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Sample records for absorption optical thickness

  1. Matrix formalism for light propagation and absorption in thick textured optical sheets.

    PubMed

    Eisenlohr, Johannes; Tucher, Nico; Höhn, Oliver; Hauser, Hubert; Peters, Marius; Kiefel, Peter; Goldschmidt, Jan Christoph; Bläsi, Benedikt

    2015-06-01

    In this paper, we introduce a simulation formalism for determining the Optical Properties of Textured Optical Sheets (OPTOS). Our matrix-based method allows for the computationally-efficient calculation of non-coherent light propagation and absorption in thick textured sheets, especially solar cells, featuring different textures on front and rear side that may operate in different optical regimes. Within the simulated system, the angular power distribution is represented by a vector. This light distribution is modified by interaction with the surfaces of the textured sheets, which are described by redistribution matrices. These matrices can be calculated for each individual surface texture with the most appropriate technique. Depending on the feature size of the texture, for example, either ray- or wave-optical methods can be used. The comparison of the simulated absorption in a sheet of silicon for a variety of surface textures, both with the results from other simulation techniques and experimentally measured data, shows very good agreement. To demonstrate the versatility of this newly-developed approach, the absorption in silicon sheets with a large-scale structure (V-grooves) at the front side and a small-scale structure (diffraction grating) at the rear side is calculated. Moreover, with minimal computational effort, a thickness parameter variation is performed. PMID:26072875

  2. Tunable Diode Laser Atomic Absorption Spectroscopy for Detection of Potassium under Optically Thick Conditions.

    PubMed

    Qu, Zhechao; Steinvall, Erik; Ghorbani, Ramin; Schmidt, Florian M

    2016-04-01

    Potassium (K) is an important element related to ash and fine-particle formation in biomass combustion processes. In situ measurements of gaseous atomic potassium, K(g), using robust optical absorption techniques can provide valuable insight into the K chemistry. However, for typical parts per billion K(g) concentrations in biomass flames and reactor gases, the product of atomic line strength and absorption path length can give rise to such high absorbance that the sample becomes opaque around the transition line center. We present a tunable diode laser atomic absorption spectroscopy (TDLAAS) methodology that enables accurate, calibration-free species quantification even under optically thick conditions, given that Beer-Lambert's law is valid. Analyte concentration and collisional line shape broadening are simultaneously determined by a least-squares fit of simulated to measured absorption profiles. Method validation measurements of K(g) concentrations in saturated potassium hydroxide vapor in the temperature range 950-1200 K showed excellent agreement with equilibrium calculations, and a dynamic range from 40 pptv cm to 40 ppmv cm. The applicability of the compact TDLAAS sensor is demonstrated by real-time detection of K(g) concentrations close to biomass pellets during atmospheric combustion in a laboratory reactor. PMID:26938713

  3. The effect of film thickness on the optical absorption edge and optical constants of the Cr(III) organic thin films

    NASA Astrophysics Data System (ADS)

    Yakuphanoglu, F.; Sekerci, M.; Balaban, A.

    2005-05-01

    The effect of film thickness on optical properties of the Cr(III) complex having 2-pyridincarbaldehye thiosemicarbazone thin films was investigated. The analyses of the optical absorption data revealed existence of direct and indirect transitions in the optical band gap. The optical constants (refractive index and dielectric constant) of the thin films were determined. The thickness of the films causes important changes in refractive index and real part-imaginary parts of the dielectric constant. The most significant result of the present study is to indicate that thickness of the film can be used to modify in the optical band gaps and optical constant of the thin films.

  4. Nonlinear optical absorption tuning in Bi3.15Nd0.85Ti3O12 ferroelectric thin films by thickness

    NASA Astrophysics Data System (ADS)

    Li, S.; Zhong, X. L.; Cheng, G. H.; Liu, X.; Zhang, Y.; Wang, J. B.; Song, H. J.; Tan, C. B.; Li, B.

    2015-04-01

    The tunability of nonlinear optical (NLO) absorption in Bi3.15Nd0.85Ti3O12 (BNT) ferroelectric thin films was investigated through the open aperture Z-scan method with femtosecond laser pulses at the wavelength of 800 nm. NLO absorption responses of the BNT films were observed to be highly sensitive to the film thickness. As the film thickness increases from 106.8 to 139.7 nm, the NLO absorption changes from saturable absorption (SA) to reverse saturable absorption (RSA). When the film thickness further increases to 312.9 nm, the RSA effect is enhanced. A band-gap-related competition between the ground-state excitation and the two-photon absorption is responsible for the absorption switching behavior. Such a tunable NLO absorption can widen the photonic application of the BNT thin films.

  5. Optical absorption measurement system

    DOEpatents

    Draggoo, Vaughn G.; Morton, Richard G.; Sawicki, Richard H.; Bissinger, Horst D.

    1989-01-01

    The system of the present invention contemplates a non-intrusive method for measuring the temperature rise of optical elements under high laser power optical loading to determine the absorption coefficient. The method comprises irradiating the optical element with a high average power laser beam, viewing the optical element with an infrared camera to determine the temperature across the optical element and calculating the absorption of the optical element from the temperature.

  6. Nonlinear optical absorption tuning in Bi{sub 3.15}Nd{sub 0.85}Ti{sub 3}O{sub 12} ferroelectric thin films by thickness

    SciTech Connect

    Li, S.; Zhong, X. L. E-mail: jbwang@xtu.edu.cn; Zhang, Y.; Wang, J. B. E-mail: jbwang@xtu.edu.cn; Song, H. J.; Tan, C. B.; Li, B.; Cheng, G. H.; Liu, X.

    2015-04-06

    The tunability of nonlinear optical (NLO) absorption in Bi{sub 3.15}Nd{sub 0.85}Ti{sub 3}O{sub 12} (BNT) ferroelectric thin films was investigated through the open aperture Z-scan method with femtosecond laser pulses at the wavelength of 800 nm. NLO absorption responses of the BNT films were observed to be highly sensitive to the film thickness. As the film thickness increases from 106.8 to 139.7 nm, the NLO absorption changes from saturable absorption (SA) to reverse saturable absorption (RSA). When the film thickness further increases to 312.9 nm, the RSA effect is enhanced. A band-gap-related competition between the ground-state excitation and the two-photon absorption is responsible for the absorption switching behavior. Such a tunable NLO absorption can widen the photonic application of the BNT thin films.

  7. Optical Absorption in Liquid Semiconductors

    NASA Astrophysics Data System (ADS)

    Bell, Florian Gene

    An infrared absorption cell has been developed which is suitable for high temperature liquids which have absorptions in the range .1-10('3) cm('-1). The cell is constructed by clamping a gasket between two flat optical windows. This unique design allows the use of any optical windows chemically compatible with the liquid. The long -wavelength limit of the measurements is therefore limited only by the choice of the optical windows. The thickness of the cell can easily be set during assembly, and can be varied from 50 (mu)m to .5 cm. Measurements of the optical absorption edge were performed on the liquid alloy Se(,1-x)Tl(,x) for x = 0, .001, .002, .003, .005, .007, and .009, from the melting point up to 475(DEGREES)C. The absorption was found to be exponential in the photon energy over the experimental range from 0.3 eV to 1.2 eV. The absorption increased linearly with concentration according to the empirical relation (alpha)(,T)(h(nu)) = (alpha)(,1) + (alpha)(,2)x, and the absorption (alpha)(,1) was interpreted as the absorption in the absence of T1. (alpha)(,1) also agreed with the measured absorption in 100% Se at corresponding temperatures and energies. The excess absorption defined by (DELTA)(alpha) = (alpha)(,T)(h(nu))-(alpha)(,1) was interpreted as the absorption associated with Tl and was found to be thermally activated with an activation energy E(,t) = 0.5 eV. The exponential edge is explained as absorption on atoms immersed in strong electric fields surrounding ions. The strong fields give rise to an absorption tail similar to the Franz-Keldysh effect. A simple calculation is performed which is based on the Dow-Redfield theory of absorption in an electric field with excitonic effects included. The excess absorption at low photon energies is proportional to the square of the concentration of ions, which are proposed to exist in the liquid according to the relation C(,i) (PROPORTIONAL) x(' 1/2)(.)e('-E)t('/kT), which is the origin of the thermal activation

  8. Analyzing Water's Optical Absorption

    NASA Technical Reports Server (NTRS)

    2002-01-01

    A cooperative agreement between World Precision Instruments (WPI), Inc., and Stennis Space Center has led the UltraPath(TM) device, which provides a more efficient method for analyzing the optical absorption of water samples at sea. UltraPath is a unique, high-performance absorbance spectrophotometer with user-selectable light path lengths. It is an ideal tool for any study requiring precise and highly sensitive spectroscopic determination of analytes, either in the laboratory or the field. As a low-cost, rugged, and portable system capable of high- sensitivity measurements in widely divergent waters, UltraPath will help scientists examine the role that coastal ocean environments play in the global carbon cycle. UltraPath(TM) is a trademark of World Precision Instruments, Inc. LWCC(TM) is a trademark of World Precision Instruments, Inc.

  9. Optical absorption of silicon nanowires

    SciTech Connect

    Xu, T.; Lambert, Y.; Krzeminski, C.; Grandidier, B.; Stievenard, D.; Leveque, G.; Akjouj, A.; Pennec, Y.; Djafari-Rouhani, B.

    2012-08-01

    We report on simulations and measurements of the optical absorption of silicon nanowires (NWs) versus their diameter. We first address the simulation of the optical absorption based on two different theoretical methods: the first one, based on the Green function formalism, is useful to calculate the scattering and absorption properties of a single or a finite set of NWs. The second one, based on the finite difference time domain (FDTD) method, is well-adapted to deal with a periodic set of NWs. In both cases, an increase of the onset energy for the absorption is found with increasing diameter. Such effect is experimentally illustrated, when photoconductivity measurements are performed on single tapered Si nanowires connected between a set of several electrodes. An increase of the nanowire diameter reveals a spectral shift of the photocurrent intensity peak towards lower photon energies that allow to tune the absorption onset from the ultraviolet radiations to the visible light spectrum.

  10. Solar absorption in thick and multilayered glazings

    SciTech Connect

    Powles, Rebecca; Curcija, Dragan; Kohler, Christian

    2002-02-01

    Thick and multilayered glazings generally have a nonuniform distribution of absorbed solar radiation which is not taken into account by current methods for calculating the center of glass solar gain and thermal performance of glazing systems. This paper presents a more accurate method for calculating the distribution of absorbed solar radiation inside thick and multilayered glazings and demonstrates that this can result in a small but significant difference in steady-state temperature profile and Solar Heat Gain Coefficient for some types of glazing systems when compared to the results of current methods. This indicates that a more detailed approach to calculating the distribution of absorbed solar radiation inside glazings and resulting thermal performance may be justified for certain applications.

  11. Optical absorption in trilayer graphene

    NASA Astrophysics Data System (ADS)

    Li, Xiao; Zhang, Fan; Niu, Qian

    2013-03-01

    We use a low energy effective model to analyze the optical responses of trilayer graphene samples. We first show that optical absorption of the ABA-stacked trilayer has strong dependence on both the Fermi energy and optical frequency, which is in sharp contrast to that of ABC-stacked trilayer graphene. Secondly, we are able to determine the possible existence of trigonal warping effects in the bandstructure of ABC-stacked trilayer graphene by a divergence in the absorption spectra at around 10 meV. In addition, we can partially distinguish the vairious broken symmetry states driven by electron-electron interactions in ABC-stacked trilayer graphene. In particular, the quantum anomalous Hall (QAH) state is sensitive to the polarization of the incident light, giving a way to detect its possible existence.

  12. Perfect electromagnetic absorption at one-atom-thick scale

    SciTech Connect

    Li, Sucheng; Duan, Qian; Li, Shuo; Yin, Qiang; Lu, Weixin; Li, Liang; Hou, Bo; Gu, Bangming; Wen, Weijia

    2015-11-02

    We experimentally demonstrate that perfect electromagnetic absorption can be realized in the one-atom thick graphene. Employing coherent illumination in the waveguide system, the absorbance of the unpatterned graphene monolayer is observed to be greater than 94% over the microwave X-band, 7–13 GHz, and to achieve a full absorption, >99% in experiment, at ∼8.3 GHz. In addition, the absorption characteristic manifests equivalently a wide range of incident angle. The experimental results agree very well with the theoretical calculations. Our work accomplishes the broadband, wide-angle, high-performance absorption in the thinnest material with simple configuration.

  13. Optically thick line widths in pyrotechnic flares

    NASA Technical Reports Server (NTRS)

    Douda, B. E.; Exton, R. J.

    1975-01-01

    Experimentally determined sodium line widths for pyrotechnic flares are compared with simple analytical, optically-thick-line-shape calculations. Three ambient pressure levels are considered (760, 150 and 30 torr) for three different flare compositions. The measured line widths range from 1.3 to 481 A. The analytic procedure emphasizes the Lorentz line shape as observed under optically-thick conditions. Calculated widths are in good agreement with the measured values over the entire range.

  14. Aerosol optical thickness measurements during FIFE '89

    NASA Technical Reports Server (NTRS)

    Halthore, Rangasayi N.; Bruegge, Carol J.; Markham, Brian L.

    1990-01-01

    The measurements used for correction and calibration are presented which permit the estimation of atmospheric effects on reflected and transmitted solar radiation. Four sun-photometers are calibrated and used to derive aerosol optical thicknesses that agree with expected uncertainties, and lower values and higher values are associated with cool dry northerly flows and warm humid southerly flows, respectively. The rapid increase in the vertical aerosol optical thickness after sunrise is related to the growth of the mixing layer which can be inferred from the 2D maps of the instantaneous aerosol number densities.

  15. Study of effective optical thickness in photopolymer for application.

    PubMed

    Wang, Heng; Wang, Jian; Liu, Hongpeng; Yu, Dan; Sun, Xiudong; Zhang, Jingwen

    2012-06-15

    The impact of the effective optical thickness of a photopolymer on its holographic performance was studied. To overcome the attenuation of gratings for a better uniformity, a multilayer approach was introduced, by adjusting concentrations of dye along the depth of photopolymer to compensate the attenuation of recording light due to absorption. Multilayer photopolymers with thicknesses over 500 μm were designed, fabricated, and characterized experimentally, exhibiting better Bragg selectivity. More holograms were stored in multilayer material by angular multiplexing, and the cumulative grating strength was enhanced, leading towards larger holographic storage capacity. PMID:22739868

  16. Optically thick outflows in ultraluminous supersoft sources

    NASA Astrophysics Data System (ADS)

    Urquhart, R.; Soria, R.

    2016-02-01

    Ultraluminous supersoft sources (ULSs) are defined by a thermal spectrum with colour temperatures ˜0.1 keV, bolometric luminosities ˜ a few 1039 erg s-1, and almost no emission above 1 keV. It has never been clear how they fit into the general scheme of accreting compact objects. To address this problem, we studied a sample of seven ULSs with extensive Chandra and XMM-Newton coverage. We find an anticorrelation between fitted temperatures and radii of the thermal emitter, and no correlation between bolometric luminosity and radius or temperature. We compare the physical parameters of ULSs with those of classical supersoft sources, thought to be surface-nuclear-burning white dwarfs, and of ultraluminous X-ray sources (ULXs), thought to be super-Eddington stellar-mass black holes. We argue that ULSs are the sub-class of ULXs seen through the densest wind, perhaps an extension of the soft-ultraluminous regime. We suggest that in ULSs, the massive disc outflow becomes effectively optically thick and forms a large photosphere, shrouding the inner regions from our view. Our model predicts that when the photosphere expands to ≳ 105 km and the temperature decreases below ≈50 eV, ULSs become brighter in the far-UV but undetectable in X-rays. Conversely, we find that harder emission components begin to appear in ULSs when the fitted size of the thermal emitter is smallest (interpreted as a shrinking of the photosphere). The observed short-term variability and absorption edges are also consistent with clumpy outflows. We suggest that the transition between ULXs (with a harder tail) and ULSs (with only a soft thermal component) occurs at blackbody temperatures of ≈150 eV.

  17. Absorption Optics of Aqueous Foams

    NASA Astrophysics Data System (ADS)

    Bandyopadhyay, Ranjini; Gittings, Alex; Durian, D. J.

    2002-11-01

    Aqueous foams are composed of gas bubbles packed together in a small volume of soapy water. The large number of gas-liquid interfaces in foams results in very strong scattering of light, which explains the opaque nature of conventional aqueous foams such as shaving foams and mousse. For dry foams, the interfaces can take the following three forms: the soap films where two bubbles meet, the triangular plateau borders where three soap films meet and the vertices where four plateau borders meet. Previous experiments have shown that most of the scattering occurs from the plateau borders 2,3 and the transport mean free path of light (l*), the bubble radius (R) and the liquid fraction of foam (epsilon) is related through the relation l*=R/(epsilon0.5). To understand the reflection and scattering of light at the gas-bubble interfaces, we study the absorption of photons in the liquid network as a function of the foam absorptivity. We do this to confirm if the time spent by the photons in the liquid phase is proportional to the liquid fraction of the foam. Our results indicate that for a specific range of liquid fractions (0.05 is less than e is less than 0.1), the photons seem to get trapped in the liquid network. This result is independent of the absorptivity of the foam and leads us to conclude that under appropriate conditions, an aqueous foam behaves very much like an optical fiber network. Aqueous foam is generated in the lab by the method of turbulent mixing of N2 gas with a jet of alpha-olefin-sulfonate (AOS) solution. The foam has been made absorbing by dissolving small quantities of rhodamine dye (R = 0.005 g/l, R = 0.01 g/l and R = 0.0124 g/l) in the AOS solution. The transmission of photons through the foams of liquid fractions 0.0297 is less than e is less than 0.35 has been studied using Diffuse Transmission Spectroscopy (DTS). For each liquid fraction, the transport mean free path l* (the length over which the photon travels before it gets completely

  18. Modeling optical absorption for thermoreflectance measurements

    NASA Astrophysics Data System (ADS)

    Yang, Jia; Ziade, Elbara; Schmidt, Aaron J.

    2016-03-01

    Optical pump-probe techniques based on thermoreflectance, such as time domain thermoreflectance and frequency domain thermoreflectance (FDTR), have been widely used to characterize the thermal conductivity of thin films and the thermal conductance across interfaces. These techniques typically use a transducer layer to absorb the pump light and improve the thermoreflectance signal. The transducer, however, complicates the interpretation of the measured signal because the approximation that all the energy from the pump beam is deposited at the transducer surface is not always accurate. In this paper, we consider the effect of laser absorption in the top layer of a multilayer sample, and derive an analytical solution for the thermoreflectance signal in the diffusion regime based on volumetric heating. We analyze the measurement sensitivity to the pump absorption depth for transducers with different thermal conductivities, and investigate the additional effect of probe laser penetration depth on the measured signal. We validate our model using FDTR measurements on 490 nm thick amorphous silicon films deposited on fused silica and silicon substrates.

  19. Computing Temperatures in Optically Thick Protoplanetary Disks

    NASA Technical Reports Server (NTRS)

    Capuder, Lawrence F.. Jr.

    2011-01-01

    We worked with a Monte Carlo radiative transfer code to simulate the transfer of energy through protoplanetary disks, where planet formation occurs. The code tracks photons from the star into the disk, through scattering, absorption and re-emission, until they escape to infinity. High optical depths in the disk interior dominate the computation time because it takes the photon packet many interactions to get out of the region. High optical depths also receive few photons and therefore do not have well-estimated temperatures. We applied a modified random walk (MRW) approximation for treating high optical depths and to speed up the Monte Carlo calculations. The MRW is implemented by calculating the average number of interactions the photon packet will undergo in diffusing within a single cell of the spatial grid and then updating the packet position, packet frequencies, and local radiation absorption rate appropriately. The MRW approximation was then tested for accuracy and speed compared to the original code. We determined that MRW provides accurate answers to Monte Carlo Radiative transfer simulations. The speed gained from using MRW is shown to be proportional to the disk mass.

  20. Geometrical interpretation of optical absorption

    SciTech Connect

    Monzon, J. J.; Barriuso, A. G.; Sanchez-Soto, L. L.; Montesinos-Amilibia, J. M.

    2011-08-15

    We reinterpret the transfer matrix for an absorbing system in very simple geometrical terms. In appropriate variables, the system appears as performing a Lorentz transformation in a (1 + 3)-dimensional space. Using homogeneous coordinates, we map that action on the unit sphere, which is at the realm of the Klein model of hyperbolic geometry. The effects of absorption appear then as a loxodromic transformation, that is, a rhumb line crossing all the meridians at the same angle.

  1. Modelling Gaussian beam propagation through thick nonlinear refractive and absorptive media

    NASA Astrophysics Data System (ADS)

    Namarathne, D.; Walden, S.; Shortell, M.; Jaatinen, E.

    2016-04-01

    A novel numerical finite difference beam propagation method developed for quadratic refractive index media is presented and applied to TEM00 Gaussian beams propagating through nonlinear optical media. The beam's diffraction through the medium was calculated by using the nonlinear Schrodinger equation on small slices which proved to be effective for thick samples. The performance of the model was compared to experimental z-scan observations of colloidal ZnO particles at low cw and high pulsed peak powers at a wavelength of 532 nm. Different optical behaviours were observed in these two power regimes. Negligible nonlinear absorption and refraction were observed at low cw powers, with strong defocusing arising through thermal lensing in the colloidal solution. For the pulsed experiments with peak powers up to 43-kW and 7-ns pulses, values for the intensity-dependent absorption were determined to be β = 1.0 × 10^{ - 10} {text{m/W}} and n_{{2{text{R}}}} = 2.0 × 10^{ - 18} {text{m}}2 /{text{W}}. Despite the very different nonlinear and thermal-optical behaviours in two power regimes, there was good agreement between the model and observations. This demonstrates the effectiveness of the approach in extracting the nonlinear properties of a medium even if it is not optically thin and in the case when a sample displays both strong nonlinear refraction and absorption.

  2. Further advancement of differential optical absorption spectroscopy: theory of orthogonal optical absorption spectroscopy.

    PubMed

    Liudchik, Alexander M

    2014-08-10

    A modified version of the differential optical absorption spectroscopy (DOAS) method is presented. The technique is called orthogonal optical absorption spectroscopy (OOAS). A widespread variant of DOAS with smoothing of the registered spectrum and absorption cross sections being made employing a polynomial regression is a particular case of OOAS. The concept of OOAS provides a variety of new possibilities for constructing computational schemes and analyzing the influence of different error sources on calculated concentrations. PMID:25320931

  3. Single-molecule imaging by optical absorption

    NASA Astrophysics Data System (ADS)

    Celebrano, Michele; Kukura, Philipp; Renn, Alois; Sandoghdar, Vahid

    2011-02-01

    To date, optical studies of single molecules at room temperature have relied on the use of materials with high fluorescence quantum yield combined with efficient spectral rejection of background light. To extend single-molecule studies to a much larger pallet of substances that absorb but do not fluoresce, scientists have explored the photothermal effect, interferometry, direct attenuation and stimulated emission. Indeed, very recently, three groups have succeeded in achieving single-molecule sensitivity in absorption. Here, we apply modulation-free transmission measurements known from absorption spectrometers to image single molecules under ambient conditions both in the emissive and strongly quenched states. We arrive at quantitative values for the absorption cross-section of single molecules at different wavelengths and thereby set the ground for single-molecule absorption spectroscopy. Our work has important implications for research ranging from absorption and infrared spectroscopy to sensing of unlabelled proteins at the single-molecule level.

  4. Optical absorption analysis and optimization of gold nanoshells.

    PubMed

    Tuersun, Paerhatijiang; Han, Xiang'e

    2013-02-20

    Gold nanoshells, consisting of a nanoscale dielectric core coated with an ultrathin gold shell, have wide biomedical applications due to their strong optical absorption properties. Gold nanoshells with high absorption efficiencies can help to improve these applications. We investigate the effects of the core material, surrounding medium, core radius, and shell thickness on the absorption spectra of gold nanoshells by using the light-scattering theory of a coated sphere. Our results show that the position and intensity of the absorption peak can be tuned over a wide range by manipulating the above-mentioned parameters. We also obtain the optimal absorption efficiencies and structures of hollow gold nanoshells and gold-coated SiO(2) nanoshells embedded in water at wavelengths of 800, 820, and 1064 nm. The results show that hollow gold nanoshells possess the maximum absorption efficiency (5.42) at a wavelength of 800 nm; the corresponding shell thickness and core radius are 4.8 and 38.9 nm, respectively. They can be used as the ideal photothermal conversation particles for biomedical applications. PMID:23435006

  5. Measurements of liquid film thickness, concentration, and temperature of aqueous urea solution by NIR absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Pan, R.; Jeffries, J. B.; Dreier, T.; Schulz, C.

    2016-01-01

    A multi-wavelength near-infrared (NIR) diode laser absorption sensor has been developed and demonstrated for real-time monitoring of the thickness, solute concentration, and temperature of thin films of urea-water solutions. The sensor monitors the transmittance of three near-infrared diode lasers through the thin liquid film. Film thickness, urea mass fraction, and liquid temperature were determined from measured transmittance ratios of suitable combinations of lasers. Available laser wavelengths were selected depending on the variation of the NIR absorption spectrum of the solution with temperature and solute concentration. The spectral database was measured by a Fourier transform infrared spectrometer in the range 5500-8000 cm-1 for urea solutions between 5 and 40 wt% and temperatures between 298 and 338 K. A prototype sensor was constructed, and the sensor concept was first validated with measurements using a calibration cell providing liquid layers of variable thickness (200-1500 µm), urea mass fraction (5-40 wt%) and temperature (298-318 K). Temporal variations of film thickness and urea concentration were captured during the constant-temperature evaporation of a liquid film deposited on an optically polished heated quartz flat.

  6. Coherent perfect absorption in nonlinear optics

    NASA Astrophysics Data System (ADS)

    Zheng, Yuanlin; Wan, Wenjie; Chen, Xianfeng

    2013-02-01

    Recently, a concept of time reversed lasing or coherent perfect absorber (CPA) has been proposed by A. D. Stone and co-workers, and was shortly experimentally demonstrated by them. The CPA system is illuminated coherently and monochromatically by the time reverse of the output of a lasing mode and the incident radiation is perfectly absorbed. Shortly afterwards, Stefano Longhi extended the idea to realize a CPA for colored incident light, and have theoretically shown that the time reversal of optical parametric oscillation (OPO) in a nonlinear medium could also realize a colored CPA for incident signal and idler fields which can be seemed as a kind of nonlinear CPA. Here we present the realization of such time-reversed processes in nonlinear optics regime, including time-reversed second harmonic generation (SHG) for coherent absorption at harmonic frequency of the pump and time-reversed optical parametric amplification (OPA) for coherent attenuation of colored travelling optical fields. Time reversed SHG is carried out at both phase matching and mismatching conditions, which shows parametric near perfect absorption at the harmonic frequency of the pump. The time reversal of OPA is demonstrated experimentally in a nonlinear medium to form a coherent absorber for perpendicularly polarized signal and idler travelling waves, realizing in the condition of OPA by a type II phase matching scheme. The absorption of signal/idler pair occurs at some specific phase difference. This is the first experimental demonstration of coherent absorption processes in nonlinear optics regime.

  7. Tuning nonlinear optical absorption properties of WS2 nanosheets

    NASA Astrophysics Data System (ADS)

    Long, Hui; Tao, Lili; Tang, Chun Yin; Zhou, Bo; Zhao, Yuda; Zeng, Longhui; Yu, Siu Fung; Lau, Shu Ping; Chai, Yang; Tsang, Yuen Hong

    2015-10-01

    To control the optical properties of two-dimensional (2D) materials is a long-standing goal, being of both fundamental and technological significance. Tuning nonlinear optical absorption (NOA) properties of 2D transition metal dichalcogenides in a cost effective way has emerged as an important research topic because of its possibility to custom design NOA properties, implying enormous applications including optical computers, communications, bioimaging, and so on. In this study, WS2 with different size and thickness distributions was fabricated. The results demonstrate that both NOA onset threshold, FON, and optical limiting threshold, FOL, of WS2 under the excitation of a nanosecond pulsed laser can be tuned over a wide range by controlling its size and thickness. The FON and FOL show a rapid decline with the decrease of size and thickness. Due to the edge and quantum confinement effect, WS2 quantum dots (2.35 nm) exhibit the lowest FON (0.01 J cm-2) and FOL (0.062 J cm-2) among all the samples, which are comparable to the lowest threshold achieved in graphene based materials, showing great potential as NOA materials with tunable properties.To control the optical properties of two-dimensional (2D) materials is a long-standing goal, being of both fundamental and technological significance. Tuning nonlinear optical absorption (NOA) properties of 2D transition metal dichalcogenides in a cost effective way has emerged as an important research topic because of its possibility to custom design NOA properties, implying enormous applications including optical computers, communications, bioimaging, and so on. In this study, WS2 with different size and thickness distributions was fabricated. The results demonstrate that both NOA onset threshold, FON, and optical limiting threshold, FOL, of WS2 under the excitation of a nanosecond pulsed laser can be tuned over a wide range by controlling its size and thickness. The FON and FOL show a rapid decline with the decrease of size

  8. Microwave and optical saturable absorption in graphene.

    PubMed

    Zheng, Zhiwei; Zhao, Chujun; Lu, Shunbin; Chen, Yu; Li, Ying; Zhang, Han; Wen, Shuangchun

    2012-10-01

    We report on the first experiments on saturable absorption in graphene at microwave frequency band. Almost independent of the incident frequency, microwave absorbance of graphene always decreases with increasing the power and reaches at a constant level for power larger than 80 µW, evidencing the microwave saturable absorption property of graphene. Optical saturable absorption of the same graphene sample was also experimentally confirmed by an open-aperture Z-scan technique by one laser at telecommunication band and another pico-second laser at 1053 nm, respectively. Herein, we are able to conclude that graphene is indeed a broadband saturable absorber that can operate at both microwave and optical band. PMID:23188285

  9. Ocean optics estimation for absorption, backscattering, and phase function parameters.

    PubMed

    Hakim, Ammar H; McCormick, Norman J

    2003-02-20

    We propose and test an inverse ocean optics procedure with numerically simulated data for the determination of inherent optical properties using in-water radiance measurements. If data are available at only one depth within a deep homogeneous water layer, then the single-scattering albedo and the single parameter that characterizes the Henyey-Greenstein phase function can be estimated. If data are available at two depths, then these two parameters can be determined along with the optical thickness so that the absorption and scattering coefficients, and also the backscattering coefficient, can be estimated. With a knowledge of these parameters, the albedo and Lambertian fraction of reflected radiance of the bottom can be determined if measurements are made close to the bottom. A simplified method for determining the optical properties of the water also is developed for only three irradiance-type measurements if the radiance is approximately in the asymptotic regime. PMID:12617207

  10. Aerosol optical absorption measurements with photoacoustic spectroscopy

    NASA Astrophysics Data System (ADS)

    Liu, Kun; Wang, Lei; Liu, Qiang; Wang, Guishi; Tan, Tu; Zhang, Weijun; Chen, Weidong; Gao, Xiaoming

    2015-04-01

    Many parameters related to radiative forcing in climate research are known only with large uncertainties. And one of the largest uncertainties in global radiative forcing is the contribution from aerosols. Aerosols can scatter or absorb the electromagnetic radiation, thus may have negative or positive effects on the radiative forcing of the atmosphere, respectively [1]. And the magnitude of the effect is directly related to the quantity of light absorbed by aerosols [2,3]. Thus, sensitivity and precision measurement of aerosol optical absorption is crucial for climate research. Photoacoustic spectroscopy (PAS) is commonly recognized as one of the best candidates to measure the light absorption of aerosols [4]. A PAS based sensor for aerosol optical absorption measurement was developed. A 532 nm semiconductor laser with an effective power of 160 mW was used as a light source of the PAS sensor. The PAS sensor was calibrated by using known concentration NO2. The minimum detectable optical absorption coefficient (OAC) of aerosol was determined to be 1 Mm-1. 24 hours continues measurement of OAC of aerosol in the ambient air was carried out. And a novel three wavelength PAS aerosol OAC sensor is in development for analysis of aerosol wavelength-dependent absorption Angstrom coefficient. Reference [1] U. Lohmann and J. Feichter, Global indirect aerosol effects: a review, Atmos. Chem. Phys. 5, 715-737 (2005) [2] M. Z. Jacobson, Strong radiative heating due to the mixing state of black carbon in atmospheric aerosols, Nature 409, 695-697 (2001) [3] V. Ramanathan and G. Carmichae, Global and regional climate changes due to black carbon, nature geoscience 1, 221-227 (2008) [4] W.P Arnott, H. Moosmuller, C. F. Rogers, T. Jin, and R. Bruch, Photoacoustic spectrometer for measuring light absorption by aerosol: instrument description. Atmos. Environ. 33, 2845-2852 (1999).

  11. Thickness Optimization for Petroleum Coke in Microwave Dehydrating Based on the Analysis of Dynamic Absorption Efficiency

    NASA Astrophysics Data System (ADS)

    Shang, Xiaobiao; Chen, Junruo; Peng, Jinhui; Chen, Hua; Zhang, Weifeng; Guo, Shenghui; Chen, Guo

    2015-07-01

    An analytical approach is proposed to optimize the thickness of petroleum coke for achieving maximum microwave power absorption in microwave heating based on analysis of reflection loss (RL). The microwave RL of the petroleum coke layer was studied over the moisture content range of 1%-5% at 20 °C and the petroleum coke (10% moisture content) in the temperature range of 20 to 100 °C at 2.45 GHz. The results show that RL depends sensitively on the thickness of the petroleum coke and the absorption peak shifts towards a larger thickness as the moisture content of the petroleum coke increases. There exists a matching thickness corresponding to the maximum microwave absorption, the maximum absorbing peak decreases when the thickness of petroleum coke exceeds the matching thickness. We also show that the absorption peak is found to move towards a smaller thickness region with increasing petroleum coke temperature.

  12. Tuning nonlinear optical absorption properties of WS₂ nanosheets.

    PubMed

    Long, Hui; Tao, Lili; Tang, Chun Yin; Zhou, Bo; Zhao, Yuda; Zeng, Longhui; Yu, Siu Fung; Lau, Shu Ping; Chai, Yang; Tsang, Yuen Hong

    2015-11-14

    To control the optical properties of two-dimensional (2D) materials is a long-standing goal, being of both fundamental and technological significance. Tuning nonlinear optical absorption (NOA) properties of 2D transition metal dichalcogenides in a cost effective way has emerged as an important research topic because of its possibility to custom design NOA properties, implying enormous applications including optical computers, communications, bioimaging, and so on. In this study, WS2 with different size and thickness distributions was fabricated. The results demonstrate that both NOA onset threshold, F(ON), and optical limiting threshold, F(OL), of WS2 under the excitation of a nanosecond pulsed laser can be tuned over a wide range by controlling its size and thickness. The F(ON) and F(OL) show a rapid decline with the decrease of size and thickness. Due to the edge and quantum confinement effect, WS2 quantum dots (2.35 nm) exhibit the lowest F(ON) (0.01 J cm(-2)) and F(OL) (0.062 J cm(-2)) among all the samples, which are comparable to the lowest threshold achieved in graphene based materials, showing great potential as NOA materials with tunable properties. PMID:26456545

  13. Linear and nonlinear optical absorption coefficients of spherical dome shells

    NASA Astrophysics Data System (ADS)

    Guo, Kangxian; Liu, Guanghui; Huang, Lu; Zheng, Xianyi

    2015-08-01

    Linear and nonlinear optical absorption coefficients of spherical dome shells are theoretically investigated within analytical wave functions and numerical quantized energy levels. Our results show that the inner radius, the outer radius and the cut-off angle of spherical dome shells have great influences on linear and nonlinear optical absorption coefficients as well as the total optical absorption coefficients. It is found that with the increase of the inner radius and the outer radius, linear and nonlinear optical absorption coefficients exhibit a blueshift and a redshift, respectively. However, with the increase of the cut-off angle, linear and nonlinear optical absorption coefficients do not shift. Besides, the resonant peaks of linear and nonlinear optical absorption coefficients climb up and then decrease with increasing the cut-off angle. The influences of the incident optical intensity on the total optical absorption coefficients are studied. It is found that the bleaching effect occurs at higher incident optical intensity.

  14. Multiplexed Holographic Optical Data Storage In Thick Bacteriorhodopsin Films

    NASA Technical Reports Server (NTRS)

    Downie, John D.; Timucin, Dogan A.; Gary, Charles K.; Ozcan, Meric; Smithey, Daniel T.; Crew, Marshall

    1998-01-01

    The optical data storage capacity of photochromic bacteriorhodopsin films is investigated by means of theoretical calculations, numerical simulations, and experimental measurements on sequential recording of angularly multiplexed diffraction gratings inside a thick D85N BR film.

  15. Sub-natural width resonances in Cs vapor confined in micrometric thickness optical cell

    NASA Astrophysics Data System (ADS)

    Cartaleva, S.; Krasteva, A.; Sargsyan, A.; Sarkisyan, D.; Slavov, D.; Vartanyan, T.

    2013-03-01

    We present here the behavior of Electromagnetically Induced Transparency (EIT), Velocity Selective Optical Pumping (VSOP) resonances and Velocity Selective Excitation (VSE) resonances observed in Cs vapor confined in а micrometric optical cell (MC) with thickness L = 6λ, λ = 852nm. For comparison of behavior of VSE resonance another conventional optical cell with thickness L=2.5 cm is used. Cells are irradiated in orthogonal to their windows directions by probe beam scanned on the Fg = 4 → Fe= 3, 4, 5 set of transitions and pump beam fixed at the Fg = 3 → Fe = 4 transition, on the D2 line of Cs. The enhanced absorption (fluorescence) narrow VSOP resonance at the closed transition transforms into reduced absorption (fluorescence) one with small increase of atomic concentration or light intensity. A striking difference appears between the VSE resonance broadening in L = 6λ and conventional L = 2.5cm cells.

  16. Optical absorption spectra of dications of carotenoids

    SciTech Connect

    Jeevarajan, J.A.; Wei, C.C.; Jeevarajan, A.S.; Kispert, L.D.

    1996-04-04

    Quantitative optical absorption spectra of the cation radicals and the dications of canthaxanthin (I), {beta}carotene (II), 7`-cyano-7`-ethoxycarbonyl-7`-apo-{beta}-carotene (III), and 7`,7`-dimethyl-7`-apo-{beta}-carotene (IV) in dichloromethane solution are reported. Exclusive formation of dications occurs when the carotenoids are oxidized with ferric chloride. Addition of neutral carotenoid to the dications results in equilibrium formation of cation radicals. Oxidation with iodine in dichloromethane affords only cation radicals; electrochemical oxidation under suitable conditions yields both dications and cation radicals. Values of the optical parameters depend on the nature of the oxidative medium. The oscillator strengths calculated for gas phase cation radicals and dications of I-IV using the INDO/S method show the same trend as the experimental values. 31 refs., 4 figs., 2 tabs.

  17. Threshold thickness for applying diffusion equation in thin tissue optical imaging

    NASA Astrophysics Data System (ADS)

    Zhang, Yunyao; Zhu, Jingping; Cui, Weiwen; Nie, Wei; Li, Jie; Xu, Zhenghong

    2014-08-01

    We investigated the suitability of the semi-infinite model of the diffusion equation when using diffuse optical imaging (DOI) to image thin tissues with double boundaries. Both diffuse approximation and Monte Carlo methods were applied to simulate light propagation in the thin tissue model with variable optical parameters and tissue thicknesses. A threshold value of the tissue thickness was defined as the minimum thickness in which the semi-infinite model exhibits the same reflected intensity as that from the double-boundary model and was generated as the final result. In contrast to our initial hypothesis that all optical properties would affect the threshold thickness, our results show that only absorption coefficient is the dominant parameter and the others are negligible. The threshold thickness decreases from 1 cm to 4 mm as the absorption coefficient grows from 0.01 mm-1 to 0.2 mm-1. A look-up curve was derived to guide the selection of the appropriate model during the optical diagnosis of thin tissue cancers. These results are useful in guiding the development of the endoscopic DOI for esophageal, cervical and colorectal cancers, among others.

  18. Multilayer graphene stacks grown by different methods-thickness measurements by X-ray diffraction, Raman spectroscopy and optical transmission

    SciTech Connect

    Tokarczyk, M. Kowalski, G.; Kępa, H.; Grodecki, K.; Drabińska, A.; Strupiński, W.

    2013-12-15

    X-ray diffraction, Raman spectroscopy and Optical absorption estimates of the thickness of graphene multi layer stacks (number of graphene layers) are presented for three different growth techniques. The objective of this work was focused on comparison and reconciliation of the two already widely used methods for thickness estimates (Raman and Absorption) with the calibration of the X-ray method as far as Scherer constant K is concerned and X-ray based Wagner-Aqua extrapolation method.

  19. Global patterns of cloud optical thickness variation with temperature

    NASA Technical Reports Server (NTRS)

    Tselioudis, George; Rossow, William B.; Rind, David

    1992-01-01

    The International Satellite Cloud Climatology Project dataset is used to correlate variations of cloud optical thickness and cloud temperature in today's atmosphere. The analysis focuses on low clouds in order to limit the importance of changes in cloud vertical extent, particle size, and water phase. Coherent patterns of change are observed on several time and space scales. On the planetary scale, clouds in colder, higher latitudes are found to be optically thicker than clouds in warmer, lower latitudes. On the seasonal scale, winter clouds are, for the most part, optically thicker than summer clouds. The logarithmic derivative of cloud optical thickness with temperature is used to describe the sign and magnitude of the optical thickness-temperature correlation. The seasonal, latitudinal, and day-to-day variations of this relation are examined for Northern Hemisphere clouds in 1984. In cold continental clouds, optical thickness increases with temperature, consistent with the temperature variation of the adiabatic cloud water content. In warm continental and in almost all maritime clouds, however, optical thickness decreases with temperature.

  20. Metaporous layer to overcome the thickness constraint for broadband sound absorption

    SciTech Connect

    Yang, Jieun; Lee, Joong Seok; Kim, Yoon Young

    2015-05-07

    The sound absorption of a porous layer is affected by its thickness, especially in a low-frequency range. If a hard-backed porous layer contains periodical arrangements of rigid partitions that are coordinated parallel and perpendicular to the direction of incoming sound waves, the lower bound of the effective sound absorption can be lowered much more and the overall absorption performance enhanced. The consequence of rigid partitioning in a porous layer is to make the first thickness resonance mode in the layer appear at much lower frequencies compared to that in the original homogeneous porous layer with the same thickness. Moreover, appropriate partitioning yields multiple thickness resonances with higher absorption peaks through impedance matching. The physics of the partitioned porous layer, or the metaporous layer, is theoretically investigated in this study.

  1. Correction of Rayleigh Scattering Effects in Cloud Optical Thickness Retrievals

    NASA Technical Reports Server (NTRS)

    Wang, Meng-Hua; King, Michael D.

    1997-01-01

    We present results that demonstrate the effects of Rayleigh scattering on the 9 retrieval of cloud optical thickness at a visible wavelength (0.66 Am). The sensor-measured radiance at a visible wavelength (0.66 Am) is usually used to infer remotely the cloud optical thickness from aircraft or satellite instruments. For example, we find that without removing Rayleigh scattering effects, errors in the retrieved cloud optical thickness for a thin water cloud layer (T = 2.0) range from 15 to 60%, depending on solar zenith angle and viewing geometry. For an optically thick cloud (T = 10), on the other hand, errors can range from 10 to 60% for large solar zenith angles (0-60 deg) because of enhanced Rayleigh scattering. It is therefore particularly important to correct for Rayleigh scattering contributions to the reflected signal from a cloud layer both (1) for the case of thin clouds and (2) for large solar zenith angles and all clouds. On the basis of the single scattering approximation, we propose an iterative method for effectively removing Rayleigh scattering contributions from the measured radiance signal in cloud optical thickness retrievals. The proposed correction algorithm works very well and can easily be incorporated into any cloud retrieval algorithm. The Rayleigh correction method is applicable to cloud at any pressure, providing that the cloud top pressure is known to within +/- 100 bPa. With the Rayleigh correction the errors in retrieved cloud optical thickness are usually reduced to within 3%. In cases of both thin cloud layers and thick ,clouds with large solar zenith angles, the errors are usually reduced by a factor of about 2 to over 10. The Rayleigh correction algorithm has been tested with simulations for realistic cloud optical and microphysical properties with different solar and viewing geometries. We apply the Rayleigh correction algorithm to the cloud optical thickness retrievals from experimental data obtained during the Atlantic

  2. Periodically Diameter-Modulated Semiconductor Nanowires for Enhanced Optical Absorption.

    PubMed

    Ko, Minjee; Baek, Seong-Ho; Song, Bokyung; Kang, Jang-Won; Kim, Shin-Ae; Cho, Chang-Hee

    2016-04-01

    A diameter-modulated silicon nanowire array to enhance the optical absorption across broad spectral range is presented. Periodic shape engineering is achieved using conventional semiconductor processes and the unique optical properties are analyzed. The periodicity in the diameter of the silicon nanowires enables stronger and more closely spaced optical resonances, leading to broadband absorption enhancement. PMID:26833855

  3. Optical coherence tomography as film thickness measurement technique

    NASA Astrophysics Data System (ADS)

    Manallah, Aissa; Bouafia, Mohamed; Meguellati, Said

    2015-01-01

    Optical coherence tomography (OCT) is a powerful optical method, noninvasive and noncontact diagnostic method. Although it is usually used for medical examinations, particularly in ocular exploration; it can also be used in optical metrology as measure technique. In this work, we use OCT to measure thicknesses of films. In OCT, depth profiles are constructed by measuring the time delay of back reflected light by interferometry measurements. Frequency in k-space is proportional to optical path difference. Then the reflectivity profile is obtained by a Fourier transformation, and the difference between two successive peaks of the resulting spectrum gives the film thickness. Several films, food-type, of different thicknesses were investigated and the results were very accurate.

  4. EFFECT OF DUST ON Ly{alpha} PHOTON TRANSFER IN AN OPTICALLY THICK HALO

    SciTech Connect

    Yang Yang; Shu Chiwang; Roy, Ishani; Fang Lizhi

    2011-10-01

    We investigate the effects of dust on Ly{alpha} photons emergent from an optically thick medium by solving the integro-differential equation of radiative transfer of resonant photons. To solve the differential equations numerically, we use the weighted essentially non-oscillatory method. Although the effects of dust on radiative transfer are well known, the resonant scattering of Ly{alpha} photons makes the problem non-trivial. For instance, if the medium has an optical depth of dust absorption and scattering of {tau}{sub a} >> 1, {tau} >> 1, and {tau} >> {tau}{sub a}, the effective absorption optical depth in a random walk scenario would be equal to {radical}({tau}{sub a}({tau}{sub a}+{tau})). We show, however, that for a resonant scattering at frequency {nu}{sub 0}, the effective absorption optical depth would be even larger than {tau}({nu}{sub 0}). If the cross section of dust scattering and absorption is frequency-independent, the double-peaked structure of the frequency profile given by the resonant scattering is basically dust-independent. That is, dust causes neither narrowing nor widening of the width of the double-peaked profile. One more result is that the timescales of the Ly{alpha} photon transfer in an optically thick halo are also basically independent of the dust scattering, even when the scattering is anisotropic. This is because those timescales are mainly determined by the transfer in the frequency space, while dust scattering, either isotropic or anisotropic, does not affect the behavior of the transfer in the frequency space when the cross section of scattering is wavelength-independent. This result does not support the speculation that dust will lead to the smoothing of the brightness distribution of a Ly{alpha} photon source with an optically thick halo.

  5. Measurements of the optical absorption coefficient of Ar8+ ion implanted silicon layers using the photothermal radiometry and the modulated free carrier absorption methods

    NASA Astrophysics Data System (ADS)

    Chrobak, Ł.; Maliński, M.; Pawlak, M.

    2014-11-01

    This paper presents a method of the measurement of the optical absorption coefficient of the Ar8+ ions implanted layers in the p-type silicon substrate. The absorption coefficient is calculated using a value of the attenuation of amplitudes of a photothermal radiometry (PTR) and/or a modulation free carrier absorption (MFCA) signals and the implanted layer thickness calculated by means of the TRIM program. The proposed method can be used to indicate the amorphization of the ions implanted layers.

  6. Tissue thickness calculation in ocular optical coherence tomography

    PubMed Central

    Alonso-Caneiro, David; Read, Scott A.; Vincent, Stephen J.; Collins, Michael J.; Wojtkowski, Maciej

    2016-01-01

    Thickness measurements derived from optical coherence tomography (OCT) images of the eye are a fundamental clinical and research metric, since they provide valuable information regarding the eye’s anatomical and physiological characteristics, and can assist in the diagnosis and monitoring of numerous ocular conditions. Despite the importance of these measurements, limited attention has been given to the methods used to estimate thickness in OCT images of the eye. Most current studies employing OCT use an axial thickness metric, but there is evidence that axial thickness measures may be biased by tilt and curvature of the image. In this paper, standard axial thickness calculations are compared with a variety of alternative metrics for estimating tissue thickness. These methods were tested on a data set of wide-field chorio-retinal OCT scans (field of view (FOV) 60° x 25°) to examine their performance across a wide region of interest and to demonstrate the potential effect of curvature of the posterior segment of the eye on the thickness estimates. Similarly, the effect of image tilt was systematically examined with the same range of proposed metrics. The results demonstrate that image tilt and curvature of the posterior segment can affect axial tissue thickness calculations, while alternative metrics, which are not biased by these effects, should be considered. This study demonstrates the need to consider alternative methods to calculate tissue thickness in order to avoid measurement error due to image tilt and curvature. PMID:26977367

  7. Multilayer injection moulding of thick-walled optical plastics parts

    NASA Astrophysics Data System (ADS)

    Hopmann, Ch.; Neuss, A.; Weber, M.; Walach, P.

    2014-05-01

    Optical components are often thick-walled. The cycle time of precise polymer optics with a wall thickness of more than 20 mm exceeds several minutes. The multilayer injection moulding or compression moulding lowers the cycle time and increases the quality of the moulded parts. For the production of multilayer moulded lenses the mould design plays an important role. An innovative mould concept is presented with the possiblity to produce double or triple layer lenses. To ensure the quality and the endurance of multilayer moulded optical components in their applications, the cohesion in the interface is important. Tensile shear tests show the ability of multilayer moulded parts with high cohesion values for optical applications.

  8. Thickness dependent optical and electrical properties of CdSe thin films

    NASA Astrophysics Data System (ADS)

    Purohit, A.; Chander, S.; Nehra, S. P.; Lal, C.; Dhaka, M. S.

    2016-05-01

    The effect of thickness on the optical and electrical properties of CdSe thin films is investigated in this paper. The films of thickness 445 nm, 631 nm and 810 nm were deposited on glass and ITO coated glass substrates using thermal evaporation technique. The deposited thin films were thermally annealed in air atmosphere at temperature 100°C and were subjected to UV-Vis spectrophotometer and source meter for optical and electrical analysis respectively. The absorption coefficient is observed to increase with photon energy and found maximum in higher photon energy region. The extinction coefficient and refractive index are also calculated. The electrical analysis shows that the electrical resistivity is observed to be decreased with thickness.

  9. Optical absorption in semiconductor nanorings under electric and magnetic fields

    NASA Astrophysics Data System (ADS)

    Zhang, Tong-Yi; Cao, Jun-Cheng; Zhao, Wei

    2005-01-01

    The optical absorption in semiconductor nanorings under a lateral DC field and a perpendicular magnetic field is numerically simulated by coherent wave approach. The exciton dominated optical absorption is compared with the free-carrier interband absorption to demonstrate the key role of Coulomb interaction between electron and hole. The influence of the lateral DC field and the perpendicular magnetic field on the optical absorption are discussed in detail. It shows that the lateral DC field can significantly enhance the Aharonov-Bohm effect of the neutral excitons in semiconductor nanorings.

  10. Quantitative materials analysis of micro devices using absorption-based thickness measurements

    NASA Astrophysics Data System (ADS)

    Sim, L. M.; Wog, B. S.; Spowage, A. C.

    2006-01-01

    Preliminary work in designing an X-ray inspection machine with the capability of providing quantitative thickness analysis based on absorption measurements has been demonstrated. This study attempts to use the gray levels data to investigate the nature and thickness of occluded features and materials within devices. The investigation focused on metallic materials essential to semiconductor and MEMS technologies such as tin, aluminium, copper, silver, iron and zinc. The materials were arranged to simulate different feature thicknesses and sample geometries. The X-ray parameters were varied in-order to modify the X-ray energy spectrum with the aim of optimising the measurement conditions for each sample. The capability of the method to resolve differences in thicknesses was found to be highly dependent on the material. The thickness resolution with aluminium was the poorest due to its low radiographic density. The thickness resolutions achievable for silver and tin were significantly better and of the order of 0.015 mm and 0.025 mm respectively. From the linear relationship between the X-ray attenuation and sample thickness established, the energy dependent linear attenuation coefficient for each material was determined for a series of specific energy spectra. A decrease in the linear attenuation coefficient was observed as the applied voltage and thickness of the material increased. The results provide a platform for the development of a novel absorption-based thickness measurement system that can be optimised for a range of industrial applications.

  11. Investigation on optical absorption properties of ion irradiated single walled carbon nanotubes

    SciTech Connect

    Vishalli, Dharamvir, Keya; Kaur, Ramneek; Raina, K. K.; Avasthi, D. K.; Jeet, Kiran

    2015-08-28

    In the present study change in the optical absorption properties of single walled carbon nanotubes (SWCNTs) under nickel ion (60 MeV) irradiation at various fluences has been investigated. Langmuir Blodgett technique is used to deposit SWCNT thin film of uniform thickness. AFM analysis shows a network of interconnected bundles of nanotubes. UV-Vis-NIR absorption spectra indicate that the sample mainly contain SWCNTs of semiconducting nature. It has been found in absorption spectra that there is decrease in the intensity of the characteristic SWCNT peaks with increase in fluence. At fluence value 1×10{sup 14} ions/cm{sup 2} there is almost complete suppression of the characteristic SWCNTs peaks.The decrease in the optical absorption with increase in fluence is due to the increase in the disorder in the system which leads to the decrease in optically active states.

  12. Properties of multilayer optical systems formed by layers with small absorption in inclined falling of radiation

    NASA Astrophysics Data System (ADS)

    Karyaev, Konstantin V.; Zhoga, Eugene V.; Putilin, Eduard S.

    2000-10-01

    Multilayer dielectric systems find wide employment in different fields of science and engineering. Dielectric systems, formed by layers with small absorption, attract particular interest. Value of absorption, as a rule, depends on structure of the system (order and optical thickness of layers), angle of incidence and wavelength of radiation. Experiment shows that there are peaks of absorption on certain angles of incidence and wavelength, but behavior of absorption wasn't studied well. Model of a system, formed by isotropic layers settled on semiinfinite substate proved to be a good approximation for many of real optical systems. We studied pecularities in spectral dependencies of reflection, transmission and absorption coefficients in dependance on the angle of incidence and wavelength of falling radiation with flat wave front. Problem was solved on the basis of Maxwell equations and corresponding boundary conditions.

  13. Cloud optical thickness feedbacks in the CO2 climate problem

    NASA Technical Reports Server (NTRS)

    Somerville, R. C. J.

    1985-01-01

    A radiative-convective equilibrium model is developed and applied to study cloud optical thickness feedbacks in the CO2 climate problem. The basic hypothesis is that in the warmer and moister CO2-rich atmosphere, cloud liquid water content will generally be larger than at present, so that cloud optical thickness will be larger too. For clouds other than thin cirrus, the result is to increase the albedo more than to increase the greenhouse effect. Thus the sign of the feedback is negative: cloud optical properties alter in such a way as to reduce the surface and tropospheric warming caused by the addition of CO2. This negative feedback can be substantial. When observational estimates of the temperature dependence of cloud liquid water content are employed in the model, the surface temperature change due to doubling CO2 is reduced by about one half.

  14. Thickness identification of two-dimensional materials by optical imaging.

    PubMed

    Wang, Ying Ying; Gao, Ren Xi; Ni, Zhen Hua; He, Hui; Guo, Shu Peng; Yang, Huan Ping; Cong, Chun Xiao; Yu, Ting

    2012-12-14

    Two-dimensional materials, e.g. graphene and molybdenum disulfide (MoS(2)), have attracted great interest in recent years. Identification of the thickness of two-dimensional materials will improve our understanding of their thickness-dependent properties, and also help with scientific research and applications. In this paper, we propose to use optical imaging as a simple, quantitative and universal way to identify the thickness of two-dimensional materials, i.e. mechanically exfoliated graphene, nitrogen-doped chemical vapor deposition grown graphene, graphene oxide and mechanically exfoliated MoS(2). The contrast value can easily be obtained by reading the red (R), green (G) and blue (B) values at each pixel of the optical images of the sample and substrate, and this value increases linearly with sample thickness, in agreement with our calculation based on the Fresnel equation. This method is fast, easily performed and no expensive equipment is needed, which will be an important factor for large-scale sample production. The identification of the thickness of two-dimensional materials will greatly help in fundamental research and future applications. PMID:23154446

  15. Absorption Filter Based Optical Diagnostics in High Speed Flows

    NASA Technical Reports Server (NTRS)

    Samimy, Mo; Elliott, Gregory; Arnette, Stephen

    1996-01-01

    Two major regimes where laser light scattered by molecules or particles in a flow contains significant information about the flow are Mie scattering and Rayleigh scattering. Mie scattering is used to obtain only velocity information, while Rayleigh scattering can be used to measure both the velocity and the thermodynamic properties of the flow. Now, recently introduced (1990, 1991) absorption filter based diagnostic techniques have started a new era in flow visualization, simultaneous velocity and thermodynamic measurements, and planar velocity measurements. Using a filtered planar velocimetry (FPV) technique, we have modified the optically thick iodine filter profile of Miles, et al., and used it in the pressure-broaden regime which accommodates measurements in a wide range of velocity applications. Measuring velocity and thermodynamic properties simultaneously, using absorption filtered based Rayleigh scattering, involves not only the measurement of the Doppler shift, but also the spectral profile of the Rayleigh scattering signal. Using multiple observation angles, simultaneous measurement of one component velocity and thermodynamic properties in a supersonic jet were measured. Presently, the technique is being extended for simultaneous measurements of all three components of velocity and thermodynamic properties.

  16. Simultaneous measurement of group refractive index and thickness of optical samples using optical coherence tomography

    SciTech Connect

    Cheng, Hsu-Chih; Liu, Yi-Cheng

    2010-02-10

    Optical coherence tomography (OCT), based on a Michelson interferometer and utilizing low coherence light as the optical source, is a novel technique for the noninvasive imaging of optical scattering media. A simple OCT scheme based on a 3x3 fiber coupler is presented for the simultaneous measurement of the refractive index and thickness of optical samples. The proposed system enables the refractive index and thickness to be determined without any prior knowledge of the sample parameters and is characterized by a simple and compact configuration, a straightforward measurement procedure, and a low cost. The feasibility of the proposed approach is demonstrated experimentally using BK7 and B270 optical glass samples.

  17. Deep and Clear Optical Imaging of Thick Inhomogeneous Samples

    PubMed Central

    Andilla, Jordi; Maandhui, Amina; Frongia, Céline; Lobjois, Valérie; Ducommun, Bernard; Lorenzo, Corinne

    2012-01-01

    Inhomogeneity in thick biological specimens results in poor imaging by light microscopy, which deteriorates as the focal plane moves deeper into the specimen. Here, we have combined selective plane illumination microscopy (SPIM) with wavefront sensor adaptive optics (wao). Our waoSPIM is based on a direct wavefront measure using a Hartmann-Shack wavefront sensor and fluorescent beads as point source emitters. We demonstrate the use of this waoSPIM method to correct distortions in three-dimensional biological imaging and to improve the quality of images from deep within thick inhomogeneous samples. PMID:22558226

  18. Ultraviolet absorption of common spacecraft contaminants. [to control effects of contaminants on optical systems

    NASA Technical Reports Server (NTRS)

    Colony, J. A.

    1979-01-01

    Organic contamination of ultraviolet optical systems is discussed. Degradation of signal by reflection, scattering, interference, and absorption is shown. The first three processes depend on the physical state of the contaminant while absorption depends on its chemical structure. The latter phenomenon is isolated from the others by dissolving contaminants in cyclohexane and determining absorption spectra from 2100A to 3600A. A variety of materials representing the types of contaminants responsible for most spaceflight hardware problems is scanned and the spectra is presented. The effect of thickness is demonstrated for the most common contaminant, di(2 ethyl hexyl)phthalate, by scanning successive dilutions.

  19. Ultrasound-modulated optical tomography for thick tissue imaging

    NASA Astrophysics Data System (ADS)

    Wang, Lihong V.; Zhao, Xuemei; Jacques, Steven L.

    1995-12-01

    Continuous-wave ultrasonic modulation of scattered laser light has been used to image objects in tissue-simulating turbid media for the first time. We hypothesize that the ultrasound wave focused into the turbid media modulates the laser light passing through the ultrasonic focal spot. The modulated laser light collected by a photomultiplier tube reflects the local mechanical and optical properties in the focal zone. Buried objects in 5-cm thick tissue phantoms are located with millimeter resolution by scanning and detecting alterations of the ultrasound-modulated optical signal. Ultrasound-modulated optical tomography separates the conflict between signal and resolution in purely optical imaging of tissue and does not rely on ballistic or quasi-ballistic photons but on the abundant diffuse photons. The imaging resolution is determined by the focused ultrasonic wave. This technique has the potential to provide a noninvasive, nonionizing, inexpensive diagnostic tool for diseases such as breast cancer.

  20. Synthesis and nonlinear optical absorption of novel chalcone derivative compounds

    NASA Astrophysics Data System (ADS)

    Rahulan, K. Mani; Balamurugan, S.; Meena, K. S.; Yeap, G.-Y.; Kanakam, Charles C.

    2014-03-01

    3-(4-(dimethylamino)phenyl)-1-(4-(4-(hydroxymethyl)-1H-1,2,3-triazol-1-yl)phenyl)prop-2-en-1-one was synthesized and its third order nonlinear optical properties have been investigated using a z-scan technique with nanosecond laser pulses at 532 nm. The nonlinear absorption behavior of the compound in chloroform presents a distinct difference at different laser intensity. Interestingly, the compound showed a switchover from saturable absorption (SA) to reverse saturable absorption (RSA) with the increase of excitation intensity. Our studies suggest that compound could be used as a potential candidate for optical device applications such as optical limiters.

  1. Ray vector fields, prismatic effect, and thick astigmatic optical systems.

    PubMed

    Harris, W F

    1996-06-01

    The application of the concept of ray vector fields to optical systems is reexamined. Paraxial or linear optics defines a four-dimensional ray vector field for any optical system: the vector field maps the incident ray vector into the emergent ray vector. In the case of thin systems, including thin astigmatic lenses, one can define a vector field of reduced dimensionality: the vector field is two-dimensional and maps the ray's incident position into the change in reduced direction. When the index of refraction is the same before and after a thin system, the change in reduced direction is the reduced deflection through the system or the reduced prismatic effect. Contrary to what has recently been claimed, this type of two-dimensional vector field does not apply in general to thick systems. However, a number of different types of two-dimensional vector fields can be defined for various particular classes of optical systems. Thick systems differ qualitatively from thin systems. They do not have equivalent thin lenses and cannot generally be replaced by thin lenses. Equations are derived for the change in reduced direction and deflection for a ray through optical systems in general and through separated two- and three-lens systems in particular. PMID:8807654

  2. DEEP SILICATE ABSORPTION FEATURES IN COMPTON-THICK ACTIVE GALACTIC NUCLEI PREDOMINANTLY ARISE DUE TO DUST IN THE HOST GALAXY

    SciTech Connect

    Goulding, A. D.; Forman, W. R.; Jones, C.; Trichas, M.; Alexander, D. M.; Mullaney, J. R.; Bauer, F. E.; Hickox, R. C.

    2012-08-10

    We explore the origin of mid-infrared (mid-IR) dust extinction in all 20 nearby (z < 0.05) bona fide Compton-thick (N{sub H} > 1.5 Multiplication-Sign 10{sup 24} cm{sup -2}) active galactic nuclei (AGNs) with hard energy (E > 10 keV) X-ray spectral measurements. We accurately measure the silicate absorption features at {lambda} {approx} 9.7 {mu}m in archival low-resolution (R {approx} 57-127) Spitzer Infrared Spectrograph spectroscopy, and show that only a minority ( Almost-Equal-To 45%) of nearby Compton-thick AGNs have strong Si-absorption features (S{sub 9.7} = ln (f{sub int}/f{sub obs}) {approx}> 0.5) which would indicate significant dust attenuation. The majority ( Almost-Equal-To 60%) are star formation dominated (AGN:SB < 0.5) at mid-IR wavelengths and lack the spectral signatures of AGN activity at optical wavelengths, most likely because the AGN emission lines are optically extinguished. Those Compton-thick AGNs hosted in low-inclination-angle galaxies exhibit a narrow range in Si-absorption (S{sub 9.7} {approx} 0-0.3), which is consistent with that predicted by clumpy-torus models. However, on the basis of the IR spectra and additional lines of evidence, we conclude that the dominant contribution to the observed mid-IR dust extinction is dust located in the host galaxy (i.e., due to disturbed morphologies, dust lanes, galaxy inclination angles) and not necessarily a compact obscuring torus surrounding the central engine.

  3. Dynamics of photoinduced dichroism and birefringence in optically thick azopolymers

    SciTech Connect

    Ponomarev, Yu V; Ivanov, Yu V; Rumyantsev, Yu A; Gromchenko, A A

    2009-01-31

    Dynamics of photoinduced dichroism and birefringence have been studied experimentally and theoretically (with the help of the Dumont model) by using some comb-shaped azopolymers. It is shown that the dynamics of trans-isomer concentration and their angular distribution anisotropy can be restored from the experimentally found dichroism dynamics, with the concentration and anisotropy being averaged over the thickness for optically thick samples. At the initial stage of photoinduced anisotropy when the active role of the polymer matrix can be neglected, the experimental time dependence of dichroism is shown to comply well with the Dumont model even if the orientation memory is neglected, provided that only a part of trans-isomers participates in trans-isomerisation. (nonlinear optical phenomena)

  4. Cloud-radiation interactions - Effects of cirrus optical thickness feedbacks

    NASA Technical Reports Server (NTRS)

    Somerville, Richard C. J.; Iacobellis, Sam

    1987-01-01

    The paper is concerned with a cloud-radiation feedback mechanism which may be an important component of the climate changes expected from increased atmospheric concentrations of carbon dioxide and other trace greenhouse gases. A major result of the study is that cirrus cloud optical thickness feedbacks may indeed tend to increase the surface warming due to trace gas increases. However, the positive feedback from cirrus appears to be generally weaker than the negative effects due to lower clouds. The results just confirm those of earlier research indicating that the net effect of cloud optical thickness feedbacks may be a negative feedback which may substantially (by a factor of about 2) reduce the surface warming due to the doubling of CO2, even in the presence of cirrus clouds.

  5. Determination of graphene layer thickness using optical image processing

    NASA Astrophysics Data System (ADS)

    Cook, Monica; Mani, R. G.

    2015-03-01

    Graphene, a single atomic layer of carbon arranged in a hexagonal lattice structure, is a valuable material in a wide range of research. A significant impediment to graphene research is the need to manually characterize the thickness of high-quality graphene produced via mechanical exfoliation. Traditional methods of characterizing the layer thickness of graphene, including Raman spectroscopy and atomic force microscopy, require expensive equipment and can be damaging to the graphene sample. We examine here a known alternative method for quantitatively determining the layer thickness of graphene on SiO2/Si based on optical image processing, which is quick, inexpensive, and non-invasive. Using RGB images of a candidate graphene sample and a background image, taken with a simple optical microscope and charge-coupled device (CCD) camera, we process the images with an algorithm based on Fresnel's law to obtain the contrast spectrum. Each layer of graphene exhibits a unique contrast spectrum for its particular substrate, which is measured and used for accurate layer identification. We also discuss how this algorithm can be generalized to characterize the thickness of other promising two-dimensional materials as well as more complex structures on a variety of substrates.

  6. Optical absorption enhancement of CdTe nanostructures by low-energy nitrogen ion bombardment

    NASA Astrophysics Data System (ADS)

    Akbarnejad, E.; Ghoranneviss, M.; Mohajerzadeh, S.; Hantehzadeh, M. R.; Asl Soleimani, E.

    2016-02-01

    In this paper we present the fabrication of cadmium telluride (CdTe) nanostructures by means of RF magnetron sputtering followed by low-energy ion implantation and post-thermal treatment. We have thoroughly studied the structural, optical, and morphological properties of these nanostructures. The effects of nitrogen ion bombardment on the structural parameters of CdTe nanostructures such as crystal size, microstrain, and dislocation density have been examined. From x-ray diffractometer (XRD) analysis it could be deduced that N+ ion fluence and annealing treatment helps to form (3 0 0) orientation in the crystalline structure of cadmium-telluride films. Fluctuations in optical properties like the optical band gap and absorption coefficient as a function of N+ ion fluences have been observed. The annealing of the sample irradiated by a dose of 1018 ions cm-2 has led to great enhancement in the optical absorption over a wide range of wavelengths with a thickness of 250 nm. The enhanced absorption is significantly higher than the observed value in the original CdTe layer with a thickness of 3 μm. Surface properties such as structure, grain size and roughness are noticeably affected by varying the nitrogen fluences. It is speculated that nitrogen bombardment and post-annealing treatment results in a smaller optical band gap, which in turn leads to higher absorption. Nitrogen bombardment is found to be a promising method to increase efficiency of thin film solar cells.

  7. View angle dependence of cloud optical thicknesses retrieved by MODIS

    NASA Technical Reports Server (NTRS)

    Marshak, Alexander; Varnai, Tamas

    2005-01-01

    This study examines whether cloud inhomogeneity influences the view angle dependence of MODIS cloud optical thickness (tau) retrieval results. The degree of cloud inhomogeneity is characterized through the local gradient in 11 microns brightness temperature. The analysis of liquid phase clouds in a one year long global dataset of Collection 4 MODIS data reveals that while optical thickness retrievals give remarkably consistent results for all view directions if clouds are homogeneous, they give much higher tau-values for oblique views than for overhead views if clouds are inhomogeneous and the sun is fairly oblique. For solar zenith angles larger than 55deg, the mean optical thickness retrieved for the most inhomogeneous third of cloudy pixels is more than 30% higher for oblique views than for overhead views. After considering a variety of possible scenarios, the paper concludes that the most likely reason for the increase lies in three-dimensional radiative interactions that are not considered in current, one-dimensional retrieval algorithms. Namely, the radiative effect of cloud sides viewed at oblique angles seems to contribute most to the enhanced tau-values. The results presented here will help understand cloud retrieval uncertainties related to cloud inhomogeneity. They complement the uncertainty estimates that will start accompanying MODIS cloud products in Collection 5 and may eventually help correct for the observed view angle dependent biases.

  8. Control of enhanced optical absorption in {mu}c-Si

    SciTech Connect

    Kalkan, A.K.; Fonash, S.J.

    1997-07-01

    The influence of grain size on the enhanced optical absorption of {micro}c-Si has been investigated using films of various grain sizes prepared by solid phase crystallization. The authors show that they can control this grain size and therefore the degree of absorption changes. For grain sizes below a threshold range significant absorption enhancement can be seen in the photon energy range of 1 to {approximately}3 eV and the absorption characteristics of these films show that the dominant mode of optical transitions is indirect. A correlation between first order Raman peak broadening and enhanced absorption was found suggesting both effects are related to confinement. A simple model was developed to see how confinement in the crystallites could influence indirect optical transitions.

  9. Measurement of compressed breast thickness by optical stereoscopic photogrammetry

    SciTech Connect

    Tyson, Albert H.; Mawdsley, Gordon E.; Yaffe, Martin J.

    2009-02-15

    The determination of volumetric breast density (VBD) from mammograms requires accurate knowledge of the thickness of the compressed breast. In attempting to accurately determine VBD from images obtained on conventional mammography systems, the authors found that the thickness reported by a number of mammography systems in the field varied by as much as 15 mm when compressing the same breast or phantom. In order to evaluate the behavior of mammographic compression systems and to be able to predict the thickness at different locations in the breast on patients, they have developed a method for measuring the local thickness of the breast at all points of contact with the compression paddle using optical stereoscopic photogrammetry. On both flat (solid) and compressible phantoms, the measurements were accurate to better than 1 mm with a precision of 0.2 mm. In a pilot study, this method was used to measure thickness on 108 volunteers who were undergoing mammography examination. This measurement tool will allow us to characterize paddle surface deformations, deflections and calibration offsets for mammographic units.

