Development of a Differential Optical Absorption Spectroscopy System Using HighLuminance LED for Measurement of NO2

NASA Astrophysics Data System (ADS)

Fukuchi, Tetsuo; Nayuki, Takuya; Mori, Hideto; Goto, Naohiko; Fujii, Takashi; Nemoto, Koshichi

A differential optical absorption spectroscopy (DOAS) system for measurement of atmospheric NO2 was developed. The system uses a battery-operated, high luminance LED and a fiber-coupled spectrometer, and is portable. Laboratory experiments using a gas cell of length 0.22 m with varying NO2 concentrations were performed to evaluate the sensitivity of the DOAS system. The DOAS measurement results are in agreement with NO2 concentrations obtained simultaneously by a FT-IR (Fourier Transform Infrared) system for NO2 concentrations down to 20 ppm. Experiments with an optical path length of 93 m were also performed, and NO2 concentrations down to 0.20 ppm were measured. Since measurement of atmospheric NO2, which is in the order of several tens of ppb, requires optical path lengths of several hundred m, system improvements to improve the signal detection are necessary.

Biomass burning dominates brown carbon absorption in the rural southeastern United States

NASA Astrophysics Data System (ADS)

Washenfelder, R. A.; Attwood, A. R.; Brock, C. A.; Guo, H.; Xu, L.; Weber, R. J.; Ng, N. L.; Allen, H. M.; Ayres, B. R.; Baumann, K.; Cohen, R. C.; Draper, D. C.; Duffey, K. C.; Edgerton, E.; Fry, J. L.; Hu, W. W.; Jimenez, J. L.; Palm, B. B.; Romer, P.; Stone, E. A.; Wooldridge, P. J.; Brown, S. S.

2015-01-01

carbon aerosol consists of light-absorbing organic particulate matter with wavelength-dependent absorption. Aerosol optical extinction, absorption, size distributions, and chemical composition were measured in rural Alabama during summer 2013. The field site was well located to examine sources of brown carbon aerosol, with influence by high biogenic organic aerosol concentrations, pollution from two nearby cities, and biomass burning aerosol. We report the optical closure between measured dry aerosol extinction at 365 nm and calculated extinction from composition and size distribution, showing agreement within experiment uncertainties. We find that aerosol optical extinction is dominated by scattering, with single-scattering albedo values of 0.94 ± 0.02. Black carbon aerosol accounts for 91 ± 9% of the total carbonaceous aerosol absorption at 365 nm, while organic aerosol accounts for 9 ± 9%. The majority of brown carbon aerosol mass is associated with biomass burning, with smaller contributions from biogenically derived secondary organic aerosol.

Nonlinear absorption properties of ZnO and Al doped ZnO thin films under continuous and pulsed modes of operations

NASA Astrophysics Data System (ADS)

Sandeep, K. M.; Bhat, Shreesha; Dharmaprakash, S. M.

2018-06-01

In the present investigation, we present the variations in nonlinear optical (NLO) properties of undoped and Al doped ZnO (AZO) films under two different off-resonant regimes using continuous and pulsed mode lasers. Z-scan open aperture experiment is performed to quantify nonlinear absorption constant and imaginary component of third order susceptibility. Reverse saturable absorption (RSA) and saturable absorption (SA) behaviors are noticed in both undoped and AZO films under pulsed mode and continuous wavelength (CW) regime respectively. The RSA and SA behavior observed in the films are attributed to two photon absorption (TPA) and thermal lensing properties respectively. The thermal lensing is assisted by the thermo-optic effects within the films due to the continuous illumination of the laser.

Low-cost 420nm blue laser diode for tissue cutting and hemostasis

NASA Astrophysics Data System (ADS)

Linden, Kurt J.

2016-03-01

This paper describes the use of a 420 nm blue laser diode for possible surgery and hemostasis. The optical absorption of blood-containing tissue is strongly determined by the absorption characteristics of blood. Blood is primarily comprised of plasma (yellowish extracellular fluid that is approximately 95% water by volume) and formed elements: red blood cells (RBCs), white blood cells (WBCs) and platelets. The RBCs (hemoglobin) are the most numerous, and due to the spectral absorption characteristics of hemoglobin, the optical absorption of blood has a strong relative maximum value in the 420 nm blue region of the optical spectrum. Small, low-cost laser diodes emitting at 420 nm with tens of watts of continuous wave (CW) optical power are becoming commercially available. Experiments on the use of such laser diodes for tissue cutting with simultaneous hemostasis were carried out and are here described. It was found that 1 mm deep x 1 mm wide cuts can be achieved in red meat at a focused laser power level of 3 W moving at a velocity of ~ 1 mm/s. The peripheral necrosis and thermal damage zone extended over a width of approximately 0.5 mm adjacent to the cuts. Preliminary hemostasis experiments were carried out with fresh equine blood in Tygon tubing, where it was demonstrated that cauterization can occur in regions of intentional partial tubing puncture.

Ultrafast recovery time and broadband saturable absorption properties of black phosphorus suspension

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

Wang, Yingwei; Huang, Guanghui; Chen, Jiazhang

2015-08-31

As a new type of two-dimensional crystal material, black phosphorus (BP) exhibits excellent electronics and optical performance. Herein, we focus on carrier relaxation dynamics and nonlinear optical properties of BP suspension. Atomic force microscopy, transmission electron microscopy, and optical transmission spectrum are employed to characterize the structure and linear optical properties of the BP. Additionally, pump-probe experiments at wavelength of 1550 nm were carried out to study the carrier dynamics in BP suspension, and ultrafast recovery time was observed (τ{sub s} = 24 ± 2 fs). Furthermore, we demonstrate the saturable absorption signals by open aperture Z-scan experiments at wavelengths of 1550 nm, 532 nm, and 680 nm. Themore » results indicate that BP has broadband saturable absorption properties and the nonlinear absorption coefficients were determined to be β{sub 2} = −0.20 ± 0.08 × 10{sup −3 }cm/GW (532 nm), β{sub 2} = −0.12 ± 0.05 × 10{sup −3 }cm/GW (680 nm), and β{sub 2} = −0.15 ± 0.09 × 10{sup −3 }cm/GW (1550 nm)« less

Magneto-optical absorption and cyclotron-phonon resonance in graphene monolayer

NASA Astrophysics Data System (ADS)

Hoi, Bui Dinh; Phuong, Le Thi Thu; Phong, Tran Cong

2018-03-01

The optical absorption power by Dirac fermions in a graphene monolayer subjected to a perpendicular magnetic field is calculated using a projection operator technique. The electron-optical phonon interaction with optical deformation potential is taken into account. By varying the photon frequency (energy), we observe in the absorption power a series of cyclotron-phonon resonance (CPR) peaks (i.e., the phonon-assisted cyclotron resonance). It is seen that the resonant photon energy is linearly proportional to the square root of the magnetic field. Also, the half width at half maximum (HWHM) of CPR peaks depends on the magnetic field by the law HWHM = 7.42 √{B } but does not depend on the temperature. In particular, the magnetic field and temperature dependences of the position and HWHM of CPR peaks are in good agreement with those obtained recently by the perturbation theory and an experiment in graphene.

Optical Absorbance Enhancement in PbS QD/Cinnamate Ligand Complexes.

PubMed

Kroupa, Daniel M; Vörös, Márton; Brawand, Nicholas P; Bronstein, Noah; McNichols, Brett W; Castaneda, Chloe V; Nozik, Arthur J; Sellinger, Alan; Galli, Giulia; Beard, Matthew C

2018-06-08

We studied the optical absorption enhancement in colloidal suspensions of PbS quantum dots (QD) upon ligand exchange from oleate to a series of cinnamate ligands. By combining experiments and ab initio simulations, we elucidate physical parameters that govern the optical absorption enhancement. We find that, within the cinnamate/PbS QD system, the optical absorption enhancement scales linearly with the electronic gap of the ligand, indicating that the ligand/QD coupling occurs equally efficient between the QD and ligand HOMO and their respective LUMO levels. Disruption of the conjugation that connects the aromatic ring and its substituents to the QD core causes a reduction of the electronic coupling. Our results further support the notion that the ligand/QD complex should be considered as a distinct chemical system with emergent behavior rather than a QD core with ligands whose sole purpose is to passivate surface dangling bonds and prevent agglomeration.

Optical absorption in recycled waste plastic polyethylene

NASA Astrophysics Data System (ADS)

Aji, M. P.; Rahmawati, I.; Priyanto, A.; Karunawan, J.; Wati, A. L.; Aryani, N. P.; Susanto; Wibowo, E.; Sulhadi

2018-03-01

We investigated the optical properties of UV spectrum absorption in recycled waste plastic from polyethylene polymer type. Waste plastic polyethylene showed an optical spectrum absorption after it’s recycling process. Spectrum absorption is determined using spectrophotometer UV-Nir Ocean Optics type USB 4000. Recycling method has been processed using heating treatment around the melting point temperature of the polyethylene polymer that are 200°C, 220°C, 240°C, 260°C, and 280°C. In addition, the recycling process was carried out with time variations as well, which are 1h, 1.5h, 2h, and 2.5h. The result of this experiment shows that recycled waste plastic polyethylene has a spectrum absorption in the ∼ 340-550 nm wavelength range. The absorbance spectrum obtained from UV light which is absorbed in the orbital n → π* and the orbital π → π*. This process indicates the existence of electron transition phenomena. This mechanism is affected by the temperature and the heating time where the intensity of absorption increases and widens with the increase of temperature and heating time. Furthermore this study resulted that the higher temperature affected the enhancement of the band gap energy of waste plastic polyethylene. These results show that recycled waste plastic polyethylene has a huge potential to be absorber materials for solar cell.

Creating semiconductor metafilms with designer absorption spectra

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

Kim, Soo Jin; Fan, Pengyu; Kang, Ju-Hyung

The optical properties of semiconductors are typically considered intrinsic and fixed. Here we leverage the rapid developments in the field of optical metamaterials to create ultrathin semiconductor metafilms with designer absorption spectra. We show how such metafilms can be constructed by placing one or more types of high-index semiconductor antennas into a dense array with subwavelength spacings. It is argued that the large absorption cross-section of semiconductor antennas and their weak near-field coupling open a unique opportunity to create strongly absorbing metafilms whose spectral absorption properties directly reflect those of the individual antennas. Using experiments and simulations, we demonstrate thatmore » near-unity absorption at one or more target wavelengths of interest can be achieved in a sub-50-nm-thick metafilm using judiciously sized and spaced Ge nanobeams. The ability to create semiconductor metafilms with custom absorption spectra opens up new design strategies for planar optoelectronic devices and solar cells.« less

One-shot calculation of temperature-dependent optical spectra and phonon-induced band-gap renormalization

NASA Astrophysics Data System (ADS)

Zacharias, Marios; Giustino, Feliciano

2016-08-01

Recently, Zacharias et al. [Phys. Rev. Lett. 115, 177401 (2015), 10.1103/PhysRevLett.115.177401] developed an ab initio theory of temperature-dependent optical absorption spectra and band gaps in semiconductors and insulators. In that work, the zero-point renormalization and the temperature dependence were obtained by sampling the nuclear wave functions using a stochastic approach. In the present work, we show that the stochastic sampling of Zacharias et al. can be replaced by fully deterministic supercell calculations based on a single optimal configuration of the atomic positions. We demonstrate that a single calculation is able to capture the temperature-dependent band-gap renormalization including quantum nuclear effects in direct-gap and indirect-gap semiconductors, as well as phonon-assisted optical absorption in indirect-gap semiconductors. In order to demonstrate this methodology, we calculate from first principles the temperature-dependent optical absorption spectra and the renormalization of direct and indirect band gaps in silicon, diamond, and gallium arsenide, and we obtain good agreement with experiment and with previous calculations. In this work we also establish the formal connection between the Williams-Lax theory of optical transitions and the related theories of indirect absorption by Hall, Bardeen, and Blatt, and of temperature-dependent band structures by Allen and Heine. The present methodology enables systematic ab initio calculations of optical absorption spectra at finite temperature, including both direct and indirect transitions. This feature will be useful for high-throughput calculations of optical properties at finite temperature and for calculating temperature-dependent optical properties using high-level theories such as G W and Bethe-Salpeter approaches.

Optical Nonlinearities in Semiconductors for Limiting.

NASA Astrophysics Data System (ADS)

Wu, Yuan-Yen

I have conducted detailed experimental and theoretical studies of the nonlinear optical properties of semiconductor materials useful for optical limiting. I have constructed optical limiters utilizing two-photon absorption along with photogenerated carrier defocusing as well as the bound electronic nonlinearity using the semiconducting material ZnSe. I have optimized the focusing geometry to achieve a large dynamic range while maintaining a low limiting energy for the device. The ZnSe monolithic optical limiter has achieved a limiting energy as low as 13 nJ (corresponding to 300W peak power) and a dynamic range as large as 10 ^5 at 532 nm using psec pulses. Theoretical analysis showed that the ZnSe device has a broad-band response covering the wavelength range from 550 nm to 800 nm. Moreover, I found that existing theoretical models (e.g. the Auston model and the band-resonant model using Boltzmann statistics) adequately describe the photo-generated carriers refractive nonlinearity in ZnSe. Material nonlinear optical parameters, such as the two-photon absorption coefficient beta _2 = 5.5 cm/GW, the refraction per unit carrier density sigma_{rm n} = -0.8cdot 10^ {-21}cm^3 and the bound electronic refraction n_2 = -4cdot 10^{ -11}esu, have been measured via time-integrated beam distortion experiments in the near field. A numerical code has been written to simulate the beam distortion in order to extract the previously mentioned material parameters. In addition, I have performed time-resolved distortion measurements that provide an intuitive picture of the carrier generation process via two-photon absorption. I also characterized the optical nonlinearities in a ZnSe Fabry-Perot thin film structure (an interference filter). I concluded that the nonlinear absorption alone in the thin film is insufficient to build an effective optical limiter, as it did not show a net change in refraction using psec pulses. An innovative numerical program was developed to simulate the nonlinear beam propagation inside the Fabry-Perot structure. For comparison, pump-probe experiments were performed using both thin film and bulk ZnSe. The results showed relatively long carrier lifetimes (>300 psec) in both samples. A numerical code was written to fit the pump-probe experimental results. The fitting yielded that carrier lifetimes (recombination through traps), radiative decay rate, two-photon absorption coefficient as well as the free carrier absorption coefficient for ZnSe bulk material.

Ultra-fast nonlinear optical properties and photophysical mechanism of a novel pyrene derivative

NASA Astrophysics Data System (ADS)

Zhang, Youwei; Yang, Junyi; Xiao, Zhengguo; Song, Yinglin

2016-10-01

The third-order nonlinear optical properties of 1-(pyrene-1-y1)-3-(3-methylthiophene) acrylic keton named PMTAK was investigated by using Z-scan technique. The light sources for picoseconds(ps) and femtosecond(fs) Z-scan were a mode-locked Nd: YAG laser (21 ps, 532 nm,10 Hz) and an Yb: KGW based fiber laser (190 fs, 515 nm,532 nm, 20 Hz), respectively. In the two cases, reverse saturation absorption(RSA) are observed. The dynamics of the sample's optical nonlinearity is discussed via the femtosecond time-resolved pump probe with phase object at 515nm. We believe that the molecules in excited state of particle population count is caused by two-photon absorption(TPA). The five-level theoretical model is used to analysis the optical nonlinear mechanism. Combining with the result of picosecond Z-scan experiment, a set of optical nonlinear parameters are calculated out. The femtosecond Z-scan experiment is taken to confirm these parameters. The obvious excited-state nonlinearity is found by the set of parameters. The result shows that the sample has good optical nonlinearity which indicates it has potential applications in nonlinear optics field.

Quantification of the dynamic changes in the absorption coefficient of liquid water at erbium:YAG and carbon dioxide laser wavelengths

NASA Astrophysics Data System (ADS)

Shori, Ramesh K.

The interaction of high-intensity, short-pulsed radiation with liquid water results in dynamic changes in the optical absorption coefficient of water. These changes and their implications, as related to mid-infrared laser ablation of tissue, were not investigated until the late 1980's and early 1990's. Classical models of absorption and heating do not explain the dynamic, non-linear changes in water. The objective of the present work was to quantify the dynamic changes in the absorption coefficient of liquid water as a function of incident energy at three clinically relevant infrared wavelengths (λ = 2.94, 9.6, 10.6 μm). To investigate the changes in the absorption spectrum of water in the 3-μm band, a stable, high-energy Q- switched Er:YAG laser emitting 2.94-μm radiation in a near-perfect TEMoo spatial beam profile was developed. Key to the development of this laser was careful attention to the gain medium, optical pump system, system optics, and the thermal system. The final system design was capable of emitting 110 mJ/pulse at of 2-4 Hz with a lamp lifetime exceeding 12 million pulses The laser was used in two sets of experiments in order to quantify the above changes. First, the laser was used to measure the velocity of the shock front produced by vaporizing a gelatin-based tissue phantom. The measured shock velocity was related to the optical energy absorbed by the tissue phantom and the absorption coefficient, based on the pressure relationships derived using a 1-D piston model for an expanding plume. The shock front velocity measurements indicate that the absorption coefficient is constant for incident fluences less than 20 J/cm2, a result consistent with transmission data. For higher fluences, the data indicate a decrease in the absorption coefficient, which is again consistent with transmission data. Quantification of the absorption coefficient can, however, not be made without violating assumptions that form the basis for the 1-D piston model. Second, the laser was used to measure the optical transmission across water layers of known thicknesses. The data were used to develop a Dynamic Saturable Absorption (DSA) model to predict the dynamic changes in the absorption coefficient of water as a function of incident energy. The DSA model, based in part upon the homogeneous broadening of an atomic transition in a laser gain medium, accurately predicts the absorption coefficient of water over a wide range of incident fluences. One sees saturation of the absorption at both high and low fluence with a monotonic decrease in absorption with increasing fluence. Transmission measurements were also made at 9.6 and 10.6 μm using a TEA CO2 laser. The data show essentially no change in the absorption coefficient as the fluence is varied. The results from the experiments make a significant contribution towards an understanding of the relationship among the dynamic optical properties of water and clinically relevant properties such as ablation rate and residual thermal damage.

Optical absorption of suspended graphene based metal plasmonic grating in the visible range

NASA Astrophysics Data System (ADS)

Han, Y. X.; Chen, B. B.; Yang, J. B.; He, X.; Huang, J.; Zhang, J. J.; Zhang, Z. J.

2018-05-01

We employ finite-difference time-domain ( FDTD) method and Raman spectroscopy to study the properties of graphene, which is suspended on a gold/SiO2/Si grating structure with different trench depth of SiO2 layer. The absorption enhancement of suspended graphene and plasmonic resonance of metal grating are investigated in the visible range using 2D FDTD method. Moreover, it is found that the intensity of the Raman features depends very sensitively on the trench depth of SiO2 layer. Raman enhancement in our experiments is attributed to the enhanced optical absorption of graphene by near-field coupling based metal plasmonic grating. The enhanced absorption of suspended graphene modulated by localized surface plasmon resonance (LSPR) offers a potential application for opto-electromechanical devices.

Nonlinear optical interactions in silicon waveguides

NASA Astrophysics Data System (ADS)

Kuyken, B.; Leo, F.; Clemmen, S.; Dave, U.; Van Laer, R.; Ideguchi, T.; Zhao, H.; Liu, X.; Safioui, J.; Coen, S.; Gorza, S. P.; Selvaraja, S. K.; Massar, S.; Osgood, R. M.; Verheyen, P.; Van Campenhout, J.; Baets, R.; Green, W. M. J.; Roelkens, G.

2017-03-01

The strong nonlinear response of silicon photonic nanowire waveguides allows for the integration of nonlinear optical functions on a chip. However, the detrimental nonlinear optical absorption in silicon at telecom wavelengths limits the efficiency of many such experiments. In this review, several approaches are proposed and demonstrated to overcome this fundamental issue. By using the proposed methods, we demonstrate amongst others supercontinuum generation, frequency comb generation, a parametric optical amplifier, and a parametric optical oscillator.

