5 edge. We decompose the spectra into contributions of electronic state blocking and photo-induced band shifts at a carrier density of 8 × 10 20  cm -3 . Separate electron and hole relaxation times are observed as a function of hot carrier energies. A first-order electron and hole decay of ∼1 ps suggests a Shockley-Read-Hall recombination mechanism. The simultaneous observation of electrons and holes with extreme ultraviolet transient absorption spectroscopy paves the way for investigating few- to sub-femtosecond dynamics of both holes and electrons in complex semiconductor materials and across junctions.

Direct and simultaneous observation of ultrafast electron and hole dynamics in germanium

PubMed Central

Zürch, Michael; Chang, Hung-Tzu; Borja, Lauren J.; Kraus, Peter M.; Cushing, Scott K.; Gandman, Andrey; Kaplan, Christopher J.; Oh, Myoung Hwan; Prell, James S.; Prendergast, David; Pemmaraju, Chaitanya D.; Neumark, Daniel M.; Leone, Stephen R.

2017-01-01

Understanding excited carrier dynamics in semiconductors is crucial for the development of photovoltaics and efficient photonic devices. However, overlapping spectral features in optical pump-probe spectroscopy often render assignments of separate electron and hole carrier dynamics ambiguous. Here, ultrafast electron and hole dynamics in germanium nanocrystalline thin films are directly and simultaneously observed by ultrafast transient absorption spectroscopy in the extreme ultraviolet at the germanium M4,5 edge. We decompose the spectra into contributions of electronic state blocking and photo-induced band shifts at a carrier density of 8 × 1020 cm−3. Separate electron and hole relaxation times are observed as a function of hot carrier energies. A first-order electron and hole decay of ∼1 ps suggests a Shockley–Read–Hall recombination mechanism. The simultaneous observation of electrons and holes with extreme ultraviolet transient absorption spectroscopy paves the way for investigating few- to sub-femtosecond dynamics of both holes and electrons in complex semiconductor materials and across junctions. PMID:28569752