  10. Broadband optical limiting and nonlinear optical absorption properties of a novel hyperbranched conjugated polymer

    NASA Astrophysics Data System (ADS)

    Li, Chao; Liu, Chunling; Li, Quanshui; Gong, Qihuang

    2004-12-01

    The nonlinear transmittance of a novel hyperbranched conjugated polymer named DMA-HPV has been measured in CHCl 3 solution using a nanosecond optical parametric oscillator. DMA-HPV shows excellent optical limiting performance in the visible region from 490 to 610 nm. An explanation based on the combination of two-photon absorption and reverse saturable absorption was proposed for its huge and broadband nonlinear optical absorption.

  11. Coal thickness gauge using RRAS techniques, part 1. [radiofrequency resonance absorption

    NASA Technical Reports Server (NTRS)

    Rollwitz, W. L.; King, J. D.

    1978-01-01

    A noncontacting sensor having a measurement range of 0 to 6 in or more, and with an accuracy of 0.5 in or better is needed to control the machinery used in modern coal mining so that the thickness of the coal layer remaining over the rock is maintained within selected bounds. The feasibility of using the radiofrequency resonance absorption (RRAS) techniques of electron magnetic resonance (EMR) and nuclear magnetic resonance (NMR) as the basis of a coal thickness gauge is discussed. The EMR technique was found, by analysis and experiments, to be well suited for this application.

  12. Polarization and Thickness Dependent Absorption Properties of Black Phosphorus: New Saturable Absorber for Ultrafast Pulse Generation

    NASA Astrophysics Data System (ADS)

    Li, Diao; Jussila, Henri; Karvonen, Lasse; Ye, Guojun; Lipsanen, Harri; Chen, Xianhui; Sun, Zhipei

    2015-10-01

    Black phosphorus (BP) has recently been rediscovered as a new and interesting two-dimensional material due to its unique electronic and optical properties. Here, we study the linear and nonlinear optical properties of BP flakes. We observe that both the linear and nonlinear optical properties are anisotropic and can be tuned by the film thickness in BP, completely different from other typical two-dimensional layered materials (e.g., graphene and the most studied transition metal dichalcogenides). We then use the nonlinear optical properties of BP for ultrafast (pulse duration down to ~786 fs in mode-locking) and large-energy (pulse energy up to >18 nJ in Q-switching) pulse generation in fiber lasers at the near-infrared telecommunication band ~1.5 μm. We observe that the output of our BP based pulsed lasers is linearly polarized (with a degree-of-polarization ~98% in mode-locking, >99% in Q-switching, respectively) due to the anisotropic optical property of BP. Our results underscore the relatively large optical nonlinearity of BP with unique polarization and thickness dependence, and its potential for polarized optical pulse generation, paving the way to BP based nonlinear and ultrafast photonic applications (e.g., ultrafast all-optical polarization switches/modulators, frequency converters etc.).

  13. Polarization and Thickness Dependent Absorption Properties of Black Phosphorus: New Saturable Absorber for Ultrafast Pulse Generation

    PubMed Central

    Li, Diao; Jussila, Henri; Karvonen, Lasse; Ye, Guojun; Lipsanen, Harri; Chen, Xianhui; Sun, Zhipei

    2015-01-01

    Black phosphorus (BP) has recently been rediscovered as a new and interesting two-dimensional material due to its unique electronic and optical properties. Here, we study the linear and nonlinear optical properties of BP flakes. We observe that both the linear and nonlinear optical properties are anisotropic and can be tuned by the film thickness in BP, completely different from other typical two-dimensional layered materials (e.g., graphene and the most studied transition metal dichalcogenides). We then use the nonlinear optical properties of BP for ultrafast (pulse duration down to ~786 fs in mode-locking) and large-energy (pulse energy up to >18 nJ in Q-switching) pulse generation in fiber lasers at the near-infrared telecommunication band ~1.5 μm. We observe that the output of our BP based pulsed lasers is linearly polarized (with a degree-of-polarization ~98% in mode-locking, >99% in Q-switching, respectively) due to the anisotropic optical property of BP. Our results underscore the relatively large optical nonlinearity of BP with unique polarization and thickness dependence, and its potential for polarized optical pulse generation, paving the way to BP based nonlinear and ultrafast photonic applications (e.g., ultrafast all-optical polarization switches/modulators, frequency converters etc.). PMID:26514090

  14. OPTICALLY THICK H I DOMINANT IN THE LOCAL INTERSTELLAR MEDIUM: AN ALTERNATIVE INTERPRETATION TO ''DARK GAS''

    SciTech Connect

    Fukui, Y.; Torii, K.; Yamamoto, H.; Okamoto, R.; Hayakawa, T.; Tachihara, K.; Sano, H.; Onishi, T.

    2015-01-01

    Dark gas in the interstellar medium (ISM) is believed to not be detectable either in CO or H I radio emission, but it is detectable by other means including γ rays, dust emission, and extinction traced outside the Galactic plane at |b| > 5°. In these analyses, the 21 cm H I emission is usually assumed to be completely optically thin. We have reanalyzed the H I emission from the whole sky at |b| > 15° by considering temperature stratification in the ISM inferred from the Planck/IRAS analysis of the dust properties. The results indicate that the H I emission is saturated with an optical depth ranging from 0.5 to 3 for 85% of the local H I gas. This optically thick H I is characterized by spin temperature in the range 10 K-60 K, significantly lower than previously postulated in the literature, whereas such low temperature is consistent with emission/absorption measurements of the cool H I toward radio continuum sources. The distribution and the column density of the H I are consistent with those of the dark gas suggested by γ rays, and it is possible that the dark gas in the Galaxy is dominated by optically thick cold H I gas. This result implies that the average density of H I is 2-2.5 times higher than that derived on the optically thin assumption in the local ISM.

  15. The dynamics of radiation-driven, optically thick winds

    NASA Astrophysics Data System (ADS)

    Shen, Rong-Feng; Nakar, Ehud; Piran, Tsvi

    2016-06-01

    Recent observation of some luminous transient sources with low colour temperatures suggests that the emission is dominated by optically thick winds driven by super-Eddington accretion. We present a general analytical theory of the dynamics of radiation pressure-driven, optically thick winds. Unlike the classical adiabatic stellar wind solution whose dynamics are solely determined by the sonic radius, here the loss of the radiation pressure due to photon diffusion also plays an important role. We identify two high mass-loss rate regimes (dot{M} > L_Edd/c^2). In the large total luminosity regime, the solution resembles an adiabatic wind solution. Both the radiative luminosity, L, and the kinetic luminosity, Lk, are super-Eddington with L < Lk and L ∝ L_k^{1/3}. In the lower total luminosity regime, most of the energy is carried out by the radiation with Lk < L ≈ LEdd. In a third, low mass-loss regime (dot{M} < L_Edd/c^2), the wind becomes optically thin early on and, unless gas pressure is important at this stage, the solution is very different from the adiabatic one. The results are independent from the energy generation mechanism at the foot of the wind; therefore, they are applicable to a wide range of mass ejection systems, from black hole accretion, to planetary nebulae, and to classical novae.

  16. Exploring the origin of high optical absorption in conjugated polymers.

    PubMed

    Vezie, Michelle S; Few, Sheridan; Meager, Iain; Pieridou, Galatia; Dörling, Bernhard; Ashraf, Raja Shahid; Goñi, Alejandro R; Bronstein, Hugo; McCulloch, Iain; Hayes, Sophia C; Campoy-Quiles, Mariano; Nelson, Jenny

    2016-07-01

    The specific optical absorption of an organic semiconductor is critical to the performance of organic optoelectronic devices. For example, higher light-harvesting efficiency can lead to higher photocurrent in solar cells that are limited by sub-optimal electrical transport. Here, we compare over 40 conjugated polymers, and find that many different chemical structures share an apparent maximum in their extinction coefficients. However, a diketopyrrolopyrrole-thienothiophene copolymer shows remarkably high optical absorption at relatively low photon energies. By investigating its backbone structure and conformation with measurements and quantum chemical calculations, we find that the high optical absorption can be explained by the high persistence length of the polymer. Accordingly, we demonstrate high absorption in other polymers with high theoretical persistence length. Visible light harvesting may be enhanced in other conjugated polymers through judicious design of the structure. PMID:27183327

  17. Electromagnetic Wave Absorption On Powder Sheets: Effect Of Thickness And Particle Size

    NASA Astrophysics Data System (ADS)

    Hong, S. H.; Cho, E. K.; Cho, H. J.; Lee, J. J.; Sohn, K. Y.; Nam, J. M.; Moon, B. G.; Song, Y. S.; Park, W. W.

    2008-04-01

    Complex permeability and power absorption of electromagnetic wave absorber have been studied by varying the particle size of soft-magnetic powder and thickness of consolidated powder sheet. Relative permeability increased proportional to the particle size in <100 MHz range. But, as the frequency increased, the relative permeability of the sheet made of smaller particles decreased slower than that of larger particles. This is due to the increasing contribution of eddy current loss with increasing frequency.

  18. Absorptive carbon nanotube electrodes: Consequences of optical interference loss in thin film solar cells

    NASA Astrophysics Data System (ADS)

    Tait, Jeffrey G.; de Volder, Michaël F. L.; Cheyns, David; Heremans, Paul; Rand, Barry P.

    2015-04-01

    A current bottleneck in the thin film photovoltaic field is the fabrication of low cost electrodes. We demonstrate ultrasonically spray coated multiwalled carbon nanotube (CNT) layers as opaque and absorptive metal-free electrodes deposited at low temperatures and free of post-deposition treatment. The electrodes show sheet resistance as low as 3.4 Ω □-1, comparable to evaporated metallic contacts deposited in vacuum. Organic photovoltaic devices were optically simulated, showing comparable photocurrent generation between reflective metal and absorptive CNT electrodes for photoactive layer thickness larger than 600 nm when using archetypal poly(3-hexylthiophene) (P3HT) : (6,6)-phenyl C61-butyric acid methyl ester (PCBM) cells. Fabricated devices clearly show that the absorptive CNT electrodes display comparable performance to solution processed and spray coated Ag nanoparticle devices. Additionally, other candidate absorber materials for thin film photovoltaics were simulated with absorptive contacts, elucidating device design in the absence of optical interference and reflection.A current bottleneck in the thin film photovoltaic field is the fabrication of low cost electrodes. We demonstrate ultrasonically spray coated multiwalled carbon nanotube (CNT) layers as opaque and absorptive metal-free electrodes deposited at low temperatures and free of post-deposition treatment. The electrodes show sheet resistance as low as 3.4 Ω □-1, comparable to evaporated metallic contacts deposited in vacuum. Organic photovoltaic devices were optically simulated, showing comparable photocurrent generation between reflective metal and absorptive CNT electrodes for photoactive layer thickness larger than 600 nm when using archetypal poly(3-hexylthiophene) (P3HT) : (6,6)-phenyl C61-butyric acid methyl ester (PCBM) cells. Fabricated devices clearly show that the absorptive CNT electrodes display comparable performance to solution processed and spray coated Ag nanoparticle

  19. Water Absorption and Thickness Swelling Behavior of Polypropylene Reinforced with Hybrid Recycled Newspaper and Glass Fiber

    NASA Astrophysics Data System (ADS)

    Shakeri, Alireza; Ghasemian, Ali

    2010-04-01

    This study aims to investigate the moisture absorption of recycled newspaper fiber and recycled newspaper-glass fiber hybrid reinforced polypropylene composites to study their suitability in outdoor applications. In this work composite materials were made from E-glass fiber (G), recycled newspaper (NP) and polypropylene (PP), by using internal mixing and hot-pressing molding. Long-term water absorption (WA) and thickness swelling (TS) kinetics of the composites was investigated with water immersion. It was found that the WA and TS increase with NP content in composite and water immersion time before an equilibrium condition was reached. Composites made from the NP show comparable results as those made of the hybrid fiber. The results suggest that the water absorption and thickness swelling composite decrease with increasing glass fiber contents in hybrid fiber composite. It is interesting to find that the WA and TS can be reduced significantly with incorporation of a coupling agent (maleated polypropylene) in the composite formulation. Further studies were conducted to model the water diffusion and thickness swelling of the composites. Diffusion coefficients and swelling rate parameters in the models were obtained by fitting the model predictions with the experimental data.

  20. Variability of aerosol optical thickness and atmospheric turbidity in Tunisia

    NASA Astrophysics Data System (ADS)

    Masmoudi, M.; Chaabane, M.; Medhioub, K.; Elleuch, F.

    The aerosol optical thickness (AOT) τa computed from the spectral sun photometer in Thala (Tunisia) exhibited variability ranging from approximately 0.03 to greater than 2.0 at 870 nm for March-October 2001. These measurements are compared to the aerosol optical thickness computed in Ouagadougou (Burkina-Faso), Banizoumbou (Niger), IMC Oristano (Sardinia) and Rome Tor Vergata (Italy). Analysis of τa data from this observation network suggests that there is a high temporal and spatial variability of τa in the different sites. The Angström wavelength exponent α was found to vary with the magnitude of the aerosol optical thickness, with values as high as 1.5 for very low τa, and values of -0.1 for high τa situations. The relationship between the two parameters τa and α is investigated. Values of the turbidity coefficient β have been determined in Thala (Tunisia) for 8 months in 2001 based on a direct fitting method of the Angström power law expression using sun photometer data. The monthly averaged values of the turbidity coefficient β vary between 0.15 and 0.33. The months of July and October experienced the highest turbidity, while April experienced the lowest aerosol loading on average. The turbidity shows a maximum and minimum values for the Southwest and the Northwest wind directions, respectively. The single scattering albedo ωo for the 870 nm wavelength obtained from solar aureole data in Thala is analysed according to the particles' origin.

  1. UV-B optical thickness observations of the atmosphere

    NASA Astrophysics Data System (ADS)

    Kirchhoff, V. W. J. H.; Silva, A. A.; Costa, C. A.; Leme, N. Paes; PavãO, H. G.; Zaratti, F.

    2001-02-01

    The optical thickness of the atmosphere, τ, was deduced from measurements of narrowband direct solar UV-B radiation. A measurement campaign was organized to obtain the radiation at three different sites, during the month of August 1999, using the same methods and instruments, in order to deduce the atmospheric optical thickness in the spectral UV-B range (280-320 nm). The three observation sites were chosen to cover a wide range of measurement conditions; located near the tropical Atlantic Ocean (Natal, 5.8°S, 35.2°W), on the Andes mountains (La Paz, 16.5°S, 68.1°W), and in the biomass burning area of central Brazil (Campo Grande, 19.2°S, 54.3°W). The UV-B measurements were made with a Brewer spectrophotometer at each site. Since the instrument measures atmospheric ozone and SO2 simultaneously, it is possible, from the total atmospheric optical thickness τ, to deduce the aerosol optical thickness τaerosol. The results have been combined in different ways to compare with satellite data, showing good performance. Time variations as short as about 10 min can be seen. On clear days the time variations are relatively small, as expected. On the other hand, for the biomass burning site, for conditions of mixed air masses (the instrument is not looking directly at plumes) one can see very large variations in τ in relatively short time intervals, for example, for one case, from 3.5 to 7.0 in about 30 min. Absolute values for τ at Natal and La Paz were near 2.0 and at Campo Grande, between 2.5 and 3.0, but with occasional highs of about 4.5. For τaerosol, Natal and La Paz had values between 0.0 and 0.4, whereas Campo Grande had most values near 0.4, with occasional highs near 1.0, 1.2, and 2.2.

  2. Features of X-ray Absorption Densitometry of Large-size Objects with Variable Thickness

    NASA Astrophysics Data System (ADS)

    Osipov, S.; Chakhlov, S.; Osipov, O.; Badin, S.; Abashkin, A.

    2016-01-01

    Features of formation and processing of the primary radiometric signals in the digital high-energy X-ray absorption densitometers for the homogeneous objects with variable thickness are examined. The densitometer's equation based on the polynomial approximation of the object's ray thickness dependence from its mass thickness is proposed. Guidance to select the capacity of the analog-digital converter is given. There is one example of the densitometer's equation coefficients calculation to examine the carbon, aluminum and steel wares with the mass density from 15 to 80 g/cm2. It was shown that disagreement of the experimental and estimated values of the ray thickness for the similar mass thicknesses of the testing object is conditioned by the scattered radiation. On the high-energy digital radiography set with the X-ray source - the betatron MIB-4.5/9 the accuracy of the experimental estimation of the density was within 0.0086 g/cm3 for the steel ware thickness from 25 to 100 mm.

  3. Enhancing optical absorption in InP and GaAs utilizing profile etching

    NASA Technical Reports Server (NTRS)

    Bailey, Sheila G.; Fatemi, Navid S.; Landis, Geoffrey A.

    1991-01-01

    The current state of profile etching in GaAs and InP is summarized, including data on novel geometries attainable as a function of etchant temperature, composition, and rate; substrate orientation; carrier concentration; and oxide thickness between substrate and photoresist. V-grooved solar cells were manufactured with both GaAs and InP, and the improved optical absorption was demonstrated. Preferred parameters for various applications are listed and discussed.

  4. Enhancing optical absorption in InP and GaAs utilizing profile etching

    NASA Technical Reports Server (NTRS)

    Bailey, Sheila G.; Fatemi, Navid S.; Landis, Geoffrey A.

    1991-01-01

    The current state of profile etching in GaAs and InP is summarized, including data on novel geometries attainable as a function of etchant temperature, composition, and rate; substrate orientation; carrier concentration; and oxide thickness between substrate and photoresist. V-grooved solar cells have been manufactured with both GaAs and InP, and the improved optical absorption demonstrated. Preferred parameters for various applications are listed and discussed.

  5. [Study of retrieving formaldehyde with differential optical absorption spectroscopy].

    PubMed

    Li, Yu-Jin; Xie, Pin-Hua; Qin, Min; Qu, Xiao-Ying; Hu, Lin

    2009-01-01

    The present paper introduces the method of retrieving the concentration of HCHO with differential optical absorption spectroscopy (DOAS). The authors measured ambient HCHO in Beijing region with the help of differential optical absorption spectroscopy instrument made by ourself, and discussed numerous factors in retrieving the concentration of HCHO with differential optical absorption spectroscopy (DOAS), especially, the choice of HCHO wave band, how to avoid absorption of ambient SO2, NO2 and O3, and the influence of the Xenon lamp spectrum structure on the absorption of ambient HCHO. The authors achieved the HCHO concentration by simultaneously retrieving the concentrations of HCHO, SO2, NO2 and O3 with non-linear least square fitting method, avoiding the effect of choosing narrow wave of HCHO and the residual of SO2, NO2, O3 and the Xenon lamp spectrum structure in retrieving process to attain the concentration of HCHO, Finally the authors analyzed the origin of error in retrieving the concentration of HCHO with differential optical absorption spectroscopy (DOAS), and the total error is within 13.7% in this method. PMID:19385238

  6. Fluorescence measurements for evaluating the application of multivariate analysis techniques to optically thick environments.

    SciTech Connect

    Reichardt, Thomas A.; Timlin, Jerilyn Ann; Jones, Howland D. T.; Sickafoose, Shane M.; Schmitt, Randal L.

    2010-09-01

    Laser-induced fluorescence measurements of cuvette-contained laser dye mixtures are made for evaluation of multivariate analysis techniques to optically thick environments. Nine mixtures of Coumarin 500 and Rhodamine 610 are analyzed, as well as the pure dyes. For each sample, the cuvette is positioned on a two-axis translation stage to allow the interrogation at different spatial locations, allowing the examination of both primary (absorption of the laser light) and secondary (absorption of the fluorescence) inner filter effects. In addition to these expected inner filter effects, we find evidence that a portion of the absorbed fluorescence is re-emitted. A total of 688 spectra are acquired for the evaluation of multivariate analysis approaches to account for nonlinear effects.

  7. Applying UV cameras for SO2 detection to distant or optically thick volcanic plumes

    USGS Publications Warehouse

    Kern, Christoph; Werner, Cynthia; Elias, Tamar; Sutton, A. Jeff; Lübcke, Peter

    2013-01-01

    Ultraviolet (UV) camera systems represent an exciting new technology for measuring two dimensional sulfur dioxide (SO2) distributions in volcanic plumes. The high frame rate of the cameras allows the retrieval of SO2 emission rates at time scales of 1 Hz or higher, thus allowing the investigation of high-frequency signals and making integrated and comparative studies with other high-data-rate volcano monitoring techniques possible. One drawback of the technique, however, is the limited spectral information recorded by the imaging systems. Here, a framework for simulating the sensitivity of UV cameras to various SO2 distributions is introduced. Both the wavelength-dependent transmittance of the optical imaging system and the radiative transfer in the atmosphere are modeled. The framework is then applied to study the behavior of different optical setups and used to simulate the response of these instruments to volcanic plumes containing varying SO2 and aerosol abundances located at various distances from the sensor. Results show that UV radiative transfer in and around distant and/or optically thick plumes typically leads to a lower sensitivity to SO2 than expected when assuming a standard Beer–Lambert absorption model. Furthermore, camera response is often non-linear in SO2 and dependent on distance to the plume and plume aerosol optical thickness and single scatter albedo. The model results are compared with camera measurements made at Kilauea Volcano (Hawaii) and a method for integrating moderate resolution differential optical absorption spectroscopy data with UV imagery to retrieve improved SO2 column densities is discussed.

  8. Absorption-edge calculations of inorganic nonlinear optical crystals

    NASA Astrophysics Data System (ADS)

    Wu, Kechen; Chen, Chuangtian

    1992-03-01

    A theoretical model suitable for calculating absorption edges of inorganic nonlinear optical (NLO) crystals is introduced. This model is proved to be useful to elucidate the relationship between electronic structures of NLO-active groups and macroscopic properties of absorption edges on the UV side of most of the inorganic nonlinear optical crystals. A systematic calculation of absorption edges on the UV side for several important inorganic NLO crystals is carried out by means of DV-SCM-Xα method and all calculated results are in good agreement with experimental data. These inorganic NLO crystals include LiB3O5(LBO), β-BaB2O4(BBO), KB5, KDP, Na2SbF5, Ba2TiSi2O8, iodate and NaNO2. The calculated energy level structures of LiB3O5 and β-BaB2O4 crystals are compared with the measured XPS spectra. The unusual transparent spectra of KB5 and KDP crystals are partly explained from the microstructure point of view. The effect of lone electron pair in iodate and NaNO2 crystals on their absorption edges are discussed. All these results show that Anionic Group Theory of Nonlinear Optical Crystals is useful to evaluate the absorption edges of the inorganic nonlinear optical crystal and is a powerful tool in a Molecular Engineering approach to search for new nonlinear optical materials.

  9. Tracing the sub-photospheric layers of optically thick winds

    NASA Astrophysics Data System (ADS)

    Graefener, G.

    2013-06-01

    Towards the end of their evolution hot massive stars develop strong stellar winds and appear as emission line stars, such as WR stars or LBVs. The quanitative description of the mass loss in these important pre-SN phases is hampered by unkowns such as wind clumping and porosity, and by an incomplete theoretical understanding of optically thick stellar winds. Even the stellar radii in these phases are badly undestood as they are often variable (LBVs), or deviate from theoretical expectations (WR stars). Here we present a new semi-empirical method that helps to tackle these problems. By analysing a large sample of Galactic WR stars we gain information about deep wind layers near the sonic point which are otherwise not directly observable. We find evidence that these layers are clumped, with clumping factors comparable to the ones observed in the winds of WR stars. Moreover, density and temperature near the sonic point seem to follow a relation which is ubiqitous for optically thick winds, and which may be responsible for the peculiar radius properties of these objects.

  10. Properties of optically thick coronae around accreting black holes

    NASA Astrophysics Data System (ADS)

    Belmont, R.; Różańska, A.; Malzac, J.; Czerny, B.; Petrucci, P.-O.

    2015-12-01

    Accreting black holes are complex sources exhibiting several spectral components (disc, jet, hot corona etc). The exact nature and the interplay between these components is still uncertain, and constraining the accretion flow in the vicinity of the compact object has become a key problem to understand the general physics of accretion and ejection. In the past years, the X-ray spectra of several X-ray binaries and AGN have suggested the existence of a new type of coronae in the inner part of their accretion disk. These coronae are warm (about 1 keV) and have Thomson optical depths of about τ ≈ 10, much larger than the standard comptonizing medium inferred in black hole systems. However, simple radiative models based on the diffusion approximation are unable to sustain a large temperature over such high optical depths, therefore questioning existence of these thick coronae. Here we investigate the radiative and hydrostatic properties of slabs, thick coronae covering a standard accretion disc. A precise modelling of the radiation transfer shows that the observed temperature inversion can be reproduced, provided that most of the accretion power is dissipated in this upper layer and that the medium is strongly magnetised.

  11. Distributed Bragg Reflectors With Reduced Optical Absorption

    DOEpatents

    Klem, John F.

    2005-08-16

    A new class of distributed Bragg reflectors has been developed. These distributed Bragg reflectors comprise interlayers positioned between sets of high-index and low-index quarter-wave plates. The presence of these interlayers is to reduce photon absorption resulting from spatially indirect photon-assisted electronic transitions between the high-index and low-index quarter wave plates. The distributed Bragg reflectors have applications for use in vertical-cavity surface-emitting lasers for use at 1.55 .mu.m and at other wavelengths of interest.

  12. Optical design of transparent metal grids for plasmonic absorption enhancement in ultrathin organic solar cells.

    PubMed

    Kim, Inho; Lee, Taek Seong; Jeong, Doo Seok; Lee, Wook Seong; Kim, Won Mok; Lee, Kyeong-Seok

    2013-07-01

    Transparent metal grid combining with plasmonic absorption enhancement is a promising replacement to indium tin oxide thin films. We numerically demonstrate metal grids in one or two dimension lead to plasmonic absorption enhancements in ultrathin organic solar cells. In this paper, we study optical design of metal grids for plasmonic light trapping and identify different plasmonic modes of the surface plasmon polaritons excited at the interfaces of glass/metal grids, metal grids/active layers, and the localized surface plasmon resonance of the metal grids using numerical calculations. One dimension metal grids with the optimal design of a width and a period lead to the absorption enhancement in the ultrathin active layers of 20 nm thickness by a factor of 2.6 under transverse electric polarized light compared to the case without the metal grids. Similarly, two dimensional metal grids provide the absorption enhancement by a factor of 1.8 under randomly polarized light. PMID:24104493

  13. Electronic structure and optic absorption of phosphorene under strain

    NASA Astrophysics Data System (ADS)

    Duan, Houjian; Yang, Mou; Wang, Ruiqiang

    2016-07-01

    We studied the electronic structure and optic absorption of phosphorene (monolayer of black phosphorus) under strain. Strain was found to be a powerful tool for the band structure engineering. The in-plane strain in armchair or zigzag direction changes the effective mass components along both directions, while the vertical strain only has significant effect on the effective mass in the armchair direction. The band gap is narrowed by compressive in-plane strain and tensile vertical strain. Under certain strain configurations, the gap is closed and the energy band evolves to the semi-Dirac type: the dispersion is linear in the armchair direction and is gapless quadratic in the zigzag direction. The band-edge optic absorption is completely polarized along the armchair direction, and the polarization rate is reduced when the photon energy increases. Strain not only changes the absorption edge (the smallest photon energy for electron transition), but also the absorption polarization.

  14. Effect of pectin on jejunal glucose absorption and unstirred layer thickness in normal man.

    PubMed Central

    Flourie, B; Vidon, N; Florent, C H; Bernier, J J

    1984-01-01

    The effect of high methoxy apple pectin, a carbohydrate gelling agent, on the intestinal absorption of glucose, water, and sodium was studied in man. The effect of intraluminal fibre was evaluated in 22 healthy volunteers by the intestinal perfusion technique under an occlusive balloon. The test solutions (NaCl 130 mM, KCl 5 mM, glucose or mannitol 30 mM, PEG 4000 5 g/l) were perfused just beyond the ligament of Treitz at a rate of 10 ml/min. A 25 cm segment was studied. Three concentrations of pectin were tested: 6, 10, and 15 g/l. The effect of this pectin at two concentrations, 6 and 10 g/l, on the jejunal unstirred layer thickness was evaluated in nine other healthy subjects by an electrical technique. In mannitol solution, pectin reversed water and sodium absorption, whatever its concentration was, while in glucose solution it significantly reduced absorption of water and sodium at 10 and 15 g/l only (p less than 0.01). It significantly reduced glucose absorption at all concentrations (p less than 0.01). This reduction was found to be correlated with the solution viscosity (p less than 0.01). Pectin did not alter the glucose dependent sodium transport but increased significantly (p less than 0.001) the unstirred layer thickness. These results suggested that, in healthy man, pectin acutely given may impair intestinal absorption by means of an increased unstirred layer resistance. This effect could contribute to the diminished postprandial glycaemia observed in human subjects fed pectin. PMID:6432635

  15. Effect of pectin on jejunal glucose absorption and unstirred layer thickness in normal man.

    PubMed

    Flourie, B; Vidon, N; Florent, C H; Bernier, J J

    1984-09-01

    The effect of high methoxy apple pectin, a carbohydrate gelling agent, on the intestinal absorption of glucose, water, and sodium was studied in man. The effect of intraluminal fibre was evaluated in 22 healthy volunteers by the intestinal perfusion technique under an occlusive balloon. The test solutions (NaCl 130 mM, KCl 5 mM, glucose or mannitol 30 mM, PEG 4000 5 g/l) were perfused just beyond the ligament of Treitz at a rate of 10 ml/min. A 25 cm segment was studied. Three concentrations of pectin were tested: 6, 10, and 15 g/l. The effect of this pectin at two concentrations, 6 and 10 g/l, on the jejunal unstirred layer thickness was evaluated in nine other healthy subjects by an electrical technique. In mannitol solution, pectin reversed water and sodium absorption, whatever its concentration was, while in glucose solution it significantly reduced absorption of water and sodium at 10 and 15 g/l only (p less than 0.01). It significantly reduced glucose absorption at all concentrations (p less than 0.01). This reduction was found to be correlated with the solution viscosity (p less than 0.01). Pectin did not alter the glucose dependent sodium transport but increased significantly (p less than 0.001) the unstirred layer thickness. These results suggested that, in healthy man, pectin acutely given may impair intestinal absorption by means of an increased unstirred layer resistance. This effect could contribute to the diminished postprandial glycaemia observed in human subjects fed pectin. PMID:6432635

  16. Optical absorption spectra of palladium doped gold cluster cations

    SciTech Connect

    Kaydashev, Vladimir E.; Janssens, Ewald Lievens, Peter

    2015-01-21

    Photoabsorption spectra of gas phase Au{sub n}{sup +} and Au{sub n−1}Pd{sup +} (13 ≤ n ≤ 20) clusters were measured using mass spectrometric recording of wavelength dependent Xe messenger atom photodetachment in the 1.9–3.4 eV photon energy range. Pure cationic gold clusters consisting of 15, 17, and 20 atoms have a higher integrated optical absorption cross section than the neighboring sizes. It is shown that the total optical absorption cross section increases with size and that palladium doping strongly reduces this cross section for all investigated sizes and in particular for n = 14–17 and 20. The largest reduction of optical absorption upon Pd doping is observed for n = 15.

  17. [Spectral calibration for space-borne differential optical absorption spectrometer].

    PubMed

    Zhou, Hai-Jin; Liu, Wen-Qing; Si, Fu-Qi; Zhao, Min-Jie; Jiang, Yu; Xue, Hui

    2012-11-01

    Space-borne differential optical absorption spectrometer is used for remote sensing of atmospheric trace gas global distribution. This instrument acquires high accuracy UV/Vis radiation scattered or reflected by air or earth surface, and can monitor distribution and variation of trace gases based on differential optical absorption spectrum algorithm. Spectral calibration is the premise and base of quantification of remote sensing data of the instrument, and the precision of calibration directly decides the level of development and application of the instrument. Considering the characteristic of large field, wide wavelength range, high spatial and spectral resolution of the space-borne differential optical absorption spectrometer, a spectral calibration method is presented, a calibration device was built, the equation of spectral calibration was calculated through peak searching and regression analysis, and finally the full field spectral calibration of the instrument was realized. The precision of spectral calibration was verified with Fraunhofer lines of solar light. PMID:23387142

  18. Nonlinear intersubband optical absorption in a semiconductor quantum well

    NASA Technical Reports Server (NTRS)

    Ahn, D.; Chuang, S. L.

    1987-01-01

    The third-order nonlinear intersubband absorption in a semiconductor quantum well is studied theoretically using the density matrix formalism including intrasubband relaxation. It is shown that the peak absorption is reduced by half for an optical intensity 1 MW/sq cm for the well size L = 126.5 A with 3.0 x 10 to the 16th/cu cm electrons.

  19. Optical Defocus Rapidly Changes Choroidal Thickness in Schoolchildren

    PubMed Central

    Liu, Manli; Lee, Roger Pak Kin; Sun, Yuan; Zhang, Ting; Lam, Chuen; Liu, Quan; To, Chi Ho

    2016-01-01

    The current study aimed to examine the short-term choroidal response to optical defocus in schoolchildren. Myopic schoolchildren aged 8–16 were randomly allocated to control group (CG), myopic defocus group (MDG) and hyperopic defocus group (HDG) (n = 17 per group). Children in MDG and HDG received additional +3D and -3D lenses, respectively, to their full corrections on the right eyes. Full correction was given to their left eyes, and on both eyes in the CG. Axial length (AXL) and subfoveal choroidal thickness (SFChT) were then measured by spectral domain optical coherence tomography. Children wore their group-specific correction for 2 hours after which any existing optical defocus was removed, and subjects wore full corrections for another 2 hours. Both the AXL and SFChT were recorded hourly for 4 hours. The mean refraction of all subjects was -3.41 ± 0.37D (± SEM). SFChT thinned when exposed to hyperopic defocus for 2 hours but less thinning was observed in response to myopic defocus compared to the control group (p < 0.05, two-way ANOVA). Removal of optical defocus significantly decreased SFChT in the MDG and significantly increased SFChT in the HDG after 1 and 2 hours (mean percentage change at 2-hour; control vs. hyperopic defocus vs. myopic defocus; -0.33 ± 0.59% vs. 3.04 ± 0.60% vs. -1.34 ± 0.74%, p < 0.01). Our results showed short-term exposure to myopic defocus induced relative choroidal thickening while hyperopic defocus led to choroidal thinning in children. This rapid and reversible choroidal response may be an important clinical parameter in gauging retinal response to optical defocus in human myopia. PMID:27537606

  20. Imaging heterogeneous absorption distribution of advanced breast cancer by optical tomography

    NASA Astrophysics Data System (ADS)

    Xu, Yan; Zhu, Quing

    2010-11-01

    Tumor vascular patterns of advanced breast cancers are complex and heterogeneous. Two typical light absorption patterns of periphery enhancement and posterior shadowing have been observed when imaging these advanced cancers using optical tomography guided by ultrasound. We perform a series simulation and phantom experiments to systemically evaluate the effects of target parameters, target locations, and target optical properties on imaging periphery enhancement absorption distribution using reflection geometry. Large tumors are modeled as concentric semiellipsoidal targets of different outer shell and inner core optical properties. We show that larger targets of more than 3 to 4 cm diameter with outer shell thicknesses less than 1 cm can be resolved at a depth less than 3 cm. A clinical example is given to show the complex vasculature distributions seen from an advanced cancer.

  1. Cloud optical thickness feedbacks in the CO2 climate problem

    NASA Technical Reports Server (NTRS)

    Somerville, R. C. J.; Remer, L. A.

    1984-01-01

    A radiative-convective equilibrium model is developed and applied to study cloud optical thickness feedbacks in the CO2 climate problem. The basic hypothesis is that in the warmer and moister CO2-rich atmosphere, cloud liquid water content will generally be larger too. For clouds other than thin cirrus the result is to increase the albedo more than to increase the greenhouse effect. Thus, the sign of the feedback is negative: cloud optical properties act as a thermostat and alter in such a way as to reduce the surface and tropospheric warming caused by the addition of CO2. This negative feedback can be substantial. When observational estimates of the temperature dependence of cloud liquid water content are employed in the model, the surface temperature change caused by doubling CO2 is reduced by about one half. This result is obtained for global and annual average conditions, no change in cloud amount or altitude, and constant relative humidity. These idealizations, together with other simplifications typical of one-dimensional radiative-convective climate models, render the result tentative. Further study of cloud optical property feedbacks is warranted, however, because the climate is apparently so sensitive to them.

  2. Optical Absorption Spectra of Sodium Borate Cobalt Doped Glasses

    SciTech Connect

    Elokr, M. M.; Hassan, M. A.; Yaseen, A. M.; Elokr, R.

    2007-02-14

    Glassy system: xNa2O-(100-x-y)B2O3-yCo3O4 has been prepared by conventional melt quenching technique. Optical absorption spectra have been obtained in the range 300 - 2500 nm at room temperature. An absorption edge was observed in the near UV range, the analysis of which reveals that indirect transition is the dominant absorption mechanism. All prepared samples exhibit blue color, indicating that the Co ions are acted upon by tetrahedral ligand field. Obtained spectra were used to estimate some ligand field parameters.

  3. Metal nanoparticles enhanced optical absorption in thin film solar cells

    NASA Astrophysics Data System (ADS)

    Xie, Wanlu; Liu, Fang; Qu, Di; Xu, Qi; Huang, Yidong

    2011-12-01

    The plasmonic enhanced absorption for thin film solar cells with silver nanoparticles (NPs) deposited on top of the amorphous silicon film (a-Si:H) solar cells and embedded inside the active layer of organic solar cells (OSCs) has been simulated and analyzed. Obvious optical absorption enhancement is obtained not only at vertical incidence but also at oblique incidence. By properly adjusting the period and size of NPs, an increased absorption enhancement of about 120% and 140% is obtained for a-Si:H solar cells and OSCs, respectively.

  4. Optical absorption of several nanostructures arrays for silicon solar cells

    NASA Astrophysics Data System (ADS)

    Xu, Zhaopeng; Qiao, Huiling; Huangfu, Huichao; Li, Xiaowei; Guo, Jingwei; Wang, Haiyan

    2015-12-01

    To improve the efficiency and reduce the cost of solar cells, it's important to enhance the light absorption. Within the visible solar spectrum based on optimization simulations by COMSOL Multiphysics, the optical absorption of silicon cylindrical nanowires, nanocones and inverted nanocones was calculated respectively. The results reveal that the average absorption for the nanocones between 400 and 800 nm is 70.2%, which is better than cylindrical nanowires (55.3%), inverted nanocones (42.3%) and bulk silicon (42.2%). In addition, more than 95% of light from 630 to 800 nm is reflected for inverted nanocones, which can be used to enhance infrared reflection in photovoltaic devices.

  5. Differential optical absorption spectrometer for measurement of tropospheric pollutants

    NASA Astrophysics Data System (ADS)

    Evangelisti, F.; Baroncelli, A.; Bonasoni, P.; Giovanelli, G.; Ravegnani, F.

    1995-05-01

    Our institute has recently developed a differential optical absorption spectrometry system called the gas analyzer spectrometer correlating optical absorption differences (GASCOAD), which features as a detector a linear image sensor that uses an artificial light source for long-path tropospheric-pollution monitoring. The GASCOAD, its method of eliminating interference from background sky light, and subsequent spectral analysis are reported and discussed. The spectrometer was used from 7 to 22 February 1993 in Milan, a heavily polluted metropolitan area, to measure the concentrations of SO2, NO2, O3, and HNO2 averaged over a 1.7-km horizontal light path. The findings are reported and briefly discussed.

  6. Background Maritime Aerosol: Their Optical Thickness and Scattering Properties

    NASA Technical Reports Server (NTRS)

    Kaufman, Yoram J.; Smirnov, Alexander; Holben, Brent N.; Dubovik, Oleg; Einaudi, Franco (Technical Monitor)

    2001-01-01

    The effect of human induced change in the aerosol concentration and properties, or the aerosol response to climate change (e.g. droughts producing fires or dust) should be measured relative to a "background aerosol". How to define this background aerosol, so that it is both measurable and useful? Here we use 10 stations located in the Pacific, Atlantic and Indian Oceans to answer this question. Using a data set of the spectral optical thickness measured by the Aerosol Robotic network (AERONET), extending 1-3 years, we find the background conditions for these stations. The oceanic background aerosol is the result of ocean emission and spray, and some residual long lived continental aerosol. Its source is very broadly spread and is expected to vary little in time. Pollution or dust sources are from specific locations, emitted and transported to the measuring site in specific combination of meteorological conditions. Therefore they are expected to vary with time. It follows that the background aerosol can be identified as the median for conditions with small variations. To define the background we compute the median of N consequent measurements. We use N=50 that in average cloudy conditions corresponds to 2-3 days of measurements and N=100 (4-5 days). Most high polluted or dusty conditions correspond to data sequences with high standard deviation (greater than 0.02 in optical thickness) and are excluded. From the remaining N point running medians with low standard deviations we derive again the median. This excludes those rare cases of pollution or dust that is stable during the N measurements. The results show that the background aerosol over the Pacific Ocean is characterize by optical thickness of 0.055 at 500 nm and Angstrom exponent of 0.74. Over the Atlantic Ocean the values are 0.070 and 1.1 respectively, with little influence of the assumed value of N (50 or 100). The derivation of the background uses 20,000 and 5000 medians respectively that passed the

  7. Optical constants and transient absorption of solution-deposited RuO2 thin films

    NASA Astrophysics Data System (ADS)

    Owrutsky, Jeffrey; Compton, Ryan; Long, James; Chrevin, Christopher; Bussmann, Konrad; Dunkelberger, Adam; Spann, Bryan; Palin, Irina; Rolison, Debra; Cunningham, Paul; Melinger, Joseph; Desario, Paul; Weidinger, Dan; Heilweil, Edwin

    2015-03-01

    Optical and electrical conductivity properties are determined for the promising, broadband transparent conductor material, solution-deposited RuO2 nanostructured films. The 10-30 nm thick films or nanoskins are less conductive but more optically transmissive than polycrystalline, sputtered RuO2 films which are inherently metallic. The optical constants (0.6 to 4.5 eV) determined by ellipsometry show that ɛ1 is positive for the nanoskins in the spectral region investigated so they are not plasmonic. Transient picosecond absorption with visible (400 nm) pump and various probe wavelengths (visible and THz) are performed for nanoskins calcined to different temperatures. When heated to 200°C the absorption increases in the visible and THz. After heating to 300°C, the films become more polycrystalline and there is evidence for the appearance of a new absorption. Deceased absorptions or bleaches are observed in the THz and for longer visible wavelengths (> 750 nm). The absorption is ascribed to a damped plasmon band of the crystalline nanoparticles formed in the film upon heating.

  8. 3D resolved mapping of optical aberrations in thick tissues

    PubMed Central

    Zeng, Jun; Mahou, Pierre; Schanne-Klein, Marie-Claire; Beaurepaire, Emmanuel; Débarre, Delphine

    2012-01-01

    We demonstrate a simple method for mapping optical aberrations with 3D resolution within thick samples. The method relies on the local measurement of the variation in image quality with externally applied aberrations. We discuss the accuracy of the method as a function of the signal strength and of the aberration amplitude and we derive the achievable resolution for the resulting measurements. We then report on measured 3D aberration maps in human skin biopsies and mouse brain slices. From these data, we analyse the consequences of tissue structure and refractive index distribution on aberrations and imaging depth in normal and cleared tissue samples. The aberration maps allow the estimation of the typical aplanetism region size over which aberrations can be uniformly corrected. This method and data pave the way towards efficient correction strategies for tissue imaging applications. PMID:22876353

  9. Aerosol Optical Thickness Variability in the New York Metropolitan Area

    NASA Astrophysics Data System (ADS)

    Liepert, B. G.

    2003-12-01

    In July 2003 this field study was performed as part of the NASA Goddard Institute for Space Studies Summer Program "Institute for Climate and Planets". The spatial variability of aerosol spectral optical thickness (AOT) in the New York Metropolitan area was measured with a hand held sun photometer "Microtops II". Measurements were taken on board of a cruise ship around Manhattan, and several transects from North to South and East to West within New York City including on top of the Empire State Building. These data are compared to other available ground observations of urban aerosols and to satellite data from MODIS. Consequences of the spatial variability of the effect of urban aerosols on climate will be discussed.

  10. Time-dependent, optically thick accretion onto a black hole

    NASA Technical Reports Server (NTRS)

    Gilden, D. L.; Wheeler, J. C.

    1980-01-01

    A fully relativistic hydrodynamics code which incorporates diffusive radiation transport is used to study time-dependent, spherically symmetric, optically thick accretion onto a black hole. It is found that matter free-falls into the hole regardless of whether the diffusion time scale is longer or shorter than the dynamical time. Nonadiabatic heating due to magnetic field reconnection is included. The internal energy thus generated affects the flow in a purely relativistic way, again ensuring free-fall collapse of the inflowing matter. Any matter enveloping a black hole will thus be swallowed on a dynamical time scale with relatively small net release of energy. The inclusion of angular momentum will not necessarily affect this conclusion.

  11. Fringe biasing: A variance reduction technique for optically thick meshes

    SciTech Connect

    Smedley-Stevenson, R. P.

    2013-07-01

    Fringe biasing is a stratified sampling scheme applicable to Monte Carlo thermal radiation transport codes. The thermal emission source in optically thick cells is partitioned into separate contributions from the cell interiors (where the likelihood of the particles escaping the cells is virtually zero) and the 'fringe' regions close to the cell boundaries. Thermal emission in the cell interiors can now be modelled with fewer particles, the remaining particles being concentrated in the fringes so that they are more likely to contribute to the energy exchange between cells. Unlike other techniques for improving the efficiency in optically thick regions (such as random walk and discrete diffusion treatments), fringe biasing has the benefit of simplicity, as the associated changes are restricted to the sourcing routines with the particle tracking routines being unaffected. This paper presents an analysis of the potential for variance reduction achieved from employing the fringe biasing technique. The aim of this analysis is to guide the implementation of this technique in Monte Carlo thermal radiation codes, specifically in order to aid the choice of the fringe width and the proportion of particles allocated to the fringe (which are interrelated) in multi-dimensional simulations, and to confirm that the significant levels of variance reduction achieved in simulations can be understood by studying the behaviour for simple test cases. The variance reduction properties are studied for a single cell in a slab geometry purely absorbing medium, investigating the accuracy of the scalar flux and current tallies on one of the interfaces with the surrounding medium. (authors)

  12. Feasibility test of line sensors for optical tissue thickness estimation

    NASA Astrophysics Data System (ADS)

    Stüber, Patrick; Wissel, Tobias; Wagner, Benjamin; Schweikard, Achim; Ernst, Floris

    2015-05-01

    Purpose Line sensors are cheap, fast and have high quantum effciencies. Here, we investigate whether these sensors can replace an area image sensor for the purpose of tissue thickness measurements. Material and Methods As part of a subject study high dynamic range (HDR) images of three subjects were acquired with an area image sensor. To simulate a line sensor as realistic as possible single or multiple lines were extracted from these HDR images. Thereby, horizontally extracted lines correspond to a parallel orientation of the line sensor relative to the incident angle of a laser beam. Vertically extracted lines correspond to an orthogonal orientation. Then, optical features were determined and converted into a tissue thickness using a machine learning algorithm. Results For the tested subjects the worst root mean square error (RMSE) of the learning process was 0:385 mm. The best RMSE was 0:222 mm. For all subjects, the mean RMSE and the standard deviation of RMSE values decreases with a larger number of extracted lines. The orientation of the line sensor turned out to be important for the RMSE. Vertically oriented line sensors achieve lower RMSEs than horizontally oriented sensors because of the influence of the incident angle. Furthermore, the head-pose of the subject seems to be important for the accuracy. Conclusion Line sensors deliver comparable results to previously analysed area image sensors. Nevertheless, the scattering of the values is higher and the size and orientation of the sensor and the head-pose have an influence on the RMSE of the learning process. Therefore, line sensors are feasible for tissue thickness estimation but they are a trade-off between accuracy and speed.

  13. High-resolution in-depth imaging of optically cleared thick samples using an adaptive SPIM

    PubMed Central

    Masson, Aurore; Escande, Paul; Frongia, Céline; Clouvel, Grégory; Ducommun, Bernard; Lorenzo, Corinne

    2015-01-01

    Today, Light Sheet Fluorescence Microscopy (LSFM) makes it possible to image fluorescent samples through depths of several hundreds of microns. However, LSFM also suffers from scattering, absorption and optical aberrations. Spatial variations in the refractive index inside the samples cause major changes to the light path resulting in loss of signal and contrast in the deepest regions, thus impairing in-depth imaging capability. These effects are particularly marked when inhomogeneous, complex biological samples are under study. Recently, chemical treatments have been developed to render a sample transparent by homogenizing its refractive index (RI), consequently enabling a reduction of scattering phenomena and a simplification of optical aberration patterns. One drawback of these methods is that the resulting RI of cleared samples does not match the working RI medium generally used for LSFM lenses. This RI mismatch leads to the presence of low-order aberrations and therefore to a significant degradation of image quality. In this paper, we introduce an original optical-chemical combined method based on an adaptive SPIM and a water-based clearing protocol enabling compensation for aberrations arising from RI mismatches induced by optical clearing methods and acquisition of high-resolution in-depth images of optically cleared complex thick samples such as Multi-Cellular Tumour Spheroids. PMID:26576666

  14. High-resolution in-depth imaging of optically cleared thick samples using an adaptive SPIM

    NASA Astrophysics Data System (ADS)

    Masson, Aurore; Escande, Paul; Frongia, Céline; Clouvel, Grégory; Ducommun, Bernard; Lorenzo, Corinne

    2015-11-01

    Today, Light Sheet Fluorescence Microscopy (LSFM) makes it possible to image fluorescent samples through depths of several hundreds of microns. However, LSFM also suffers from scattering, absorption and optical aberrations. Spatial variations in the refractive index inside the samples cause major changes to the light path resulting in loss of signal and contrast in the deepest regions, thus impairing in-depth imaging capability. These effects are particularly marked when inhomogeneous, complex biological samples are under study. Recently, chemical treatments have been developed to render a sample transparent by homogenizing its refractive index (RI), consequently enabling a reduction of scattering phenomena and a simplification of optical aberration patterns. One drawback of these methods is that the resulting RI of cleared samples does not match the working RI medium generally used for LSFM lenses. This RI mismatch leads to the presence of low-order aberrations and therefore to a significant degradation of image quality. In this paper, we introduce an original optical-chemical combined method based on an adaptive SPIM and a water-based clearing protocol enabling compensation for aberrations arising from RI mismatches induced by optical clearing methods and acquisition of high-resolution in-depth images of optically cleared complex thick samples such as Multi-Cellular Tumour Spheroids.

  15. AIR MONITORING BY DIFFERENTIAL OPTICAL ABSORPTION SPECTROMETRY IN BAYTOWN, TEXAS

    EPA Science Inventory

    This report documents the results of a field study carried out in Baytown, Texas in August 1993. ne goal of the field study was to evaluate calibration and audit procedures for a differential optical absorption spectrometry (DOAS) system. he other major goal of the study was to c...

  16. MODIS Retrievals of Cloud Optical Thickness and Particle Radius

    NASA Technical Reports Server (NTRS)

    Platnick, S.; King, M. D.; Ackerman, S. A.; Gray, M.; Moody, E.; Arnold, G. T.; Einaudi, Franco (Technical Monitor)

    2000-01-01

    The Moderate Resolution Imaging Spectroradiometer (MODIS) provides an unprecedented opportunity for global cloud studies with 36 spectral bands from the visible through the infrared, and spatial resolution from 250 m to 1 km at nadir. In particular, all solar window bands useful for simultaneous retrievals of cloud optical thickness and particle size (0.67, 0.86, 1.2, 1.6, 2.1, and 3.7 micron bands) are now available on a single satellite instrument/platform for the first time. An operational algorithm for the retrieval of these optical and cloud physical properties (including water path) have been developed for both liquid and ice phase clouds. The product is archived into two categories: pixel-level retrievals at 1 km spatial resolution (referred to as a Level-2 product) and global gridded statistics (Level-3 product). An overview of the MODIS cloud retrieval algorithm and early level-2 and -3 results will be presented. A number of MODIS cloud validation activities are being planned, including the recent Southern Africa Regional Science Initiative 2000 (SAFARI-2000) dry season campaign conducted in August/September 2000. The later part of the experiment concentrated on MODIS validation in the Namibian stratocumulus regime off the southwest coast of Africa. Early retrieval results from this regime will be discussed.

  17. Focused optical and acoustic beams in media with nonlinear absorption

    NASA Astrophysics Data System (ADS)

    Rudenko, O. V.; Sukhorukov, A. A.

    1996-11-01

    Optical and acoustic beams are known to be useful for medical and biological applications, such as diagnostics, surgery, etc. At high intensities both nonlinear lens effects and nonlinear absorption can be significant for the beams. The nonlinear absorption arises due to two-photon optical processes or acoustic shock wave formation. The present work is devoted to the theoretical description of nonlinear beam propagation and focal spot formation taking into account the competition between focusing, diffraction and absorption. We derived a new nonlinear integro- differential equation describing the spatial evolution of the beam width. The general analytical solution of this equation is obtained for arbitrary boundary conditions. The simple formulas are derived for the angle divergence in the far field, as well as for beam width at nonlinear waist. The results of the analysis of these key parameters in different situations are presented.

  18. Tunable enhanced optical absorption of graphene using plasmonic perfect absorbers

    SciTech Connect

    Cai, Yijun; Zhu, Jinfeng; Liu, Qing Huo

    2015-01-26

    Enhancement and manipulation of light absorption in graphene is a significant issue for applications of graphene-based optoelectronic devices. In order to achieve this purpose in the visible region, we demonstrate a design of a graphene optical absorber inspired by metal-dielectric-metal metamaterial for perfect absorption of electromagnetic waves. The optical absorbance ratios of single and three atomic layer graphene are enhanced up to 37.5% and 64.8%, respectively. The graphene absorber shows polarization-dependence and tolerates a wide range of incident angles. Furthermore, the peak position and bandwidth of graphene absorption spectra are tunable in a wide wavelength range through a specific structural configuration. These results imply that graphene in combination with plasmonic perfect absorbers have a promising potential for developing advanced nanophotonic devices.

  19. Optical absorption of polar and semipolar InGaN/GaN quantum wells for blue to green converter structures

    SciTech Connect

    Neuschl, B. Helbing, J.; Thonke, K.

    2014-11-14

    The optical absorption of indium gallium nitride (InGaN)/GaN multi quantum wells (QWs) is analyzed theoretically and experimentally. For different sample structures, either planar or three-dimensional, including QWs with different tilts relative to the (0001) plane of the wurtzite crystal, the room temperature absorption spectra were measured. We observe increasing absorption for larger indium content in the active zone and for increasing QW thickness. The semipolar structures with their reduced internal electric field are favorable with respect to the spectral absorption when compared with polar samples. Numerical k ⋅ p based simulations for quantum wells with variable thickness, indium content, and orientation are in accordance with the experimental results. By taking all QW energy eigenstates in all bands as well as the orientation dependent transition probabilities into account, the spectral absorption for arbitrary sample structures can be calculated.

  20. Retrieval of aerosol optical thickness over snow using AATSR observations

    NASA Astrophysics Data System (ADS)

    Istomina, Larysa; von Hoyningen-Huene, Wolfgang; Rozanov, Vladimir; Kokhanovsky, Alexander; Burrows, John P.

    Remote sensing of aerosols experiences lack of products over very bright surfaces, such as deserts and snow, due to difficulties with the subtraction of the surface reflection contribution, when a small error in accounting for surface reflectance can cause a large error in retrieved aerosol optical thickness (AOT). Cloud screening over bright surface is also not easy because of low contrast between clouds and surface in visible range of spectrum, and additional infrared chan-nels are not always available. Luckily, AATSR instrument onboard ENVISAT has necessary features to solve both of these problems. In current work we present an improved version of discussed earlier [1,2] dual-view algorithm to retrieve AOT over snow. The retrieval algorithm still consists of cloud screening, based on spectral shape analysis of AATSR pixel in order to extract clear snow pixels, and of AOT retrieval over snow and water. Current version of AOT retrieval over open ocean now contains improved accounting for ocean reflectance (in previous version the ocean was assumed to be absolutely black). The AOT retrieval over snow has been improved to account more accurately for the bidirectional features of the surface reflection function. For this we now use the approach described in [4] instead of [3], which has been used in the previous version of the retrieval. The accuracy of both approaches [3] and [4] has been evaluated via comparison to forward radiative-transfer model for the case of a very bright surface. The new algorithm has been applied to various scenes in European Arctic and Alaska in different scales, up to global AOT maps. The correspondence of AOT over snow to AOT over water is quite good, which proves the reliability of the retrieval. The algorithm has been validated against AERONET and other Arctic ground based AOT data and shows reasonably good correlation. The presented cloud screening method has been validated via comparison to MODIS cloud mask and Micro Pulse Lidar data

  1. Optical absorption of thin film on a Lambertian reflector substrate

    NASA Astrophysics Data System (ADS)

    Sheng, P.

    1984-05-01

    A formula is derived for calculating the optical absorption of thin films deposited on a Lambertian reflector substrate. It is shown that compared with the case of flat reflecting substrate, the incoherent absorption is enhanced by a factor of m x epsilon (1) in the weak absorption limit, where epsilon (1) is the real part of the film dielectric constant and m near two is a slightly varying function of epsilon (1). For a 0.5-micron a-SiH(x) (bandgap 1.7 eV) solar cell with a Lambertian reflector substrate, the total absorption in terms of the short-circuit current is calculated to be 18.63 mA/sq cm.

  2. Marcasite revisited: Optical absorption gap at room temperature

    NASA Astrophysics Data System (ADS)

    Sánchez, C.; Flores, E.; Barawi, M.; Clamagirand, J. M.; Ares, J. R.; Ferrer, I. J.

    2016-03-01

    Jagadeesh and Seehra published in 1980 that the marcasite band gap energy is 0.34 eV. However, recent calculations and experimental approximations accomplished by several research groups point out that the marcasite band gap energy should be quite similar to that of pyrite (of the order of 0.8-1.0 eV). By using diffuse reflectance spectroscopy (DRS) we have determined that marcasite has no optical absorption gap at photon energies 0.06 ≤ hν ≤ 0.75 eV and that it has two well defined optical transitions at ~ 0.9 eV and ~ 2.2 eV quite similar to those of pyrite. Marcasite optical absorption gap appears to be Eg ≅ 0.83 ± 0.02 eV and it is due to an allowed indirect transition.

  3. Study on optical weak absorption of borate crystals

    NASA Astrophysics Data System (ADS)

    Li, Xiaomao; Hu, Zhanggui; Yue, Yinchao; Yu, Xuesong; Lin, Zheshuai; Zhang, Guochun

    2013-10-01

    Borate crystal is an important type of nonlinear optical crystals used in frequency conversion in all-solid-state lasers. Especially, LiB3O5 (LBO), CsB3O5 (CBO) and CsLiB6O10 (CLBO) are the most advanced. Although these borate crystals are all constructed by the same anionic group-(B3O7)5-, they show different nonlinear optical properties. In this study, bulk weak absorption values of three borate crystals have been studied at 1064 nm by a photothermal common-path interferometer. The bulk weak absorption values of them along [1 0 0], [0 1 0] and [0 0 1] directions were obtained, respectively, to be approximately 17.5 ppm cm-1, 15 ppm cm-1 and 20 ppm cm-1 (LBO); 80 ppm cm-1, 100 ppm cm-1 and 40 ppm cm-1 (CBO); 600 ppm cm-1, 600 ppm cm-1 and 150 ppm cm-1 (CLBO) at 1064 nm. The results showed an obvious discrepancy of the values of these crystals along three axis directions. A correlation between the bulk weak absorption property and crystal intrinsic structure was then discussed. It is found that the bulk weak absorption values strongly depend on the interstitial area surrounded by the B-O frames. The interstitial area is larger, the bulk weak absorption value is higher.

  4. Confronting simulations of optically thick gas in massive halos with observations at z = 2-3

    SciTech Connect

    Fumagalli, Michele; Hennawi, Joseph F.; Prochaska, J. Xavier; Kasen, Daniel; Dekel, Avishai; Ceverino, Daniel; Primack, Joel

    2014-01-01

    Cosmological hydrodynamic simulations predict the physical state of baryons in the circumgalactic medium (CGM), which can be directly tested via quasar absorption line observations. We use high-resolution 'zoom-in' simulations of 21 galaxies to characterize the distribution of neutral hydrogen around halos in the mass range M {sub vir} ∼ 2 × 10{sup 11} to 4 × 10{sup 12} M {sub ☉} at z ∼ 2. We find that both the mass fraction of cool (T ≤ 3 × 10{sup 4} K) gas and the covering fraction of optically thick Lyman limit systems (LLSs) depend only weakly on halo mass, even around the critical value for the formation of stable virial shocks. The covering fraction of LLSs interior to the virial radius varies between f {sub c} ∼ 0.05-0.2, with significant scatter among halos. Our simulations of massive halos (M {sub vir} ≥ 10{sup 12} M {sub ☉}) underpredict the covering fraction of optically thick gas observed in the quasar CGM by a large factor. The reason for this discrepancy is unclear, but several possibilities are discussed. In the lower mass halos (M {sub vir} ≥ 5 × 10{sup 11} M {sub ☉}) hosting star-forming galaxies, the predicted covering factor agrees with observations; however, current samples of quasar-galaxy pairs are too small for a conclusive comparison. To overcome this limitation, we propose a new observable: the small-scale autocorrelation function of optically thick absorbers detected in the foreground of close quasar pairs. We show that this new observable can constrain the underlying dark halos hosting LLSs at z ∼ 2-3, as well as the characteristic size and covering factor of the CGM.

  5. Optical Thickness and Effective Radius Retrievals of Liquid Water Clouds over Ice and Snow Surface

    NASA Technical Reports Server (NTRS)

    Platnick, S.; King, M. D.; Tsay, S.-C.; Arnold, G. T.; Gerber, H.; Hobbs, P. V.; Rangno, A.

    1999-01-01

    Cloud optical thickness and effective radius retrievals from solar reflectance measurements traditionally depend on a combination of spectral channels that are absorbing and non-absorbing for liquid water droplets. Reflectances in non-absorbing channels (e.g., 0.67, 0.86 micrometer bands) are largely dependent on cloud optical thickness, while longer wavelength absorbing channels (1.6, 2.1, and 3.7 micrometer window bands) provide cloud particle size information. Retrievals are complicated by the presence of an underlying ice/snow surface. At the shorter wavelengths, sea ice is both bright and highly variable, significantly increasing cloud retrieval uncertainty. However, reflectances at the longer wavelengths are relatively small and may be comparable to that of dark open water. Sea ice spectral albedos derived from Cloud Absorption Radiometer (CAR) measurements during April 1992 and June 1995 Arctic field deployments are used to illustrate these statements. A modification to the traditional retrieval technique is devised. The new algorithm uses a combination of absorbing spectral channels for which the snow/ice albedo is relatively small. Using this approach, preliminary retrievals have been made with the MODIS Airborne Simulator (MAS) imager flown aboard the NASA ER-2 during FIRE-ACE. Data from coordinated ER-2 and University of Washington CV-580 aircraft observations of liquid water stratus clouds on June 3 and June 6, 1998 have been examined. Size retrievals are compared with in situ cloud profile measurements of effective radius made with the CV-580 PMS FSSP probe, and optical thickness retrievals are compared with extinction profiles derived from the Gerber Scientific "g-meter" probe. MAS retrievals are shown to be in good agreement with the in situ measurements.

  6. Two-Photon-Absorption Scheme for Optical Beam Tracking

    NASA Technical Reports Server (NTRS)

    Ortiz, Gerardo G.; Farr, William H.

    2011-01-01

    A new optical beam tracking approach for free-space optical communication links using two-photon absorption (TPA) in a high-bandgap detector material was demonstrated. This tracking scheme is part of the canonical architecture described in the preceding article. TPA is used to track a long-wavelength transmit laser while direct absorption on the same sensor simultaneously tracks a shorter-wavelength beacon. The TPA responsivity was measured for silicon using a PIN photodiode at a laser beacon wavelength of 1,550 nm. As expected, the responsivity shows a linear dependence with incident power level. The responsivity slope is 4.5 x 10(exp -7) A/W2. Also, optical beam spots from the 1,550-nm laser beacon were characterized on commercial charge coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) imagers with as little as 13.7 microWatts of optical power (see figure). This new tracker technology offers an innovative solution to reduce system complexity, improve transmit/receive isolation, improve optical efficiency, improve signal-to-noise ratio (SNR), and reduce cost for free-space optical communications transceivers.

  7. Infrared absorption study of hydrogen incorporation in thick nanocrystalline diamond films

    SciTech Connect

    Tang, C.J.; Neves, A.J.; Carmo, M.C.

    2005-05-30

    We present an infrared (IR) optical absorbance study of hydrogen incorporation in nanocrystalline diamond films. The thick nanocrystalline diamond films were synthesized by microwave plasma-assisted chemical vapor deposition and a high growth rate about 3.0 {mu}m/h was achieved. The morphology, phase quality, and hydrogen incorporation were assessed by means of scanning electron microscopy, Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR). Large amount of hydrogen bonded to nanocrystalline diamond is clearly evidenced by the huge CH stretching band in the FTIR spectrum. The mechanism of hydrogen incorporation is discussed in light of the growth mechanism of nanocrystalline diamond. This suggests the potential of nanocrystalline diamond for IR electro-optical device applications.

  8. Enhanced terahertz emission by coherent optical absorption in ultrathin semiconductor films on metals.

    PubMed

    Ramakrishnan, Gopakumar; Ramanandan, Gopika K P; Adam, Aurèle J L; Xu, Man; Kumar, Nishant; Hendrikx, Ruud W A; Planken, Paul C M

    2013-07-15

    We report on the surprisingly strong, broadband emission of coherent terahertz pulses from ultrathin layers of semiconductors such as amorphous silicon, germanium and polycrystalline cuprous oxide deposited on gold, upon illumination with femtosecond laser pulses. The strength of the emission is surprising because the materials are considered to be bad (amorphous silicon and polycrystalline cuprous oxide) or fair (amorphous germanium) terahertz emitters at best. We show that the strength of the emission is partly explained by cavity-enhanced optical absorption. This forces most of the light to be absorbed in the depletion region of the semiconductor/metal interface where terahertz generation occurs. For an excitation wavelength of 800 nm, the strongest terahertz emission is found for a 25 nm thick layer of amorphous germanium, a 40 nm thick layer of amorphous silicon and a 420 nm thick layer of cuprous oxide, all on gold. The emission from cuprous oxide is similar in strength to that obtained with optical rectification from a 300 μm thick gallium phosphide crystal. As an application of our findings we demonstrate how such thin films can be used to turn standard optical components, such as paraboloidal mirrors, into self-focusing terahertz emitters. PMID:23938530

  9. Analysis of cloud optical thickness retrieved from CIMEL measurements

    NASA Astrophysics Data System (ADS)

    Marshak, A.; Barker, H.; Evans, K.; Pavloski, C.; Knyazikhin, Y.; Holben, B.; Wiscombe, W.

    2002-05-01

    When conditions are inappropriate to make AERONET measurements that are suitable for aerosol studies, new measurements related to cloud physics can be made instead. As such, several AERONET CIMEL sunphotometers have been equipped with a new "cloud mode." This mode allows the CIMELs to make measurements of zenith radiance when the Sun in blocked by clouds. When in cloud mode, a CIMEL points straight up every 10-15 minutes and takes 10 measurements over a 9 second time interval at four wavelengths: 440, 670, 870, and 1020 nm. For cloudy conditions above green vegetation, the spectral contrast in surface albedo dominates over Rayleigh and aerosol effects; this makes normalized zenith radiances almost indistinguishable at 440 and 670 as well as at 870 and 1020 nm. We have developed a new method for retrieving cloud optical thickness, even for broken clouds, that uses data from the 670 and 870 nm channels to build a Normalized Difference Cloud Index (NDCI). The retrieval can be improved if, in addition to CIMEL zenith radiances, surface downward flux measurements at both wavelengths are also available. Based on theoretical calculations and preliminary analysis of CIMEL measurements at the ARM Central Facility in Oklahoma, there is good correlation between NDCI and cloud liquid water path retrieved from microwave radiometer for cloudy sky above green vegetation.

  10. Mechanical characterization of unplasticised polyvinylchloride thick pipes by optical methods

    NASA Astrophysics Data System (ADS)

    Mihaylova, E.; Potelon, B.; Reddy, S.; Toal, V.; Smith, C.

    2004-06-01

    In this work a number of techniques (electronic speckle pattern interferometry, holographic interferometry, strain gauge and finite element method) are brought to bear in order to establish consistency in the results of strain measurement. This is necessary if optical non-destructive testing methods, such as those used here, are to gain acceptance for routine industrial use. The FE model provides a useful check. Furthermore, ESPI fringe data facilitates the extension of FE models, an approach that is of growing importance in component testing. The use of in-plane and out-of-plane sensitive electronic speckle pattern interferometry (ESPI) for non-destructive material characterization of thick unplasticised polyvinylchloride (uPVC) pipes is presented. A test rig has been designed for stressing pipes by internal pressure. ESPI gives a complete mapping of the displacement field over the area imaged by the video camera. The results for the strain of uPVC obtained from ESPI data and from strain gauges are in good agreement. The value of Young's modulus has been obtained from the fringe data and compared with results obtained using holographic interferometry and from strain gauge measurements. The FE model also produces fringe data that is consistent with the ESPI results.

  11. Optical quantification of epithelial layer thickness as a measure of oral inflammation

    NASA Astrophysics Data System (ADS)

    Hattery, David W.; Hattery, Brenda; Hassan, Moinuddin; Chernomordik, Victor V.; Vogel, Abby; Hekmat, Farid; Gandjbakhche, Amir H.

    2003-06-01

    For individuals with cancer risk factors, reducing tissue inflammation may reduce the risk of developing cancer. This is the basis of several clinical trials evaluating potential chemoprevention drugs. These trials require quantitative assessments of inflammation which, for the oral epithelium, are traditionally provided by punch biopsies. To reduce patient discomfort and morbidity, we have developed a non-invasive alternative using diffuse reflectance spectroscopy. Though any optical system has the potential for probing near-surface structures, traditional methods of accounting for scattering of photons are generally invalid for typical epithelial thicknesses. We have previously developed a theory that is valid in this regime and validated it with Monte Carlo simulations. We use a differential measure with acute sensitivity to small changes in layer scattering coefficients. To assess the capability of the approach to quantify epithelial thickness, detailed Monte Carlo simulations and measurements on phantom models of a two layered structure have been performed. Preliminary results from this work show that our key feature varies less than 20 percent despite four-fold changes in scattering coefficients and ten-fold changes in absorption coefficients. This indicates that the method will be of practical clinical value for quantifying epithelial thickness in vivo.

  12. Absorption characteristics of optically complex inland waters: Implications for water optical classification

    NASA Astrophysics Data System (ADS)

    Shi, Kun; Li, Yunmei; Li, Lin; Lu, Heng

    2013-06-01

    Multiple bio-optical measurements were conducted in inland waters of China, including Lake Taihu [spring and autumn], Lake Chaohu, Lake Dianchi, and Three Gorges Reservoirs. The variations in the absorption characteristics of chromophoric dissolved organic matter (CDOM), phytoplankton, and non-algal particles (NAP) and their relative contributions to total absorption among these waters were analyzed. The obtained results indicated that these areas are representative of the optically complex inland waters characterized by strong regional variations of their absorption properties. By means of the relative contributions of NAP and phytoplankton to the total water absorption at 550 and 675 nm, these waters were classified into three optical water types, each one having specific biogeochemical and optical properties. Two of the types were distinct and corresponded to waters that are optically controlled by NAP (Type I) and dominated by phytoplankton (Type III). Type II was related to relatively optically mixed waters where the absorption properties are controlled by NAP and phytoplankton. Additionally, the differences in remote-sensing reflectance (Rrs) spectra among the three classified water types were clarified to establish optical criteria for identifying these water types. On this basis, the classification criteria for MERIS images were developed, which allowed one to cluster every Rrs spectrum into one of the three water types by comparing the values from band 6, band 8, and band 9 of MERIS images. The proposed criteria were subsequently conducted to map the water types of Lake Taihu using MERIS images.

  13. Thick optical films for the conduction of optical and infrared radiation

    SciTech Connect

    Bain, C.N.; Gordon, B.A.; Knasel, T.M.; Malinowski, R.L.