Absorption spectra and optical transitions in InAs/GaAs self-assembled quantum dots

NASA Astrophysics Data System (ADS)

Cusack, M. A.; Briddon, P. R.; Jaros, M.

1997-08-01

We have applied the multiband effective mass/valence force field method to the calculation of optical transitions and absorption spectra in InAs/GaAs self-organized dots of different sizes. We have found that the apparently conflicting assignments of luminescence features to optical transitions in different experiments are in fact entirely compatible with each other. Whether the optical signature of a dot is constructed from transitions between states of the same quantum numbers, or via additional processes between the ground conduction state and a low-lying valence state depends on the aspect ratio of the quantum dot radius and height. The states involved can be predicted from a simple particle in a rigid rectangular box model.

Photoelectron transport tuning of self-assembled subbands

NASA Astrophysics Data System (ADS)

Xiong, Zhengwei; Wang, Xinmin; Wu, Weidong; Wang, Xuemin; Peng, Liping; Zhao, Yan; Yan, Dawei; Jiang, Tao; Shen, Changle; Zhan, Zhiqiang; Cao, Linhong; Li, Weihua

2016-02-01

Conventionally, electrical transport of quantum subbands occurs at very high electric fields, indicating that the medium is easy to break down. In the experiments and practical applications, the extreme condition is difficult to satisfy. For quantum information transmission, low power consumption and convenient implementation are what we expect. In this paper, we engineered a special quantum dot array (QDA) embedded in a single crystal matrix. By external optical field excitation, we found a series of subbands made of the self-assembled QDA discretely located in the matrix. Changing the spacing between the quantum dots leads to the variation of subband spacing. Artificially manipulating the microcosmic QDA system can bring interesting macroscopic effects, such as an enhanced absorption intensity in the ultraviolet range, a blue-shift of the surface plasmon resonance peak and nonlinear absorption changed from two-photon absorption to saturated absorption. The intrinsic mechanism of the subband optical response was revealed due to the strong quantum confinement effect and dominant intraband transitions. The weak surface plasmon resonance absorption of Ni QDA gave an excellent figure of merit of the order of 10-10. The composite films are expectation enough to become a prime candidate for nonlinear applications near 532 nm. Therefore with interplay of the weak optical field and subbands, we achieved a tunable photoelectron transport process.Conventionally, electrical transport of quantum subbands occurs at very high electric fields, indicating that the medium is easy to break down. In the experiments and practical applications, the extreme condition is difficult to satisfy. For quantum information transmission, low power consumption and convenient implementation are what we expect. In this paper, we engineered a special quantum dot array (QDA) embedded in a single crystal matrix. By external optical field excitation, we found a series of subbands made of the self-assembled QDA discretely located in the matrix. Changing the spacing between the quantum dots leads to the variation of subband spacing. Artificially manipulating the microcosmic QDA system can bring interesting macroscopic effects, such as an enhanced absorption intensity in the ultraviolet range, a blue-shift of the surface plasmon resonance peak and nonlinear absorption changed from two-photon absorption to saturated absorption. The intrinsic mechanism of the subband optical response was revealed due to the strong quantum confinement effect and dominant intraband transitions. The weak surface plasmon resonance absorption of Ni QDA gave an excellent figure of merit of the order of 10-10. The composite films are expectation enough to become a prime candidate for nonlinear applications near 532 nm. Therefore with interplay of the weak optical field and subbands, we achieved a tunable photoelectron transport process. Electronic supplementary information (ESI) available: Tables 1 and 2. See DOI: 10.1039/c5nr07861j

A method of reducing background fluctuation in tunable diode laser absorption spectroscopy

NASA Astrophysics Data System (ADS)

Yang, Rendi; Dong, Xiaozhou; Bi, Yunfeng; Lv, Tieliang

2018-03-01

Optical interference fringe is the main factor that leads to background fluctuation in gas concentration detection based on tunable diode laser absorption spectroscopy. The interference fringes are generated by multiple reflections or scatterings upon optical surfaces in optical path and make the background signal present an approximated sinusoidal oscillation. To reduce the fluctuation of the background, a method that combines dual tone modulation (DTM) with vibration reflector (VR) is proposed in this paper. The combination of DTM and VR can make the unwanted periodic interference fringes to be averaged out and the effectiveness of the method in reducing background fluctuation has been verified by simulation and real experiments in this paper. In the detection system based on the proposed method, the standard deviation (STD) value of the background signal is decreased to 0.0924 parts per million (ppm), which is reduced by a factor of 16 compared with that of wavelength modulation spectroscopy. The STD value of 0.0924 ppm corresponds to the absorption of 4 . 328 × 10-6Hz - 1 / 2 (with effective optical path length of 4 m and integral time of 0.1 s). Moreover, the proposed method presents a better stable performance in reducing background fluctuation in long time experiments.

Effect of Ram and Zenith Exposure on the Optical Properties of Polymers in Space

NASA Technical Reports Server (NTRS)

Li, Yuachun; de Groh, Kim K.; Banks, Bruce A.; Leneghan, Halle; Asmar, Olivia

2017-01-01

The temperature of spacecraft is influenced by the solar absorptance and thermal emittance of the external spacecraft materials. Optical and thermal properties can degrade over time in the harsh low Earth orbital (LEO) space environment where spacecraft external materials are exposed to various forms of radiation, thermal cycling, and atomic oxygen. Therefore, it is important to test the durability of spacecraft materials in the space environment. One objective of the Polymers and Zenith Polymers Experiments was to determine the effect of LEO space exposure on the optical properties of various spacecraft polymers. These experiments were flown as part of the Materials International Space Station Experiment 7 (MISSE 7) mission on the exterior of the International Space Station (ISS) for 1.5 years. Samples were flown in ram, wake or zenith directions, receiving varying amounts of atomic oxygen and solar radiation exposure. Total and diffuse reflectance and transmittance of flight and corresponding control samples were obtained post-flight using a Cary 5000 UV-Vis-NIR Spectrophotometer. Integrated air mass zero solar absorptance (s) of the flight and control samples were computed from the total transmittance and reflectance, and compared. The optical data are compared with similar polymers exposed to space for four years as part of MISSE 2, and with atomic oxygen erosion data, to help understand the degradation of these polymers in the space environment. Results show that prolonged space exposure increases the solar absorptance of some materials. Knowing which polymers remain stable will benefit future spacecraft design.

Determination of the atomic density of rubidium-87

NASA Astrophysics Data System (ADS)

Zhao, Meng; Zhang, Kai; Chen, Li-Qing

2015-09-01

Atomic density is a basic and important parameter in quantum optics, nonlinear optics, and precision measurement. In the past few decades, several methods have been used to measure atomic density, such as thermionic effect, optical absorption, and resonance fluorescence. The main error of these experiments stemmed from depopulation of the energy level, self-absorption, and the broad bandwidth of the laser. Here we demonstrate the atomic density of 87Rb vapor in paraffin coated cell between 297 K and 334 K mainly using fluorescence measurement. Optical pumping, anti-relaxation coating, and absorption compensation approaches are used to decrease measurement error. These measurement methods are suitable for vapor temperature at dozens of degrees. The fitting function for the experimental data of 87Rb atomic density is given. Project supported by the Natural Science Foundation of China (Grant Nos. 11274118 and 11474095), the Innovation Program of Shanghai Municipal Education Commission of China (Grant No. 13ZZ036), and the Fundamental Research Funds for the Central Universities of China.

Optical feedback cavity-enhanced absorption spectroscopy with a 3.24 μm interband cascade laser

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

Manfred, K. M.; Ritchie, G. A. D.; Lang, N.

2015-06-01

The development of interband cascade lasers (ICLs) has made the strong C-H transitions in the 3 μm spectral region increasingly accessible. We present the demonstration of a single mode distributed feedback ICL coupled to a V-shaped optical cavity in an optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS) experiment. We achieved a minimum detectable absorption coefficient, α{sub min}, of (7.1±0.2)×10{sup −8} cm{sup −1} for a spectrum of CH{sub 4} at 3.24 μm with a two second acquisition time (100 scans averaged). This corresponds to a detection limit of 3 ppb CH{sub 4} at atmospheric pressure, which is comparable to previously reported OF-CEAS instruments with diodemore » lasers or quantum cascade lasers. The ability to frequency lock an ICL source in the important 3 μm region to an optical cavity holds great promise for future spectroscopic applications.« less

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.

The role of scattering and absorption on the optical properties of birefringent polycrystalline ceramics: Modeling and experiments on ruby (Cr:Al2O3)

NASA Astrophysics Data System (ADS)

Penilla, E. H.; Hardin, C. L.; Kodera, Y.; Basun, S. A.; Evans, D. R.; Garay, J. E.

2016-01-01

Light scattering due to birefringence has prevented the use of polycrystalline ceramics with anisotropic optical properties in applications such as laser gain media. However, continued development of processing technology has allowed for very low porosity and fine grains, significantly improving transparency and is paving the way for polycrystalline ceramics to be used in demanding optical applications. We present a method for producing highly transparent Cr3+ doped Al2O3 (ruby) using current activated pressure assisted densification. The one-step doping/densification process produces fine grained ceramics with well integrated (doped) Cr, resulting in good absorption and emission. In order to explain the light transmission properties, we extend the analytical model based on the Rayleigh-Gans-Debye approximation that has been previously used for undoped alumina to include absorption. The model presented captures reflection, scattering, and absorption phenomena in the ceramics. Comparison with measured transmission confirms that the model adequately describes the properties of polycrystalline ruby. In addition the measured emission spectra and emission lifetime are found to be similar to single crystals, confirming the high optical quality of the ceramics.

Investigation of third-order nonlinear and optical power limiting properties of terphenyl derivatives

NASA Astrophysics Data System (ADS)

Kamath, Laxminarayana; Manjunatha, K. B.; Shettigar, Seetharam; Umesh, G.; Narayana, B.; Samshuddin, S.; Sarojini, B. K.

2014-03-01

A series of new chalcones containing terphenyl as a core and with different functional groups has been successfully synthesized by Claisen-Schmidt condensation method in search of new nonlinear optical (NLO) materials. Molecular structural characterization for the compounds was achieved by FTIR and single crystal X-ray diffraction. The third-order NLO absorption and refraction coefficients were simultaneously determined by Z-scan technique. The measurements were performed at 532 nm with 7 ns laser pulses using a Nd:YAG laser in solution form. The Z-scan experiments reveal that the compounds exhibit strong nonlinear refraction coefficient of the order 10-11 esu and the molecular two photon absorption cross section is 10-46 cm4 s/photon. The results also show that the structures of the compounds have great impact on NLO properties. The compounds show optical power limiting behavior due to two-photon absorption (TPA).

Nanocrystalline silicon thin films and grating structures for solar cells

NASA Astrophysics Data System (ADS)

Juneja, Sucheta; Sudhakar, Selvakumar; Khonina, Svetlana N.; Skidanov, Roman V.; Porfirevb, Alexey P.; Moissev, Oleg Y.; Kazanskiy, Nikolay L.; Kumar, Sushil

2016-03-01

Enhancement of optical absorption for achieving high efficiencies in thin film silicon solar cells is a challenge task. Herein, we present the use of grating structure for the enhancement of optical absorption. We have made grating structures and same can be integrated in hydrogenated micro/nanocrystalline silicon (μc/nc-Si: H) thin films based p-i-n solar cells. μc/nc-Si: H thin films were grown using plasma enhanced chemical vapor deposition method. Grating structures integrated with μc/nc-Si: H thin film solar cells may enhance the optical path length and reduce the reflection losses and its characteristics can be probed by spectroscopic and microscopic technique with control design and experiment.

Simulate different environments TDLAS On the analysis of the test signal strength

NASA Astrophysics Data System (ADS)

Li, Xin; Zhou, Tao; Jia, Xiaodong

2014-12-01

TDLAS system is the use of the wavelength tuning characteristics of the laser diode, for detecting the absorption spectrum of the gas absorption line. Detecting the gas space, temperature, pressure and flow rate and concentration. The use of laboratory techniques TDLAS gas detection, experimental simulation engine combustion water vapor and smoke. using an optical lens system receives the signal acquisition and signal interference test analysis. Analog water vapor and smoke in two different environments in the sample pool interference. In both experiments environmental interference gas absorption in the optical signal acquisition, signal amplitude variation analysis, and records related to the signal data. In order to study site conditions in the engine combustion process for signal acquisition provides an ideal experimental data .

Enhancement of two photon absorption with Ni doping in the dilute magnetic semiconductor ZnO crystalline nanorods

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

Rana, Amit Kumar; Kumar, Yogendra; Arjunan, M.S.

2015-12-07

In this letter, we have investigated the third-order optical nonlinearities of high-quality Ni doped ZnO nanorods crystallized in wurtzite lattice, prepared by the wet chemical method. In our experiments, we found that the two photon absorption coefficient (β) increases by as much as 14 times, i.e., 7.6 ± 0.4 to 112 ± 6 cm/GW, when the Ni doping is increased from 0% to 10%. The substantial enhancement in β is discussed in terms of the bandgap scaling and Ni doping. Furthermore, we also show that the optical bandgap measured by UV-Vis and photoluminescence spectroscopies, continuously redshift with increasing Ni doping concentration.more » We envision that the strong nonlinear optical properties together with their dilute magnetic effects, they form an important class of materials for potential applications in magneto-optical and integrated optical chips.« less

Enhancement of two photon absorption with Ni doping in the dilute magnetic semiconductor ZnO crystalline nanorods

NASA Astrophysics Data System (ADS)

Rana, Amit Kumar; J, Aneesh; Kumar, Yogendra; M. S, Arjunan; Adarsh, K. V.; Sen, Somaditya; Shirage, Parasharam M.

2015-12-01

In this letter, we have investigated the third-order optical nonlinearities of high-quality Ni doped ZnO nanorods crystallized in wurtzite lattice, prepared by the wet chemical method. In our experiments, we found that the two photon absorption coefficient (β) increases by as much as 14 times, i.e., 7.6 ± 0.4 to 112 ± 6 cm/GW, when the Ni doping is increased from 0% to 10%. The substantial enhancement in β is discussed in terms of the bandgap scaling and Ni doping. Furthermore, we also show that the optical bandgap measured by UV-Vis and photoluminescence spectroscopies, continuously redshift with increasing Ni doping concentration. We envision that the strong nonlinear optical properties together with their dilute magnetic effects, they form an important class of materials for potential applications in magneto-optical and integrated optical chips.

Two-step reconstruction method using global optimization and conjugate gradient for ultrasound-guided diffuse optical tomography.

PubMed

Tavakoli, Behnoosh; Zhu, Quing

2013-01-01

Ultrasound-guided diffuse optical tomography (DOT) is a promising method for characterizing malignant and benign lesions in the female breast. We introduce a new two-step algorithm for DOT inversion in which the optical parameters are estimated with the global optimization method, genetic algorithm. The estimation result is applied as an initial guess to the conjugate gradient (CG) optimization method to obtain the absorption and scattering distributions simultaneously. Simulations and phantom experiments have shown that the maximum absorption and reduced scattering coefficients are reconstructed with less than 10% and 25% errors, respectively. This is in contrast with the CG method alone, which generates about 20% error for the absorption coefficient and does not accurately recover the scattering distribution. A new measure of scattering contrast has been introduced to characterize benign and malignant breast lesions. The results of 16 clinical cases reconstructed with the two-step method demonstrates that, on average, the absorption coefficient and scattering contrast of malignant lesions are about 1.8 and 3.32 times higher than the benign cases, respectively.

Quantum quench of Kondo correlations in optical absorption.

PubMed

Latta, C; Haupt, F; Hanl, M; Weichselbaum, A; Claassen, M; Wuester, W; Fallahi, P; Faelt, S; Glazman, L; von Delft, J; Türeci, H E; Imamoglu, A

2011-06-29

The interaction between a single confined spin and the spins of an electron reservoir leads to one of the most remarkable phenomena of many-body physics--the Kondo effect. Electronic transport measurements on single artificial atoms, or quantum dots, have made it possible to study the effect in great detail. Here we report optical measurements on a single semiconductor quantum dot tunnel-coupled to a degenerate electron gas which show that absorption of a single photon leads to an abrupt change in the system Hamiltonian and a quantum quench of Kondo correlations. By inferring the characteristic power-law exponents from the experimental absorption line shapes, we find a unique signature of the quench in the form of an Anderson orthogonality catastrophe, induced by a vanishing overlap between the initial and final many-body wavefunctions. We show that the power-law exponent that determines the degree of orthogonality can be tuned using an external magnetic field, which unequivocally demonstrates that the observed absorption line shape originates from Kondo correlations. Our experiments demonstrate that optical measurements on single artificial atoms offer new perspectives on many-body phenomena previously studied using transport spectroscopy only.

Examination of contrast mechanisms in optoacoustic imaging of thermal lesions

NASA Astrophysics Data System (ADS)

Richter, Christian; Spirou, Gloria; Oraevsky, Alexander A.; Whelan, William M.; Kolios, Michael C.

2006-02-01

Optoacoustic Imaging is based on the thermal expansion of tissue caused by a temperature rise due to absorption of short laser pulses. At constant laser fluence, optoacoustic image contrast is proportional to differences in optical absorption and the thermoacoustic efficiency, expressed by the Grueuneisen parameter, Γ. Γ is proportional to the thermal expansion coefficient, the sound velocity squared and the inverse heat capacity at constant pressure. In thermal therapies, these parameters may be modified in the treated area. In this work experiments were performed to examine the influence of these parameters on image contrast. A Laser Optoacoustic Imaging System (LOIS, Fairway Medical Technologies, Houston, Texas) was used to image tissue phantoms comprised of cylindrical Polyvinyl Chloride Plastisol (PVCP) optical absorbing targets imbedded in either gelatin or PVCP as the background medium. Varying concentrations of Black Plastic Color (BPC) and titanium dioxide (TiO II) were added to targets and background to yield desired tissue relevant optical absorption and effective scattering coefficients, respectively. In thermal therapy experiments, ex-vivo bovine liver was heated with laser fibres (805nm laser at 5 W for 600s) to create regions of tissue coagulation. Lesions formed in the liver tissue were visible using the LOIS system with reasonable correspondence to the actual region of tissue coagulation. In the phantom experiments, contrast could be seen with low optical absorbing targets (μ a of 0.50cm -1 down to 0.13cm-1) embedded in a gelatin background (see manuscript for formula). Therefore, the data suggest that small objects (< 5mm) with low absorption coefficients (in the range < 1cm -1) can be imaged using LOIS. PVCP-targets in gelatin were visible, even with the same optical properties as the gelatin, but different Γ. The enhanced contrast may also be caused by differences in the mechanical properties between the target and the surrounding medium. PVCP-targets imbedded in PVCP produced poorer image contrast than PVCP-targets in gelatin with comparable optical properties. The preliminary investigation in tissue equivalent phantoms indicates that in addition to tissue optical properties, differences in mechanical properties between heated and unheated tissues may be responsible for image contrast. Furthermore, thermal lesions in liver tissue, ex-vivo, can be visualized using an optoacoustic system.

The manifestation of optical centers in UV-Vis absorption and luminescence spectra of white blood human cells

NASA Astrophysics Data System (ADS)

Terent'yeva, Yu G.; Yashchuk, V. M.; Zaika, L. A.; Snitserova, O. M.; Losytsky, M. Yu

2016-12-01

A white blood human cells spectral investigation is presented. The aim of this series of experiments was to obtain and analyze the absorption and luminescence (fluorescence and phosphorescence) spectra at room temperature and at 78 K of newly isolated white blood human cells and their organelles. As a result the optical centers and possible biochemical components that form the studied spectra where identified. Also the differences between the spectra of abnormal cells (B-cell chronic lymphocytic leukemia BCLL) and normal ones were studied for the whole cells and individual organelles.

Effect of silver nanoparticles on the fluorescence of Pb2+ and compositional dependence of Sm3+ fluorescence in borate glasses

NASA Astrophysics Data System (ADS)

Olumoroti, Akinloluwa T.