    1981-01-01

    Experimental results are presented for the characteristics of thick optical films, which can be used to direct and conduct optical and IR radiation, for the case of light concentration onto solar cells. Incident light is trapped within a thin, flat sheet of transparent material by a diffuse selective surface on the back of the transparent layer, and so directed that total internal reflection occurs, with some of the captured light finding its way back to the photovoltaic cells attached to the back of the layer. A Monte Carlo computer model is used to analyze this system, whose achievable gain depends on layer thickness, trapping material refraction index, and solar cell shape and size. Results indicate that gains of a factor of two in power output are obtainable for the case of sparsely-packed solar cell arrays and lower factors for more densely-packed arrays.

  14. Anomalous nonlinear absorption in epsilon-near-zero materials: optical limiting and all-optical control.

    PubMed

    Vincenti, M A; de Ceglia, D; Scalora, Michael

    2016-08-01

    We investigate nonlinear absorption in films of epsilon-near-zero materials. The combination of large local electric fields at the fundamental frequency and material losses at the harmonic frequencies induce unusual intensity-dependent phenomena. We predict that the second-order nonlinearity of a low-damping, epsilon-near-zero slab produces an optical limiting effect that mimics a two-photon absorption process. Anomalous absorption profiles that depend on low permittivity values at the pump frequency are also predicted for third-order nonlinearities. These findings suggest new opportunities for all-optical light control and novel ways to design reconfigurable and tunable nonlinear devices. PMID:27472631

  15. Birefringence and anisotropic optical absorption in porous silicon

    SciTech Connect

    Efimova, A. I. Krutkova, E. Yu.; Golovan', L. A.; Fomenko, M. A.; Kashkarov, P. K.; Timoshenko, V. Yu.

    2007-10-15

    The refractive indices and the coefficients of optical absorption by free charge carriers and local vibrations in porous silicon (por-Si) films, comprising nanometer-sized silicon residues (nanocrystals) separated by nanometer-sized pores (nanopores) formed in the course of electrochemical etching of the initial single crystal silicon, have been studied by polarization-resolved IR absorption spectroscopy techniques. It is shown that the birefringence observed in por-Si is related to the anisotropic shapes of nanocrystals and nanopores, while the anisotropy (dichroism) of absorption by the local vibrational modes is determined predominantly by the microrelief of the surface of nanocrystals. It is demonstrated that silicon-hydrogen surface bonds in nanocrystals can be restored by means of selective hydrogen thermodesorption with the formation of a considerable number of H-terminated surface Si-Si dimers.

  16. Neuron absorption study and mid-IR optical excitations

    NASA Astrophysics Data System (ADS)

    Guo, Dingkai; Chen, Xing; Vadala, Shilpa; Leach, Jennie; Kostov, Yordan; Bewley, William W.; Kim, Chul-Soo; Kim, Mijin; Canedy, Chadwick L.; Merritt, Charles D.; Vurgaftman, Igor; Meyer, Jerry R.; Choa, Fow-Sen

    2012-02-01

    Neuronal optical excitation can provide non-contacting tools to explore brain circuitry and a durable stimulation interface for cardiac pacing and visual as well as auditory sensory neuronal stimulation. To obtain accurate absorption spectra, we scan the transmission of neurons in cell culture medium, and normalize it by subtracting out the absorption spectrum of the medium alone. The resulting spectra show that the main neuronal absorption peaks are in the 3000- 6000nm band, although there is a smaller peak near 1450nm. By coupling the output of a 3μm interband cascade laser (ICL) into a mid-IR fluorozirconate fiber, we can effectively deliver more than 1J/cm2 photon intensity to the excitation site for neuronal stimulation.

  17. Optical absorption of ion-beam sputtered amorphous silicon coatings

    NASA Astrophysics Data System (ADS)

    Steinlechner, Jessica; Martin, Iain W.; Bassiri, Riccardo; Bell, Angus; Fejer, Martin M.; Hough, Jim; Markosyan, Ashot; Route, Roger K.; Rowan, Sheila; Tornasi, Zeno

    2016-03-01

    Low mechanical loss at low temperatures and a high index of refraction should make silicon optimally suited for thermal noise reduction in highly reflective mirror coatings for gravitational wave detectors. However, due to high optical absorption, amorphous silicon (aSi) is unsuitable for being used as a direct high-index coating material to replace tantala. A possible solution is a multimaterial design, which enables exploitation of the excellent mechanical properties of aSi in the lower coating layers. The possible number of aSi layers increases with absorption reduction. In this work, the optimum heat treatment temperature of aSi deposited via ion-beam sputtering was investigated and found to be 450 °C . For this temperature, the absorption after deposition of a single layer of aSi at 1064 nm and 1550 nm was reduced by more than 80%.

  18. Probing molecular chirality by coherent optical absorption spectra

    SciTech Connect

    Jia, W. Z.; Wei, L. F.

    2011-11-15

    We propose an approach to sensitively probe the chirality of molecules by measuring their coherent optical-absorption spectra. It is shown that quantum dynamics of the cyclic three-level chiral molecules driven by appropriately designed external fields is total-phase dependent. This will result in chirality-dependent absorption spectra for the probe field. As a consequence, the charality-dependent information in the spectra (such as the locations and relative heights of the characteristic absorption peaks) can be utilized to identify molecular chirality and determinate enantiomer excess (i.e., the percentages of different enantiomers). The feasibility of the proposal with chiral molecules confined in hollow-core photonic crystal fiber is also discussed.

  19. Remark on: the neutron spherical optical-model absorption.

    SciTech Connect

    Smith, A. B.; Nuclear Engineering Division

    2007-06-30

    The energy-dependent behavior of the absorption term of the spherical neutron optical potential for doubly magic {sup 208}Pb and the neighboring {sup 209}Bi is examined. These considerations suggest a phenomenological model that results in an intuitively attractive energy dependence of the imaginary potential that provides a good description of the observed neutron cross sections and that is qualitatively consistent with theoretical concepts. At the same time it provides an alternative to some of the arbitrary assumptions involved in many conventional optical-model interpretations reported in the literature and reduces the number of the parameters of the model.

  20. Ultraviolet optical absorptions of semiconducting copper phosphate glasses

    NASA Technical Reports Server (NTRS)

    Bae, Byeong-Soo; Weinberg, Michael C.

    1993-01-01

    Results are presented of a quantitative investigation of the change in UV optical absorption in semiconducting copper phosphate glasses with batch compositions of 40, 50, and 55 percent CuO, as a function of the Cu(2+)/Cu(total) ratio in the glasses for each glass composition. It was found that optical energy gap, E(opt), of copper phosphate glass is a function of both glass composition and Cu(2+)/Cu(total) ratio in the glass. E(opt) increases as the CuO content for fixed Cu(2+)/Cu(total) ratio and the Cu(2+)/Cu(total) ratio for fixed glass composition are reduced.

  1. Study on the elemental mercury absorption cross section based on differential optical absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Zheng, Haiming; Yao, Penghui

    2015-08-01

    With the method of ultraviolet absorption spectrum, the exact absorption cross-section with the light source of the low-pressure mercury lamp was determined, during which the optimum wavelength for mercury concentrations inversion was 253.69 nm, the highest detection limit was 0.177 μg/cm3, and the lowest detection limit was 0.034 μg/cm3. Furthermore, based on the differential optical absorption spectroscopy(DOAS), the relationship between the integral parameters (IP) and the concentration as well as the signal-noise ration (SNR) under the conditions of gas flow was determined and the lowest detection limit was figured out to be 0.03524 μg/cm3, providing a method of DOAS to de-noise through the comparison between the mercury concentration values produced by DOAS and that produced by the wavelet de-noising method (db5). It turned out that the differential optical absorption spectroscopy had a strong anti-interference ability, while the wavelet de-noising method was not suitable for measuring the trace concentration change.

  2. Optical absorption spectrum of Cu 2+ in calcium tartrate tetrahydrate

    NASA Astrophysics Data System (ADS)

    Swamy, Y. K. R.; Reddy, P. P.; Reddy, Y. P.

    1980-02-01

    Copper doped single crystals of calcium tartrate tetrahydrate are grown from silica gel. The optical absorption spectrum is investigated with polarised and unpolarised beams of incident light. The spectrum is attributed to the Cu 2+ ion in C 4V symmetry associated with spin-orbit coupling. The following crystal field parameters are evaluated: Dq = 1000 cm -1; λ = -830 cm -1; Ds = 1540 cm -1; Dt = 470 cm -1.

  3. Electron paramagnetic resonance and optical absorption spectral studies on chalcocite

    NASA Astrophysics Data System (ADS)

    Reddy, S. Lakshmi; Fayazuddin, Md.; Frost, Ray L.; Endo, Tamio

    2007-11-01

    A chalcocite mineral sample of Shaha, Congo is used in the present study. An electron paramagnetic resonance (EPR) study on powdered sample confirms the presence of Mn(II), Fe(III) and Cu(II). Optical absorption spectrum indicates that Fe(III) impurity is present in octahedral structure whereas Cu(II) is present in rhombically distorted octahedral environment. Mid-infrared results are due to water and sulphate fundamentals.

  4. Electron paramagnetic resonance and optical absorption spectral studies on chalcocite.

    PubMed

    Reddy, S Lakshmi; Fayazuddin, Md; Frost, Ray L; Endo, Tamio

    2007-11-01

    A chalcocite mineral sample of Shaha, Congo is used in the present study. An electron paramagnetic resonance (EPR) study on powdered sample confirms the presence of Mn(II), Fe(III) and Cu(II). Optical absorption spectrum indicates that Fe(III) impurity is present in octahedral structure whereas Cu(II) is present in rhombically distorted octahedral environment. Mid-infrared results are due to water and sulphate fundamentals. PMID:17324611

  5. Estimation of aerosol optical properties considering hygroscopicity and light absorption

    NASA Astrophysics Data System (ADS)

    Jung, Chang Hoon; Lee, Ji Yi; Kim, Yong Pyo

    2015-03-01

    In this study, the influences of water solubility and light absorption on the optical properties of organic aerosols were investigated. A size-resolved model for calculating optical properties was developed by combining thermodynamic hygroscopic growth and aerosol dynamics models. The internal mixtures based on the homogeneous and core-shell mixing were compared. The results showed that the radiative forcing (RF) of Water Soluble Organic Carbon (WSOC) aerosol can be estimated to range from -0.07 to -0.49 W/m2 for core-shell mixing and from -0.09 to -0.47 W/m2 for homogeneous mixing under the simulation conditions (RH = 60%). The light absorption properties of WSOC showed the mass absorption efficiency (MAE) of WSOC can be estimated 0.43-0.5 m2/g, which accounts for 5-10% of the MAE of elemental carbon (EC). The effect on MAE of increasing the imaginary refractive index of WSOC was also calculated, and it was found that increasing the imaginary refractive index by 0.001i enhanced WSOC aerosol absorption by approximately 0.02 m2/g. Finally, the sensitivity test results revealed that changes in the fine mode fraction (FMF) and in the geometric mean diameter of the accumulation mode play important roles in estimating RF during hygroscopic growth.

  6. The Retrieval of Aerosol Optical Thickness Using the MERIS Instrument

    NASA Astrophysics Data System (ADS)

    Mei, L.; Rozanov, V. V.; Vountas, M.; Burrows, J. P.; Levy, R. C.; Lotz, W.

    2015-12-01

    Retrieval of aerosol properties for satellite instruments without shortwave-IR spectral information, multi-viewing, polarization and/or high-temporal observation ability is a challenging problem for spaceborne aerosol remote sensing. However, space based instruments like the MEdium Resolution Imaging Spectrometer (MERIS) and the successor, Ocean and Land Colour Instrument (OLCI) with high calibration accuracy and high spatial resolution provide unique abilities for obtaining valuable aerosol information for a better understanding of the impact of aerosols on climate, which is still one of the largest uncertainties of global climate change evaluation. In this study, a new Aerosol Optical Thickness (AOT) retrieval algorithm (XBAER: eXtensible Bremen AErosol Retrieval) is presented. XBAER utilizes the global surface spectral library database for the determination of surface properties while the MODIS collection 6 aerosol type treatment is adapted for the aerosol type selection. In order to take the surface Bidirectional Reflectance Distribution Function (BRDF) effect into account for the MERIS reduce resolution (1km) retrieval, a modified Ross-Li mode is used. The AOT is determined in the algorithm using lookup tables including polarization created using Radiative Transfer Model SCIATRAN3.4, by minimizing the difference between atmospheric corrected surface reflectance with given AOT and the surface reflectance calculated from the spectral library. The global comparison with operational MODIS C6 product, Multi-angle Imaging SpectroRadiometer (MISR) product, Advanced Along-Track Scanning Radiometer (AATSR) aerosol product and the validation using AErosol RObotic NETwork (AERONET) show promising results. The current XBAER algorithm is only valid for aerosol remote sensing over land and a similar method will be extended to ocean later.

  7. Weak Hard X-Ray Emission from Two Broad Absorption Line Quasars Observed with NuStar: Compton-Thick Absorption or Intrinsic X-Ray Weakness?

    NASA Technical Reports Server (NTRS)

    Luo, B.; Brandt, W. N.; Alexander, D. M.; Harrison, F. A.; Stern, D.; Bauer, F. E.; Boggs, S. E.; Christensen, F. E.; Comastri, A.; Craig, W. W..; Fabian, A. C.; Farrah, D.; Fiore, F.; Fuerst, F.; Grefenstette, B. W.; Hailey, C. J.; Hickox, R.; Madsen, K. K.; Matt, G.; Ogle, P.; Risaliti, G.; Saez, C.; Teng, S. H.; Walton, D. J.; Zhang, W. W.

    2013-01-01

    We present Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray observations of two X-ray weak broad absorption line (BAL) quasars, PG 1004+130 (radio loud) and PG 1700+518 (radio quiet). Many BAL quasars appear X-ray weak, probably due to absorption by the shielding gas between the nucleus and the accretion-disk wind. The two targets are among the optically brightest BAL quasars, yet they are known to be significantly X-ray weak at rest-frame 2-10 keV (16-120 times fainter than typical quasars). We would expect to obtain approx. or equal to 400-600 hard X-ray (is greater than or equal to 10 keV) photons with NuSTAR, provided that these photons are not significantly absorbed N(sub H) is less than or equal to 10(exp24) cm(exp-2). However, both BAL quasars are only detected in the softer NuSTAR bands (e.g., 4-20 keV) but not in its harder bands (e.g., 20-30 keV), suggesting that either the shielding gas is highly Compton-thick or the two targets are intrinsically X-ray weak. We constrain the column densities for both to be N(sub H) 7 × 10(exp 24) cm(exp-2) if the weak hard X-ray emission is caused by obscuration from the shielding gas. We discuss a few possibilities for how PG 1004+130 could have Compton-thick shielding gas without strong Fe Ka line emission; dilution from jet-linked X-ray emission is one likely explanation. We also discuss the intrinsic X-ray weakness scenario based on a coronal-quenching model relevant to the shielding gas and disk wind of BAL quasars. Motivated by our NuSTAR results, we perform a Chandra stacking analysis with the Large Bright Quasar Survey BAL quasar sample and place statistical constraints upon the fraction of intrinsically X-ray weak BAL quasars; this fraction is likely 17%-40%.

  8. WEAK HARD X-RAY EMISSION FROM TWO BROAD ABSORPTION LINE QUASARS OBSERVED WITH NuSTAR: COMPTON-THICK ABSORPTION OR INTRINSIC X-RAY WEAKNESS?

    SciTech Connect

    Luo, B.; Brandt, W. N.; Alexander, D. M.; Hickox, R.; Harrison, F. A.; Fuerst, F.; Grefenstette, B. W.; Madsen, K. K.; Stern, D.; Bauer, F. E.; Boggs, S. E.; Craig, W. W.; Christensen, F. E.; Comastri, A.; Fabian, A. C.; Farrah, D.; Fiore, F.; Hailey, C. J.; Matt, G.; Ogle, P.; and others

    2013-08-01

    We present Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray observations of two X-ray weak broad absorption line (BAL) quasars, PG 1004+130 (radio loud) and PG 1700+518 (radio quiet). Many BAL quasars appear X-ray weak, probably due to absorption by the shielding gas between the nucleus and the accretion-disk wind. The two targets are among the optically brightest BAL quasars, yet they are known to be significantly X-ray weak at rest-frame 2-10 keV (16-120 times fainter than typical quasars). We would expect to obtain Almost-Equal-To 400-600 hard X-ray ({approx}> 10 keV) photons with NuSTAR, provided that these photons are not significantly absorbed (N{sub H} {approx}< 10{sup 24} cm{sup -2}). However, both BAL quasars are only detected in the softer NuSTAR bands (e.g., 4-20 keV) but not in its harder bands (e.g., 20-30 keV), suggesting that either the shielding gas is highly Compton-thick or the two targets are intrinsically X-ray weak. We constrain the column densities for both to be N{sub H} Almost-Equal-To 7 Multiplication-Sign 10{sup 24} cm{sup -2} if the weak hard X-ray emission is caused by obscuration from the shielding gas. We discuss a few possibilities for how PG 1004+130 could have Compton-thick shielding gas without strong Fe K{alpha} line emission; dilution from jet-linked X-ray emission is one likely explanation. We also discuss the intrinsic X-ray weakness scenario based on a coronal-quenching model relevant to the shielding gas and disk wind of BAL quasars. Motivated by our NuSTAR results, we perform a Chandra stacking analysis with the Large Bright Quasar Survey BAL quasar sample and place statistical constraints upon the fraction of intrinsically X-ray weak BAL quasars; this fraction is likely 17%-40%.

  9. On the satellite retrieval of Saharan dust optical thickness over land: Two different approaches

    SciTech Connect

    Tanre, D. ); Legrand, M. )

    1991-03-20

    Two approaches are presented to retrieve the desert aerosol optical thickness over land from satellite. One approach uses the infrared imagery, and the other uses contrast reduction in visible imagery. The retrieved aerosol optical thicknesses from Meteosat data are shown in good agreement with simultaneous ground-based measurements. Advantages as well as deficiencies of both methods are compared.

  10. Photorefractive acousto-optic imaging in thick scattering media at 790 nm with a Sn(2)P(2)S(6):Te crystal.

    PubMed

    Farahi, Salma; Montemezzani, Germano; Grabar, Alexander A; Huignard, Jean-Pierre; Ramaz, François

    2010-06-01

    Acousto-optic imaging is based on ultrasound modulation of multiply scattered light in thick media. We experimentally demonstrate the possibility to perform a self-adaptive wavefront holographic detection at 790nm, within the optical therapeutic window where absorption of biological tissues is minimized. A high-gain Te-doped Sn(2)P(2)S(6) crystal is used for this purpose. Optical absorbing objects embedded within a thick scattering phantom are imaged by use of pulsed ultrasound to get a dynamic millimetric axial resolution. Our technique represents an interesting approach for breast cancer detection. PMID:20517420

  11. Optical measurements of absorption changes in two-layered diffusive media

    NASA Astrophysics Data System (ADS)

    Fabbri, Francesco; Sassaroli, Angelo; Henry, Michael E.; Fantini, Sergio

    2004-04-01

    We have used Monte Carlo simulations for a two-layered diffusive medium to investigate the effect of a superficial layer on the measurement of absorption variations from optical diffuse reflectance data processed by using: (a) a multidistance, frequency-domain method based on diffusion theory for a semi-infinite homogeneous medium; (b) a differential-pathlength-factor method based on a modified Lambert-Beer law for a homogeneous medium and (c) a two-distance, partial-pathlength method based on a modified Lambert-Beer law for a two-layered medium. Methods (a) and (b) lead to a single value for the absorption variation, whereas method (c) yields absorption variations for each layer. In the simulations, the optical coefficients of the medium were representative of those of biological tissue in the near-infrared. The thickness of the first layer was in the range 0.3-1.4 cm, and the source-detector distances were in the range 1-5 cm, which is typical of near-infrared diffuse reflectance measurements in tissue. The simulations have shown that (1) method (a) is mostly sensitive to absorption changes in the underlying layer, provided that the thickness of the superficial layer is ~0.6 cm or less; (2) method (b) is significantly affected by absorption changes in the superficial layer and (3) method (c) yields the absorption changes for both layers with a relatively good accuracy of ~4% for the superficial layer and ~10% for the underlying layer (provided that the absorption changes are less than 20-30% of the baseline value). We have applied all three methods of data analysis to near-infrared data collected on the forehead of a human subject during electroconvulsive therapy. Our results suggest that the multidistance method (a) and the two-distance partial-pathlength method (c) may better decouple the contributions to the optical signals that originate in deeper tissue (brain) from those that originate in more superficial tissue layers.

  12. LASER APPLICATIONS AND OTHER TOPICS: Theory and optimization of the parameters of a polarization method for the measurement of weak absorption in optical materials

    NASA Astrophysics Data System (ADS)

    Glebov, L. B.; Dokuchaev, V. G.; Petrovskiĭ, G. T.

    1987-06-01

    A theoretical analysis is made of a polarization calorimetric method for the determination of weak absorption in optical materials. Several variants of the method are considered and the optimal conditions for its application are identified. The sensitivity of the method is ~1 dB/km for a sample 1 cm thick. It is shown that the method can be used to determine absorption in optically anisotropic materials.

  13. Optical absorption of nanoporous silicon: quasiparticle band gaps and absorption spectra

    NASA Astrophysics Data System (ADS)

    Shi, Guangsha; Kioupakis, Emmanouil

    2013-03-01

    Silicon is an earth-abundant material of great importance in semiconductors electronics, but its photovoltaic applications are limited by the low absorption coefficient in the visible due to its indirect band gap. One strategy to improve the absorbance is to perforate silicon with nanoscale pores, which introduce carrier scattering that enables optical transitions across the indirect gap. We used density functional and many-body perturbation theory in the GW approximation to investigate the electronic and optical properties of porous silicon for various pore sizes, spacings, and orientations. Our calculations include up to 400 atoms in the unit cell. We will discuss the connection of the band-gap value and absorption coefficient to the underlying nanopore geometry. The absorption coefficient in the visible range is found to be optimal for appropriately chosen nanopore size, spacing, and orientation. Our work allows us to predict porous-silicon structures that may have optimal performance in photovoltaic applications. This research was supported as part of CSTEC, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science. Computational resources were provided by the DOE NERSC facility.

  14. [Retrieval of monocyclic aromatic hydrocarbons with differential optical absorption spectroscopy].

    PubMed

    Xie, Pin-Hua; Fu, Qiang; Liu, Jian-Guo; Liu, Wen-Qing; Qin, Min; Li, Ang; Liu, Shi-Sheng; Wei, Qing-Nong

    2006-09-01

    Differential optical absorption spectroscopy (DOAS) technique has been used to measure trace gases in the atmosphere by their strongly structured absorption of radiation in the UV and visible spectral range, e. g. SO2, NO2, O3 etc. However, unlike the absorption spectra of SO2 and NO2, the analysis of aromatic compounds is difficult and strongly suffers from the cross interference of other absorbers (Herzberg bands of oxygen, ozone and sulfur dioxide), especially with relatively low concentrations of aromatic compounds in the atmosphere. In the present paper, the DOAS evaluation of aromatic compounds was performed by nonlinear least square fit with two interpolated oxygen optical density spectra at different path lengths and reference spectra of ozone at different temperature and SO2 cross section to correct the interference from absorbers of O2, O3 and SO2. The measurement of toluene, benzene, (m, p, o) xylene and phenol with a DOAS system showed that DOAS method is suitable for monocyclic aromatic compounds monitoring in the atmosphere. PMID:17112022

  15. Optical Absorption Cross Section of Individual Multi-Walled Carbon Nanotubes in the Visible Region.

    PubMed

    Shahzad, Muhammad Imran; Shahzad, Nadia; Tagliaferro, Alberto

    2016-01-01

    The aim of the present work is to determine the optical absorption cross section for visible radiation of various types of multiwall carbon nanotubes (MWCNTs) having different dimensions through macroscopic optical measurements. This is achieved by dispersing MWCNTs in polydimethylsiloxane (PDMS) and preparing composite films. Different percentages (0.0% to 1.5%) of each MWCNTs type were mixed into the PDMS matrix using high speed mechanical stirring (~1000 rpm) and ultrasonication (~37 kHz) to reach optimal dispersion. By using doctor blading technique, 100 µm thick uniform films were produced on glass. They were then thermally cured and detached from the glass to get flexible and self-standing films. Field-Emission Scanning Electron Microscope (FESEM) analysis of cryo-fractured composite samples was used to check the dispersion of MWCNTs in PDMS, while Raman spectroscopy and FTIR were employed to rule out possible structural changes of the polymer in the composite that would have altered its optical properties. Total and specular reflection and transmission spectra were measured for all films. The absorption coefficient, which represents the fractional absorption per unit length and is proportional to the concentration of absorbing sites (i.e., MWCNTs at photon energies upon which PDMS is non-absorbing), was extracted. For each MWCNTs type, the absorption cross section of an individual MWCNT was obtained from the slope of absorption coefficient versus MWCNTs number density curve. It was found to be related with MWCNT volume. This method can be applied to all other nanoparticles as far as they can be dispersed in a host transparent matrix. PMID:27398474

  16. Degree of interdependence among atmospheric optical thicknesses in spectral bands between 0.36-2.4 micron

    NASA Technical Reports Server (NTRS)

    Fraser, R. S.

    1975-01-01

    The degree of dependence among the atmospheric optical thicknesses that are measured in nonselective absorption bands is studied. The observations were made previously in many spectral bands within the range 0.36-2.4 micron from near sea level in two continents where urban and industrial pollutions were weak. The sample covariance matrices and corresponding eigenvalues and eigenvectors are computed. The two highest eigenvalues account for 90% of the total variance in 10 spectral bands within the range 0.4-1.6 micron. The linear regression of the optical thickness on the total precipitable water vapor is computed to determine the attenuation coefficient that is associated with water vapor. This coefficient shows a rapid power-law decrease with wavelength in the visible spectrum and indicates that numerous water particles of radius 0.03-0.06 micron cause the attenuation.

  17. Optical Absorption Spectra of Hydrous Wadsleyite to 32 GPa

    NASA Astrophysics Data System (ADS)

    Thomas, S.; Goncharov, A. F.; Jacobsen, S. D.; Bina, C. R.; Frost, D. J.

    2009-05-01

    Optical absorption spectra of high-pressure minerals can be used as indirect tools to calculate radiative conductivity of the Earth's interior [e.g., 1]. Recent high-pressure studies show that e.g. ringwoodite, γ-(Mg,Fe)2SiO4, does not become opaque in the near infrared and visible region, as previously assumed, but remains transparent to 21.5 GPa [2]. Therefore, it has been concluded that radiative heat transfer does not necessarily become blocked at high pressures of the mantle and ferromagnesian minerals actually could contribute to the heat flow in the Earth's interior [2]. In this study we use gem-quality single-crystals of hydrous Fe-bearing wadsleyite, β-(Mg,Fe)2SiO4, that were synthesized at 18 GPa and 1400 °C in a multianvil apparatus. Crystals were analyzed by Mössbauer and Raman spectroscopy, electron microprobe analysis and single-crystal X-ray diffraction. For absorption measurements a double-polished 50 μm sized single-crystal of wadsleyite was loaded in a diamond-anvil cell with neon as pressure medium. Optical absorption spectra were recorded at ambient conditions as well as up to 32 GPa from 400 to 50000 cm-1. At ambient pressure the absorption spectrum reveals two broad bands at - 10000 cm-1 and -15000 cm-1, and an absorption edge in the visible-ultraviolet range. With increasing pressure the absorption spectrum changes, both bands continuously shift to higher frequencies as has been observed for ringwoodite [2], but is contrary to earlier presumptions for wadsleyite [3]. Here, we will discuss band assignment along with the influence of iron, compare our results to previous absorption studies of mantle materials [2], and analyze possible implications for radiative conductivity of the transition zone. References: [1] Goncharov et al. (2008), McGraw Yearbook Sci. Tech., 242-245. [2] Keppler & Smyth (2005), Am. Mineral., 90 1209-1212. [3] Ross (1997), Phys. Chem. Earth, 22 113-118.

  18. Optical Hydrogen Absorption Consistent with a Bow Shock Leading the Hot Jupiter HD 189733b

    NASA Astrophysics Data System (ADS)

    Cauley, Paul Wilson; Redfield, Seth; Jensen, Adam

    2015-08-01

    Bow shocks are ubiquitous astrophysical phenomena resulting from the supersonic passage of an object through a gas. Recently, pre-transit absorption in UV metal transitions of the hot Jupiter exoplanets HD 189733b and WASP12-b have been interpreted as being caused by material compressed in a planetary bow shock. Here we present a robust detection of a time-resolved pre-transit, as well as in-transit, absorption signature around the hot Jupiter exoplanet HD 189733b using high spectral resolution observations of several hydrogen Balmer lines. The line shape of the pre-transit feature and the shape of the time series absorption provide the strongest constraints on the morphology and physical characteristics of extended structures around an exoplanet. The in-transit measurements confirm the exospheric Hα detection of Jensen et al. (2012) although the absorption depth measured here is ~50% lower. The pre-transit absorption feature occurs 125 minutes before the predicted optical transit, a projected linear distance to the stellar disk of 7.2 Rp. The absorption strength observed in the Balmer lines indicates an optically thick, but physically small, geometry. We model this signal as the early ingress of a planetary bow shock. If the bow shock is mediated by a planetary magnetosphere, the large standoff distance derived from the model suggests a large planetary magnetic field strength. Better knowledge of exoplanet magnetic field strengths is crucial to understanding the role these fields play in star-planet interactions and protecting planets in the habitable zone from dangerous stellar flares.

  19. Absorption enhancement through Fabry-Pérot resonant modes in a 430 nm thick InGaAs/GaAsP multiple quantum wells solar cell

    SciTech Connect

    Behaghel, B.; Tamaki, R.; Watanabe, K.; Sodabanlu, H.; Vandamme, N.; Dupuis, C.; Bardou, N.; Cattoni, A.; Okada, Y.; Sugiyama, M.; Collin, S.; Guillemoles, J.-F.

    2015-02-23

    We study light management in a 430 nm-thick GaAs p-i-n single junction solar cell with 10 pairs of InGaAs/GaAsP multiple quantum wells (MQWs). The epitaxial layer transfer on a gold mirror improves light absorption and increases the external quantum efficiency below GaAs bandgap by a factor of four through the excitation of Fabry-Perot resonances. We show a good agreement with optical simulation and achieve around 10% conversion efficiency. We demonstrate numerically that this promising result can be further improved by anti-reflection layers. This study paves the way to very thin MQWs solar cells.

  20. Management of light absorption in extraordinary optical transmission based ultra-thin-film tandem solar cells

    NASA Astrophysics Data System (ADS)

    Mashooq, Kishwar; Talukder, Muhammad Anisuzzaman

    2016-05-01

    Although ultra-thin-film solar cells can be attractive in reducing the cost, they suffer from low absorption as the thickness of the active layer is usually much smaller than the wavelength of incident light. Different nano-photonic techniques, including plasmonic structures, are being explored to increase the light absorption in ultra-thin-film solar cells. More than one layer of active materials with different energy bandgaps can be used in tandem to increase the light absorption as well. However, due to different amount of light absorption in different active layers, photo-generated currents in different active layers will not be the same. The current mismatch between the tandem layers makes them ineffective in increasing the efficiency. In this work, we investigate the light absorption properties of tandem solar cells with two ultra-thin active layers working as two subcells and a metal layer with periodically perforated holes in-between the two subcells. While the metal layer helps to overcome the current mismatch, the periodic holes increase the absorption of incident light by helping extraordinary optical transmission of the incident light from the top to the bottom subcell, and by coupling the incident light to plasmonic and photonic modes within ultra-thin active layers. We extensively study the effects of the geometry of holes in the intermediate metal layer on the light absorption properties of tandem solar cells with ultra-thin active layers. We also study how different metals in the intermediate layer affect the light absorption; how the geometry of holes in the intermediate layer affects the absorption when the active layer materials are changed; and how the intermediate metal layer affects the collection of photo-generated electron-hole pairs at the terminals. We find that in a solar cell with 6,6-phenyl C61-butyric acid methyl ester top subcell and copper indium gallium selenide bottom subcell, if the periodic holes in the metal layer are square or

  1. Absorptance Measurements of Optical Coatings - A Round Robin

    SciTech Connect

    Chow, R; Taylor, J R; Wu, Z L; Boccara, C A; Broulik, U; Commandre, M; DiJon, J; Fleig, C; Giesen, A; Fan, Z X; Kuo, P K; Lalezari, R; Moncur, K; Obramski, H-J; Reicher, D; Ristau, D; Roche, P; Steiger, B; Thomsen, M; von Gunten, M

    2000-10-26

    An international round robin study was conducted on the absorption measurement of laser-quality coatings. Sets of optically coated samples were made by a ''reactive DC magnetron'' sputtering and an ion beam sputtering deposition process. The sample set included a high reflector at 514 nm and a high reflector for the near infrared (1030 to 1318 nm), single layers of silicon dioxide, tantalum pentoxide, and hafnium dioxide. For calibration purposes, a sample metalized with hafnium and an uncoated, superpolished fused silica substrate were also included. The set was sent to laboratory groups for absorptance measurement of these coatings. Whenever possible, each group was to measure a common, central area and another area specifically assigned to the respective group. Specific test protocols were also suggested in regards to the laser exposure time, power density, and surface preparation.

  2. Optical Path Switching Based Differential Absorption Radiometry for Substance Detection

    NASA Technical Reports Server (NTRS)

    Sachse, Glen W. (Inventor)

    2000-01-01

    A system and method are provided for detecting one or more substances. An optical path switch divides sample path radiation into a time series of alternating first polarized components and second polarized components. The first polarized components are transmitted along a first optical path and the second polarized components along a second optical path. A first gasless optical filter train filters the first polarized components to isolate at least a first wavelength band thereby generating first filtered radiation. A second gasless optical filter train filters the second polarized components to isolate at least a second wavelength band thereby generating second filtered radiation. The first wavelength band and second wavelength band are unique. Further, spectral absorption of a substance of interest is different at the first wavelength band as compared to the second wavelength band. A beam combiner combines the first and second filtered radiation to form a combined beam of radiation. A detector is disposed to monitor magnitude of at least a portion of the combined beam alternately at the first wavelength band and the second wavelength band as an indication of the concentration of the substance in the sample path.

  3. Macular thickness as a predictor of loss of visual sensitivity in ethambutol-induced optic neuropathy

    PubMed Central

    Peng, Chun-xia; Zhang, Ai-di; Chen, Bing; Yang, Bing-jian; Wang, Qiu-hong; Yang, Mo; Wei, Shi-hui

    2016-01-01

    Ethambutol is a common cause of drug-related optic neuropathy. Prediction of the onset of ethambutol-induced optic neuropathy and consequent drug withdrawal may be an effective method to stop visual loss. Previous studies have shown that structural injury to the optic nerve occurred earlier than the damage to visual function. Therefore, we decided to detect structural biomarkers marking visual field loss in early stage ethambutol-induced optic neuropathy. The thickness of peripapillary retinal nerve fiber layer, macular thickness and visual sensitivity loss would be observed in 11 ethambutol-induced optic neuropathy patients (22 eyes) using optical coherence tomography. Twenty-four healthy age- and sex-matched participants (48 eyes) were used as controls. Results demonstrated that the temporal peripapillary retinal nerve fiber layer thickness and average macular thickness were thinner in patients with ethambutol-induced optic neuropathy compared with healthy controls. The average macular thickness was strongly positively correlated with central visual sensitivity loss (r2 =0.878, P=0.000). These findings suggest that optical coherence tomography can be used to efficiently screen patients. Macular thickness loss could be a potential factor for predicting the onset of ethambutol-induced optic neuropathy. PMID:27127488

  4. Macular thickness as a predictor of loss of visual sensitivity in ethambutol-induced optic neuropathy.

    PubMed

    Peng, Chun-Xia; Zhang, Ai-di; Chen, Bing; Yang, Bing-Jian; Wang, Qiu-Hong; Yang, Mo; Wei, Shi-Hui

    2016-03-01

    Ethambutol is a common cause of drug-related optic neuropathy. Prediction of the onset of ethambutol-induced optic neuropathy and consequent drug withdrawal may be an effective method to stop visual loss. Previous studies have shown that structural injury to the optic nerve occurred earlier than the damage to visual function. Therefore, we decided to detect structural biomarkers marking visual field loss in early stage ethambutol-induced optic neuropathy. The thickness of peripapillary retinal nerve fiber layer, macular thickness and visual sensitivity loss would be observed in 11 ethambutol-induced optic neuropathy patients (22 eyes) using optical coherence tomography. Twenty-four healthy age- and sex-matched participants (48 eyes) were used as controls. Results demonstrated that the temporal peripapillary retinal nerve fiber layer thickness and average macular thickness were thinner in patients with ethambutol-induced optic neuropathy compared with healthy controls. The average macular thickness was strongly positively correlated with central visual sensitivity loss (r (2) =0.878, P=0.000). These findings suggest that optical coherence tomography can be used to efficiently screen patients. Macular thickness loss could be a potential factor for predicting the onset of ethambutol-induced optic neuropathy. PMID:27127488

  5. Photoacoustic determination of optical absorption to extinction ratio in aerosols.

    PubMed

    Roessler, D M; Faxvog, F R

    1980-02-15

    The photoacoustic technique has been used in conjunction with an optical transmission measurement to determine the fraction of light absorbed in cigarette and acetylene smoke aerosols. At 0.5145-microm wavelength,the absorption-to-extinction fraction is 0.01 +/- 0.003 for cigarette smoke and is in excellent agreement with predictions from Mie theory for smoke particles having a refractive index of 1.45-0.00133i and a median diameter in the 0.15-0.65-microm range. For acetylene smoke the absorbed fraction was 0.85 +/- 0.05. PMID:20216896

  6. Optical absorption and scattering spectra of pathological stomach tissues

    NASA Astrophysics Data System (ADS)

    Giraev, K. M.; Ashurbekov, N. A.; Lakhina, M. A.

    2011-03-01

    Diffuse reflection spectra of biotissues in vivo and transmission and reflection coefficients for biotissues in vitro are measured over 300-800 nm. These data are used to determine the spectral absorption and scattering indices and the scattering anisotropy factor for stomach mucous membranes under normal and various pathological conditions (chronic atrophic and ulcerous defects, malignant neoplasms). The most importan tphysiological (hemodynamic and oxygenation levels) and structural-morphological (scatterer size and density) parameters are also determined. The results of a morphofunctional study correlate well with the optical properties and are consistent with data from a histomorphological analysis of the corresponding tissues.

  7. [The Effects of Skin Thickness on Optical Transmission Characteristics in Fruits Tissues].

    PubMed

    Shi, Shu-ning; Tan, Zuo-jun; Xie, Jing; Lu, Jun

    2015-07-01

    Fruit quality inspection techniques play a very important role in the production and consumption of fruits. In the field of quality non-destructive inspection and grading for fruits, the light-based techniques using optical properties of fruit products were widely used as one of the most practical and the most successful techniques. Quantitative understanding of light interaction with fruits is critical to designing better optical systems for inspection of food quality. In this paper, a fruit model consisted of two layer tissues was developed using Monte Carlo simulations to explore the light transport process and properties in the pome fruits, such as apples and mandarins, which were used as the thin-skinned and thick-skinned fruits respectively. The simulation results obtained are based on the assumption that the light source is a Gaussian beam at the wavelength 808 nm. This paper reports that the effects of skin thickness on light transmission characteristics in fruit tissues, including diffuse reflectance, transmittance, absorptivity, penetration depth etc. The inspection efficiency of flesh tissues was also demonstrated. The results indicated that the transmittance and the penetration depth decreases with the fruit skin increasing. As for the absorbed energy density, the fruit skin tissues have the wider distribution at the radial distance than the fruit flesh tissues. The absorbed energy density always tended to decrease with the inside depth of the fruit tissues increasing, especially decreased more apparently at the radial direction. The diffuse reflectance at the radial distance from 0.2 to 1.2 cm decreased with the decreasing of fruit skin, however it showed the inverse relationship in the radial distance range from 1.2 to 4.0 cm, the diffuse reflectance decreases with the increasing fruit skin. This paper proposed that the interaction between light and fruits skin in transmission or reflective approach, should be considered for developing optical

  8. All-optical reservoir computer based on saturation of absorption.

    PubMed

    Dejonckheere, Antoine; Duport, François; Smerieri, Anteo; Fang, Li; Oudar, Jean-Louis; Haelterman, Marc; Massar, Serge

    2014-05-01

    Reservoir computing is a new bio-inspired computation paradigm. It exploits a dynamical system driven by a time-dependent input to carry out computation. For efficient information processing, only a few parameters of the reservoir needs to be tuned, which makes it a promising framework for hardware implementation. Recently, electronic, opto-electronic and all-optical experimental reservoir computers were reported. In those implementations, the nonlinear response of the reservoir is provided by active devices such as optoelectronic modulators or optical amplifiers. By contrast, we propose here the first reservoir computer based on a fully passive nonlinearity, namely the saturable absorption of a semiconductor mirror. Our experimental setup constitutes an important step towards the development of ultrafast low-consumption analog computers. PMID:24921786

  9. Measurement of absolute optical thickness of mask glass by wavelength-tuning Fourier analysis.

    PubMed

    Kim, Yangjin; Hbino, Kenichi; Sugita, Naohiko; Mitsuishi, Mamoru

    2015-07-01

    Optical thickness is a fundamental characteristic of an optical component. A measurement method combining discrete Fourier-transform (DFT) analysis and a phase-shifting technique gives an appropriate value for the absolute optical thickness of a transparent plate. However, there is a systematic error caused by the nonlinearity of the phase-shifting technique. In this research the absolute optical-thickness distribution of mask blank glass was measured using DFT and wavelength-tuning Fizeau interferometry without using sensitive phase-shifting techniques. The error occurring during the DFT analysis was compensated for by using the unwrapping correlation. The experimental results indicated that the absolute optical thickness of mask glass was measured with an accuracy of 5 nm. PMID:26125394

  10. Plasmon enhanced broadband optical absorption in ultrathin silicon nanobowl array for photoactive devices applications

    NASA Astrophysics Data System (ADS)

    Sun, Rui-Nan; Peng, Kui-Qing; Hu, Bo; Hu, Ya; Zhang, Fu-Qiang; Lee, Shuit-Tong

    2015-07-01

    Both photonic and plasmonic nanostructures are key optical components of photoactive devices for light harvesting, enabling solar cells with significant thickness reduction, and light detectors capable of detecting photons with sub-band gap energies. In this work, we study the plasmon enhanced broadband light absorption and electrical properties of silicon nanobowl (SiNB) arrays. The SiNB-metal photonic-plasmonic nanostructure-based devices exhibited superior light-harvesting ability across a wide range of wavelengths up to the infrared regime well below the band edge of Si due to effective optical coupling between the SiNB array and incident sunlight, as well as electric field intensity enhancement around metal nanoparticles due to localized surface plasmon resonance. The photonic-plasmonic nanostructure is expected to result in infrared-light detectors and high-efficiency solar cells by extending light-harvesting to infrared frequencies.

  11. Plasmon enhanced broadband optical absorption in ultrathin silicon nanobowl array for photoactive devices applications

    SciTech Connect

    Sun, Rui-Nan; Peng, Kui-Qing Hu, Bo; Hu, Ya; Zhang, Fu-Qiang; Lee, Shuit-Tong

    2015-07-06

    Both photonic and plasmonic nanostructures are key optical components of photoactive devices for light harvesting, enabling solar cells with significant thickness reduction, and light detectors capable of detecting photons with sub-band gap energies. In this work, we study the plasmon enhanced broadband light absorption and electrical properties of silicon nanobowl (SiNB) arrays. The SiNB-metal photonic-plasmonic nanostructure-based devices exhibited superior light-harvesting ability across a wide range of wavelengths up to the infrared regime well below the band edge of Si due to effective optical coupling between the SiNB array and incident sunlight, as well as electric field intensity enhancement around metal nanoparticles due to localized surface plasmon resonance. The photonic-plasmonic nanostructure is expected to result in infrared-light detectors and high-efficiency solar cells by extending light-harvesting to infrared frequencies.

  12. Numerical and theoretical analysis on the absorption properties of metasurface-based terahertz absorbers with different thicknesses.

    PubMed

    Wu, Kaimin; Huang, Yongjun; Wanghuang, Tenglong; Chen, Weijian; Wen, Guangjun

    2015-01-10

    In this paper, we numerically and theoretically discuss the novel absorption properties of a conventional metasurface-based terahertz (THz) electromagnetic (EM) absorber with different dielectric thicknesses. Two absorption modes are presented in the considered frequency band due to the increased dielectric thickness, and both modes can achieve near-unity absorptions when the dielectric layers reach additional nλ(d)/2 (n=1, 2) thicknesses, where λ(d) is the operating wavelength at the peak absorption in the dielectric slabs. The surface currents between the metasurface resonators and ground plane are not associated any longer, different from the conventional thin absorbers. Moreover, the EM wave energies are completely absorbed by the metasurface resonators and dielectric layer, and the main function of ground plane is to reflect the incident EM waves back to the resonators. The discussed novel absorption properties are analyzed and explained by classical EM theory and interference theory after numerical demonstrations. These findings can broaden the potential applications of the metasurface-based absorbers in the THz frequency range for different requirements. PMID:25967629

  13. Thickness identification of epitaxial Bi2Te3 via optical contrast

    NASA Astrophysics Data System (ADS)

    Vajner, Cooper; Yan, Haoming; Guo, Lingling; Mathews, Melissa; Kuhlman, Michael; Benefield, Shellby; Ulrich, Steven; Zolghadr, Ehsan; Kung, Patrick; Li, Lin; Araujo, Paulo T.; Wang, Hung-Ta

    2016-06-01

    Two-dimensional (2D) nanosheet thickness identification is effective for rapidly determining thickness-dependent properties of 2D materials. Bismuth telluride (Bi2Te3) is a 2D material known for its promising thermoelectric properties and potential dissipationless charge transport in the topological surface states. To date, thickness measurements of Bi2Te3 2D nanosheets are mainly carried out via atomic force microscope or Raman spectroscopy. Here, we investigate a practical, rapid, inexpensive, and non-invasive thickness measurement technique that utilizes the optical contrast of Bi2Te3 2D nanosheets on a mica substrate (i.e., as-grown) and a SiO2/Si substrate (i.e., transferred). The reflected optical intensity and the corresponding contrast are studied as a function of Bi2Te3 thickness, illumination wavelength, and substrate thickness. Disagreement between experimental and calculated optical contrast values is observed, which is ascribed to the thickness-dependent refractive indices of Bi2Te3, mica thickness error, and the deviation from normal light incidence. Despite thin film interference in mica, the monotonic relationship between nanosheet’s contrast and thickness makes mica a better substrate for identifying Bi2Te3 thickness. In addition, a brief recipe is provided for such a thickness identification method to be generally applied in any laboratory.

  14. Impact of inhomogeneous optical scattering coefficient distribution on recovery of optical absorption coefficient maps using tomographic photoacoustic data

    NASA Astrophysics Data System (ADS)

    Li, Xiaoqi; Jiang, Huabei

    2013-02-01

    We present a study through extensive simulation that considers the impact of inhomogeneous optical scattering coefficient distribution on recovery of optical absorption coefficient maps using tomographic photoacoustic data collected from media mimicking breast tissue. We found that while the impact of scattering heterogeneities/targets is modest on photoacoustic recovery of optical absorption coefficients, the impact of scattering contrast caused by adipose tissue, a layer of normal tissue along the boundary of the breast, is dramatic on reconstruction of optical absorption coefficients using photoacoustic data—up to 25.8% relative error in recovering the absorption coefficient is estimated in such cases. To overcome this problem, we propose a new method to enhance photoacoustic recovery of the optical absorption coefficient in heterogeneous media by considering inhomogeneous scattering coefficient distribution provided by diffuse optical tomography (DOT). Results from extensive simulations show that photoacoustic recovery of absorption coefficient maps can be improved considerably with a priori scattering information from DOT.

  15. Faraday rotation density measurements of optically thick alkali metal vapors

    NASA Astrophysics Data System (ADS)

    Vliegen, E.; Kadlecek, S.; Anderson, L. W.; Walker, T. G.; Erickson, C. J.; Happer, William

    2001-03-01

    We investigate the measurement of alkali number densities using the Faraday rotation of linearly polarized light. We find that the alkali number density may be reliably extracted even in regimes of very high buffer gas pressure, and very high alkali number density. We have directly verified our results in potassium using absorption spectroscopy on the second resonance (4 2S→5 2P).

  16. Metal incorporated M-DNA: structure, magnetism, optical absorption

    NASA Astrophysics Data System (ADS)

    Mizoguchi, Kenji

    2011-09-01

    DNA is an interesting material from the viewpoint of the materials science. This paper discusses the electronic states of the metal incorporated M-DNA complexes with several species of metal ions. M-DNA prepared by the ordinary methanol precipitation technique has been investigated with ESR, STM and optical absorption, and concluded that the metal ion hydrated with several water molecules locates in between the bases of a base pair and that the divalent metal ions are incorporated into DNA in place of two Na cations as the counter ion for PO-4in the DNA backbones. Only in Fe-DNA, it was confirmed that the Fe2+ in the FeCl2 aqueous solution reacts with DNA to form Fe-DNA complex with Fe3+, where the charge would transfer to DNA. Within 30 min, the hydrolysis of Fe2+ to form Fe3+O(OH) did not occur in the FeCl2 aqueous solution at room temperature. The optical absorption spectra of Fe-DNA is similar to that for FeCl3 with the ionic character, but definitely differs from that of Fe3+O(OH) with the covalent bonding nature, suggesting the ionic character of Fe3+ in Fe-DNA. Finally, the possible two kinds of electronic states for Zn-DNA with different bonding nature will be discussed in relation to the recent report on Zn-DNA.

  17. Control of optical bandgap energy and optical absorption coefficient by geometric parameters in sub-10 nm silicon-nanodisc array structure

    NASA Astrophysics Data System (ADS)

    Fairuz Budiman, Mohd; Hu, Weiguo; Igarashi, Makoto; Tsukamoto, Rikako; Isoda, Taiga; Itoh, Kohei M.; Yamashita, Ichiro; Murayama, Akihiro; Okada, Yoshitaka; Samukawa, Seiji

    2012-02-01

    A sub-10 nm, high-density, periodic silicon-nanodisc (Si-ND) array has been fabricated using a new top-down process, which involves a 2D array bio-template etching mask made of Listeria-Dps with a 4.5 nm diameter iron oxide core and damage-free neutral-beam etching (Si-ND diameter: 6.4 nm). An Si-ND array with an SiO2 matrix demonstrated more controllable optical bandgap energy due to the fine tunability of the Si-ND thickness and diameter. Unlike the case of shrinking Si-ND thickness, the case of shrinking Si-ND diameter simultaneously increased the optical absorption coefficient and the optical bandgap energy. The optical absorption coefficient became higher due to the decrease in the center-to-center distance of NDs to enhance wavefunction coupling. This means that our 6 nm diameter Si-ND structure can satisfy the strict requirements of optical bandgap energy control and high absorption coefficient for achieving realistic Si quantum dot solar cells.

  18. Coupled escape probability for an asymmetric spherical case: Modeling optically thick comets

    SciTech Connect

    Gersch, Alan M.; A'Hearn, Michael F.

    2014-05-20

    We have adapted Coupled Escape Probability, a new exact method of solving radiative transfer problems, for use in asymmetrical spherical situations. Our model is intended specifically for use in modeling optically thick cometary comae, although not limited to such use. This method enables the accurate modeling of comets' spectra even in the potentially optically thick regions nearest the nucleus, such as those seen in Deep Impact observations of 9P/Tempel 1 and EPOXI observations of 103P/Hartley 2.

  19. Improved optical resolution for elastomer-liquid lens at high diopter using varied thickness membrane

    NASA Astrophysics Data System (ADS)

    Huang, Hanyang; Wei, Kang; Wang, Qian; Zhao, Yi

    2016-03-01

    Adaptive elastomer-liquid lens can find a variety of optical applications due to the tunable optical powers without additional lens replacement or displacement. Most current elastomer-liquid lenses use elastomer membrane with a constant thickness. This approach, however, suffers from substantial optical aberration due to the edge clamping effect. In this study, a varied thickness elastomer membrane with customized aspherical profile is designed and developed to encapsulate a plano-convex liquid lens. Such varied thickness membrane is fabricated by double-side replica molding against a deformed elastomer-liquid lens membrane with a constant thickness. Such configuration could alleviate the edge clamping effect. Simulation and experimental results both show that the lens with a varied thickness membrane exhibits improved optical resolutions at both the center and the peripheral regions at the back focal length of 10 mm comparing to the lens with a constant thickness membrane. This study provides an effective solution to suppress the optical aberrations without sacrifice of the optical aperture.

  20. Optical performance and metallic absorption in nanoplasmonic systems.

    PubMed

    Arnold, Matthew D; Blaber, Martin G

    2009-03-01

    Optical metrics relating to metallic absorption in representative plasmonic systems are surveyed, with a view to developing heuristics for optimizing performance over a range of applications. We use the real part of the permittivity as the independent variable; consider strengths of particle resonances, resolving power of planar lenses, and guiding lengths of planar waveguides; and compare nearly-free-electron metals including Al, Cu, Ag, Au, Li, Na, and K. Whilst the imaginary part of metal permittivity has a strong damping effect, field distribution is equally important and thus factors including geometry, real permittivity and frequency must be considered when selecting a metal. Al performs well at low permittivities (e.g. sphere resonances, superlenses) whereas Au & Ag only perform well at very negative permittivities (shell and rod resonances, LRSPP). The alkali metals perform well overall but present engineering challenges. PMID:19259225

  1. Optical re-injection in cavity-enhanced absorption spectroscopy

    PubMed Central

    Leen, J. Brian; O’Keefe, Anthony

    2014-01-01

    Non-mode-matched cavity-enhanced absorption spectrometry (e.g., cavity ringdown spectroscopy and integrated cavity output spectroscopy) is commonly used for the ultrasensitive detection of trace gases. These techniques are attractive for their simplicity and robustness, but their performance may be limited by the reflection of light from the front mirror and the resulting low optical transmission. Although this low transmitted power can sometimes be overcome with higher power lasers and lower noise detectors (e.g., in the near-infrared), many regimes exist where the available light intensity or photodetector sensitivity limits instrument performance (e.g., in the mid-infrared). In this article, we describe a method of repeatedly re-injecting light reflected off the front mirror of the optical cavity to boost the cavity's circulating power and deliver more light to the photodetector and thus increase the signal-to-noise ratio of the absorption measurement. We model and experimentally demonstrate the method's performance using off-axis cavity ringdown spectroscopy (OA-CRDS) with a broadly tunable external cavity quantum cascade laser. The power coupled through the cavity to the detector is increased by a factor of 22.5. The cavity loss is measured with a precision of 2 × 10−10 cm−1/\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{upgreek} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} }{}$\\sqrt {{\\rm Hz;}}$\\end{document} Hz ; an increase of 12 times over the standard off-axis configuration without reinjection and comparable to the best reported sensitivities in the mid-infrared. Finally, the re-injected CRDS system is used to measure the spectrum of several volatile organic compounds, demonstrating the improved ability to resolve weakly absorbing spectroscopic features. PMID:25273701

  2. Optical re-injection in cavity-enhanced absorption spectroscopy.

    PubMed

    Leen, J Brian; O'Keefe, Anthony

    2014-09-01

    Non-mode-matched cavity-enhanced absorption spectrometry (e.g., cavity ringdown spectroscopy and integrated cavity output spectroscopy) is commonly used for the ultrasensitive detection of trace gases. These techniques are attractive for their simplicity and robustness, but their performance may be limited by the reflection of light from the front mirror and the resulting low optical transmission. Although this low transmitted power can sometimes be overcome with higher power lasers and lower noise detectors (e.g., in the near-infrared), many regimes exist where the available light intensity or photodetector sensitivity limits instrument performance (e.g., in the mid-infrared). In this article, we describe a method of repeatedly re-injecting light reflected off the front mirror of the optical cavity to boost the cavity's circulating power and deliver more light to the photodetector and thus increase the signal-to-noise ratio of the absorption measurement. We model and experimentally demonstrate the method's performance using off-axis cavity ringdown spectroscopy (OA-CRDS) with a broadly tunable external cavity quantum cascade laser. The power coupled through the cavity to the detector is increased by a factor of 22.5. The cavity loss is measured with a precision of 2 × 10(-10) cm(-1)/√Hz; an increase of 12 times over the standard off-axis configuration without reinjection and comparable to the best reported sensitivities in the mid-infrared. Finally, the re-injected CRDS system is used to measure the spectrum of several volatile organic compounds, demonstrating the improved ability to resolve weakly absorbing spectroscopic features. PMID:25273701

  3. Optical re-injection in cavity-enhanced absorption spectroscopy

    SciTech Connect

    Leen, J. Brian O’Keefe, Anthony

    2014-09-15

    Non-mode-matched cavity-enhanced absorption spectrometry (e.g., cavity ringdown spectroscopy and integrated cavity output spectroscopy) is commonly used for the ultrasensitive detection of trace gases. These techniques are attractive for their simplicity and robustness, but their performance may be limited by the reflection of light from the front mirror and the resulting low optical transmission. Although this low transmitted power can sometimes be overcome with higher power lasers and lower noise detectors (e.g., in the near-infrared), many regimes exist where the available light intensity or photodetector sensitivity limits instrument performance (e.g., in the mid-infrared). In this article, we describe a method of repeatedly re-injecting light reflected off the front mirror of the optical cavity to boost the cavity's circulating power and deliver more light to the photodetector and thus increase the signal-to-noise ratio of the absorption measurement. We model and experimentally demonstrate the method's performance using off-axis cavity ringdown spectroscopy (OA-CRDS) with a broadly tunable external cavity quantum cascade laser. The power coupled through the cavity to the detector is increased by a factor of 22.5. The cavity loss is measured with a precision of 2 × 10{sup −10} cm{sup −1}/√(Hz;) an increase of 12 times over the standard off-axis configuration without reinjection and comparable to the best reported sensitivities in the mid-infrared. Finally, the re-injected CRDS system is used to measure the spectrum of several volatile organic compounds, demonstrating the improved ability to resolve weakly absorbing spectroscopic features.

  4. Excitonic Effects and Optical Absorption Spectrum of Doped Graphene

    NASA Astrophysics Data System (ADS)

    Jornada, Felipe; Deslippe, Jack; Louie, Steven

    2012-02-01

    First-principles calculations based on the GW-Bethe-Salpeter Equation (GW-BSE) approach and subsequent experiments have shown large excitonic effects in the optical absorbance of graphene. Here we employ the GW-BSE formalism to probe the effects of charge carrier doping and of having an external electric field on the absorption spectrum of graphene. We show that the absorbance peak due to the resonant exciton exhibits systematic changes in both its position and profile when graphene is gate doped by carriers, in excellent agreement to very recent measurementsootnotetextTony F. Heinz, private communications.. We analyze the various contributions to these changes in the absorption spectrum, such as the effects of screening by carriers to the quasiparticle energies and electron-hole interactions. This work was supported by National Science Foundation Grant No. DMR10-1006184, the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, and the U.S. DOD - Office of Naval Research under RTC Grant No. N00014-09-1-1066. Computer time was provided by NERSC.

  5. Effects of diabetic keratopathy on corneal optical density, central corneal thickness, and corneal endothelial cell counts

    PubMed Central

    Gao, Feng; Lin, Tao; Pan, Yingzhe

    2016-01-01

    Diabetic keratopathy is an ocular complication that occurs with diabetes. In the present study, the effect of diabetic keratopathy on corneal optical density, central corneal thickness, and corneal endothelial cell count was investigated. One hundred and eighty diabetic patients (360 eyes) were enrolled in the study during the period from March, 2012 to March, 2013. The patients were divided into three age groups: <5, 5–10 and >10 years, with 60 patients per group (120 eyes). During the same period, 60 healthy cases (120 eyes) were selected and labeled as the normal control group. The Pentacam was used to measure the corneal optical density, and central corneal thickness. Specular microscopy was used to examine the corneal endothelial cell density. The coefficient of partial correlation was used to control age and correlate the analysis between the corneal optical density, corneal endothelial cell density, and central corneal thickness. The stage of the disease, the medial and intimal corneal optical density and central corneal thickness was analyzed in the diabetes group. The corneal optical density in the diabetes group increased compared with that of the normal control group. The medial and intimal corneal optical density and central corneal thickness were positively correlated with the course of the disease. However, the corneal endothelial cell density was not associated with the course of diabetes. There was a positive association between the medial and intimal corneal optical density and central corneal thickness of the diabetic patients. In conclusion, the results of the present study show that medial and intimal corneal optical density and central corneal thickness were sensitive indicators for early diabetic keratopathy.

  6. Prospective Study on Retinal Nerve Fibre Layer Thickness Changes in Isolated Unilateral Retrobulbar Optic Neuritis

    PubMed Central

    Yau, Gordon S. K.; Lee, Jacky W. Y.; Lau, Patrick P. K.; Tam, Victor T. Y.; Wong, Winnie W. Y.; Yuen, Can Y. F.

    2013-01-01

    Purpose. To investigate the retinal nerve fibre layer (RNFL) thickness after unilateral acute optic neuritis using optical coherence tomography (OCT). Patients and Methods. This prospective cohort study recruited consecutive patients with a first episode of isolated, unilateral acute optic neuritis. RNFL thickness and visual acuity (VA) of the attack and normal fellow eye were measured at presentation and 3 months in both the treatment and nontreatment groups. Results. 11 subjects received systemic steroids and 9 were treated conservatively. The baseline RNFL thickness was similar in the attack and fellow eye (P ≥ 0.4). At 3 months, the attack eye had a thinner temporal (P = 0.02) and average (P = 0.05) RNFL compared to the fellow eye. At 3 months, the attack eye had significant RNFL thinning in the 4 quadrants and average thickness (P ≤ 0.0002) compared to baseline. The RNFL thickness between the treatment and nontreatment groups was similar at baseline and 3 months (P ≥ 0.1). Treatment offered better VA at 3 months (0.1 ± 0.2 versus 0.3 ± 0.2 LogMAR, P = 0.04). Conclusion. Generalized RNFL thinning occurred at 3 months after a first episode of acute optic neuritis most significantly in the temporal quadrant and average thickness. Visual improvement with treatment was independent of RNFL thickness. PMID:24459442

  7. Thickness and microstructure effects in the optical and electrical properties of silver thin films

    SciTech Connect

    Ding, Guowen Clavero, César; Schweigert, Daniel; Le, Minh

    2015-11-15

    The optical and electrical response of metal thin films approaching thicknesses in the range of the electron mean free path is highly affected by electronic scattering with the interfaces and defects. Here, we present a theoretical and experimental study on how thickness and microstructure affect the properties of Ag thin films. We are able to successfully model the electrical resistivity and IR optical response using a thickness dependent electronic scattering time. Remarkably, the product of electronic scattering time and resistivity remains constant regardless of the thickness (τx ρ = C), with a value of 59 ± 2 μΩ cm ⋅ fs for Ag films in the investigated range from 3 to 74 nm. Our findings enable us to develop a theoretically framework that allows calculating the optical response of metal thin films in the IR by using their measured thickness and resistivity. An excellent agreement is found between experimental measurements and predicted values. This study also shows the theoretical lower limit for emissivity in Ag thin films according to their microstructure and thickness. Application of the model presented here will allow rapid characterization of the IR optical response of metal thin films, with important application in a broad spectrum of fundamental and industrial applications, including optical coatings, low-emissivity windows and semiconductor industry.

  8. Retrieval of Aerosol Profiles using Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS)

    NASA Astrophysics Data System (ADS)

    Yilmaz, Selami; Frieß, Udo; Apituley, Arnoud; Henzing, Bas; Baars, Holger; Heese, Birgit; Althausen, Dietrich; Adam, Mariana; Putaud, Jean-Philippe; Zieger, Paul; Platt, Ulrich

    2010-05-01

    Multi Axis Differential Absorption Spectroscopy (MAX-DOAS) is a well established measurement technique to derive atmospheric trace gas profiles. Using MAX-DOAS measurements of trace gases with a known vertical profile, like the oxygen-dimer O4, it is possible to retrieve information on atmospheric aerosols. Based on the optimal estimation method, we have developed an algorithm which fits simultaneously measured O4 optical densities and relative intensities at several wavelengths and elevation angles to values simulated by a radiative transfer model. Retrieval parameters are aerosol extinction profile and optical properties such as single scattering albedo, phase function and Angström exponent. In 2008 and 2009 several intercomparison campaigns with established aerosol measurement techniques took place in Cabauw/Netherlands, Melpitz/Germany, Ispra/Italy and Leipzig/Germany, where simultaneous DOAS, lidar, Sun photometer and Nephelometer measurements were performed. Here we present results of the intercomparisons for cloud free conditions. The correlation of the aerosol optical thickness retrieved by the DOAS technique and the Sun photometer shows coefficients of determination from 0.96 to 0.98 and slopes from 0.94 to 1.07. The vertical structure of the DOAS retrieved aerosol extinction profiles compare favourably with the structures seen by the backscatter lidar. However, the vertical spatial development of the boundary layer is reproduced with a lower resolution by the DOAS technique. Strategies for the near real-time retrieval of trace gas profiles, aerosol profiles and optical properties will be discussed as well.

  9. THE COMPTON-THICK SEYFERT 2 NUCLEUS OF NGC 3281: TORUS CONSTRAINTS FROM THE 9.7 {mu}m SILICATE ABSORPTION

    SciTech Connect

    Sales, Dinalva A.; Pastoriza, M. G.; Riffel, R.; Winge, C.

    2011-09-01

    We present mid-infrared (mid-IR) spectra of the Compton-thick Seyfert 2 galaxy NGC 3281, obtained with the Thermal-Region Camera Spectrograph at the Gemini-South telescope. The spectra present a very deep silicate absorption at 9.7 {mu}m, and [S IV] 10.5 {mu}m and [Ne II] 12.7 {mu}m ionic lines, but no evidence of polycyclic aromatic hydrocarbon emission. We find that the nuclear optical extinction is in the range 24 mag {<=} A{sub V} {<=} 83 mag. A temperature T = 300 K was found for the blackbody dust continuum component of the unresolved 65 pc nucleus and the region at 130 pc SE, while the region at 130 pc NW reveals a colder temperature (200 K). We describe the nuclear spectrum of NGC 3281 using a clumpy torus model that suggests that the nucleus of this galaxy hosts a dusty toroidal structure. According to this model, the ratio between the inner and outer radius of the torus in NGC 3281 is R{sub 0}/R{sub d} = 20, with 14 clouds in the equatorial radius with optical depth of {tau}{sub V} = 40 mag. We would be looking in the direction of the torus equatorial radius (i = 60{sup 0}), which has outer radius of R{sub 0} {approx} 11 pc. The column density is N{sub H} {approx} 1.2 x 10{sup 24} cm{sup -2} and the iron K{alpha} equivalent width ({approx}0.5-1.2 keV) is used to check the torus geometry. Our findings indicate that the X-ray absorbing column density, which classifies NGC 3281 as a Compton-thick source, may also be responsible for the absorption at 9.7 {mu}m providing strong evidence that the silicate dust responsible for this absorption can be located in the active galactic nucleus torus.

  10. Volume polarization holographic recording in thick photopolymer for optical memory.

    PubMed

    Lin, Shiuan Huei; Cho, Sheng-Lung; Chou, Shin-Fu; Lin, June Hua; Lin, Chih Min; Chi, Sien; Hsu, Ken Yuh

    2014-06-16

    Based on a vector wave theory of volume holograms, dependence of holographic reconstruction on the polarization states of the writing and reading beams is discussed. It is found that under paraxial approximation the circular polarization holograms provide a better distinction of the reading beams. Characteristics of recording polarization holograms in thick phenanthrenequinone-doped poly(methyl methacrylate) (PQ/PMMA) photopolymer are experimentally investigated. It is found that the circular polarization holographic recording possesses better dynamic range and material sensitivity, and a uniform spatial frequency response over a wide range. The performance is comparable to that of the intensity holographic recording in PQ/PMMA. Based on theoretical analyses and the material properties, a polarization multiplexing holographic memory using circularly polarization recording configuration for increasing storage capacity has been designed and experimentally demonstrated. PMID:24977588

  11. Masking technique for coating thickness control on large and strongly curved aspherical optics.

    PubMed

    Sassolas, B; Flaminio, R; Franc, J; Michel, C; Montorio, J-L; Morgado, N; Pinard, L

    2009-07-01

    We discuss a method to control the coating thickness deposited onto large and strongly curved optics by ion beam sputtering. The technique uses an original design of the mask used to screen part of the sputtered materials. A first multielement mask is calculated from the measured two-dimensional coating thickness distribution. Then, by means of an iterative process, the final mask is designed. By using such a technique, it has been possible to deposit layers of tantalum pentoxide having a high thickness gradient onto a curved substrate 500 mm in diameter. Residual errors in the coating thickness profile are below 0.7%. PMID:19571934

  12. Measurement of optical thickness variation of BK7 plate by wavelength tuning interferometry.

    PubMed

    Kim, Yangjin; Hibino, Kenichi; Sugita, Naohiko; Mitsuishi, Mamoru

    2015-08-24

    This paper presents the derivation of a 17-sample phase-shifting algorithm that can compensate the miscalibration and first-order nonlinearity of phase shift error, coupling error, and bias modulation of the intensity and satisfy the fringe contrast maximum condition. The phase error of measurements performed using the 17-sample algorithm is discussed and compared with those of measurements obtained using other algorithms. Finally, the optical thickness variation of a BK7 optically transparent plate obtained using a wavelength tuning Fizeau interferometer and the 17-sample algorithm are presented. The experimental results indicate that the optical thickness variation measurement accuracy for the BK7 plate was 3 nm. PMID:26368260

  13. Development of a non-contact center thickness optical metrology system

    NASA Astrophysics Data System (ADS)

    Thorpe, Michael J.; Brasseur, Jason K.; Roos, Peter A.

    2015-09-01

    The last place an optics manufacturer wants to physically touch a lens is at the center. However, this is precisely what is currently done to measure center thickness of lenses. Using contact methods, the question is not whether the optic is damaged, it is whether the resulting damage is acceptably low. At Bridger Photonics, we have proven the feasibility of a non-contact center thickness metrology system to address this need. The apparatus uses a technique similar to swept-frequency optical coherence tomography to measure both physical thickness and optical thickness. From these measurements, the group index of refraction can also be determined. Moreover, the phase index can be determined, given the Sellmeier coefficients. In this presentation, we will report our demonstrated measurement range of 75 mm optical thickness (larger possible), as low as 20 nm precision, and group index of refraction determined to better than 5 parts is 105. We believe the metrology system resulting from these proof-of-principle demonstrations will be a valuable tool for precision optics manufacturing.

  14. In situ measurements of the optical absorption of dioxythiophene-based conjugated polymers

    NASA Astrophysics Data System (ADS)

    Hwang, J.; Schwendeman, I.; Ihas, B. C.; Clark, R. J.; Cornick, M.; Nikolou, M.; Argun, A.; Reynolds, J. R.; Tanner, D. B.

    2011-05-01

    Conjugated polymers can be reversibly doped by electrochemical means. This doping introduces new subband-gap optical absorption bands in the polymer while decreasing the band-gap absorption. To study this behavior, we have prepared an electrochemical cell allowing in situ measurements of the optical properties of the polymer. The cell consists of a thin polymer film deposited on gold-coated Mylar behind which is another polymer that serves as a counterelectrode. An infrared transparent window protects the upper polymer from ambient air. By adding a gel electrolyte and making electrical connections to the polymer-on-gold films, one may study electrochromism in a wide spectral range. As the cell voltage (the potential difference between the two electrodes) changes, the doping level of the conjugated polymer films is changed reversibly. Our experiments address electrochromism in poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-dimethylpropylenedioxythiophene) (PProDOT-Me2). This closed electrochemical cell allows the study of the doping induced subband-gap features (polaronic and bipolaronic modes) in these easily oxidized and highly redox switchable polymers. We also study the changes in cell spectra as a function of polymer thickness and investigate strategies to obtain cleaner spectra, minimizing the contributions of water and gel electrolyte features.

  15. The optically thick O III spectrum. I - Diagnostic ratios involving the intercombination lines

    NASA Technical Reports Server (NTRS)

    Kastner, S. O.; Bhatia, A. K.

    1989-01-01

    An escape-probability calculation of the optically thick O III spectrum is carried out to obtain the optical depth dependence of the intercombination doublet at 1663 A and of resonance lines between the 2p2, 2s2p3, and 2p4 configurations. The effect of optical depth on diagnostic ratios involving the intercombination lines is quantitatively established. The general question raised is whether such effects may occur in actual sources.

  16. Dual-role plasma absorption probe to study the effects of sheath thickness on the measurement of electron density

    NASA Astrophysics Data System (ADS)

    Li, Bin; Li, Hong; Chen, Zhipeng; Xie, Jinlin; Liu, Wandong

    2010-08-01

    A sensitive plasma absorption probe (PAP) is reported for measuring electron density in processing plasmas. The sheath formed around the probe tip is important for the resonance of surface waves. For determining the absolute electron density from the absorption frequency of the sensitive PAP, a proper value of sheath thickness relative to the Debye length is required to be assigned in the data processing. In this paper, a dual-role PAP has been proposed to study the effects of sheath thickness on the measurement of electron density. It is used as a Langmuir probe and a sensitive PAP simultaneously. Based on these two functions, the sheath thickness is calibrated before the measurement of electron density. The calibrated value is assigned in the data processing to replace the fitting coefficient used in the previous work. Therefore, the measurement error caused by an inaccurately assigned sheath thickness can be minimized effectively. Because of the bi-functional characteristic, the dual-role PAP is an independent diagnostic tool.

  17. Constructing Uniform Core-Shell PPy@PANI Composites with Tunable Shell Thickness toward Enhancement in Microwave Absorption.

    PubMed

    Tian, Chunhua; Du, Yunchen; Xu, Ping; Qiang, Rong; Wang, Ying; Ding, Ding; Xue, Jianlei; Ma, Jun; Zhao, Hongtao; Han, Xijiang

    2015-09-16

    Highly uniform core-shell composites, polypyrrole@polyaniline (PPy@PANI), have been successfully constructed by directing the polymerization of aniline on the surface of PPy microspheres. The thickness of PANI shells, from 30 to 120 nm, can be well controlled by modulating the weight ratio of aniline and PPy microspheres. PPy microspheres with abundant carbonyl groups have very strong affinity to the conjugated chains of PANI, which is responsible for the spontaneous formation of uniform core-shell microstructures. However, the strong affinity between PPy microspheres and PANI shells does not promote the diffusion or reassembly of two kinds of conjugated chains. Coating PPy microspheres with PANI shells increases the complex permittivity and creates the mechanism of interfacial polarization, where the latter plays an important role in increasing the dielectric loss of PPy@PANI composites. With a proper thickness of PANI shells, the moderate dielectric loss will produce well matched characteristic impedance, so that the microwave absorption properties of these composites can be greatly enhanced. Although PPy@PANI composites herein consume the incident electromagnetic wave by absolute dielectric loss, their performances are still superior or comparable to most PANI-based composites ever reported, indicating that they can be taken as a new kind of promising lightweight microwave absorbers. More importantly, microwave absorption of PPy@PANI composites can be simply modulated not only by the thickness of the absorbers, but also the shell thickness to satisfy the applications in different frequency bands. PMID:26322386

  18. Optical Absorption Microspectroscopy (μ-OAS) Based on Schwarzschild-Type Cassegrain Optics.

    PubMed

    Chassé, Mathieu; Lelong, Gérald; van Nijnatten, Peter; Schoofs, Ivo; de Wolf, Jürgen; Galoisy, Laurence; Calas, Georges

    2015-04-01

    A new experimental setup, combining a custom-designed Schwarzschild-type Cassegrain-based microscope and an ultraviolet-visible-near infrared (UV-Vis-NIR) spectrophotometer, has been developed, focusing the light beam down to 20 μm diameter. Optical absorption spectra (in the 300-2500 nm range) have been measured on micrometer-sized natural glass inclusions providing information on iron speciation in magmatic melts. The absence of contribution from the host crystal matrix provides a test of the efficiency of micro-focusing. A microthermometric stage has been adapted on the microscope for measuring optical absorption spectra up to 900 K with application to the thermochromism of minute natural spinel crystals (MgAl2O4:Fe(2+),Cr(3+)). This experimental setup provides an easy and fast way to follow the evolution of spectral properties and color of glasses or crystals with temperature as well as the possibility of measuring spatially resolved optical absorption spectra. PMID:25741926

  19. Measurement of absolute optical thickness distribution of a mask-glass by wavelength tuning interferometry

    NASA Astrophysics Data System (ADS)

    Hibino, Kenichi; Yangjin, Kim; Bitou, Youichi; Ohsawa, Sonko; Sugita, Naohiko; Mitsuishi, Mamoru

    2008-08-01

    The surface flatness and the uniformity in thickness and refractive index of a mask-blank glass have been requested in semiconductor industry. The absolute optical thickness of a mask-blank glass of seven-inch square and 3mm thickness was measured by three-surface interferometry in a wavelength tuning Fizeau interferometer. Wavelength-tuning interferometry can separate in frequency space the three interference signals of the surface shape and the optical thickness. The wavelength of a tunable laser diode source was scanned linearly from 632 nm to 642 nm and a CCD detector recorded two thousand interference images. The number of phase variation of the interference fringes during the wavelength scanning was counted by a temporal discrete Fourier transform. The initial and final phases of the interferograms before and after the scanning were measured by a phase shifting technique with fine tunings of the wavelengths at 632 nm and 642 nm. The optical thickness defined by the group refractive index at the central wavelength of 337 nm can be measured by this technique. Experimental results show that the cross talk in multiple-surface interferometry caused a systematic error of 2.0 microns in the measured optical thickness.

  20. Parametric distortion of the optical absorption edge of a magnetic semiconductor by a strong laser field

    SciTech Connect

    Nunes, O.A.C.

    1985-09-15

    The influence of a strong laser field on the optical absorption edge of a direct-gap magnetic semiconductor is considered. It is shown that as the strong laser intensity increases the absorption coefficient is modified so as to give rise to an absorption tail below the free-field forbidden gap. An application is made for the case of the EuO.

  1. Ripeness of 'Sun Bright' tomato using the optical absorption and scattering properties

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Maturity is one of the most important factors in determining the processing and eating quality of tomato. The objective of this research was to test the suitability of optical absorption and scattering properties for evaluating the maturity of tomatoes. Optical absorption and reduced scattering coef...

  2. Macular thickness and macular volume measurements using spectral domain optical coherence tomography in normal Nepalese eyes

    PubMed Central

    Pokharel, Amrit; Shrestha, Gauri Shankar; Shrestha, Jyoti Baba

    2016-01-01

    Purpose To record the normative values for macular thickness and macular volume in normal Nepalese eyes. Methods In all, 126 eyes of 63 emmetropic subjects (mean age: 21.17±6.76 years; range: 10–37 years) were assessed for macular thickness and macular volume, using spectral domain-optical coherence tomography over 6×6 mm2 in the posterior pole. A fast macular thickness protocol was employed. Statistics such as the mean, median, standard deviation, percentiles, and range were used, while a P-value was set at 0.05 to test significance. Results Average macular thickness and total macular volume were larger in males compared to females. With each year of increasing age, these variables decreased by 0.556 μm and 0.0156 mm3 for average macular thickness and total macular volume, respectively. The macular thickness was greatest in the inner superior section and lowest at the center of the fovea. The volume was greatest in the outer nasal section and thinnest in the fovea. The central subfield thickness (r=−0.243, P=0.055) and foveal volume (r=0.216, P=0.09) did not correlate with age. Conclusion Males and females differ significantly with regard to macular thickness and macular volume measurements. Reports by other studies that the increase in axial length reduced thickness and volume, were negated by this study which found a positive correlation among axial length, thickness, and volume. PMID:27041990

  3. Analysis of Normal Peripapillary Choroidal Thickness via Spectral Domain Optical Coherence Tomography

    PubMed Central

    Ho, Joseph; Branchini, Lauren; Regatieri, Caio; Krishnan, Chandrasekharan; Fujimoto, James G.; Duker, Jay S.

    2011-01-01

    PURPOSE To analyze the normal peripapillary choroidal thickness utilizing a commercial spectral domain optical coherence tomography (OCT) device and determine the inter-grader reproducibility of this method. DESIGN Retrospective, non-comparative, non-interventional case series. PARTICIPANTS Thirty-six eyes of 36 normal patients seen at the New England Eye Center between April and September 2010. METHODS All patients underwent high-definition scanning with the Cirrus HD-OCT. Two raster scans were obtained per eye, a horizontal and a vertical scan, both of which were centered at the optic nerve. Two independent graders individually measured the choroidal thickness. Choroidal thickness was measured from the posterior edge of the retinal pigment epithelium to the choroid-scleral junction at 500 μm intervals away from the optic nerve in the superior, inferior, nasal and temporal quadrants. Statistical analysis was conducted to compare mean choroidal thicknesses. Inter-grader reproducibility was assessed by intraclass correlation coefficient and Pearson’s correlation coefficient. Average choroidal thickness in each quadrant was compared to retinal nerve fiber layer (RNFL) thickness in their respective quadrants. MAIN OUTCOME MEASURES Peripapillary choroidal thickness, intraclass coefficient, Pearson’s correlation coefficient. RESULTS The peripapillary choroid in the inferior quadrant was significantly thinner compared to all other quadrants (p< 0.001). None of the other quadrants were significantly different from each other in terms of thickness. The inferior peripapillary choroid was significantly thinner compared to all other quadrants at all distances measured away from the optic nerve (p< 0.001). Generally, the peripapillary choroid increases in thickness the farther it was away from the optic nerve and eventually approaching a plateau. Intraclass correlation coefficient ranged from 0.62 to 0.93 and Pearson’s correlation coefficient ranged from 0.74 to 0.95 (p

  4. The INTEGRAL/IBIS AGN catalogue - I. X-ray absorption properties versus optical classification

    NASA Astrophysics Data System (ADS)

    Malizia, A.; Bassani, L.; Bazzano, A.; Bird, A. J.; Masetti, N.; Panessa, F.; Stephen, J. B.; Ubertini, P.

    2012-11-01

    In this work we present the most comprehensive INTEGRAL active galactic nucleus (AGN) sample. It lists 272 AGN for which we have secure optical identifications, precise optical spectroscopy and measured redshift values plus X-ray spectral information, i.e. 2-10 and 20-100 keV fluxes plus column density. Here we mainly use this sample to study the absorption properties of active galaxies, to probe new AGN classes and to test the AGN unification scheme. We find that half (48 per cent) of the sample is absorbed, while the fraction of Compton-thick AGN is small (˜7 per cent). In line with our previous analysis, we have however shown that when the bias towards heavily absorbed objects which are lost if weak and at large distance is removed, as it is possible in the local Universe, the above fractions increase to become 80 and 17 per cent. We also find that absorption is a function of source luminosity, which implies some evolution in the obscuration properties of AGN. A few peculiar classes, so far poorly studied in the hard X-ray band, have been detected and studied for the first time such as 5 X-ray bright optically normal galaxies, 5 type 2 QSOs and 11 low-ionization nuclear emission regions. In terms of optical classification, our sample contains 57 per cent of type 1 and 43 per cent of type 2 AGN; this subdivision is similar to that found in X-rays if unabsorbed versus absorbed objects are considered, suggesting that the match between optical and X-ray classifications is overall good. Only a small percentage of sources (12 per cent) does not fulfil the expectation of the unified theory as we find 22 type 1 AGN which are absorbed and 10 type 2 AGN which are unabsorbed. Studying in depth these outliers we found that most of the absorbed type 1 AGN have X-ray spectra characterized by either complex or warm/ionized absorption more likely due to ionized gas located in an accretion disc wind or in the biconical structure associated with the central nucleus, therefore

  5. Continuous wavelet-transform analysis of photoacoustic signal waveform to determine optical absorption coefficient

    NASA Astrophysics Data System (ADS)

    Hirasawa, T.; Ishihara, M.; Tsujita, K.; Hirota, K.; Irisawa, K.; Kitagaki, M.; Fujita, M.; Kikuchi, M.

    2012-02-01

    In photo-acoustic (PA) imaging, valuable medical applications based on optical absorption spectrum such as contrast agent imaging and blood oxygen saturation measurement have been investigated. In these applications, there is an essential requirement to determine optical absorption coefficients accurately. In present, PA signal intensities have been commonly used to determine optical absorption coefficients. This method achieves practical accuracy by combining with radiative transfer analysis. However, time consumption of radiative transfer analysis and effects of signal generation efficiencies were problems of this method. In this research, we propose a new method to determine optical absorption coefficients using continuous wavelet transform (CWT). We used CWT to estimate instantaneous frequencies of PA signals which reflects optical absorption distribution. We validated the effectiveness of CWT in determination of optical absorption coefficients through an experiment. In the experiment, planar shaped samples were illuminated to generate PA signal. The PA signal was measured by our fabricated PA probe in which an optical fiber and a ring shaped P(VDFTrFE) ultrasound sensor were coaxially aligned. Optical properties of samples were adjusted by changing the concentration of dye solution. Tunable Ti:Sapphire laser (690 - 1000 nm) was used as illumination source. As a result, we confirmed strong correlation between optical absorption coefficients of samples and the instantaneous frequency of PA signal obtained by CWT. Advantages of this method were less interference of light transfer and signal generation efficiency.

  6. Optically thick cascade to the O I 3s 3S state in the Earth's thermosphere

    NASA Technical Reports Server (NTRS)

    Cotton, Daniel M.; Chakrabarti, Supriya; Gladstone, G. Randall

    1993-01-01

    The electron impact excitation cross section for the O I (1304 A) emission is enhanced in the terrestrial thermosphere owing to an optically thick cascade mechanism. Values for the contribution of the cascade have been calculated and deduced from measured 1304-A airglow emissions to between o and 200%. We have developed a model to calculate a large portion of the optically thick cascade contribution, including contributions from the radiative entrapment of the O I (1040, 1027, and 989 A) lines. High-resolution spectroscopic data from a sounding rocket experiment are analyzed using this model. The optically thick cascade contribution for the three lower lying states was evaluated to be 24.5% and compares well with recent calculations. The data, however, support a total contribution of 40%. The 15.5% difference is likely due to the contribution from higher Rydberg states.

  7. Baseline Maritime Aerosol: Methodology to Derive the Optical Thickness and Scattering Properties

    NASA Technical Reports Server (NTRS)

    Kaufman, Yoram J.; Smirnov, Alexander; Holben, Brent N.; Dubovik, Oleg; Einaudi, Franco (Technical Monitor)

    2001-01-01

    Satellite Measurements of the global distribution of aerosol and their effect on climate should be viewed in respect to a baseline aerosol. In this concept, concentration of fine mode aerosol particles is elevated above the baseline by man-made activities (smoke or urban pollution), while coarse mode by natural processes (e.g. dust or sea-spray). Using 1-3 years of measurements in 10 stations of the Aerosol Robotic network (ACRONET we develop a methodology and derive the optical thickness and properties of this baseline aerosol for the Pacific and Atlantic Oceans. Defined as the median for periods of stable optical thickness (standard deviation < 0.02) during 2-6 days, the median baseline aerosol optical thickness over the Pacific Ocean is 0.052 at 500 am with Angstrom exponent of 0.77, and 0.071 and 1.1 respectively, over the Atlantic Ocean.

  8. Measurement of film thickness up to several hundreds of nanometers using optical waveguide lightmode spectroscopy.

    PubMed

    Picart, Catherine; Gergely, Csilla; Arntz, Youri; Voegel, Jean-Claude; Schaaf, Pierre; Cuisinier, Frédéric J G; Senger, Bernard

    2004-10-15

    Up to now, most studies based on optical waveguide lightmode spectroscopy (OWLS) were dedicated to thin adlayers, assumed to be isotropic and homogeneous, for which data analysis was based on an approximation of the mode equations valid when the thickness is small with respect to the wavelength of the laser light. The aim of the present paper is to extend the use of OWLS to thicker deposited layers (up to approximately 400 nm). Both the simplified and extended models are compared in terms of optical parameters, i.e. the refractive index nA, the thickness dA, and the optical mass QA, for experimental data obtained with polyelectrolyte multilayer films. The deviation of these parameters can be quite large when derived using the simplified model instead of the extended model. This observation evidences that OWLS is well suited for the study of "thick" films if the appropriate model is applied to the data analysis. PMID:15494239

  9. Magneto-optical Kerr effect in NiZn ferrite films of variable thickness

    NASA Astrophysics Data System (ADS)

    Calle, C.; Calle, V. H.; Cuéllar, F.; Cortés, A.; Arias, D.; Lopera, W.; Prieto, P.; Guzmán, O.; Mendoza, G. A.

    2006-10-01

    NiZn ferrites films deposited by RF sputtering technique on (1 0 0)-Si substrates have been studied by the magneto-optical Kerr effect. The coercivity behavior as a function of the thickness indicates a spin reversal mainly governed by the single domain regime. The Jiles-Atherton Model was used to fit the experimental hysteresis loop. The k pinning parameter of the model increases by increasing film thicknesses

  10. Laboratory atomic transition data for precise optical quasar absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Murphy, Michael T.; Berengut, Julian C.

    2014-02-01

    Quasar spectra reveal a rich array of important astrophysical information about galaxies which intersect the quasar line of sight. They also enable tests of the variability of fundamental constants over cosmological time- and distance-scales. Key to these endeavours are the laboratory frequencies, isotopic and hyperfine structures of various metal-ion transitions. Here, we review and synthesize the existing information about these quantities for 43 transitions which are important for measuring possible changes in the fine-structure constant, α, using optical quasar spectra, i.e. those of Na, Mg, Al, Si, Ca, Cr, Mn, Fe, Ni and Zn. We also summarize the information currently missing that precludes more transitions being used. We present an up-to-date set of coefficients, q, which define the sensitivity of these transitions to variations in α. New calculations of isotopic structures and q-coefficients are performed for Si II and Ti II, including Si II λ1808 and Ti IIλλ1910.6/1910.9 for the first time. Finally, simulated absorption-line spectra are used to illustrate the systematic errors expected if the isotopic/hyperfine structures are omitted from profile fitting analyses. To ensure transparency, repeatability and currency of the data and calculations, we supply a comprehensive data base as Supporting Information. This will be updated as new measurements and calculations are performed.

  11. Enhanced Optical Absorption Induced by Dense Nanocavities Inside Titania Nanorods

    SciTech Connect

    Han,W.; Wu, L.; Klie, R.; Zhu, Y.

    2007-01-01

    Titania, a wide band gap semiconductor, can generate powerful oxidants and reductants by absorbing photon energies. Titania has been extensively used in photoelectrochemical systems, such as dye-sensitized titania, a wide band gap semiconductor, can generate powerful oxidants and reductants by absorbing photon energies. To improve the photoreactivity of titania, several approaches, including doping and metal loading have been proposed. Nanocavities are isolated entities inside a solid and hence are very different from nanoporous, whose pores (often amorphous and irregular) connect together and open to the surface. Dense polyhedral nanocavities inside single-crystalline anatase titania nanorods were successfully synthesized by simply heating titanate nanorods. The size of the nanocavities is typically about 10 nm. The surfaces of the nanocavity polyhedron are determined to be the crystallographic low-index planes of the titania crystal. We found that these dense nanocavities significantly enhance the optical absorption coefficient of titania in the near-ultraviolet region, thereby providing a new approach to increasing the photoreactivity of the titania nanorods in the applications related to absorbing photons.

  12. Skin dose rate conversion factors after contamination with radiopharmaceuticals: influence of contamination area, epidermal thickness and percutaneous absorption.

    PubMed

    Covens, P; Berus, D; Caveliers, V; Struelens, L; Vanhavere, F; Verellen, D

    2013-06-01

    Skin contamination with radiopharmaceuticals can occur during biomedical research and daily nuclear medicine practice as a result of accidental spills, after contact with bodily fluids of patients or by inattentively touching contaminated materials. Skin dose assessment should be carried out by repeated quantification to map the course of the contamination together with the use of appropriate skin dose rate conversion factors. Contamination is generally characterised by local spots on the palmar surface of the hand and complete decontamination is difficult as a result of percutaneous absorption. This specific issue requires special consideration as to the skin dose rate conversion factors as a measure for the absorbed dose rate to the basal layer of the epidermis. In this work we used Monte Carlo simulations to study the influence of the contamination area, the epidermal thickness and the percutaneous absorption on the absorbed skin dose rate conversion factors for a set of 39 medical radionuclides. The results show that the absorbed dose to the basal layer of the epidermis can differ by up to two orders of magnitude from the operational quantity Hp(0.07) when using an appropriate epidermal thickness in combination with the effect of percutaneous absorption. PMID:23519114

  13. Characterization of ion-assisted induced absorption in A-Si thin-films used for multivariate optical computing

    NASA Astrophysics Data System (ADS)

    Nayak, Aditya B.; Price, James M.; Dai, Bin; Perkins, David; Chen, Ding Ding; Jones, Christopher M.

    2015-06-01

    Multivariate optical computing (MOC), an optical sensing technique for analog calculation, allows direct and robust measurement of chemical and physical properties of complex fluid samples in high-pressure/high-temperature (HP/HT) downhole environments. The core of this MOC technology is the integrated computational element (ICE), an optical element with a wavelength-dependent transmission spectrum designed to allow the detector to respond sensitively and specifically to the analytes of interest. A key differentiator of this technology is it uses all of the information present in the broadband optical spectrum to determine the proportion of the analyte present in a complex fluid mixture. The detection methodology is photometric in nature; therefore, this technology does not require a spectrometer to measure and record a spectrum or a computer to perform calculations on the recorded optical spectrum. The integrated computational element is a thin-film optical element with a specific optical response function designed for each analyte. The optical response function is achieved by fabricating alternating layers of high-index (a-Si) and low-index (SiO2) thin films onto a transparent substrate (BK7 glass) using traditional thin-film manufacturing processes (e.g., ion-assisted e-beam vacuum deposition). A proprietary software and process are used to control the thickness and material properties, including the optical constants of the materials during deposition to achieve the desired optical response function. The ion-assisted deposition is useful for controlling the densification of the film, stoichiometry, and material optical constants as well as to achieve high deposition growth rates and moisture-stable films. However, the ion-source can induce undesirable absorption in the film; and subsequently, modify the optical constants of the material during the ramp-up and stabilization period of the e-gun and ion-source, respectively. This paper characterizes the unwanted

  14. Optical absorption in ion-implanted lead lanthanum zirconate titanate ceramics

    SciTech Connect

    Seager, C.H.; Land, C.E.

    1984-08-15

    Optical absorption measurements have been performed on unmodified and on ion-implanted lead lanthanum zirconate titanate ceramics using the photothermal deflection spectroscopy technique. Bulk absorption coefficients depend on the average grain size of the material while the absorption associated with the ion-damaged layers does not. The damage-induced surface absorptance correlates well with the photosensitivity observed in implanted PLZT devices, supporting earlier models for the enhanced imaging efficiency of the materials.

  15. Retrieval of the atmospheric compounds using a spectral optical thickness information

    SciTech Connect

    Ioltukhovski, A.A.

    1995-03-01

    A spectral inversion technique for retrieval of the atmospheric gases and aerosols contents is proposed. This technique based upon the preliminary measurement or retrieval of the spectral optical thickness. The existence of a priori information about the spectral cross sections for some of the atmospheric components allows to retrieve the relative contents of these components in the atmosphere. Method of smooth filtration makes possible to estimate contents of atmospheric aerosols with known cross sections and to filter out other aerosols; this is done independently from their relative contribution to the optical thickness.

  16. A Simple Empirical Equation to Calculate Cloud Optical Thickness Using Shortwave Broadband Measurements

    SciTech Connect

    Barnard, James C.; Long, Charles N.

    2004-07-01

    In this paper, we present an empirical equation that can be used to estimate shortwave cloud optical thickness from measurements and analysis of shortwave broadband irradiances. When applied to a time series of broadband observations, this method can predict cloud optical thickness distributions that are very similar to those obtained using the Min algorithm (Min and Harrison, 1996). When considering a number of geographically diverse sites, medians of equation-derived distributions and Min-derived distributions differ by less than 10%. The equation is designed for fully overcast skies, surface albedos less than 0.3, and the cosine of the solar zenith angle must be greater than 0.15.

  17. Full-field optical thickness profilometry of semitransparent thin films with transmission densitometry

    SciTech Connect

    Johnson, Jay; Harris, Tequila

    2010-05-20

    A novel bidirectional thickness profilometer based on transmission densitometry was designed to measure the localized thickness of semitransparent films on a dynamic manufacturing line. The densitometer model shows that, for materials with extinction coefficients between 0.3 and 2.9 D/mm, 100-500 {mu}m measurements can be recorded with less than {+-}5% error at more than 10,000 locations in real time. As a demonstration application, the thickness profiles of 75 mmx100 mm regions of polymer electrolyte membrane (PEM) were determined by converting the optical density of the sample to thickness with the Beer-Lambert law. The PEM extinction coefficient was determined to be 1.4 D/mm, with an average thickness error of 4.7%.

  18. Carbon-Nitrogen-Oxygen Line Radiation and the X-ray Bowen Fluorescence Mechanism in Optically Thick, Highly Ionized Media

    NASA Technical Reports Server (NTRS)

    Sako, Masao

    2003-01-01

    Radiative transfer effects due to overlapping X-ray lines in a high-temperature, optically thick, highly ionized medium are investigated. One particular example, in which the O VIII Lyalpha doublet (2(sup 2) P(sub 1/2,3/2)-1(sup 2) S(sub 1/2) coincides in frequency with the N VII Lyzeta lines (7(sup 2) P(sub 1/2,3/2)-1(sup 2) S(sub 1/2) is studied in detail to illustrate the effects on the properties of the emergent line spectrum. We solve the radiative transfer equation to study the energy transport of resonance-line radiation in a static, infinite, plane-parallel geometry, which is used to compute the destruction/escape probabilities for each of the lines for various total optical thicknesses of the medium, as well as destruction probabilities by sources of underlying photoelectric opacity. It is found that a large fraction of the O vIII Lyalpha line radiation can be destroyed by N VII, which can result in a reversal of the O VIII Lyalpha/N VII Lyalpha line intensity ratio similar to what may be seen under nonsolar abundances. Photoelectric absorption by ionized carbon and nitrogen can also subsequently increase the emission-line intensities of these ions. We show that line ratios, which are directly proportional to the abundance ratios in optically thin plasmas, are not good indicators of the true CNO abundances. Conversely, global spectral modeling that assumes optically thin conditions may yield incorrect abundance estimates when compared with observations, especially if the optical depth is large. Other potentially important overlapping lines and continua in the X-ray band are also identified, and their possible relevance to recent high-resolution spectroscopic observations with Chandra and XMM-Newton are briefly discussed.

  19. Optical Coherence Tomography Assisted Retinal Nerve Fibre Layer Thickness Profile in High Myopia

    PubMed Central

    Malakar, Mousumi; Askari, Syed Nasir; Ashraf, Humayun; Ahuja, Anupam; Asghar, Adil

    2015-01-01

    Introduction: To evaluate the association of high myopia with retinal nerve fibre layer (RNFL) thickness by Fourier domain optical coherence tomography (FD OCT). Materials and Methods: Fifty highly myopic eyes (25 patients) and forty emmetropic eyes (20 Normal subject) were randomly selected after excluding concomitant ophthalmic disorder and RNFL thickness measured using the Fourier domain optical coherence tomography (FD OCT). Results: The overall mean RNFL thickness in the myopic groups and control were 87.89 μm and 111.64 μm respectively. The mean retinal nerve fibre thickness was significantly less in myopic eyes as compared to control group (p =0.0001). Retinal nerve fibre layer thickness shows topographic double hump pattern in both the groups (myopes and emmetropes). Conclusion: Retinal nerve fibre thickness was significantly less in myopic eyes as compared to emmetropic eyes. The retinal nerve fibre layer thinning in high myopes may be confused with open angle glaucoma, a disease also prevalent in high myopes. There is therefore a need to have retinal nerve fibre layer thickness normogram for high myopes of a given population group to avoid wrong interpretation. PMID:25859476

  20. Utilizing the MODIS 1.38 micrometer Channel for Cirrus Cloud Optical Thickness Retrievals: Algorithm and Retrieval Uncertainties

    NASA Technical Reports Server (NTRS)

    Meyer, Kerry; Platnick, Steven

    2010-01-01

    The cloud products from the Moderate Resolution Imaging Spectroradiometers (MODIS) on Terra and Aqua have been widely used within the atmospheric research community. The retrieval algorithms, however, oftentimes have difficulty detecting and retrieving thin cirrus, due to sensitivities to surface reflectance. Conversely, the 1.38 micron channel, located within a strong water vapor absorption band, is quite useful for detecting thin cirrus clouds since the signal from the surface can be blocked or substantially attenuated by the absorption of atmospheric water vapor below cirrus. This channel, however, suffers from nonnegligible attenuation due to the water vapor located above and within the cloud layer. Here we provide details of a new technique pairing the 1.38 micron and 1.24 micron channels to estimate the above/in-cloud water vapor attenuation and to subsequently retrieve thin cirrus optical thickness (tau) from attenuation-corrected 1.38 p.m reflectance measurements. In selected oceanic cases, this approach is found to increase cirrus retrievals by up to 38% over MOD06. For these cases, baseline 1.38 micron retrieval uncertainties are estimated to be between 15 and 20% for moderately thick cirrus (tau > 1), with the largest error source being the unknown cloud effective particle radius, which is not retrieved with the described technique. Uncertainties increase to around 90% for the thinnest clouds (tau < 0.5) where instrument and surface uncertainties dominate.

  1. Non-contact high precision measurement of surface form tolerances and central thickness for optical elements

    NASA Astrophysics Data System (ADS)

    Lou, Ying

    2010-10-01

    The traditional contact measuring methods could not satisfy the current optical elements measuring requirements. Noncontact high precision measuring theory, principle and instrument of the surface form tolerances and central thickness for optical elements were studied in the paper. In comparison with other types of interferometers, such as Twyman-Green and Mach-Zehnder, a Fizeau interferometer has the advantages of having fewer optical components, greater accuracy, and is easier to use. Some relations among the 3/A(B/C), POWER/PV and N/ΔN were studied. The PV with POWER removed can be the reference number of ΔN. The chromatic longitudinal aberration of a special optical probe can be used for non-contanct central thickness measurement.

  2. Retinal nerve fiber layer thickness in normal Indian pediatric population measured with optical coherence tomography.

    PubMed

    Pawar, Neelam; Maheshwari, Devendra; Ravindran, Meenakshi; Ramakrishnan, Renagappa

    2013-11-11

    Purpose: To measure the peripapillary retinal nerve fiber layer (RNFL) thickness in normal Indian pediatric population. Subjects and Methods: 120 normal Indian children ages 5-17 years presenting to the Pediatric Clinic were included in this observational cross-sectional study. RNFL thickness was measured with stratus optical coherence tomography (OCT). Children with strabismus or amblyopia, with neurological, metabolic, vascular, or other disorders and those with abnormal optic discs were excluded. One eye of each subject was randomly selected for statistical analysis. The effect of age, refraction and gender on RNFL thickness was investigated statistically. Result: OCT measurements were obtained in 120 of 130 (92.3%) subjects. Mean age was 10.8 ± 3.24 years (range 5-17). Average RNFL thickness was (± SD) 106.11 ± 9.5 μm (range 82.26-146.25). The RNFL was thickest inferiorly (134.10 ± 16.16 μm) and superiorly (133.44 ± 15.50 μm), thinner nasally (84.26 ± 16.43 μm), and thinnest temporally (70.72 ± 14.80 μm). In univariate regression analysis, age had no statistical significant effect on RNFL thickness (P = 0.7249) and refraction had a significant effect on RNFL thickness (P = 0.0008). Conclusion: OCT can be used to measure RNFL thickness in children. Refraction had an effect on RNFL thickness. In normal children, variation in RNFL thickness is large. The normative data provided by this study may assist in identifying changes in RNFL thickness in Indian children. PMID:24212231

  3. Thickness and topographic inspection of RPG contact lenses by optical triangulation

    NASA Astrophysics Data System (ADS)

    Costa, Manuel F. M.

    2001-06-01

    Optical triangulation as a non-destructive test method extensively proved its usefulness on the dimensional and topographic inspection of a large range of objects and surfaces. In this communication the issue of microtopographic and thickness inspection of hard contact lenses (RPG) is addressed. The use of optical triangulation is discussed based on the results of the application of our MICROTOP.03.MFC microtopographer to this kind of tasks will be presented.

  4. Glass Composition-Dependent Silicate Absorption Peaks in FTIR Spectroscopy: Implications for Measuring Sample Thickness and Molecular H2O

    NASA Astrophysics Data System (ADS)

    McIntosh, I. M.; Nichols, A. R.; Schipper, C. I.; Stewart, R. B.

    2015-12-01

    Fourier-transform infrared spectroscopy (FTIR) is often used to measure the H2O and CO2 contents of volcanic glasses. A key advantage of FTIR over other analytical techniques is that it can reveal not only total H2O concentration but also H2O speciation, i.e. how much H2O is present as molecular H2O (H2Om) and how much as hydroxyl groups (OH) bound to the silicate network. This H2O speciation data can be used to investigate cooling rate and glass transition temperature of volcanic glasses, and to interpret H2O contents of pyroclasts affected by partial bubble resorption during cooling or secondary hydration after deposition. FTIR in transmitted light requires sample wafers polished on both sides of known thickness. Thickness is commonly measured using a micrometer but this may damage fragile samples and in samples with non-uniform thickness, e.g. vesicular samples, it is difficult to position at the exact location of FTIR analysis. Furthermore, in FTIR images or maps of such samples it is impractical to determine the thickness across the whole of the analysed area, resulting either in only a selection of the collected data being processed quantitatively and the rest being unused, or results being presented in terms of absorbance, which does not account for variations in thickness.It is known that FTIR spectra contain absorption peaks related to the glass aluminosilicate network at wavenumbers of ~2000, ~1830 and ~1600 cm-1 [1]. These have been shown to be proportional to sample thickness at the analysis location for one obsidian composition with up to 0.66 wt% H2O [2]. We test whether this calibration can be applied more widely by analysing a range of synthetic and natural glasses (andesitic to rhyolitic) to examine how the position and relative intensities of the different silicate absorption peaks vary with composition and H2O content. Our data show that even minor differences in composition necessitate a unique calibration. Furthermore, importantly we show how

  5. Investigation of the screen optics of thick CsI(Tl) detectors

    NASA Astrophysics Data System (ADS)

    Howansky, Adrian; Peng, Boyu; Suzuki, Katsuhiko; Yamashita, Masanori; Lubinsky, A. R.; Zhao, Wei

    2015-03-01

    Flat panel imagers (FPI) are becoming the dominant detector technology for digital x-ray imaging. In indirect FPI, the scintillator that provides the highest image quality is Thallium (Tl) doped Cesium Iodide (CsI) with columnar structure. The maximum CsI thickness used in existing FPI is ~600 microns, due to concerns of loss in spatial resolution and light output with further increase in thickness. The goal of the present work is to investigate the screen-optics for CsI with thicknesses much larger than that used in existing FPI, so that the knowledge can be used to improve imaging performance in dose sensitive and higher energy applications, such as cone-beam CT (CBCT). Columnar CsI(Tl) scintillators up to 1 mm in thickness with different screen-optical design were investigated experimentally. Pulse height spectra (PHS) were measured to determine the Swank factor at x-ray energies between 25 and 75 keV, and to derive depth-dependent light escape efficiency i.e. gain. Detector presampling MTF, NPS and DQE were measured using a high-resolution CMOS optical sensor. Optical Monte Carlo simulation was performed to estimate optical parameters for each screen design and derive depth-dependent gain and MTF, from which overall MTF and DQE were calculated and compared with measured results. The depth-dependent imaging performance parameters were then used in a cascaded linear system model (CLSM) to investigate detector performance under screen- and sensor-side irradiation conditions. The methodology developed for understanding the optics of thick CsI(Tl) will lead to detector optimization in CBCT.

  6. Nocturnal Measurements of HONO by Differential Optical Absorption Spectroscopy

    NASA Astrophysics Data System (ADS)

    Wojtal, P.; McLaren, R.

    2011-12-01

    Differential optical absorption spectroscopy (DOAS) was used to quantify the concentration of HONO, NO2 and SO2 in the nocturnal urban atmosphere at York University over a period of one year. These measurements form a comprehensive HONO data set, including a large range of temperatures, relative humidity, surface conditions (snow, water, dry, etc.) and NO2 concentrations. Laboratory studies and observations within the nocturnal boundary layer reported in the literature suggest heterogeneous conversion of NO2 on surface adsorbed water as the major nighttime source of HONO. HONO formation and photolysis is believed to represent a major source term in the hydroxyl radical budget in polluted continental regions. Currently, most air quality models tend to significantly underpredict HONO, caused by the lack of understanding of HONO formation processes and the parameters that affect its concentration. Recently, we reported nocturnal pseudo steady states (PSS) of HONO in an aqueous marine environment and a conceptual model for HONO formation on aqueous surfaces was proposed. The data set collected at York University is being analyzed with a view towards further understanding the nighttime HONO formation mechanism and testing several hypotheses: 1) A HONO PSS can exist during certain times at night in an urban area in which the HONO concentration is independent of NO2, given the surface contains sufficient water coverage and is saturated with nitrogen containing precursors; 2) The concentration of HONO is positively correlated with temperature during periods where a PSS exists; 3) Different conversion efficiencies of NO2 to HONO exist on dry, wet and snow surfaces; 4) HONO formation has a NO2 order dependence between 0 and 2nd order, dependant on NO2 concentration, relative humidity, etc. The data set will be presented along with statistical analysis that sheds new light on the source of HONO in urban areas at night.

  7. Optical absorption components of light-modulated absorption spectrum of CdS

    NASA Technical Reports Server (NTRS)

    Conway, E. J.; Long, E. R.

    1975-01-01

    The amplitude and decay coefficient of light-induced modulation of absorption (LIMA) was measured as a function of wavelength from 535 to 850 nm for single-crystal CdS. The decay coefficient exhibited a discontinuous resonance at 710 nm which was due to the overlap and cancellation of two opposing absorption changes. A method was developed to separate these opposing absorption changes using the measured decay coefficients. The discrete-level-to-band energy for one absorption change was found to be 1.64 eV. An improved model was developed which contains two associated levels in the band gap separated by 0.32 eV.

  8. Impact of the H 2 anneal on the structural and optical properties of thin and thick Ge layers on Si; Low temperature surface passivation of Ge by Si

    NASA Astrophysics Data System (ADS)

    Hartmann, J. M.; Abbadie, A.; Barnes, J. P.; Fédéli, J. M.; Billon, T.; Vivien, L.

    2010-02-01

    Using a low temperature/high temperature strategy, we have grown thin (0.27 μm) and thick (2.45 μm) Ge layers on Si(0 0 1) substrates that we have submitted to various constant temperature (750 °C) or cyclic (750 °C/890 °C) H 2 anneals, the objective being to identify those yielding the smoothest surfaces, the lowest threading dislocations densities (TDDs) and the highest near infra-red optical absorptions. The best trade-off for thin layers was 750 °C, 60 min H 2 anneals. Using longer duration 750 °C anneals and especially 750 °C/890 °C cyclic anneals indeed yielded rougher surfaces and vastly degraded optical absorption (deleterious formation of GeSi alloys). By contrast, short 750 °C/890 °C thermal cyclings yielded the best metrics in thick Ge layers (while being at the same time the best in terms of throughput): root mean square surface roughness around 0.8 nm, TDD around 10 7 cm -2, slightly tensily-strained layers (which a plus for optical absorption as the absorption edge is shifted to higher wavelengths), a limited penetration of Si into Ge (and thus absorption coefficients at 1.3 and 1.55 μm almost equal to those of as-grown layers), etc. We have also described the low temperature (450 °C/525 °C) process that we have developed to passivate Ge surfaces thanks to SiH 4 prior to gate stack deposition. Si layer thickness should be below 20 Å in order to have conformal deposition. A transition of the growth front to 3 dimensions has indeed been evidenced for 20 Å and higher.

  9. Influence of cloud optical thickness on surface diffuse light and carbon uptake in forests and croplands

    NASA Astrophysics Data System (ADS)

    Cheng, S. J.; Steiner, A. L.; Nadelhoffer, K. J.

    2014-12-01

    Accurately modeling atmospheric CO2 removal by terrestrial ecosystems requires an understanding of how atmospheric conditions change the rate of photosynthesis across major vegetation types. Diffuse light, which is created from interactions between incident solar radiation and atmospheric aerosols and clouds, has been postulated to increase carbon uptake in terrestrial ecosystems. To determine how cloud conditions affect carbon uptake through its influence on diffuse light, we quantify the relationship between cloud optical thickness, which indicates surface light attenuation by clouds, and surface diffuse light. We then examine the relationship between cloud optical thickness and gross primary productivity (GPP) to determine whether cloud properties could modulate GPP in temperate ecosystems. Surface diffuse light and GPP data are obtained from publically available Ameriflux data (Mead Crop sites, University of Michigan Biological Station, Morgan Monroe, and Howland Forest) and cloud optical thickness data over the Ameriflux sites are retrieved from NASA's Moderate Resolution Imaging Spetroradiometer. We compare the response of GPP to cloud optical thickness between croplands and forests, as well as within ecosystem types to determine ecosystem-specific responses and the role of plant community composition on ecosystem-level GPP under varying cloud conditions. By linking atmospheric cloud properties to surface light conditions and ecosystem carbon fluxes, we refine understanding of land-atmosphere carbon cycling and how changes in atmospheric cloud conditions may influence the future of the land carbon sink.

  10. An optical method for measuring the thickness of a falling condensate in gravity assisted heat pipe

    NASA Astrophysics Data System (ADS)

    Kasanický, Martin; Lenhard, Richard; Kaduchová, Katarína; Malcho, Milan

    2015-05-01

    A large number of variables is the main problem of designing systems which uses heat pipes, whether it is a traditional - gravity, or advanced - capillary, pulsating, advanced heat pipes. This article is a methodology for measuring the thickness of the falling condensate in gravitational heat pipes, with using the optical triangulation method, and the evaluation of risks associated with this method.

  11. Performance analysis of optical coherence tomography in the context of a thickness estimation task

    NASA Astrophysics Data System (ADS)

    Huang, Jinxin; Yao, Jianing; Cirucci, Nick; Ivanov, Trevor; Rolland, Jannick P.

    2015-12-01

    Thickness estimation is a common task in optical coherence tomography (OCT). This study discusses and quantifies the intensity noise of three commonly used broadband sources, such as a supercontinuum source, a superluminescent diode (SLD), and a swept source. The performance of the three optical sources was evaluated for a thickness estimation task using both the fast Fourier transform (FFT) and maximum-likelihood (ML) estimators. We find that the source intensity noise has less impact on a thickness estimation task compared to the width of the axial point-spread function (PSF) and the trigger jittering noise of a swept source. Findings further show that the FFT estimator yields biased estimates, which can be as large as 10% of the thickness under test in the worst case. The ML estimator is by construction asymptotically unbiased and displays a 10× improvement in precision for both the supercontinuum and SLD sources. The ML estimator also shows the ability to estimate thickness that is at least 10× thinner compared to the FFT estimator. Finally, findings show that a supercontinuum source combined with the ML estimator enables unbiased nanometer-class thickness estimation with nanometer-scale precision.

  12. Performance analysis of optical coherence tomography in the context of a thickness estimation task.

    PubMed

    Huang, Jinxin; Yao, Jianing; Cirucci, Nick; Ivanov, Trevor; Rolland, Jannick P

    2015-12-01

    Thickness estimation is a common task in optical coherence tomography (OCT). This study discusses and quantifies the intensity noise of three commonly used broadband sources, such as a supercontinuum source, a superluminescent diode (SLD), and a swept source. The performance of the three optical sources was evaluated for a thickness estimation task using both the fast Fourier transform (FFT) and maximum-likelihood (ML) estimators. We find that the source intensity noise has less impact on a thickness estimation task compared to the width of the axial point-spread function (PSF) and the trigger jittering noise of a swept source. Findings further show that the FFT estimator yields biased estimates, which can be as large as 10% of the thickness under test in the worst case. The ML estimator is by construction asymptotically unbiased and displays a 10× improvement in precision for both the supercontinuum and SLD sources. The ML estimator also shows the ability to estimate thickness that is at least 10× thinner compared to the FFT estimator. Finally, findings show that a supercontinuum source combined with the ML estimator enables unbiased nanometer-class thickness estimation with nanometer-scale precision. PMID:26378988

  13. Utilizing Optical Coherence Tomography in the Nondestructive and Noncontact Measurement of Egg Shell Thickness

    PubMed Central

    2014-01-01

    The goal of this study was to measure the thickness of egg shells without any contact and by utilizing a nondestructive method that sends infrared light beam on the egg. We obtain measurement resolutions on the order of 7 μm up to a penetration depth of 1.7 mm from the actual surface of the egg shell. The measurement results we obtained show that optical coherence tomography can be used to accurately determine the egg shell thickness. Scanning the light beam over the surface allows for measuring the egg profile and monitoring the variations of shell thickness. Since this information gives a quantitative value for the uniformity of the egg shell structure, we anticipate that optical coherence tomography may be used in the quantitative evaluation of egg quality in in-line automated inspection systems. PMID:25133208

  14. Optically thick X-ray transfer - The shell game. [transmission through gas surrounding cosmic x ray source

    NASA Technical Reports Server (NTRS)

    Langer, S. H.; Ross, R. R.; Mccray, R.

    1978-01-01

    This paper investigates the radiative transfer of X-rays through a shell that is optically thick to Compton scattering, surrounding a point source of continuum X-rays. The emission and absorption of X-rays due to K-shell transitions of iron are included. The calculations are done in two entirely independent ways: by Monte Carlo simulation and by solving a Fokker-Planck diffusion equation. The emergent spectra agree very well for Thomson depths of at least about 2. The validity is confirmed of the modification to the Fokker-Planck equation of Kompaneets (1957) that is required when the photon energy is large compared with the average thermal energy of the electrons. A procedure is also developed for treating models of compact X-ray sources consisting of incomplete shells.

  15. Tunable van Hove Singularities and Optical Absorption of Twisted Bilayer Graphene

    NASA Astrophysics Data System (ADS)

    Liang, Yufeng; Yang, Li

    2013-03-01

    We perform the first-principles GW-Bethe-Salpeter Equation (BSE) simulation to study the optical absorption spectra of isolated twisted bilayer graphene (TBLG). The twisting generates new van Hove singularities (VHS), and these VHSs and corresponding optical absorption peaks can be tuned in a wide range by the twist angle. Enhanced electron-electron and electron-hole interactions are shown to be important to understand both optical absorption peak positions and their lineshapes. With these many-electron effects included, our calculation satisfactorily explains recent experimental measurements.

  16. Retinal Nerve Fiber Layer Thickness Measurement Comparison Using Spectral Domain and Swept Source Optical Coherence Tomography

    PubMed Central

    Ha, Ahnul; Lee, Seung Hyen; Lee, Eun Ji

    2016-01-01

    Purpose To investigate the retinal nerve fiber layer (RNFL) thickness concordance when measured by spectral domain (SD) and swept source (SS) optical coherence tomography (OCT), and to compare glaucoma-discriminating capability. Methods RNFL thicknesses were measured with the scan circle, centered on the optic nerve head, in 55 healthy, 41 glaucoma suspected, and 87 glaucomatous eyes. The RNFL thickness measured by the SD-OCT (sdRNFL thickness) and SS-OCT (ssRNFL thickness) were compared using the t-test. Bland-Altman analysis was performed to examine their agreement. We compared areas under the receiver operating characteristics curve and examined sdRNFL and ssRNFL thickness for discriminating glaucomatous eyes from healthy eyes, and from glaucoma suspect eyes. Results The average ssRNFL thickness was significantly greater than sdRNFL thickness in healthy (110.0 ± 7.9 vs. 100.1 ± 6.8 µm, p < 0.001), glaucoma suspect (96.8 ± 9.3 vs. 89.6 ± 7.9 µm, p < 0.001), and glaucomatous eyes (74.3 ± 14.2 vs. 69.1 ± 12.4 µm, p = 0.011). Bland-Altman analysis showed that there was a tendency for the difference between ssRNFL and sdRNFL to increase in eyes with thicker RNFL. The area under the curves of the average sdRNFL and ssRNFL thickness for discriminating glaucomatous eyes from healthy eyes (0.984 vs. 0.986, p = 0.491) and glaucoma suspect eyes (0.936 vs. 0.918, p = 0.132) were comparable. Conclusions There was a tendency for ssRNFL thickness to increase, compared with sdRNFL thickness, in eyes with thicker RNFL. The ssRNFL thickness had comparable diagnostic capability compared with sdRNFL thickness for discriminating glaucomatous eyes from healthy eyes and glaucoma suspect eyes. PMID:27051263

  17. Effect of optic nerve sheath fenestration for idiopathic intracranial hypertension on retinal nerve fiber layer thickness.

    PubMed

    Starks, Victoria; Gilliland, Grant; Vrcek, Ivan; Gilliland, Connor

    2016-01-01

    The objective of the study was to evaluate whether optic nerve sheath fenestration in patients with idiopathic intracranial hypertension was associated with improvement in visual field pattern deviation and optical coherence tomography retinal nerve fiber layer thickness.The records of 13 eyes of 11 patients who underwent optic nerve sheath fenestration were reviewed. The subjects were patients of a clinical practice in Dallas, Texas. Charts were reviewed for pre- and postoperative visual field pattern deviation (PD) and retinal nerve fiber layer thickness (RNFL).PD and RNFL significantly improved after surgery. Average PD preoperatively was 8.51 DB and postoperatively was 4.80 DB (p = 0.0002). Average RNFL preoperatively was 113.63 and postoperatively was 102.70 (p = 0.01). The preoperative PD and RNFL did not correlate strongly.Our results demonstrate that PD and RNFL are improved after optic nerve sheath fenestration. The pre- and postoperative RNFL values were compared to the average RNFL value of healthy optic nerves obtained from the literature. Post-ONSF RNFL values were significantly closer to the normal value than preoperative. RNFL is an objective parameter for monitoring the optic nerve after optic nerve sheath fenestration. This study adds to the evidence that OCT RNFL may be an effective monitoring tool for patients with IIH and that it continues to be a useful parameter after ONSF. PMID:26928128

  18. Form, figure, and thickness measurement of freeform and conformal optics with non-contact sensors

    NASA Astrophysics Data System (ADS)

    DeFisher, Scott; Fess, Edward; Matthews, Greg

    2014-05-01

    Advancements in optical manufacturing technology allow optical designers to implement freeform and conformal shapes in their systems. Metrology of the shapes has traditionally been difficult, especially at the sub-micron level. Contact measuring systems typically lack the accuracy required for optical qualification and can damage the surface. Interferometric systems are unable to handle high spherical departures and may require complicated lateral calibration to generate feedback for deterministic grinding and polishing. OptiPro has developed UltraSurf, a noncontact coordinate measuring machine to determine the form, figure, and thickness of freeform and conformal optics. We integrated several non-contact sensors that acquire surface information through different optical principles. Each probe has strength and weaknesses relative to an optic's material properties, surface finish, and figure error. The measuring probe is scanned over the optical surface while maintaining perpendicularity and a constant focal offset. Measurements of freeform and conformal shapes will be presented. The scanning method of UltraSurf and the non-contact probes will also be shown. The form, figure, and thickness data will highlight the capabilities of UltraSurf to measure freeform surfaces. Comparisons between accuracy and measureable surface departure will be made with current metrology systems such as coordinate measuring machines, interferometers, and profilometers. Additionally, methods for defining a freeform or conformal surface for metrology analysis and manufacturing will be discussed.

  19. Realistic reflectance spectrum of thin films covering a transparent optically thick substrate

    SciTech Connect

    Cesaria, M. Caricato, A. P.; Martino, M.

    2014-07-21

    A spectrophotometric strategy is presented and discussed for calculating realistically the reflectance spectrum of an absorbing film deposited over a thick transparent or semi-transparent substrate. The developed route exploits simple mathematics, has wide range of applicability (high-to-weak absorption regions and thick-to-ultrathin films), rules out numerical and curve-fitting procedures as well as model-functions, inherently accounts for the non-measurable contribution of the film-substrate interface as well as substrate backside, and describes the film reflectance spectrum as determined by the experimental situation (deposition approach and parameters). The reliability of the method is tested on films of a well-known material (indium tin oxide) by deliberately changing film thickness and structural quality through doping. Results are found consistent with usual information yielded by reflectance, its inherent relationship with scattering processes and contributions to the measured total reflectance.

  20. Tuning optical and three photon absorption properties in graphene oxide-polyvinyl alcohol free standing films

    NASA Astrophysics Data System (ADS)

    Karthikeyan, B.; Udayabhaskar, R.; Hariharan, S.

    2016-07-01

    We report the optical and nonlinear optical properties of graphene oxide (GO)-polyvinyl alcohol (PVA) free standing films. The composite polymer films were prepared in ex-situ method. The variation in optical absorption spectra and optical constants with the amount of GO loading was noteworthy from the optical absorption spectroscopic studies. Nonlinear optical studies done at 532 nm using 5 ns laser pulses show three photon absorption like behaviour. Both steady state and time resolved fluorescence studies reveal that the GO was functioning as a pathway for the decay of fluorescence from PVA. This is attributed to the energy level modifications of GO through hydroxyl groups with PVA. Raman spectroscopy also supports the interaction between GO and PVA ions through OH radicals.

  1. Lens thickness assessment: anterior segment optical coherence tomography versus A-scan ultrasonography

    PubMed Central

    Hamzeh, Nikoo; Moghimi, Sasan; Latifi, Golshan; Mohammadi, Massood; Khatibi, Nassim; Lin, Shan C.

    2015-01-01

    AIM To assess lens thickness measurements with anterior segment-optical coherence tomography (AS-OCT) in comparison with A-scan ultrasonography (A-scan US). METHODS There were 218 adult subjects (218 eyes) aged 59.2±9.2y enrolled in this prospective cross-sectional study. Forty-three eyes had open angles and 175 eyes had narrow angles. Routine ophthalmic exam was performed and nuclear opacity was graded using the Lens Opacities Classification System III (LOCS III). Lens thickness was measured by AS-OCT (Visante OCT, Carl Zeiss Meditec, Dublin, CA, USA). The highest quality image was selected for each eye and lens thickness was calculated using ImageJ software. Lens thickness was also measured by A-scan US. RESULTS Interclass correlations showed a value of 99.7% for intra-visit measurements and 95.3% for inter-visit measurements. The mean lens thickness measured by AS-OCT was not significantly different from that of A-scan US (4.861±0.404 vs 4.866±0.351 mm, P=0.74). Lens thickness values obtained from the two instruments were highly correlated overall (Pearson correlation coefficient=0.81, P<0.001), and in all LOCS III specific subgroups except in grade 5 of nuclear opacity. Bland-Altman analysis revealed a 95% limit of agreement from -0.45 to 0.46 mm. Lens thickness difference between the two instruments became smaller as the lens thickness increased and AS-OCT yielded smaller values than A-scan US in thicker lens (β=-0.29, P<0.001) CONCLUSION AS-OCT-derived lens thickness measurement is valid and comparable to the results obtained by A-scan US. It can be used as a reliable noncontact method for measuring lens thickness in adults with or without significant cataract. PMID:26682164

  2. Quantitative spectral domain optical coherence tomography thickness parameters in type II diabetes

    PubMed Central

    Gella, Laxmi; Raman, Rajiv; Sharma, Tarun

    2016-01-01

    Purpose: To elucidate the changes in retinal thickness and individual layer thickness in subjects with diabetic retinopathy (DR) using spectral domain optical coherence tomography (SDOCT). Materials and Methods: A total of 251 eyes from 170 subjects were included in this study. The study sample was subdivided into nondiabetic subjects; subjects with diabetes but no DR; subjects with mild, moderate, and severe nonproliferative DR (NPDR); and proliferative DR. Various retinal thickness parameters were assessed using SDOCT. Results: The mean age of the study population was 55.34 ± 9.02 years (range: 32–80 years) and 56.6% of the subjects were males. Men had significantly greater central foveal thickness, central subfield thickness, retinal nerve fiber layer thickness, and retinal thickness in all the quadrants of 3 mm and 6 mm zones compared to women (P < 0.001). Superior (293.11 ± 25.46 vs. 285.25 ± 19.17; P = 0.044) and temporal (282.10 ± 25.26 vs. 272.46 ± 16.21; P = 0.011) quadrants showed an increased retinal thickness in any DR group when compared with diabetic subjects without DR. Photoreceptor layer thickness was significantly reduced in diabetic subjects with no DR when compared with nondiabetic subjects and also in cases of severe NPDR when compared with mild and moderate NPDR. Conclusion: Here, we analyze the quantitative retinal thickness parameters in diabetic subjects using SDOCT. Neuronal degenerative changes such as photoreceptor and retinal pigment epithelial thinning in case of DR are also reported. PMID:27013826

  3. Correlation of Retinal Nerve Fiber Layer Thickness and Axial Length on Fourier Domain Optical Coherence Tomography

    PubMed Central

    Dhasmana, Renu; Nagpal, R.C.

    2016-01-01

    Introduction The assessment of the peripapillary Retinal Nerve Fiber Layer (RNFL) thickness has been an important tool for evaluating and diagnosing glaucoma and its progression. Literature suggests that myopic eyes are at an increased risk for developing glaucoma. This study gives an insight into the relationship of RNFL thickness to the axial length in normal population. Aim To correlate the RNFL thickness and the axial length in normal individuals with Fourier domain Optical Coherence Tomography (OCT). Materials and Methods In the current study, 298 eyes of 149 normal individuals (10 years or older) with or without refractive error were recruited. The RNFL thickness was measured using Optovue (RTVue) three-dimensional Fourier domain OCT. Results We observed an inverse relationship between average RNFL thickness and increasing axial length(p=0.003). Maximum RNFL thickness was seen in the Infero-Temporal (IT) quadrant and minimum in the Supero-Nasal (SN) quadrant. RNFL thickness did not show any tendency to decline with age using the Pearsons correlation (r=0.07). Females had an increased RNFL thickness in the Supero-Temporal (ST) and Infero-Nasal (IN) quadrant (p-value 0.046 and 0.02) in comparison to males. There was a statistically significant thinning in Ganglion Cell Complex (GCC) with increasing axial length (p-value 0.000) Conclusion The current study suggests that the average RNFL thickness does not decrease with age. The RNFL and GCC thickness shows an inverse correlation with axial length of the eyeball hence observations have to be carefully interpreted in myopic eyes. Clinicians need to keep the anatomical variations in RNFL for better patient management. PMID:27190850

  4. Optical coherence tomography enables accurate measurement of equine cartilage thickness for determination of speed of sound.

    PubMed

    Puhakka, Pia H; Te Moller, Nikae C R; Tanska, Petri; Saarakkala, Simo; Tiitu, Virpi; Korhonen, Rami K; Brommer, Harold; Virén, Tuomas; Jurvelin, Jukka S; Töyräs, Juha

    2016-08-01

    Background and purpose - Arthroscopic estimation of articular cartilage thickness is important for scoring of lesion severity, and measurement of cartilage speed of sound (SOS)-a sensitive index of changes in cartilage composition. We investigated the accuracy of optical coherence tomography (OCT) in measurements of cartilage thickness and determined SOS by combining OCT thickness and ultrasound (US) time-of-flight (TOF) measurements. Material and methods - Cartilage thickness measurements from OCT and microscopy images of 94 equine osteochondral samples were compared. Then, SOS in cartilage was determined using simultaneous OCT thickness and US TOF measurements. SOS was then compared with the compositional, structural, and mechanical properties of cartilage. Results - Measurements of non-calcified cartilage thickness using OCT and microscopy were significantly correlated (ρ = 0.92; p < 0.001). With calcified cartilage included, the correlation was ρ = 0.85 (p < 0.001). The mean cartilage SOS (1,636 m/s) was in agreement with the literature. However, SOS and the other properties of cartilage lacked any statistically significant correlation. Interpretation - OCT can give an accurate measurement of articular cartilage thickness. Although SOS measurements lacked accuracy in thin equine cartilage, the concept of SOS measurement using OCT appears promising. PMID:27164159

  5. Macular Thickness Assessed with Optical Coherence Tomography in Young Chinese Myopic Patients

    PubMed Central

    Zhao, Minghui; Wu, Qiang; Hu, Ping; Jia, Lili

    2015-01-01

    Purpose. To evaluate the variations in macular thickness in young Chinese myopic persons and the association with axial length (AL), spherical equivalence refraction (SE), age, intraocular pressure, and sex. Methods. In total, 133 young Chinese myopic subjects between 18 and 30 years of age were selected. The macular thickness was assessed using third-generation optical coherence tomography. AL, intraocular pressure, and SE were also measured. Results. The mean central foveal thickness was 191.1 ± 15.3 µm. The macula was consistently thinner in women than in men. Central foveal thickness had a significant positive correlation with AL and a negative correlation with SE. In the inner and outer regions, the macular thickness had a positive correlation with SE and negative correlation with AL. Conclusions. The retina was thinner in women than in men. Associated with myopic progression and AL extension, the central foveal thickness increased, while the retinal thickness of the inner and outer regions decreased. PMID:26609427

  6. Retinal Thickness Measurement Obtained with Spectral Domain Optical Coherence Tomography Assisted Optical Biopsy Accurately Correlates with Ex Vivo Histology

    PubMed Central

    Ferguson, Lee R.; Grover, Sandeep; Dominguez II, James M.; Balaiya, Sankarathi; Chalam, Kakarla V.

    2014-01-01

    Background This study determines ‘correlation constants’ between the gold standard histological measurement of retinal thickness and the newer spectral-domain optical coherence tomography (SD-OCT) technology in adult C57BL/6 mice. Methods Forty-eight eyes from adult mice underwent SD-OCT imaging and then were histologically prepared for frozen sectioning with H&E staining. Retinal thickness was measured via 10x light microscopy. SD-OCT images and histological sections were standardized to three anatomical sites relative to the optic nerve head (ONH) location. The ratios between SD-OCT to histological thickness for total retinal thickness (TRT) and six sublayers were defined as ‘correlation constants’. Results Mean (± SE) TRT for SD-OCT and histological sections was 210.95 µm (±1.09) and 219.58 µm (±2.67), respectively. The mean ‘correlation constant’ for TRT between the SD-OCT and histological sections was 0.96. The retinal thickness for all sublayers measured by SD-OCT vs. histology were also similar, the ‘correlation constant’ values ranged from 0.70 to 1.17. All SD-OCT and histological measurements demonstrated highly significant (p<0.01) strong positive correlations. Conclusion This study establishes conversion factors for the translation of ex vivo data into in vivo information; thus enhancing the applicability of SD-OCT in translational research. PMID:25360629

  7. Thickness dependent optical properties of PEMA and (PEMA)0.85/(ZnO)0.15 nanocomposite films deposited by spray pyrolysis technique on ITO substrate

    NASA Astrophysics Data System (ADS)

    Thakur, Anjna; Thakur, Priya; Yadav, Kamlesh

    2016-05-01

    In this paper, poly (ethyl methacrylate) (PEMA) and (PEMA)0.85/(ZnO)0.15 nanocomposite films for 2, 3, 4 and 5 minutes have been deposited by spray pyrolysis technique on indium tin oxide (ITO) coated substrate. The effect of thickness of the film on the morphological and optical properties of PEMA and (PEMA)0.85/(ZnO)0.15 nanocomposite films are studied. The morphological and optical properties of pure PEMA and (PEMA)0.85/(ZnO)0.15 nanocomposite films are compared. The field emission scanning electron microscopy (FESEM) shows that as the thickness of film increases, uniformity of films increases. It is found from UV-Visible spectra that the energy band gap decreases with increasing the deposition time and refractive index increases with increasing the thickness of the film. The band gap of the nanocomposites is found less than the pure polymer film and opposite trend is observed for refractive index. The optical absorption of PEMA/ZnO nanocomposite films is higher than pure PEMA film. The thickness of the nanocomposite film plays a significant role in the tunability of the optical properties.

  8. Patterned submicrometer-thick optical polarizing films using stretched silver island multilayers

    NASA Astrophysics Data System (ADS)

    Baba, Kazutaka; Sato, Yoshinori; Yoshitake, Tsutomu; Miyagi, Mitsunobu

    2000-04-01

    We demonstrate a patterned submicrometer-thick optical polarizing film in which non-polarizing areas are formed where the light transmits insensitively to polarization. The polarizing film is fabricated by stretching a silver island multilayer consisting of thin glass layers and silver island layers composed of silver nanoclusters of high density. By stretching the silver island multilayer at a temperature higher than the glass annealing point, the silver islands are elongated along the stretching direction and the large optical anisotropy is induced in the silver island multilayer. In this optical polarizing film, the non- polarizing areas can be easily formed by laser irradiation with high power density as the optical anisotorpy is reduce das the elongated silver islands become spherical ones from the thermal deformation in the irradiated area. We have successfully patterned the optical polarizing films fabricated for the wavelength of 800 nm by laser writing with a 1 W-class carbon dioxide laser. In order to confirm that the optical anisotropy is reduced in the laser written are, the optical characteristics of that area have been measured. In most commercially available optical polarizers including a polarization beam splitter and various polarizing prisms, it is difficult to form the transparent non-polarizing areas. Therefore, the demonstrated patterned optical polarizing films are useful for switchable spatial modulators and filters.

  9. Multi-spectral optical absorption in substrate-free nanowire arrays

    SciTech Connect

    Zhang, Junpeng; Chia, Andrew; Boulanger, Jonathan; LaPierre, Ray; Dhindsa, Navneet; Khodadad, Iman; Saini, Simarjeet

    2014-09-22

    A method is presented of fabricating gallium arsenide (GaAs) nanowire arrays of controlled diameter and period by reactive ion etching of a GaAs substrate containing an indium gallium arsenide (InGaP) etch stop layer, allowing the precise nanowire length to be controlled. The substrate is subsequently removed by selective etching, using the same InGaP etch stop layer, to create a substrate-free GaAs nanowire array. The optical absorptance of the nanowire array was then directly measured without absorption from a substrate. We directly observe absorptance spectra that can be tuned by the nanowire diameter, as explained with rigorous coupled wave analysis. These results illustrate strong optical absorption suitable for nanowire-based solar cells and multi-spectral absorption for wavelength discriminating photodetectors. The solar-weighted absorptance above the bandgap of GaAs was 94% for a nanowire surface coverage of only 15%.

  10. Ultrasensitive optical absorption in graphene based on bound states in the continuum

    PubMed Central

    Zhang, Mingda; Zhang, Xiangdong

    2015-01-01

    We have designed a sphere-graphene-slab structure so that the electromagnetic wave can be well confined in the graphene due to the formation of a bound state in a continuum (BIC) of radiation modes. Based on such a bound state, we have realized strong optical absorption in the monolayer graphene. Such a strong optical absorption exhibits many advantages. It is ultrasensitive to the wavelength because the Q factor of the absorption peak can be more than 2000. By taking suitable BICs, the selective absorption for S and P waves has not only been realized, but also all-angle absorption for the S and P waves at the same time has been demonstrated. We have also found that ultrasensitive strong absorptions can appear at any wavelength from mid-infrared to far-infrared band. These phenomena are very beneficial to biosensing, perfect filters and waveguides. PMID:25652437

  11. Experimental measurements of the spectral absorption coefficient of pure fused silica optical fibers.

    PubMed

    Moore, Travis J; Jones, Matthew R

    2015-02-20

    Knowledge of the spectral absorption coefficient of fused silica optical fibers is important in modeling heat transfer in the processes and applications in which these fibers are used. An experimental method used to measure the spectral absorption coefficient of optical fibers is presented. Radiative energy from a blackbody radiator set at different temperatures is directed through the optical fibers and into an FTIR spectrometer. Spectral instrument response functions are calculated for different fiber lengths. The ratios of the slopes of the instrument response functions for the different lengths of fibers are used to solve for the spectral absorption coefficient of the fibers. The spectral absorption coefficient of low OH pure fused silica optical fibers is measured between the wavelengths 1.5 and 2.5 μm. PMID:25968202

  12. AEROSOL OPTICAL PROPERTIES AND BIOGENIC SOA: EFFECT ON HYGROSCOPIC PROPERTIES AND LIGHT ABSORPTION

    EPA Science Inventory

    This study will provide a comprehensive characterization of optical properties of biogenic SOA and their sensitivity to anthropogenic influence. Several parameters critical for climate modeling, such as absorption cross-section, single scattering albedo and sensitivity to R...

  13. Quantification of biofilm thickness using a swept source based optical coherence tomography system

    NASA Astrophysics Data System (ADS)

    Ratheesh Kumar, M.; Murukeshan, V. M.; Seah, L. K.; Shearwood, C.

    2015-07-01

    Optical coherence tomography (OCT) is a non-invasive, non-contact optical measurement and imaging technique that relies on low coherence interferometry. Apart from bio-imaging applications, the applicability of OCT can be extended to metrological investigations because of the inherent capability of optical interferometry to perform precise measurement with high sensitivity. In this paper, we demonstrate the feasibility of OCT for the measurement of the refractive index and thickness of bacterial biofilm structures grown in a flow cell. In OCT, the depth profiles are constructed by measuring the magnitude and time delay of back reflected light from the scattering sites by means of optical interferometry. The optical distance between scattering points can be obtained by measuring the separation between the point spread functions (PSF) at the respective points in the A-scan data. The refractive index of the biofilm is calculated by measuring the apparent shift in the position of the PSF corresponding to a reference surface, caused by the biofilm growth. In our experiment, the base layer of the flow cell is used as the reference surface. It is observed that the calculated refractive index of the biofilm is close to that of water, and agrees well with the previously reported value. Finally, the physical thickness of the biofilm is calculated by dividing the optical path length by the calculated value of refractive index.

  14. Application of maximum-likelihood estimation in optical coherence tomography for nanometer-class thickness estimation

    NASA Astrophysics Data System (ADS)

    Huang, Jinxin; Yuan, Qun; Tankam, Patrice; Clarkson, Eric; Kupinski, Matthew; Hindman, Holly B.; Aquavella, James V.; Rolland, Jannick P.

    2015-03-01

    In biophotonics imaging, one important and quantitative task is layer-thickness estimation. In this study, we investigate the approach of combining optical coherence tomography and a maximum-likelihood (ML) estimator for layer thickness estimation in the context of tear film imaging. The motivation of this study is to extend our understanding of tear film dynamics, which is the prerequisite to advance the management of Dry Eye Disease, through the simultaneous estimation of the thickness of the tear film lipid and aqueous layers. The estimator takes into account the different statistical processes associated with the imaging chain. We theoretically investigated the impact of key system parameters, such as the axial point spread functions (PSF) and various sources of noise on measurement uncertainty. Simulations show that an OCT system with a 1 μm axial PSF (FWHM) allows unbiased estimates down to nanometers with nanometer precision. In implementation, we built a customized Fourier domain OCT system that operates in the 600 to 1000 nm spectral window and achieves 0.93 micron axial PSF in corneal epithelium. We then validated the theoretical framework with physical phantoms made of custom optical coatings, with layer thicknesses from tens of nanometers to microns. Results demonstrate unbiased nanometer-class thickness estimates in three different physical phantoms.

  15. Discrepancy between ambient annealing and H+ implantation in optical absorption of ZnO

    NASA Astrophysics Data System (ADS)

    Lv, Jinpeng; Li, Chundong

    2016-05-01

    The discrepancy between sub-bandgap absorption in ZnO induced by thermal annealing and H+ implantation is investigated in this study for the first time. Results indicate that nonreductive annealing-induced optical absorption is independent of annealing ambient, and can be assigned to VO, whereas the absorption centers caused by H+ implantation and H2 annealing are primarily associated with VO and ionized Zni.

  16. Optical absorption in 3D topological insulator Bi2Te3 with applications to THz detectors (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Sengupta, Parijat; Bellotti, Enrico

    2015-08-01

    Topological insulators (TI) are a new class of materials that have an energy gap in bulk but possess gapless states bound to the sample surface or edge that have been theoretically predicted and experimentally observed [1]. The topological state in Bi2Te3 is characterized by a linear dispersion and a Dirac cone at the Γpoint. The optical absorption on the surface of a TI is given by the standard graphene-like απ/2 when a linear dispersion is assumed. Realistically, at k-points away from Γ, higher order cubic terms in k that represent the underlying hexagonal symmetry [2] of the crystal dominate and give rise to warping of bands. The optical absorption of a ferromagnetic coated gapped 3D TI film with warping terms considered is longer απ/2 but significantly modified. We demonstrate, by using wave functions from a continuum-Hamiltonian and Fermi-golden rule, the absorption spectrum on the surface of a TI as a function of the chemical potential, film-thickness and incident photon energy. A linear response theory based calculation is also performed using the Kubo formula to determine the longitudinal optical conductivity whose real part gives absorption as a function of photon frequency. The absorption in materials with Dirac fermions which is significantly higher than in normal THz detectors [3] can be further modulated in a TI by explicitly including the warping term making them highly efficient and tunable photodetectors. [1] M.Hasan and C.Kane, Rev.Mod.Phys. 82, 3045(2010) [2] L.Fu, Phys.Rev.Lett.103, 266801(2009) [3] X.Zhang et al., Phys. Rev B, 82, 245107(2010)

  17. Wolf-Rayet optically thick winds with Alfvén waves

    NASA Astrophysics Data System (ADS)

    Keller, G. R.; Jatenco-Pereira, V.