Borate glasses have been widely studied due to their good optical and mechanical properties. Lead and bismuth (PbO/Bi2O 3:B2O3) borate glasses belong to a family of heavy metal oxide (HMO) glasses which are well known to be chemically durable, stable against atmospheric moisture, have low melting temperatures and good corrosion resistance. The first part of this work deals with lead borate glasses with silver nanoparticles (NPs) introduced into the glass matrix. Transmission electron microscopy characterization is done to verify the nucleation of NPs. Fluorescence and optical absorption experiments are then carried out after different heat treatment duration to investigate the influence of silver NPs on the optical properties of lead (Pb2+) by comparing with a glass sample without silver NPs. Optical absorption experiments show that a well-defined surface plasmon resonance (SPR) peak due to Ag NPs can be observed only for samples that were annealed for 36 hrs. Pb2+ fluorescence spectra reveal that the presence of silver NPs creates new emission centers for Pb2+ ions by altering their chemical environment. The second part of the work involves the use of samarium (a rare earth ion) as a dopant in lead and bismuth borate glasses. The concentration of samarium (Sm3+) is fixed and the base glass composition is varied. The goal is to investigate the compositional dependence of optical properties of samarium in the base glass (PbO/Bi2O3:B 2O3). Optical absorption spectra have been collected and the oscillator strength of each transition - including the hypersensitive - is obtained. The Optical absorption edge is found to shift toward lower energies with increasing PbO/Bi2O3 concentration. Both the oscillator strength and the peak position of the hypersensitive transition show significant variation with glass composition. Strong interaction between Sm3+ ions and Pb2+/Bi3+ ions can also be seen from the variations in the fluorescence emission properties of Sm3+ as a function of base glass composition. Studying the variation of these optical properties will help to create the optimum rare-earth ion-host configuration for possible technological applications. This is the thrust of our future investigations of these glass systems. Keywords: Borate glasses, nanoparticles, fluorescence, transmission electron microscopy, optical absorption, surface plasmon resonance, rare-earth (RE) ions, oscillator strength, hypersensitive transition (HST).

Optical gain coefficients of silicon: a theoretical study

NASA Astrophysics Data System (ADS)

Tsai, Chin-Yi

2018-05-01

A theoretical model is presented and an explicit formula is derived for calculating the optical gain coefficients of indirect band-gap semiconductors. This model is based on the second-order time-dependent perturbation theory of quantum mechanics by incorporating all the eight processes of photon/phonon emission and absorption between the band edges of the conduction and valence bands. Numerical calculation results are given for Si. The calculated absorption coefficients agree well with the existing fitting formula of experiment data with two modes of phonons: optical phonons with energy of 57.73 meV and acoustic phonons with energy of 18.27 meV near (but not exactly at) the zone edge of the X-point in the dispersion relation of phonons. These closely match with existing data of 57.5 meV transverse optical (TO) phonons at the X4-point and 18.6 meV transverse acoustic (TA) phonons at the X3-point of the zone edge. The calculated results show that the material optical gain of Si will overcome free-carrier absorption if the energy separation of quasi-Fermi levels between electrons and holes exceeds 1.15 eV.

Optical tomographic imaging for breast cancer detection

NASA Astrophysics Data System (ADS)

Cong, Wenxiang; Intes, Xavier; Wang, Ge

2017-09-01

Diffuse optical breast imaging utilizes near-infrared (NIR) light propagation through tissues to assess the optical properties of tissues for the identification of abnormal tissue. This optical imaging approach is sensitive, cost-effective, and does not involve any ionizing radiation. However, the image reconstruction of diffuse optical tomography (DOT) is a nonlinear inverse problem and suffers from severe illposedness due to data noise, NIR light scattering, and measurement incompleteness. An image reconstruction method is proposed for the detection of breast cancer. This method splits the image reconstruction problem into the localization of abnormal tissues and quantification of absorption variations. The localization of abnormal tissues is performed based on a well-posed optimization model, which can be solved via a differential evolution optimization method to achieve a stable reconstruction. The quantification of abnormal absorption is then determined in localized regions of relatively small extents, in which a potential tumor might be. Consequently, the number of unknown absorption variables can be greatly reduced to overcome the underdetermined nature of DOT. Numerical simulation experiments are performed to verify merits of the proposed method, and the results show that the image reconstruction method is stable and accurate for the identification of abnormal tissues, and robust against the measurement noise of data.

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

DOEpatents

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.

2nd-order optical model of the isotopic dependence of heavy ion absorption cross sections for radiation transport studies

NASA Astrophysics Data System (ADS)

Cucinotta, Francis A.; Yan, Congchong; Saganti, Premkumar B.

2018-01-01

Heavy ion absorption cross sections play an important role in radiation transport codes used in risk assessment and for shielding studies of galactic cosmic ray (GCR) exposures. Due to the GCR primary nuclei composition and nuclear fragmentation leading to secondary nuclei heavy ions of charge number, Z with 3 ≤ Z ≥ 28 and mass numbers, A with 6 ≤ A ≥ 60 representing about 190 isotopes occur in GCR transport calculations. In this report we describe methods for developing a data-base of isotopic dependent heavy ion absorption cross sections for interactions. Calculations of a 2nd-order optical model solution to coupled-channel solutions to the Eikonal form of the nucleus-nucleus scattering amplitude are compared to 1st-order optical model solutions. The 2nd-order model takes into account two-body correlations in the projectile and target ground-states, which are ignored in the 1st-order optical model. Parameter free predictions are described using one-body and two-body ground state form factors for the isotopes considered and the free nucleon-nucleon scattering amplitude. Root mean square (RMS) matter radii for protons and neutrons are taken from electron and muon scattering data and nuclear structure models. We report on extensive comparisons to experimental data for energy-dependent absorption cross sections for over 100 isotopes of elements from Li to Fe interacting with carbon and aluminum targets. Agreement between model and experiments are generally within 10% for the 1st-order optical model and improved to less than 5% in the 2nd-order optical model in the majority of comparisons. Overall the 2nd-order optical model leads to a reduction in absorption compared to the 1st-order optical model for heavy ion interactions, which influences estimates of nuclear matter radii.

Active correction of thermal lensing through external radiative thermal actuation.

PubMed

Lawrence, Ryan; Ottaway, David; Zucker, Michael; Fritschel, Peter

2004-11-15

Absorption of laser beam power in optical elements induces thermal gradients that may cause unwanted phase aberrations. In precision measurement applications, such as laser interferometric gravitational-wave detection, corrective measures that require mechanical contact with or attachments to the optics are precluded by noise considerations. We describe a radiative thermal corrector that can counteract thermal lensing and (or) thermoelastic deformation induced by coating and substrate absorption of collimated Gaussian beams. This radiative system can correct anticipated distortions to a high accuracy, at the cost of an increase in the average temperature of the optic. A quantitative analysis and parameter optimization is supported by results from a simplified proof-of-principle experiment, demonstrating the method's feasibility for our intended application.

Utilizing Near-IR Tunable Laser Absorption Spectroscopy to Study Detonation and Combustion Systems

DTIC Science & Technology

2014-03-27

debris, such as soot . Velocity curves for the other equivalence ratios studied in this experiment are shown in Appendix A. Some of these curves show a...James R. Gord. “Measurements of OH mole fraction and temperature up to 20 kHz by using a diode-laser based UV absorption sensor ”. Applied Optics, 44...Davidson, and R.K. Hanson. “CO concentration and temperature sensor for combustion gases using quantum-cascade laser absorption near 4.7µm”. Applied

Nonlinear bleaching, absorption, and scattering of 532-nm-irradiated plasmonic nanoparticles

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

Liberman, V.; Sworin, M.; Kingsborough, R. P.

2013-02-07

Single-pulse irradiation of Au and Ag suspensions of nanospheres and nanodisks with 532-nm 4-ns pulses has identified complex optical nonlinearities while minimizing material damage. For all materials tested, we observe competition between saturable absorption (SA) and reverse SA (RSA), with RSA behavior dominating for intensities above {approx}50 MW/cm{sup 2}. Due to reduced laser damage in single-pulse experiments, the observed intrinsic nonlinear absorption coefficients are the highest reported to date for Au nanoparticles. We find size dependence to the nonlinear absorption enhancement for Au nanoparticles, peaking in magnitude for 80-nm nanospheres and falling off at larger sizes. The nonlinear absorption coefficientsmore » for Au and Ag spheres are comparable in magnitude. On the other hand, the nonlinear absorption for Ag disks, when corrected for volume fraction, is several times higher. These trends in nonlinear absorption are correlated to local electric field enhancement through quasi-static mean-field theory. Through variable size aperture measurements, we also separate nonlinear scattering from nonlinear absorption. For all materials tested, we find that nonlinear scattering is highly directional and that its magnitude is comparable to that of nonlinear absorption. These results indicate methods to improve the efficacy of plasmonic nanoparticles as optical limiters in pulsed laser systems.« less

Quantifying organic aerosol single scattering albedo over tropical biomass burning regions using ground-based observation

NASA Astrophysics Data System (ADS)

Chu, J. E.

2016-12-01

Despite growing evidence of light-absorbing organic aerosols (OAs), OA light absorption has been poorly understood due to difficulties in aerosol light absorption measurements. In this study, we developed an empirical method to quantify OA single scattering albedo (SSA), the ratio of light scattering to extinction, using ground-based Aerosol Robotic Network (AERONET) observation. Our method includes partitioning fine-mode aerosol optical depth (fAOD) to individual aerosol's optical depth (AOD), separating black carbon and OA absorption aerosol optical depths, and finally binding OA SSA and sulfate+nitrate AOD. Our best estimate of OA SSA over tropical biomass burning region is 0.91 at 550nm with a range of 0.82-0.93. It implies the common OA SSA values of 0.96-1.0 in aerosol CTMs and GCMs significantly underrepresent OA light absorption. Model experiments with prescribed OA SSA showed that the enhanced absorption of solar radiation due to light absorbing OA yields global mean radiative forcing is +0.09 Wm-2 at the TOA, +0.21 Wm-2 at the atmosphere, and -0.12 Wm-2 at the surface. Compared to the previous assessment of OA radiative forcing reported in AeroCom II project, our result indicate that OA light absorption causes TOA radiative forcing by OA to change from negative (i.e., cooling effect) to positive (warming effect).

Investigating the origins of double photopeaks in CsI:Tl samples through activator mapping

NASA Astrophysics Data System (ADS)

Onken, Drew R.; Gridin, Sergii; Williams, Richard T.; Williams, Charles B.; Donati, George L.; Gayshan, Vadim; Vasyukov, Sergey; Gektin, Alex

2018-06-01

Careful examination of the origins of double photopeaks in CsI:Tl provides a foundation for exploring the relationship between activator homogeneity and photopeak resolution in scintillators. In rare cases, certain CsI:Tl crystals exhibit a second photopeak in the pulse-height spectrum. A combination of optical mapping and ICP-MS measurements reveals the presence of two distinct regions with differing Tl concentrations in these crystals. The oscillator strength of the 299 nm absorption A-band of Tl in CsI was measured to be 0.0526 ± 0.0008; this parameter can be used to quantify activator concentration from the optical absorption. Using published measurements of luminescence intensity versus Tl concentration, the distributions of Tl measured from optical absorption maps of the samples were reconstructed into photopeaks in good agreement with experiment. The distribution of Tl concentrations in these particular crystals allowed examining luminescence pulse shape as a function of Tl concentration.

Application of the fiber-optic perfusion fluorometer to absorption and exsorption studies in hairless mouse skin.

PubMed

Shackleford, J M; Yielding, K L

1987-09-01

This study was undertaken to test the fiber-optic perfusion fluorometer as a direct means of evaluating skin absorption and exsorption in hairless mice. Skin-barrier compromise was accomplished in the absorption experiments by application of dimethyl sulfoxide to the skin surface or by partial removal of the stratum corneum with sticky tape. Absorbed fluorescein was measured easily in unanesthetized control (skin-barrier intact) and experimental mice. Unabsorbed chemical did not fluoresce 15 minutes after application, although it was present on the surface of the skin as a dry powder. The time course of fluorescein elimination from the skin was related to a rapid phase (vascular removal) and a slow phase (reservoir entrapment). In the exsorption experiments the fluorescein was injected intraperitoneally. Back skin on the right side was swabbed with either dimethyl sulfoxide or 1% capsaicin in alcohol prior to the injections, and differences in skin fluorescence on the left (control) and right sides were recorded. One application of dimethyl sulfoxide or capsaicin increased the level of skin exsorption. Three applications of dimethyl sulfoxide almost doubled the amount of exsorbed dye, whereas three applications of the capsaicin inhibited the exsorption process. It was concluded that the fiber-optic perfusion fluorometer provides an excellent technique in support of other methods of investigating the skin.

Quantification and Reconstruction in Photoacoustic Tomography

NASA Astrophysics Data System (ADS)

Guo, Zijian

Optical absorption is closely associated with many physiological important parameters, such as the concentration and oxygen saturation of hemoglobin. Conventionally, accurate quantification in PAT requires knowledge of the optical fluence attenuation, acoustic pressure attenuation, and detection bandwidth. We circumvent this requirement by quantifying the optical absorption coefficients from the acoustic spectra of PA signals acquired at multiple optical wavelengths. We demonstrate the method using the optical-resolution photoacoustic microscopy (OR-PAM) and the acoustical-resolution photoacoustic microscopy (AR-PAM) in the optical ballistic regime and in the optical diffusive regime, respectively. The data acquisition speed in photoacoustic computed tomography (PACT) is limited by the laser repetition rate and the number of parallel ultrasound detecting channels. Reconstructing an image with fewer measurements can effectively accelerate the data acquisition and reduce the system cost. We adapted Compressed Sensing (CS) for the reconstruction in PACT. CS-based PACT was implemented as a non-linear conjugate gradient descent algorithm and tested with both phantom and in vivo experiments. Speckles have been considered ubiquitous in all scattering-based coherent imaging technologies. As a coherent imaging modality based on optical absorption, photoacoustic (PA) tomography (PAT) is generally devoid of speckles. PAT suppresses speckles by building up prominent boundary signals, via a mechanism similar to that of specular reflection. When imaging smooth boundary absorbing targets, the speckle visibility in PAT, which is defined as the ratio of the square root of the average power of speckles to that of boundaries, is inversely proportional to the square root of the absorber density. If the surfaces of the absorbing targets have uncorrelated height fluctuations, however, the boundary features may become fully developed speckles. The findings were validated by simulations and experiments. The first- and second-order statistics of PAT speckles were also studied experimentally. While the amplitude of the speckles follows a Gaussian distribution, the autocorrelation of the speckle patterns tracks that of the system point spread function.

Magneto-Optical Signature of Massless Kane Electrons in Cd 3 As 2

DOE PAGES

Akrap, A.; Hakl, M.; Tchoumakov, S.; ...

2016-09-21

Here, we report on optical reflectivity experiments performed on Cd 3As 2 over a broad range of photon energies and magnetic fields. The presence of 3D massless charge carriers are clearly indicated in the observed response. The specific cyclotron resonance absorption in the quantum limit implies that we are probing massless Kane electrons rather than symmetry-protected 3D Dirac particles. Furthermore, the latter may appear at a smaller energy scale and are not directly observed in our infrared experiments.

Design and performance of BOREAS, the beamline for resonant X-ray absorption and scattering experiments at the ALBA synchrotron light source

DOE PAGES

Barla, Alessandro; Nicolas, Josep; Cocco, Daniele; ...

2016-10-07

The optical design of the BOREAS beamline operating at the ALBA synchrotron radiation facility is described. BOREAS is dedicated to resonant X-ray absorption and scattering experiments using soft X-rays, in an unusually extended photon energy range from 80 to above 4000 eV, and with full polarization control. Its optical scheme includes a fixed-included-angle, variable-line-spacing grating monochromator and a pair of refocusing mirrors, equipped with benders, in a Kirkpatrick–Baez arrangement. It is equipped with two end-stations, one for X-ray magnetic circular dichroism and the other for resonant magnetic scattering. In conclusion, the commissioning results show that the expected beamline performance ismore » achieved both in terms of energy resolution and of photon flux at the sample position.« less

Gbit/s-operation of graphene electro-absorption modulators in a passive polymer waveguide platform for data and telecommunications

NASA Astrophysics Data System (ADS)

Kleinert, M.; Reinke, P.; Bach, H.-G.; Brinker, W.; Zawadzki, C.; Dietrich, A.; de Felipe, D.; Keil, N.; Schell, M.

2017-02-01

Graphene with its high carrier mobility as well as its tunable light absorption is an attractive active material for highspeed electro-absorption modulators (EAMs). Large-area CVD-grown graphene monolayers can be transferred onto arbitrary substrates to add active optoelectronic properties to intrinsically passive photonic integration platforms. In this work, we present graphene-based EAMs integrated in passive polymer waveguides. To facilitate modulation frequencies in the GHz range, a 50 Ω termination resistor as well as a DC blocking capacitor are integrated with graphene EAMs for the first time. Large signal data transmission experiments were carried out across the O, C and L optical communications bands. The fastest devices exhibit a 3-dB bandwidth of more than 4 GHz. Our analytical model of the modulation response for the graphene-based EAMs is in good agreement with the measurement results. It predicts that bandwidths greater than 50 GHz are possible with future device iterations. Owing to the absorption properties of the graphene layers, the devices are expected to be functional at smaller wavelengths of interest for optical interconnects and data-communications as well, offering a novel flexibility for the integration of high-speed functionalities in optoelectronic integrated circuits. Our work is the first step towards an Active Optical Printed Circuit Board, hiding the optics completely inside the board and thus removing entry barriers in manufacturing. We believe this will lead to the same success as observed in Active Optical Cables for short range optically wired connections.

Frequency domain photothermoacoustic signal amplitude dependence on the optical properties of water: turbid polyvinyl chloride-plastisol system.

PubMed

Spirou, Gloria M; Mandelis, Andreas; Vitkin, I Alex; Whelan, William M

2008-05-10

Photoacoustic (more precisely, photothermoacoustic) signals generated by the absorption of photons can be related to the incident laser fluence rate. The dependence of frequency domain photoacoustic (FD-PA) signals on the optical absorption coefficient (micro(a)) and the effective attenuation coefficient (micro(eff)) of a turbid medium [polyvinyl chloride-plastisol (PVCP)] with tissuelike optical properties was measured, and empirical relationships between these optical properties and the photoacoustic (PA) signal amplitude and the laser fluence rate were derived for the water (PVCP system with and without optical scatterers). The measured relationships between these sample optical properties and the PA signal amplitude were found to be linear, consistent with FD-PA theory: micro(a)=a(A/Phi)-b and micro(eff)=c(A/Phi)+d, where Phi is the laser fluence, A is the FD-PA amplitude, and a, ...,d are empirical coefficients determined from the experiment using linear frequency-swept modulation and a lock-in heterodyne detection technique. This quantitative technique can easily be used to measure the optical properties of general turbid media using FD-PAs.

Mechano-optic logic gate controlled by third-order nonlinear optical properties in a rotating ZnO:Au thin film

NASA Astrophysics Data System (ADS)

Carrillo-Delgado, C.; García-Gil, C. I.; Trejo-Valdez, M.; Torres-Torres, C.; García-Merino, J. A.; Martínez-Gutiérrez, H.; Khomenko, A. V.; Torres-Martínez, R.

2016-01-01

Measurements of the third-order nonlinear optical properties exhibited by a ZnO thin solid film deposited on a SnO2 substrate are presented. The samples were prepared by a spray pyrolysis processing route. Scanning electron microscopy analysis and UV-Vis spectroscopy studies were carried out. The picosecond response at 1064 nm was explored by the z-scan technique. A large optical Kerr effect with two-photon absorption was obtained. The inhibition of the nonlinear optical absorption together with a noticeable enhancement in the optical Kerr effect in the sample was achieved by the incorporation of Au nanoparticles into the ZnO film. Additionally, a two-wave mixing configuration at 532 nm was performed and an optical Kerr effect was identified as the main cause of the nanosecond third-order optical nonlinearity. The relaxation time of the photothermal response of the sample was estimated to be about 1 s when the sample was excited by nanosecond single-shots. The rotation of the sample during the nanosecond two-wave mixing experiments was analyzed. It was stated that a non-monotonic relation between rotating frequency and pulse repetition rate governs the thermal contribution to the nonlinear refractive index exhibited by a rotating film. Potential applications for switching photothermal interactions in rotating samples can be contemplated. A rotary logic system dependent on Kerr transmittance in a two-wave mixing experiment was proposed.