    2010-08-01

    The Wolf-Rayet (WR) stars are hot luminous objects which are suffering an extreme mass loss via a continuous stellar wind. The high values of mass loss rates and high terminal velocities of the WR stellar winds constitute a challenge to the theories of radiation driven winds. Several authors incorporated magnetic forces to the line driven mechanism in order to explain these characteristics of the wind. Observations indicate that the WR stellar winds may reach, at the photosphere, velocities of the order of the terminal values, which means that an important part of the wind acceleration occurs at the optically thick region. The aim of this study is to analyze a model in which the wind in a WR star begins to be accelerated in the optically thick part of the wind. We used as initial conditions stellar parameters taken from the literature and solved the energy, mass and momentum equations. We demonstrate that the acceleration only by radiative forces is prevented by the general behavior of the opacities. Combining radiative forces plus a flux of Alfvén waves, we found in the simulations a fast drop in the wind density profile which strongly reduces the extension of the optically thick region and the wind becomes optically thin too close its base. The understanding how the WR wind initiate is still an open issue.

  18. Effect of UV Absorption on Fabrication of Fiber-Optic Bragg Gratings

    NASA Technical Reports Server (NTRS)

    Wang, Ying; Sharma, Anup; Burdine, Robert (Technical Monitor)

    2000-01-01

    UV light is used to fabricate fiber-optic gratings also heats up the fiber due to absorption by either the fiber-buffer, fiber-cladding, doped with titania or a thin coating of paint. Significant enhancement in the rate of grating fabrication is observed due to UV light absorption.

  19. OPTICAL ABSORPTION AND PHOTOLUMINESCENCE IN PRISTINE AND PHOTOPOLYMERIZED C60 SOLID FILMS

    EPA Science Inventory

    The optical absorption (OA) and photoluminescence (PL) spectra of pristine, oxygen-free C60 films in the vicinity of the absorption edge across the highest-occupied-molecular-orbital to lowest-unoccupied-molecular-orbital (HOMO-LUMO) gap are studied to elucidate the nature of the...

  20. Differential optical absorption techniques for diagnostics of coal gasification. Technical progress report, April-June 1983

    SciTech Connect

    Not Available

    1983-08-01

    The application of differential optical absorption (DOA) techniques for the in-situ determination of the chemical composition of coal gasification process streams is investigated. Absorption spectra of relevant molecular species and the temperature and pressure effects on DOA-determined spectral characteristics of these species will be determined and cataloged. A system will be configured, assembled, and tested. 10 references, 1 figure.

  1. Non-contact optical measurement of lens capsule thickness during simulated accommodation

    NASA Astrophysics Data System (ADS)

    Ziebarth, Noel; Manns, Fabrice; Acosta, Ana-Carolina; Parel, Jean-Marie

    2005-04-01

    Purpose: To non-invasively measure the thickness of the anterior and posterior lens capsule, and to determine if it significantly changes during accommodation. Methods: Anterior and posterior capsule thickness was measured on post-mortem lenses using a non-contact optical system using a focus-detection technique. The optical system uses a 670nm laser beam delivered to a single-mode fiber coupler. The output of the fiber coupler is focused on the tissue surface using an aspheric lens (NA=0.68) mounted on a translation stage with a motorized actuator. Light reflected from the sample surface is collected by the fiber coupler and sent to a photoreceiver connected to a computer-controlled data acquisition system. Optical intensity peaks are detected when the aspheric lens is focused on the capsule boundaries. The capsule thickness is equal to the distance traveled between two peaks multiplied by the capsule refractive index. Anterior and posterior lens capsule thickness measurements were performed on 18 cynomolgus (age average: 6+/-1 years, range: 4-7 years) eyes, 1 rhesus (age: 2 years) eye, and 12 human (age average: 65+/-16, range: 47-92) eyes during simulated accommodation. The mounted sample was placed under the focusing objective of the optical system so that the light was incident on the center pole. Measurements were taken of the anterior lens capsule in the unstretched and the stretched 5mm states. The lens was flipped, and the same procedure was performed for the posterior lens capsule. Results: The precision of the optical system was determined to be +/-0.5um. The resolution is 4um and the sensitivity is 52dB. The human anterior lens capsule thickness was 6.0+/-1.2um unstretched and 4.9+/-0.9um stretched (p=0.008). The human posterior lens capsule was 5.7+/-1.2um unstretched and 5.7+/-1.4um stretched (p=0.974). The monkey anterior lens capsule thickness was 5.9+/-1.9um unstretched and 4.8+/-1.0um stretched (p=0.002). The monkey posterior lens capsule was 5

  2. Automatic airway wall segmentation and thickness measurement for long-range optical coherence tomography images

    NASA Astrophysics Data System (ADS)

    Qi, Li; Huang, Shenghai; Heidari, Andrew E.; Dai, Cuixia; Zhu, Jiang; Zhang, Xuping; Chen, Zhongping

    2016-03-01

    We present an automatic segmentation method for delineation and quantitative thickness measurement of multiple layers in endoscopic airway optical coherence tomography (OCT) images. The boundaries of the mucosa and the sub-mucosa layers were extracted using a graph-theory-based dynamic programming algorithm. The algorithm was tested with pig airway OCT images acquired with a custom built long range endoscopic OCT system. The performance of the algorithm was demonstrated by cross-validation between auto and manual segmentation experiments. Quantitative thicknesses changes in the mucosal layers are obtained automatically for smoke inhalation injury experiments.

  3. CHOROIDAL THICKNESS IN PATIENTS WITH DIABETIC RETINOPATHY ANALYZED BY SPECTRAL-DOMAIN OPTICAL COHERENCE TOMOGRAPHY

    PubMed Central

    REGATIERI, CAIO V.; BRANCHINI, LAUREN; CARMODY, JILL; FUJIMOTO, JAMES G.; DUKER, JAY S.

    2012-01-01

    Purpose This study was designed to examine choroidal thickness in patients with diabetes using spectral-domain optical coherence tomography. Methods Forty-nine patients (49 eyes) with diabetes and 24 age-matched normal subjects underwent high-definition raster scanning using spectral-domain optical coherence tomography with frame enhancement software. Patients with diabetes were classified into 3 groups: 11 patients with mild or moderate nonproliferative diabetic retinopathy and no macular edema, 18 patients with nonproliferative diabetic retinopathy and diabetic macular edema, and 20 patients with treated proliferative diabetic retinopathy and no diabetic macular edema (treated proliferative diabetic retinopathy). Choroidal thickness was measured from the posterior edge of the retinal pigment epithelium to the choroid/sclera junction at 500-μm intervals up to 2,500 μm temporal and nasal to the fovea. Results Reliable measurements of choroidal thickness were obtainable in 75.3% of eyes examined. Mean choroidal thickness showed a pattern of thinnest choroid nasally, thickening in the subfoveal region, and thinning again temporally in normal subjects and patients with diabetes. Mean subfoveal choroidal thickness was thinner in patients with diabetic macular edema (63.3 μm, 27.2%, P < 0.05) or treated proliferative diabetic retinopathy (69.6 μm, 30.0%, P < 0.01), compared with normal subjects. There was no difference between nonproliferative diabetic retinopathy and normal subjects. Conclusion Choroidal thickness is altered in diabetes and may be related to the severity of retinopathy. Presence of diabetic macular edema is associated with a significant decrease in the choroidal thickness. PMID:22374157

  4. Unified theory of electron-phonon renormalization and phonon-assisted optical absorption

    NASA Astrophysics Data System (ADS)

    Patrick, Christopher E.; Giustino, Feliciano

    2014-09-01

    We present a theory of electronic excitation energies and optical absorption spectra which incorporates energy-level renormalization and phonon-assisted optical absorption within a unified framework. Using time-independent perturbation theory we show how the standard approaches for studying vibronic effects in molecules and those for addressing electron-phonon interactions in solids correspond to slightly different choices for the non-interacting Hamiltonian. Our present approach naturally leads to the Allen-Heine theory of temperature-dependent energy levels, the Franck-Condon principle, the Herzberg-Teller effect and to phonon-assisted optical absorption in indirect band gap materials. In addition, our theory predicts sub-gap phonon-assisted optical absorption in direct gap materials, as well as an exponential edge which we tentatively assign to the Urbach tail. We also consider a semiclassical approach to the calculation of optical absorption spectra which simultaneously captures energy-level renormalization and phonon-assisted transitions and is especially suited to first-principles electronic structure calculations. We demonstrate this approach by calculating the phonon-assisted optical absorption spectrum of bulk silicon.

  5. Studying Velocity Turbulence from Doppler-broadened Absorption Lines: Statistics of Optical Depth Fluctuations

    SciTech Connect

    Lazarian, A.; Pogosyan, D.

    2008-10-10

    We continue our work on developing techniques for studying turbulence with spectroscopic data. We show that Doppler-broadened absorption spectral lines, in particular, saturated absorption lines, can be used within the framework of the previously introduced technique termed the velocity coordinate spectrum (VCS). The VCS relates the statistics of fluctuations along the velocity coordinate to the statistics of turbulence; thus, it does not require spatial coverage by sampling directions in the plane of the sky. We consider lines with different degree of absorption and show that for lines of optical depth less than one, our earlier treatment of the VCS developed for spectral emission lines is applicable, if the optical depth is used instead of intensity. This amounts to correlating the logarithms of absorbed intensities. For larger optical depths and saturated absorption lines, we show that only wings of the line are available for the analysis. In terms of the VCS formalism, this results in introducing an additional window, whose size decreases with the increase of the optical depth. As a result, strongly saturated absorption lines only carry the information about the small-scale turbulence. Nevertheless, the contrast of the fluctuations corresponding to the small-scale turbulence increases with the increase of the optical depth, which provides advantages for studying turbulence by combining lines with different optical depths. By combining different absorption lines one can develop a tomography of the turbulence in the interstellar gas in all its complexity.

  6. Influence of electron transport layer thickness on optical properties of organic light-emitting diodes

    SciTech Connect

    Liu, Guohong; Liu, Yong; Li, Baojun; Zhou, Xiang

    2015-06-07

    We investigate experimentally and theoretically the influence of electron transport layer (ETL) thickness on properties of typical N,N′-diphenyl-N,N′-bis(1-naphthyl)-[1,1′-biphthyl]-4,4′-diamine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq{sub 3}) heterojunction based organic light-emitting diodes (OLEDs), where the thickness of ETL is varied to adjust the distance between the emitting zone and the metal electrode. The devices showed a maximum current efficiency of 3.8 cd/A when the ETL thickness is around 50 nm corresponding to an emitter-cathode distance of 80 nm, and a second maximum current efficiency of 2.6 cd/A when the ETL thickness is around 210 nm corresponding to an emitter-cathode distance of 240 nm. We adopt a rigorous electromagnetic approach that takes parameters, such as dipole orientation, polarization, light emitting angle, exciton recombination zone, and diffusion length into account to model the optical properties of devices as a function of varying ETL thickness. Our simulation results are accurately consistent with the experimental results with a widely varying thickness of ETL, indicating that the theoretical model may be helpful to design high efficiency OLEDs.

  7. Two-photon absorption and optical-limiting properties of a novel organic compound

    NASA Astrophysics Data System (ADS)

    Ye, Lihua; Zhang, Junxiang; Cui, Yiping; Li, Zhenhua; He, Anzhi

    2002-09-01

    The two-photon absorption and applications become the hot points in the recent photoelectronic material research field. The two-photon absorption materials can be applied to many fields such as up-conversion lasing, optical limiting, optical stabilization, three-dimension optical storage, three-dimension micro-machining, et al. Especially studies of optical power limiting have become more interesting to the research community because of the need for automatic protection of optical sensors against intense laser radiation. Here we report the observation of the TPA and optical power limiting property of a novel double conjugated molecule DSBDR1 in solution. The linear absorption spectral is observed using a scanning spectrophotometer. Using Nd:YAG laser pulse as exciting laser, the incident pulse energy and the transmitted pulse energy are respectively recorded by an energy meter. Then we obtain the nonlinear absorption coefficient of the novel double conjugated molecule in THF. Figures show that the molecule exhibts the large TPA cross-section and excellent optical limiting at 1064 nm. The nonlinear absorption mechanism of the novel organic compound is finally analyzed.

  8. Extension and statistical analysis of the GACP aerosol optical thickness record

    NASA Astrophysics Data System (ADS)

    Geogdzhayev, Igor V.; Mishchenko, Michael I.; Li, Jing; Rossow, William B.; Liu, Li; Cairns, Brian

    2015-10-01

    The primary product of the Global Aerosol Climatology Project (GACP) is a continuous record of the aerosol optical thickness (AOT) over the oceans. It is based on channel-1 and -2 radiance data from the Advanced Very High Resolution Radiometer (AVHRR) instruments flown on successive National Oceanic and Atmospheric Administration (NOAA) platforms. We extend the previous GACP dataset by four years through the end of 2009 using NOAA-17 and -18 AVHRR radiances recalibrated against MODerate resolution Imaging Spectroradiometer (MODIS) radiance data, thereby making the GACP record almost three decades long. The temporal overlap of over three years of the new NOAA-17 and the previous NOAA-16 record reveals an excellent agreement of the corresponding global monthly mean AOT values, thereby confirming the robustness of the vicarious radiance calibration used in the original GACP product. The temporal overlap of the NOAA-17 and -18 instruments is used to introduce a small additive adjustment to the channel-2 calibration of the latter resulting in a consistent record with increased data density. The Principal Component Analysis (PCA) of the newly extended GACP record shows that most of the volcanic AOT variability can be isolated into one mode responsible for ~ 12% of the total variance. This conclusion is confirmed by a combined PCA analysis of the GACP, MODIS, and Multi-angle Imaging SpectroRadiometer (MISR) AOTs during the volcano-free period from February 2000 to December 2009. We show that the modes responsible for the tropospheric AOT variability in the three datasets agree well in terms of correlation and spatial patterns. A previously identified negative AOT trend which started in the late 1980s and continued into the early 2000s is confirmed. Its magnitude and duration indicate that it was caused by changes in tropospheric aerosols. The latest multi-satellite segment of the GACP record shows that this trend tapered off, with no noticeable AOT change after 2002. This

  9. Extension and Statistical Analysis of the GACP Aerosol Optical Thickness Record.

    NASA Technical Reports Server (NTRS)

    Geogdzhayev, Igor V.; Mishchenko, Michael I.; Li, Jing; Rossow, William B.; Liu, Li; Cairns, Brian

    2015-01-01

    The primary product of the Global Aerosol Climatology Project (GACP) is a continuous record of the aerosol optical thickness (AOT) over the oceans. It is based on channel-1 and -2 radiance data from the Advanced Very High Resolution Radiometer (AVHRR) instruments flown on successive National Oceanic and Atmospheric Administration (NOAA) platforms. We extend the previous GACP dataset by four years through the end of 2009 using NOAA-17 and -18 AVHRR radiances recalibrated against MODerate resolution Imaging Spectroradiometer (MODIS) radiance data, thereby making the GACP record almost three decades long. The temporal overlap of over three years of the new NOAA-17 and the previous NOAA-16 record reveals an excellent agreement of the corresponding global monthly mean AOT values, thereby confirming the robustness of the vicarious radiance calibration used in the original GACP product. The temporal overlap of the NOAA-17 and -18 instruments is used to introduce a small additive adjustment to the channel-2 calibration of the latter resulting in a consistent record with increased data density. The Principal Component Analysis (PCA) of the newly extended GACP record shows that most of the volcanic AOT variability can be isolated into one mode responsible for 12% of the total variance. This conclusion is confirmed by a combined PCA analysis of the GACP, MODIS, andMulti-angle Imaging SpectroRadiometer (MISR) AOTs during the volcano-free period fromFebruary 2000 to December 2009.We show that the modes responsible for the tropospheric AOT variability in the three datasets agree well in terms of correlation and spatial patterns. A previously identified negative AOT trend which started in the late 1980s and continued into the early 2000s is confirmed. Its magnitude and duration indicate that it was caused by changes in tropospheric aerosols. The latest multi-satellite segment of the GACP record shows that this trend tapered off, with no noticeable AOT change after 2002. This

  10. Extension, validation, and analysis of the multi-decadal GACP/AVHRR aerosol optical thickness record

    NASA Astrophysics Data System (ADS)

    Mishchenko, M. I.; Geogdzhayev, I. V.

    2015-12-01

    The main product of the Global Aerosol Climatology Project (GACP) is a continuous record of the aerosol optical thickness (AOT) over the oceans based on channel-1 and -2 radiances from successively flown AVHRR instruments. We extend the previous GACP dataset by four years though the end of 2009 using NOAA-17 and -18 AVHRR data recalibrated against MODIS radiances according to Heidinger et al. (2010), thereby making the GACP record almost three decades long. The temporal overlap of the new NOAA-17 and the previous NOAA-16 record reveals an excellent agreement of the corresponding global monthly mean AOT values, thereby confirming the robustness of the vicarious radiance calibration used in the original GACP product. A comprehensive set of monthly mean AOT data from coastal and insular AERONET stations was used to validate GACP retrievals for the period 1995-2009. To put the GACP performance in broader perspective, we also compared AERONET and MODIS Aqua level-2 data for 2003-2009 using the same methodology. Monthly mean AOTs from the two over-the-ocean satellite datasets are well correlated with the ground-based values, the correlation coefficients being 0.81-0.85 for GACP and 0.74-0.79 for MODIS. Regression analyses demonstrated that the GACP mean AOTs are approximately 17%-27% lower than the AERONET values on average, while the MODIS mean AOTs are 5%-25% higher. The previously identified negative trend in the global GACP AOT which started in the late 1980s and continued into the early 2000s was confirmed. Its magnitude and duration indicate that it was caused by changes in tropospheric aerosols. The latest multi-satellite segment of the GACP record shows that this trend tapered off, with no noticeable AOT change after 2002. This result is consistent with the MODIS and MISR AOT records as well as with the recent gradual reversal from brightening to dimming revealed by surface flux measurements in many aerosol producing regions. Thus the robustness of the GACP

  11. A novel technique for estimating aerosol optical thickness trends using meteorological parameters

    NASA Astrophysics Data System (ADS)

    Emetere, Moses E.; Akinyemi, M. L.; Akin-Ojo, O.

    2016-02-01

    Estimating aerosol optical thickness (AOT) over regions can be tasking if satellite data set over such region is very scanty. Therefore a technique whose application captures real-time events is most appropriate for adequate monitoring of risk indicators. A new technique i.e. arithmetic translation of pictorial model (ATOPM) was developed. The ATOPM deals with the use mathematical expression to compute other meteorological parameters obtained from satellite or ground data set. Six locations within 335 × 230 Km2 area of a selected portion of Nigeria were chosen and analyzed -using the meteorological data set (1999-2012) and MATLAB. The research affirms the use of some parameters (e.g. minimum temperature, cloud cover, relative humidity and rainfall) to estimate the aerosol optical thickness. The objective of the paper was satisfied via the use of other meteorological parameters to estimate AOT when the satellite data set over an area is scanty.

  12. Absorption Coefficient Imaging by Near-Field Scanning Optical Microscopy in Bacteria

    NASA Astrophysics Data System (ADS)

    de Paula, Ana M.; Chaves, Claudilene R.; Silva, Haroldo B.; Weber, Gerald

    2003-06-01

    We present a method for obtaining a position-dependent absorption coefficient from near-field scanning optical transmission microscopy. We show that the optical transmission intensity can be combined with the topography, resulting into an absorption coefficient that simplifies the analysis of different materials within a sample. The method is tested with the dye rhodamine 6G, and we show some analysis in biological samples such as bacteria Klebsiella pneumoniae and Pseudomonas aeruginosa . The calculated absorption coefficient images show important details of the bacteria, in particular for P. aeruginosa , in which membrane vesicles are clearly seen.

  13. Systems having optical absorption layer for mid and long wave infrared and methods for making the same

    SciTech Connect

    Kuzmenko, Paul J

    2013-10-01

    An optical system according to one embodiment includes a substrate; and an optical absorption layer coupled to the substrate, wherein the optical absorption layer comprises a layer of diamond-like carbon, wherein the optical absorption layer absorbs at least 50% of mid wave infrared light (3-5 .mu.m wavelength) and at least 50% of long wave infrared light (8-13 .mu.m wavelength). A method for applying an optical absorption layer to an optical system according to another embodiment includes depositing a layer of diamond-like carbon of an optical absorption layer above a substrate using plasma enhanced chemical vapor deposition, wherein the optical absorption layer absorbs at least 50% of mid wave infrared light (3-5 .mu.m wavelength) and at least 50% of long wave infrared light (8-13 .mu.m wavelength). Additional systems and methods are also presented.

  14. Macular Microcysts in Mitochondrial Optic Neuropathies: Prevalence and Retinal Layer Thickness Measurements

    PubMed Central

    Carbonelli, Michele; La Morgia, Chiara; Savini, Giacomo; Cascavilla, Maria Lucia; Borrelli, Enrico; Chicani, Filipe; do V. F. Ramos, Carolina; Salomao, Solange R.; Parisi, Vincenzo; Sebag, Jerry; Bandello, Francesco; Sadun, Alfredo A.; Carelli, Valerio; Barboni, Piero

    2015-01-01

    Purpose To investigate the thickness of the retinal layers and to assess the prevalence of macular microcysts (MM) in the inner nuclear layer (INL) of patients with mitochondrial optic neuropathies (MON). Methods All patients with molecularly confirmed MON, i.e. Leber’s Hereditary Optic Neuropathy (LHON) and Dominant Optic Atrophy (DOA), referred between 2010 and 2012 were enrolled. Eight patients with MM were compared with two control groups: MON patients without MM matched by age, peripapillary retinal nerve fiber layer (RNFL) thickness, and visual acuity, as well as age-matched controls. Retinal segmentation was performed using specific Optical coherence tomography (OCT) software (Carl Zeiss Meditec). Macular segmentation thickness values of the three groups were compared by one-way analysis of variance with Bonferroni post hoc corrections. Results MM were identified in 5/90 (5.6%) patients with LHON and 3/58 (5.2%) with DOA. The INL was thicker in patients with MON compared to controls regardless of the presence of MM [133.1±7μm vs 122.3±9μm in MM patients (p<0.01) and 128.5±8μm vs. 122.3±9μm in no-MM patients (p<0.05)], however the outer nuclear layer (ONL) was thicker in patients with MM (101.4±1mμ) compared to patients without MM [77.5±8mμ (p<0.001)] and controls [78.4±7mμ (p<0.001)]. ONL thickness did not significantly differ between patients without MM and controls. Conclusion The prevalence of MM in MON is low (5-6%), but associated with ONL thickening. We speculate that in MON patients with MM, vitreo-retinal traction contributes to the thickening of ONL as well as to the production of cystic spaces. PMID:26047507

  15. Designing Ligand-Enhanced Optical Absorption of Thiolated Gold Nanoclusters

    SciTech Connect

    Sementa, Luca; Barcaro, Giovanni; Dass, Amala; Stener, Mauro; Fortunelli, Alessandro

    2015-05-07

    The optical spectra of thiolated Au25(SR)18/Au23(SR)16 clusters with different R residues are investigated via TDDFT simulations. Significant enhancements in the optical region and effective electron delocalization are simultaneously achieved by tuning the ligands' steric hindrance and electronic conjugating features, producing a resonance phenomenon between the Au–S core motif and the ligand fragments.

  16. Optical path switching based differential absorption radiometry for substance detection

    NASA Technical Reports Server (NTRS)

    Sachse, Glen W. (Inventor)

    2003-01-01

    An optical path switch divides sample path radiation into a time series of alternating first polarized components and second polarized components. The first polarized components are transmitted along a first optical path and the second polarized components along a second optical path. A first gasless optical filter train filters the first polarized components to isolate at least a first wavelength band thereby generating first filtered radiation. A second gasless optical filter train filters the second polarized components to isolate at least a second wavelength band thereby generating second filtered radiation. A beam combiner combines the first and second filtered radiation to form a combined beam of radiation. A detector is disposed to monitor magnitude of at least a portion of the combined beam alternately at the first wavelength band and the second wavelength band as an indication of the concentration of the substance in the sample path.

  17. Optical path switching based differential absorption radiometry for substance detection

    NASA Technical Reports Server (NTRS)

    Sachse, Glen W. (Inventor)

    2005-01-01

    An optical path switch divides sample path radiation into a time series of alternating first polarized components and second polarized components. The first polarized components are transmitted along a first optical path and the second polarized components along a second optical path. A first gasless optical filter train filters the first polarized components to isolate at least a first wavelength band thereby generating first filtered radiation. A second gasless optical filter train filters the second polarized components to isolate at least a second wavelength band thereby generating second filtered radiation. A beam combiner combines the first and second filtered radiation to form a combined beam of radiation. A detector is disposed to monitor magnitude of at least a portion of the combined beam alternately at the first wavelength band and the second wavelength band as an indication of the concentration of the substance in the sample path.

  18. Influence of laser radiation on induced absorption spectra of pure quartz glass optical fibers

    NASA Astrophysics Data System (ADS)

    Dianov, Y. M.; Karpechev, V. N.; Korniyenko, L. S.; Rybaltovskiy, A. O.; Chernov, P. V.

    1986-01-01

    The influence of laser radiation on radiation color centers and their associated induced absorption in the spectra of irradiated glass optical fibers is investigated. The glass fiber specimens employed had 40 to 50 micron diameter cores made of day pure quartz glass. The optical fibers were 6 to 20 meters long, produced by chemical precipitation from the gaseous phase and clad with reflecting borosilicate glass. Spectral measurements of the induced absorption in the ultraviolet region were made using an FEU-71 photodetector and a sounding radiation source. The stimulated laser emission power in the cross section of the optical fiber was measured by a photodiode; the absorption spectra were recorded by the fragment method. Eight different types of color centers were isolated whose bands cover practically the entire observed absorption spectra. The connection found between color centers and a 340 nm absorption band, and color center with absorption in the infrared band, indicate that absorption in the ultraviolet band can have a significant influence on the amount of induced absorption in the infrared band.

  19. influence of film thickness on optical constants of antimony-based bismuth-doped super-resolution mask layer

    NASA Astrophysics Data System (ADS)

    Lu, Xinmiao; Wu, Yiqun; Wang, Yang; Wei, Jinsong

    As the demand for ultrahigh density information storage continues to grow, recording mark size of several tens nanometer which is smaller than the optical diffraction limit is required in optical memory. Functional film super-resolution technique is one of practical approaches to overcome the optical diffraction limit. Optical constants are important parameters to optical films as super-resolution masks. In this paper, the influence of film thickness on optical constants of antimony-based bismuth-doped super-resolution mask layer is investigated. The structure of the samples with different thickness was studied by X-ray diffraction. The transmission spectrum was measured by spectrophotometry. The optical constants of the films in the range of 300-800 nm were measured by spectroscopic ellipsometry. The results show that the structure of the film transforms from amorphous state to crystal state when the thickness increases from 7 nm to 300 nm. In the range of 300-800 nm, the refractive index and extinction coefficient increase with increasing wavelength. The transmission decreases rapidly when the thickness increases from 7 nm to 30 nm. The influences of film thickness on optical constants are more significant in the thickness range of 7-50 nm than that in the thickness above 50 nm.

  20. Correction of optical absorption and scattering variations in laser speckle rheology measurements

    PubMed Central

    Hajjarian, Zeinab; Nadkarni, Seemantini K.

    2014-01-01

    Laser Speckle Rheology (LSR) is an optical technique to evaluate the viscoelastic properties by analyzing the temporal fluctuations of backscattered speckle patterns. Variations of optical absorption and reduced scattering coefficients further modulate speckle fluctuations, posing a critical challenge for quantitative evaluation of viscoelasticity. We compare and contrast two different approaches applicable for correcting and isolating the collective influence of absorption and scattering, to accurately measure mechanical properties. Our results indicate that the numerical approach of Monte-Carlo ray tracing (MCRT) reliably compensates for any arbitrary optical variations. When scattering dominates absorption, yet absorption is non-negligible, diffusing wave spectroscopy (DWS) formalisms perform similar to MCRT, superseding other analytical compensation approaches such as Telegrapher equation. The computational convenience of DWS greatly simplifies the extraction of viscoelastic properties from LSR measurements in a number of chemical, industrial, and biomedical applications. PMID:24663983

  1. Correction of optical absorption and scattering variations in Laser Speckle Rheology measurements.

    PubMed

    Hajjarian, Zeinab; Nadkarni, Seemantini K

    2014-03-24

    Laser Speckle Rheology (LSR) is an optical technique to evaluate the viscoelastic properties by analyzing the temporal fluctuations of backscattered speckle patterns. Variations of optical absorption and reduced scattering coefficients further modulate speckle fluctuations, posing a critical challenge for quantitative evaluation of viscoelasticity. We compare and contrast two different approaches applicable for correcting and isolating the collective influence of absorption and scattering, to accurately measure mechanical properties. Our results indicate that the numerical approach of Monte-Carlo ray tracing (MCRT) reliably compensates for any arbitrary optical variations. When scattering dominates absorption, yet absorption is non-negligible, diffusing wave spectroscopy (DWS) formalisms perform similar to MCRT, superseding other analytical compensation approaches such as Telegrapher equation. The computational convenience of DWS greatly simplifies the extraction of viscoelastic properties from LSR measurements in a number of chemical, industrial, and biomedical applications. PMID:24663983

  2. Impact of intermediate localized states on nonlinear optical absorption of Ga-Ge-Se nanocolloidal solutions

    NASA Astrophysics Data System (ADS)

    Sebastian, Indu; Divya, S.; Nampoori, V. P. N.; Radhakrishnan, P.; Thomas, Sheenu

    2013-01-01

    We present the linear and nonlinear optical studies on nanocolloidal solutions of Ga9Ge27Se64 glass with varying concentrations. Optical bandgap of the material is found to vary with respect to the concentration of the solute in the solution. An intermediate peak in the band tail of the absorption spectra is observed due to the presence of energy band in the forbidden gap. The existence of fluorescence emission confirms the above argument. Nonlinear absorption is studied using open aperture Z-scan technique. The mechanism behind nonlinear absorption is predicted as two photon as well as two step photon absorption. Nonlinearity increases with decrease in optical bandgap which in turn depends on the concentration of the nanocolloidal solutions.

  3. Analysis of Retinal Layer Thicknesses and Their Clinical Correlation in Patients with Traumatic Optic Neuropathy

    PubMed Central

    Lee, Ju-Yeun; Cho, Kyuyeon; Park, Kyung-Ah; Oh, Sei Yeul

    2016-01-01

    The aims of this study were 1) To evaluate retinal nerve fiber layer (fRNFL) thickness and ganglion cell layer plus inner plexiform layer (GCIPL) thickness at the fovea in eyes affected with traumatic optic neuropathy (TON) compared with contralateral normal eyes, 2) to further evaluate these thicknesses within 3 weeks following trauma (defined as “early TON”), and 3) to investigate the relationship between these retinal layer thicknesses and visual function in TON eyes. Twenty-nine patients with unilateral TON were included. Horizontal and vertical spectral-domain optical coherence tomography (SD-OCT) scans of the fovea were taken in patients with unilateral TON. The main outcome measure was thickness of the entire retina, fRNFL, and GCIPL in eight areas. Thickness of each retinal layer was compared between affected and unaffected eyes. The correlation between the thickness of each retinal layer and visual function parameters, including best corrected visual acuity, color vision, P100 latency, and P100 amplitude in visual evoked potential (VEP), mean deviation (MD) and visual field index (VFI) in Humphrey visual field analysis in TON eyes was analyzed. Thicknesses of the entire retina, fRNFL, and GCIPL in SD-OCT were significantly thinner (3–36%) in all measurement areas of TON eyes compared to those in healthy eyes (all p<0.05). Whereas, only GCIPL in the outer nasal, superior, and inferior areas was significantly thinner (5–10%) in the early TON eyes than that in the control eyes (all p<0.01). A significant correlation was detected between retinal layer thicknesses and visual function parameters including color vision, P100 latency and P100 amplitude in VEP, MD, and VFI (particularly P100 latency, MD, and VFI) (r = -0.70 to 0.84). Among the retinal layers analyzed in this study, GCIPL (particularly in the superior and inferior areas) was most correlated with these five visual function parameters (r = -0.70 to 0.71). Therefore, evaluation of morphological

  4. A novel low coherence fibre optic interferometer for position and thickness measurements with unattained accuracy

    NASA Astrophysics Data System (ADS)

    Wilhelm, Rainer; Courteville, Alain; Garcia, Fabrice

    2006-04-01

    This paper presents the second generation LISE-LI of the fibre-optics Low coherence Interferometric Sensor (LISE), recently developed by FOGALE nanotech. Based on the proven concept of partial coherence interferometry, the LISE system works as a comparator of optical group delays. The group delay along the optical axis in the probe interferometer arm containing the object to be measured is compared with the group delay along the optical axis of the reference interferometer arm containing a delay line. The latter consists of a mirror that can be linearly displaced on a translation stage. The light source is a super luminescent diode emitting at near infrared wavelength (typically 1.31 μm) with a spectral bandwidth of a few tens of nm. Thanks to the limited temporal coherence of the source, multiple surfaces of the object can be detected during a single scan of the delay line. Measurement ranges are between a few mm up to 600 mm (optical thickness). The measurement zone can be placed at a working distance of up to several meters away from the instrument's exit. Applications in industry and in research laboratories include thickness measurements of individual optical elements (e.g. lenses), technical multi-layer glasses, glue and varnish layers deposited on various substrates, Si or GaAs wafers, and position measurements of multiple elements of an optical system (e.g. a photographic lens). Compared to the first generation of the system, the absolute accuracy of the second generation system is about ten times better, reaching a level of +/-100 nm for thickness measurements over the full measurement range. Following an introductory description of the measurement principle, the first part of the paper focuses on the key elements in the system design, both in hardware and detection algorithm, that ensure the high accuracy level. The second part of the paper presents an experimental validation of the achieved accuracy level. We present results of thickness measurements on

  5. The advanced characterization of aerosol properties from measurements of spectral optical thickness of the atmosphere.

    NASA Astrophysics Data System (ADS)

    Torres, Benjamin; Toledano, Carlos; Dubovik, Oleg; Litvinov, Pavel; Lapyonok, Tatyana; Fuertes, David; Tanre, Didier; Goloub, Phillipe

    The main purpose of the work is to assess the potential of using spectral optical thickness measurement for characterizing aerosol properties. While the use of these measurements is limited to the characterization of aerosol loading in the atmosphere, several studies demonstrated that these observations could be used for deriving more detailed information about aerosol, such as size distribution (King et al. 1978) and for discriminating between the extinction of fine and coarse modes of aerosol (O’Neill 2003). In this study, we test the possibilities of using AERONET inversion (Dubovik and King 2000) for improving the interpretation of measurements of optical thickness. In addition, we study the potential of synergetic scenarios for inverting optical thickness using GRASP (Generalized Retrieval of Aerosol and Surface Properties) algorithm (Dubovik et al., 2011). This algorithm uses new multi-pixel retrieval approach. According to this approach, the accuracy of aerosol retrieval can be improved if several sets of observations (e.g. observations of satellite over several pixels) are inverted together under additional a priori constraints on time and spatial variability of the retrieved parameters. The application of this approach appears to be promising for the present study. First, the retrieval stability can be improved by inverting more than a single set of spectral aerosol optical depth at once. Second, the set of spectral aerosol optical depth can be inverted together with the radiances observed in the same day. The preliminary results of using simulated data (for different scenarios and aerosol models), as well as, the applications to real data from several AERONET sites will be presented.

  6. Design of differential optical absorption spectroscopy long-path telescopes based on fiber optics.

    PubMed

    Merten, André; Tschritter, Jens; Platt, Ulrich

    2011-02-10

    We present a new design principle of telescopes for use in the spectral investigation of the atmosphere and the detection of atmospheric trace gases with the long-path differential optical absorption spectroscopy (DOAS) technique. A combination of emitting and receiving fibers in a single bundle replaces the commonly used coaxial-Newton-type combination of receiving and transmitting telescope. This very simplified setup offers a higher light throughput and simpler adjustment and allows smaller instruments, which are easier to handle and more portable. The higher transmittance was verified by ray-tracing calculations, which result in a theoretical factor threefold improvement in signal intensity compared with the old setup. In practice, due to the easier alignment and higher stability, up to factor of 10 higher signal intensities were found. In addition, the use of a fiber optic light source provides a better spectral characterization of the light source, which results in a lower detection limit for trace gases studied with this instrument. This new design will greatly enhance the usability and the range of applications of active DOAS instruments. PMID:21343997

  7. Generating Nanostructures with Multiphoton Absorption Polymerization using Optical Trap Assisted Nanopatterning

    NASA Astrophysics Data System (ADS)

    Tsai, Yu-Cheng; Leitz, Karl-Heinz; Fardel, Romain; Schmidt, Michael; Arnold, Craig B.

    The need to generate sub 100 nm features is of interest for a variety of applications including optics, optoelectronics, and plasmonics. To address this requirement, several advanced optical lithography techniques have been developed based on either multiphoton absorption polymerization or near-field effects. In this paper, we combine strengths from multiphoton absorption and near field using optical trap assisted nanopatterning (OTAN). A Gaussian beam is used to position a microsphere in a polymer precursor fluid near a substrate. An ultrafast laser is focused by that microsphere to induce multiphoton polymerization in the near field, leading additive direct-write nanoscale processing.

  8. Luminescence and photoinduced absorption in ytterbium-doped optical fibres

    SciTech Connect

    Rybaltovsky, A A; Aleshkina, S S; Likhachev, M E; Bubnov, M M; Umnikov, A A; Yashkov, M V; Gur'yanov, Aleksei N; Dianov, Evgenii M

    2011-12-31

    Photochemical reactions induced in the glass network of an ytterbium-doped fibre core by IR laser pumping and UV irradiation have been investigated by analysing absorption and luminescence spectra. We have performed comparative studies of the photoinduced absorption and luminescence spectra of fibre preforms differing in core glass composition: Al{sub 2}O{sub 3} : SiO{sub 2}, Al{sub 2}O{sub 3} : Yb{sub 2}O{sub 3} : SiO{sub 2}, and P{sub 2}O{sub 5} : Yb{sub 2}O{sub 3} : SiO{sub 2}. The UV absorption spectra of unirradiated preform core samples show strong bands peaking at 5.1 and 6.5 eV, whose excitation plays a key role in photoinduced colour centre generation in the glass network. 'Direct' UV excitation of the 5.1- and 6.5-eV absorption bands at 244 and 193 nm leads to the reduction of some of the Yb{sup 3+} ions to Yb{sup 2+}. The photodarkening of ytterbium-doped fibres by IR pumping is shown to result from oxygen hole centre generation. A phenomenological model is proposed for the IR-pumping-induced photodarkening of ytterbium-doped fibres. The model predicts that colour centre generation in the core glass network and the associated absorption in the visible range result from a cooperative effect involving simultaneous excitation of a cluster composed of several closely spaced Yb{sup 3+} ions.

  9. Thickness-dependent carrier transport and optically enhanced transconductance gain in III-VI multilayer InSe

    NASA Astrophysics Data System (ADS)

    Ho, Ching-Hwa

    2016-06-01

    Multilayer InSe with a thickness above ∼20 nm, is a direct semiconductor with a peak absorption wavelength approaching λ = 1000 nm, which is a promising candidate for solar-energy conversion and 2D optoelectronics devices. We present herein the experimental observations of thickness-dependent conductivity and photoconductive-responsivity spectrum in multilayer InSe as well as optically enhanced transconductance gain in the multilayer InSe metal-semiconductor-field-effect transistor (MESFET) illuminated by a halogen lamp. The voltage-current (V-I) measurement result shows multilayer InSe belongs to a p-type semiconductor, which can form a p-channel FET device. Thickness (t) dependent conductivity (σ) of multilayer InSe reveals about six-order variation from 5076 (Ω-cm)‑1 (t = 5 nm) to 2.56 × 10‑3 (Ω-cm)‑1 (t = 184 μm, bulk) following a relationship of σ ∝ t ‑1.38. The highest conductivity in a thin InSe (e.g. t = 5 nm) is due to the increase of carrier density when the thickness is decreased. The photoresponsivity spectrum of a Ag-InSe-Ag multilayer photoconductor demonstrates a prominent peak absorption at 1.1 ∼ 1.3 eV, matches well with the direct-free-exciton energy of the InSe. A multilayer p-InSe MESFET was tested by V-I measurement. The transconductance was measured and determined to be {g}m={≤ft|\\tfrac{\\partial {{{I}}}{{D}}}{\\partial {{{V}}}{{G}}}\\right|}{{{V}}{{SD}}={{2V}}} = ({1.25 +/- 0.008})× {10}-4≤ft(\\tfrac{{{A}}}{{{V}}}\\right). The gm value will enhance about three times when the MESFET was placed under the illumination of a tungsten halogen lamp of a lower power density ∼0.5 mW · cm‑2. All the experimental results demonstrate multilayer InSe a promising 2D material available for microelectronics and optoelectronics applications.

  10. Optical spectroscopy of sputtered nanometer-thick yttrium iron garnet films

    SciTech Connect

    Jakubisova-Liskova, Eva Visnovsky, Stefan; Chang, Houchen; Wu, Mingzhong

    2015-05-07

    Nanometer (nm)-thick yttrium iron garnet (Y{sub 3}Fe{sub 5}O{sub 12}, YIG) films present interest for spintronics. This work employs spectral ellipsometry and magneto-optic Kerr effect (MOKE) spectra to characterize nm-thick YIG films grown on single-crystal Gd{sub 3}Ga{sub 5}O{sub 12} substrates by magnetron sputtering. The thickness (t) of the films ranges between 10 nm and 40 nm. Independent on t, the polar MOKE hysteresis loops saturate in the field of about 1.8 kOe, consistent with the saturation magnetization in bulk YIG (4πM{sub s} ≈ 1.75 kG). The MOKE spectrum measured at photon energies between 1.3 eV and 4.5 eV on the 38-nm-thick film agrees with that measured on single-crystal YIG bulk materials. The MOKE spectrum of the 12-nm-thick film still preserves the structure of the bulk YIG but its amplitude at lower photon energies is modified due to the fact that the radiation penetration depth exceeds 20 nm. The t dependence of the MOKE amplitude is consistent with MOKE calculations. The results indicate that the films are stoichiometric, strain free, without Fe{sup 2+}, and preserve bulk YIG properties down to t ≈ 10 nm.

  11. Deriving in situ phytoplankton absorption for bio-optical productivity models in turbid waters

    NASA Astrophysics Data System (ADS)

    Oliver, Matthew J.; Schofield, Oscar; Bergmann, Trisha; Glenn, Scott; Orrico, Cristina; Moline, Mark

    2004-07-01

    As part of Hyperspectral Coupled Ocean Dynamics Experiment, a high-resolution hydrographic and bio-optical data set was collected from two cabled profilers at the Long-Term Ecosystem Observatory (LEO). Upwelling- and downwelling-favorable winds and a buoyant plume from the Hudson River induced large changes in hydrographic and optical structure of the water column. An absorption inversion model estimated the relative abundance of phytoplankton, colored dissolved organic matter (CDOM) and detritus, as well as the spectral exponential slopes of CDOM and detritus from in situ WET Labs nine-wavelength absorption/attenuation meter (ac-9) absorption data. Derived optical weights were proportional to the parameter concentrations and allowed for their absorptions to be calculated. Spectrally weighted phytoplankton absorption was estimated using modeled spectral irradiances and the phytoplankton absorption spectra inverted from an ac-9. Derived mean spectral absorption of phytoplankton was used in a bio-optical model estimating photosynthetic rates. Measured radiocarbon uptake productivity rates extrapolated with water mass analysis and the bio-optical modeled results agreed within 20%. This approach is impacted by variability in the maximum quantum yield (ϕmax) and the irradiance light-saturation parameter (Ek(PAR)). An analysis of available data shows that ϕmax variability is relatively constrained in temperate waters. The variability of Ek(PAR) is greater in temperate waters, but based on a sensitivity analysis, has an overall smaller impact on water-column-integrated productivity rates because of the exponential decay of light. This inversion approach illustrates the utility of bio-optical models in turbid coastal waters given the measurements of the bulk inherent optical properties.

  12. A One-Dimensional Solution of the Photoacoustic Wave Equation and its Relationship with Optical Absorption

    NASA Astrophysics Data System (ADS)

    Cywiak, D.; Barreiro-Argüelles, M. D.; Cywiak, M.; Landa-Curiel, A.; Garcia-Segundo, C.; Gutierrez-Juárez, G.

    2013-09-01

    A study based on the general solution of the one-dimensional photoacoustic (PA) wave equation for an acoustic plane source is presented. This study relies on obtaining the impulse response of the PA system considering a heating function proportional to the Lambert-Beer law and spatially bounded by a rectangle function. The PA pressure is obtained by convoluting the impulse response with the temporal profile of the exciting pulse of light. With the obtained solution, it is possible to comprise, on a single expression, the PA pressure profile for optically thin samples (whose dimensions are smaller than the optical absorption length) and optically opaque samples (whose dimensions are larger than the optical absorption length). In the limit of weak absorption, the solution is in good agreement with the one for a uniform distribution of energy. Also, a study of the dependence of the acoustic pressure with the duration of the laser pulse is included.

  13. Defects forming the optical absorption edge in TlGaSe2 layered crystal

    NASA Astrophysics Data System (ADS)

    Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Şale, Yasin

    2016-09-01

    In this work, we present the results of optical experiments designed to investigate the changes in optical absorption spectra of TlGaSe2 ferroelectric-semiconductor with incommensurate (INC) phase in experimental conditions where crystal is kept several hours within the INC-phase (the regime of so called "memory" effect). The fundamental absorption of TlGaSe2, experimentally investigated by optical transmission measurements performed in the temperature range 15-300 K. An extraordinary modification of the optical absorption edge in the range of Urbach's tail is discovered as a result of the annealing within the INC-phase. The role of native defects forming the band edge in the observed phenomena in TlGaSe2 is discussed.

  14. 120nm resolution in thick samples with structured illumination and adaptive optics

    NASA Astrophysics Data System (ADS)

    Thomas, Benjamin; Sloan, Megan; Wolstenholme, Adrian J.; Kner, Peter

    2014-03-01

    μLinear Structured Illumination Microscopy (SIM) provides a two-fold increase over the diffraction limited resolution. SIM produces excellent images with 120nm resolution in tissue culture cells in two and three dimensions. For SIM to work correctly, the point spread function (PSF) and optical transfer function (OTF) must be known, and, ideally, should be unaberrated. When imaging through thick samples, aberrations will be introduced into the optical system which will reduce the peak intensity and increase the width of the PSF. This will lead to reduced resolution and artifacts in SIM images. Adaptive optics can be used to correct the optical wavefront restoring the PSF to its unaberrated state, and AO has been used in several types of fluorescence microscopy. We demonstrate that AO can be used with SIM to achieve 120nm resolution through 25m of tissue by imaging through the full thickness of an adult C. elegans roundworm. The aberrations can be corrected over a 25μm × 45μm field of view with one wavefront correction setting, demonstrating that AO can be used effectively with widefield superresolution techniques.

  15. Active probing of cloud thickness and optical depth using wide-angle imaging LIDAR.

    SciTech Connect

    Love, Steven P.; Davis, A. B.; Rohde, C. A.; Tellier, L. L.; Ho, Cheng,

    2002-01-01

    At most optical wavelengths, laser light in a cloud lidar experiment is not absorbed but merely scattered out of the beam, eventually escaping the cloud via multiple scattering. There is much information available in this light scattered far from the input beam, information ignored by traditional 'on-beam' lidar. Monitoring these off-beam returns in a fully space- and time-resolved manner is the essence of our unique instrument, Wide Angle Imaging Lidar (WAIL). In effect, WAIL produces wide-field (60{sup o} full-angle) 'movies' of the scattering process and records the cloud's radiative Green functions. A direct data product of WAIL is the distribution of photon path lengths resulting from multiple scattering in the cloud. Following insights from diffusion theory, we can use the measured Green functions to infer the physical thickness and optical depth of the cloud layer. WAIL is notable in that it is applicable to optically thick clouds, a regime in which traditional lidar is reduced to ceilometry. Section 2 covers the up-to-date evolution of the nighttime WAIL instrument at LANL. Section 3 reports our progress towards daytime capability for WAIL, an important extension to full diurnal cycle monitoring by means of an ultra-narrow magneto-optic atomic line filter. Section 4 describes briefly how the important cloud properties can be inferred from WAIL signals.

  16. Optical Constants of Silicon Carbide for Astrophysical Applications. II. Extending Optical Functions from Infrared to Ultraviolet Using Single-Crystal Absorption Spectra

    NASA Astrophysics Data System (ADS)

    Hofmeister, A. M.; Pitman, K. M.; Goncharov, A. F.; Speck, A. K.

    2009-05-01

    Laboratory measurements of unpolarized and polarized absorption spectra of various samples and crystal structures of silicon carbide (SiC) are presented from 1200-35000 cm-1 (λ ~ 8-0.28 μm) and used to improve the accuracy of optical functions (n and k) from the infrared (IR) to the ultraviolet (UV). Comparison with previous λ ~ 6-20 μm thin-film spectra constrains the thickness of the films and verifies that recent IR reflectivity data provide correct values for k in the IR region. We extract n and k needed for radiative transfer models using a new "difference method," which utilizes transmission spectra measured from two SiC single-crystals with different thicknesses. This method is ideal for near-IR to visible regions where absorbance and reflectance are low and can be applied to any material. Comparing our results with previous UV measurements of SiC, we distinguish between chemical and structural effects at high frequency. We find that for all spectral regions, 3C (β-SiC) and the \\vec{E}\\bot \\vec{c} polarization of 6H (a type of α-SiC) have almost identical optical functions that can be substituted for each other in modeling astronomical environments. Optical functions for \\vec{E} \\Vert \\vec{c} of 6H SiC have peaks shifted to lower frequency, permitting identification of this structure below λ ~ 4 μm. The onset of strong UV absorption for pure SiC occurs near 0.2 μm, but the presence of impurities redshifts the rise to 0.33 μm. Optical functions are similarly impacted. Such large differences in spectral characteristics due to structural and chemical effects should be observable and provide a means to distinguish chemical variation of SiC dust in space.

  17. Multi-wavelength measurements of aerosol optical absorption coefficients using a photoacoustic spectrometer

    NASA Astrophysics Data System (ADS)

    Liu, Qiang; Huang, Hong-Hua; Wang, Yao; Wang, Gui-Shi; Cao, Zhen-Song; Liu, Kun; Chen, Wei-Dong; Gao, Xiao-Ming

    2014-06-01

    The atmospheric aerosol absorption capacity is a critical parameter determining its direct and indirect effects on climate. Accurate measurement is highly desired for the study of the radiative budget of the Earth. A multi-wavelength (405 nm, 532 nm, 780 nm) aerosol absorption meter based on photoacoustic spectroscopy (PAS) invovling a single cylindrical acoustic resonator is developed for measuring the aerosol optical absorption coefficients (OACs). A sensitivity of 1.3 Mm-1 (at 532 nm) is demonstrated. The aerosol absorption meter is successfully tested through measuring the OACs of atmospheric nigrosin and ambient aerosols in the suburbs of Hefei city. The absorption cross section and absorption Ångström exponent (AAE) for ambient aerosol are determined for characterizing the component of the ambient aerosol.

  18. Monitoring transformer oil insulation using optical absorption properties

    NASA Astrophysics Data System (ADS)

    Rose, Benjamin P.

    As the electrical power distribution system ages, new methods of determining the quality of electrical transformer units are needed. Due to the relatively high expense of loss of service and safety hazards, a relatively cheap sensor to track the age of the insulation would aide in the progress of an intelligent power grid. The degradation of solid insulating paper releases some of the age indicating organic compounds into the oil. At present, the only available method to determine the concentration of those compounds is to perform high performance liquid chromatography (HPLC) testing in a laboratory. This is an expensive and time consuming activity that also requires transformer to be taken offline. Currently there are no sensors that can directly (on-line) measure the chemical integrity of the material. This research was focused upon one of the well known organic compounds released by paper into the transformer oil - 2-furfuraldehyde (2FAL). Previous methods of 2FAL detection were explored and expounded upon. A device was constructed to utilize light emitting diodes to optically interrogate solid discs made out of chemically active material in multiple tests. A 10 kVA distribution transformer was fitted with a special device allowing a continuous oil circulation and the optical setup. The transformer was tested while being loaded under accelerated ageing conditions. A premature failure of the distribution transformer did not allow any correlation between concentration of 2FAL and the optical signals. Previously sampled oils for a current transformer (CT) were also tested for chemical analysis in the laboratory and optical signals from the newly developed optical device were obtained. A 95% linear correlation was found between the age of the CT oil and the output of the optical device. Although the technique was validated and does seem to have merit, more tests are needed before the optical device can be recommended for use in the field.

  19. The Importance of Optical Pathlength Control for Plasma Absorption Measurements

    NASA Technical Reports Server (NTRS)

    Cruden, Brett A.; Rao, M. V. V. S.; Sharma, Surendra P.; Meyyappan, M.; Partridge, Harry (Technical Monitor)

    2001-01-01

    An inductively coupled GEC Cell with modified viewing ports has been used to measure in-situ absorption in CF4 plasmas via Fourier Transform Infrared Spectroscopy, and the results compared to those obtained in a standard viewport configuration. The viewing ports were modified so that the window boundary is inside, rather than outside, of the GEC cell. Because the absorption obtained is a spatially integrated absorption, measurements made represent an averaging of absorbing species inside and outside of the plasma. This modification is made to reduce this spatial averaging and thus allow a more accurate estimation of neutral species concentrations and temperatures within the plasmas. By reducing this pathlength, we find that the apparent CF4 consumption increases from 65% to 95% and the apparent vibrational temperature of CF4 rises by 50-75 K. The apparent fraction of etch product SiF4 decreases from 4% to 2%. The data suggests that these density changes may be due to significant temperature gradients between the plasma and chamber viewports.

  20. Improving the Total Impulse Capability of the NSTAR Ion Thruster With Thick-Accelerator-Grid Ion Optics

    NASA Technical Reports Server (NTRS)

    Soulas, George C.

    2001-01-01

    The results of performance tests with thick-accelerator-grid (TAG) ion optics are presented. TAG ion optics utilize a 50 percent thicker accelerator grid to double ion optics' service life. NSTAR ion optics were also tested to provide a baseline performance for comparison. Impingement-limited total voltages for the TAG ion optics were only 0 to 15 V higher than those of the NSTAR ion optics. Electron backstreaming limits for the TAG ion optics were 3 to 9 V higher than those for the NSTAR optics due to the increased accelerator grid thickness for the TAG ion optics. Screen grid ion transparencies for the TAG ion optics were only about 2 percent lower than those for the NSTAR optics, reflecting the lower physical screen grid open area fraction of the TAG ion optics. Accelerator currents for the TAG ion optics were 19 to 43 percent greater than those for the NSTAR ion optics due, in part, to a sudden increase in accelerator current during TAG ion optics' performance tests for unknown reasons and to the lower-than-nominal accelerator aperture diameters. Beam divergence half-angles that enclosed 95 percent of the total beam current and beam divergence thrust correction factors for the TAG ion optics were within 2 degrees and 1 percent, respectively, of those for the NSTAR ion optics.

  1. Inverted Ultrathin Organic Solar Cells with a Quasi-Grating Structure for Efficient Carrier Collection and Dip-less Visible Optical Absorption

    PubMed Central

    In, Sungjun; Park, Namkyoo

    2016-01-01

    We propose a metallic-particle-based two-dimensional quasi-grating structure for application to an organic solar cell. With the use of oblate spheroidal nanoparticles in contact with an anode of inverted, ultrathin organic solar cells (OSCs), the quasi-grating structure offers strong hybridization between localized surface plasmons and plasmonic gap modes leading to broadband (300~800 nm) and uniform (average ~90%) optical absorption spectra. Both strong optical enhancement in extreme confinement within the active layer (90 nm) and improved hole collection are thus realized. A coupled optical-electrical multi-physics optimization shows a large (~33%) enhancement in the optical absorption (corresponding to an absorption efficiency of ~47%, AM1.5G weighted, visible) when compared to a control OSC without the quasi-grating structure. That translates into a significant electrical performance gain of ~22% in short circuit current and ~15% in the power conversion efficiency (PCE), leading to an energy conversion efficiency (~6%) which is comparable to that of optically-thick inverted OSCs (3–7%). Detailed analysis on the influences of mode hybridization to optical field distributions, exciton generation rate, charge carrier collection efficiency and electrical conversion efficiency is provided, to offer an integrated understanding on the coupled optical-electrical optimization of ultrathin OSCs. PMID:26902974

  2. Inverted Ultrathin Organic Solar Cells with a Quasi-Grating Structure for Efficient Carrier Collection and Dip-less Visible Optical Absorption

    NASA Astrophysics Data System (ADS)

    in, Sungjun; Park, Namkyoo

    2016-02-01

    We propose a metallic-particle-based two-dimensional quasi-grating structure for application to an organic solar cell. With the use of oblate spheroidal nanoparticles in contact with an anode of inverted, ultrathin organic solar cells (OSCs), the quasi-grating structure offers strong hybridization between localized surface plasmons and plasmonic gap modes leading to broadband (300~800 nm) and uniform (average ~90%) optical absorption spectra. Both strong optical enhancement in extreme confinement within the active layer (90 nm) and improved hole collection are thus realized. A coupled optical-electrical multi-physics optimization shows a large (~33%) enhancement in the optical absorption (corresponding to an absorption efficiency of ~47%, AM1.5G weighted, visible) when compared to a control OSC without the quasi-grating structure. That translates into a significant electrical performance gain of ~22% in short circuit current and ~15% in the power conversion efficiency (PCE), leading to an energy conversion efficiency (~6%) which is comparable to that of optically-thick inverted OSCs (3-7%). Detailed analysis on the influences of mode hybridization to optical field distributions, exciton generation rate, charge carrier collection efficiency and electrical conversion efficiency is provided, to offer an integrated understanding on the coupled optical-electrical optimization of ultrathin OSCs.

  3. Optical absorption properties of dispersed gold and silver alloy nanoparticles.

    PubMed

    Wilcoxon, Jess

    2009-03-01

    The oldest topic in nanoscience is the size-dependent optical properties of gold and silver colloids or nanoparticles, first investigated scientifically by Michael Faraday in 1857. In the modern era, advances in both synthesis and characterization have resulted in new insights into the size-dependent absorbance of Au and Ag nanoparticles with sizes below the classical limit for Mie theory. In this paper we discuss the synthesis and properties of core/shell and nanoalloy particles of Au and Ag, compare them to particles of pure gold and silver, and discuss how alloying affects nanoparticle chemical stability. We show that composition, size, and nanostructure (e.g., core/shell vs quasi-random nanoalloy) can all be employed to adjust the optical absorbance properties. The type of nanostructure--core/shell vs alloy--is reflected in their optical absorbance features. PMID:19708105

  4. Spatially resolved optical absorption spectroscopy of single- and few-layer MoS2 by hyperspectral imaging

    NASA Astrophysics Data System (ADS)

    Castellanos-Gomez, Andres; Quereda, Jorge; van der Meulen, Herko P.; Agraït, Nicolás; Rubio-Bollinger, Gabino

    2016-03-01

    The possibility of spatially resolving the optical properties of atomically thin materials is especially appealing as they can be modulated at the micro- and nanoscale by reducing their thickness, changing the doping level or applying a mechanical deformation. Therefore, optical spectroscopy techniques with high spatial resolution are necessary to get a deeper insight into the properties of two-dimensional (2D) materials. Here we study the optical absorption of single- and few-layer molybdenum disulfide (MoS2) in the spectral range from 1.24 eV to 3.22 eV (385 nm to 1000 nm) by developing a hyperspectral imaging technique that allows one to probe the optical properties with diffraction limited spatial resolution. We find hyperspectral imaging very suited to study indirect bandgap semiconductors, unlike photoluminescence which only provides high luminescence yield for direct gap semiconductors. Moreover, this work opens the door to study the spatial variation of the optical properties of other 2D systems, including non-semiconducting materials where scanning photoluminescence cannot be employed.

  5. Spatially resolved optical absorption spectroscopy of single- and few-layer MoS₂ by hyperspectral imaging.

    PubMed

    Castellanos-Gomez, Andres; Quereda, Jorge; van der Meulen, Herko P; Agraït, Nicolás; Rubio-Bollinger, Gabino

    2016-03-18

    The possibility of spatially resolving the optical properties of atomically thin materials is especially appealing as they can be modulated at the micro- and nanoscale by reducing their thickness, changing the doping level or applying a mechanical deformation. Therefore, optical spectroscopy techniques with high spatial resolution are necessary to get a deeper insight into the properties of two-dimensional (2D) materials. Here we study the optical absorption of single- and few-layer molybdenum disulfide (MoS2) in the spectral range from 1.24 eV to 3.22 eV (385 nm to 1000 nm) by developing a hyperspectral imaging technique that allows one to probe the optical properties with diffraction limited spatial resolution. We find hyperspectral imaging very suited to study indirect bandgap semiconductors, unlike photoluminescence which only provides high luminescence yield for direct gap semiconductors. Moreover, this work opens the door to study the spatial variation of the optical properties of other 2D systems, including non-semiconducting materials where scanning photoluminescence cannot be employed. PMID:26876671

  6. Vertical and horizontal corneal epithelial thickness profiles determined by ultra-high resolution optical coherence tomography

    PubMed Central

    Du, Chixin; Wang, Jianhua; Cui, Lele; Shen, Meixiao; Yuan, Yimin

    2011-01-01

    Purpose To measure vertical and horizontal thickness profiles of the central and peripheral corneal epithelium and determine if daytime changes occur. Methods Forty eyes of 20 normal subjects were imaged by ultra-high resolution spectral domain optical coherence tomography to profile the corneal epithelial thickness from the edge of Bowman’s layer to the central cornea across the vertical and horizontal meridians. Measurements were made at 10:00 AM and again at 6, 8 hours later. Results The baseline vertical meridional epithelial thickness was thinnest, 42.9±4.1 μm, at the edge of Bowman’s layer in the superior region. It increased in thickness (p<0.01), towards the central cornea. The central epithelium averaged 52.5±2.4 μm, becoming thickest, 55.2±2.5 μm, in the inferior pericentral region. It thinned towards the inferior periphery, reaching 51.3±5.1 μm at the edge of Bowman’s layer (p<0.01). Along the horizontal meridian, the epithelium was thickest at the nasal side, 58.6±5.1 μm, and temporal side, 59.3±6.6 μm, near the edges of Bowman’s layer. It thinned towards the central cornea. There were no significant changes in the epithelial thickness at any location over 8 hours. Conclusion Epithelial thickness varied over the horizontal and vertical meridians and appeared stable during the daytime. PMID:22357393

  7. Reflectivity and thickness analysis of epiretinal membranes using spectral-domain optical coherence tomography

    PubMed Central

    Kuriyan, Ajay E.; DeBuc, Delia Cabrera; Smiddy, William E.

    2016-01-01

    AIM To compare thickness and reflectivity spectral domain optical coherence tomography (SD-OCT) findings in patients with idiopathic epiretinal membranes (ERMs), before and after ERM peeling surgery, with normal controls. METHODS A retrospective study analyzed SD-OCTs of eyes with ERMs undergoing ERM peeling surgery by one surgeon from 2008 to 2010 and normal control eyes. SD-OCTs were analyzed using a customized algorithm to measure reflectivity and thickness. The relationship between the SD-OCT findings and best corrected visual acuity (BCVA) outcomes was also studied. RESULTS Thirty-four ERM eyes and 12 normal eyes were identified. Preoperative eyes had high reflectivity and thickness of the group of layers from the internal limiting membrane (ILM) to the retinal pigment epithelium (RPE) and the group of layers from the ILM to the external limiting membrane (ELM). The values of reflectivity of these two groups of layers decreased postoperatively, but were still higher than normal eyes. In contrast, preoperative eyes had lower reflectivity of two 10×15 pixel regions of interest (ROIs) incorporating: 1) ELM + outer nuclear layer (ONL) and 2) photoreceptor layer (PRL) + RPE, compared to controls. The values of reflectivity of these ROIs increased postoperatively, but were still lower than normal controls. A larger improvement in BCVA postoperatively was correlated with a greater degree of abnormal preoperative reflectivity and thickness findings. CONCLUSION Quantitative differences in reflectivity and thickness between preoperative, postoperative, and normal SD-OCTs allow assessment of changes in the retina secondary to ERM. Our study identified hyperreflective inner retina changes and hyporeflective outer retina changes in patients with ERMs. SD-OCT quantitative measures of reflectivity and/or thickness of specific groups of retinal layers and/or ROIs correlate with improvement in BCVA. PMID:26949617

  8. Association of Optic Radiation Integrity with Cortical Thickness in Children with Anisometropic Amblyopia.

    PubMed

    Qi, Shun; Mu, Yun-Feng; Cui, Long-Biao; Li, Rong; Shi, Mei; Liu, Ying; Xu, Jun-Qing; Zhang, Jian; Yang, Jian; Yin, Hong

    2016-02-01

    Previous studies have indicated regional abnormalities of both gray and white matter in amblyopia. However, alterations of cortical thickness associated with changes in white matter integrity have rarely been reported. In this study, structural magnetic resonance imaging and diffusion tensor imaging (DTI) data were obtained from 15 children with anisometropic amblyopia and 15 age- and gender-matched children with normal sight. Combining DTI and surface-based morphometry, we examined a potential linkage between disrupted white matter integrity and altered cortical thickness. The fractional anisotropy (FA) values in the optic radiations (ORs) of children with anisometropic amblyopia were lower than in controls (P < 0.05). The cortical thickness in amblyopic children was lower than controls in the following subregions: lingual cortex, lateral occipitotemporal gyrus, cuneus, occipital lobe, inferior parietal lobe, and temporal lobe (P < 0.05, corrected), but was higher in the calcarine gyrus (P < 0.05, corrected). Node-by-node correlation analysis of changes in cortical thickness revealed a significant association between a lower FA value in the OR and diminished cortical thickness in the following subregions: medial lingual cortex, lateral occipitotemporal gyrus, lateral, superior, and medial occipital cortex, and lunate cortex. We also found a relationship between changes of cortical thickness and white matter OR integrity in amblyopia. These findings indicate that developmental changes occur simultaneously in the OR and visual cortex in amblyopia, and provide key information on complex damage of brain networks in anisometropic amblyopia. Our results also support the hypothesis that the pathogenesis of anisometropic amblyopia is neurodevelopmental. PMID:26769488

  9. Selectivity of the optical-absorption method based on an instrumental pick out of Fourier components in the absorption spectrum

    NASA Astrophysics Data System (ADS)

    Pisarevsky, Yu. V.; Kolesnikov, S. A.; Kolesnikova, E. S.; Turutin, Yu. A.; Konopelko, L. A.; Shor, N. B.

    2016-06-01

    The introduction of interference-polarization filters (IPFs) in the structure of an optical-absorption analyzer makes it possible to pick out a harmonic (a Fourier component of the absorption spectrum) providing measurement with the highest sensitivity. The selectivity of such a method of analysis is determined by overlapping the oscillations of the measured and interfering components. By the example of measurement in benzene in the presence of an interfering component (toluene), the possibility is considered for the optimization of selectivity due to the variation of the path-difference dispersion for ordinary and extraordinary interfering rays. The metrological characteristics of the interference-polarization analyzer of C6H6 confirming the results of calculations are given.

  10. Optical spectrum of bottom-up graphene nanoribbons: towards efficient atom-thick excitonic solar cells

    PubMed Central

    Villegas, Cesar E. P.; Mendonça, P. B.; Rocha, A. R.

    2014-01-01

    Recently, atomically well-defined cove-shaped graphene nanoribbons have been obtained using bottom-up synthesis. These nanoribbons have an optical gap in the visible range of the spectrum which make them candidates for donor materials in photovoltaic devices. From the atomistic point of view, their electronic and optical properties are not clearly understood. Therefore, in this work we carry out ab-initio density functional theory calculations combine with many-body perturbation formalism to study their electronic and optical properties. Through the comparison with experimental measurements, we show that an accurate description of the nanoribbon's optical properties requires the inclusion of electron-hole correlation effects. The energy, binding energy and the corresponding excitonic transitions involved are analyzed. We found that in contrast to zigzag graphene nanoribbons, the excitonic peaks in the absorption spectrum are a consequence of a group of transitions involving the first and second conduction and valence bands. Finally, we estimate some relevant optical properties that strengthen the potential of these nanoribbons for acting as a donor materials in photovoltaic. PMID:25301001

  11. Nonlinear optical properties of thick composite media with vanadium dioxide nanoparticles. I. Self-defocusing of radiation in the visible and near-IR regions

    NASA Astrophysics Data System (ADS)

    Ostrosablina, A. A.; Sidorov, A. I.

    2005-07-01

    This paper presents the experimental and theoretical results of a study of the interaction of pulsed laser radiation with thick composite media containing nanoparticles of vanadium dioxide (VO2). It establishes that the reversible semiconductor-metal phase transition that occurs in VO2 nanoparticles under the action of radiation can produce self-defocusing of radiation in the visible and near-IR regions because of the formation of a photoinduced dynamic lens. An analysis is carried out of how the radiation intensity affects the dynamics of these processes. It is shown that photoinduced absorption and scattering play a role in forming the nonlinear optical response.

  12. Subwavelength-resolution photoacoustic microscopy for label-free detection of optical absorption in vivo

    NASA Astrophysics Data System (ADS)

    Zhang, Chi; Maslov, Konstantin; Wang, Lihong V.

    2011-03-01

    Mainstream optical microscopy technologies normally detect fluorescence or scattering, which may require undesirable labeling, but cannot directly sense optical absorption, which provides essential biological functional information. Here we reported in vivo and label-free subwavelength-resolution photoacoustic microscopy (SW-PAM) by using a waterimmersion optical objective with a 1.23 NA. Capable of detecting nonfluorescent endogenous pigments, SW-PAM provides exquisitely high optical-absorption contrast. And, as a result of background-free detection, the sensitivity of SW-PAM to optical absorption reaches 100%. SW-PAM was demonstrated with wide-field optical microscopy by imaging gold nanospheres, ex vivo cells, and in vivo vasculature and melanoma. It was shown that SW-PAM has approached the ultimate diffraction-limited optical resolution-220 nm resolution at 532 nm wavelength. Subcellular organelles, such as melanosomes, can be resolved by SW-PAM. Vasculature and early-stage melanoma were imaged with 21:1 and 34:1 contrasts, respectively, without labeling. For all these applications, SW-PAM has contrasts orders of magnitude higher than wide-field optical microscopy. Therefore, SW-PAM is expected to join the mainstream microscopy technologies.

  13. Theoretical prediction of optical absorption maxima for photosensory receptor mutants

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Kazutomo; Yamato, Takahisa

    2006-10-01

    We found a linear correlation between the theoretically predicted shifts and experimentally observed absorption spectra for various mutants of photoactive yellow protein, a photosensory receptor. Excitation energies of mutants were evaluated by the combination of the high level ab initio calculation for the chromophore inside and the low level ab initio calculation for the surrounding protein environment. Importantly, the electronic states of these two regions were treated both as variables and they are solved consistently to each other. The protein-chromophore interaction has been accurately reproduced by this method.

  14. Retrieval of subvisual cirrus cloud optical thickness from limb-scatter measurements

    NASA Astrophysics Data System (ADS)

    Wiensz, J. T.; Degenstein, D. A.; Lloyd, N. D.; Bourassa, A. E.