Microwave generation in an electro-absorption modulator integrated with a DFB laser subject to optical injection.

PubMed

Zhu, Ning Hua; Zhang, Hong Guang; Man, Jiang Wei; Zhu, Hong Liang; Ke, Jian Hong; Liu, Yu; Wang, Xin; Yuan, Hai Qing; Xie, Liang; Wang, Wei

2009-11-23

This paper presents a new technique to generate microwave signal using an electro-absorption modulator (EAM) integrated with a distributed feedback (DFB) laser subject to optical injection. Experiments show that the frequency of the generated microwave can be tuned by changing the wavelength of the external laser or adjusting the bias voltage of the EAM. The frequency response of the EAM is studied and found to be unsmooth due to packaging parasitic effects and four-wave mixing effect occurring in the active layer of the DFB laser. It is also demonstrated that an EA modulator integrated in between two DFB lasers can be used instead of the EML under optical injection. This integrated chip can be used to realize a monolithically integrated tunable microwave source.

Application of ultrasound-tagged photons for measurement of amplitude of vibration of tissue caused by ultrasound: theory, simulation, and experiments.

PubMed

Devi, C Usha; Vasu, R M; Sood, A K

2006-01-01

We investigate the modulation of an optical field caused by its interaction with an ultrasound beam in a tissue mimicking phantom. This modulation appears as a modulation in the intensity autocorrelation, which is measured by a photon counting correlator. The factors contributing to the modulation are: 1. amplitude of vibration of the particles of the tissue, 2. refractive index modulation, and 3. absorption coefficient in the region of the tissue intercepted by the ultrasound beam and light. We show in this work that a significant part of the contribution to this modulation comes from displacement of the tissue particles, which in turn is governed by the elastic properties of the tissue. We establish, both through simulations and experiments using an optical elastography phantom, the effects of the elasticity and absorption coefficient variations on the modulation of intensity autocorrelation. In the case where there is no absorption coefficient variation, we suggest that the depth of modulation can be calibrated to measure the displacement of tissue particles that, in turn, can be used to measure the tissue elasticity.

Population transfer and rapid passage effects in a low pressure gas using a continuous wave quantum cascade laser.

PubMed

McCormack, E A; Lowth, H S; Bell, M T; Weidmann, D; Ritchie, G A D

2012-07-21

A continuous wave quantum cascade laser (cw-QCL) operating at 10 μm has been used to record absorption spectra of low pressure samples of OCS in an astigmatic Herriott cell. As a result of the frequency chirp of the laser, the spectra show clearly the effects of rapid passage on the absorption line shape. At the low chirp rates that can be obtained with the cw-QCL, population transfer between rovibrational quantum states is predicted to be much more efficient than in typical pulsed QCL experiments. This optical pumping is investigated by solving the Maxwell Bloch equations to simulate the propagation of the laser radiation through an inhomogeneously broadened two-level system. The calculated absorption profiles show good quantitative agreement with those measured experimentally over a range of chirp rates and optical thicknesses. It is predicted that at a low chirp rate of 0.13 MHz ns(-1), the population transfer between rovibrational quantum states is 12%, considerably more than that obtained at the higher chirp rates utilised in pulsed QCL experiments.

One-shot calculation of temperature-dependent optical spectra and phonon-induced band-gap renormalization

NASA Astrophysics Data System (ADS)

Zacharias, Marios; Giustino, Feliciano

Electron-phonon interactions are of fundamental importance in the study of the optical properties of solids at finite temperatures. Here we present a new first-principles computational technique based on the Williams-Lax theory for performing predictive calculations of the optical spectra, including quantum zero-point renormalization and indirect absorption. The calculation of the Williams-Lax optical spectra is computationally challenging, as it involves the sampling over all possible nuclear quantum states. We develop an efficient computational strategy for performing ''one-shot'' finite-temperature calculations. These require only a single optimal configuration of the atomic positions. We demonstrate our methodology for the case of Si, C, and GaAs, yielding absorption coefficients in good agreement with experiment. This work opens the way for systematic calculations of optical spectra at finite temperature. This work was supported by the UK EPSRC (EP/J009857/1 and EP/M020517/) and the Leverhulme Trust (RL-2012-001), and the Graphene Flagship (EU-FP7-604391).

Calibration-free quantification of absolute oxygen saturation based on the dynamics of photoacoustic signals

PubMed Central

Xia, Jun; Danielli, Amos; Liu, Yan; Wang, Lidai; Maslov, Konstantin; Wang, Lihong V.

2014-01-01

Photoacoustic tomography (PAT) is a hybrid imaging technique that has broad preclinical and clinical applications. Based on the photoacoustic effect, PAT directly measures specific optical absorption, which is the product of the tissue-intrinsic optical absorption coefficient and the local optical fluence. Therefore, quantitative PAT, such as absolute oxygen saturation (sO2) quantification, requires knowledge of the local optical fluence, which can be estimated only through invasive measurements or sophisticated modeling of light transportation. In this work, we circumvent this requirement by taking advantage of the dynamics in sO2. The new method works when the sO2 transition can be simultaneously monitored with multiple wavelengths. For each wavelength, the ratio of photoacoustic amplitudes measured at different sO2 states is utilized. Using the ratio cancels the contribution from optical fluence and allows calibration-free quantification of absolute sO2. The new method was validated through both phantom and in vivo experiments. PMID:23903146

X-ray Experiments for Students at the SLS Optics Beamline

NASA Astrophysics Data System (ADS)

Flechsig, U.; Als-Nielsen, J.; Jaggi, A.; Krempaský, J.; Oberta, P.; Spielmann, S.; van der Veen, J. F.

2010-06-01

We present a X-ray training course for students. The course covers fundamental properties of synchrotron radiation and basic techniques like scattering and absorption. We prepared ten experiments together with a tutorial. The whole course takes about a week. A first student group from the University of Copenhagen passed the course in June 2009. The experiments were performed at the optics beamline of the Swiss Light Source which can be part-time allocated for training purposes. Two experiments are described in more detail: scattering from a hanging drop of water turning into ice and measurement of the power of a pink synchrotron beam using a simple calorimeter.

Determination of the optical absorption spectra of thin layers from their photoacoustic spectra

NASA Astrophysics Data System (ADS)

Bychto, Leszek; Maliński, Mirosław; Patryn, Aleksy; Tivanov, Mikhail; Gremenok, Valery

2018-05-01

This paper presents a new method for computations of the optical absorption coefficient spectra from the normalized photoacoustic amplitude spectra of thin semiconductor samples deposited on the optically transparent and thermally thick substrates. This method was tested on CuIn(Te0.7Se0.3)2 thin films. From the normalized photoacoustic amplitude spectra, the optical absorption coefficient spectra were computed with the new formula as also with the numerical iterative method. From these spectra, the value of the energy gap of the thin film material and the type of the optical transitions were determined. From the experimental optical transmission spectra, the optical absorption coefficient spectra were computed too, and compared with the optical absorption coefficient spectra obtained from photoacoustic spectra.

Third order nonlinear optical response exhibited by mono- and few-layers of WS 2

DOE PAGES

Torres-Torres, Carlos; Perea-López, Néstor; Elías, Ana Laura; ...

2016-04-13

In this work, strong third order nonlinear optical properties exhibited by WS 2 layers are presented. Optical Kerr effect was identified as the dominant physical mechanism responsible for these third order optical nonlinearities. An extraordinary nonlinear refractive index together with an important contribution of a saturated absorptive response was observed to depend on the atomic layer stacking. Comparative experiments performed in mono- and few-layer samples of WS 2 revealed that this material is potentially capable of modulating nonlinear optical processes by selective near resonant induced birefringence. In conclusion, we envision applications for developing all-optical bidimensional nonlinear optical devices.

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.

Size dependent nonlinear optical properties of spin coated zinc oxide-polystyrene nanocomposite films

NASA Astrophysics Data System (ADS)

Jeeju, Pullarkat P.; Jayalekshmi, S.; Chandrasekharan, K.; Sudheesh, P.

2012-11-01

Using simple wet chemical method at room temperature, zinc oxide (ZnO) nanoparticles embedded in polystyrene (PS) matrix were synthesized. The size of the ZnO nanoparticles could be varied by varying the precursor concentration, reaction time and stirring speed. Transparent films of ZnO/PS nanocomposites of thickness around 1 μm were coated on ultrasonically cleaned glass substrates by spin coating. The optical absorptive nonlinearity in ZnO/PS nanocomposite films was investigated using open aperture Z-scan technique with nanosecond laser pulses at 532 nm. The results indicate optical limiting type nonlinearity in the films due to two-photon absorption in ZnO. These films also show a self-defocusing type negative nonlinear refraction in closed aperture Z-scan experiment. The observed nonlinear absorption is strongly dependent on particle size and the normalized transmittance could be reduced to as low as 0.43 by the suitable choice of the ZnO nanoparticle size. These composite films can hence be used as efficient optical limiters for sensor protection. The much-pronounced nonlinear response of these composite films, compared to pure ZnO, combined with the improved stability of ZnO nanoparticles in the PS matrix offer prospects of application of these composite films in the fabrication of stable non-linear optical devices.

Development of UV Optical Measurements of Nitric Oxide and Hydroxyl Radical at the Exit of High Pressure Gas Turbine Combustors

NASA Technical Reports Server (NTRS)

Liscinsky, D. S.; Knight, B. A.; Shirley, J. A.

1998-01-01

Measurements of nitric oxide (NO) and hydroxyl radical (OR) have been made in a laboratory flat flame at pressures up to 30 atm using line-of-sight resonant absorption. Data are reported at equivalence ratios of 0.98 and 1.3 and pressures of 1, 5, 10, 20 and 30 atm. The performance of the in-situ LTV absorption technique with assessed at these elevated pressures by comparing the measured absorption with those predicted by detailed theoretical spectroscopic models for NO and OH. Previous to this experiment the resonant models had not been verified at pressures greater than two atmospheres. Agreement within 25% was found between the measurements and predictions with only slight modification of the existing models for both NO and OH to account for line center shifting and pressure broadening. Continuum interference of hot oxygen (O2) on the NO absorption spectra was not significant in the interpretation of the data. The optical methods used in this study are distinct from laser-based diagnostics such as laser induced fluorescence and, hence, have the potential to provide independent verification of the laser-based measurements. The methodology is also of sufficient simplicity to be hardened into a portable optical measurement system that can be deployed in gas turbine engine test cells. A miniature fiber optic couple portable instrument is described.

Sensitive And Selective Chemical Sensor With Nanostructured Surfaces.

DOEpatents

Pipino, Andrew C. R.

2003-02-04

A chemical sensor is provided which includes an optical resonator including a nanostructured surface comprising a plurality of nanoparticles bound to one or more surfaces of the resonator. The nanoparticles provide optical absorption and the sensor further comprises a detector for detecting the optical absorption of the nanoparticles or their environment. In particular, a selective chemical interaction is provided which modifies the optical absorption of the nanoparticles or their environment, and an analyte is detected based on the modified optical absorption. A light pulse is generated which enters the resonator to interrogate the modified optical absorption and the exiting light pulse is detected by the detector.

Absorption and fluorescence spectra of heterocyclic isomers from long-range-corrected density functional theory in polarizable continuum approach.

PubMed

Kityk, Andriy V

2012-03-22

Long-range-corrected (LC) DFT/TDDFT methods may provide adequate description of ground and excited state properties; however, accuracy of such an approach depends much on a range separation (exchange screening) representing adjustable model parameter. Its relation to a size or specific of molecular systems has been explored in numerous studies, whereas the effect of solvent environment is usually ignored during the evaluation of state properties. To benchmark and assess the quality of the LC-DFT/TDDFT formalism, we report the optical absorption and fluorescence emission energies of organic heterocyclic isomers, DPIPQ and PTNA, calculated by LC-BLYP DFT/TDDFT method in the polarizable continuum (PCM) approach. The calculations are compared with the optical absorption and fluorescence spectra measured in organic solvents of different polarity. Despite a considerable structural difference, both dyes exhibit quite similar range separations being somewhat different for the optical absorption and fluorescence emission processes. Properly parametrized LC-BLYP xc-potential well reproduces basic features of the optical absorption spectra including the electronic transitions to higher excited states. The DFT/TDDFT/PCM analysis correctly predicts the solvation trends although solvatochromic shifts of the electronic transition energies appear to be evidently underestimated in most cases, especially for the fluorescence emission. Considering the discrepancy between the experiment and theory, evaluated state dipole moments and solvation corrections to the exchange screening are analyzed. The results of the present study emphasize the importance of a solvent-dependent range separation in DFT/TDDFT/PCM calculations for investigating excited state properties. © 2012 American Chemical Society

Noise-Immune Cavity-Enhanced Optical Heterodyne Molecular Spectrometry Modelling Under Saturated Absorption

NASA Astrophysics Data System (ADS)

Dupré, Patrick

2015-06-01

The Noise-Immune Cavity-Enhanced Optical Heterodyne Molecular Spectrometry (NICE-OHMS) is a modern technique renowned for its ultimate sensitivity, because it combines long equivalent absorption length provided by a high finesse cavity, and a detection theoretically limited by the sole photon-shot-noise. One fallout of the high finesse is the possibility to accumulating strong intracavity electromagnetic fields (EMF). Under this condition, molecular transitions can be easy saturated giving rise to the usual Lamb dips (or hole burning). However, the unusual shape of the basically trichromatic EMF (due to the RF lateral sidebands) induces nonlinear couplings, i.e., new crossover transitions. An analytical methodology will be presented to calculate spectra provided by NICE-OHMS experiments. It is based on the solutions of the equations of motion of an open two-blocked-level system performed in the frequency-domain (optically thin medium). Knowing the transition dipole moment, the NICE-OHMS signals (``absorption-like'' and ``dispersion-like'') can be simulated by integration over the Doppler shifts and by paying attention to the molecular Zeeman sublevels and to the EMF polarization The approach has been validated by discussion experimental data obtained on two transitions of {C2H2} in the near-infrared under moderated saturation. One of the applications of the saturated absorption is to be able to simultaneously determine the transition intensity and the density number while only one these 2 quantities can only be assessed in nonlinear absorption. J. Opt. Soc. Am. B 32, 838 (2015) Optics Express 16, 14689 (2008)

High temperature measurement of water vapor absorption

NASA Technical Reports Server (NTRS)

Keefer, Dennis; Lewis, J. W. L.; Eskridge, Richard

1985-01-01

An investigation was undertaken to measure the absorption coefficient, at a wavelength of 10.6 microns, for mixtures of water vapor and a diluent gas at high temperature and pressure. The experimental concept was to create the desired conditions of temperature and pressure in a laser absorption wave, similar to that which would be created in a laser propulsion system. A simplified numerical model was developed to predict the characteristics of the absorption wave and to estimate the laser intensity threshold for initiation. A non-intrusive method for temperature measurement utilizing optical laser-beam deflection (OLD) and optical spark breakdown produced by an excimer laser, was thoroughly investigated and found suitable for the non-equilibrium conditions expected in the wave. Experiments were performed to verify the temperature measurement technique, to screen possible materials for surface initiation of the laser absorption wave and to attempt to initiate an absorption wave using the 1.5 kW carbon dioxide laser. The OLD technique was proven for air and for argon, but spark breakdown could not be produced in helium. It was not possible to initiate a laser absorption wave in mixtures of water and helium or water and argon using the 1.5 kW laser, a result which was consistent with the model prediction.

Characterization of Advanced Avalanche Photodiodes for Water Vapor Lidar Receivers

NASA Technical Reports Server (NTRS)

Refaat, Tamer F.; Halama, Gary E.; DeYoung, Russell J.

2000-01-01

Development of advanced differential absorption lidar (DIAL) receivers is very important to increase the accuracy of atmospheric water vapor measurements. A major component of such receivers is the optical detector. In the near-infrared wavelength range avalanche photodiodes (APD's) are the best choice for higher signal-to-noise ratio, where there are many water vapor absorption lines. In this study, characterization experiments were performed to evaluate a group of silicon-based APD's. The APD's have different structures representative of different manufacturers. The experiments include setups to calibrate these devices, as well as characterization of the effects of voltage bias and temperature on the responsivity, surface scans, noise measurements, and frequency response measurements. For each experiment, the setup, procedure, data analysis, and results are given and discussed. This research was done to choose a suitable APD detector for the development of an advanced atmospheric water vapor differential absorption lidar detection system operating either at 720, 820, or 940 nm. The results point out the benefits of using the super low ionization ratio (SLIK) structure APD for its lower noise-equivalent power, which was found to be on the order of 2 to 4 fW/Hz(sup (1/2)), with an appropriate optical system and electronics. The water vapor detection systems signal-to-noise ratio will increase by a factor of 10.

First-Principle Calculation of Quasiparticle Excitations and Optical Absorption in NiO

NASA Astrophysics Data System (ADS)

Li, Je-Luen; Rignanese, Gian-Marco; Louie, Steven G.

2001-03-01

We present a first-principle study of the quasiparticle excitations and optical absorption spectrum in NiO. The ground state electronic structure is calculated with the generalized gradient approximation in density functional theory and ab initio pseudopotential. The quasiparticle energies are then computed employing the GW approximation. In addition to comparing to photoemisson result, comparison between the measured and calculated complex dielectric function helps to identify the onset of excitations in this system. We illustrate some subtleties of pseudopotential calculations: the effect of including 3 s and 3p electrons in Ni pseudopotential; the difference between using velocity and momentum operators in the RPA dielectric function. Finally, we discuss a recent effort to solve the Bethe-Salpeter equation for the optical spectrum in this spin polarized system to address the remaining discrepancy between theory and experiment.

Ellipsometry study of optical parameters of AgIn5S8 crystals

NASA Astrophysics Data System (ADS)

Isik, Mehmet; Gasanly, Nizami

2015-12-01

AgIn5S8 crystals grown by Bridgman method were characterized for optical properties by ellipsometry measurements. Spectral dependence of optical parameters; real and imaginary parts of the pseudodielectric function, pseudorefractive index, pseudoextinction coefficient, reflectivity and absorption coefficient were obtained from ellipsometry experiments carried out in the 1.2-6.2 eV range. Direct band gap energy of 1.84 eV was found from the analysis of absorption coefficient vs. photon energy. The oscillator energy, dispersion energy and zero-frequency refractive index, high-frequency dielectric constant values were found from the analysis of the experimental data using Wemple-DiDomenico and Spitzer-Fan models. Crystal structure and atomic composition ratio of the constituent elements in the AgIn5S8 crystal were revealed from structural characterization techniques of X-ray diffraction and energy dispersive spectroscopy.

Polarization-insensitive techniques for optical signal processing

NASA Astrophysics Data System (ADS)

Salem, Reza

2006-12-01

This thesis investigates polarization-insensitive methods for optical signal processing. Two signal processing techniques are studied: clock recovery based on two-photon absorption in silicon and demultiplexing based on cross-phase modulation in highly nonlinear fiber. The clock recovery system is tested at an 80 Gb/s data rate for both back-to-back and transmission experiments. The demultiplexer is tested at a 160 Gb/s data rate in a back-to-back experiment. We experimentally demonstrate methods for eliminating polarization dependence in both systems. Our experimental results are confirmed by theoretical and numerical analysis.

Passive thermo-optic feedback for robust athermal photonic systems

DOEpatents

Rakich, Peter T.; Watts, Michael R.; Nielson, Gregory N.

2015-06-23

Thermal control devices, photonic systems and methods of stabilizing a temperature of a photonic system are provided. A thermal control device thermally coupled to a substrate includes a waveguide for receiving light, an absorption element optically coupled to the waveguide for converting the received light to heat and an optical filter. The optical filter is optically coupled to the waveguide and thermally coupled to the absorption element. An operating point of the optical filter is tuned responsive to the heat from the absorption element. When the operating point is less than a predetermined temperature, the received light is passed to the absorption element via the optical filter. When the operating point is greater than or equal to the predetermined temperature, the received light is transmitted out of the thermal control device via the optical filter, without being passed to the absorption element.

Complete chirp analysis of a gain-switched pulse using an interferometric two-photon absorption autocorrelation.

PubMed

Chin, Sang Hoon; Kim, Young Jae; Song, Ho Seong; Kim, Dug Young

2006-10-10

We propose a simple but powerful scheme for the complete analysis of the frequency chirp of a gain-switched optical pulse using a fringe-resolved interferometric two-photon absorption autocorrelator. A frequency chirp imposed on the gain-switched pulse from a laser diode was retrieved from both the intensity autocorrelation trace and the envelope of the second-harmonic interference fringe pattern. To verify the accuracy of the proposed phase retrieval method, we have performed an optical pulse compression experiment by using dispersion-compensating fibers with different lengths. We have obtained close agreement by less than a 1% error between the compressed pulse widths and numerically calculated pulse widths.

Coherent perfect absorption in one-sided reflectionless media

PubMed Central

Wu, Jin-Hui; Artoni, M.; La Rocca, G. C.

2016-01-01

In optical experiments one-sided reflectionless (ORL) and coherent perfect absorption (CPA) are unusual scattering properties yet fascinating for their fundamental aspects and for their practical interest. Although these two concepts have so far remained separated from each other, we prove that the two phenomena are indeed strictly connected. We show that a CPA–ORL connection exists between pairs of points lying along lines close to each other in the 3D space-parameters of a realistic lossy atomic photonic crystal. The connection is expected to be a generic feature of wave scattering in non-Hermitian optical media encompassing, as a particular case, wave scattering in parity-time (PT) symmetric media. PMID:27759020

Multimodal optical setup based on spectrometer and cameras combination for biological tissue characterization with spatially modulated illumination

NASA Astrophysics Data System (ADS)

Baruch, Daniel; Abookasis, David

2017-04-01

The application of optical techniques as tools for biomedical research has generated substantial interest for the ability of such methodologies to simultaneously measure biochemical and morphological parameters of tissue. Ongoing optimization of optical techniques may introduce such tools as alternative or complementary to conventional methodologies. The common approach shared by current optical techniques lies in the independent acquisition of tissue's optical properties (i.e., absorption and reduced scattering coefficients) from reflected or transmitted light. Such optical parameters, in turn, provide detailed information regarding both the concentrations of clinically relevant chromophores and macroscopic structural variations in tissue. We couple a noncontact optical setup with a simple analysis algorithm to obtain absorption and scattering coefficients of biological samples under test. Technically, a portable picoprojector projects serial sinusoidal patterns at low and high spatial frequencies, while a spectrometer and two independent CCD cameras simultaneously acquire the reflected diffuse light through a single spectrometer and two separate CCD cameras having different bandpass filters at nonisosbestic and isosbestic wavelengths in front of each. This configuration fills the gaps in each other's capabilities for acquiring optical properties of tissue at high spectral and spatial resolution. Experiments were performed on both tissue-mimicking phantoms as well as hands of healthy human volunteers to quantify their optical properties as proof of concept for the present technique. In a separate experiment, we derived the optical properties of the hand skin from the measured diffuse reflectance, based on a recently developed camera model. Additionally, oxygen saturation levels of tissue measured by the system were found to agree well with reference values. Taken together, the present results demonstrate the potential of this integrated setup for diagnostic and research applications.

Effects of interlayer screening and temperature on dielectric functions of graphene by first-principles

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

Yang, J. Y.; Liu, L. H., E-mail: lhliu@hit.edu.cn; Department of Physics, Harbin Institute of Technology, Harbin 150001

2016-07-21

The dielectric functions of few-layer graphene and the related temperature dependence are investigated from the atomic scale using first-principles calculations. Compared with ellipsometry experiments in the spectral range of 190–2500 nm, the normalized optical constants of mono-layer graphene demonstrate good agreement and further validate first-principles calculations. To interpret dielectric function of mono-layer graphene, the electronic band structure and density of states are analyzed. By comparing dielectric functions of mono-, bi-, and tri-layer graphene, it shows that interlayer screening strengthens intraband transition and greatly enhances the absorption peak located around 1 eV. The strengthened optical absorption is intrinsically caused by the increasing electronmore » states near the Fermi level. To investigate temperature effect, the first-principles calculations and lattice dynamics are combined. The lattice vibration enhances parallel optical absorption peak around 1 eV and induces redshift. Moreover, it is observed that the van der Waals force plays a key role in keeping the interlayer distance stable during dynamics simulations.« less

Sensitive Spectroscopic Analysis of Biomarkers in Exhaled Breath

NASA Astrophysics Data System (ADS)

Bicer, A.; Bounds, J.; Zhu, F.; Kolomenskii, A. A.; Kaya, N.; Aluauee, E.; Amani, M.; Schuessler, H. A.

2018-06-01

We have developed a novel optical setup which is based on a high finesse cavity and absorption laser spectroscopy in the near-IR spectral region. In pilot experiments, spectrally resolved absorption measurements of biomarkers in exhaled breath, such as methane and acetone, were carried out using cavity ring-down spectroscopy (CRDS). With a 172-cm-long cavity, an efficient optical path of 132 km was achieved. The CRDS technique is well suited for such measurements due to its high sensitivity and good spectral resolution. The detection limits for methane of 8 ppbv and acetone of 2.1 ppbv with spectral sampling of 0.005 cm-1 were achieved, which allowed to analyze multicomponent gas mixtures and to observe absorption peaks of 12CH4 and 13CH4. Further improvements of the technique have the potential to realize diagnostics of health conditions based on a multicomponent analysis of breath samples.

Liquid crystal mediated active nano-plasmonic based on the formation of hybrid plasmonic-photonic modes

NASA Astrophysics Data System (ADS)

Mehrzad, Hossein; Mohajerani, Ezeddin

2018-02-01

The present study aims to demonstrate how active hybrid nano-plasmonic modes become excited due to the coupling of localized plasmonic resonance and Fabry-Perot (FP) optical modes. The proposed structure includes an integration of a micro-cavity filled with liquid crystals with high anisotropy and a layer of gold nanoislands (NIs). The optical absorption of NI is controllably discretized to the narrow-width modes, called "hybrid modes (HM)," due to the interplay between FP and plasmonic modes. HM could demonstrate a strongly intensified and diminished absorption, compared to the absorption of the bare gold layer. Based on the active plasmonic experiments, the HM boosted the figure of merit related to activation capability up to 40 times and subsequently experienced impressive spectral shifts, leading to very wavelength-selective changes. The theoretical simulation of the HM is provided to suggest relevant insights into the experimental results.

Bulk and surface electronic structures of MgO

NASA Astrophysics Data System (ADS)

Schönberger, U.; Aryasetiawan, F.

1995-09-01

The bulk electronic structure of MgO is calculated from first principles including correlation effects within the GW approximation. The band gap, the position of the 2s O band, and the valence band width are in good agreement with experiment. From the quasiparticle band structure, optical transitions corresponding to the main optical absorption peaks are identified. The energy-loss spectrum is also calculated and compared with experiment. The surface electronic structure of MgO(100) is calculated self-consistently within the local-density approximation. It is found that states observed in a recent photoemission experiment outside the bulk allowed states are close to surface states.

Nonlinear optical switching and optical limiting in colloidal CdSe quantum dots investigated by nanosecond Z-scan measurement

NASA Astrophysics Data System (ADS)

Valligatla, Sreeramulu; Haldar, Krishna Kanta; Patra, Amitava; Desai, Narayana Rao

2016-10-01

The semiconductor nanocrystals are found to be promising class of third order nonlinear optical materials because of quantum confinement effects. Here, we highlight the nonlinear optical switching and optical limiting of cadmium selenide (CdSe) quantum dots (QDs) using nanosecond Z-scan measurement. The intensity dependent nonlinear absorption and nonlinear refraction of CdSe QDs were investigated by applying the Z-scan technique with 532 nm, nanosecond laser pulses. At lower intensities, the nonlinear process is dominated by saturable absorption (SA) and it is changed to reverse saturable absorption (RSA) at higher intensities. The SA behaviour is attributed to the ground state bleaching and the RSA is ascribed to free carrier absorption (FCA) of CdSe QDs. The nonlinear optical switching behaviour and reverse saturable absorption makes CdSe QDs are good candidate for all-optical device and optical limiting applications.

Correction for specimen movement and rotation errors for in-vivo Optical Projection Tomography

PubMed Central

Birk, Udo Jochen; Rieckher, Matthias; Konstantinides, Nikos; Darrell, Alex; Sarasa-Renedo, Ana; Meyer, Heiko; Tavernarakis, Nektarios; Ripoll, Jorge

2010-01-01

The application of optical projection tomography to in-vivo experiments is limited by specimen movement during the acquisition. We present a set of mathematical correction methods applied to the acquired data stacks to correct for movement in both directions of the image plane. These methods have been applied to correct experimental data taken from in-vivo optical projection tomography experiments in Caenorhabditis elegans. Successful reconstructions for both fluorescence and white light (absorption) measurements are shown. Since no difference between movement of the animal and movement of the rotation axis is made, this approach at the same time removes artifacts due to mechanical drifts and errors in the assumed center of rotation. PMID:21258448

Near infrared spectrum simulation applied to human skin for diagnosis

NASA Astrophysics Data System (ADS)

Tsai, Chen-Mu; Fang, Yi-Chin; Wang, Chih-Yu; Chiu, Pin-Chun; Wu, Guo-Ying; Zheng, Wei-Chi; Chemg, Shih-Hao

2007-11-01

This research proposes a new method for skin diagnose using near infrared as the light source (750nm~1300nm). Compared to UV and visible light, near infrared might penetrate relatively deep into biological soft tissue in some cases although NIR absorption property of tissue is not a constant for water, fat, and collagen etc. In the research, NIR absorption and scattering properties for skin are discussed firstly using the theory of molecule vibration from Quantum physics and Solid State Physics; secondly the practical model for various NIR absorption spectrum to skin tissue are done by optical simulation for human skin. Finally, experiments are done for further identification of proposed model for human skin and its reaction to near infrared. Results show success with identification from both theory and experiments.

Physical and Optical Studies of Bi3+-Modified Erbium Doped Tellurite Glasses

NASA Astrophysics Data System (ADS)

Marzuki, Ahmad; Ega Fausta, Devara

2018-03-01

Er3+-doped tellurite glasses with various compositions (in mole%): 54TeO2-(41-x)ZnO-xBi2O3-2Na2O-3Er2O3 (x = 1, 2, 3, 4, and 5) were prepared with melt quenching method. Studies was aimed at investigating the effect of Bi3+ ion content on the physical and optical properties of the glasses. The density, refractive index, optical absorption, and optical energy band gap measurements were carried out at room temperature using pycnometer, Brewster angle method, and UV-VIS-NIR spectrophotometer, respectively. From the experiment, it was shown that the density and refractive index of the glasses increased with the increase of Bi3+ ions concentration. The absorption band intensity of electronic transition from 4I15/2 to 4H11/2 exhibited an increase as the Bi3+ ions concentration increase suggesting that incorporating Bi3+ ions into this glasses might improve the pumping efficiency.

Negative optical spin torque wrench of a non-diffracting non-paraxial fractional Bessel vortex beam

NASA Astrophysics Data System (ADS)

Mitri, F. G.

2016-10-01

An absorptive Rayleigh dielectric sphere in a non-diffracting non-paraxial fractional Bessel vortex beam experiences a spin torque. The axial and transverse radiation spin torque components are evaluated in the dipole approximation using the radiative correction of the electric field. Particular emphasis is given on the polarization as well as changing the topological charge α and the half-cone angle of the beam. When α is zero, the axial spin torque component vanishes. However, when α becomes a real positive number, the vortex beam induces left-handed (negative) axial spin torque as the sphere shifts off-axially from the center of the beam. The results show that a non-diffracting non-paraxial fractional Bessel vortex beam is capable of inducing a spin reversal of an absorptive Rayleigh sphere placed arbitrarily in its path. Potential applications are yet to be explored in particle manipulation, rotation in optical tweezers, optical tractor beams, and the design of optically-engineered metamaterials to name a few areas.

Host Model Uncertainty in Aerosol Radiative Forcing Estimates - The AeroCom Prescribed Experiment

NASA Astrophysics Data System (ADS)

Stier, P.; Kinne, S.; Bellouin, N.; Myhre, G.; Takemura, T.; Yu, H.; Randles, C.; Chung, C. E.

2012-04-01

Anthropogenic and natural aerosol radiative effects are recognized to affect global and regional climate. However, even for the case of identical aerosol emissions, the simulated direct aerosol radiative forcings show significant diversity among the AeroCom models (Schulz et al., 2006). Our analysis of aerosol absorption in the AeroCom models indicates a larger diversity in the translation from given aerosol radiative properties (absorption optical depth) to actual atmospheric absorption than in the translation of a given atmospheric burden of black carbon to the radiative properties (absorption optical depth). The large diversity is caused by differences in the simulated cloud fields, radiative transfer, the relative vertical distribution of aerosols and clouds, and the effective surface albedo. This indicates that differences in host model (GCM or CTM hosting the aerosol module) parameterizations contribute significantly to the simulated diversity of aerosol radiative forcing. The magnitude of these host model effects in global aerosol model and satellites retrieved aerosol radiative forcing estimates cannot be estimated from the diagnostics of the "standard" AeroCom forcing experiments. To quantify the contribution of differences in the host models to the simulated aerosol radiative forcing and absorption we conduct the AeroCom Prescribed experiment, a simple aerosol model and satellite retrieval intercomparison with prescribed highly idealised aerosol fields. Quality checks, such as diagnostic output of the 3D aerosol fields as implemented in each model, ensure the comparability of the aerosol implementation in the participating models. The simulated forcing variability among the models and retrievals is a direct measure of the contribution of host model assumptions to the uncertainty in the assessment of the aerosol radiative effects. We will present the results from the AeroCom prescribed experiment with focus on the attribution to the simulated variability to parametric and structural model uncertainties. This work will help to prioritise areas for future model improvements and ultimately lead to uncertainty reduction.

Optical properties of human colon tissues in the 350 – 2500 nm spectral range

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

Bashkatov, A N; Genina, E A; Kochubey, V I

2014-08-31

We present the optical characteristics of the mucosa and submucosa of human colon tissue. The experiments are performed in vitro using a LAMBDA 950 spectrophotometer in the 350 – 2500 nm spectral range. The absorption and scattering coefficients and the scattering anisotropy factor are calculated based on the measured diffuse reflectance and total and collimated transmittance spectra using the inverse Monte Carlo method. (laser biophotonics)

A comparative review of optical surface contamination assessment techniques

NASA Technical Reports Server (NTRS)

Heaney, James B.

1987-01-01

This paper will review the relative sensitivities and practicalities of the common surface analytical methods that are used to detect and identify unwelcome adsorbants on optical surfaces. The compared methods include visual inspection, simple reflectometry and transmissiometry, ellipsometry, infrared absorption and attenuated total reflectance spectroscopy (ATR), Auger electron spectroscopy (AES), scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS), and mass accretion determined by quartz crystal microbalance (QCM). The discussion is biased toward those methods that apply optical thin film analytical techniques to spacecraft optical contamination problems. Examples are cited from both ground based and in-orbit experiments.

Single layer of MX3(M = Ti, Zr; X = S, Se, Te): a new platform for nano-electronics and optics

NASA Astrophysics Data System (ADS)

Jin, Yingdi; Li, Xingxing; Yang, Jinlong

A serial of two dimensional titanium and zirconium trichalcogenides nanosheets MX3 (M=Ti, Zr; X=S, Se, Te) are investigated based on first-principles calculations. The evaluated low cleavage energy indicates that stable two dimensional monolayers can be exfoliated from their bulk crystals in experiment. Electronic studies reveal very rich electronic properties in these monolayers, including metallic TiTe3 and ZrTe3, direct band gap semiconductor TiS3 and indirect band gap semiconductors TiSe3, ZrS3 and ZrSe3. The band gaps of all the semiconductors are between 0.57~1.90 eV, which implies their potential applications in nano-electronics. And the calculated effective masses demonstrate highly anisotropic conduction properties for all the semiconductors. Optically, TiS3 and TiSe3 monolayers exhibit good light absorption in the visible and near-infrared region respectively, indicating their potential applications in optical devices. In particular, the highly anisotropic optical absorption of TiS3 monolayer suggests it could be used in designing nano optical waveguide polarizers.

EDGES result versus CMB and low-redshift constraints on ionization histories

NASA Astrophysics Data System (ADS)

Witte, Samuel; Villanueva-Domingo, Pablo; Gariazzo, Stefano; Mena, Olga; Palomares-Ruiz, Sergio

2018-05-01

We examine the results from the Experiment to Detect the Global Epoch of Reionization Signature (EDGES), which has recently claimed the detection of a strong absorption in the 21 cm hyperfine transition line of neutral hydrogen, at redshifts demarcating the early stages of star formation. More concretely, we study the compatibility of the shape of the EDGES absorption profile, centered at a redshift of z ˜17.2 , with measurements of the reionization optical depth, the Gunn-Peterson optical depth, and Lyman-α emission from star-forming galaxies, for a variety of possible reionization models within the standard Λ CDM framework (that is, a Universe with a cosmological constant Λ and cold dark matter CDM). When, conservatively, we only try to accommodate the location of the absorption dip, we identify a region in the parameter space of the astrophysical parameters that successfully explains all of the aforementioned observations. However, one of the most abnormal features of the EDGES measurement is the absorption amplitude, which is roughly a factor of 2 larger than the maximum allowed value in the Λ CDM framework. We point out that the simple considered astrophysical models that produce the largest absorption amplitudes are unable to explain the depth of the dip and of reproducing the observed shape of the absorption profile.

Multispectral breast imaging using a ten-wavelength, 64 x 64 source/detector channels silicon photodiode-based diffuse optical tomography system.

PubMed

Li, Changqing; Zhao, Hongzhi; Anderson, Bonnie; Jiang, Huabei

2006-03-01

We describe a compact diffuse optical tomography system specifically designed for breast imaging. The system consists of 64 silicon photodiode detectors, 64 excitation points, and 10 diode lasers in the near-infrared region, allowing multispectral, three-dimensional optical imaging of breast tissue. We also detail the system performance and optimization through a calibration procedure. The system is evaluated using tissue-like phantom experiments and an in vivo clinic experiment. Quantitative two-dimensional (2D) and three-dimensional (3D) images of absorption and reduced scattering coefficients are obtained from these experiments. The ten-wavelength spectra of the extracted reduced scattering coefficient enable quantitative morphological images to be reconstructed with this system. From the in vivo clinic experiment, functional images including deoxyhemoglobin, oxyhemoglobin, and water concentration are recovered and tumors are detected with correct size and position compared with the mammography.

Connections Between Theory and Experiment for Gold and Silver Nanoclusters.

PubMed

Weerawardene, K L Dimuthu M; Häkkinen, Hannu; Aikens, Christine M

2018-04-20

Ligand-stabilized gold and silver nanoparticles are of tremendous current interest in sensing, catalysis, and energy applications. Experimental and theoretical studies have closely interacted to elucidate properties such as the geometric and electronic structures of these fascinating systems. In this review, the interplay between theory and experiment is described; areas such as optical absorption and doping, where the theory-experiment connections are well established, are discussed in detail; and the current status of these connections in newer fields of study, such as luminescence, transient absorption, and the effects of solvent and the surrounding environment, are highlighted. Close communication between theory and experiment has been extremely valuable for developing an understanding of these nanocluster systems in the past decade and will undoubtedly continue to play a major role in future years.

Connections Between Theory and Experiment for Gold and Silver Nanoclusters

NASA Astrophysics Data System (ADS)

Weerawardene, K. L. Dimuthu M.; Häkkinen, Hannu; Aikens, Christine M.