    2013-01-01

    We present a technique for estimating the optical thickness of subvisual cirrus clouds detected by OSIRIS (Optical Spectrograph and Infrared Imaging System), a limb-viewing satellite instrument that measures scattered radiances from the UV to the near-IR. The measurement set is composed of a ratio of limb radiance profiles at two wavelengths that indicates the presence of cloud-scattering regions. Cross-sections and phase functions from an in situ database are used to simulate scattering by cloud-particles. With appropriate configurations discussed in this paper, the SASKTRAN successive-orders of scatter radiative transfer model is able to simulate accurately the in-cloud radiances from OSIRIS. Configured in this way, the model is used with a multiplicative algebraic reconstruction technique (MART) to retrieve the cloud extinction profile for an assumed effective cloud particle size. The sensitivity of these retrievals to key auxiliary model parameters is shown, and it is shown that the retrieved extinction profile, for an assumed effective cloud particle size, models well the measured in-cloud radiances from OSIRIS. The greatest sensitivity of the retrieved optical thickness is to the effective cloud particle size. Since OSIRIS has an 11-yr record of subvisual cirrus cloud detections, the work described in this manuscript provides a very useful method for providing a long-term global record of the properties of these clouds.

  15. Confined optical-phonon-assisted cyclotron resonance in quantum wells via two-photon absorption process

    NASA Astrophysics Data System (ADS)

    Phuc, Huynh Vinh; Hien, Nguyen Dinh; Dinh, Le; Phong, Tran Cong

    2016-06-01

    The effect of confined phonons on the phonon-assisted cyclotron resonance (PACR) via both one and two photon absorption processes in a quantum well is theoretically studied. We consider cases when electrons are scattered by confined optical phonons described by the Fuchs-Kliewer slab, Ridley's guided, and Huang-Zhu models. The analytical expression of the magneto-optical absorption coefficient (MOAC) is obtained by relating it to the transition probability for the absorption of photons. It predicts resonant peaks caused by transitions between Landau levels and electric subband accompanied by confined phonons emission in the absorption spectrum. The MOAC and the full-width at half-maximum (FWHM) for the intra- and inter-subband transitions are given as functions of the magnetic field, temperature, and quantum well width. In narrow quantum wells, the phonon confinement becomes more important and should be taken into account in studying FWHM.

  16. Magnetic field control of the intraband optical absorption in two-dimensional quantum rings

    SciTech Connect

    Olendski, O.; Barakat, T.

    2014-02-28

    Linear and nonlinear optical absorption coefficients of the two-dimensional semiconductor ring in the perpendicular magnetic field B are calculated within independent electron approximation. Characteristic feature of the energy spectrum are crossings of the levels with adjacent nonpositive magnetic quantum numbers as the intensity B changes. It is shown that the absorption coefficient of the associated optical transition is drastically decreased at the fields corresponding to the crossing. Proposed model of the Volcano disc allows to get simple mathematical analytical results, which provide clear physical interpretation. An interplay between positive linear and intensity-dependent negative cubic absorption coefficients is discussed; in particular, critical light intensity at which additional resonances appear in the total absorption dependence on the light frequency is calculated as a function of the magnetic field and levels' broadening.

  17. Optical absorption characteristics in the assessment of powder phosphor-based x-ray detectors: from nano- to micro-scale.

    PubMed

    Liaparinos, P F

    2015-11-21

    X-ray phosphor-based detectors have enormously improved the quality of medical imaging examinations through the optimization of optical diffusion. In recent years, with the development of science and technology in the field of materials, improved powder phosphors require structural and optical properties that contribute to better optical signal propagation. The purpose of this paper was to provide a quantitative and qualitative understanding of the optical absorption characteristics in the assessment of powder phosphor-based detectors (from nano- scale up to micro-scale). Variations on the optical absorption parameters (i.e. the light extinction coefficient [Formula: see text] and the percentage probability of light absorption p%) were evaluated based on Mie calculations examining a wide range of light wavelengths, particle refractive indices and sizes. To model and assess the effects of the aforementioned parameters on optical diffusion, Monte Carlo simulation techniques were employed considering: (i) phosphors of different layer thickness, 100 μm (thin layer) and 300 μm (thick layer), respectively, (ii) light extinction coefficient values, 1, 3 and 6 μm(-1), and (iii) percentage probability of light absorption p% in the range 10(-4)-10(-2). Results showed that the [Formula: see text] coefficient is high for phosphor grains in the submicron scale and for low light wavelengths. At higher wavelengths (above 650 nm), optical quanta follow approximately similar depths until interaction for grain diameter 500 nm and 1 μm. Regarding the variability of the refractive index, high variations of the [Formula: see text] coefficient occurred above 1.6. Furthermore, results derived from Monte Carlo modeling showed that high spatial resolution phosphors can be accomplished by increasing the [Formula: see text] parameter. More specifically, the FWHM was found to decrease (i.e. higher resolution): (i) 4.8% at 100 μm and (ii) 9.5%, at 300 μm layer thickness. This study

  18. Optical absorption characteristics in the assessment of powder phosphor-based x-ray detectors: from nano- to micro-scale

    NASA Astrophysics Data System (ADS)

    Liaparinos, P. F.

    2015-11-01

    X-ray phosphor-based detectors have enormously improved the quality of medical imaging examinations through the optimization of optical diffusion. In recent years, with the development of science and technology in the field of materials, improved powder phosphors require structural and optical properties that contribute to better optical signal propagation. The purpose of this paper was to provide a quantitative and qualitative understanding of the optical absorption characteristics in the assessment of powder phosphor-based detectors (from nano- scale up to micro-scale). Variations on the optical absorption parameters (i.e. the light extinction coefficient {{m}\\text{ext}} and the percentage probability of light absorption p%) were evaluated based on Mie calculations examining a wide range of light wavelengths, particle refractive indices and sizes. To model and assess the effects of the aforementioned parameters on optical diffusion, Monte Carlo simulation techniques were employed considering: (i) phosphors of different layer thickness, 100 μm (thin layer) and 300 μm (thick layer), respectively, (ii) light extinction coefficient values, 1, 3 and 6 μm-1, and (iii) percentage probability of light absorption p% in the range 10-4-10-2. Results showed that the {{m}\\text{ext}} coefficient is high for phosphor grains in the submicron scale and for low light wavelengths. At higher wavelengths (above 650 nm), optical quanta follow approximately similar depths until interaction for grain diameter 500 nm and 1 μm. Regarding the variability of the refractive index, high variations of the {{m}\\text{ext}} coefficient occurred above 1.6. Furthermore, results derived from Monte Carlo modeling showed that high spatial resolution phosphors can be accomplished by increasing the {{m}\\text{ext}} parameter. More specifically, the FWHM was found to decrease (i.e. higher resolution): (i) 4.8% at 100 μm and (ii) 9.5%, at 300 μm layer thickness. This study attempted to

  19. Optical fiber direct-sensing biosensor applied in detecting biolayer thickness of nanometer grade

    NASA Astrophysics Data System (ADS)

    Sun, Yan; Li, Mingming; Zhao, Hong; Yang, Yu Xiao; Zhang, Lu

    2006-02-01

    An optical fiber biosensor is introduced herein, which could directly detect biological interaction such as immunoreactions of antigens and antibodies without destroy the biolayer. The test is based on the theory of multilayer-reflection principle in white-light interferometry. When immunoreactions occur, the reflected spectrum phase shifts. Immunoreactions could be detected by means of reflected spectrum phase shifting, or by biolayer thickness changing. Continuously detecting of thickness changing on a fractional nanometer scale with subsecond repetition times is allowed in this system. The detecting system has high sensitivity, high precision, high speed, cost effective and working on a high reliability. The bioprobe is easy integrated as a BlAcore. The system and the experimental results on the reaction of rabbit-IgG with anti-rabbit-IgG are described in this paper. A sandwich method was adopted in the experiments.

  20. Systems Issues Pertaining to Holographic Optical Data Storage in Thick Bacteriorhodopsin Films

    NASA Technical Reports Server (NTRS)

    Downie, John D.; Timucin, Dogan A.; Gary, Charles K.; Oezcan, Meric; Smithey, Daniel T.; Crew, Marshall; Lau, Sonie (Technical Monitor)

    1998-01-01

    The optical data storage capacity and raw bit-error-rate achievable with thick photochromic bacteriorhodopsin (BR) films are investigated for sequential recording and read- out of angularly- and shift-multiplexed digital holograms inside a thick blue-membrane D85N BR film. We address the determination of an exposure schedule that produces equal diffraction efficiencies among each of the multiplexed holograms. This exposure schedule is determined by numerical simulations of the holographic recording process within the BR material, and maximizes the total grating strength. We also experimentally measure the shift selectivity and compare the results to theoretical predictions. Finally, we evaluate the bit-error-rate of a single hologram, and of multiple holograms stored within the film.

  1. Morphometric Analysis of Peripapillary Thickness in Hypertensives and Normotensives using Optical Coherence Tomography (OCT)

    PubMed Central

    Bhandary, Sulatha V.; Rao, Lavanya G.; Kapoor, Smita

    2016-01-01

    Introduction Hypotension following antihypertensive treatment is associated with retinal nerve fibre loss. There are studies that have reported the changes in RNFL in hypertensives. Aim To compare the Retinal Nerve Fibre Layer (RNFL) thickness using Optical Coherence Tomography (OCT) in hypertensive and normotensive individuals. Materials and Methods The cross-sectional study was conducted from October 2012 to September 2014 to compare the RNFL thickness using SD OCT in hypertensive {no other ocular or systemic co-morbidity, vision better or equal to 6/9 (n=30)} and normotensive (n=30) individuals. Results Statistically significant RNFL loss was detected in hypertensives (98.31 ± 7.01) when compared to the normotensives (102.51 ± 8.72) p=0.001. Conclusion Significant loss of RNFL in hypertensives point towards the altered autoregulation and warrants larger studies to assess the clinical relevance.

  2. Quantification of cell-free layer thickness and cell distribution of blood by optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Lauri, Janne; Bykov, Alexander; Fabritius, Tapio

    2016-04-01

    A high-speed optical coherence tomography (OCT) with 1-μm axial resolution was applied to assess the thickness of a cell-free layer (CFL) and a spatial distribution of red blood cells (RBC) next to the microchannel wall. The experiments were performed in vitro in a plain glass microchannel with a width of 2 mm and height of 0.2 mm. RBCs were suspended in phosphate buffered saline solution at the hematocrit level of 45%. Flow rates of 0.1 to 0.5 ml/h were used to compensate gravity induced CFL. The results indicate that OCT can be efficiently used for the quantification of CFL thickness and spatial distribution of RBCs in microcirculatory blood flow.

  3. Mass specific optical absorption coefficients of mineral dust components measured by a multi wavelength photoacoustic spectrometer

    NASA Astrophysics Data System (ADS)

    Utry, N.; Ajtai, T.; Pintér, M.; Tombácz, E.; Illés, E.; Bozóki, Z.; Szabó, G.

    2014-09-01

    Mass specific optical absorption coefficients of various mineral dust components including silicate clays (illite, kaolin and bentonite), oxides (quartz, hematite and rutile), and carbonate (limestone) were determined at wavelengths of 1064, 532, 355 and 266 nm. These values were calculated from aerosol optical absorption coefficients measured by a multi-wavelength photoacoustic (PA) instrument, the mass concentration and the number size distribution of the generated aerosol samples as well as the size transfer functions of the measuring instruments. These results are expected to have considerable importance in global radiative forcing calculations. They can also serve as reference for validating calculated wavelength dependent imaginary parts (κ) of complex refractive indices which up to now have been typically deduced from bulk phase measurements by using indirect measurement methods. Accordingly, the presented comparison of the measured and calculated aerosol optical absorption spectra revealed the strong need for standardized sample preparation and measurement methodology in case of bulk phase measurements.

  4. Optical nonlinear absorption characteristics of Sb{sub 2}Se{sub 3} nanoparticles

    SciTech Connect

    Muralikrishna, Molli Kiran, Aditha Sai Ravikanth, B. Sowmendran, P. Muthukumar, V. Sai Venkataramaniah, Kamisetti

    2014-04-24

    In this work, we report for the first time, the nonlinear optical absorption properties of antimony selenide (Sb{sub 2}Se{sub 3}) nanoparticles synthesized through solvothermal route. X-ray diffraction results revealed the crystalline nature of the nanoparticles. Electron microscopy studies revealed that the nanoparticles are in the range of 10 - 40 nm. Elemental analysis was performed using EDAX. By employing open aperture z-scan technique, we have evaluated the effective two-photon absorption coefficient of Sb{sub 2}Se{sub 3} nanoparticles to be 5e-10 m/W at 532 nm. These nanoparticles exhibit strong intensity dependent nonlinear optical absorption and hence could be considered to have optical power limiting applications in the visible range.

  5. Enhanced light absorption in graphene via a liquid-crystalline optical diode

    NASA Astrophysics Data System (ADS)

    Pantazi, Aikaterini Iria; Yannopapas, Vassilios

    2016-09-01

    We demonstrate theoretically that light absorption in graphene can be boosted via a light-trapping mechanism based on a liquid-crystalline optical diode. The optical diode consists of twisted-nematic and nematic liquid-crystalline slabs. In particular, we show that, using a proper optical-diode setup, the absorption in a single graphene layer can be enhanced by a factor of four. By varying the pitch of the twisted-nematic liquid-crystalline slabs comprising the diode, one can tune the operating spectral region of the diode and thus enhance the absorption of graphene within a desired spectral window. Our calculations are based on Berreman's 4×4 method which treats anisotropic, isotropic and/ or inhomogeneous layered systems on equal footing.

  6. Strain- and twist-engineered optical absorption of few-layer black phosphorus

    NASA Astrophysics Data System (ADS)

    Jia, Qian; Kong, XiangHua; Qiao, JingSi; Ji, Wei

    2016-09-01

    Density functional and many-body perturbation theories calculations were carried out to investigate fundamental and optical bandgap, exciton binding energy and optical absorption property of normal and strain- and twist-engineered few-layer black phosphorus (BP). We found that the fundamental bandgaps of few layer BP can be engineered by layer stacking and in-plane strain, with linear relationships to their associated exciton binding energies. The strain-dependent optical absorption behaviors are also anisotropic that the position of the first absorption peak monotonically blue-shifts as the strain applies to either direction for incident light polarized along the armchair direction, but this is not the case for that along the zigzag direction. Given those striking properties, we proposed two prototype devices for building potentially more balanced light absorbers and light filter passes, which promotes further applications and investigations of BP in nanoelectronics and optoelectronics.

  7. 1- and 2-photon absorption by laser-cooled 85Rb using an optical nanofiber

    NASA Astrophysics Data System (ADS)

    Russell, L.; Daly, M.; Chormaic, S. Nic

    2012-09-01

    The characteristics of a cold cloud of 85Rb can be non-destructively examined using an optical nanofiber. The nanofiber is a submicron-diameter cylindrical waveguide fabricated from commercially-available optical fiber using a heat-and-pull rig. The nanofiber can be used as a 'dark' or 'bright' probe depending on whether laser light is coupled into the nanofiber. We demonstrate the use of an optical nanofiber as an absorption spectroscopy tool for cold atoms. A frequency-scanned probe beam is launched through the nanofiber and the resonant light is absorbed at the waist of the nanofiber by nearby cold 85Rb atoms. We present recent singlephoton absorption results and comment on the role of surface interactions. Future work on 2-photon absorption using excited state electronic transitions in 85Rb is discussed.

  8. [Retrieval of tropospheric NO2 by multi axis differential optical absorption spectroscopy].

    PubMed

    Xu, Jin; Xie, Pin-hua; Si, Fu-qi; Dou, Ke; Li, Ang; Liu, Yu; Liu, Wen-qing

    2010-09-01

    A method of retrieving NO2 in troposphere based on multi axis differential optical absorption spectroscopy (MAX-DOAS) was introduced. The differential slant column density (dSCD) of NO2 was evaluated by differential optical absorption spectroscopy (DOAS), removing the Fraunhofer structure and Ring effect. Combining the results of different observing directions, the tropospheric NO2 differential slant column density (deltaSCD) was evaluated, and the air mass factor (AMF) was calculated with the radiative transfer model SCIATRAN and the tropospheric NO2 vertical column density (VCD) was retrieved. To ensure the accuracy of the results, it was compared with the results of long path differential optical absorption spectroscopy (LP-DOAS), a good accordance was shown with the correlation coefficients of 0.94027 and 0.96924. PMID:21105419

  9. Instability of photoinduced optical absorption of Bi12SiO20: Al crystals

    NASA Astrophysics Data System (ADS)

    Panchenko, T. V.; Dyachenko, A. A.; Khmelenko, O. V.

    2015-04-01

    The results of the experimental investigation of the instability of the establishment and relaxation of a photochromic effect in aluminum-doped Bi12SiO20 crystals have been presented. The oscillating and nonmonotonic kinetic dependences of the photoinduced optical absorption have been observed. The absorption oscillations are associated with the competition of the formation and destruction of [AlSiO4]0 photochromic centers.

  10. Optical absorption of Ni2+ and Ni3+ ions in gadolinium gallium garnet epitaxial films

    NASA Astrophysics Data System (ADS)

    Vasileva, N. V.; Gerus, P. A.; Sokolov, V. O.; Plotnichenko, V. G.

    2012-12-01

    Single-crystal Ni-doped gadolinium gallium garnet films were grown for the first time from supercooled Bi2O3-B2O3-based melt solutions by liquid-phase epitaxy. Optical absorption bands due to Ni2+, Ni3+ and Bi3+ ions were observed in those films. Interpretation and tabulation of all absorption bands of nickel ions occupying octahedral and tetrahedral sites in the garnet lattice are presented.

  11. Mapping retinal thickness and macular edema by high-speed three-dimensional optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Zhou, Qienyuan; Trost, Peter K.; Lo, Pak-Wai; Hitzenberger, Christoph K.

    2004-07-01

    Conventional OCT generates one or few cross-sections of the retina and requires predetermination of measurement location and geometry. Because retinal pathologies are usually irregular and 3-dimensional in nature, a retinal imaging device with both high depth resolution and high lateral resolution is desired. The lateral resolution of the conventional OCT system is limited by sampling density, which in turn is limited by the speed of the system. In this paper, we present a three-dimensional optical coherence retinal tomograph (3D-OCT) which combines the rapid transversal imaging mode of a confocal scanning laser ophthalmoscope (cSLO) with the depth resolution of optical coherence tomography (OCT) to achieve high speed 3-D imaging. In contrary to the conventional OCT which performs adjacent A-scans to form a cross-section image (B-scan) perpendicular to the retinal surface, 3D-OCT acquires section images (C-scan) parallel to the retinal surface at defined depths across the thickness of the retina. Three-dimensional distribution of light-remitting sites within the retina is recorded at a depth resolution of ~12 μm (in eye) and lateral resolution of 10μm x 20μm within 1.2 seconds. In this paper, we present the results of in vivo retinal imaging of healthy volunteers and diabetic patients, retinal thickness mapping, and macular edema detection with the 3D-OCT device. Reproducibility of retinal thickness mapping ranges from 16 μm ~ 35 μm for different study subjects. Detailed retinal thickness map allows ready identification of location and area of macular thickening. C-scan images and continuous longitudinal cross section images provide visualization of pathological changes in the retina, such as presence of cyst formation and hard exudates. The need to predetermine measurement location and geometry is eliminated in 3D-OCT, in contrast to conventional OCT.

  12. The Impact of Subsampling on MODIS Level-3 Statistics of Cloud Optical Thickness and Effective Radius

    NASA Technical Reports Server (NTRS)

    Oreopoulos, Lazaros

    2004-01-01

    The MODIS Level-3 optical thickness and effective radius cloud product is a gridded l deg. x 1 deg. dataset that is derived from aggregation and subsampling at 5 km of 1 km, resolution Level-2 orbital swath data (Level-2 granules). This study examines the impact of the 5 km subsampling on the mean, standard deviation and inhomogeneity parameter statistics of optical thickness and effective radius. The methodology is simple and consists of estimating mean errors for a large collection of Terra and Aqua Level-2 granules by taking the difference of the statistics at the original and subsampled resolutions. It is shown that the Level-3 sampling does not affect the various quantities investigated to the same degree, with second order moments suffering greater subsampling errors, as expected. Mean errors drop dramatically when averages over a sufficient number of regions (e.g., monthly and/or latitudinal averages) are taken, pointing to a dominance of errors that are of random nature. When histograms built from subsampled data with the same binning rules as in the Level-3 dataset are used to reconstruct the quantities of interest, the mean errors do not deteriorate significantly. The results in this paper provide guidance to users of MODIS Level-3 optical thickness and effective radius cloud products on the range of errors due to subsampling they should expect and perhaps account for, in scientific work with this dataset. In general, subsampling errors should not be a serious concern when moderate temporal and/or spatial averaging is performed.

  13. Accretion disk boundary layers in cataclysmic variables. 1: Optically thick boundary layers

    NASA Technical Reports Server (NTRS)

    Popham, Robert; Narayan, Ramesh

    1995-01-01

    We develop numerical models of accretions disks in cataclysmic variables (CVs), including and emphasizing the boundary layer region where the accretion disk meets the accreting white dwarf. We confine ourselves to solutions where the boundary layer region is vertically optically thick, and find that these solutions share several common features. The angular and radial velocities of the accreting material drop rapidly in a dynamical boundary layer, which has a radial width approximately 1%-3% of the white dwarf radius. The energy dissipated in this region diffuses through the inner part of the disk and is radiated from the disk surface in a thermal boundary layer, which has a radial width comparable to the disk thickness, approximately 5%-15% of the white dwarf radius. We examine the dependence of the boundary layer structure on the mass accretion rate, the white dwarf mass and rotation rate, and the viscosity parameter alpha. We delineate the boundary between optically thick and optically thin boundary layer solutions as a function of these parameters and suggest that by means of a careful comparison with observations it may be possible to estimate alpha in CVs. We derive an expression for the total boundary layer luminosities as a function of the parameters and show that it agrees well with the luminosites of our numerical solutions. Finally, we calcuate simple blackbody continuum spectra of the boundary layer and disk emission for our solutions and compare these to soft X-ray, EUV, and He II emission-line observations of CVs. We show that, through such comparisons, it may be possible to determine the rotation rates of the accreting stars in CVs, and perhaps also the white dwarf masses and the accretion rates. The spectra are quite insensitive to alpha, so the uncertainty in this parameter does not affect such comparisons.

  14. Nonlinear dynamics of optical absorption of intense beams

    NASA Astrophysics Data System (ADS)

    Corbett, D.; van Oosten, C. L.; Warner, M.

    2008-07-01

    On traversing materials with absorbing dyes, weak optical beams decay exponentially (a Beer profile), while intense beams develop in time a profile that is spatially linear until at great depth it becomes spatially exponential. This anomalous, deep penetration, due to photobleaching of surface layers, is important for heavy dye loading and intense beams, for instance in photo-actuation. We address the problem of the evolution in time from initial Beer’s Law to a finally deeply-penetrating optical profile in dyes. Our largely analytic solution of the coupled, nonlinear, partial differential equations governing the spatiotemporal decay of the Poynting flux and the nonlinear population dynamics of the photo-active molecules under intense irradiation has application to optomechanical devices.

  15. Polyethylene laser welding based on optical absorption variations

    NASA Astrophysics Data System (ADS)

    Galtieri, G.; Visco, A.; Nocita, D.; Torrisi, L.; Ceccio, G.; Scolaro, C.

    2016-04-01

    Polymeric materials, both pure and containing nanostructures, can be prepared as thin sheets in order to produce joints with an interface between an optically transparent sheet and an optically absorbent substrate to be welded by infrared pulsed laser irradiation. The Laser Transmission Welding (LTW) technique has been successfully applied in order to join two or more thermoplastic polymeric sheets that must have a similar chemical composition. In this research work, polymeric joints of Ultra High Molecular Weight Polyethylene sheets were realized, characterized and welded. Some polymer sheets were doped, at different concentrations, with carbon nano-particles absorbent the laser radiation. A pulsed laser operating in the wavelength region 532 nm with intensity of the order of 109 Watt/cm2 was employed to be transmitted by the transparent polymer and to be absorbed by the carbon enriched surface. At the interface of the two polymers the released energy induces melting, that is assisted by pressure, producing a fast and resistant welding zone. Mechanical and optical characterizations and surface analyses are presented and discussed.

  16. Charge-transfer optical absorption mechanism of DNA:Ag-nanocluster complexes

    NASA Astrophysics Data System (ADS)

    Longuinhos, R.; Lúcio, A. D.; Chacham, H.; Alexandre, S. S.

    2016-05-01

    Optical properties of DNA:Ag-nanoclusters complexes have been successfully applied experimentally in Chemistry, Physics, and Biology. Nevertheless, the mechanisms behind their optical activity remain unresolved. In this work, we present a time-dependent density functional study of optical absorption in DNA:Ag4. In all 23 different complexes investigated, we obtain new absorption peaks in the visible region that are not found in either the isolated Ag4 or isolated DNA base pairs. Absorption from red to green are predominantly of charge-transfer character, from the Ag4 to the DNA fragment, while absorption in the blue-violet range are mostly associated to electronic transitions of a mixed character, involving either DNA-Ag4 hybrid orbitals or intracluster orbitals. We also investigate the role of exchange-correlation functionals in the calculated optical spectra. Significant differences are observed between the calculations using the PBE functional (without exact exchange) and the CAM-B3LYP functional (which partly includes exact exchange). Specifically, we observe a tendency of charge-transfer excitations to involve purines bases, and the PBE spectra error is more pronounced in the complexes where the Ag cluster is bound to the purines. Finally, our results also highlight the importance of adding both the complementary base pair and the sugar-phosphate backbone in order to properly characterize the absorption spectrum of DNA:Ag complexes.

  17. Aerosol optical thickness from Brewer spectrophotometers and an investigation into the stray-light effect.

    PubMed

    Silva, Abel A; Kirchhoff, Volker W J H

    2004-04-20

    The Langley method has been applied to the measurements of direct solar radiation made by Brewer spectrophotometers to obtain the aerosol optical thickness (AOT) of the atmosphere in the ultraviolet-B range. In several cases the AOT increased with wavelength, which raises suspicion about the stray-light effect. To investigate the quality of the AOT measurements and the possibility of stray light, we conducted a campaign by using single- and double-monochromator Brewers. The campaign's results have shown that both Brewers' AOT values are in good agreement and that stray light is not an important effect for AOT at wavelengths above 306 nm. PMID:15119618

  18. Cooperative Emission of a Pulse Train in an Optically Thick Scattering Medium

    NASA Astrophysics Data System (ADS)

    Kwong, C. C.; Yang, T.; Delande, D.; Pierrat, R.; Wilkowski, D.

    2015-11-01

    An optically thick cold atomic cloud emits a coherent flash of light in the forward direction when the phase of an incident probe field is abruptly changed. Because of cooperativity, the duration of this phenomena can be much shorter than the excited lifetime of a single atom. Repeating periodically the abrupt phase jump, we generate a train of pulses with short repetition time, high intensity contrast, and high efficiency. In this regime, the emission is fully governed by cooperativity even if the cloud is dilute.

  19. Elastohydrodynamic film thickness measurements of artificially produced surface dents and grooves. [using optical interferometry

    NASA Technical Reports Server (NTRS)

    Wedeven, L. D.; Cusano, C.

    1978-01-01

    Elastohydrodynamic (EHD) film thickness measurements using optical interferometry were made of artificially produced dents and grooves under rolling and sliding conditions. These measurements are compared to stylus traces of the dent and groove profiles to determine the local deformation associated with micro-EHD pressure generation. The surface geometry associated with the dents and grooves became intimately involved in the lubrication process itself, creating local pressure variations that substantially deformed the local surface geometry, particularly under sliding conditions. The rolling results implied surface initiated fatigue, and the sliding results showed clearly the EHD surface interactions that must occur prior to scuffing failure.

  20. Retrieval of aerosol optical thickness over land from airborne polarized measurements in Tianjin and Tangshan

    NASA Astrophysics Data System (ADS)

    Wang, Han; Sun, Xiaobing; Hou, Weizhen; Chen, Cheng; Hong, Jin

    2015-03-01

    New developed sensor was called Atmosphere Multi-angle Polarization Radiometer (AMPR). It provides airborne multi-spectral, multi-angular and polarized measurements. Based on the measurements, a method to retrieve aerosol optical thickness (AOT) was developed. To reduce the ambiguity in retrieval algorithm, the key characteristics of aerosol model over East Asia are constrained. Initial surface reflectance was estimated from measurements at 1640 nm. With iteration the surface polarized reflectance tends to the real value together with AOT. Retrieved cases were selected from measurements in Tianjin. Validation between AOTs from AMPR and CE318 is encouraging. The AOTs along the track shows reasonable temporal and spatial variation.

  1. Extended Pre-Transit Structures and the Exosphere Detected for HD189733b in Optical Hydrogen Balmer Line Absorption

    NASA Astrophysics Data System (ADS)

    Redfield, Seth; Cauley, P. Wilson; Jensen, Adam G.; Barman, Travis; Endl, Michael; Cochran, William

    2015-12-01

    We present two separate observations of HD189733b in the three strongest hydrogen Balmer lines (H-alpha, H-beta, and H-gamma), with HiRES on Keck I that show definitive in-transit absorption, confirming the detection with the HET by Jensen et al. (2012), as well as, significant pre-transit absorption. Recently, pre-transit absorption in UV metal transitions of the hot Jupiter exoplanets HD 189733b and WASP12-b have been interpreted as being caused by material compressed in a planetary bow shock, however our observations are the first to densely time-sample and redundantly detect these extended planetary structures. While our first observations (obtained in 2013 and presented in Cauley et al. 2015), were consistent with a bow shock, our subsequent observation taken in August 2015 show pre-transit absorption but with a pattern that is inconsistent with the 2013 model. Instead, the observations indicate significant variability in the strength and timing of the pre-transit absorption. We also find differences in the strength of the in-transit exospheric absorption as well. These changes could be indicative of variability in the extreme stellar wind properties found at just 8 stellar radii, which could drive the extended atmospheric interaction between star and planet. The pre-transit absorption in 2013 was first observed 65 minutes prior to transit (corresponding to a linear distance of ~7 planetary radii), although it could have started earlier. The pre-transit signal in 2015, which is well sampled, is first detected 165 minutes prior to transit (a linear distance of ~17 planetary radii). The line shape of the pre-transit feature and the shape of the time series absorption provide the strongest constraints on the morphology and physical characteristics of extended structures around the exoplanet. The absorption strength observed in the Balmer lines indicates an optically thick, but physically small, geometry. If part of this extended structure is a bow shock mediated

  2. Absorption spectroscopy of powdered materials using time-resolved diffuse optical methods.

    PubMed

    D'Andrea, Cosimo; Obraztsova, Ekaterina A; Farina, Andrea; Taroni, Paola; Lanzani, Guglielmo; Pifferi, Antonio

    2012-11-10

    In this paper a novel method, based on time-resolved diffuse optical spectroscopy, is proposed to measure the absorption of small amounts of nanostructured powder materials independent of scattering. Experimental validation, in the visible and near-infrared spectral range, has been carried out on India Inkparticles. The effectiveness of the technique to measure scattering-free absorption is demonstrated on carbon nanotubes. The comparison between the absorption spectra acquired by the proposed method and conventional measurements performed with a commercial spectrophotometer is discussed. PMID:23142900

  3. The Optical Absorption Coefficient of Bean Seeds Investigated Using Photoacoustic Spectroscopy

    NASA Astrophysics Data System (ADS)

    Sanchez-Hernandez, G.; Hernandez-Aguilar, C.; Dominguez-Pacheco, A.; Cruz-Orea, A.; Perez-Reyes, M. C. J.; Martinez, E. Moreno

    2015-06-01

    A knowledge about seed optical parameters is of great relevance in seed technology practice. Such parameters provide information about its absorption and reflectance, which could be useful for biostimulation processes, by light sources, in early stages of seed germination. In the present research photoacoustic spectroscopy (PAS) and the Rosencwaig and Gersho model were used to determine the optical absorption coefficient () of five varieties of bean seeds ( Phaseolus vulgaris L.), of different productive cycles; the seeds were biostimulated by laser treatment to evaluate the effects of biostimulation pre-sowing. It was found that the bean varieties V1, V2, V4, and V5 were optically opaque in the visible spectrum; in the case of the V3 variety, this sample was optically transparent from 680 nm. The varieties of the studied bean seeds showed significant statistical differences in sizes and also in their optical absorption spectra. The biostimulation effects showed that the seed samples with a higher optical penetration length had a positive biostimulation, in the percentage of germination, obtaining an enhancement of 47 % compared to the control sample. The utility of PAS for the optical characterization of seeds has been demonstrated in this study of the laser biostimulation process of this kind of samples.

  4. Optical absorption and luminescence study of cobalt-doped magnesium aluminosilicate glass ceramics

    NASA Astrophysics Data System (ADS)

    Malyarevich, A. M.; Denisov, I. A.; Yumashev, K. V.; Dymshits, O. S.; Zhilin, A. A.

    2002-08-01

    Linear and nonlinear optical properties of cobalt-doped magnesium aluminosilicate transparent glass ceramics that were prepared under different conditions have been studied. It has been shown that absorption and luminescence spectra and absorption bleaching of these glass ceramics are defined mainly by tetrahedrally coordinated Co 2+ ions located in magnesium aluminum spinel nanocrystals. The lifetimes of the 4 T 1 ( 4 F) and 4 T 2 ( 4 F) excited states of the tetrahedral Co 2+ ions were found to be in the ranges 2540 and 120450 ns, respectively, depending on the Co concentration. 2002 Optical Society of America

  5. Thermally induced nonlinear optical absorption in metamaterial perfect absorbers

    NASA Astrophysics Data System (ADS)

    Guddala, Sriram; Kumar, Raghwendra; Ramakrishna, S. Anantha

    2015-03-01

    A metamaterial perfect absorber consisting of a tri-layer (Al/ZnS/Al) metal-dielectric-metal system with top aluminium nano-disks was fabricated by laser-interference lithography and lift-off processing. The metamaterial absorber had peak resonant absorbance at 1090 nm and showed nonlinear absorption for 600ps laser pulses at 1064 nm wavelength. A nonlinear saturation of reflectance was measured to be dependent on the average laser power incident and not the peak laser intensity. The nonlinear behaviour is shown to arise from the heating due to the absorbed radiation and photo-thermal changes in the dielectric properties of aluminium. The metamaterial absorber is seen to be damage resistant at large laser intensities of 25 MW/cm2.

  6. Thermally induced nonlinear optical absorption in metamaterial perfect absorbers

    SciTech Connect

    Guddala, Sriram Kumar, Raghwendra; Ramakrishna, S. Anantha

    2015-03-16

    A metamaterial perfect absorber consisting of a tri-layer (Al/ZnS/Al) metal-dielectric-metal system with top aluminium nano-disks was fabricated by laser-interference lithography and lift-off processing. The metamaterial absorber had peak resonant absorbance at 1090 nm and showed nonlinear absorption for 600ps laser pulses at 1064 nm wavelength. A nonlinear saturation of reflectance was measured to be dependent on the average laser power incident and not the peak laser intensity. The nonlinear behaviour is shown to arise from the heating due to the absorbed radiation and photo-thermal changes in the dielectric properties of aluminium. The metamaterial absorber is seen to be damage resistant at large laser intensities of 25 MW/cm{sup 2}.

  7. Laser modulation of optical absorption in ZnSe

    NASA Technical Reports Server (NTRS)

    Major, R. W.

    1971-01-01

    The possibility of producing and detecting laser induced modulation of absorption (LIMA) in ZnSe crystals using a moderate laser intensity of about 6 mw output was investigated. The modulation is smaller than that previously obtained with higher laser photon flux, but is not too difficult to detect. Modulation of the order of a few parts in 10 to the 5th power, up to one part in 10 to the 4th power appears typical at the present. LIMA pulse shapes were recorded with varying system resolutions at a half dozen wavelengths in the visible, from 4800 A to 6000 A. Detailed data were taken, particularly at 5000 A, for a range of time intervals following laser pulse turn-on. Quantitative study of the excitation and decay kinetics of these is underway, though analysis is not complete. Major features are discussed with attention centered upon the detailed measurements made most recently at 5000 A.

  8. Spatial coherence effect on layer thickness determination in narrowband full-field optical coherence tomography

    SciTech Connect

    Safrani, Avner; Abdulhalim, Ibrahim

    2011-06-20

    Longitudinal spatial coherence (LSC) is determined by the spatial frequency content of an optical beam. The use of lenses with a high numerical aperture (NA) in full-field optical coherence tomography and a narrowband light source makes the LSC length much shorter than the temporal coherence length, hence suggesting that high-resolution 3D images of biological and multilayered samples can be obtained based on the low LSC. A simplified model is derived, supported by experimental results, which describes the expected interference output signal of multilayered samples when high-NA lenses are used together with a narrowband light source. An expression for the correction factor for the layer thickness determination is found valid for high-NA objectives. Additionally, the method was applied to a strongly scattering layer, demonstrating the potential of this method for high-resolution imaging of scattering media.

  9. Spatio-temporal variability of satellite derived aerosol optical thickness and ground measurements over East China

    NASA Astrophysics Data System (ADS)

    Meng, Fei; Shi, Tongguang

    2016-04-01

    Two-year records of Visible Infrared Imaging Radiometer Suite (VIIRS) Intermediate Product (IP) data on the aerosol optical thickness (AOT) at 550 nm were evaluated by comparing them with sun-sky radiometer measurements from the Chinese sun hazemeter network (CSHNET) and the aerosol robotic network (AERONET). The monthly and seasonal variations in the aerosol optical properties over eastern China were then investigated using collocated VIIRS IP data and CSHNET and AERONET measurements.Results show that the performances of the current VIIRS IP AOT retrievals at the provisional stage were consistent with ground measurements. Similar characteristics of seasonal and monthly variations were found among the measurements, though the observational methodologies were different, showing maxima in the summer and spring and minima in the winter and autumn.

  10. HAC: Band Gap, Photoluminescence, and Optical/Near-Infrared Absorption

    NASA Technical Reports Server (NTRS)

    Witt, Adolf N.; Ryutov, Dimitri; Furton, Douglas G.

    1996-01-01

    We report results of laboratory measurements which illustrate the wide range of physical properties found among hydrogenated amorphous carbon (HAC) solids. Within this range, HAC can match quantitatively the astronomical phenomena ascribed to carbonaceous coatings on interstellar grains. We find the optical band gap of HAC to be well correlated with other physical properties of HAC of astronomical interest, and conclude that interstellar HAC must be fairly hydrogen-rich with a band gap of E(sub g) is approx. greater than 2.0 eV.

  11. Determination of the optical thickness and effective particle radius of clouds from reflected solar radiation measurements. I - Theory

    NASA Technical Reports Server (NTRS)

    Nakajima, Teruyuki; King, Michael D.

    1990-01-01

    A method is presented for determining the optical thickness and effective particle radius of stratiform cloud layers from reflected solar radiation measurements. A detailed study is presented which shows that the cloud optical thickness (tau c) and effective particle radius (r/e/) of water clouds can be determined solely from reflection function measurements at 0.75 micron and 2.16 microns, provided tau c is not less than 4 and r(e) is not less than 6 microns. For optically thin clouds, the retrieval becomes ambiguous, resulting in two possible solutions for the effective radius and optical thickness. Adding a third channel near 1.65 micron does not improve the situation noticeably, whereas the addition of a channel near 3.70 microns reduces the ambiguity in deriving the effective radius. The effective radius determined by the above procedure corresponds to the droplet radius at some optical depth within the cloud layer.

  12. Effect of Sn on the optical band gap determined using absorption spectrum fitting method

    SciTech Connect

    Heera, Pawan; Kumar, Anup; Sharma, Raman

    2015-05-15

    We report the preparation and the optical studies on tellurium rich glasses thin films. The thin films of Se{sub 30}Te{sub 70-x} Sn{sub x} system for x= 0, 1.5, 2.5 and 4.5 glassy alloys prepared by melt quenching technique are deposited on the glass substrate using vacuum thermal evaporation technique. The analysis of absorption spectra in the spectral range 400nm–4000 nm at room temperature obtained from UV-VIS-NIR spectrophotometer [Perkin Elmer Lamda-750] helps us in the optical characterization of the thin films under study. The absorption spectrum fitting method is applied by using the Tauc’s model for estimating the optical band gap and the width of the band tail of the thin films. The optical band gap is calculated and is found to decrease with the Sn content.

  13. Monitoring of volcanic sulphur dioxide emissions using differential absorption lidar (DIAL), differential optical absorption spectroscopy (DOAS), and correlation spectroscopy (COSPEC)

    NASA Astrophysics Data System (ADS)

    Weibring, P.; Edner, H.; Svanberg, S.; Cecchi, G.; Pantani, L.; Ferrara, R.; Caltabiano, T.

    1998-10-01

    The total fluxes of sulphur dioxide from the Italian volcanoes Etna, Stromboli, and Vulcano were studied using optical remote sensing techniques in three shipborne field experiments (1992, 1994, and 1997). The main purpose of the experiments was to compare active (laser) techniques with passive monitoring. Differential absorption lidar (DIAL) measurements were implemented by placing the Swedish mobile lidar system on board the Italian research vessel Urania, sailing under the volcanic plumes. Simultaneously, the passive differential optical absorption spectroscopy (DOAS) technique was used for assessing the total overhead gas burden. Finally, correlation spectroscopy (COSPEC) was also implemented in one of the campaigns. Differences in integrated gas column assessment are expected and observed, mostly connected to complex scattering conditions influencing the passive measurements. Since such measurements are much employed in routine volcanic monitoring it is of great interest to model and provide corrections to the raw data obtained. Lidar measurements proved to be quite useful for this purpose. By combining the integrated gas concentration over the plume cross section with wind velocity data, SO2 fluxes of the order of 1000, 100, and 10 tonnes/day were measured for Mt. Etna, Stromboli, and Vulcano, respectively.

  14. Retrieval of aerosol optical thickness from PROBA-CHRIS images acquired over a coniferous forest

    NASA Astrophysics Data System (ADS)

    Maffei, Carmine; Leone, Antonio P.; Menenti, Massimo; Pippi, Ivan; Maselli, Fabio; Antonelli, Paolo

    2005-10-01

    In the present work we show the potential of multiangular hyperspectral PROBA-CHRIS data to estimate aerosol optical properties over dense dark vegetation. Data acquired over San Rossore test site (Pisa, Italy) have been used together with simultaneous ground measurements. Additionally, spectral measurement over the canopy have been performed to describe the directional behavior of a Pinus pinaster canopy. Determination of aerosol properties from optical remote sensing images over land is an under-determined problem, and some assumptions have to be made on both the aerosol and the surface being imaged. Radiance measured on multiple directions add extra information that help in reducing retrieval ambiguity. Nevertheless, multiangular observations don't allow to ignore directional spectral properties of vegetation canopies. Since surface reflectivity is the parameter we wish to determine with remote sensing after atmospheric correction, at least the shape of the bi-directional reflectance factor has to be assumed. We have adopted a Rahman BRF, and have estimated its geometrical parameters from ground spectral measurements. The inversion of measured radiance to obtain aerosol optical properties has been performed, allowing simultaneous retrieval of aerosol model and optical thickness together with the vegetation reflectivity parameter of the Rahman model.

  15. Optical in-situ monitoring system for simultaneous measurement of thickness and curvature of thick layer stacks during hydride vapor phase epitaxy growth of GaN

    NASA Astrophysics Data System (ADS)

    Semmelroth, K.; Berwian, P.; Schröter, C.; Leibiger, G.; Schönleber, M.; Friedrich, J.

    2015-10-01

    For improved real-time process control we integrated a novel optical in-situ monitoring system in a vertical reactor for hydride vapor phase epitaxy (HVPE) growth of gallium nitride (GaN) bulk crystals. The in-situ monitoring system consists of a fiber-optical interferometric sensor in combination with an optimized differential measuring head. The system only needs one small optical path perpendicular to the center of the layer stack typically consisting of sapphire as substrate and GaN. It can handle sample distances up to 1 m without difficulty. The in-situ monitoring system is simultaneously measuring the optical layer thicknesses of the GaN/sapphire layer stack and the absolute change of the distance between the measuring head and the backside of the layer stack. From this data it is possible to calculate the thickness of the growing GaN up to a thickness of about 1000 μm and the absolute change in curvature of the layer stack. The performance of the in-situ monitoring system is shown and discussed based on the measured interference signals recorded during a short-time and a long-time HVPE growth run.

  16. Influence of Ag thickness on structural, optical, and electrical properties of ZnS/Ag/ZnS multilayers prepared by ion beam assisted deposition

    SciTech Connect

    Leng Jian; Yu Zhinong; Xue Wei; Zhang Ting; Jiang Yurong; Zhang Jie; Zhang Dongpu

    2010-10-15

    The structural, optical, and electrical characteristics of zinc sulfide (ZnS)/Ag/ZnS (ZAZ) multilayer films prepared by ion beam assisted deposition on k9 glass have been investigated as a function of Ag layer thickness. The characteristics of ZAZ multilayer are significantly improved up insertion of optimal Ag thickness between ZnS layers. The results show that due to bombardment of Ar ion beam, distinct Ag islands evolve into continuous Ag films at a thin Ag thickness of about 4 nm. The thinner Ag film as a thickness of 2 nm leads to high sheet resistance and low transmittance for the interface scattering induced by the Ag islands or noncontinuous films; and when the Ag thickness is over 4 nm, the ZAZ multilayer exhibits a remarkably reduced sheet resistance between 7-80 {Omega}/sq for the increase in carrier concentration and mobility of Ag layer, and a high transmittance over 90% for the interference phenomena of multilayers and low absorption and surface scattering of Ag layer. The ZAZ multilayer with 14 nm Ag film has a figure of merit up to 6.32x10{sup -2} {Omega}{sup -1}, an average transmittance over 92% and a sheet resistance of 7.1 {Omega}/sq. The results suggest that ZAZ film has better optoelectrical properties than conditional indium tin oxide single layer.

  17. Retrieve Optically Thick Ice Cloud Microphysical Properties by Using Airborne Dual-Wavelength Radar Measurements

    NASA Technical Reports Server (NTRS)

    Wang, Zhien; Heymsfield, Gerald M.; Li, Lihua; Heymsfield, Andrew J.

    2005-01-01

    An algorithm to retrieve optically thick ice cloud microphysical property profiles is developed by using the GSFC 9.6 GHz ER-2 Doppler Radar (EDOP) and the 94 GHz Cloud Radar System (CRS) measurements aboard the high-altitude ER-2 aircraft. In situ size distribution and total water content data from the CRYSTAL-FACE field campaign are used for the algorithm development. To reduce uncertainty in calculated radar reflectivity factors (Ze) at these wavelengths, coincident radar measurements and size distribution data are used to guide the selection of mass-length relationships and to deal with the density and non-spherical effects of ice crystals on the Ze calculations. The algorithm is able to retrieve microphysical property profiles of optically thick ice clouds, such as, deep convective and anvil clouds, which are very challenging for single frequency radar and lidar. Examples of retrieved microphysical properties for a deep convective clouds are presented, which show that EDOP and CRS measurements provide rich information to study cloud structure and evolution. Good agreement between IWPs derived from an independent submillimeter-wave radiometer, CoSSIR, and dual-wavelength radar measurements indicates accuracy of the IWC retrieved from the two-frequency radar algorithm.

  18. Measuring the thickness of the peritoneal membrane in mice with optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Alwafi, Reem; Dickinson, Mark; Brenchley, Paul; Walkin, Louise

    2011-06-01

    The detection and diagnosis of diseases have improved in recent years. Developments in diagnostic techniques have helped to improve treatment in the early stages and to avoid many risks to patients. One such technique is optical coherence tomography (OCT), which is used in many medical applications to perform internal microstructural imaging of the human body at high resolution (typically 10 μm), at high speed and in real time. OCT is non-invasive and can be used as a contact or non-contact technique to obtain an image. In medicine, there are many applications that involve OCT, such as in ophthalmology, gastroenterology, cardiology and oncology. This work demonstrates the use of an OCT system incorporating a swept laser source with a high sweep rate of 16 kHz over a wide range of wavelengths (1260 nm to 1390 nm) to measure the thickness of the peritoneal membrane in mice of different sizes and weights. The real axial line speed is limited by the source that is used in the OCT system. The optical source has a bandwidth of ▵λ =110 nm, centred at λ0 =1325 nm. The aim of this study is to investigate the thickening of the peritoneal membrane which can occur during prolonged peritoneal dialysis in mice. As part of this preliminary study, healthy mice of different weights were euthanized and the thickness of the peritoneal membrane was measured using OCT. The aim was to gather data on the expected range of thicknesses present in healthy animals for future studies. For this work, two locations on the peritoneal membrane of each of 20 mice were imaged.

  19. Gas concentration measurement by optical similitude absorption spectroscopy: methodology and experimental demonstration.

    PubMed

    Anselmo, Christophe; Welschinger, Jean-Yves; Cariou, Jean-Pierre; Miffre, Alain; Rairoux, Patrick

    2016-06-13

    We propose a new methodology to measure gas concentration by light-absorption spectroscopy when the light source spectrum is larger than the spectral width of one or several molecular gas absorption lines. We named it optical similitude absorption spectroscopy (OSAS), as the gas concentration is derived from a similitude between the light source and the target gas spectra. The main OSAS-novelty lies in the development of a robust inversion methodology, based on the Newton-Raphson algorithm, which allows retrieving the target gas concentration from spectrally-integrated differential light-absorption measurements. As a proof, OSAS is applied in laboratory to the 2ν3 methane absorption band at 1.66 µm with uncertainties revealed by the Allan variance. OSAS has also been applied to non-dispersive infra-red and the optical correlation spectroscopy arrangements. This all-optics gas concentration retrieval does not require the use of a gas calibration cell and opens new tracks to atmospheric gas pollution and greenhouse gases sources monitoring. PMID:27410280

  20. Greatly Enhanced Optical Absorption of a Defective MoS2 Monolayer through Oxygen Passivation.

    PubMed

    Shu, Huabing; Li, Yunhai; Niu, Xianghong; Wang, Jinlan

    2016-05-25

    Structural defects in the molybdenum disulfide (MoS2) monolayer are widely reported and greatly degrade the transport and photoluminescence. However, how they influence the optical absorption properties remains unclear. In this work, by employing many-body perturbation theory calculations, we investigate the influence of sulfur vacancies (SVs), the main type of intrinsic defects in the MoS2 monolayer, on the optical absorption and exciton effect. Our calculations reveal that the presence of SVs creates localized midgap states in the bandgap, which results in a dramatic red-shift of the absorption peak and stronger absorbance in the visible light and near-infrared region. Nevertheless, the SVs can be finely repaired by oxygen passivation and are beneficial to the formation of the stable localized excitons, which greatly enhance the optical absorption in the spectral range. The defect-mediated/-engineered absorption mechanism is well understood, which offers insightful guides for improving the performance of two-dimensional dichalcogenide-based optoelectronic devices. PMID:27144902

  1. Accounting for nanometer-thick adventitious carbon contamination in X-ray absorption spectra of carbon-based materials.

    PubMed

    Mangolini, Filippo; McClimon, J Brandon; Rose, Franck; Carpick, Robert W

    2014-12-16

    Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy is a powerful technique for characterizing the composition and bonding state of nanoscale materials and the top few nanometers of bulk and thin film specimens. When coupled with imaging methods like photoemission electron microscopy, it enables chemical imaging of materials with nanometer-scale lateral spatial resolution. However, analysis of NEXAFS spectra is often performed under the assumption of structural and compositional homogeneity within the nanometer-scale depth probed by this technique. This assumption can introduce large errors when analyzing the vast majority of solid surfaces due to the presence of complex surface and near-surface structures such as oxides and contamination layers. An analytical methodology is presented for removing the contribution of these nanoscale overlayers from NEXAFS spectra of two-layered systems to provide a corrected photoabsorption spectrum of the substrate. This method relies on the subtraction of the NEXAFS spectrum of the overlayer adsorbed on a reference surface from the spectrum of the two-layer system under investigation, where the thickness of the overlayer is independently determined by X-ray photoelectron spectroscopy (XPS). This approach is applied to NEXAFS data acquired for one of the most challenging cases: air-exposed hard carbon-based materials with adventitious carbon contamination from ambient exposure. The contribution of the adventitious carbon was removed from the as-acquired spectra of ultrananocrystalline diamond (UNCD) and hydrogenated amorphous carbon (a-C:H) to determine the intrinsic photoabsorption NEXAFS spectra of these materials. The method alters the calculated fraction of sp(2)-hybridized carbon from 5 to 20% and reveals that the adventitious contamination can be described as a layer containing carbon and oxygen ([O]/[C] = 0.11 ± 0.02) with a thickness of 0.6 ± 0.2 nm and a fraction of sp(2)-bonded carbon of 0.19 ± 0.03. This

  2. Fabricating silver nanoplate/hybrid silica gel glasses and investigating their nonlinear optical absorption behavior

    NASA Astrophysics Data System (ADS)

    Zheng, Chan; Wenzhe, Chen; Xiaoyun, Ye; Cai, Shuguang; Xiao, Xueqing

    2014-03-01

    Silver nanoplate/hybrid silica gel glasses were prepared via the sol-gel technique. Analysis of ultraviolet-visible spectroscopy extinction spectra confirmed the successful incorporation of silver nanoplates into the hybrid silica gel glasses. The silver nanoplate/hybrid silica gel glass composites are completely noncrystalline because of their low doping level compared with that of the silica matrix. The nonlinear optical absorption behavior of the silver nanoplate/hybrid silica gel glass composites was studied via open-aperture Z-scan technique with 4 ns pulse durations at 532 nm and 1064 nm. The nonlinear optical properties of silver nanoplates are maintained after they were introduced into silica gel glasses. Furthermore, the silver nanoplate/hybrid silica gel glasses exhibit intensity-dependent transformation from saturable absorption (SA) to reverse saturable absorption (RSA). The SA behavior at low excitation intensity can be attributed to the bleaching of ground-state surface plasmon resonance absorption induced by the retarded electronic relaxation process in solid-state gel glasses. By contrast, the RSA at high incident influence may have resulted from excited-state absorption and two-photon absorption.

  3. Relationship of the optical absorption and scattering properties with mechanical and structural properties of apple tissue

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Optical absorption and scattering properties of fruit change with the physiological and biochemical activities in the tissue during ripening and postharvest storage. But it has not been well understood on how these changes are related to the structural and mechanical properties of fruit. This resear...

  4. Atomistic simulations of the optical absorption of type-II CdSe/ZnTe superlattices

    PubMed Central

    2012-01-01

    We perform accurate tight binding simulations to design type-II short-period CdSe/ZnTe superlattices suited for photovoltaic applications. Absorption calculations demonstrate a very good agreement with optical results with threshold strongly depending on the chemical species near interfaces. PMID:23031315

  5. Optical absorption and luminescence in neutron-irradiated, silica-based fibers

    SciTech Connect

    Cooke, D.W.; Farnum, E.H.; Clinard, F.W.

    1995-04-01

    The objectives of this work are to assess the effects of thermal annealing and photobleaching on the optical absorption of neutron-irradiated, silica fibers of the type proposed for use in ITER diagnostics, and to measure x-ray induced luminescence of unirradiated (virgin) and neutron-irradiated fibers.

  6. LONG PATH DIFFERENTIAL OPTICAL ABSORPTION SPECTROMETER AND EPA-APPROVED FIXED POINT METHODS INTERCOMPARISON

    EPA Science Inventory

    Differential optical absorption spectrometry (DOAS) has been used by a number of investigators over the past 10 years to measure a wide range of gaseous air pollutants. ecently OPSIS AB, Lund, Sweden, has developed and made commercially available DOAS instrument that has a number...

  7. AIR QUALITY MONITORING IN ATLANTA WITH THE DIFFERENTIAL OPTICAL ABSORPTION SPECTROMETER

    EPA Science Inventory

    During July and August of 1990, a differential optical absorption spectrometer (DOAS) made by OPSIS Inc. was used to measure gaseous air pollutants over three separate open paths in Atlanta, GA. ver path 1 (1099 m) and path 2 (1824 m), ozone (O3), sulfur dioxide (SO2), nitrogen d...

  8. Improving optical absorptivity of natural dyes for fabrication of efficient dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Hemmatzadeh, Reza; Mohammadi, Ahmad

    2013-11-01

    Efficient and cheap dye-sensitized solar cells (DSSCs) were fabricated using natural dyes from Pastinaca sativa and Beta vulgaris. Natural dyes are environmentally and economically superior to ruthenium-based dyes because they are nontoxic and cheap. However, the conversion efficiency of dye-sensitized solar cells based on natural dyes is low. One way to improve the DSSC performance is to enhance the absorptivity of extracted dyes. We investigated the influence of various factors in the extraction process, such as utilization of different extraction approaches, the acidity of extraction solvent, and different compounds of solvents on the optical absorption spectra. It was found that we could considerably enhance the optical absorptivity of dye and consequently the performance of DSSC by choosing a proper mixture of ethanol and water for extracting solvent and also the acidity of dye solution.

  9. Cell damage in near-infrared multimode optical traps as a result of multiphoton absorption

    NASA Astrophysics Data System (ADS)

    König, K.; Liang, H.; Berns, M. W.; Tromberg, B. J.

    1996-07-01

    We report on cell damage of single cells confined in continuous-wave (cw), near-infrared (NIR) multimode optical traps as a result of multiphoton absorption phenomena. Trapping beams at NIR wavelengths less than 800 nm are capable of damaging cells through a two-photon absorption process. Cell damage is more pronounced in multimode cw traps compared with single-frequency true cw NIR traps because of transient power enhancement by longitudinal mode beating. Partial mode locking in tunable cw Ti:sapphire lasers used as trapping beam sources can produce unstable subnanosecond pulses at certain wavelengths that amplify multiphoton absorption effects significantly. We recommend the use of single-frequency long-wavelength NIR trapping beams for optical micromanipulation of vital cells.

  10. Optical-loss suppressed InGaN laser diodes using undoped thick waveguide structure

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Masao; Imafuji, Osamu; Nozaki, Shinichiro; Hagino, Hiroyuki; Takigawa, Shinichi; Katayama, Takuma; Tanaka, Tsuyoshi

    2016-02-01

    We propose optical-loss suppressed thick-optical-waveguide (TOW) InGaN laser diodes (LDs) without operatingvoltage increase. A record high continuous-wave (CW) output of 7.2W for a single-emitting InGaN LD is achieved without thermal peak-out in the light-current curve. The TOW enables to confine major part of the propagating light into a transparent undoped region, and thus significantly reduces the optical-loss. An electron-overflow-suppression (EOS) layer placed between the waveguide layer and a p-cladding layer plays an important role to reduce the operating voltage after introduction of the undoped TOW layer. We executed a self-consisted calculation of voltage-current characteristics taking into account Schrödinger and Poisson equations in conjunction with a carrier continuity equation. The calculation result indicates possible presence of conductivity-modulation in the waveguide filled with electrons reflected backward by the EOS layer and holes injected from the p-type cladding layer. We successfully demonstrated the optical-loss suppressed operation resulting in the slope efficiency (SE) increase from 2.0W/A to 2.5W/A. It is noted that the operating voltage of the TOW LD is nearly identical to the conventional LD thanks to the above conductivitymodulation phenomenon. The presented result suggests that our TOW structure can overcome the optical-loss drawback of the InGaN LDs, and hence will lead them to the applications requiring high wattage light sources.

  11. Optical absorption of neutron-irradiated silica fibers

    SciTech Connect

    Cooke, D.W.; Farnum, E.H.; Bennett, B.L.

    1996-10-01

    Induced-loss spectra of silica-based optical fibers exposed to high (10{sup 23} n-m{sup {minus}2}) and low (10{sup 21} n-m{sup {minus}2}) fluences of neutrons at the Los Alamos Spallation Radiation Effects Facility (LASREF) have been measured. Two types of fibers consisting of a pure fused silica core with fluorine-doped ({approximately}4 mole %) cladding were obtained from Fiberguide Industries and used in the as-received condition. Anhydroguide{trademark} and superguide{trademark} fibers contained less than 1 ppm, and 600 to 800 ppm of OH, respectively. The data suggest that presently available silica fibers can be used in plasma diagnostics, but the choice and suitability depends upon the spectral region of interest. Low-OH content fibers can be used for diagnostic purposes in the interval {approximately}800 to 1400 mn if the exposure is to high-fluence neutrons. For low-fluence neutron exposures, the low-OH content fibers are best suited for use in the interval {approximately}800 to 2000 nm, and the high-OH content fibers are the choice for the interval {approximately}400 to 800 nm.

  12. Modeling of mineral dust in the atmosphere: Sources, transport, and optical thickness

    NASA Technical Reports Server (NTRS)

    Tegen, Ina; Fung, Inez

    1994-01-01

    A global three-dimensional model of the atmospheric mineral dust cycle is developed for the study of its impact on the radiative balance of the atmosphere. The model includes four size classes of minearl dust, whose source distributions are based on the distributions of vegetation, soil texture and soil moisture. Uplift and deposition are parameterized using analyzed winds and rainfall statistics that resolve high-frequency events. Dust transport in the atmosphere is simulated with the tracer transport model of the Goddard Institute for Space Studies. The simulated seasonal variations of dust concentrations show general reasonable agreement with the observed distributions, as do the size distributions at several observing sites. The discrepancies between the simulated and the observed dust concentrations point to regions of significant land surface modification. Monthly distribution of aerosol optical depths are calculated from the distribution of dust particle sizes. The maximum optical depth due to dust is 0.4-0.5 in the seasonal mean. The main uncertainties, about a factor of 3-5, in calculating optical thicknesses arise from the crude resolution of soil particle sizes, from insufficient constraint by the total dust loading in the atmosphere, and from our ignorance about adhesion, agglomeration, uplift, and size distributions of fine dust particles (less than 1 micrometer).

  13. An Optically Thick Disk Wind in GRO J1655–40?

    NASA Astrophysics Data System (ADS)

    Shidatsu, M.; Done, C.; Ueda, Y.

    2016-06-01

    We revisited the unusual wind in GRO J1655‑40, detected with Chandra in 2005 April, using long-term Rossi X-ray Timing Explorer X-ray data and simultaneous optical/near-infrared photometric data. This wind is the most convincing case for magnetic driving in black hole binaries, as it has an inferred launch radius that is a factor of 10 smaller than the thermal wind prediction. However, the optical and near-infrared (OIR) fluxes monotonically increase around the Chandra observation, whereas the X-ray flux monotonically decreases from 10 days beforehand. Yet the optical and near-infrared fluxes are from the outer, irradiated disk, so for them to increase implies that the X-rays likewise increased. We applied a new irradiated disk model to the multi-wavelength spectral energy distributions. Fitting the OIR fluxes, we estimated the intrinsic luminosity at the Chandra epoch was ≳ 0.7{L}{{Edd}}, which is more than one order of magnitude larger than the observed X-ray luminosity. These results could be explained if a Compton-thick, almost completely ionized gas was present in the wind and strong scattering reduced the apparent X-ray luminosity. The effects of scattering in the wind should then be taken into account for discussion of the wind-driving mechanism. Radiation pressure and Compton heating may also contribute to powering the wind at this high luminosity.

  14. Observation of temperature dependence of the IR hydroxyl absorption bands in silica optical fiber

    NASA Astrophysics Data System (ADS)

    Yu, Li; Bonnell, Elizabeth; Homa, Daniel; Pickrell, Gary; Wang, Anbo; Ohodnicki, P. R.; Woodruff, Steven; Chorpening, Benjamin; Buric, Michael

    2016-07-01

    This study reports on the temperature dependent behavior of silica based optical fibers upon exposure to high temperatures in hydrogen and ambient air. The hydroxyl absorption bands in the wavelength range of 1000-2500 nm of commercially available multimode fibers with pure silica and germanium doped cores were examined in the temperature range of 20-800 °C. Two hydroxyl-related infrared absorption bands were observed: ∼2200 nm assigned to the combination of the vibration mode of Si-OH bending and the fundamental hydroxyl stretching mode, and ∼1390 nm assigned to the first overtone of the hydroxyl stretching. The absorption in the 2200 nm band decreased in intensity, while the 1390 nm absorption band shifted to longer wavelengths with an increase in temperature. The observed phenomena were reversible with temperature and suspected to be due, in part, to the conversion of the OH spectral components into each other and structural relaxation.

  15. Optical monitor for real time thickness change measurements via lateral-translation induced phase-stepping interferometry

    DOEpatents

    Rushford, Michael C.

    2002-01-01

    An optical monitoring instrument monitors etch depth and etch rate for controlling a wet-etching process. The instrument provides means for viewing through the back side of a thick optic onto a nearly index-matched interface. Optical baffling and the application of a photoresist mask minimize spurious reflections to allow for monitoring with extremely weak signals. A Wollaston prism enables linear translation for phase stepping.

  16. Absorption and spectra of optical parameters in amorphous solid solutions of the Se-S system

    SciTech Connect

    Djalilov, N. Z.; Damirov, G. M.

    2011-04-15

    A study of the optical properties of the Se-S system has revealed a correlation between the dependences of optical absorption coefficient {alpha}, effective concentration of charged defects N{sub t}, and characteristic energy E{sub 0} corresponding to the Urbach optical absorption in the spectral region where the Urbach rule works for the Se-S system on the S concentration. These optical properties are controlled by charged defects. It is shown that concentrations of intrinsic charged defects can be changed by variation in composition of the Se-S system. Reflectance spectra of amorphous solid solutions of the Se-S system are studied within the energy range 1-6 eV. Using the Kramers-Kronig method, spectral dependences of optical constants and derivative optical and dielectric functions are calculated. Variation in the spectra of optical parameters with composition of the Se-S system are explained within a cluster model in which the density of electron states is a function of atomic configurations in clusters, i.e., of the character of a short-range order.

  17. Optical absorption in lithiated tungsten oxide thin films: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Berggren, Lars; Jonsson, Jacob C.; Niklasson, Gunnar A.

    2007-10-01

    Amorphous tungsten oxide exhibits electrochromism when intercalated with protons, lithium, sodium, and other ions. Thin films of the material were prepared by dc magnetron sputtering and then electrochemically intercalated with lithium. The optical absorption in the wavelength range of 300-2500nm was measured for a number of lithium concentrations. The optical absorption shows a maximum for lithium/tungsten ratios of 0.3-0.5. The optical spectra can be fitted by a superposition of three Gaussian peaks, representing the three possible electronic transitions between W6+, W5+, and W4+ sites. The variation of the peak strength with lithium concentration is consistent with an extended site-saturation theory.

  18. Optical pendulum effect in one-dimensional diffraction-thick porous silicon based photonic crystals

    SciTech Connect

    Novikov, V. B. Svyakhovskiy, S. E.; Maydykovskiy, A. I.; Murzina, T. V.; Mantsyzov, B. I.

    2015-11-21

    We present the realization of the multiperiodic optical pendulum effect in 1D porous silicon photonic crystals (PhCs) under dynamical Bragg diffraction in the Laue scheme. The diffraction-thick PhC contained 360 spatial periods with a large variation of the refractive index of adjacent layers of 0.4. The experiments reveal switching of the light leaving the PhC between the two spatial directions, which correspond to Laue diffraction maxima, as the fundamental wavelength or polarization of the incident light is varied. A similar effect can be achieved when the temperature of the sample or the intensity of the additional laser beam illuminating the crystal are changed. We show that in our PhC structures, the spectral period of the pendulum effect is down to 5 nm, while the thermal period is about 10 °C.

  19. Implications of Satellite Swath Width on Global Aerosol Optical Thickness Statistics

    NASA Technical Reports Server (NTRS)

    Colarco, Peter; Kahn, Ralph; Remer, Lorraine; Levy, Robert; Welton, Ellsworth

    2012-01-01

    We assess the impact of swath width on the statistics of aerosol optical thickness (AOT) retrieved by satellite as inferred from observations made by the Moderate Resolution Imaging Spectroradiometer (MODIS). We sub-sample the year 2009 MODIS data from both the Terra and Aqua spacecraft along several candidate swaths of various widths. We find that due to spatial sampling there is an uncertainty of approximately 0.01 in the global, annual mean AOT. The sub-sampled monthly mean gridded AOT are within +/- 0.01 of the full swath AOT about 20% of the time for the narrow swath sub-samples, about 30% of the time for the moderate width sub-samples, and about 45% of the time for the widest swath considered. These results suggest that future aerosol satellite missions with only a narrow swath view may not sample the true AOT distribution sufficiently to reduce significantly the uncertainty in aerosol direct forcing of climate.

  20. Heat Transfer Modeling and Validation for Optically Thick Alumina Fibrous Insulation

    NASA Technical Reports Server (NTRS)

    Daryabeigi, Kamran

    2009-01-01

    Combined radiation/conduction heat transfer through unbonded alumina fibrous insulation was modeled using the diffusion approximation for modeling the radiation component of heat transfer in the optically thick insulation. The validity of the heat transfer model was investigated by comparison to previously reported experimental effective thermal conductivity data over the insulation density range of 24 to 96 kg/cu m, with a pressure range of 0.001 to 750 torr (0.1 to 101.3 x 10(exp 3) Pa), and test sample hot side temperature range of 530 to 1360 K. The model was further validated by comparison to thermal conductivity measurements using the transient step heating technique on an insulation sample at a density of 144 kg/cu m over a pressure range of 0.001 to 760 torr, and temperature range of 290 to 1090 K.

  1. Label-free imaging of thick tissue at 1550 nm using a femtosecond optical parametric generator.

    PubMed

    Trägårdh, Johanna; Robb, Gillian; Gadalla, Kamal K E; Cobb, Stuart; Travis, Christopher; Oppo, Gian-Luca; McConnell, Gail

    2015-08-01

    We have developed a simple wavelength-tunable optical parametric generator (OPG), emitting broadband ultrashort pulses with peak wavelengths at 1530-1790 nm, for nonlinear label-free microscopy. The OPG consists of a periodically poled lithium niobate crystal, pumped at 1064 nm by a ultrafast Yb:fiber laser with high pulse energy. We demonstrate that this OPG can be used for label-free imaging, by third-harmonic generation, of nuclei of brain cells and blood vessels in a >150 μm thick brain tissue section, with very little decay of intensity with imaging depth and no visible damage to the tissue at an incident average power of 15 mW. PMID:26258338

  2. Retrieval of particle size distribution from aerosol optical thickness using an improved particle swarm optimization algorithm

    NASA Astrophysics Data System (ADS)

    Mao, Jiandong; Li, Jinxuan

    2015-10-01

    Particle size distribution is essential for describing direct and indirect radiation of aerosols. Because the relationship between the aerosol size distribution and optical thickness (AOT) is an ill-posed Fredholm integral equation of the first type, the traditional techniques for determining such size distributions, such as the Phillips-Twomey regularization method, are often ambiguous. Here, we use an approach based on an improved particle swarm optimization algorithm (IPSO) to retrieve aerosol size distribution. Using AOT data measured by a CE318 sun photometer in Yinchuan, we compared the aerosol size distributions retrieved using a simple genetic algorithm, a basic particle swarm optimization algorithm and the IPSO. Aerosol size distributions for different weather conditions were analyzed, including sunny, dusty and hazy conditions. Our results show that the IPSO-based inversion method retrieved aerosol size distributions under all weather conditions, showing great potential for similar size distribution inversions.

  3. Choroidal Thickness and En Face Optical Coherence Tomography Imaging in Autoimmune Retinopathy.

    PubMed

    Polascik, Breanna A; Grewal, Dilraj S; Jiramongkolchai, Kim; Fekrat, Sharon

    2016-04-01

    A 57-year-old white woman developed autoimmune retinopathy (AIR) in both eyes associated with bilateral autoimmune sensorineural hearing loss. Laboratory testing was positive for 68kDa (heat-shock protein) and 136kDa (human interstitial retinoid-binding protein). Extensive cancer screening was negative. Spectral-domain optical coherence tomography enhanced depth imaging demonstrated a markedly thickened choroid in both eyes. En face imaging showed a distinctive pattern of granular hyperreflective foveal dots. The concurrent sensorineural hearing loss was thought to be of autoimmune origin and also responded to immunosuppressive treatment. Eyes with non-paraneoplastic, seropositive AIR may have associated increased choroidal thickness. Audiology testing should be considered. [Ophthalmic Surg Lasers Imaging Retina. 2016;47:362-365.]. PMID:27065377

  4. Optical pendulum effect in one-dimensional diffraction-thick porous silicon based photonic crystals

    NASA Astrophysics Data System (ADS)

    Novikov, V. B.; Svyakhovskiy, S. E.; Maydykovskiy, A. I.; Murzina, T. V.; Mantsyzov, B. I.

    2015-11-01

    We present the realization of the multiperiodic optical pendulum effect in 1D porous silicon photonic crystals (PhCs) under dynamical Bragg diffraction in the Laue scheme. The diffraction-thick PhC contained 360 spatial periods with a large variation of the refractive index of adjacent layers of 0.4. The experiments reveal switching of the light leaving the PhC between the two spatial directions, which correspond to Laue diffraction maxima, as the fundamental wavelength or polarization of the incident light is varied. A similar effect can be achieved when the temperature of the sample or the intensity of the additional laser beam illuminating the crystal are changed. We show that in our PhC structures, the spectral period of the pendulum effect is down to 5 nm, while the thermal period is about 10 °C.