2018-04-01

Ligand-stabilized gold and silver nanoparticles are of tremendous current interest in sensing, catalysis, and energy applications. Experimental and theoretical studies have closely interacted to elucidate properties such as the geometric and electronic structures of these fascinating systems. In this review, the interplay between theory and experiment is described; areas such as optical absorption and doping, where the theory-experiment connections are well established, are discussed in detail; and the current status of these connections in newer fields of study, such as luminescence, transient absorption, and the effects of solvent and the surrounding environment, are highlighted. Close communication between theory and experiment has been extremely valuable for developing an understanding of these nanocluster systems in the past decade and will undoubtedly continue to play a major role in future years.

Shortwave Radiative Fluxes, Solar-Beam Transmissions, and Aerosol Properties: TARFOX and ACE-2 Find More Absorption from Flux Radiometry than from Other Measurements

NASA Technical Reports Server (NTRS)

Russell, Philip B.; Redemann, J.; Schmid, B.; Livingston, J. M.; Bergstrom, R. W.; Ramirez, S. A.; Hipskind, R. Stephen (Technical Monitor)

2001-01-01

The Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) and the Second Aerosol Characterization Experiment (ACE-2) made simultaneous measurements of shortwave radiative fluxes, solar-beam transmissions, and the aerosols affecting those fluxes and transmissions. Besides the measured fluxes and transmissions, other obtained properties include aerosol scattering and absorption measured in situ at the surface and aloft; aerosol single scattering albedo retrieved from skylight radiances; and aerosol complex refractive index derived by combining profiles of backscatter, extinction, and size distribution. These measurements of North Atlantic boundary layer aerosols impacted by anthropogenic pollution revealed the following characteristic results: (1) Better agreement among different types of remote measurements of aerosols (e.g., optical depth, extinction, and backscattering from sunphotometers, satellites, and lidars) than between remote and in situ measurements; 2) More extinction derived from transmission measurements than from in situ measurements; (3) Larger aerosol absorption inferred from flux radiometry than from other measurements. When the measured relationships between downwelling flux and optical depth (or beam transmission) are used to derive best-fit single scattering albedos for the polluted boundary layer aerosol, both TARFOX and ACE-2 yield midvisible values of 0.90 +/- 0.04. The other techniques give larger single scattering albedos (i.e. less absorption) for the polluted boundary layer, with a typical result of 0.95 +/- 0.04. Although the flux-based results have the virtue of describing the column aerosol unperturbed by sampling, they are subject to questions about representativeness and other uncertainties (e.g., unknown gas absorption). Current uncertainties in aerosol single scattering albedo are large in terms of climate effects. They also have an important influence on aerosol optical depths retrieved from satellite radiances. More tests are needed of the consistency among different methods and of the effects of changing humidity on aerosol.

Statistical Fine Structure of Inhomogeneously Broadened Absorption Lines.

DTIC Science & Technology

1987-07-31

inhomogeneously broadened optical absorption of pentacene n p-terphenyl at liquid helium temperatures... SFS is the actual frequency- ependent, time...statistical fine structure (SFS) in the inhomogeneously broadened optical absorption of pentacene in p-terphenyl at liquid helium temperatures. SFS is the...quite difficult . -2- We have observed for the first time statistical fine structure in the inhomogeneously broadened optical absorption of pentacene

Application of the Mattis-Bardeen theory in strongly disordered superconductors

NASA Astrophysics Data System (ADS)

Seibold, G.; Benfatto, L.; Castellani, C.

2017-10-01

The low-energy optical conductivity of conventional superconductors is usually well described by Mattis-Bardeen (MB) theory, which predicts the onset of absorption above an energy corresponding to twice the superconducing (SC) gap parameter Δ . Recent experiments on strongly disordered superconductors have challenged the application of the MB formulas due to the occurrence of additional spectral weight at low energies below 2 Δ . Here we identify three crucial items that have to be included in the analysis of optical-conductivity data for these systems: (a) the correct identification of the optical threshold in the Mattis-Bardeen theory and its relation with the gap value extracted from the measured density of states, (b) the gauge-invariant evaluation of the current-current response function needed to account for the optical absorption by SC collective modes, and (c) the inclusion into the MB formula of the energy dependence of the density of states present already above Tc. By computing the optical conductivity in the disordered attractive Hubbard model, we analyze the relevance of all these items, and we provide a compelling scheme for the analysis and interpretation of the optical data in real materials.

Linking Aerosol Optical Properties Between Laboratory, Field, and Model Studies

NASA Astrophysics Data System (ADS)

Murphy, S. M.; Pokhrel, R. P.; Foster, K. A.; Brown, H.; Liu, X.

2017-12-01

The optical properties of aerosol emissions from biomass burning have a significant impact on the Earth's radiative balance. Based on measurements made during the Fourth Fire Lab in Missoula Experiment, our group published a series of parameterizations that related optical properties (single scattering albedo and absorption due to brown carbon at multiple wavelengths) to the elemental to total carbon ratio of aerosols emitted from biomass burning. In this presentation, the ability of these parameterizations to simulate the optical properties of ambient aerosol is assessed using observations collected in 2017 from our mobile laboratory chasing wildfires in the Western United States. The ambient data includes measurements of multi-wavelength absorption, scattering, and extinction, size distribution, chemical composition, and volatility. In addition to testing the laboratory parameterizations, this combination of measurements allows us to assess the ability of core-shell Mie Theory to replicate observations and to assess the impact of brown carbon and mixing state on optical properties. Finally, both laboratory and ambient data are compared to the optical properties generated by a prominent climate model (Community Earth System Model (CESM) coupled with the Community Atmosphere Model (CAM 5)). The discrepancies between lab observations, ambient observations and model output will be discussed.

Pulse duration dependent nonlinear optical response in black phosphorus dispersions

NASA Astrophysics Data System (ADS)

Tang, Shana; He, Zhiliang; Liang, Guowen; Chen, Si; Ge, Yanqi; Sang, David K.; Lu, Jianxin; Lu, Shunbin; Wen, Qiao; Zhang, Han

2018-01-01

Black phosphorus (BP), is the most thermodynamically stable allotrope of phosphorus, the narrow direct band gap and the strong light-matter interaction make BP a promising nonlinear optical (NLO) nano-material. In this paper, we use the open aperture Z- scan method to measure the NLO property of BP dispersion. Saturable absorption was observed in the BP material through the excitation of Ti: sapphire laser at 800 nm. Three different excitation pulse duration (100 fs, 1 ps and 10 ps) were used in the experiments, and BP exhibited different NLO performance. The results show that nonlinear absorption coefficient and figure of merit of BP nanosheets are proportional to the pulse duration while saturable intensity is opposite to pulse duration.

Strong anisotropic optical conductivity in two-dimensional puckered structures: The role of the Rashba effect

NASA Astrophysics Data System (ADS)

Saberi-Pouya, S.; Vazifehshenas, T.; Salavati-fard, T.; Farmanbar, M.; Peeters, F. M.

2017-08-01

We calculate the optical conductivity of an anisotropic two-dimensional system with Rashba spin-flip excitation within the Kubo formalism. We show that the anisotropic Rashba effect caused by an external field significantly changes the magnitude of the spin splitting. Furthermore, we obtain an analytical expression for the longitudinal optical conductivity associated with interband transitions as a function of the frequency for arbitrary polarization angle. We find that the diagonal components of the optical conductivity tensor are direction dependent and the optical absorption spectrum exhibits a strongly anisotropic absorption window. The height and width of this absorption window are very sensitive to the anisotropy of the system. While the height of absorption peak increases with increasing effective mass anisotropy ratio, the peak intensity is larger when the light polarization is along the armchair direction. Moreover, the absorption peak width becomes broader as the density-of-states mass or Rashba interaction is enhanced. These features in the optical absorption spectrum can be used to determine parameters relevant for spintronics.

Magnetic hyperthermia study in water based magnetic fluids containing TMAOH coated Fe3O4 using infrared thermography

NASA Astrophysics Data System (ADS)

Lahiri, B. B.; Ranoo, Surojit; Philip, John

2017-01-01

We study the alternating magnetic field induced heating of a water based ferrofluid containing tetramethyl ammonium hydroxide coated iron oxide nanoparticles using infrared thermography and compare the results obtained from the conventional fiber optic temperature sensor. Experiments are performed on ferrofluid samples of five different concentrations and under four different external field amplitudes at a fixed frequency. The temperature rise curves measured using both the infrared thermography and fiber optic sensor are found to be very similar up to a certain time interval, above which deviations are observed, which are attributed to the internal and external convection phenomena. A correction methodology is developed to account for the convection losses. The convection corrected specific absorption rate is found to be in good agreement with the values obtained from the conventional fiber optic temperature sensor, within a maximum error of ±3.4%. The highest specific absorption rate obtained in the present study is 135.98 (±4.6) W/gFe for a sample concentration of 3 wt.%, at an external field amplitude and a frequency of 63.0 kA m-1 and 126 kHz, respectively. The specific absorption rate is found to decrease with increasing sample concentration, due to the enhancement of dipolar interaction with increasing sample concentration due to agglomeration. This study validates the efficacy and universal applicability of IRT as an alternate, real time, non-contact and wide area temperature measurement methodology for magnetic fluid hyperthermia experiments without any sample contamination.

Measurement of radiation damage on an epoxy-based optical glue

NASA Astrophysics Data System (ADS)

Huang, H. C.; Peng, K. C.; Sahu, S. K.; Ueno, K.; Chang, Y. H.; Wang, C. H.; Hou, W. S.

1997-02-01

We measured the radiation damage on an optical glue called Eccobond-24, which is a candidate for CsI and BGO crystal calorimeters of the BELLE detector of the KEK B-factory. Absorption spectrophotometry in the range 300-800 nm was used to monitor the radiation damage. The maximum equivalent dose was 1.64 Mrad. The glue shows effects of damage, but is acceptable for the radiation level in the above-mentioned experiment.

First-principles study of structural, electronic, and optical properties of surface defects in GaAs(001) - β2(2x4)

NASA Astrophysics Data System (ADS)

Bacuyag, Dhonny; Escaño, Mary Clare Sison; David, Melanie; Tani, Masahiko

2018-06-01

We performed first-principles calculations based on density functional theory (DFT) to investigate the role of point defects in the structural, electronic, and optical properties of the GaAs(001)- β2(2x4). In terms of structural properties, AsGa is the most stable defect structure, consistent with experiments. With respect to the electronic structure, band structures revealed the existence of sub-band and midgap states for all defects. The induced sub-bands and midgap states originated from the redistributions of charges towards these defects and neighboring atoms. The presence of these point defects introduced deep energy levels characteristic of EB3 (0.97 eV), EL4 (0.52 eV), and EL2 (0.82 eV) for AsGa, GaAs, GaV, respectively. The optical properties are found to be strongly related to these induced gap states. The calculated onset values in the absorption spectra, corresponding to the energy gaps, confirmed the absorption below the known bulk band gap of 1.43 eV. These support the possible two-step photoabsorption mediated by midgap states as observed in experiments.

The THz time domain spectra of SrB4O7 crystal

NASA Astrophysics Data System (ADS)

Wang, Yali; Hou, Bihui; Wang, Haiyan; Zhao, Guozhong; Shi, Yishi

2010-11-01

SrB4O7 (SBO) is a promising nonlinear optical crystal. It has the orthorhombic structure with group classified as Pnm2. The sample for the experiment was cut along the (001) plane and twin polishing with 1.632mm thickness. It exhibits a wider transparency range from UV to far-IR. And its absorption edge lies at 160nm. The forbidden band gap is about 7.76eV. The THz spectra of SBO crystal had been studied from 0.1 to 2.5THz. The THz time domain spectrum of SBO shows the strong resonance characters. In THz experiment, the vertical incident electromagnetic waves radiate the polished side twice along (001) orientation. The crystal turned 90 degrees relative to the first in the vertical direction. There are different optical properties in two directions. We gained the curves of the refractive index and absorption coefficient dependence of frequency in the region of 0.1-2.5THz. The absorption curves shows opposite parabola character. One is upward opening and the largest absorption coefficient is 10cm-1. The other is down opening and the less absorption coefficient is 1cm-1. The refractive index n is stable linear with frequency and it is 3 from 0.4THz to 2.5THz. But the refractive index of two directions shows the opposite tendency from 0.1 to 0.4THz. The reason of the difference is that polarized beam radiates the orthorhombic crystal. The properties of the sample show that it is possible to apply it to laser field.

Low Earth Orbit Environmental Durability of Recently Developed Thermal Control Coatings

NASA Technical Reports Server (NTRS)

Jaworske, Donald A.

2015-01-01

The Materials International Space Station Experiment provided a means to expose materials and devices to the low Earth orbit environment on the exterior of the International Space Station. By returning the specimens to Earth after flight, the specimens could be evaluated by comparison with pre-flight measurements. One area of continuing interest is thermal control paints and coatings that are applied to exterior surfaces of spacecraft. Though traditional radiator coatings have been available for decades, recent work has focused on new coatings that offer custom deposition or custom optical properties. The custom deposition of interest is plasma spraying and one type of coating recently developed as part of a Small Business Innovative Research effort was designed to be plasma sprayed onto radiator surfaces. The custom optical properties of interest are opposite to those of a typical radiator coating, having a combination of high solar absorptance and low infrared emittance for solar absorber applications, and achieved in practice via a cermet coating. Selected specimens of the plasma sprayed coatings and the solar absorber coating were flown on Materials International Space Station Experiment 7, and were recently returned to Earth for post-flight analyses. For the plasma sprayed coatings in the ram direction, one specimen increased in solar absorptance and one specimen decreased in solar absorptance, while the plasma sprayed coatings in the wake direction changed very little in solar absorptance. For the cermet coating deployed in both the ram and wake directions, the solar absorptance increased. Interestingly, all coatings showed little change in infrared emittance.

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

NASA Astrophysics Data System (ADS)

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

2012-06-01

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

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

PubMed Central

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

2012-01-01

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

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

PubMed

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

2012-06-01

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

First principles electron-correlated calculations of optical absorption in magnesium clusters★

NASA Astrophysics Data System (ADS)

Shinde, Ravindra; Shukla, Alok

2017-11-01

In this paper, we report large-scale configuration interaction (CI) calculations of linear optical absorption spectra of various isomers of magnesium clusters Mgn (n = 2-5), corresponding to valence transitions. Geometry optimization of several low-lying isomers of each cluster was carried out using coupled-cluster singles doubles (CCSD) approach, and these geometries were subsequently employed to perform ground and excited state calculations using either the full-CI (FCI) or the multi-reference singles-doubles configuration interaction (MRSDCI) approach, within the frozen-core approximation. Our calculated photoabsorption spectrum of magnesium dimer (Mg2) is in excellent agreement with the experiments both for peak positions, and intensities. Owing to the sufficiently inclusive electron-correlation effects, these results can serve as benchmarks against which future experiments, as well as calculations performed using other theoretical approaches, can be tested. Supplementary material in the form of one pdf fille available from the Journal web page at http://https://doi.org/10.1140/epjd/e2017-80356-6.

Application of focused-beam flat-sample method to synchrotron powder X-ray diffraction with anomalous scattering effect

NASA Astrophysics Data System (ADS)

Tanaka, M.; Katsuya, Y.; Matsushita, Y.

2013-03-01

The focused-beam flat-sample method (FFM), which is a method for high-resolution and rapid synchrotron X-ray powder diffraction measurements by combination of beam focusing optics, a flat shape sample and an area detector, was applied for diffraction experiments with anomalous scattering effect. The advantages of FFM for anomalous diffraction were absorption correction without approximation, rapid data collection by an area detector and good signal-to-noise ratio data by focusing optics. In the X-ray diffraction experiments of CoFe2O4 and Fe3O4 (By FFM) using X-rays near the Fe K absorption edge, the anomalous scattering effect between Fe/Co or Fe2+/Fe3+ can be clearly detected, due to the change of diffraction intensity. The change of observed diffraction intensity as the incident X-ray energy was consistent with the calculation. The FFM is expected to be a method for anomalous powder diffraction.

Broadband optical absorption by tunable Mie resonances in silicon nanocone arrays

DOE PAGES

Wang, Z. Y.; Zhang, R. J.; Wang, S. Y.; ...

2015-01-15

Nanostructure arrays such as nanowire, nanopillar, and nanocone arrays have been proposed to be promising antireflection structures for photovoltaic applications due to their great light trapping ability. In this paper, the optical properties of Si nanopillar and nanocone arrays in visible and infrared region were studied by both theoretical calculations and experiments. The results show that the Mie resonance can be continuously tuned across a wide range of wavelength by varying the diameter of the nanopillars. However, Si nanopillar array with uniform diameter exhibits only discrete resonance mode, thus can't achieve a high broadband absorption. On the other hand, themore » Mie resonance wavelength in a Si nanocone array can vary continuously as the diameters of the cross sections increase from the apex to the base. Therefore Si nanocone arrays can strongly interact with the incident light in the broadband spectrum and the absorbance by Si nanocone arrays is higher than 95% over the wavelength from 300 to 2000 nm. In addition to the Mie resonance, the broadband optical absorption of Si nanocone arrays is also affected by Wood-Rayleigh anomaly effect and metal impurities introduced in the fabrication process.« less

Broadband optical absorption by tunable Mie resonances in silicon nanocone arrays

PubMed Central

Wang, Z. Y.; Zhang, R. J.; Wang, S. Y.; Lu, M.; Chen, X.; Zheng, Y. X.; Chen, L. Y.; Ye, Z.; Wang, C. Z.; Ho, K. M.

2015-01-01

Nanostructure arrays such as nanowire, nanopillar, and nanocone arrays have been proposed to be promising antireflection structures for photovoltaic applications due to their great light trapping ability. In this paper, the optical properties of Si nanopillar and nanocone arrays in visible and infrared region were studied by both theoretical calculations and experiments. The results show that the Mie resonance can be continuously tuned across a wide range of wavelength by varying the diameter of the nanopillars. However, Si nanopillar array with uniform diameter exhibits only discrete resonance mode, thus can't achieve a high broadband absorption. On the other hand, the Mie resonance wavelength in a Si nanocone array can vary continuously as the diameters of the cross sections increase from the apex to the base. Therefore Si nanocone arrays can strongly interact with the incident light in the broadband spectrum and the absorbance by Si nanocone arrays is higher than 95% over the wavelength from 300 to 2000 nm. In addition to the Mie resonance, the broadband optical absorption of Si nanocone arrays is also affected by Wood-Rayleigh anomaly effect and metal impurities introduced in the fabrication process. PMID:25589290

In situ sensing of subsurface contamination--part I: near-infrared spectral characterization of alkanes, aromatics, and chlorinated hydrocarbons.

PubMed

Klavarioti, Maria; Kostarelos, Konstantinos; Pourjabbar, Anahita; Ghandehari, Masoud

2014-05-01

There is an imperative need for a chemical sensor capable of remote, in situ, long-term monitoring of chemical species at sites containing toxic chemical spills, specifically at chemical waste dumps, landfills, and locations with underground storage tanks. In the current research, a series of experiments were conducted measuring the near-infrared optical absorption of alkanes, aromatics, and chlorinated hydrocarbons. A spectral library was then developed to characterize the optical spectra of liquid hydrocarbons. Near-infrared analysis was chosen due to compatibility with optical fibers. The goal was to differentiate between classes of hydrocarbons and to also discriminate between compounds within a class of similar molecular structures. It was observed that unique absorption spectra can be obtained for each hydrocarbon, and this uniqueness can be used to discriminate between hydrocarbons from different families. Statistical analyses, namely, principal component analysis (PCA) and correlation coefficient (Spearman and Pearson methods), were attempted to match absorption spectra from an unknown hydrocarbon with the database with limited success. An algorithm was subsequently written to identify the characteristic peaks of each hydrocarbon that could be used to match data from an unknown chemical species with the database.

Tuning the nonlinear optical absorption in Au/BaTiO3 nanocomposites with gold nanoparticle concentration

NASA Astrophysics Data System (ADS)

Bijeesh, M. M.; Shakhi, P. K.; Varier, Geetha K.; Nandakumar, P.