  5. THE ANGULAR DISTRIBUTION OF Ly{alpha} RESONANT PHOTONS EMERGING FROM AN OPTICALLY THICK MEDIUM

    SciTech Connect

    Yang Yang; Shu Chiwang; Roy, Ishani; Fang Lizhi

    2013-07-20

    We investigate the angular distribution of Ly{alpha} photons scattering or emerging from an optically thick medium. Since the evolution of specific intensity I in frequency space and angular space are coupled with each other, we first develop the WENO numerical solver to find the time-dependent solutions of the integro-differential equation of I in frequency and angular space simultaneously. We first show that the solutions with the Eddington approximation, which assume that I is linearly dependent on the angular variable {mu}, yield similar frequency profiles of the photon flux as those without the Eddington approximation. However, the solutions of the {mu} distribution evolution are significantly different from those given by the Eddington approximation. First, the angular distribution of I is found to be substantially dependent on the frequency of the photons. For photons with the resonant frequency {nu}{sub 0}, I contains only a linear term of {mu}. For photons with frequencies at the double peaks of the flux, the {mu}-distribution is highly anisotropic; most photons are emitted radially forward. Moreover, either at {nu}{sub 0} or at the double peaks, the {mu} distributions actually are independent of the initial {mu} distribution of photons of the source. This is because the photons with frequencies either at {nu}{sub 0} or the double peaks undergo the process of forgetting their initial conditions due to resonant scattering. We also show that the optically thick medium is a collimator of photons at the double peaks. Photons from the double peaks form a forward beam with a very small opening angle.

  6. The Angular Distribution of Lyα Resonant Photons Emerging from an Optically Thick Medium

    NASA Astrophysics Data System (ADS)

    Yang, Yang; Roy, Ishani; Shu, Chi-Wang; Fang, Li-Zhi

    2013-07-01

    We investigate the angular distribution of Lyα photons scattering or emerging from an optically thick medium. Since the evolution of specific intensity I in frequency space and angular space are coupled with each other, we first develop the WENO numerical solver to find the time-dependent solutions of the integro-differential equation of I in frequency and angular space simultaneously. We first show that the solutions with the Eddington approximation, which assume that I is linearly dependent on the angular variable μ, yield similar frequency profiles of the photon flux as those without the Eddington approximation. However, the solutions of the μ distribution evolution are significantly different from those given by the Eddington approximation. First, the angular distribution of I is found to be substantially dependent on the frequency of the photons. For photons with the resonant frequency ν0, I contains only a linear term of μ. For photons with frequencies at the double peaks of the flux, the μ-distribution is highly anisotropic; most photons are emitted radially forward. Moreover, either at ν0 or at the double peaks, the μ distributions actually are independent of the initial μ distribution of photons of the source. This is because the photons with frequencies either at ν0 or the double peaks undergo the process of forgetting their initial conditions due to resonant scattering. We also show that the optically thick medium is a collimator of photons at the double peaks. Photons from the double peaks form a forward beam with a very small opening angle.

  7. Optical instrument for measurement of vaginal coating thickness by drug delivery formulations

    NASA Astrophysics Data System (ADS)

    Henderson, Marcus H.; Peters, Jennifer J.; Walmer, David K.; Couchman, Grace M.; Katz, David F.

    2005-03-01

    An optical device has been developed for imaging the human vaginal epithelial surfaces, and quantitatively measuring distributions of coating thickness of drug delivery formulations—such as gels—applied for prophylaxis, contraception or therapy. The device consists of a rigid endoscope contained within a 27-mm-diam hollow, polished-transparent polycarbonate tube (150mm long) with a hemispherical cap. Illumination is from a xenon arc. The device is inserted into, and remains stationary within the vagina. A custom gearing mechanism moves the endoscope relative to the tube, so that it views epithelial surfaces immediately apposing its outer surface (i.e., 150mm long by 360° azimuthal angle). Thus, with the tube fixed relative to the vagina, the endoscope sites local regions at distinct and measurable locations that span the vaginal epithelium. The returning light path is split between a video camera and photomultiplier. Excitation and emission filters in the light path enable measurement of fluorescence of the sited region. Thus, the instrument captures video images simultaneously with photometric measurement of fluorescence of each video field [˜10mm diameter; formulations are labeled with 0.1%w/w United States Pharmacoepia (USP) injectable sodium fluorescein]. Position, time and fluorescence measurements are continuously displayed (on video) and recorded (to a computer database). The photomultiplier output is digitized to quantify fluorescence of the endoscope field of view. Quantification of the thickness of formulation coating of a surface sited by the device is achieved due to the linear relationship between thickness and fluorescence intensity for biologically relevant thin layers (of the order of 0.5mm). Summary measures of coating have been developed, focusing upon extent, location and uniformity. The device has begun to be applied in human studies of model formulations for prophylaxis against infection with HIV and other sexually transmitted pathogens.

  8. Optical instrument for measurement of vaginal coating thickness by drug delivery formulations

    SciTech Connect

    Henderson, Marcus H.; Peters, Jennifer J.; Walmer, David K.; Couchman, Grace M.; Katz, David F.

    2005-03-01

    An optical device has been developed for imaging the human vaginal epithelial surfaces, and quantitatively measuring distributions of coating thickness of drug delivery formulations - such as gels - applied for prophylaxis, contraception or therapy. The device consists of a rigid endoscope contained within a 27-mm-diam hollow, polished-transparent polycarbonate tube (150 mm long) with a hemispherical cap. Illumination is from a xenon arc. The device is inserted into, and remains stationary within the vagina. A custom gearing mechanism moves the endoscope relative to the tube, so that it views epithelial surfaces immediately apposing its outer surface (i.e., 150 mm long by 360 deg. azimuthal angle). Thus, with the tube fixed relative to the vagina, the endoscope sites local regions at distinct and measurable locations that span the vaginal epithelium. The returning light path is split between a video camera and photomultiplier. Excitation and emission filters in the light path enable measurement of fluorescence of the sited region. Thus, the instrument captures video images simultaneously with photometric measurement of fluorescence of each video field [{approx}10 mm diameter; formulations are labeled with 0.1% w/w United States Pharmacoepia (USP) injectable sodium fluorescein]. Position, time and fluorescence measurements are continuously displayed (on video) and recorded (to a computer database). The photomultiplier output is digitized to quantify fluorescence of the endoscope field of view. Quantification of the thickness of formulation coating of a surface sited by the device is achieved due to the linear relationship between thickness and fluorescence intensity for biologically relevant thin layers (of the order of 0.5 mm). Summary measures of coating have been developed, focusing upon extent, location and uniformity. The device has begun to be applied in human studies of model formulations for prophylaxis against infection with HIV and other sexually

  9. Choroidal thickness measurements with optical coherence tomography in branch retinal vein occlusion

    PubMed Central

    Coban-Karatas, Muge; Altan-Yaycioglu, Rana; Ulas, Burak; Sizmaz, Selcuk; Canan, Handan; Sariturk, Cagla

    2016-01-01

    AIM To evaluate central macular thickness (CMT) and mean choroidal thickness (MCT) in eyes with branch retinal vein occlusion (BRVO), before and after ranibizumab treatment using spectral domain-optical coherence tomography (SD-OCT). METHODS Forty-two patients with unilateral BRVO and macular edema were included in this study. There were 25 men and 17 women. Using SD-OCT, choroidal thickness was measured at 500 µm intervals up to 1500 µm temporal and nasal to the fovea. MCT was calculated based on the average of the 7 locations. All the eyes with BRVO were treated with intravitreal ranibizumab (0.5 mg/0.05 mL). Comparisons between the BRVO and fellow eyes were analyzed using Mann-Whitney U test. Pre-injection and post-injection measurements were analyzed using Wilcoxon test and repeated measure analysis. RESULTS At baseline, there was a significant difference between the BRVO and fellow eyes in MCT [BRVO eyes 245 (165-330) µm, fellow eyes 229 (157-327) µm] and CMT [BRVO eyes 463 (266-899) µm, fellow eyes 235 (148-378) µm (P=0.041, 0.0001, respectively)]. Following treatment, CMT [295 (141-558) µm] and MCT [229 (157-329) µm] decreased significantly compared to the baseline measurements (P=0.001, 0.006, respectively). Also BCVA (logMAR) improved significantly (P=0.0001) in the BRVO eyes following treatment. After treatment CMT [BRVO eyes 295 (141-558) µm, fellow eyes 234 (157-351) µm] and MCT [BRVO eyes 229 (157-329) µm, fellow eyes 233 (162-286) µm] values did not reveal any significant difference in BRVO eyes and fellow eyes (P=0.051, 0.824, respectively). CONCLUSION In eyes with BRVO, CMT and MCT values are greater than the fellow eyes, and decrease significantly following ranibizumab injection. PMID:27275430

  10. Label-free measurements of membrane tether thickness using optical tweezers combined with SLIM

    NASA Astrophysics Data System (ADS)

    Sarshar, Mohammad; Wong, Winson T.; Anvari, Bahman

    2015-03-01

    Various cellular activities such as motility, division, and endocytosis involve a change in the cell shape. The mechanical interactions between the cell membrane and cytoskeleton play an important role in regulating changes in the cell shape. Tether formation from cell membranes provides a technique to characterize the mechanical properties of cell membranes and membrane-cytoskeleton interactions. Accurate measurement of the nano-scale tether diameter is relevant to quantification of membrane tension, bending modulus, and adhesion energy of the membrane-cytoskeleton structure. We have integrated optical tweezers with quantitative phase imaging, based on spatial light interference microscopy (SLIM), to simultaneously form tethers from HEK-293 cells and measure their diameters. Tether thickness along the illumination axis was measured using the quantitative phase map of the sample, and the refractive index (RI) mismatch between the sample and the surrounding media. The RI of the tethers ranged from 1.354 to 1.368 (cell culture medium RI=1.337). Our SLIM imaging system provided a 38 nm resolution in tether thickness measurements. Tether diameter fluctuations of <100 nm were resolved on tethers that ranged between 600-900 nm in diameter. Our integrated platform also provides the ability to simultaneously manipulate and image cell organelles in a non-contact and marker-free manner at nanometer spatial resolution.

  11. Crystal structure and nonlinear optical absorption of a new chalcone derivative: a promising candidate for optical switching

    NASA Astrophysics Data System (ADS)

    Chandra Shekhara Shetty, T.; Raghavendra, S.; Chidan Kumar, C. S.; Dharmaprakash, S. M.

    2016-07-01

    A new nonlinear optical material, 4-[(2 E)-3-(3-fluorophenyl) prop-2-enoyl] benzonitrile (3FPB), belonging to chalcone family was synthesized and characterized by FTIR and linear absorption spectroscopy. Single-crystal X-ray diffraction reveals that the new material crystallizes in monoclinic system with P21/c space group and lattice parameters a = 6.4841(2) Å, b = 13.6038(5) Å, c = 14.6418(6) Å, α = 90.00°, β = 94.552(2)° and γ = 90°. The crystallographic perfection of the synthesized material has been analyzed by X-ray powder diffraction. The X-ray powder diffraction peaks of the sample were indexed with hkl values. The UV-visible spectrum for 3FPB crystals showed the optical transmittance window and a lower cutoff wavelength of absorption at 343 nm. The direct transition band gap energy and indirect transition energy gap were determined using Tauc's plots. The thermal stability and melting point of the material have been investigated by thermogravimetric analysis/differential thermal analysis (TGA/DTA). The Thermogravimetric curve showed the absence of any phase transition before melting point. Third-order nonlinear absorption and optical limiting experiment were carried out using open-aperture Z-scan experiment with Nd:YAG laser nanosecond pulses at a wavelength of 532 nm.

  12. Nonlinear optical absorption and refraction in a strained anisotropic multi-level quantum dot system

    NASA Astrophysics Data System (ADS)

    Negi, C. M. S.; Gupta, Saral K.; Kumar, Dharmendra; Kumar, Jitendra

    2013-08-01

    Linear and nonlinear optical properties of disc shaped anisotropic multi-level quantum dot (QD) system has been theoretically investigated. The effect of dot size, shape anisotropy, strain and incident optical intensity on linear absorption, nonlinear absorption and nonlinear refractive index has been explored. The QD is modeled by in-plane anisotropic parabolic potential along x-y plane and by finite well potential along growth direction (z-axis). The contribution of strain is incorporated through various deformation potentials. The energy and wave function calculations are performed by multi-band envelope function approach based on k.p theory. The formulation is applied to the CdSe/CdS QD system. The numerical results show that, dot size, anisotropy and optical intensity have important effect on linear and nonlinear optical properties. The effect of strain is simultaneous red and blue shift of heavy hole (hh) and light hole (lh) transitions, respectively, which is clearly visible in terms of well resolved optical spectra. The theoretical results obtained are compared with the available experimental data and the results are in good agreement. Large blue shift and enhancement in magnitude of linear and nonlinear optical spectra of QD with size, anisotropy and strain make QD a promising candidate for application in tunable Nano-optoelectronic devices.

  13. Recent Progress Towards Quantum Dot Solar Cells with Enhanced Optical Absorption.

    PubMed

    Zheng, Zerui; Ji, Haining; Yu, Peng; Wang, Zhiming

    2016-12-01

    Quantum dot solar cells, as a promising candidate for the next generation solar cell technology, have received tremendous attention in the last 10 years. Some recent developments in epitaxy growth and device structures have opened up new avenues for practical quantum dot solar cells. Unfortunately, the performance of quantum dot solar cells is often plagued by marginal photon absorption. In this review, we focus on the recent progress made in enhancing optical absorption in quantum dot solar cells, including optimization of quantum dot growth, improving the solar cells structure, and engineering light trapping techniques. PMID:27216604

  14. Comparison of liposome entrapment parameters by optical and atomic absorption spectrophotometry.

    PubMed

    Yoss, N L; Popescu, O; Pop, V I; Porutiu, D; Kummerow, F A; Benga, G

    1985-01-01

    Methods for the complete characterization of liposomes prepared by ether-injection are described in detail. The validity of atomic absorption spectrophotometry for measuring markers of trapped volume was checked by comparative determinations of markers with established optical spectrophotometrical methods. The favorable results using atomic absorption spectrophotometry to quantitate the marker Mn2+ are of particular relevance as manganese ion is also the paramagnetic probe in n.m.r. measurements of water permeability of liposomes; our results indicate that in such measurements no other marker need be incorporated. PMID:3986305

  15. Recent Progress Towards Quantum Dot Solar Cells with Enhanced Optical Absorption

    NASA Astrophysics Data System (ADS)

    Zheng, Zerui; Ji, Haining; Yu, Peng; Wang, Zhiming

    2016-05-01

    Quantum dot solar cells, as a promising candidate for the next generation solar cell technology, have received tremendous attention in the last 10 years. Some recent developments in epitaxy growth and device structures have opened up new avenues for practical quantum dot solar cells. Unfortunately, the performance of quantum dot solar cells is often plagued by marginal photon absorption. In this review, we focus on the recent progress made in enhancing optical absorption in quantum dot solar cells, including optimization of quantum dot growth, improving the solar cells structure, and engineering light trapping techniques.

  16. Apparatus and method for measurement of weak optical absorptions by thermally induced laser pulsing

    DOEpatents

    Cremers, David A.; Keller, Richard A.

    1985-01-01

    The thermal lensing phenomenon is used as the basis for measurement of weak optical absorptions when a cell containing the sample to be investigated is inserted into a normally continuous-wave operation laser-pumped dye laser cavity for which the output coupler is deliberately tilted relative to intracavity circulating laser light, and pulsed laser output ensues, the pulsewidth of which can be related to the sample absorptivity by a simple algorithm or calibration curve. A minimum detection limit of less than 10.sup.-5 cm.sup.-1 has been demonstrated using this technique.

  17. Apparatus and method for measurement of weak optical absorptions by thermally induced laser pulsing

    DOEpatents

    Cremers, D.A.; Keller, R.A.

    1982-06-08

    The thermal lensing phenomenon is used as the basis for measurement of weak optical absorptions when a cell containing the sample to be investigated is inserted into a normally continuous-wave operation laser-pumped dye laser cavity for which the output coupler is deliberately tilted relative to intracavity circulating laser light, and pulsed laser output ensues, the pulsewidth of which can be rlated to the sample absorptivity by a simple algorithm or calibration curve. A minimum detection limit of less than 10/sup -5/ cm/sup -1/ has been demonstrated using this technique.

  18. Correlation analysis of optical absorption cross section and rate coefficient measurements in reacting systems

    SciTech Connect

    Hessler, J.P.; Ogren, P.J.

    1992-08-31

    A technique was developed for determining relative importance and correlation between reactions making up a complex kinetic system. This technique was used to investigate measurements of optical absorption cross sections and the correlation between cross sections and measured rate coefficients. It is concluded that (1) species, initial conditions, and temporal regions may be identified where cross sections may be measured without interference from the kinetic behavior of the observed species and (2) experiments designed to measure rate coefficients will always be correlated with the absorption cross section of the observed species. This correlation may reduce the accuracy of rate coefficient measurements.

  19. Apparatus and method for measurement of weak optical absorptions by thermally induced laser pulsing

    DOEpatents

    Cremers, D.A.; Keller, R.A.

    1985-10-01

    The thermal lensing phenomenon is used as the basis for measurement of weak optical absorptions when a cell containing the sample to be investigated is inserted into a normally continuous-wave operation laser-pumped dye laser cavity for which the output coupler is deliberately tilted relative to intracavity circulating laser light, and pulsed laser output ensues, the pulsewidth of which can be related to the sample absorptivity by a simple algorithm or calibration curve. A minimum detection limit of less than 10[sup [minus]5] cm[sup [minus]1] has been demonstrated using this technique. 6 figs.

  20. Optical absorption and luminescence studies of fast neutron-irradiated complex oxides for jewellery applications

    NASA Astrophysics Data System (ADS)

    Mironova-Ulmane, N.; Skvortsova, V.; Popov, A. I.

    2016-07-01

    We studied the optical absorption and luminescence of agate (SiO2), topaz (Al2[SiO4](F,OH)2), beryl (Be3Al2Si6O18), and prehnite (Ca2Al(AlSi3O10)(OH)2) doped with different concentrations of transition metal ions and exposed to fast neutron irradiation. The exchange interaction between the impurity ions and the defects arising under neutron irradiation causes additional absorption as well as bands' broadening in the crystals. These experimental results allow us to suggest the method for obtaining new radiation-defect induced jewellery colors of minerals due to neutron irradiation.

  1. EPR, optical absorption and luminescence studies of Cr3+-doped antimony phosphate glasses

    NASA Astrophysics Data System (ADS)

    De Vicente, F. S.; Santos, F. A.; Simões, B. S.; Dias, S. T.; Siu Li, M.

    2014-12-01

    Antimony phosphate glasses (SbPO) doped with 3 and 6 mol% of Cr3+ were studied by Electron Paramagnetic Resonance (EPR), UV-VIS optical absorption and luminescence spectroscopy. The EPR spectra of Cr3+-doped glasses showed two principal resonance signals with effective g values at g = 5.11 and g = 1.97. UV-VIS optical absorption spectra of SbPO:Cr3+ presented four characteristics bands at 457, 641, 675, and 705 nm related to the transitions from 4A2(F) to 4T1(F), 4T2(F), 2T1(G), and 2E(G), respectively, of Cr3+ ions in octahedral symmetry. Optical absorption spectra of SbPO:Cr3+ allowed evaluating the crystalline field Dq, Racah parameters (B and C) and Dq/B. The calculated value of Dq/B = 2.48 indicates that Cr3+ ions in SbPO glasses are in strong ligand field sites. The optical band gap for SbPO and SbPO:Cr3+ were evaluated from the UV optical absorption edges. Luminescence measurements of pure and Cr3+-doped glasses excited with 350 nm revealed weak emission bands from 400 to 600 nm due to the 3P1 → 1S0 electronic transition from Sb3+ ions. Cr3+-doped glasses excited with 415 nm presented Cr3+ characteristic luminescence spectra composed by two broad bands, one band centered at 645 nm (2E → 4A2) and another intense band from 700 to 850 nm (4T2 → 4A2).

  2. Cadmium sulfide and lead sulfide quantum dots in glass: Processing, growth, and optical absorption

    NASA Astrophysics Data System (ADS)

    Rao, Pratima Gattu Naga

    Glasses containing cadmium sulfide and lead sulfide particles were prepared, and their properties were studied. These particles exhibit quantum confinement behavior when they are smaller than their Bohr exciton radii. Quantum confinement leads to size dependence in the optical absorption of particles. This size dependence can tune the optical absorption of the material to a particular wavelength or energy and possibly enhances the nonlinear optical absorption of the particles. These properties have potential applications in photonic devices. To control the growth of these semiconductor particles in glass, the glass processing conditions were studied. CdS-doped glasses were initially prepared with CdO and ZnS. The sublimation temperature for ZnS is at 1185°C; whereas, CdO sublimes at 1559°C, and CdS at 980°C. Loss of both cadmium and sulfur was observed in open crucible melts, even when CdO and ZnS were used. Improvements in glass processing were made by use of preheat and a cover during the glass melting, resulting in better retention of both dopants. Direct CdS addition to the glasses was possible with these improvements, thus eliminating complications of zinc incorporation during the growth of the semiconductor particles. These methods were successfully applied to the synthesis of PbS-doped glasses. CdS and PbS particles were grown in alkali borosilicate glasses, and their optical absorption spectra were measured as a function of heat treatment temperature and time. The position of the absorption peak and edge shifted to longer wave-lengths, or lower energies, with longer heat treatments at a constant temperature. Both CdS and PbS particles exhibited quantum confinement. These measurements were used to calculate particle sizes from quantum confinement models. Comparisons with transmission electron microscopy (TEM) demonstrated that the 1-term effective-mass approximation was appropriate for estimating CdS particle sizes. A sophisticated four-band envelope

  3. Satellite retrieved cloud optical thickness sensitive to surface wind speed in the subarctic marine boundary layer

    NASA Astrophysics Data System (ADS)

    Glantz, Paul

    2010-07-01

    The optical and microphysical properties of low level marine clouds, presented over the Norwegian Sea and Barents Sea, have been investigated for the period 2000-2006. The air masses were transported for more or less seven days over the warmer North Atlantic before they arrived at the area investigated. The main focus in this study is on investigating the relationship between cloud optical thickness (COT) and surface wind speed (U10 m) using satellite retrievals in combination with operational meteorological data. A relatively strong correlation (R2 = 0.97) is obtained for wind speeds up to 12 m s - 1, in air masses that were probably to a major degree influenced by wind shears and to a minor degree by buoyancy. The relationship (U2.5) is also in between those most commonly found in the literature for water vapor (~U1) and sea salt (~U3.4). The present results highlight the magnitude of marine sea-spray influence on COT and their global climatic importance.

  4. Localized modes in optics of photonic liquid crystals with local anisotropy of absorption

    NASA Astrophysics Data System (ADS)

    Belyakov, V. A.; Semenov, S. V.

    2016-05-01

    The localized optical modes in spiral photonic liquid crystals are theoretically studied for the certainty at the example of chiral liquid crystals (CLCs) for the case of CLC with an anisotropic local absorption. The model adopted here (absence of dielectric interfaces in the structures under investigation) makes it possible to get rid of mixing of polarizations on the surfaces of the CLC layer and of the defect structure and to reduce the corresponding equations to only the equations for light with polarization diffracting in the CLC. The dispersion equations determining connection of the edge mode (EM) and defect mode (DM) frequencies with the CLC layer parameters (anisotropy of local absorption, CLC order parameter) and other parameters of the DMS are obtained. Analytic expressions for the transmission and reflection coefficients of CLC layer and DMS for the case of CLC with an anisotropic local absorption are presented and analyzed. It is shown that the CLC layers with locally anisotropic absorption reduce the EM and DM lifetimes (and increase the lasing threshold) in the way different from the case of CLC with an isotropic local absorption. Due to the Borrmann effect revealing of which is different at the opposite stop-band edges in the case of CLC layers with an anisotropic local absorption the EM life-times for the EM frequencies at the opposite stop-bands edges may be significantly different. The options of experimental observations of the theoretically revealed phenomena are briefly discussed.

  5. The tuning of light-matter coupling and dichroism in graphene for enhanced absorption: Implications for graphene-based optical absorption devices

    NASA Astrophysics Data System (ADS)

    Rakheja, Shaloo; Sengupta, Parijat

    2016-03-01

    The inter-band optical absorption in graphene characterized by its fine-structure constant has a universal value of 2.3% independent of the material parameters. However, for several graphene-based photonic applications, enhanced optical absorption is highly desired. In this work, we quantify the tunability of optical absorption in graphene via the Fermi level, angle of incidence of the incident polarized light, and the dielectric constants of the surrounding dielectric media in which graphene is embedded. The influence of impurities adsorbed on the surface of graphene on the Lorentzian broadening of the spectral function of the density of states is analytically evaluated within the equilibrium Green’s function formalism. In all the cases, we find that absorption of light graphene embedded in dielectric medium is significantly higher than 2.3%. We also compute the differential absorption of right and left circularly-polarized light in graphene that is uniaxially and optically strained. The preferential absorption or circular dichroism is investigated for armchair and zigzag strain and the interplay of k-space and velocity anisotropy is examined. Finally, we relate circular dichroism to the Berry curvature of gapped graphene and explain the connection to parameters that define the underlying Hamiltonian.

  6. Optically detected X-ray absorption spectroscopy measurements as a means of monitoring corrosion layers on copper.

    PubMed

    Dowsett, Mark G; Adriaens, Annemie; Jones, Gareth K C; Poolton, Nigel; Fiddy, Steven; Nikitenko, Sergé

    2008-11-15

    XANES and EXAFS information is conventionally measured in transmission through the energy-dependent absorption of X-rays or by observing X-ray fluorescence, but secondary fluorescence processes, such as the emission of electrons and optical photons (e.g., 200-1000 nm), can also be used as a carrier of the XAS signatures, providing complementary information such as improved surface specificity. Where the near-visible photons have a shorter range in a material, the data will be more surface specific. Moreover, optical radiation may escape more readily than X-rays through liquid in an environmental cell. Here, we describe a first test of optically detected X-ray absorption spectroscopy (ODXAS) for monitoring electrochemical treatments on copper-based alloys, for example, heritage metals. Artificially made corrosion products deposited on a copper substrate were analyzed in air and in a 1% (w/v) sodium sesquicarbonate solution to simulate typical conservation methods for copper-based objects recovered from marine environments. The measurements were made on stations 7.1 and 9.2 MF (SRS Daresbury, UK) using the mobile luminescence end station (MoLES), supplemented by XAS measurements taken on DUBBLE (BM26 A) at the ESRF. The ODXAS spectra usually contain fine structure similar to that of XAS spectra measured in X-ray fluorescence. Importantly, for the compounds examined, the ODXAS is significantly more surface specific, and >98% characteristic of thin surface layers of 0.5-1.5-microm thickness in cases where X-ray measurements are dominated by the substrate. However, EXAFS and XANES from broadband optical measurements are superimposed on a high background due to other optical emission modes. This produces statistical fluctuations up to double what would be expected from normal counting statistics because the data retain the absolute statistical fluctuation in the original raw count, while losing up to 70% of their magnitude when background is removed. The problem may be

  7. Variation in optical-absorption edge in SiN{sub x} layers with silicon clusters

    SciTech Connect

    Efremov, M. D. Volodin, V. A.; Marin, D. V.; Arzhannikova, S. A.; Kamaev, G. N.; Kochubei, S. A.; Popov, A. A.

    2008-02-15

    Using optical methods, data on optical constants are obtained for silicon nitride films synthesized by plasma-chemical vapor deposition (PCVD). Models for calculating the permittivity in the model of inhomogeneous phase mixture of silicon and silicon nitride are considered. It is found that the optical-absorption edge (E{sub g}) and the photoluminescence peak shift to longer wavelengths with increasing nitrogen atomic fraction x in sin{sub x} films. When x approaches the value 4/3 characteristic for stoichiometric silicon nitride Si{sub 3}N{sub 4}, a nonlinear sharp increase in E{sub g} is observed. Using Raman scattering, Si-Si bonds are revealed, which confirms the direct formation of silicon clusters during the film deposition. The relation between the composition of nonstoichiometric silicon nitride films, values of permittivity, and the optical-band width is established for light transmission.

  8. Optical absorption and scattering properties of bulk porcine muscle phantoms from interstitial radiance measurements in 650-900 nm range

    NASA Astrophysics Data System (ADS)

    Grabtchak, Serge; Montgomery, Logan G.; Whelan, William M.

    2014-05-01

    We demonstrated the application of relative radiance-based continuous wave (cw) measurements for recovering absorption and scattering properties (the effective attenuation coefficient, the diffusion coefficient, the absorption coefficient and the reduced scattering coefficient) of bulk porcine muscle phantoms in the 650-900 nm spectral range. Both the side-firing fiber (the detector) and the fiber with a spherical diffuser at the end (the source) were inserted interstitially at predetermined locations in the phantom. The porcine phantoms were prostate-shaped with ˜4 cm in diameter and ˜3 cm thickness and made from porcine loin or tenderloin muscles. The described method was previously validated using the diffusion approximation on simulated and experimental radiance data obtained for homogenous Intralipid-1% liquid phantom. The approach required performing measurements in two locations in the tissue with different distances to the source. Measurements were performed on 21 porcine phantoms. Spectral dependences of the effective attenuation and absorption coefficients for the loin phantom deviated from corresponding dependences for the tenderloin phantom for wavelengths <750 nm. The diffusion constant and the reduced scattering coefficient were very close for both phantom types. To quantify chromophore presence, the plot for the absorption coefficient was matched with a synthetic absorption spectrum constructed from deoxyhemoglobin, oxyhemoglobin and water. The closest match for the porcine loin spectrum was obtained with the following concentrations: 15.5 µM (±30% s.d.) Hb, 21 µM (±30% s.d.) HbO2 and 0.3 (±30% s.d.) fractional volume of water. The tenderloin absorption spectrum was best described by 30 µM Hb (±30% s.d), 19 µM (±30% s.d.) HbO2 and 0.3 (±30% s.d.) fractional volume of water. The higher concentration of Hb in tenderloin was consistent with a dark-red appearance of the tenderloin phantom. The method can be applied to a number of biological

  9. Optical absorption signature of a self-assembled dye monolayer on graphene

    PubMed Central

    Sghaier, Tessnim; Le Liepvre, Sylvain; Fiorini, Céline; Douillard, Ludovic

    2016-01-01

    Summary A well-organized monolayer of alkylated perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI) has been formed onto CVD graphene transferred on a transparent substrate. Its structure has been probed by scanning tunnelling microscopy and its optical properties by polarized transmission spectroscopy at varying incidence. The results show that the transition dipoles of adsorbed PTCDI are all oriented parallel to the substrate. The maximum absorption is consistent with the measured surface density of molecules and their absorption cross section. The spectrum presents mainly a large red-shift of the absorption line compared with the free molecules dispersed in solution, whereas the relative strengths of the vibronic structures are preserved. These changes are attributed to non-resonant interactions with the graphene layer and the neighbouring molecules. PMID:27547603

  10. Optical absorption of dilute nitride alloys using self-consistent Green's function method

    NASA Astrophysics Data System (ADS)

    Seifikar, Masoud; O'Reilly, Eoin P.; Fahy, Stephen

    2014-01-01

    We have calculated the optical absorption for InGaNAs and GaNSb using the band anticrossing (BAC) model and a self-consistent Green's function (SCGF) method. In the BAC model, we include the interaction of isolated and pair N levels with the host matrix conduction and valence bands. In the SCGF approach, we include a full distribution of N states, with non-parabolic conduction and light-hole bands, and parabolic heavy-hole and spin-split-off bands. The comparison with experiments shows that the first model accounts for many features of the absorption spectrum in InGaNAs; including the full distribution of N states improves this agreement. Our calculated absorption spectra for GaNSb alloys predict the band edges correctly but show more features than are seen experimentally. This suggests the presence of more disorder in GaNSb alloys in comparison with InGaNAs.

  11. Optical absorption and radiative heat transport in olivine at high temperature

    NASA Technical Reports Server (NTRS)

    Shankland, T. J.; Nitsan, U.; Duba, A. G.

    1979-01-01

    Results are presented of measurements of the optical absorption spectra (300-8000 nm) of olivine as a function of temperature (300-1700 K) under conditions of controlled and known oxygen fugacity within the stability field of the samples. The absorption spectra are used to calculate the temperature-dependent radiative transfer coefficient of olivine and to numerically study the accuracy of the method. The present absorption measurements in olivine under oxidizing conditions known to be within the olivine stability field indicate that the effective radiative conductivity K(R) is lower than that obtained in previous studies under different experimental conditions. The lower value of K(R) makes it more likely that some of the earth's internal heat is removed by convection and less likely that thermal models involving conduction and radiation alone will satisfactorily explain thermal conditions in the earth's mantle.

  12. Optical absorption and emission characterization of P3HT: graphene composite for its prospective photovoltaic application

    NASA Astrophysics Data System (ADS)

    Singh, Joginder; Prasad, Neetu; Nirwal, Varun Singh; Gautam, Khyati; Peta, Koteswara Rao; Bhatnagar, P. K.

    2016-05-01

    In the present work, regioregular P3HT (Poly (3-hexylthiophene-2, 5-diyl) was blended with graphene nanopowder and the optical spectroscopic characterization of the composite has been performed. It was observed that at low concentration of graphene (up to 0.1 wt %) there is no significant variation in absorption intensity or wavelength range. But at higher concentration (> 0.1 wt %) the absorption intensity starts reducing. Whereas, the photoluminescence of the composite solution quenches as we increase the concentration of graphene. It reveals that charge recombination decreases with increase in concentration (0.05 to 0.5 wt %) of graphene. Therefore 0.1 wt % seems to be the optimized concentration of graphene in the composite for which appropriate quenching of PL was observed without any significant reduction in absorption of photons. Thus maximum efficiency in P3HT: graphene composite photovoltaic cell is expected for 0.1 wt % of graphene concentration in our typical case.

  13. Investigation of Third Order Optical Nonlinearity and Reverse Saturable Absorption of Octa-alkoxy Metallophthalocyanines

    NASA Technical Reports Server (NTRS)

    Sanghadasa, Mohan; Shin, In-Seek; Barr, Thomas A.; Clark, Ronald D.; Guo, Huai-Song; Martinez, Angela; Penn, Benjamin G.

    1998-01-01

    In recent years, there has been a growing interest in the development of passive optical power limiters for the protection of the human eye and solid-state sensors from damage caused by energetic light pulses and also for other switching applications. One of the key issues involved is the search for appropriate materials that show effective reverse saturable absorption. Phthalocyanines seem to be good candidates for such applications because of their higher third order nonlinearity and the unique electronic absorption characteristics. A series of 1,4,8,11,15, 18,22,25-octa-alkoxy metallophthalocyanines containing various central metal atoms such as zinc, copper, palladium, cobalt and nickel were characterized for their third order nonlinearity and for their nonlinear absorptive properties to evaluate their suitability to function as reverse saturable absorbers.

  14. Active optics for dynamical correction of fluctuations of atmospheric refraction on a differential optical absorption spectroscopy device.

    PubMed

    Fuentes-Inzunza, Rodrigo A; Gutiérrez, Javier; Saavedra, Carlos

    2012-10-20

    We have designed and developed a feedback mechanism for continuous monitoring in a long-pass differential optical absorption spectroscopy (LP-DOAS) setup. This allows one to correct photo-thermal deflection due to the local fluctuations refraction index of the air. For this purpose, using an unbalanced beam splitter, a small fraction of the collected DOAS signal is imaged onto a low-cost CCD camera using a biconvex lens, while the other portion of the signal is coupled into a fiber optic for trace gas detection. By monitoring the registered signal at the CCD camera, a feedback mechanism acting on the transversal position of the lens is able to compensate an arbitrary transversal displacement of the collected signal at the focal plane of the receiver telescope, allowing an optimal coupling into the optical fiber. PMID:23089775

  15. Short optical pulse generation at 40 GHz with a bulk electro-absorption modulator packaged device

    NASA Astrophysics Data System (ADS)

    Langlois, Patrick; Moore, Ronald; Prosyk, Kelvin; O'Keefe, Sean; Oosterom, Jill A.; Betty, Ian; Foster, Robert; Greenspan, Jonathan; Singh, Priti

    2003-12-01

    Short optical pulse generation at 40GHz and 1540nm wavelength is achieved using fully packaged bulk quaternary electro-absorption modulator modules. Experimental results obtained with broadband and narrowband optimized packaged modules are presented and compared against empirical model predictions. Pulse duty cycle, extinction ratio and chirp are studied as a function of sinusoidal drive voltage and detuning between operating wavelength and modulator absorption band edge. Design rules and performance trade-offs are discussed. Low-chirp pulses with a FWHM of ~12ps and sub-4ps at a rate of 40GHz are demonstrated. Optical time-domain demultiplexing of a 40GHz to a 10GHz pulse train is also demonstrated with better than 20dB extinction ratio.

  16. Radiation Induced Optical Absorption of Cubic Lead Fluoride Crystals and the Effect of Annealing

    NASA Astrophysics Data System (ADS)

    Ren, Guo-Hao; Chen, Xiao-Feng; Li, Huan-Ying; Wu, Yun-Tao; Shi, Hong-Sheng; Qin, Lai-Shun

    2014-08-01

    Transparent and colorless lead fluoride crystals with sizes of 20 × 20 × 20 (mm3) are irradiated with several doses of γ-rays from a 60 Co source. Their transmittance spectra before and after irradiation are measured, and a new parameter ΔT = Tb - Ta is defined to evaluate the irradiation damage. Three optical absorption bands peaking at 270 nm, 370 nm and 500 nm are found in the plots of ΔT versus wavelength, and their intensities increase with the irradiation dose. These optical absorption bands, except the one at 270 nm, can recover spontaneously with time. Thermal annealing treatment can enhance this recovery of the transmittance, while the optimum annealing temperature for different samples depends on the irradiation dose.

  17. Phosphorescence, near-infrared absorption and nonlinear optical property of a new chiral organic crystal

    NASA Astrophysics Data System (ADS)

    Zhang, Bei; Zhao, Yu-Mei; Yong, Guo-Ping

    2014-02-01

    A new enantiomerically pure compound was synthesized by the single step reduced reaction from 2-(imidazo[1,2-a]pyridin-2-yl)-2-oxo-N-(pyridin-2-yl)acetamide via chiral induction with D-tartaric acid in good yield. Single crystal data confirm this compound crystallizes in chiral space group P21. Transmission spectrum reveals that the crystal has low UV cut-off of 372 nm and has a good transmittance in the entire visible and near-infrared (NIR)region to 1100 nm, indicating its optical application. Kurtz powder test shows a good second harmonic generation (SHG) which also demonstrates its chiral structure. Moreover, this material exhibits blue phosphorescence with quantum yield of 3.6% and unusually NIR absorption between 1500 nm and 2500 nm. Therefore, this new chiral crystal is a promising multifunctional material for the blue phosphorescence, NIR absorption and nonlinear optical (NLO) applications.

  18. Enhanced Reverse Saturable Absorption and Optical Limiting in Heavy-Atom Substituted Phthalocyanines

    NASA Technical Reports Server (NTRS)

    Perry, J. W.; Mansour, K.; Marder, S. R.; Alvarez, D., Jr.; Perry, K. J.; Choong, I.

    1994-01-01

    The reverse saturable absorption and optical limiting response of metal phthalocyaninies can be enhanced by using the heavy-atom effect. Phthalocyanines containing heavy metal atoms, such as In, Sn, and Pb show nearly a factor of two enhancement in the ratio of effective excited-state to ground-state absorption cross sections compared to those containing lighter atoms, such as Al and Si. In an f/8 optical geometry, homogeneous solutions of heavy metal phthalocyanines, at 30% linear transmission, limit 8-ns, 532-nm laser pulses to less than or equal to 3 (micro)J (the energy for 50% probability of eye damage) for incident pulses up to 800 (micro)J.

  19. Coherent Control of the Optical Absorption in a Plasmonic Lattice Coupled to a Luminescent Layer

    NASA Astrophysics Data System (ADS)

    Pirruccio, Giuseppe; Ramezani, Mohammad; Rodriguez, Said Rahimzadeh-Kalaleh; Rivas, Jaime Gómez

    2016-03-01

    We experimentally demonstrate the coherent control, i.e., phase-dependent enhancement and suppression, of the optical absorption in an array of metallic nanoantennas covered by a thin luminescent layer. The coherent control is achieved by using two collinear, counterpropagating, and phase-controlled incident waves with wavelength matching the absorption spectrum of dye molecules coupled to the array. Symmetry arguments shed light on the relation between the relative phase of the incident waves and the excitation efficiency of the optical resonances of the system. This coherent control is associated with a phase-dependent distribution of the electromagnetic near fields in the structure which enables a significant reduction of the unwanted dissipation in the metallic structures.

  20. Solar energy absorption characteristics and the effects of heat on the optical properties of several coatings

    NASA Technical Reports Server (NTRS)

    Lowery, J. R.

    1981-01-01

    The solar energy absorption characteristics of several high temperature coatings were determined and effects of heat on these coatings were evaluated. Included in the investigation were an electroplated alloy of black chrome and vanadium, electroplated black chrome, and chemically colored 316 stainless steel. Each of the coatings possessed good selective solar energy absorption properties at laboratory ambient temperature. Measured at a temperature of 700 K (800 F), the emittances of black chrome, black chrome vanadium, and colored stainless steel were 0.11, 0.61, and 0.15, respectively. Black chrome and black chrome vanadium did not degrade optically in the presence of high heat (811 K (1000 F)). Chemically colored stainless steel showed slight optical degradation when exposed to moderately high heat (616 K (650 F)0, but showed more severe degradation at exposure temperatures beyond this level. Each of the coatings showed good corrosion resistance to a salt spray environment.

  1. Simultaneous measurement of thermal diffusivity and optical absorption coefficient using photothermal radiometry. II Multilayered solids

    NASA Astrophysics Data System (ADS)

    Salazar, Agustín; Fuente, Raquel; Apiñaniz, Estibaliz; Mendioroz, Arantza; Celorrio, R.

    2011-08-01

    The aim of this work is to analyze the ability of modulated photothermal radiometry to retrieve the thermal diffusivity and the optical absorption coefficient of layered materials simultaneously. First, we extend the thermal quadrupole method to calculate the surface temperature of semitransparent multilayered materials. Then, this matrix method is used to evaluate the influence of heat losses by convection and radiation, the influence of the use of thin paint layers on the accuracy of thermal diffusivity measurements, and the effect of lateral heat diffusion due to the use of Gaussian laser beams. Finally, we apply the quadrupole method to retrieve (a) the thermal contact resistance in glass stacks and (b) the thermal diffusivity and optical absorption coefficient depth profiles in heterogeneous materials with continuously varying physical properties, as is the case of functionally graded materials and partially cured dental resins.

  2. Coherent Control of the Optical Absorption in a Plasmonic Lattice Coupled to a Luminescent Layer.

    PubMed

    Pirruccio, Giuseppe; Ramezani, Mohammad; Rodriguez, Said Rahimzadeh-Kalaleh; Rivas, Jaime Gómez

    2016-03-11

    We experimentally demonstrate the coherent control, i.e., phase-dependent enhancement and suppression, of the optical absorption in an array of metallic nanoantennas covered by a thin luminescent layer. The coherent control is achieved by using two collinear, counterpropagating, and phase-controlled incident waves with wavelength matching the absorption spectrum of dye molecules coupled to the array. Symmetry arguments shed light on the relation between the relative phase of the incident waves and the excitation efficiency of the optical resonances of the system. This coherent control is associated with a phase-dependent distribution of the electromagnetic near fields in the structure which enables a significant reduction of the unwanted dissipation in the metallic structures. PMID:27015478

  3. Fiber-optic thermometer using temperature dependent absorption, broadband detection, and time domain referencing

    NASA Technical Reports Server (NTRS)

    Adamovsky, Grigory; Piltch, Nancy D.

    1986-01-01

    A fiber-optic thermometer based on temperature dependent absorption in Nd(3+) doped glass is demonstrated over the 298-573 K range. A broadband detection technique allows the use of the complete spectrum of a pulse modulated light emitting diode. A fiber-optic recirculating loop is employed to construct a reference channel in the time domain by generating a train of pulses from one initial pulse. A theoretical model is developed, and experimental data are shown to compare well with the theory. Possible sources of error and instability are identified, and ways to enhance the performance of the system are proposed.

  4. 'Diamondlike' carbon films - Optical absorption, dielectric properties, and hardness dependence on deposition parameters

    NASA Technical Reports Server (NTRS)

    Natarajan, V.; Lamb, J. D.; Woollam, J. A.; Liu, D. C.; Gulino, D. A.

    1985-01-01

    An RF plasma deposition system was used to prepare amorphous 'diamondlike' carbon films. The source gases for the RF system include methane, ethylene, propane, and propylene, and the parameters varied were power, dc substrate bias, and postdeposition anneal temperature. Films were deposited on various substrates. The main diagnostics were optical absorption in the visible and in the infrared, admittance as a function of frequency, hardness, and Auger and ESCA spectroscopy. Band gap is found to depend strongly on RF power level and band gaps up to 2.7 eV and hardness up to 7 Mohs were found. There appears to be an inverse relationship between hardness and optical band gap.

  5. Tunable Optical Limiting Action due to Non-linear Absorption in ZnO/Ag Nanocomposites

    NASA Astrophysics Data System (ADS)

    Radhu, S.; Vijayan, C.; Sandeep, Suchand; Philip, Reji

    2011-07-01

    ZnO/Ag nanocomposites with different silver concentration are successfully synthesized by solvothermal method. The characterization of the as- synthesized samples is done using XRD, UV-visible spectroscopy and HRTEM and the results indicate that the composites consist of silver nanoparticles attached to the ZnO nanoparticles. The optical non-linearity in these samples is studied using open aperture Z-scan technique and the experimental results agree well with a theoretical model involving two- photon absorption. It is found that the parameters of optical limiting can be tuned in a broad band by varying the silver concentration in the samples.

  6. Time Course of Macular and Peripapillary Inner Retinal Thickness in Non-arteritic Anterior Ischaemic Optic Neuropathy Using Spectral-Domain Optical Coherence Tomography

    PubMed Central

    Goto, Katsutoshi; Miki, Atsushi; Araki, Syunsuke; Mizukawa, Kenichi; Nakagawa, Masaki; Takizawa, Go; Ieki, Yoshiaki; Kiryu, Junichi

    2016-01-01

    ABSTRACT To report a time course of the ganglion cell complex (GCC) and circumpapillary retinal nerve fibre layer (cpRNFL) thicknesses using spectral-domain optical coherence tomography in patients with non-arteritic anterior ischaemic optic neuropathy (NAION), five patients with unilateral NAION were studied (the average age of 66.8 ± 7.8 years old). Forty-one age-matched normal controls were also enrolled. The GCC and cpRNFL thicknesses were measured at the initial visit and at 1, 3, 6, and 12 months using RTVue-100. The GCC thickness and the cpRNFL thickness of the patients were compared with those of the normal controls. The GCC thickness in the NAION patients was 96.49 μm at the initial visit, 84.28 μm at 1 month, 74.26 μm at 3 months, 71.23 μm at 6 months, and 69.51 μm at 12 months. The values at 1, 3, 6, and 12 months were significantly reduced (p < 0.01). The cpRNFL thickness at the initial visit was significantly increased, whereas the values at 6 and 12 months were significantly reduced (p < 0.01). The GCC thickness is more useful for the detection of retinal ganglion cell loss at an early stage than the cpRNFL thickness, because the GCC thickness is unaffected by optic disc swelling at the initial visit, unlike the cpRNFL thickness. PMID:27110047

  7. Molecular level all-optical logic with chlorophyll absorption spectrum and polarization sensitivity

    NASA Astrophysics Data System (ADS)

    Raychaudhuri, B.; Bhattacharyya (Bhaumik), S.

    2008-06-01

    Chlorophyll is suggested as a suitable medium for realizing optical Boolean logic at the molecular level in view of its wavelength-selective property and polarization sensitivity in the visible region. Spectrophotometric studies are made with solutions of total chlorophyll and chromatographically isolated components, viz. chlorophyll a and b and carotenoids extracted from pumpkin leaves of different maturity stages. The absorption features of matured chlorophyll with two characteristic absorption peaks and one transmission band are molecular properties and independent of concentration. A qualitative explanation of such an absorption property is presented in terms of a ‘particle in a box’ model and the property is employed to simulate two-input optical logic operations. If both of the inputs are either red or blue, absorption is high. If either one is absent and replaced by a wavelength of the transmission band, e.g. green, absorption is low. Assigning these values as 0 s or 1 s, AND and OR operations can be performed. A NOT operation can be simulated with the transmittance instead of the absorbance. Also, the shift in absorbance values for two different polarizations of the same monochromatic light can simulate two logical states with a single wavelength. Cyclic change in absorbance is noted over a rotation of 360° for both red and blue peaks, although the difference is not very large. Red monochromatic light with polarizations apart by 90°, corresponding to maximum and minimum absorption, respectively, may be assigned as the two logical states. The fluorescence emissions for different pigment components are measured at different excitation wavelengths and the effect of fluorescence on the red absorbance is concluded to be negligible.

  8. Optical and ultraviolet absorption studies of cool gas in the Milky Way halo

    NASA Technical Reports Server (NTRS)

    Danly, L.

    1990-01-01

    This paper focuses on the contributions from absorption techniques to the knowledge of halo gas with temperatures below 10 to the 5th K. The results from observations of the neutral and singly ionized species on the nature of cool gas in the halo, its structure and its kinematics are presented. An overview of past and optical and ultraviolet observational studies of halo gas is included.

  9. Diffuse reflection of light by cellulose pulp and optical absorption of aqueous residual lignin solutions

    NASA Astrophysics Data System (ADS)

    Belov, N. P.; Sherstobitova, A. S.; Yaskov, A. D.

    2011-03-01

    Within Kubelka-Munk theory using the Lorenz relations, we have determined the correlation between the optical diffuse reflectance spectra R(λ) of cellulose pulp in the visible range (380-760 nm) and ultraviolet absorption (λ = 200-400 nm) of aqueous solutions containing residual lignins. The data obtained can be used to monitor and predict the results of digestion and bleach plants in the paper and pulp industry.

  10. Toward absorption contrast imaging of biological tissues in vivo by using photothermal optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Makita, Shuichi; Hong, Young-Joo; Yasuno, Yoshiaki

    2014-03-01

    Optical coherence tomography has been proven in the last two decades its clinical value by providing 3D non-invasive in vivo biopsy of the biological samples. In addition to structural information given by the backscattered intensity, the optical absorption will also provide another powerful contrast. Optical absorbers in biological tissues exhibits important role such as hemoglobin and melanin. However, current methods of absorption contrast take long time and not suitable for in vivo imaging. Toward in vivo absorption contrast imaging, we developed photothermal OCT system by combining swept-source OCT system and excitation laser. A swept-source OCT system is used with a wavelength swept laser at 1310 nm with a scanning rate and range of 47 kHz and of 100 nm, respectively. Photocurrents from balanced photoreceivers are sampled by a high-speed digitizer by using k-clock from the source to sample optical spectrum in k-linear domain. The sensitivity of 107 dB for two polarization channels is achieved. At the sample arm, the OCT probe beam and an excitation laser are combined by a dielectric mirror. The fiber-coupled laser diode of 406 nm wavelength is used for excitation since the absorption of hemoglobin has peak around this wavelength. In order to evaluate the ability of this system, phase stability of the system was measured. The standard deviation of the phase shift is measured as 0.0028 radians, where the signal-to-noise-limited value is approximately 0.001. Several issues for in vivo case, motion, blood flow, thermal damage, and etc. will be addressed here.

  11. Third order nonlinear optical susceptibility of fluorescein-containing polymers determined by electro-absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Gomez-Sosa, Gustavo; Beristain, Miriam F.; Ortega, Alejandra; Martínez-Viramontes, Jaquelin; Ogawa, Takeshi; Fernández-Hernández, Roberto C.; Tamayo-Rivera, Lis; Reyes-Esqueda, Jorge-Alejandro; Isoshima, Takashi; Hara, Masahiko

    2012-03-01

    Novel polymers containing xanthene groups with high dye concentrations were prepared, and their third order nonlinear optical properties were studied by electroabsorption spectroscopy technique. The polymers were amorphous with refractive indices above 1.6 in the non-resonant region. The UV-Visible absorption spectra indicate the fluoresceins molecules in the polymers are H-aggregated. They showed third order nonlinear susceptibility, χ(3) (-ω:ω, 0, 0), of 2.5-3.5 × 10-12 esu.

  12. Order and disorder and their influences on optical absorption of glasses in the gap region

    NASA Astrophysics Data System (ADS)

    Baník, Ivan; Kubliha, Marian; Labaš, Vladimír; Lukovičová, Jozefa; Pavlendová, Gabriela; Šín, Peter

    2016-07-01

    The exponential increase of the absorption coefficient near the absorption edge is usually explained by existence of the density-of-states tails. Among the quoted theoretical models which are widely used to explain the manifestations of the Urbach rule in semiconductors, are the Sumi-Toyozava and the Dow-Redfield models and ab initio (from begining) theory. Our barrier-cluster-heating model assumes the different creating mechanism of exponential tails. The energy by optical transition is provided to electrons except from photons also from vibration of microregion. It deals about the replenishment of absented photons energy, which is smaller as gap width. Absented energy needed for the transition by light absorption is acumulated in certain microregions of material in the form of vibrational energy. At absorption sufficiently big package of accumulated energy can be used. Energy of emptied microarea is filled by phonons from surrounding of microarea (as result of temperature status of surrounding), resp. phonons of optical background wich are created in given microarea at non radiative recombination of carriers. In this work simplified process at derivating of Urbach rule is listed.

  13. Optical-feedback cavity-enhanced absorption spectroscopy in a linear cavity: model and experiments

    NASA Astrophysics Data System (ADS)

    Manfred, Katherine M.; Ciaffoni, Luca; Ritchie, Grant A. D.

    2015-08-01

    Optical-feedback cavity-enhanced absorption spectroscopy is a highly sensitive trace gas sensing technique that relies on feedback from a resonant intracavity field to successively lock the laser to the cavity as the wavelength is scanned across a molecular absorption with a comb of resonant frequencies. V-shaped optical cavities have been favoured in the past in order to avoid additional feedback fields from non-resonant reflections that potentially suppress the locking to the resonant cavity frequency. A model of the laser-cavity coupling demonstrates, however, that the laser can stably lock to a resonant linear cavity, within certain constraints on the relative intensity of the two feedback sources. By mode mismatching the field into the linear cavity, we have shown that it is theoretically and practically possible to spatially filter out the unwanted non-resonant component in order for the resonant field to dominate the feedback competition at the laser. A 5.3 cw quantum cascade laser scanning across a absorption feature demonstrated stable locking to achieve a minimum detectable absorption coefficient of for 1-s averaging. Detailed investigations of feedback effects on the laser output verified the validity of our theoretical models.

  14. [Concentration retrieving method of SO2 using differential optical absorption spectroscopy based on statistics].

    PubMed

    Liu, Bin; Sun, Chang-Ku; Zhang, Chi; Zhao, Yu-Mei; Liu, Jun-Ping

    2011-01-01

    A concentration retrieving method using statistics is presented, which is applied in differential optical absorption spectroscopy (DOAS) for measuring the concentration of SO2. The method uses the standard deviation of the differential absorption to represents the gas concentration. Principle component analysis (PCA) method is used to process the differential absorption spectrum. In the method, the basis data for the concentration retrieval of SO2 is the combination of the PCA processing result, the correlation coefficient, and the standard deviation of the differential absorption. The method is applied to a continuous emission monitoring system (CEMS) with optical path length of 0.3 m. Its measuring range for SO2 concentration is 0-5 800 mg x m(-3). The nonlinear calibration and the temperature compensation for the system were executed. The full scale error of the retrieving concentration is less than 0.7% FS. And the measuring result is -4.54 mg x m(-3) when the concentration of SO2 is zero. PMID:21428087

  15. Doubling absorption in nanowire solar cells with dielectric shell optical antennas.

    PubMed

    Kim, Sun-Kyung; Zhang, Xing; Hill, David J; Song, Kyung-Deok; Park, Jin-Sung; Park, Hong-Gyu; Cahoon, James F

    2015-01-14

    Semiconductor nanowires (NWs) often exhibit efficient, broadband light absorption despite their relatively small size. This characteristic originates from the subwavelength dimensions and high refractive indices of the NWs, which cause a light-trapping optical antenna effect. As a result, NWs could enable high-efficiency but low-cost solar cells using small volumes of expensive semiconductor material. Nevertheless, the extent to which the antenna effect can be leveraged in devices will largely determine the economic viability of NW-based solar cells. Here, we demonstrate a simple, low-cost, and scalable route to dramatically enhance the optical antenna effect in NW photovoltaic devices by coating the wires with conformal dielectric shells. Scattering and absorption measurements on Si NWs coated with shells of SiN(x) or SiO(x) exhibit a broadband enhancement of light absorption by ∼ 50-200% and light scattering by ∼ 200-1000%. The increased light-matter interaction leads to a ∼ 80% increase in short-circuit current density in Si photovoltaic devices under 1 sun illumination. Optical simulations reproduce the experimental results and indicate the dielectric-shell effect to be a general phenomenon for groups IV, II-VI, and III-V semiconductor NWs in both lateral and vertical orientations, providing a simple route to approximately double the efficiency of NW-based solar cells. PMID:25546325

  16. Isothermal annealing of a 620 nm optical absorption band in Brazilian topaz crystals

    NASA Astrophysics Data System (ADS)

    Isotani, Sadao; Matsuoka, Masao; Albuquerque, Antonio Roberto Pereira Leite

    2013-04-01

    Isothermal decay behaviors, observed at 515, 523, 562, and 693 K, for an optical absorption band at 620 nm in gamma-irradiated Brazilian blue topaz were analyzed using a kinetic model consisting of O- bound small polarons adjacent to recombination centers (electron traps). The kinetic equations obtained on the basis of this model were solved using the method of Runge-Kutta and the fit parameters describing these defects were determined with a grid optimization method. Two activation energies of 0.52±0.08 and 0.88±0.13 eV, corresponding to two different structural configurations of the O- polarons, explained well the isothermal decay curves using first-order kinetics expected from the kinetic model. On the other hand, thermoluminescence (TL) emission spectra measured at various temperatures showed a single band at 400 nm in the temperature range of 373-553 K in which the 620 nm optical absorption band decreased in intensity. Monochromatic TL glow curve data at 400 nm extracted from the TL emission spectra observed were found to be explained reasonably by using the knowledge obtained from the isothermal decay analysis. This suggests that two different structural configurations of O- polarons are responsible for the 620 nm optical absorption band and that the thermal annealing of the polarons causes the 400 nm TL emission band.

  17. Initial Results of Optical Vortex Laser Absorption Spectroscopy in the HYPER-I Device

    NASA Astrophysics Data System (ADS)

    Yoshimura, Shinji; Asai, Shoma; Aramaki, Mitsutoshi; Terasaka, Kenichiro; Ozawa, Naoya; Tanaka, Masayoshi; Morisaki, Tomohiro

    2015-11-01

    Optical vortex beams have a potential to make a new Doppler measurement, because not only parallel but perpendicular movement of atoms against the beam axis causes the Doppler shift of their resonant absorption frequency. As the first step of a proof-of-principle experiment, we have performed the optical vortex laser absorption spectroscopy for metastable argon neutrals in an ECR plasma produced in the HYPER-I device at the National Institute for Fusion Science, Japan. An external cavity diode laser (TOPTICA, DL100) of which center wavelength was 696.735 nm in vacuum was used for the light source. The Hermite-Gaussian (HG) beam was converted into the Laguerre-Gaussian (LG) beam (optical vortex) by a computer-generated hologram displayed on the spatial light modulator (Hamamatsu, LCOS-SLM X10468-07). In order to make fast neutral flow across the LG beam, a high speed solenoid valve system was installed on the HYPER-I device. Initial results including the comparison of absorption spectra for HG and LG beams will be presented. This study was supported by NINS young scientists collaboration program for cross-disciplinary study, NIFS collaboration research program (NIFS13KOAP026), and JSPS KAKENHI grant number 15K05365.

  18. X-RAY ABSORPTION SPECTROSCOPY OF YB3+-DOPED OPTICAL FIBERS

    SciTech Connect

    Citron, Robert; Kropf, A.J.

    2008-01-01

    Optical fibers doped with Ytterbium-3+ have become increasingly common in fiber lasers and amplifiers. Yb-doped fibers provide the capability to produce high power and short pulses at specific wavelengths, resulting in highly effective gain media. However, little is known about the local structure, distribution, and chemical coordination of Yb3+ in the fibers. This information is necessary to improve the manufacturing process and optical qualities of the fibers. Five fibers doped with Yb3+ were studied using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy and X-ray Absorption Near Edge Spectroscopy (XANES), in addition to Yb3+ mapping. The Yb3+ distribution in each fiber core was mapped with 2D and 1D intensity scans, which measured X-ray fluorescence over the scan areas. Two of the five fibers examined showed highly irregular Yb3+ distributions in the core center. In four of the five fibers Yb3+ was detected outside of the given fiber core dimensions, suggesting possible Yb3+ diffusion from the core, manufacturing error, or both. X-ray absorption spectroscopy (XAS) analysis has so far proven inconclusive, but did show that the fibers had differing EXAFS spectra. The Yb3+ distribution mapping proved highly useful, but additional modeling and examination of fiber preforms must be conducted to improve XAS analysis, which has been shown to have great potential for the study of similar optical fi bers.

  19. Resolving ice cloud optical thickness biases between CALIOP and MODIS using infrared retrievals

    NASA Astrophysics Data System (ADS)

    Holz, Robert E.; Platnick, Steven; Meyer, Kerry; Vaughan, Mark; Heidinger, Andrew; Yang, Ping; Wind, Gala; Dutcher, Steven; Ackerman, Steven; Amarasinghe, Nandana; Nagle, Fredrick; Wang, Chenxi

    2016-04-01

    Despite its importance as one of the key radiative properties that determines the impact of upper tropospheric clouds on the radiation balance, ice cloud optical thickness (IOT) has proven to be one of the more challenging properties to retrieve from space-based remote sensing measurements. In particular, optically thin upper tropospheric ice clouds (cirrus) have been especially challenging due to their tenuous nature, extensive spatial scales, and complex particle shapes and light-scattering characteristics. The lack of independent validation motivates the investigation presented in this paper, wherein systematic biases between MODIS Collection 5 (C5) and CALIOP Version 3 (V3) unconstrained retrievals of tenuous IOT (< 3) are examined using a month of collocated A-Train observations. An initial comparison revealed a factor of 2 bias between the MODIS and CALIOP IOT retrievals. This bias is investigated using an infrared (IR) radiative closure approach that compares both products with MODIS IR cirrus retrievals developed for this assessment. The analysis finds that both the MODIS C5 and the unconstrained CALIOP V3 retrievals are biased (high and low, respectively) relative to the IR IOT retrievals. Based on this finding, the MODIS and CALIOP algorithms are investigated with the goal of explaining and minimizing the biases relative to the IR. For MODIS we find that the assumed ice single-scattering properties used for the C5 retrievals are not consistent with the mean IR COT distribution. The C5 ice scattering database results in the asymmetry parameter (g) varying as a function of effective radius with mean values that are too large. The MODIS retrievals have been brought into agreement with the IR by adopting a new ice scattering model for Collection 6 (C6) consisting of a modified gamma distribution comprised of a single habit (severely roughened aggregated columns); the C6 ice cloud optical property models have a constant g ≈ 0.75 in the mid-visible spectrum

  20. Resolving ice cloud optical thickness biases between CALIOP and MODIS using infrared retrievals

    NASA Astrophysics Data System (ADS)

    Holz, R. E.; Platnick, S.; Meyer, K.; Vaughan, M.; Heidinger, A.; Yang, P.; Wind, G.; Dutcher, S.; Ackerman, S.; Amarasinghe, N.; Nagle, F.; Wang, C.

    2015-10-01

    Despite its importance as one of the key radiative properties that determines the impact of upper tropospheric clouds on the radiation balance, ice cloud optical thickness (IOT) has proven to be one of the more challenging properties to retrieve from space-based remote sensing measurements. In particular, optically thin upper tropospheric ice clouds (cirrus) have been especially challenging due to their tenuous nature, extensive spatial scales, and complex particle shapes and light scattering characteristics. The lack of independent validation motivates the investigation presented in this paper, wherein systematic biases between MODIS Collection 5 (C5) and CALIOP Version 3 (V3) unconstrained retrievals of tenuous IOT (< 3) are examined using a month of collocated A-Train observations. An initial comparison revealed a factor of two bias between the MODIS and CALIOP IOT retrievals. This bias is investigated using an infrared (IR) radiative closure approach that compares both products with MODIS IR cirrus retrievals developed for this assessment. The analysis finds that both the MODIS C5 and the unconstrained CALIOP V3 retrievals are biased (high and low, respectively) relative to the IR IOT retrievals. Based on this finding, the MODIS and CALIOP algorithms are investigated with the goal of explaining and minimizing the biases relative to the IR. For MODIS we find that the assumed ice single scattering properties used for the C5 retrievals are not consistent with the mean IR COT distribution. The C5 ice scattering database results in the asymmetry parameter (g) varying as a function of effective radius with mean values that are too large. The MODIS retrievals have been brought into agreement with the IR by adopting a new ice scattering model for Collection 6 (C6) consisting of a modified gamma distribution comprised of a single habit (severely roughened aggregated columns); the C6 ice cloud optical property models have a constant g ~ 0.75 in the mid-visible spectrum

  1. Automated measurement of epidermal thickness from optical coherence tomography images using line region growing

    NASA Astrophysics Data System (ADS)

    Delacruz, Jomer; Weissman, Jesse; Gossage, Kirk

    2010-02-01

    Optical Coherence Tomography (OCT) is a non-invasive imaging modality that acquires cross sectional images of tissue in-vivo. It accelerates skin diagnosis by eliminating invasive biopsy and laborious histology in the process. Dermatologists have widely used it for looking at morphology of skin diseases such as psoriasis, dermatitis, basal cell carcinoma etc. Skin scientists have also successfully used it for looking at differences in epidermal thickness and its underlying structure with respect to age, body sites, ethnicity, gender, and other related factors. Similar to other in-vivo imaging systems, OCT images suffer from a high degree of speckle and noise content, which hinders examination of tissue structures. Most of the previous work in OCT segmentation of skin was done manually. This compromised the quality of the results by limiting the analyses to a few frames per area. In this paper, we discuss a region growing method for automatic identification of the upper and lower boundaries of the epidermis in living human skin tissue. This image analysis method utilizes images obtained from a frequency-domain OCT. This system is high-resolution and high-speed, and thus capable of capturing volumetric images of the skin in short time. The three-dimensional (3D) data provides additional information that is used in the segmentation process to help compensate for the inherent noise in the images. This method not only provides a better estimation of the epidermal thickness, but also generates a 3D surface map of the epidermal-dermal junction, from which underlying topography can be visualized and further quantified.

  2. Three-dimensional printed optical phantoms with customized absorption and scattering properties.

    PubMed

    Diep, Phuong; Pannem, Sanjana; Sweer, Jordan; Lo, Justine; Snyder, Michael; Stueber, Gabriella; Zhao, Yanyu; Tabassum, Syeda; Istfan, Raeef; Wu, Junjie; Erramilli, Shyamsunder; Roblyer, Darren

    2015-11-01

    Three-dimensional (3D) printing offers the promise of fabricating optical phantoms with arbitrary geometry, but commercially available thermoplastics provide only a small range of physiologically relevant absorption (µa) and reduced scattering (µs`) values. Here we demonstrate customizable acrylonitrile butadiene styrene (ABS) filaments for dual extrusion 3D printing of tissue mimicking optical phantoms. µa and µs` values were adjusted by incorporating nigrosin and titanium dioxide (TiO2) in the filament extrusion process. A wide range of physiologically relevant optical properties was demonstrated with an average repeatability within 11.5% for µa and 7.71% for µs`. Additionally, a mouse-simulating phantom, which mimicked both the geometry and optical properties of a hairless mouse with an implanted xenograft tumor, was printed using dual extrusion methods. 3D printed tumor optical properties matched the live tumor with less than 3% error at a wavelength of 659 nm. 3D printing with user defined optical properties may provide a viable method for durable optically diffusive phantoms for instrument characterization and calibration. PMID:26600987

  3. Three-dimensional printed optical phantoms with customized absorption and scattering properties

    PubMed Central

    Diep, Phuong; Pannem, Sanjana; Sweer, Jordan; Lo, Justine; Snyder, Michael; Stueber, Gabriella; Zhao, Yanyu; Tabassum, Syeda; Istfan, Raeef; Wu, Junjie; Erramilli, Shyamsunder; Roblyer, Darren

    2015-01-01

    Three-dimensional (3D) printing offers the promise of fabricating optical phantoms with arbitrary geometry, but commercially available thermoplastics provide only a small range of physiologically relevant absorption (µa) and reduced scattering (µs`) values. Here we demonstrate customizable acrylonitrile butadiene styrene (ABS) filaments for dual extrusion 3D printing of tissue mimicking optical phantoms. µa and µs` values were adjusted by incorporating nigrosin and titanium dioxide (TiO2) in the filament extrusion process. A wide range of physiologically relevant optical properties was demonstrated with an average repeatability within 11.5% for µa and 7.71% for µs`. Additionally, a mouse-simulating phantom, which mimicked both the geometry and optical properties of a hairless mouse with an implanted xenograft tumor, was printed using dual extrusion methods. 3D printed tumor optical properties matched the live tumor with less than 3% error at a wavelength of 659 nm. 3D printing with user defined optical properties may provide a viable method for durable optically diffusive phantoms for instrument characterization and calibration. PMID:26600987

  4. [Study on removing the lamp spectrum structure in differential optical absorption spectroscopy].

    PubMed

    Qu, Xiao-ying; Li, Yu-jin

    2010-11-01

    Differential optical absorption spectroscopy (DOAS) technique has been used to measure trace gases in the atmosphere by their strongly structured absorption of radiation in the UV and visible spectral range, and nowadays this technique has been widely utilized to measure trace polluted gases in the atmosphere e.g. SO2, NO2, O3, HCHO, etc. However, there exists lamp (xenon lamp or deuteriumlamp) spectrum structure in the measured band (300-700 nm) of the absorption spectra of atmosphere, which badly impacts on precision of retrieving the concentration of trace gases in the atmosphere. People home and abroad generally employ two ways to handle this problem, one is segmenting band retrieving method, another is remedial retrieving method. In the present paper, a new retrieving method to deal with this trouble is introduced. The authors used moving-window average smoothing method to obtain the slow part of the absorption spectra of atmosphere, then achieved the lamp (xenon lamp in the paper) spectrum structure in the measured band of the absorption spectra of atmosphere. The authors analyzed and retrieved the measured spectrum of the atmosphere, and the result is better than the forenamed ways. Chi-square of residuum is 2.995 x 10(-4), and this method was proved to be able to avoid shortcoming of choosing narrowband and disadvantage of discovering the new component of atmosphere in retrieving the concentration of air pollutants and measuring the air pollutants. PMID:21284148

  5. All-Optical Switching in Bacteriorhodopsin Based on Excited-State Absorption

    NASA Astrophysics Data System (ADS)

    Roy, Sukhdev

    2008-03-01

    Switching light with light is of tremendous importance for both fundamental and applied science. The advent of nano-bio-photonics has led to the design, synthesis and characterization of novel biomolecules that exhibit an efficient nonlinear optical response, which can be utilized for designing all-optical biomolecular switches. Bacteriorhodopsin (bR) protein found in the purple membrane of Halobacterium halobium has been the focus of intense research due to its unique properties that can also be tailored by physical, chemical and genetic engineering techniques to suit desired applications. The talk would focus on our recent results on all-optical switching in bR and its mutants, based on excited-state absorption, using the pump-probe technique. We would discuss the all-optical control of various features of the switching characteristics such as switching contrast, switching time, switching pump intensity, switched probe profile and phase, and relative phase-shift. Optimized conditions for all-optical switching that include optimized values of the small-signal absorption coefficient (for cw case), the pump pulse width and concentration for maximum switching contrast (for pulsed case), would be presented. We would discuss the desired optimal spectral and kinetic properties for device applications. We would also discuss the application of all-optical switching to design low power all-optical computing devices, such as, spatial light modulators, logic gates and multiplexers and compare their performance with other natural photoreceptors such as pharaonis phoborhodopsin, proteorhodopsin, photoactive yellow protein and the blue light plant photoreceptor phototropin.