2018-06-01

We report on the nonlinear optical absorption coefficient of Au/BaTiO3 nanocomposite films and its dependence on gold nanoparticle concentration. Au/BaTiO3 nanocomposite films with different molar ratio of Au/Ba are prepared by sol-gel technique and characterized by X-ray diffraction, UV Visible absorption spectroscopy and high resolution transmission electron microscopy. An open aperture Z-scan technique is employed to study the third order nonlinear optical properties of Au/BaTiO3 thin films. An Nd:YAG laser operating at 532 nm wavelength having a pulse width of 5 ns is used for the measurements. The two-photon absorption coefficient of the films increases linearly with gold nanoparticle concentration and significant enhancement of nonlinear optical absorption is observed. This ability to fine tune the nonlinear optical coefficients of Au/BaTiO3 films would be handy in optical device applications.

Subbarrier absorption in a stationary superlattice

NASA Technical Reports Server (NTRS)

Arutyunyan, G. M.; Nerkararyan, K. V.

1984-01-01

The calculation of the interband absorption coefficient was carried out in the classical case, when the frequency of light was assumed to bind two miniband subbarrier states of different bands. The influence of two dimensional Mott excitons on this absorption was studied and a comparison was made with the experiment. All of these considerations were done taking into account the photon wave vector (the phase spatial heterogeneity). The basic traits of the energy spectra of superlattice semiconductors, their kinetic and optical properties, and possible means of electromagnetic wave intensification were examined. By the density matrix method, a theory of electrical and electromagnetic properties of superlattices was suggested.

Super-resolution atomic force photoactivated microscopy of biological samples (Conference Presentation)

NASA Astrophysics Data System (ADS)

Lee, Seunghyun; Kim, Hyemin; Shin, Seungjun; Doh, Junsang; Kim, Chulhong

2017-03-01

Optical microscopy (OM) and photoacoustic microscopy (PAM) have previously been used to image the optical absorption of intercellular features of biological cells. However, the optical diffraction limit ( 200 nm) makes it difficult for these modalities to image nanoscale inner cell structures and the distribution of internal cell components. Although super-resolution fluorescence microscopy, such as stimulated emission depletion microscopy (STED) and stochastic optical reconstruction microscopy (STORM), has successfully performed nanoscale biological imaging, these modalities require the use of exogenous fluorescence agents, which are unfavorable for biological samples. Our newly developed atomic force photoactivated microscopy (AFPM) can provide optical absorption images with nanoscale lateral resolution without any exogenous contrast agents. AFPM combines conventional atomic force microscopy (AFM) and an optical excitation system, and simultaneously provides multiple contrasts, such as the topography and magnitude of optical absorption. AFPM can detect the intrinsic optical absorption of samples with 8 nm lateral resolution, easily overcoming the diffraction limit. Using the label-free AFPM system, we have successfully imaged the optical absorption properties of a single melanoma cell (B16F10) and a rosette leaf epidermal cell of Arabidopsis (ecotype Columbia (Col-0)) with nanoscale lateral resolution. The remarkable images show the melanosome distribution of a melanoma cell and the biological structures of a plant cell. AFPM provides superior imaging of optical absorption with a nanoscale lateral resolution, and it promises to become widely used in biological and chemical research.

Structural, electronic, and optical properties of representative Cu-flavonoid complexes.

PubMed

Lekka, Ch E; Ren, Jun; Meng, Sheng; Kaxiras, Efthimios

2009-05-07

We present density functional theory (DFT) results on the structural, electronic, and optical properties of Cu-flavonoid complexes for molar ratios 1:1, 1:2, and 1:3. We find that the preferred chelating site is close to the 4-oxo group and in particular the 3-4 site followed by the 3'-4' dihydroxy group in ring B. For the Cu-quercetin complexes, the large bathochromic shift of the first absorbance band upon complexation, which is in good agreement with experimental UV-vis spectra, results from the reduction of the electronic energy gap. The HOMO states for these complexes are characterized by pi-bonding between the Cu d orbitals and the C, O p orbitals except for the case of 1:1 complex (spin minority), which corresponds to sigma-type bonds. The LUMO states are attributed to the contribution of Cu p(z) orbitals. Consequently, the main features of the first optical absorption maxima are essentially due to pi --> pi transitions, while the 1:1 complex exhibits also sigma --> pi transitions. Our optical absorption calculations based on time-dependent DFT demonstrate that the 1:1 complex is responsible for the spectroscopic features at pH 5.5, whereas the 1:2 complex is mainly the one responsible for the characteristic spectra at pH 7.4. These theoretical predictions explain in detail the behavior of the optical absorption for the Cu-flavonoid complexes observed in experiments and are thus useful in elucidating the complexation mechanism and antioxidant activity of flavonoids.

Effects of acoustic- and optical-phonon sidebands on the fundamental optical-absorption edge in crystals and disordered semiconductors

NASA Astrophysics Data System (ADS)

Grein, C. H.; John, Sajeev

1990-04-01

We present the results of a parameter-free first-principles theory for the fine structure of the Urbach optical-absorption edge in crystalline and disordered semiconductors. The dominant features are recaptured by means of a simple physical argument based on the most probable potential-well analogy. At finite temperatures, the overall linear exponential Urbach behavior of the subgap optical-absorption coefficient is a consequence of multiple LA-phonon emission and absorption sidebands that accompany the electronic transition. The fine structure of subgap absorption spectra observed in some materials is accounted for by multiple TO-, LO-, and TA-phonon absorption and emission sidebands. Good agreement is found with experimental data on crystalline silicon. The effects of nonadiabaticity in the electron-phonon interaction are calculated.

Constraining Aerosol Optical Models Using Ground-Based, Collocated Particle Size and Mass Measurements in Variable Air Mass Regimes During the 7-SEAS/Dongsha Experiment

NASA Technical Reports Server (NTRS)

Bell, Shaun W.; Hansell, Richard A.; Chow, Judith C.; Tsay, Si-Chee; Wang, Sheng-Hsiang; Ji, Qiang; Li, Can; Watson, John G.; Khlystov, Andrey

2012-01-01

During the spring of 2010, NASA Goddard's COMMIT ground-based mobile laboratory was stationed on Dongsha Island off the southwest coast of Taiwan, in preparation for the upcoming 2012 7-SEAS field campaign. The measurement period offered a unique opportunity for conducting detailed investigations of the optical properties of aerosols associated with different air mass regimes including background maritime and those contaminated by anthropogenic air pollution and mineral dust. What appears to be the first time for this region, a shortwave optical closure experiment for both scattering and absorption was attempted over a 12-day period during which aerosols exhibited the most change. Constraints to the optical model included combined SMPS and APS number concentration data for a continuum of fine and coarse-mode particle sizes up to PM2.5. We also take advantage of an IMPROVE chemical sampler to help constrain aerosol composition and mass partitioning of key elemental species including sea-salt, particulate organic matter, soil, non sea-salt sulphate, nitrate, and elemental carbon. Our results demonstrate that the observed aerosol scattering and absorption for these diverse air masses are reasonably captured by the model, where peak aerosol events and transitions between key aerosols types are evident. Signatures of heavy polluted aerosol composed mostly of ammonium and non sea-salt sulphate mixed with some dust with transitions to background sea-salt conditions are apparent in the absorption data, which is particularly reassuring owing to the large variability in the imaginary component of the refractive indices. Extinctive features at significantly smaller time scales than the one-day sample period of IMPROVE are more difficult to reproduce, as this requires further knowledge concerning the source apportionment of major chemical components in the model. Consistency between the measured and modeled optical parameters serves as an important link for advancing remote sensing and climate research studies in dynamic aerosol-rich environments like Dongsha.

Synthesis of Silver Nanoprisms with Variable Size and Investigation of Their Optical Properties: A First-Year Undergraduate Experiment Exploring Plasmonic Nanoparticles

ERIC Educational Resources Information Center

Frank, Andrew J.; Cathcart, Nicole; Maly, Kenneth E.; Kitaev, Vladimir

2010-01-01

A robust and reasonably simple experiment is described that introduces students to the visualization of nanoscale properties and is intended for a first-year laboratory. Silver nanoprisms (NPs) that display different colors due to variation of their plasmonic absorption with respect to size are prepared. Control over the size of the silver…

Multiple-Path-Length Optical Absorbance Cell

NASA Technical Reports Server (NTRS)

2001-01-01

An optical absorbance cell that offers a selection of multiple optical path lengths has been developed as part of a portable spectrometric instrument that measures absorption spectra of small samples of water and that costs less than does a conventional, non-portable laboratory spectrometer. The instrument is intended, more specifically, for use in studying colored dissolved organic matter (CDOM) in seawater, especially in coastal regions. Accurate characterization of CDOM is necessary for building bio-optical mathematical models of seawater. The multiple path lengths of the absorption cell afford a wide range of sensitivity needed for measuring the optical absorbances associated with the wide range of concentrations of CDOM observed in nature. The instrument operates in the wavelength range of 370 to 725 nm. The major subsystems of the instrument (see figure) include a color-balanced light source; the absorption cell; a peristaltic pump; a high-precision, low-noise fiber optic spectrometer; and a laptop or other personal computer. A fiber-optic cable transmits light from the source to the absorption cell. Other optical fibers transmit light from the absorption cell to the spectrometer,

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.

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

PubMed Central

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

2013-01-01

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

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

PubMed

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

2013-09-01

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

Phantom Preparation and Optical Property Determination

NASA Astrophysics Data System (ADS)

He, Di; He, Jie; Mao, Heng

2018-12-01

Tissue-like optical phantoms are important in testing new imaging algorithms. Homogeneous optical phantoms with determined optical properties are the first step of making a proper heterogeneous phantom for multi-modality imaging. Typical recipes for such phantoms consist of epoxy resin, hardener, India ink and titanium oxide. By altering the concentration of India ink and titanium oxide, we are able to get multiple homogeneous phantoms with different absorption and scattering coefficients by carefully mixing all the ingredients. After fabricating the phantoms, we need to find their individual optical properties including the absorption and scattering coefficients. This is achieved by solving diffusion equation of each phantom as a homogeneous slab under canonical illumination. We solve the diffusion equation of homogeneous slab in frequency domain and get the formula for theoretical measurements. Under our steady-state diffused optical tomography (DOT) imaging system, we are able to obtain the real distribution of the incident light produced by a laser. With this source distribution we got and the formula we derived, numerical experiments show how measurements change while varying the value of absorption and scattering coefficients. Then we notice that the measurements alone will not be enough for us to get unique optical properties for steady-state DOT problem. Thus in order to determine the optical properties of a homogeneous slab we want to fix one of the coefficients first and use optimization methods to find another one. Then by assemble multiple homogeneous slab phantoms with different optical properties, we are able to obtain a heterogeneous phantom suitable for testing multi-modality imaging algorithms. In this paper, we describe how to make phantoms, derive a formula to solve the diffusion equation, demonstrate the non-uniqueness of steady-state DOT problem by analysing some numerical results of our formula, and finally propose a possible way to determine optical properties for homogeneous slab for our future work.

Changing of optical absorption and scattering coefficients in nonlinear-optical crystal lithium triborate before and after interaction with UV-radiation

NASA Astrophysics Data System (ADS)

Demkin, Artem S.; Nikitin, Dmitriy G.; Ryabushkin, Oleg A.

2016-04-01

In current work optical properties of LiB3O5 (LBO) crystal with ultraviolet (UV) (λ= 266 nm) induced volume macroscopic defect (track) are investigated using novel piezoelectric resonance laser calorimetry technique. Pulsed laser radiation of 10 W average power at 532 nm wavelength, is consecutively focused into spatial regions with and without optical defect. For these cases exponential fitting of crystal temperature kinetics measured during its irradiation gives different optical absorption coefficients α1 = 8.1 • 10-4 cm-1 (region with defect) and α =3.9ṡ10-4 cm-1 (non-defected region). Optical scattering coefficient is determined as the difference between optical absorption coefficients measured for opaque and transparent lateral facets of the crystal respectively. Measurements reveal that scattering coefficient of LBO in the region with defect is three times higher than the optical absorption coefficient.

Optical state-of-charge monitor for batteries

DOEpatents

Weiss, Jonathan D.

1999-01-01

A method and apparatus for determining the instantaneous state-of-charge of a battery in which change in composition with discharge manifests itself as a change in optical absorption. In a lead-acid battery, the sensor comprises a fiber optic system with an absorption cell or, alternatively, an optical fiber woven into an absorbed-glass-mat battery. In a lithium-ion battery, the sensor comprises fiber optics for introducing light into the anode to monitor absorption when lithium ions are introduced.

Achieving an ultra-narrow multiband light absorption meta-surface via coupling with an optical cavity.

PubMed

Liu, Zhengqi; Liu, Guiqiang; Liu, Xiaoshan; Huang, Shan; Wang, Yan; Pan, Pingping; Liu, Mulin

2015-06-12

Resonant plasmonic and metamaterial absorbers are of particular interest for applications in a wide variety of nanotechnologies including thermophotovoltaics, photothermal therapy, hot-electron collection and biosensing. However, it is rather challenging to realize ultra-narrow absorbers using plasmonic materials due to large optical losses in metals that inevitably decrease the quality of optical resonators. Here, we theoretically report methods to achieve an ultra-narrow light absorption meta-surface by using photonic modes of the optical cavities, which strongly couple with the plasmon resonances of the metallic nanostructures. Multispectral light absorption with absorption amplitude exceeding 99% and a bandwidth approaching 10 nm is achieved at the optical frequencies. Moreover, by introducing a thick dielectric coupling cavity, the number of absorption bands can be strongly increased and the bandwidth can even be narrowed to less than 5 nm due to the resonant spectrum splitting enabled by strong coupling between the plasmon resonances and the optical cavity modes. Designing such optical cavity-coupled meta-surface structures is a promising route for achieving ultra-narrow multiband absorbers, which can be used in absorption filters, narrow-band multispectral thermal emitters and thermophotovoltaics.

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

PubMed

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

2016-01-01

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

Multispectral photoacoustic microscopy of lipids using a pulsed supercontinuum laser.

PubMed

Buma, Takashi; Conley, Nicole C; Choi, Sang Won

2018-01-01

We demonstrate optical resolution photoacoustic microscopy (OR-PAM) of lipid-rich tissue between 1050-1714 nm using a pulsed supercontinuum laser based on a large-mode-area photonic crystal fiber. OR-PAM experiments of lipid-rich samples show the expected optical absorption peaks near 1210 and 1720 nm. These results show that pulsed supercontinuum lasers are promising for OR-PAM applications such as label-free histology of lipid-rich tissue and imaging small animal models of disease.

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

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

Karthikeyan, B., E-mail: bkarthik@nitt.edu; Hariharan, S.; Udayabhaskar, R.

2016-07-11

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 throughmore » hydroxyl groups with PVA. Raman spectroscopy also supports the interaction between GO and PVA ions through OH radicals.« less

Determination of band gap in epitaxial delafossite Cu oxide using optical techniques

NASA Astrophysics Data System (ADS)

Cabrera, Alejandro; Wheatley, R.; Seifert, B.; Wallentowitz, S.; Joshi, T.; Lederman, D.

Highly epitaxial delafossite CuFeO2 and CuFe1-xGaxO2 films were grown using Pulsed Laser Deposition techniques. The sample thicknesses were estimated to be 21 nm, 75 nm.The estimated gallium fraction of substituted ferric atoms was x =0.25 for the composite sample. We present the study of the fundamental band gap(s) for each sample via observation of their respective optical absorption properties in the NIR-VIS region using transmittance and diffuse reflection spectroscopy. Predominant absorption edges measured were between 1.1eV and 3.1eV from transmittance spectra. The sample of CuFe1-xGaxO2 showed measurable absorption features located at 2.4eV and 2.8eV. This study also found evidence of changes between apparent absorption edges between transmittance and diffuse reflectance spectroscopies of each sample and it may be resultant from absorption channels via surface states. Future photoluminescence experiments are planned to determine the photo-induced semiconductor behavior of these materials. ACNOWLEDGEMENTS: This work was supported by FONDECyT 1130372 and Proyecto Anillo ACT1409 at PUC and supported in part by the WV Higher Education Policy Commission (Grant HEPC.dsr.12.29) and by FAME sponsored by MARCO and DARPA (contract # 2013-MA-2382).

Investigation on nonlinear optical properties of MoS2 nanoflakes grown on silicon and quartz substrates

NASA Astrophysics Data System (ADS)

Bayesteh, Samaneh; Zahra Mortazavi, Seyedeh; Reyhani, Ali

2018-05-01

In this study, MoS2 nanoflakes were directly grown on different substrates—Si/SiO2 and quartz—by one-step thermal chemical vapor deposition using MoO3 and sulfide powders as precursors. Scanning electron microscopy and x-ray diffraction patterns demonstrated the formation of MoS2 structures on both substrates. Moreover, UV-visible and photoluminescence analysis confirmed the formation of MoS2 few-layer structures. According to Raman spectroscopy, by assessment of the line width and frequency shift differences between the and A 1g, it was inferred that the MoS2 grown on the silicon substrate was monolayer and that grown on the quartz substrate was multilayer. In addition, open-aperture and close-aperture Z-scan techniques were employed to study the nonlinear optical properties including nonlinear absorption and nonlinear refraction of the grown MoS2. All experiments were performed using a diode laser with a wavelength of 532 nm as the light source. It is noticeable that both samples demonstrate obvious self-defocusing behavior. The monolayer MoS2 grown on the silicon substrate displayed considerable two-photon absorption while, the multilayer MoS2 synthesized on the quartz exhibited saturable absorption. In general, few-layered MoS2 would be useful for the development of nanophotonic devices like optical limiters, optical switchers, etc.

Noninvasive imaging of absolute PpIX concentration distribution in nonmelanoma skin tumors at pre-PDT

NASA Astrophysics Data System (ADS)

Sunar, Ulas; Rohrbach, Daniel; Morgan, Janet; Zeitouni, Natalie

2013-03-01

Photodynamic Therapy (PDT) has proven to be an effective treatment option for nonmelanoma skin cancers. The ability to quantify the concentration of drug in the treated area is crucial for effective treatment planning as well as predicting outcomes. We utilized spatial frequency domain imaging for quantifying the accurate concentration of protoporphyrin IX (PpIX) in phantoms and in vivo. We correct fluorescence against the effects of native tissue absorption and scattering parameters. First we quantified the absorption and scattering of the tissue non-invasively. Then, we corrected raw fluorescence signal by compensating for optical properties to get the absolute drug concentration. After phantom experiments, we used basal cell carcinoma (BCC) model in Gli mice to determine optical properties and drug concentration in vivo at pre-PDT.

Motion Control and Optical Interrogation of a Levitating Single Nitrogen Vacancy in Vacuum.

PubMed

Conangla, Gerard P; Schell, Andreas W; Rica, Raúl A; Quidant, Romain

2018-05-24

Levitation optomechanics exploits the unique mechanical properties of trapped nano-objects in vacuum to address some of the limitations of clamped nanomechanical resonators. In particular, its performance is foreseen to contribute to a better understanding of quantum decoherence at the mesoscopic scale as well as to lead to novel ultrasensitive sensing schemes. While most efforts have focused so far on the optical trapping of low-absorption silica particles, further opportunities arise from levitating objects with internal degrees of freedom, such as color centers. Nevertheless, inefficient heat dissipation at low pressures poses a challenge because most nano-objects, even with low-absorption materials, experience photodamage in an optical trap. Here, by using a Paul trap, we demonstrate levitation in vacuum and center-of-mass feedback cooling of a nanodiamond hosting a single nitrogen-vacancy center. The achieved level of motion control enables us to optically interrogate and characterize the emitter response. The developed platform is applicable to a wide range of other nano-objects and represents a promising step toward coupling internal and external degrees of freedom.

Phonon-assisted optical absorption in BaSnO 3 from first principles

NASA Astrophysics Data System (ADS)

Monserrat, Bartomeu; Dreyer, Cyrus E.; Rabe, Karin M.