  6. A 10-year global gridded Aerosol Optical Thickness Reanalysis for climate and applied applications

    NASA Astrophysics Data System (ADS)

    Lynch, P.; Reid, J. S.; Zhang, J.; Westphal, D. L.; Campbell, J. R.; Curtis, C. A.; Hegg, D.; Hyer, E. J.; Sessions, W.; Shi, Y.; Turk, J.

    2013-12-01

    While standalone satellite and model aerosol products see wide utilization, there is a significant need of a best-available fused product on a regular grid for numerous climate and applied applications. Remote sensing and modeling technologies have now advanced to a point where aerosol data assimilation is an operational reality at numerous centers. It is inevitable that, like meteorological reanalyses, aerosol reanalyses will see heavy use in the near future. A first long term, 2003-2012 global 1x1 degree and 6-hourly aerosol optical thickness (AOT) reanalysis product has been generated. The goal of this effort is not only for climate applications, but to generate a dataset that can be used by the US Navy to understand operationally hindering aerosol events, aerosol impacts on numerical weather prediction, and application of electro-optical technologies. The reanalysis utilizes Navy Aerosol Analysis and Prediction System (NAAPS) at its core and assimilates quality controlled collection 5 Moderate Resolution Imaging Spectroradiometer (MODIS) AOD with minor corrections from Multi-angle Imaging SpectroRaditometer (MISR). A subset of this product includes Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) lidar assimilation since its launch in mid-2006. Surface aerosol sources, including dust and smoke, in the aerosol model have been regionally tuned so that fine and coarse mode AOTs best match those resolve by ground-based Aerosol Robotic Network (AERONET). The AOT difference between the model and satellite AOT is then used to adjust other aerosol processes, eg., sources, dry deposition, etc. Aerosol wet deposition is constrained with satellite-retrieved precipitation. The final AOT reanalysis is shown to exhibit good agreement with AERONET. Here we review the development of the reanalysis and consider issues particular to aerosol reanalyses that make them distinct from standard meteorological reanalyses. Considerations are also made for extending such work

  7. A comparison of neutral hydrogen 21 cm observations with UV and optical absorption-line measurements

    NASA Technical Reports Server (NTRS)

    Giovanelli, R.; York, D. G.; Shull, J. M.; Haynes, M. P.

    1978-01-01

    Several absorption components detected in visible or UV lines have been identified with emission features in new high-resolution, high signal-to-noise 21 cm observations. Stars for which direct overlap is obtained are HD 28497, lambda Ori, mu Col, HD 50896, rho Leo, HD 93521, and HD 219881. With the use of the inferred H I column densities from 21 cm profiles, rather than the integrated column densities obtained from L-alpha, more reliable densities can be derived from the existence of molecular hydrogen. Hence the cloud thicknesses are better determined; and 21 cm emission maps near these stars can be used to obtain dimensions on the plane of the sky. It is now feasible to derive detailed geometries for isolated clumps of gas which produce visual absorption features.

  8. Excited-State Absorption from Real-Time Time-Dependent Density Functional Theory: Optical Limiting in Zinc Phthalocyanine.

    PubMed

    Fischer, Sean A; Cramer, Christopher J; Govind, Niranjan

    2016-04-01

    Optical-limiting materials are capable of attenuating light to protect delicate equipment from high-intensity light sources. Phthalocyanines have attracted a lot of attention for optical-limiting applications due to their versatility and large nonlinear absorption. With excited-state absorption (ESA) being the primary mechanism for optical limiting behavior in phthalocyanines, the ability to tune the optical absorption of ground and excited states in phthalocyanines would allow for the development of advanced optical limiters. We recently developed a method for the calculation of ESA based on real-time time-dependent density functional theory propagation of an excited-state density. In this work, we apply the approach to zinc phthalocyanine, demonstrating the ability of our method to efficiently identify the optical limiting potential of a molecular complex. PMID:27007445

  9. Far-field optical imaging with subdiffraction resolution enabled by nonlinear saturation absorption

    PubMed Central

    Ding, Chenliang; Wei, Jingsong

    2016-01-01

    The resolution of far-field optical imaging is required to improve beyond the Abbe limit to the subdiffraction or even the nanoscale. In this work, inspired by scanning electronic microscopy (SEM) imaging, in which carbon (or Au) thin films are usually required to be coated on the sample surface before imaging to remove the charging effect while imaging by electrons. We propose a saturation-absorption-induced far-field super-resolution optical imaging method (SAI-SRIM). In the SAI-SRIM, the carbon (or Au) layers in SEM imaging are replaced by nonlinear-saturation-absorption (NSA) thin films, which are directly coated onto the sample surfaces using advanced thin film deposition techniques. The surface fluctuant morphologies are replicated to the NSA thin films, accordingly. The coated sample surfaces are then imaged using conventional laser scanning microscopy. Consequently, the imaging resolution is greatly improved, and subdiffraction-resolved optical images are obtained theoretically and experimentally. The SAI-SRIM provides an effective and easy way to achieve far-field super-resolution optical imaging for sample surfaces with geometric fluctuant morphology characteristics. PMID:26727415

  10. Far-field optical imaging with subdiffraction resolution enabled by nonlinear saturation absorption

    NASA Astrophysics Data System (ADS)

    Ding, Chenliang; Wei, Jingsong

    2016-01-01

    The resolution of far-field optical imaging is required to improve beyond the Abbe limit to the subdiffraction or even the nanoscale. In this work, inspired by scanning electronic microscopy (SEM) imaging, in which carbon (or Au) thin films are usually required to be coated on the sample surface before imaging to remove the charging effect while imaging by electrons. We propose a saturation-absorption-induced far-field super-resolution optical imaging method (SAI-SRIM). In the SAI-SRIM, the carbon (or Au) layers in SEM imaging are replaced by nonlinear-saturation-absorption (NSA) thin films, which are directly coated onto the sample surfaces using advanced thin film deposition techniques. The surface fluctuant morphologies are replicated to the NSA thin films, accordingly. The coated sample surfaces are then imaged using conventional laser scanning microscopy. Consequently, the imaging resolution is greatly improved, and subdiffraction-resolved optical images are obtained theoretically and experimentally. The SAI-SRIM provides an effective and easy way to achieve far-field super-resolution optical imaging for sample surfaces with geometric fluctuant morphology characteristics.

  11. Far-field optical imaging with subdiffraction resolution enabled by nonlinear saturation absorption.

    PubMed

    Ding, Chenliang; Wei, Jingsong

    2016-01-01

    The resolution of far-field optical imaging is required to improve beyond the Abbe limit to the subdiffraction or even the nanoscale. In this work, inspired by scanning electronic microscopy (SEM) imaging, in which carbon (or Au) thin films are usually required to be coated on the sample surface before imaging to remove the charging effect while imaging by electrons. We propose a saturation-absorption-induced far-field super-resolution optical imaging method (SAI-SRIM). In the SAI-SRIM, the carbon (or Au) layers in SEM imaging are replaced by nonlinear-saturation-absorption (NSA) thin films, which are directly coated onto the sample surfaces using advanced thin film deposition techniques. The surface fluctuant morphologies are replicated to the NSA thin films, accordingly. The coated sample surfaces are then imaged using conventional laser scanning microscopy. Consequently, the imaging resolution is greatly improved, and subdiffraction-resolved optical images are obtained theoretically and experimentally. The SAI-SRIM provides an effective and easy way to achieve far-field super-resolution optical imaging for sample surfaces with geometric fluctuant morphology characteristics. PMID:26727415

  12. All-Optical Wavelength Conversion by Picosecond Burst Absorption in Colloidal PbS Quantum Dots.

    PubMed

    Geiregat, Pieter; Houtepen, Arjan J; Van Thourhout, Dries; Hens, Zeger

    2016-01-26

    All-optical approaches to change the wavelength of a data signal are considered more energy- and cost-effective than current wavelength conversion schemes that rely on back and forth switching between the electrical and optical domains. However, the lack of cost-effective materials with sufficiently adequate optoelectronic properties hampers the development of this so-called all-optical wavelength conversion. Here, we show that the interplay between intraband and band gap absorption in colloidal quantum dots leads to a very strong and ultrafast modulation of the light absorption after photoexcitation in which slow components linked to exciton recombination are eliminated. This approach enables all-optical wavelength conversion at rates matching state-of-the-art convertors in speed, yet with cost-effective solution-processable materials. Moreover, the stronger light-matter interaction allows for implementation in small-footprint devices with low switching energies. Being a generic property, the demonstrated effect opens a pathway toward low-power integrated photonics based on colloidal quantum dots as the enabling material. PMID:26692112

  13. Electronic states of DNA and M-DNA studied by optical absorption

    NASA Astrophysics Data System (ADS)

    Tsuburaya, Makoto; Sakamoto, Hirokazu; Mizoguchi, Kenji

    2014-02-01

    To unveil the electronic states of divalent metal ion incorporated M-DNAs, where M is Mg, Mn, Ni, Co, or Fe, optical absorption spectra have been studied in aqueous solutions of single-stranded (SS) 30mer DNA of poly(dA) (adenine), poly(dG) (guanine), poly(dT) (thymine), poly(dC) (cytosine), salmon-sperm DNA (B-DNA), and M-DNA. The absorption spectrum of the double-stranded (DS) B-DNA can be reproduced with the sum of the four absorption spectra of the SS oligo-DNAs in the ratio corresponding to the composition of B-DNA. This observation suggests that the interactions between complementary strands of DS DNA are negligibly weaker than the bandwidths of the optical spectra. In the metal-incorporated M-DNAs, except for Fe-DNA, the absorption spectra show no significant qualitative change from that of B-DNA. Quantitatively, however, the absorption intensity decreases by ≈15% uniquely in a DS poly(dA)-poly(dT) solution with adding MCl2, while nothing happens quantitatively and qualitatively in any SS oligo-DNA and DS poly(dG)-poly(dC) solutions, suggesting some suppression of the electronic excitation only in the Adenine-M-Thymine complex. In contrast, remarkable differences have been observed in Fe-DNA, prepared with FeCl2 and B-DNA. New absorption bands appear in the intragap energy of Fe-DNA, in addition to the suppression of the interband absorption peak of DNA at 4.8 eV. The intragap absorption is attributed to the appearance of Fe3+ species with the same spectral feature as that of FeCl3, that is, purely ionic Fe3+ species. This observation suggests that FeCl2+B-DNA forms Fe-DNA with hydrated Fe3+ ions with ionic bonds. Thus, it is concluded that the charge transfer from Fe2+ to DNA has occurred in Fe-DNA and that the transferred charges are expected to be located in the nearby bases.

  14. Retrievals of Thick Cloud Optical Depth from the Geoscience Laser Altimeter System (GLAS) by Calibration of Solar Background Signal

    NASA Technical Reports Server (NTRS)

    Yang, Yuekui; Marshak, Alexander; Chiu, J. Christine; Wiscombe, Warren J.; Palm, Stephen P.; Davis, Anthony B.; Spangenberg, Douglas A.; Nguyen, Louis; Spinhirne, James D.; Minnis, Patrick

    2008-01-01

    Laser beams emitted from the Geoscience Laser Altimeter System (GLAS), as well as other space-borne laser instruments, can only penetrate clouds to a limit of a few optical depths. As a result, only optical depths of thinner clouds (< about 3 for GLAS) are retrieved from the reflected lidar signal. This paper presents a comprehensive study of possible retrievals of optical depth of thick clouds using solar background light and treating GLAS as a solar radiometer. To do so we first calibrate the reflected solar radiation received by the photon-counting detectors of GLAS' 532 nm channel, which is the primary channel for atmospheric products. The solar background radiation is regarded as a noise to be subtracted in the retrieval process of the lidar products. However, once calibrated, it becomes a signal that can be used in studying the properties of optically thick clouds. In this paper, three calibration methods are presented: (I) calibration with coincident airborne and GLAS observations; (2) calibration with coincident Geostationary Operational Environmental Satellite (GOES) and GLAS observations of deep convective clouds; (3) calibration from the first principles using optical depth of thin water clouds over ocean retrieved by GLAS active remote sensing. Results from the three methods agree well with each other. Cloud optical depth (COD) is retrieved from the calibrated solar background signal using a one-channel retrieval. Comparison with COD retrieved from GOES during GLAS overpasses shows that the average difference between the two retrievals is 24%. As an example, the COD values retrieved from GLAS solar background are illustrated for a marine stratocumulus cloud field that is too thick to be penetrated by the GLAS laser. Based on this study, optical depths for thick clouds will be provided as a supplementary product to the existing operational GLAS cloud products in future GLAS data releases.

  15. Evaluation of SIMBADA measurements of marine reflectance and aerosol optical thickness during ACE-Asia and AOPEX

    NASA Astrophysics Data System (ADS)

    Frouin, Robert; Loisel, Hubert; Poteau, Antoine

    2010-10-01

    The SIMBADA radiometer was designed to check the radiometric calibration of satellite ocean-color sensors and evaluate the atmospheric correction of ocean-color imagery. It measures marine reflectance and aerosol optical thickness in 11 spectral bands covering the spectral range 350 to 870 nm. Aerosol optical thickness is obtained by viewing the sun disk and marine reflectance by viewing the ocean surface through a vertical polarizer that minimizes sun glint and reflected skylight. The measurements made by SIMBADA during ACE-Asia (March-April 2001, Japan Sea) and AOPEX (July-August 2004, Mediterranean Sea) are compared with those made concomitantly by other ocean radiometers and sun photometers, i.e., MER, PRR, SPMR, Trios, TSRB, and BOUSSOLE instruments for marine reflectance and CIMEL and Microtops for aerosol optical thickness. Agreement is generally good between the various measurements or estimates. The SIMBADA aerosol optical thickness is within +/-0.02 of the values obtained by other sun photometers. The SIMBADA marine reflectance, after correction for bi-directional effects (Q factor), does not exhibit biases when compared with estimates by other radiometers, which generally agree within +/-10%. In some cases larger discrepancies exist, and they are largely explained by differences in solar irradiance. More accurate SIMBADA estimates may be obtained by improving the radiometric calibration, the correction for angular geometry and water body polarization, the calculation of incident solar irradiance, and the selection of data minimally affected by sky reflection.

  16. Luminescence properties and optical absorption of X ray-irradiated KBr: Ce3(+), Tb(3+) crystals.

    PubMed

    Bangaru, S; Saradha, K; Muralidharan, G

    2015-03-01

    This paper reports that KBr doubly doped with Tb(3+) and Ce(3+) were prepared by Bridgman-Stockbarger method and characterized by Optical absorption, Photoluminescence (PL), Thermoluminescence (TL), Photo stimulated emission (PSL) and TL emission, after X-ray irradiation have been observed. The optical absorption measurement indicates that F and Z3 centers are formed in the crystal during X-ray irradiation process. It was attempted to incorporate a broad band of Ce(3+) sensitizer into the narrow band emission of Tb(3+) in the KBr host without reduction of emission intensity. Co-doping of Ce(3+) ions in KBr:Tb(3+) crystal showed a broad band emission due to the d-f transition of Ce(3+) and a reduction in the intensity of emission peaks due to (5)days → (7)F6 transition of Tb(3+) when they were excited at 250 nm. These results supported that an effective energy transfer occurs from Ce(3+) to Tb(3+) in the KBr host. Co-doping Ce(3+) ions greatly intensified the excitation peak at 260 nm for the emission at 390 nm of Tb(3+) which means that more lattice defects, involved in the energy absorption and transfer to Tb(3+), are formed by the Ce(3+) co-doping. The integrated light intensity is two orders of magnitude higher as compared to the undoped samples for similar doses of irradiation and heating rate. Thermoluminescence process has been identified due to thermal mobilization of F-electrons and this causes peaks at 371 K and at 427 K, 457 K in KBr: Ce(3+), Tb(3+) crystals. The defects generated by irradiation were monitored by optical absorption and trap parameters for the TL process were calculated and presented. PMID:25585645

  17. Long-term Analysis of Aerosol Optical Thickness from Satellite Retrievals over selected large agglomerations

    NASA Astrophysics Data System (ADS)

    Vountas, Marco; von Hoyningen-Huene, Wolfgang; Yoon, Jongmin; Burrows, John P.

    Aside from adverse health effect urban aerosols have potential effects on the climate system. In this study Aerosol Optical Thickness (AOT) retrievals over land are performed to study the medium to long-term trends of aerosols in large agglomerations (aka megacities). This task is challenging because of the high variability of the surface reflectance. The Bremen AErosol Retrieval (BAER) algorithm has retrieved AOT successfully over land with different satellite data in other studies. Here, the annual-and long-term trend of AOT over several regions have been analyzed using BAER based on SeaWiFS (Sea-viewing Wide Field-of-view Sensor) L1b data over a period of 11 years. Among the regions analyzed were several European regions, as well as Sao Paolo, Brazil, and Perl River Delta in south China. Practically all regions investigated showed a week negative trend in AOT (validated by AERONET), except over Perl River Delta where a comparatively strong positive trend of up to 0.007/yr could be observed.

  18. An improved method for retrieving nighttime aerosol optical thickness from the VIIRS Day/Night Band

    NASA Astrophysics Data System (ADS)

    McHardy, T. M.; Zhang, J.; Reid, J. S.; Miller, S. D.; Hyer, E. J.; Kuehn, R. E.

    2015-11-01

    Using Visible Infrared Imaging Radiometer Suite (VIIRS) Day/Night Band (DNB) data, a method, dubbed the "variance method", is developed for retrieving nighttime aerosol optical thickness (τ) values through the examination of the dispersion of radiance values above an artificial light source. Based on the improvement of a previous algorithm, this updated method derives a semi-quantitative indicator of nighttime τ using artificial light sources. Nighttime τ retrievals from the newly developed method are inter-compared with an interpolated value from late afternoon and early morning ground observations from four AErosol RObotic NETwork (AERONET) sites as well as column-integrated τ from one High Spectral Resolution Lidar (HSRL) site at Huntsville, AL, during the NASA Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign, providing full diel coverage. Sensitivity studies are performed to examine the effects of lunar illumination on VIIRS τ retrievals made via the variance method, revealing that lunar contamination may have a smaller impact than previously thought; however, the small sample size of this study limits the conclusiveness thus far. VIIRS τ retrievals yield a coefficient of determination (r2) of 0.60 and a root-mean-squared error (RMSE) of 0.18 when compared against straddling daytime-averaged AERONET τ values. Preliminary results suggest that artificial light sources can be used for estimating regional and global nighttime aerosol distributions in the future.

  19. Remote Sensing of Global Fire Patterns, Aerosol Optical Thickness, and Carbon Monoxide During April 1994

    NASA Technical Reports Server (NTRS)

    Christopher, Sundar A.; Wang, Min; Klich, Donna V.; Welch, Ronald M.; Nolf, Scott; Connors, Vickie S.

    1997-01-01

    Fires play a crucial role in several ecosystems. They are routinely used to burn forests in order to accommodate the needs of the expanding population, clear land for agricultural purposes, eliminate weeds and pests, regenerate nutrients in grazing and crop lands and produce energy for cooking and heating purposes. Most of the fires on earth are related to biomass burning in the tropics, although they are not confined to these latitudes. The boreal and tundra regions also experience fires on a yearly basis. The current study examines global fire patterns, Aerosol Optical Thickness (AOT) and carbon monoxide concentrations during April 9-19, 1994. Recently, global Advanced Very High Resolution Radiometer (AVHRR) data at nadir ground spatial resolution of 1 km are made available through the NASA/NOAA Pathfinder project. These data from April 9-19, 1994 are used to map fires over the earth. In summary, our analysis shows that fires from biomass burning appear to be the dominant factor for increased tropospheric CO concentrations as measured by the MAPS. The vertical transport of CO by convective activities, along with horizontal transport due to the prevailing winds, are responsible for the observed spatial distribution of CO.

  20. Post-Mortem Corneal Thickness Measurements with a Portable Optical Coherence Tomography System: a Reliability Study

    PubMed Central

    Napoli, Pietro Emanuele; Nioi, Matteo; d’Aloja, Ernesto; Fossarello, Maurizio

    2016-01-01

    The purpose of this study was to determine the repeatability and reproducibility of post-mortem central corneal thickness (CCT) measurements by using a real-time, portable optical coherence tomography (OCT) system on an animal model, and to prospectively evaluate the time-course of post-mortem changes in CCT. Forty-six ocular globes of sheep (Ovis aries) were analyzed with a portable spectral-domain OCT device by two operators at different postmortem intervals (PMIs) as follows: immediately (i.e. within 10 minutes), at the 30th minute, at the 1st, 6th, 12th, 24th and 48th hour, and later (up to the 96th hour). The coefficient of repeatability ranged from 0.3% to 3.5%, and coefficients of reproducibility ranged from 0.2% to 3.7% in the central region of the cornea. The intraclass correlation coefficients were particularly high at different PMIs, thus confirming good measurement reliability with the portable OCT. The average CCT decreased immediately and then increased thereafter, with two peaks at 6 and 24 hours after death. Our results suggest that portable OCT is a reliable tool for monitoring CCT variations after death and may be useful in characterizing corneas before explantation, detecting quantitative variations during post-mortem corneal degeneration or assessing changes in CCT for forensic implications. PMID:27457021

  1. Spatial Aspects of Multi-Sensor Data Fusion: Aerosol Optical Thickness

    NASA Technical Reports Server (NTRS)

    Leptoukh, Gregory; Zubko, V.; Gopalan, A.

    2007-01-01

    The Goddard Earth Sciences Data and Information Services Center (GES DISC) investigated the applicability and limitations of combining multi-sensor data through data fusion, to increase the usefulness of the multitude of NASA remote sensing data sets, and as part of a larger effort to integrate this capability in the GES-DISC Interactive Online Visualization and Analysis Infrastructure (Giovanni). This initial study focused on merging daily mean Aerosol Optical Thickness (AOT), as measured by the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra and Aqua satellites, to increase spatial coverage and produce complete fields to facilitate comparison with models and station data. The fusion algorithm used the maximum likelihood technique to merge the pixel values where available. The algorithm was applied to two regional AOT subsets (with mostly regular and irregular gaps, respectively) and a set of AOT fields that differed only in the size and location of artificially created gaps. The Cumulative Semivariogram (CSV) was found to be sensitive to the spatial distribution of gap areas and, thus, useful for assessing the sensitivity of the fused data to spatial gaps.

  2. Short term variability of aerosol optical thickness at Belsk for the period 2002-2010

    NASA Astrophysics Data System (ADS)

    Pietruczuk, Aleksander

    2013-11-01

    In this work variability of aerosol optical thickness (AOT) measured at Belsk, Poland is studied as well as modification of AOT during airmass advection towards Belsk. AOT measurements taken at Belsk and at AERONET stations located in eastern Germany, Belarus and Scandinavia are used as well as satellite measurements of AOT taken by MODIS instrument onboard Terra and Aqua satellites. Directions of airmass advection are determined by means of cluster analysis of airmass backward-trajectories. Changes of AOT at Belsk from day to day varies around zero regardless of time lag between measurements. The standard deviation of these measurements increases with increasing time lag. In case of advection from west and north direction such standard deviation is reduced. It gives good perspective for a persistent forecast of next day AOT. Analysis of AOT changes during airmass advection toward Belsk reveals two modes of AOT changes distributions. One of them with small increase of AOT and second one with larger increase of AOT, so-called loading mode. Loading mode dominates in case of advection from south direction whilst the first mode of AOT changes dominates in case of advection from other directions. Mean increase of AOT associated with the first mode is 0.034 ± 0.003. Analysis of backward-trajectories shows that aerosol loading occurs over urban/industrial regions located south and south-west of Belsk. Substantial aerosol loading is found during seasonal biomass burning episodes in Eastern Europe.

  3. DESPOTIC - a new software library to Derive the Energetics and SPectra of Optically Thick Interstellar Clouds

    NASA Astrophysics Data System (ADS)

    Krumholz, Mark R.

    2014-01-01

    I describe DESPOTIC, a code to Derive the Energetics and SPectra of Optically Thick Interstellar Clouds. DESPOTIC represents such clouds using a one-zone model, and can calculate line luminosities, line cooling rates, and in restricted cases line profiles using an escape probability formalism. It also includes approximate treatments of the dominant heating, cooling and chemical processes for the cold interstellar medium, including cosmic ray and X-ray heating, grain photoelectric heating, heating of the dust by infrared and ultraviolet radiation, thermal cooling of the dust, collisional energy exchange between dust and gas, and a simple network for carbon chemistry. Based on these heating, cooling and chemical rates, DESPOTIC can calculate clouds' equilibrium gas and dust temperatures, equilibrium carbon chemical state and time-dependent thermal and chemical evolution. The software is intended to allow rapid and interactive calculation of clouds' characteristic temperatures, identification of their dominant heating and cooling mechanisms and prediction of their observable spectra across a wide range of interstellar environments. DESPOTIC is implemented as a PYTHON package, and is released under the GNU General Public License.

  4. Quantification of model uncertainty in aerosol optical thickness retrieval from Ozone Monitoring Instrument (OMI) measurements

    NASA Astrophysics Data System (ADS)

    Määttä, A.; Laine, M.; Tamminen, J.; Veefkind, J. P.

    2013-09-01

    We study uncertainty quantification in remote sensing of aerosols in the atmosphere with top of the atmosphere reflectance measurements from the nadir-viewing Ozone Monitoring Instrument (OMI). Focus is on the uncertainty in aerosol model selection of pre-calculated aerosol models and on the statistical modelling of the model inadequacies. The aim is to apply statistical methodologies that improve the uncertainty estimates of the aerosol optical thickness (AOT) retrieval by propagating model selection and model error related uncertainties more realistically. We utilise Bayesian model selection and model averaging methods for the model selection problem and use Gaussian processes to model the smooth systematic discrepancies from the modelled to observed reflectance. The systematic model error is learned from an ensemble of operational retrievals. The operational OMI multi-wavelength aerosol retrieval algorithm OMAERO is used for cloud free, over land pixels of the OMI instrument with the additional Bayesian model selection and model discrepancy techniques. The method is demonstrated with four examples with different aerosol properties: weakly absorbing aerosols, forest fires over Greece and Russia, and Sahara dessert dust. The presented statistical methodology is general; it is not restricted to this particular satellite retrieval application.

  5. Post-Mortem Corneal Thickness Measurements with a Portable Optical Coherence Tomography System: a Reliability Study.

    PubMed

    Napoli, Pietro Emanuele; Nioi, Matteo; d'Aloja, Ernesto; Fossarello, Maurizio

    2016-01-01

    The purpose of this study was to determine the repeatability and reproducibility of post-mortem central corneal thickness (CCT) measurements by using a real-time, portable optical coherence tomography (OCT) system on an animal model, and to prospectively evaluate the time-course of post-mortem changes in CCT. Forty-six ocular globes of sheep (Ovis aries) were analyzed with a portable spectral-domain OCT device by two operators at different postmortem intervals (PMIs) as follows: immediately (i.e. within 10 minutes), at the 30(th) minute, at the 1(st), 6(th), 12(th), 24(th) and 48(th) hour, and later (up to the 96(th) hour). The coefficient of repeatability ranged from 0.3% to 3.5%, and coefficients of reproducibility ranged from 0.2% to 3.7% in the central region of the cornea. The intraclass correlation coefficients were particularly high at different PMIs, thus confirming good measurement reliability with the portable OCT. The average CCT decreased immediately and then increased thereafter, with two peaks at 6 and 24 hours after death. Our results suggest that portable OCT is a reliable tool for monitoring CCT variations after death and may be useful in characterizing corneas before explantation, detecting quantitative variations during post-mortem corneal degeneration or assessing changes in CCT for forensic implications. PMID:27457021

  6. Uncertainty quantification in aerosol optical thickness retrieval from Ozone Monitoring Instrument (OMI) measurements

    NASA Astrophysics Data System (ADS)

    Määttä, A.; Laine, M.; Tamminen, J.; Veefkind, J. P.

    2013-10-01

    The space borne measurements provide global view of atmospheric aerosol distribution. The Ozone Monitoring Instrument (OMI) on board NASAs Earth Observing System (EOS) Aura satellite is a Dutch-Finnish nadir-viewing solar backscatter spectrometer measuring in the ultraviolet and visible wavelengths. OMI measures several trace gases and aerosols that are important in many air quality and climate studies. The OMI aerosol measurements are used, for example, for detecting volcanic ash plumes, wild fires and transportation of desert dust. We present a methodology for improving the uncertainty quantification in the aerosols retrieval algorithm. We have used the OMI measurements in this feasibility study. Our focus is on the uncertainties originating from the pre-calculated aerosol models. These models are never complete descriptions of the reality. This aerosol model uncertainty is estimated using Gaussian processes with computational tools from spatial statistics. Our approach is based on smooth systematic differences between the observed and modelled reflectances. When acknowledging this model inadequacy in the estimation of aerosol optical thickness (AOT), the uncertainty estimates are more realistic. We present here a real world example of applying the methodology.

  7. Accommodation-induced variations in retinal thickness measured by spectral domain optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Fan, Shanhui; Sun, Yong; Dai, Cuixia; Zheng, Haihua; Ren, Qiushi; Jiao, Shuliang; Zhou, Chuanqing

    2014-09-01

    To research retinal stretching or distortion with accommodation, accommodation-induced changes in retinal thickness (RT) in the macular area were investigated in a population of young adults (n=23) by using a dual-channel spectral domain optical coherence tomography (SD-OCT) system manufactured in-house for this study. This dual-channel SD-OCT is capable of imaging the cornea and retina simultaneously with an imaging speed of 24 kHz A-line scan rate, which can provide the anatomical dimensions of the eye, including the RT and axial length. Thus, the modification of the RT with accommodation can be calculated. A significant decrease in the RT (13.50±1.25 μm) was observed during maximum accommodation. In the 4 mm×4 mm macular area centered at the fovea, we did not find a significant quadrant-dependent difference in retinal volume change, which indicates that neither retinal stretching nor distortion was quadrant-dependent during accommodation. We speculate that the changes in RT with maximum accommodation resulted from accommodation-induced ciliary muscle contractions.

  8. Optical absorption engineering in stacked plasmonic Au-SiO₂-Pd nanoantennas.

    PubMed

    Wadell, Carl; Antosiewicz, Tomasz J; Langhammer, Christoph

    2012-09-12

    The nonradiative decay of a localized surface plasmon through absorption of a captured photon and excitation of an energetic electron-hole pair is a potentially very effective way to enhance chemical reactions on metal nanoparticle surfaces, so far limited to Ag (and Au). Here we explore the possibility of efficient and spectrally widely tunable optical absorption engineering based on heterometallic optical nanoantennas. They consist of an optimized antenna element made of Au (or Ag) and a catalytically active second metallic element separated by a thin SiO(2) layer. Specifically, we find that stacked Au-SiO(2)-Pd nanodisk antennas exhibit pronounced local absorption enhancement in the catalytic Pd particle. The effect is caused by efficient power transfer from the Au disk, exhibiting a narrow low-loss resonance and acting as an antenna collecting photons, to the Pd disk due to strong coupling between the two. The Pd element thus acts as receiver that efficiently dissipates energy into electron-hole pairs owing to efficient coupling to intra and interband transitions. In fact, the energy transfer is found to be so effective that the absorption efficiency at a given wavelength can be enhanced up to 6 to 9 times, and the total absorption integrated over a wide spectral range (400-900 nm) up to 2-fold, depending on the antenna dimensions. This finding suggests a novel route toward highly efficient plasmon-enhanced catalysis on widely selectable catalytic metal particle surfaces not limited to the "classic" plasmonic metals Au and Ag. PMID:22916998

  9. Structures and optical absorption of Bi2OS2 and LaOBiS2

    NASA Astrophysics Data System (ADS)

    Miura, Akira; Mizuguchi, Yoshikazu; Takei, Takahiro; Kumada, Nobuhiro; Magome, Eisuke; Moriyoshi, Chikako; Kuroiwa, Yoshihiro; Tadanaga, Kiyoharu

    2016-02-01

    The band gaps of isostructural Bi2OS2 and LaOBiS2 were examined using optical absorption and discussed with the band structures calculated based on the crystal structures determined using synchrotron X-ray diffraction. The Bi 6p and S 3p orbitals in the Bi-S plane were computationally predicted to constitute the bands near the Fermi level. The optical reflectance spectra of Bi2OS2 and LaOBiS2 showed optical band gaps of ~1.0 eV, which were close to the computationally calculated direct band gaps of ~0.8 eV. Our results show that Bi2OS2 and LaOBiS2 are semiconductors containing direct band gaps of 0.8-1.0 eV, and they are suggested to be candidates for optoelectronic materials in the near-infrared region without highly toxic elements.

  10. Comparison of central corneal thickness measurements with three new optical devices and a standard ultrasonic pachymeter.

    PubMed Central

    Bayhan, Hasan Ali; Aslan Bayhan, Seray; Can, İzzet

    2014-01-01

    AIM To compare the RTVue spectral optical coherence tomography (SD-OCT), Sirius Scheimpflug-Placido topographer, Lenstar optical low coherence reflectometry (OLCR) and ultrasound pachymetry (USP) devices in terms of their agreement and repeatability of measuring central corneal thickness (CCT). METHODS In this prospective study, 50 eyes of 50 patients were included. Three repeated measures were obtained using SD-OCT, Scheimpflug-Placido topographer and USP and five measurements were determined with the OLCR. Bland-Altman plots were used to assess agreement among the instruments, and 95% limits of agreement (LoA) for each comparison were calculated. Intra-examiner repeatability was assessed using intraclass correlation coefficients (ICCs). RESULTS The mean CCT by SD-OCT, Scheimpflug-Placido topographer, OLCR, and USP were 525.90±34.08 µm, 525.92±34.10 µm, 530.30±35.62 µm, and 543.50±37.11 µm respectively. All 4 modalities of CCT measurements correlated closely with each other, with Pearson correlation coefficients ranging from 0.977 to 0.995. The mean differences (and upper/lower LoA) for CCT measurements were -0.05±6.77 µm (13.3/-13.3) between SD-OCT and Scheimpflug-Placido topographer, 4.38±3.79 µm (11.8/-3.1) between OLCR and SD-OCT, 4.38±6.03 µm (16.2/-7.5) between OLCR and Scheimpflug-Placido topographer, 13.20±6.46 µm (25.9/0.5) between USP and OLCR, 17.59±6.76 µm (30.8/4.3) between USP and SD-OCT, and 17.58±8.13 µm (33.5/1.6) between USP and Scheimpflug-Placido topographer. Intra-examiner repeatability was excellent for all devices with ICCs>0.98. CONCLUSION For most practical purposes, CCT measurements with the RTVue, Sirius and Lenstar can be used interchangeably. Although highly correlated, CCT measurement differences between USP and these 3 optical instruments can be significant depending on the clinical situation. PMID:24790874

  11. Hydrogen sensing via anomalous optical absorption of palladium-based metamaterials

    NASA Astrophysics Data System (ADS)

    Hierro-Rodriguez, A.; Leite, I. T.; Rocha-Rodrigues, P.; Fernandes, P.; Araujo, J. P.; Jorge, P. A. S.; Santos, J. L.; Teixeira, J. M.; Guerreiro, A.

    2016-05-01

    A palladium (Pd)-based optical metamaterial has been designed, fabricated and characterized for its application in hydrogen sensing. The metamaterial can replace Pd thin films in optical transmission schemes for sensing with performances far superior to those of conventional sensors. This artificial material consists of a palladium-alumina metamaterial fabricated using inexpensive and industrial-friendly bottom-up techniques. During the exposure to hydrogen, the system exhibits anomalous optical absorption when compared to the well-known response of Pd thin films, this phenomenon being the key factor for the sensor sensitivity. The exposure to hydrogen produces a large variation in the light transmission through the metamembrane (more than 30% with 4% in volume hydrogen-nitrogen gas mixture at room temperature and atmospheric pressure), thus avoiding the need for sophisticated optical detection systems. An optical homogenization model is proposed to explain the metamaterial response. These results contribute to the development of reliable and low-cost hydrogen sensors with potential applications in the hydrogen economy and industrial processes to name a few, and also open the door to optically study the hydrogen diffusion processes in Pd nanostructures.

  12. Hydrogen sensing via anomalous optical absorption of palladium-based metamaterials.

    PubMed

    Hierro-Rodriguez, A; Leite, I T; Rocha-Rodrigues, P; Fernandes, P; Araujo, J P; Jorge, P A S; Santos, J L; Teixeira, J M; Guerreiro, A

    2016-05-01

    A palladium (Pd)-based optical metamaterial has been designed, fabricated and characterized for its application in hydrogen sensing. The metamaterial can replace Pd thin films in optical transmission schemes for sensing with performances far superior to those of conventional sensors. This artificial material consists of a palladium-alumina metamaterial fabricated using inexpensive and industrial-friendly bottom-up techniques. During the exposure to hydrogen, the system exhibits anomalous optical absorption when compared to the well-known response of Pd thin films, this phenomenon being the key factor for the sensor sensitivity. The exposure to hydrogen produces a large variation in the light transmission through the metamembrane (more than 30% with 4% in volume hydrogen-nitrogen gas mixture at room temperature and atmospheric pressure), thus avoiding the need for sophisticated optical detection systems. An optical homogenization model is proposed to explain the metamaterial response. These results contribute to the development of reliable and low-cost hydrogen sensors with potential applications in the hydrogen economy and industrial processes to name a few, and also open the door to optically study the hydrogen diffusion processes in Pd nanostructures. PMID:27003717

  13. Quasi-Resonant Nonlinear Absorption for Optical Power Limiting: solgel-Processed Er(3+)-Doped Multicomponent Silica Glass.

    PubMed

    Maciel, G S; Biswas, A; Friend, C S; Prasad, P N

    2000-05-20

    We demonstrate optical power limiting by what we believe to be a new mechanism of nonlinear absorption, which involves a quasi-resonant ground-state absorption that is either phonon assisted or assisted by the presence of defect sites (tail absorption). Such a mechanism provides high transmittance at low intensity yet optical limiting under cw conditions. The sample used was a novel solgel-processed Er(3+)-doped multicomponent silica glass. In this system the nonlinear absorption process is achieved because the resonant excited-state ((4)I(13/2) ? (4)S(3/2)) absorption cross section is larger than the quasi-resonant ground-state ((4)I(15/2) ? (4)I(9/2)) absorption cross section. PMID:18345156

  14. Multimodal tissue imaging: using coregistered optical tomography data to estimate tissue autofluorescence intensity change due to scattering and absorption by neoplastic epithelial cells.

    PubMed

    Pahlevaninezhad, Hamid; Cecic, Ivana; Lee, Anthony M D; Kyle, Alastair H; Lam, Stephen; MacAulay, Calum; Lane, Pierre M

    2013-10-01

    Autofluorescence (AF) imaging provides valuable information about the structural and chemical states of tissue that can be used for early cancer detection. Optical scattering and absorption of excitation and emission light by the epithelium can significantly affect observed tissue AF intensity. Determining the effect of epithelial attenuation on the AF intensity could lead to a more accurate interpretation of AF intensity. We propose to use optical coherence tomography coregistered with AF imaging to characterize the AF attenuation due to the epithelium. We present imaging results from three vital tissue models, each consisting of a three-dimensional tissue culture grown from one of three epithelial cell lines (HCT116, OVCAR8, and MCF7) and immobilized on a fluorescence substrate. The AF loss profiles in the tissue layer show two different regimes, each approximately linearly decreasing with thickness. For thin cell cultures (<300 μm), the AF signal changes as AF(t)/AF(0)=1-1.3t (t is the thickness in millimeter). For thick cell cultures (>400 μm), the AF loss profiles have different intercepts but similar slopes. The data presented here can be used to estimate AF loss due to a change in the epithelial layer thickness and potentially to reduce AF bronchoscopy false positives due to inflammation and non-neoplastic epithelial thickening. PMID:24108573

  15. The effect of metal nano particle on optical absorption coefficient of multi-layer spherical quantum dot

    NASA Astrophysics Data System (ADS)

    Zamani, N.; Keshavarz, A.; Nadgaran, H.

    2016-06-01

    In this paper, we investigate the optical absorption coefficient of hybrid structure consisting of metal nano particle (MNP) coupled to multi-layer spherical quantum dot (MSQD). Energy eigenvalues and eigenfunctions of Schrödinger equation in this structure are obtained by using numerical solution (by the fourth-order Runge-Kutta method). The effect of MNP in the vicinity of MSQD is calculated by considering local field theory. Then the variation of optical absorption coefficient hybrid structure is calculated. The results show that the presence of MNP near MSQD enhances the optical absorption coefficient. Also, by changing the distance between MNP and MSQD and radius of MNP, variation of optical absorption coefficient and refractive index changes are introduced.

  16. Optical Control of Intersubband Absorption in a Multiple Quantum Well-Embedded Semiconductor Microcravity

    NASA Technical Reports Server (NTRS)

    Liu, Ansheng; Ning, Cun-Zheng

    2000-01-01

    Optical intersubband response of a multiple quantum well (MQW)-embedded microcavity driven by a coherent pump field is studied theoretically. The n-type doped MQW structure with three subbands in the conduction band is sandwiched between a semi-infinite medium and a distributed Bragg reflector (DBR). A strong pump field couples the two upper subbands and a weak field probes the two lower subbands. To describe the optical response of the MQW-embedded microcavity, we adopt a semi-classical nonlocal response theory. Taking into account the pump-probe interaction, we derive the probe-induced current density associated with intersubband transitions from the single-particle density-matrix formalism. By incorporating the current density into the Maxwell equation, we solve the probe local field exactly by means of Green's function technique and the transfer-matrix method. We obtain an exact expression for the probe absorption coefficient of the microcavity. For a GaAs/Al(sub x)Ga(sub 1-x)As MQW structure sandwiched between a GaAs/AlAs DBR and vacuum, we performed numerical calculations of the probe absorption spectra for different parameters such as pump intensity, pump detuning, and cavity length. We find that the probe spectrum is strongly dependent on these parameters. In particular, we find that the combination of the cavity effect and the Autler-Townes effect results in a triplet in the optical spectrum of the MQW system. The optical absorption peak value and its location can be feasibly controlled by varying the pump intensity and detuning.

  17. [Retrieval of the Optical Thickness and Cloud Top Height of Cirrus Clouds Based on AIRS IR High Spectral Resolution Data].

    PubMed

    Cao, Ya-nan; Wei, He-li; Dai, Cong-ming; Zhang, Xue-hai

    2015-05-01

    A study was carried out to retrieve optical thickness and cloud top height of cirrus clouds from the Atmospheric Infrared Sounder (AIRS) high spectral resolution data in 1070~1135 cm-1 IR band using a Combined Atmospheric Radiative Transfer model (CART) by brightness temperature difference between model simulation and AIRS observation. The research is based on AIRS LIB high spectral infrared observation data combined with Moderate Resolution Imaging Spectroradiometer (MODIS) cloud product data. Brightness temperature spectra based, on the retrieved cirrus optical thickness and cloud top height were simulated and compared with brightness temperature spectra of AIRS observation in the 650~1150 cm-1 band. The cirrus optical thickness and cloud top height retrieved were compared with brightness temperature of AIRS for channel 760 (900.56 cm-1, 11. 1 µm) and cirrus reflectance of MODIS cloud product. And cloud top height retrieved was compared with cloud top height from MODIS. Results show that the brightness temperature spectra simulated were basically consistent with AIRS observation under the condition of retrieval in the 650~1150 cm-1 band. It means that CART can be used to simulate AIRS brightness temperature spectra. The retrieved cirrus parameters are consistent with brightness temperature of AIRS for channel 11. 1 µm with low brightness temperature corresponding to large cirrus optical thickness and high cloud top height. And the retrieved cirrus parameters are consistent with cirrus reflectance of MODIS cloud product with high cirrus reflectance corresponding to large cirrus optical thickness and high cloud top height. Correlation coefficient of brightness temperature between retrieved cloud top height and MODIS cloud top height was relatively high. They are mostly located in the range of 8. 5~11.5 km, and their probability distribution trend is approximately identical. CART model is feasible to retrieve cirrus properties, and the retrieval is reliable. PMID

  18. Extending differential optical absorption spectroscopy for limb measurements in the UV

    NASA Astrophysics Data System (ADS)

    Puä·Ä«Te, J.; Kühl, S.; Deutschmann, T.; Platt, U.; Wagner, T.

    2009-11-01

    Methods of UV/VIS absorption spectroscopy to determine the constituents in the Earth's atmosphere from measurements of scattered light are often based on the Beer-Lambert law, like e.g. Differential Optical Absorption Spectroscopy (DOAS). Therefore they are strictly valid for weak absorptions and narrow wavelength intervals (strictly only for monochromatic radiation). For medium and strong absorption (e.g. along very long light-paths like in limb geometry) the relation between the optical depth and the concentration of an absorber is not linear anymore. As well, for large wavelength intervals the wavelength dependent differences in the travelled light-paths become important, especially in the UV, where the probability for scattering increases strongly with decreasing wavelength. However, by taking into account these dependencies, the applicability of the DOAS method can be extended also to cases with medium to strong absorptions and for broader wavelength intervals. Common approaches for this correction are the so called air mass factor modified (or extended) DOAS and the weighting function modified DOAS. These approaches take into account the wavelength dependency of the slant column densities (SCDs), but also require a-priori knowledge for the air mass factor or the weighting function calculation by radiative transfer modelling. We describe an approach that considers the fitting results obtained from DOAS, the SCDs, as a function of wavelength and vertical optical depth and expands this function into a Taylor series of both quantities. The Taylor coefficients are then applied as additional fitting parameters in the DOAS analysis. Thus the variability of the SCD in the fit window is determined by the retrieval itself. This new approach gives a description of the SCD that is as close to reality as desired (depending on the order of the Taylor expansion), and is independent from any assumptions or a-priori knowledge of the considered absorbers. In case studies for

  19. In vivo tear film thickness measurement and tear film dynamics visualization using spectral domain optical coherence tomography.

    PubMed

    Aranha Dos Santos, Valentin; Schmetterer, Leopold; Gröschl, Martin; Garhofer, Gerhard; Schmidl, Doreen; Kucera, Martin; Unterhuber, Angelika; Hermand, Jean-Pierre; Werkmeister, René M

    2015-08-10

    Dry eye syndrome is a highly prevalent disease of the ocular surface characterized by an instability of the tear film. Traditional methods used for the evaluation of tear film stability are invasive or show limited repeatability. Here we propose a new non-invasive fully automated approach to measure tear film thickness based on spectral domain optical coherence tomography and on an efficient delay estimator. Silicon wafer phantom were used to validate the thickness measurement. The technique was applied in vivo in healthy subjects. Series of tear film thickness maps were generated, allowing for the visualization of tear film dynamics. Our results show that the in vivo central tear film thickness measurements are precise and repeatable with a coefficient of variation of about 0.65% and that repeatable tear film dynamics can be observed. The presented approach could be used in clinical setting to study patients with dry eye disease and monitor their treatments. PMID:26367956

  20. Determination of layer thickness and optical constants of thin films by using a modified pattern search method.

    PubMed

    Miloua, R; Kebbab, Z; Chiker, F; Sahraoui, K; Khadraoui, M; Benramdane, N

    2012-02-15

    We propose the use of a pattern search optimization technique in combination with a seed preprocessing procedure to determine the optical constants and thickness of thin films using only the transmittance spectra. The approach is quite flexible, straightforward to implement, and efficient in reaching the best fitting. We demonstrate the effectiveness of the method in extracting optical constants, even when the films are not displaying interference fringes. Comparison to a real-coded genetic algorithm shows that the modified pattern search is fast, almost accurate, and does not need any parameter adjustments. The approach is successfully applied to extract the thickness and optical constants of spray pyrolyzed nanocrystalline CdO thin films. PMID:22344069

  1. Preparation and characterization of SiO2/TiO2/methylcellulose hybrid thick films for optical waveguides

    NASA Astrophysics Data System (ADS)

    Yang, Jun; Zhang, Xinyu; Wang, Pei; Ming, Hai; Wu, Yunxia; Xie, Jianping; Zhang, Junying

    2005-07-01

    SiO2/TiO2/methylcellulose composite materials processed by the sol-gel technique were studied for optical waveguide applications. With the help of methylcellulose, an organic binder, SiO2/TiO2/methylcellulose hybrid thick films were prepared by a single spin-coating processes. After annealing at 70 Celsius degree for an hour, 2.5-?m crack-free and dense organic--inorganic hybrid optical films with a refractive index of 1.537 were achieved. Optical losses of plane waveguide made up of those films and ordinary slide glass substrate are around 0.3 dB/cm at 650 nm. Scanning electronmicroscopy (SEM) and UV-visible spectroscopy (UV-VIS), have been used to characterize the thick films.

  2. Differences of Intrasession Reproducibility of Circumpapillary Total Retinal Thickness and Circumpapillary Retinal Nerve Fiber Layer Thickness Measurements Made with the RS-3000 Optical Coherence Tomograph

    PubMed Central

    Kita, Yoshiyuki; Hollό, Gábor; Kita, Ritsuko; Horie, Daisuke; Inoue, Makoto; Hirakata, Akito

    2015-01-01

    Purpose To evaluate the intrasession reproducibility of various thickness parameters used to diagnose and follow-up glaucoma, in particular circumpapillary total retinal thickness (cpTR) provided by the RS-3000 optical coherence tomograph (OCT). Methods Fifty-three healthy eyes of 28 subjects underwent three consecutive imaging with the RS-3000 Advance OCT (NIDEK, Aichi,Japan) to evaluate the intrasession reproducibility of circumpapillary total retinal thickness (cpTR), circumpapillary retinal nerve fiber layer thickness (cpRNFL), macular ganglion cell complex thickness (mGCC) and macular total retina thickness (mTR) measurements. Intraclass correlation (ICC), coefficient of variation (CV) and reproducibility coefficient (RC) were calculated for each parameter. Results The ICC and CV values for mean cpTR and cpRNFL were 0.987 and 0.897, and 0.60% and 2.81%, respectively. The RC values for the mean cpTR and cpRNFL were 5.95 μm and 9.04 μm, respectively. For all cpTR parameters the ICC values were higher and both the CV and RC values were lower than those for the corresponding cpRNFL parameters. The ICC and CV values for superior mGCC, inferior mGCC, superior mTR and inferior mTR were 0.983, 0.980, 0.983 and 0.988, and 0.84%, 0.98%, 0.48% and 0.43%, respectively. The RC values for superior mGCC, inferior mGCC, superior mTR and inferior mTR were 2.86 μm, 3.12 μm, 4.41μm and 4.43 μm, respectively. Conclusions Intrasession reproducibility of cpTR, mGCC and mTR measurements made on healthy eyes was high. Repeatability of cpTR measurements was better than that of the corresponding cpRNFL measurements. These results suggest that future clinical investigations addressing detection of glaucoma and glaucomatous progression with the RS-3000 OCT may benefit from focusing on the cpTR parameters. PMID:26657805

  3. Method and apparatus for enhancing surface absorption and emissivity in optical pulsed infrared nondestructive evaluation

    NASA Astrophysics Data System (ADS)

    Duan, Yuxia; Zhang, Cunlin; Jin, Wanping; Wu, Naiming

    2009-07-01

    In the application of optical pulsed infrared NDE, the visible light absorption and IR emissivity of the detected object must be considered. One of the simple methods is spraying paint on the highly reflective and low IR emissivity surface before testing. However, for some materials such as with pore space in the surface or easily to be corrupted have to be pretreated by other method and apparatus. Two kinds of apparatus for surface pretreating are designed according to the dimension of the detected object and the testing conditions. One apparatus is independent of the former detecting system, and the other is an improvement of the former system. The basic principle of the two apparatus is covering a flexible membrane of high light absorption and IR emissivity on the specimen surface by vacuum pumping. The paper also present the applications of the method, including the detection of the metal mesh material and the honeycomb structures with aluminum coating. The experimental results show that the technique of covering thin film by vacuum pump is effective for enhancing surface absorption and emissivity; moreover, it does not pollute or damage the sample. The application of the technique has practical significance, because it extends the scope of the application of the optical pulsed thermography nondestructive evaluation.

  4. A microfluidic chemical/biological sensing system based on membrane dissolution and optical absorption

    NASA Astrophysics Data System (ADS)

    Sridharamurthy, Sudheer S.; Dong, Liang; Jiang, Hongrui

    2007-01-01

    A microfluidic system to sense chemical and biological analytes using membranes dissolvable by the analyte is demonstrated. The scheme to detect the dissolution of the membrane is based on the difference in optical absorption of the membrane and the fluidic sample being assayed. The presence of the analyte in the sample chemically cleaves the membrane and causes the sample to flow into the membrane area. This causes a change in the optical absorption of the path between the light source and detector. A device comprising the microfluidic channels and the membrane is microfabricated using liquid-phase photopolymerization. A light emitting diode (LED) and a detector with an integrated amplifier are positioned and aligned on either side of the device. The state of the membrane is continuously monitored after introducing the sample. The temporal dissolution characteristics of the membrane are extracted in terms of the output voltage of the detector as a function of time. This is used to determine the concentration of the analyte. The absorption spectra of the membrane and fluidic sample are studied to determine the optimal wavelength that provides the maximum difference in absorbance between the membrane and the sample. In this work, the dissolution of a poly(acrylamide) hydrogel membrane in the presence of a reducing agent (dithiothreitol—DTT) is used as a model system. For this system, with 1 M DTT, complete membrane dissolution occurred after 65 min.

  5. On the optical absorption of the anionic GFP chromophore in vacuum, solution, and protein.

    PubMed

    Petrone, Alessio; Caruso, Pasquale; Tenuta, Silvia; Rega, Nadia

    2013-12-21

    In spite of the large number of experimental and theoretical studies, the optical absorption trend of the green fluorescent protein (GFP) chromophore in several environments has not been fully understood. We calculated at the same level of time dependent density functional theory the vertical excitation energy of the anionic GFP chromophore in the protein and in ethanol, dioxane, methanol and water solutions. As result, we reproduced for the first time the experimental trend of the absorption peaks with 0.015 eV as the standard deviation of the accuracy. This systematic error allowed us to analyze with confidence the relative weight of several solvation effects on the vertical excitation energy. Experimental trends not correlated with the solvent polarity were therefore explained with a fine balance of different steric and electronic effects on the photophysics of the chromophore. As an indirect and remarkable result, the present analysis confirms that the optical absorption of the chromophore in the gas phase is close to the value of 2.84 eV extrapolated by Dong et al. (J. Am. Chem. Soc., 2006, 128, 12038), and, as a consequence, that the protein environment induces a red shift of 0.23 eV. PMID:24177429

  6. Optical Absorption and Electron Paramagnetic Resonance studies of two different solid solutions of Pyralspite Garnet

    NASA Astrophysics Data System (ADS)

    Watanabe, S.; Espinoza, S. R. Q.; Chubaci, J. F. D.; Cano, N. F.; Cornejo, D. R.

    2015-04-01

    Two different solid solutions of pyralspite garnet have been investigated as to their optical absorption and EPR properties. The absorption band around 9850 cm-1 is due to Fe2+. After heating above 950 °C we found this band diminishes considerably; which was interpreted as Fe2+ loosing an electron to become Fe3+. The EPR spectrum of sample consisted of a straight line with angular coefficient of about 176°. After 600°C/1hr annealing, the spectrum starts deviating from a straight line. A strong typical EPR signal is observed around g = 2.0 after annealing at 850°C. We assume that with high temperature annealing a large number of Fe2+ are converted to Fe3+ as the optical absorption has shown. These results were also confirmed by chemical reaction. The susceptibility vs. magnetic field measurement has shown that the samples annealed at temperatures below 850°C present normal paramagnetic behavior, however, annealed above 900 °C, they show hysteresis, namely ferromagnetic behavior.

  7. Optical absorption depth profiling of photodegraded poly(vinylchloride) (PVC) films by quantitative photothermal deflection technique

    NASA Astrophysics Data System (ADS)

    Fu, S.-W.; Power, J. F.; Nepotchatykh, O. V.

    2000-05-01

    An improved photothermal beam deflection technique is applied for optical absorption depth profiling of UV photodegraded PVC films, for nondestructive evaluation of their decomposition mechanism. A new model-based on diffraction theory is used to describe the photothermal response (with bicell recording), induced by impulse irradiation of a depth dependent array of thin planar optical absorbers approximating the sample's depth profile. Improved techniques of alignment, sample preparation and quantitative deconvolution of the bicell impulse response have increased the signal repeatability and reduced the principal bias errors affecting this ill posed problem. By this technique and a stable solution of the inverse problem, the absorption coefficient depth profile is accurately reconstructed in PVC films. Experimental depth profiles were confirmed against destructive techniques run on identical samples of the degraded material. An excellent agreement was found between depth profiles recovered using the mirage effect and these reference methods. Observed absorption profiles were fully consistent with known patterns of depth dependent PVC degradation under nitrogen and oxygen atmospheres.

  8. VO2+ ions in zinc lead borate glasses studied by EPR and optical absorption techniques.

    PubMed

    Prakash, P Giri; Rao, J Lakshmana

    2005-09-01

    Electron paramagnetic resonance (EPR) and optical absorption spectra of vanadyl ions in zinc lead borate (ZnO-PbO-B2O3) glass system have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of VO2+ ions. The values of spin-Hamiltonian parameters indicate that the VO2+ ions in zinc lead borate glasses were present in octahedral sites with tetragonal compression and belong to C4V symmetry. The spin-Hamiltonian parameters g and A are found to be independent of V2O5 content and temperature but changing with ZnO content. The decrease in Deltag( parallel)/Deltag( perpendicular) value with increase in ZnO content indicates that the symmetry around VO2+ ions is more octahedral. The decrease in intensity of EPR signal above 10 mol% of V2O5 is attributed to a fall in the ratio of the number of V4+ ions (N4) to the number of V5+ ions (N5). The number of spins (N) participating in resonance was calculated as a function of temperature for VO2+ doped zinc lead borate glass sample and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility was calculated at various temperatures and the Curie constant was evaluated from the 1/chi-T graph. The optical absorption spectra show single absorption band due to VO2+ ions in tetragonally distorted octahedral sites. PMID:16043053

  9. Finding consistency between different views of the absorption enhancement of black carbon: An observationally constrained hybrid model to support a transition in optical properties with mass fraction

    NASA Astrophysics Data System (ADS)

    Coe, H.; Allan, J. D.; Whitehead, J.; Alfarra, M. R. R.; Villegas, E.; Kong, S.; Williams, P. I.; Ting, Y. C.; Haslett, S.; Taylor, J.; Morgan, W.; McFiggans, G.; Spracklen, D. V.; Reddington, C.

    2015-12-01

    The mixing state of black carbon is uncertain yet has a significant influence on the efficiency with which a particle absorbs light. In turn, this may make a significant contribution to the uncertainty in global model predictions of the black carbon radiative budget. Previous modelling studies that have represented this mixing state using a core-shell approach have shown that aged black carbon particles may be considerably enhanced compared to freshly emitted black carbon due to the addition of co-emitted, weakly absorbing species. However, recent field results have demonstrated that any enhancement of absorption is minor in the ambient atmosphere. Resolving these differences in absorption efficiency is important as they will have a major impact on the extent to which black carbon heats the atmospheric column. We have made morphology-independent measurements of refractory black carbon mass and associated weakly absorbing material in single particles from laboratory-generated diesel soot and black carbon particles in ambient air influenced by traffic and wood burning sources and related these to the optical properties of the particles. We compared our calculated optical properties with optical models that use varying mixing state assumptions and by characterising the behaviour in terms of the relative amounts of weakly absorbing material and black carbon in a particle we show a sharp transition in mixing occurs. We show that the majority of black carbon particles from traffic-dominated sources can be treated as externally mixed and show no absorption enhancement, whereas models assuming internal mixing tend to give the best estimate of the absorption enhancement of thickly coated black carbon particles from biofuel or biomass burning. This approach reconciles the differences in absorption enhancement previously observed and offers a systematic way of treating the differences in behaviour observed.

  10. Effect of hydrogenic impurity on linear and nonlinear optical absorption coefficients and refractive index changes in a quantum dot

    NASA Astrophysics Data System (ADS)

    Guo, Kangxian; Zhang, Zhongmin; Mou, Sen; Xiao, Bo

    2015-05-01

    The analytical expressions of linear and nonlinear optical absorption coefficients and refractive index changes in a quantum dot with a hydrogenic impurity are obtained by using the compact-density-matrix approach and iterative method. The wave functions and the energy levels are obtained by using the variational method. Numerical results show that the optical absorption coefficients and refractive index changes are strongly affected by the hydrogenic impurity.

  11. The energy spectrum and the optical absorption spectrum of C{sub 60} fullerene within the Hubbard model

    SciTech Connect

    Silant’ev, A. V.

    2015-10-15

    Anticommutator Green’s functions and the energy spectrum of C{sub 60} fullerene are calculated in the approximation of static fluctuations within the Hubbard model. On the basis of this spectrum, an interpretation is proposed for the experimentally observed optical absorption bands of C{sub 60} fullerene. The parameters of C{sub 60} fullerene that characterize it within the Hubbard model are calculated by the optical absorption spectrum.

  12. Sub-gap and band edge optical absorption in a-Si:H by photothermal deflection spectroscopy

    NASA Astrophysics Data System (ADS)

    Jackson, W. B.; Amer, N. M.

    1981-07-01

    Using photothermal deflection spectroscopy, the optical absorption of various a-Si:H films was investigated in the range of 2.1 to 0.6 eV. An absorption shoulder which depends on deposition conditions and on doping was found and was attributed to dangling bonds. The exponential edge broadens with increasing spin density.

  13. Optical limiting and dynamical two-photon absorption of porphyrin with ruthenium outlying complexes for a picosecond pulse train

    NASA Astrophysics Data System (ADS)

    Zhang, Yu-Jin; Sun, Yu-Ping; Wang, Chuan-Kui

    2016-01-01

    Propagation and nonlinear optical absorption of a picosecond pulse train in strong reverse saturable absorption (RSA) materials (free-based tetrapyridyl porphyrin H2TPyP with ruthenium (Ru) outlying complexes) are investigated by solving coupled rate equations and field intensity equation. Influence of outlying Ru groups on optical limiting (OL) properties is studied. Propagation of the front subpulses is mainly affected by linear transition between the ground state and the first excited singlet state, while intensity of the latter subpulses is attenuated by the excited state absorption (ESA). These two different absorption mechanisms result in asymmetric distribution of the transmitted pulse. It is shown that effective population transfer time from the ground state to the lowest triplet state and RSA play important roles in the OL performance and pulse shaping. Moreover, our results indicate that the porphyrins studied are ideal optical limiters because of their large ESA cross section and long lifetime of the lowest triplet state. Compounds with the presence of Ru group possess preferable power limiting ability. Ligand group attached to Ru also influences the nonlinear optical absorption of compounds. Special attention has been paid on dynamical two-photon absorption (TPA) cross section which depends crucially on the duration of the subpulse as well as time interval between subpulses. The present study provides a way to modulate nonlinear optical absorption properties of the medium by changing parameters of the pulse train.

  14. Retinal Thickness in People with Diabetes and Minimal or No Diabetic Retinopathy: Heidelberg Spectralis Optical Coherence Tomography

    PubMed Central

    Chalam, Kakarla V.; Bressler, Susan B.; Edwards, Allison R.; Berger, Brian B.; Bressler, Neil M.; Glassman, Adam R.; Grover, Sandeep; Gupta, Shailesh K.; Nielsen, Jared S.

    2012-01-01

    Purpose. To evaluate macular thickness in people with diabetes but minimal or no retinopathy using Heidelberg Spectralis optical coherence tomography (OCT). Methods. In a multicenter, cross-sectional study of mean retinal thickness, on Spectralis OCT in the nine standard OCT subfields, spanning a zone with 6-mm diameter, center point, and total retinal volume were evaluated. Central subfield (CSF) thickness was evaluated for association with demographic and clinical factors. Stratus OCT scans also were performed on each participant. Results. The analysis included 122 eyes (122 participants) with diabetes and no (n = 103) or minimal diabetic retinopathy (n = 19) and no macular retinal thickening on clinical exam. Average CSF thickness was 270 ± 24 μm. Central subfield thickness was significantly greater in males relative to females (mean 278 ± 23 μm vs. 262 ± 22 μm, P < 0.001). After adjusting for gender, no additional factors were found to be significantly associated with CSF thickness (P > 0.10). Mean Stratus OCT CSF thickness was 199 ± 24 μm. Conclusions. Mean CSF thickness is approximately 70 μm thicker when measured with Heidelberg Spectralis OCT as compared with Stratus OCT among individuals with diabetes in the absence of retinopathy or with minimal nonproliferative retinopathy and a normal macular architecture. CSF thickness values ≥320 μm for males and 305 μm for females (∼2 SDs above the average for this normative cohort) are proposed as gender-specific thickness levels to have reasonable certainty that diabetic macular edema involving the CSF is present using Spectralis measurements. PMID:23132803

  15. Effect of Hemodialysis on Retinal Thickness in Patients with Diabetic Retinopathy, with and without Macular Edema, Using Optical Coherence Tomography

    PubMed Central

    Azem, Nur; Spierer, Oriel; Shaked, Meital; Neudorfer, Meira

    2014-01-01

    Background. Effects of hemodialysis (HD) treatment on retinal thickness and macular edema are unclear. Objective. To evaluate changes in retinal thickness using optical coherence tomography (OCT) in end stage renal disease (ESRD) patients with diabetic retinopathy (DR), with and without diabetic macular edema (DME), undergoing HD. Methods. Nonrandomized prospective study. Forty eyes of DR patients with ESRD treated with HD were divided into two groups: patients with macular edema and patients without macular edema. Both eyes were analyzed. Patients underwent an ophthalmic examination including OCT measurements of retinal thickness, blood albumin and hemoglobin A1C levels, blood pressure, and body weight, 30 minutes before and after HD. Results. We found no significant effects of HD on retinal thickness among patients both with and without DME. The former showed a trend towards reduction in retinal thickness in foveal area following HD, while the latter showed an increase. There was no correlation between retinal thickness and mean blood pressure, weight, kinetic model value—Kt/V, glycemic hemoglobin, or albumin levels before and after HD. Conclusions. HD has no significant effect on retinal thickness among patients with or without DME. Further studies on larger cohorts and repeated OCT examinations are needed to confirm the preliminary findings in this study. PMID:25298889

  16. Effect of Hemodialysis on Retinal Thickness in Patients with Diabetic Retinopathy, with and without Macular Edema, Using Optical Coherence Tomography.

    PubMed

    Azem, Nur; Spierer, Oriel; Shaked, Meital; Neudorfer, Meira

    2014-01-01

    Background. Effects of hemodialysis (HD) treatment on retinal thickness and macular edema are unclear. Objective. To evaluate changes in retinal thickness using optical coherence tomography (OCT) in end stage renal disease (ESRD) patients with diabetic retinopathy (DR), with and without diabetic macular edema (DME), undergoing HD. Methods. Nonrandomized prospective study. Forty eyes of DR patients with ESRD treated with HD were divided into two groups: patients with macular edema and patients without macular edema. Both eyes were analyzed. Patients underwent an ophthalmic examination including OCT measurements of retinal thickness, blood albumin and hemoglobin A1C levels, blood pressure, and body weight, 30 minutes before and after HD. Results. We found no significant effects of HD on retinal thickness among patients both with and without DME. The former showed a trend towards reduction in retinal thickness in foveal area following HD, while the latter showed an increase. There was no correlation between retinal thickness and mean blood pressure, weight, kinetic model value-Kt/V, glycemic hemoglobin, or albumin levels before and after HD. Conclusions. HD has no significant effect on retinal thickness among patients with or without DME. Further studies on larger cohorts and repeated OCT examinations are needed to confirm the preliminary findings in this study. PMID:25298889

  17. Optical nonlinear properties of InAs quantum dots by means of transient absorption measurements

    NASA Astrophysics Data System (ADS)

    Nakamura, H.; Nishikawa, S.; Kohmoto, S.; Kanamoto, K.; Asakawa, K.

    2003-07-01

    The optical nonlinear properties of self-assembled InAs/GaAs quantum dots (QDs) were experimentally verified by means of transient absorption measurements. A saturation pulse energy Ps of 13 fJ/μm2 and an absorption recovery time τr of 55 ps were obtained from transmission bleaching and pump/probe measurements for a waveguide sample with ten-layer-stacked QDs. An absorption saturation intensity Is of 2.5×104W/cm2, calculated from Ps and τr, was found. The saturation pulse energy is up to an order of magnitude smaller than, or at least comparable with, the reported values for excitons in quantum wells of III-V compound semiconductors. The dipole length, as calculated from the absorption cross section, is of the same order as the lattice constant of the InAs QDs. The results are expected to experimentally verify that QDs show a delta-function-like density of states.

  18. Multiwavelength diode-laser absorption spectroscopy using external intensity modulation by semiconductor optical amplifiers.

    PubMed

    Karagiannopoulos, Solon; Cheadle, Edward; Wright, Paul; Tsekenis, Stylianos; McCann, Hugh

    2012-12-01

    A novel opto-electronic scheme for line-of-sight Near-IR gas absorption measurement based on direct absorption spectroscopy (DAS) is reported. A diode-laser-based, multiwavelength system is designed for future application in nonintrusive, high temporal resolution tomographic imaging of H2O in internal combustion engines. DAS is implemented with semiconductor optical amplifiers (SOAs) to enable wavelength multiplexing and to induce external intensity modulation for phase-sensitive detection. Two overtone water transitions in the Near-IR have been selected for ratiometric temperature compensation to enable concentration measurements, and an additional wavelength is used to account for nonabsorbing attenuation. A wavelength scanning approach was used to evaluate the new modulation technique, and showed excellent absorption line recovery. Fixed-wavelength, time-division-multiplexing operation with SOAs has also been demonstrated. To the best of our knowledge this is the first time SOAs have been used for modulation and switching in a spectroscopic application. With appropriate diode laser selection this scheme can be also used for other chemical species absorption measurements. PMID:23207374

  19. Dependence of Brillouin frequency shift on water absorption ratio in polymer optical fibers

    NASA Astrophysics Data System (ADS)

    Minakawa, Kazunari; Koike, Kotaro; Hayashi, Neisei; Koike, Yasuhiro; Mizuno, Yosuke; Nakamura, Kentaro

    2016-06-01

    We studied the dependence of the Brillouin frequency shift (BFS) on the water-absorption ratio in poly(methyl methacrylate)-based polymer optical fibers (POFs) to clarify the effect of the humidity on POF-based Brillouin sensors. The BFS, deduced indirectly using an ultrasonic pulse-echo technique, decreased monotonically as the water absorption ratio increased, mainly because of the decrease in the Young's modulus. For the same water absorption ratio, the BFS change was larger at a higher temperature. The maximal BFS changes (absolute values) at 40, 60, and 80 °C were 158, 285, and 510 MHz, respectively (corresponding to the temperature changes of ˜9 °C, ˜16 °C, and ˜30 °C). Thus, some countermeasure against the humidity is indispensable in implementing strain/temperature sensors based on Brillouin scattering in POFs, especially at a higher temperature. On the other hand, Brillouin-based distributed humidity sensors might be developed by exploiting the BFS dependence on water absorption in POFs.

  20. In vivo photothermal optical coherence tomography for non-invasive imaging of endogenous absorption agents

    PubMed Central

    Makita, Shuichi; Yasuno, Yoshiaki

    2015-01-01

    In vivo photothermal optical coherence tomography (OCT) is demonstrated for cross-sectional imaging of endogenous absorption agents. In order to compromise the sensitivity, imaging speed, and sample motion immunity, a new photothermal detection scheme and phase processing method are developed. Phase-resolved swept-source OCT and fiber-pigtailed laser diode (providing excitation at 406 nm) are combined to construct a high-sensitivity photothermal OCT system. OCT probe and excitation beam coaxially illuminate and are focused on tissues. The photothermal excitation and detection procedure is designed to obtain high efficiency of photothermal effect measurement. The principle and method of depth-resolved cross-sectional imaging of absorption agents with photothermal OCT has been derived. The phase-resolved thermal expansion detection algorithm without motion artifact enables in vivo detection of photothermal effect. Phantom imaging with a blood phantom and in vivo human skin imaging are conducted. A phantom with guinea-pig blood as absorber has been scanned by the photothermal OCT system to prove the concept of cross-sectional absorption agent imaging. An in vivo human skin measurement is also performed with endogenous absorption agents. PMID:26137374