2018-03-01

The perovskite BaSnO3 provides a promising platform for the realization of an earth-abundant n -type transparent conductor. Its optical properties are dominated by a dispersive conduction band of Sn 5 s states and by a flatter valence band of O 2 p states, with an overall indirect gap of about 2.9 eV . Using first-principles methods, we study the optical properties of BaSnO3 and show that both electron-phonon interactions and exact exchange, included using a hybrid functional, are necessary to obtain a qualitatively correct description of optical absorption in this material. In particular, the electron-phonon interaction drives phonon-assisted optical absorption across the minimum indirect gap and therefore determines the absorption onset, and it also leads to the temperature dependence of the absorption spectrum. Electronic correlations beyond semilocal density functional theory are key to determine the dynamical stability of the cubic perovskite structure, as well as the correct energies of the conduction bands that dominate absorption. Our work demonstrates that phonon-mediated absorption processes should be included in the design of novel transparent conductor materials.

Optical Properties and Aging of Light Absorbing Secondary Organic Aerosol

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

Liu, Jiumeng; Lin, Peng; Laskin, Alexander

2016-10-14

The light-absorbing organic aerosol (OA), commonly referred to as “brown carbon (BrC)”, has attracted considerable attention in recent years because of its potential to affect atmospheric radiation balance, especially in the ultraviolet region and thus impact photochemical processes. A growing amount of data has indicated that BrC is prevalent in the atmosphere, which has motivated numerous laboratory and field studies; however, our understanding of the relationship between the chemical composition and optical properties of BrC remains limited. We conducted chamber experiments to investigate the effect of various VOC precursors, NOx concentrations, photolysis time and relative humidity (RH) on the lightmore » absorption of selected secondary organic aerosols (SOA). Light absorption of chamber generated SOA samples, especially aromatic SOA, was found to increase with NOx concentration, at moderate RH, and for the shortest photolysis aging times. The highest mass absorption coefficients (MAC) value is observed from toluene SOA products formed under high NOx conditions at moderate RH, in which nitro-aromatics were previously identified as the major light absorbing compounds. BrC light absorption is observed to decrease with photolysis time, correlated with a decline of the organonitrate fraction of SOA. SOA formed from mixtures of aromatics and isoprene absorb less visible and UV light than SOA formed from aromatic precursors alone on a mass basis. However, the mixed-SOA absorption was underestimated when optical properties were predicted using a two-product SOA formation model, as done in many current climate models. Further investigation, including analysis on detailed mechanisms, are required to explain the discrepancy.« less

Dynamic Crushing Response of Closed-cell Aluminium Foam at Variable Strain Rates

NASA Astrophysics Data System (ADS)

Islam, M. A.; Kader, M. A.; Escobedo, J. P.; Hazell, P. J.; Appleby-Thomas, G. J.; Quadir, M. Z.

2015-06-01

The impact response of aluminium foams is essential for assessing their crashworthiness and energy absorption capacity for potential applications. The dynamic compactions of closed-cell aluminium foams (CYMAT) have been tested at variable strain rates. Microstructural characterization has also been carried out. The low strain rate impact test has been carried out using drop weight experiments while the high strain compaction test has been carried out via plate impact experiments. The post impacted samples have been examined using optical and electron microscopy to observe the microstructural changes during dynamic loading. This combination of dynamic deformation during impact and post impact microstructural analysis helped to evaluate the pore collapse mechanism and impact energy absorption characteristics.

X-ray-induced photo-chemistry and X-ray absorption spectroscopy of biological samples

PubMed Central

George, Graham N.; Pickering, Ingrid J.; Pushie, M. Jake; Nienaber, Kurt; Hackett, Mark J.; Ascone, Isabella; Hedman, Britt; Hodgson, Keith O.; Aitken, Jade B.; Levina, Aviva; Glover, Christopher; Lay, Peter A.

2012-01-01

As synchrotron light sources and optics deliver greater photon flux on samples, X-ray-induced photo-chemistry is increasingly encountered in X-ray absorption spectroscopy (XAS) experiments. The resulting problems are particularly pronounced for biological XAS experiments. This is because biological samples are very often quite dilute and therefore require signal averaging to achieve adequate signal-to-noise ratios, with correspondingly greater exposures to the X-ray beam. This paper reviews the origins of photo-reduction and photo-oxidation, the impact that they can have on active site structure, and the methods that can be used to provide relief from X-ray-induced photo-chemical artifacts. PMID:23093745

Monocrystalline CVD-diamond optics for high-power laser applications

NASA Astrophysics Data System (ADS)

Holly, C.; Traub, M.; Hoffmann, D.; Widmann, C.; Brink, D.; Nebel, C.; Gotthardt, T.; Sözbir, M. C.; Wenzel, C.

2016-03-01

The potential of diamond as an optical material for high-power laser applications in the wavelength regime from the visible spectrum (VIS) to the near infrared (NIR) is investigated. Single-crystal diamonds with lateral dimensions up to 7×7mm2 are grown with microwave plasma assisted chemical vapor deposition (MPACVD) in parallel with up to 60 substrates and are further processed to spherical optics for beam guidance and shaping. The synthetic diamonds offer superior thermal, mechanical and optical properties, including low birefringence, scattering and absorption, also around 1 μm wavelength. We present dielectric (AR and HR) coated single-crystal diamond optics which are tested under high laser power in the multi-kW regime. The thermally induced focal shift of the diamond substrates is compared to the focal shift of a standard collimating and focusing unit for laser cutting made of fused silica optics. Due to the high thermal conductivity and low absorption of the diamond substrates compared to the fused silica optics no additional focal shift caused by a thermally induced refractive index change in the diamond is observed in our experiments. We present experimental results regarding the performance of the diamond substrates with and without dielectric coatings under high power and the influences of growth induced birefringence on the optical quality. Finally, we discuss the potential of the presented diamond lenses for high-power applications in the field of laser materials processing.

Nitrogen dioxide sensing using a novel gas correlation detector

NASA Astrophysics Data System (ADS)

Kebabian, Paul L.; Annen, Kurt D.; Berkoff, Timothy A.; Freedman, Andrew

2000-05-01

A nitrogen dioxide point sensor, based on a novel nondispersive gas filter spectroscopic scheme, is described. The detection scheme relies on the fact that the absorption spectrum of nitrogen dioxide in the 400-550 nm region consists of a complicated line structure superimposed on an average broadband absorption. A compensating filter is used to remove the effect of the broadband absorption, making the sensor insensitive both to small particles in the optical path and to potentially interfering gases with broadband absorption features in the relevant wavelength region. Measurements are obtained using a remote optical absorption cell that is linked via multimode fibre optics to the source and detection optics. The incorporation of blue light emitting diodes which spectrally match the nitrogen dioxide absorption allows the employment of electronic (instead of mechanical) switching between optical paths. A sensitivity of better than 1.0 ppm m column density (1 s integration time) has been observed; improvements in electronics and thermal stabilization should increase this sensitivity.

Non linear optical investigations of silver nanoparticles synthesised by curcumin reduction

NASA Astrophysics Data System (ADS)

Dhanya, N. P.

2017-11-01

Metal nanoparticles have considerable applications in assorted fields like medicine, biology, photonics, metallurgy etc. Optical applications of Silver nanoparticles are of significant interest among researchers nowadays. In this paper, we report a single step chemical reduction of silver nanoparticles with Curcumin both as a reducing and stabilising agent at room temperature. Structural, plasmonic and non linear optical properties of the prepared nanoparticles are explored using Scanning Electron Microscope, Transmission Electron Microscope, UV absorption spectrometry, Spectroflurometry and Z scan. UV-Vis absorption studies affirm the Surface Plasmon Resonance (SPR) absorption and spectroflurometric studies announce the emission spectrum of the prepared silvernanoparticles at 520 nm. SEM and TEM images uphold the existence of uniform sized, spherical silvernanoparticles. Nonlinear optical studies are accomplished with the open aperture z scan technique in the nanosecond regime. The nonlinearity is in virtue of saturable absorption, two-photon absorption and excited state absorption. The marked nonlinearity and optical limiting of the Curcumin reduced silvernanoparticles enhances its photonic applications.

Determination of optical absorption coefficient with focusing photoacoustic imaging.

PubMed

Li, Zhifang; Li, Hui; Zeng, Zhiping; Xie, Wenming; Chen, Wei R

2012-06-01

Absorption coefficient of biological tissue is an important factor for photothermal therapy and photoacoustic imaging. However, its determination remains a challenge. In this paper, we propose a method using focusing photoacoustic imaging technique to quantify the target optical absorption coefficient. It utilizes the ratio of the amplitude of the peak signal from the top boundary of the target to that from the bottom boundary based on wavelet transform. This method is self-calibrating. Factors, such as absolute optical fluence, ultrasound parameters, and Grüneisen parameter, can be canceled by dividing the amplitudes of the two peaks. To demonstrate this method, we quantified the optical absorption coefficient of a target with various concentrations of an absorbing dye. This method is particularly useful to provide accurate absorption coefficient for predicting the outcomes of photothermal interaction for cancer treatment with absorption enhancement.

Novel utilisation of a circular multi-reflection cell applied to materials ageing experiments

NASA Astrophysics Data System (ADS)

Knox, D. A.; King, A. K.; McNaghten, E. D.; Brooks, S. J.; Martin, P. A.; Pimblott, S. M.

2015-04-01

We report on the novel utilisation of a circular multi-reflection (CMR) cell applied to materials ageing experiments. This enabled trace gas detection within a narrow interfacial region located between two sample materials and remotely interrogated with near-infrared sources combined with fibre-optic coupling. Tunable diode laser absorption spectroscopy was used to detect water vapour and carbon dioxide at wavelengths near 1,358 and 2,004 nm, respectively, with corresponding detection limits of 7 and 1,139 ppm m Hz-0.5. The minimum detectable absorption was estimated to be 2.82 × 10-3 over a 1-s average. In addition, broadband absorption spectroscopy was carried out for the detection of acetic acid, using a super-luminescent light emitting diode centred around 1,430 nm. The 69 cm measurement pathlength was limited by poor manufacturing tolerances of the spherical CMR mirrors and the consequent difficulty of collecting all the cell output light.

Single shot near edge x-ray absorption fine structure spectroscopy in the laboratory

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

Mantouvalou, I., E-mail: ioanna.mantouvalou@tu-berlin.de; Witte, K.; Martyanov, W.

With the help of adapted off-axis reflection zone plates, near edge X-ray absorption fine structure spectra at the C and N K-absorption edge have been recorded using a single 1.2 ns long soft X-ray pulse. The transmission experiments were performed with a laser-produced plasma source in the laboratory rendering time resolved measurements feasible independent on large scale facilities. A resolving power of E/ΔE ∼ 950 at the respective edges could be demonstrated. A comparison of single shot spectra with those collected with longer measuring time proves that all features of the used reference samples (silicon nitrate and polyimide) can be resolved in 1.2 ns.more » Hence, investigations of radiation sensitive biological specimen become possible due to the high efficiency of the optical elements enabling low dose experiments.« less

Spectroscopic method for Earth-satellite-Earth laser long-path absorption measurements using Retroreflector In Space (RIS)

NASA Technical Reports Server (NTRS)

Sugimoto, Nobuo; Minato, Atsushi; Sasano, Yasuhiro

1992-01-01

The Retroreflector in Space (RIS) is a single element cube-corner retroreflector with a diameter of 0.5 m designed for earth-satellite-earth laser long-path absorption experiments. The RIS is to be loaded on the Advanced Earth Observing System (ADEOS) satellite which is scheduled for launch in Feb. 1996. The orbit for ADEOS is a sun synchronous subrecurrent polar-orbit with an inclination of 98.6 deg. It has a period of 101 minutes and an altitude of approximately 800 km. The local time at descending node is 10:15-10:45, and the recurrent period is 41 days. The velocity relative to the ground is approximately 7 km/s. In the RIS experiment, a laser beam transmitted from a ground station is reflected by RIS and received at the ground station. The absorption of the intervening atmosphere is measured in the round-trip optical path.

Diagnosis of cardiovascular diseases based on diffuse optical tomography system

NASA Astrophysics Data System (ADS)

Yu, Zong-Han; Wu, Chun-Ming; Lin, Yo-Wei; Chuang, Ming-Lung; Tsai, Jui-che; Sun, Chia-Wei

2008-02-01

Diffuse optical tomography (DOT) is a technique to assess the spatial variation in absorption and scattering properties of the biological tissues. DOT provides the measurement of changes in concentrations of oxy-hemoglobin and deoxy-hemoglobin. The oxygenation images are reconstructed by the measured optical signals with nearest-neighbor pairs of sources and detectors. In our study, a portable DOT system is built with optode design on a flexible print circuit board (FPCB). In experiments, the hemodynamics temporal evolution of exercises and vessel occlusions are observed with in vivo measurements form normal subjects and some patients in intensive care unit.

Measurements of optical properties of some molten oxides

NASA Astrophysics Data System (ADS)

Nason, D. O.; Yen, C. T.; Tiller, W. A.

1990-11-01

A method based on a fine-focussed optical laser has been developed to measure the spectral reflectance and the transmittance of small ( ∽ 1 mm) liquid or single crystal materials. The measured normal spectral emittance for 633 nm light is about 0.9 for several molten refractory oxides, 0.8 for lithium niobate and 0.7 for molten sapphire. Sapphire and YAG experience a several-fold increase in emittance on melting. The absorption coefficient and the thickness for opaqueness are calculated and some consequences of the partial transparency of small hot materials, when their temperatures are measured by optical pyrometry, are discussed.

Phonon-Assisted Optical Absorption in Silicon from First Principles

NASA Astrophysics Data System (ADS)

Noffsinger, Jesse; Kioupakis, Emmanouil; Van de Walle, Chris G.; Louie, Steven G.; Cohen, Marvin L.

2012-04-01

The phonon-assisted interband optical absorption spectrum of silicon is calculated at the quasiparticle level entirely from first principles. We make use of the Wannier interpolation formalism to determine the quasiparticle energies, as well as the optical transition and electron-phonon coupling matrix elements, on fine grids in the Brillouin zone. The calculated spectrum near the onset of indirect absorption is in very good agreement with experimental measurements for a range of temperatures. Moreover, our method can accurately determine the optical absorption spectrum of silicon in the visible range, an important process for optoelectronic and photovoltaic applications that cannot be addressed with simple models. The computational formalism is quite general and can be used to understand the phonon-assisted absorption processes in general.

Influence of a fat layer on the near infrared spectra of human muscle: quantitative analysis based on two-layered Monte Carlo simulations and phantom experiments

NASA Technical Reports Server (NTRS)

Yang, Ye; Soyemi, Olusola O.; Landry, Michelle R.; Soller, Babs R.

2005-01-01

The influence of fat thickness on the diffuse reflectance spectra of muscle in the near infrared (NIR) region is studied by Monte Carlo simulations of a two-layer structure and with phantom experiments. A polynomial relationship was established between the fat thickness and the detected diffuse reflectance. The influence of a range of optical coefficients (absorption and reduced scattering) for fat and muscle over the known range of human physiological values was also investigated. Subject-to-subject variation in the fat optical coefficients and thickness can be ignored if the fat thickness is less than 5 mm. A method was proposed to correct the fat thickness influence. c2005 Optical Society of America.

An Introduction to Fast Fourier Transforms through the Study of Oscillating Reactions.

ERIC Educational Resources Information Center

Eastman, M. P.; And Others

1986-01-01

Discusses an experiment designed to introduce students to the basic principles of the fast Fourier transform and Fourier smoothing through transformation of time-dependent optical absorption data from an oscillating reaction. Uses the Belousov-Zhabotinskii reaction. Describes the experimental setup and data analysis techniques.

Thermal Control Materials on MISSE-5 with Comparison to Earlier Flight Data

NASA Technical Reports Server (NTRS)

Finckenor, Miria; Zwiener, James M.; Pippin, Gary

2007-01-01

A variety of thermal control materials were flown on the Materials on International Space Station Experiment (MISSE)-5. Several types of beta cloth, as used in multi-layer insulation blankets, were flown, including samples from the same batch as used on the International Space Station. Two candidate sunshade materials for the James Webb Space Telescope were also exposed on MISSE-5. The white thermal control coating AZ93 was applied to Kapton instead of aluminum; this sample maintained good solar absorptance and did not indicate any significant level of contamination to the MISSE-5 experiment. Marker coatings maintained their color. Thermo-optical properties are discussed, along with comparable data from MISSE-2 and the Passive Optical Sample Assembly (POSA) - I experiments.

Electromagnetically Induced Absorption (EIA) and a ``Twist'' on Nonlinear Magneto-optical Rotation (NMOR) with Cold Atoms

NASA Astrophysics Data System (ADS)

Kunz, Paul; Meyer, David; Quraishi, Qudsia

2015-05-01

Within the class of nonlinear optical effects that exhibit sub-natural linewidth features, electromagnetically induced transparency (EIT) and nonlinear magneto-optical rotation (NMOR) stand out as having made dramatic impacts on various applications including atomic clocks, magnetometry, and single photon storage. A related effect, known as electromagnetically induced absorption (EIA), has received less attention in the literature. Here, we report on the first observation of EIA in cold atoms using the Hanle configuration, where a single laser beam is used to both pump and probe the atoms while sweeping a magnetic field through zero along the beam direction. We find that, associated with the EIA peak, a ``twist'' appears in the corresponding NMOR signal. A similar twist has been previously noted by Budker et al., in the context of warm vapor optical magnetometry, and was ascribed to optical pumping through nearby hyperfine levels. By studying this feature through numerical simulations and cold atom experiments, thus rendering the hyperfine levels well resolved, we enhance the understanding of the optical pumping mechanism behind it, and elucidate its relation to EIA. Finally, we demonstrate a useful application of these studies through a simple and rapid method for nulling background magnetic fields within our atom chip apparatus.

Iris as a reflector for differential absorption low-coherence interferometry to measure glucose level in the anterior chamber

PubMed Central

Zhou, Yong; Zeng, Nan; Ji, Yanhong; Li, Yao; Dai, Xiangsong; Li, Peng; Duan, Lian; Ma, Hui; He, Yonghong

2011-01-01

We present a method of glucose concentration detection in the anterior chamber with a differential absorption optical low-coherent interferometry (LCI) technique. Back-reflected light from the iris, passing through the anterior chamber twice, was selectively obtained with the LCI technique. Two light sources, one centered within (1625 nm) and the other centered outside (1310 nm) of a glucose absorption band were used for differential absorption measurement. In the eye model and pig eye experiments, we obtained a resolution glucose level of 26.8 mg/dL and 69.6 mg/dL, respectively. This method has a potential application for noninvasive detection of glucose concentration in aqueous humor, which is related to the glucose concentration in blood. PMID:21280906

Tuning optical absorption and photoexcited recombination dynamics in La1-xSrxFeO3-δ through A-site substitution and oxygen vacancies

NASA Astrophysics Data System (ADS)

Smolin, Sergey; Scafetta, Mark; Choquette, Amber; Sfeir, Matthew; Baxter, Jason; May, Steven

We study optical absorption and recombination dynamics in La1-xSrxFeO3-δ thin films, uncovering the effects of tuning nominal Fe valence via A-site substitution and oxygen stoichiometry. Variable angle spectroscopic ellipsometry was used to measure static optical properties, revealing a linear increase in absorption coefficient at 1.25 eV and a red-shifting of the optical absorption edge with increasing Sr fraction. The absorption spectra can be similarly tuned through the introduction of oxygen vacancies, indicating the critical role that nominal Fe valence plays in optical absorption. Dynamic optoelectronic properties were studied with ultrafast transient reflectance spectroscopy, revealing similar nanosecond photoexcited carrier lifetimes for oxygen deficient and stoichiometric films with the same nominal Fe valence. These results demonstrate that while the static optical absorption is strongly dependent on Fe valence tuned through cation or anion stoichiometry, oxygen vacancies do not appear to play a significantly detrimental role in the recombination kinetics. Nsf: ECCS-1201957, MRI DMR-0922929, MRI DMR-1040166. This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704.

A Novel QEPAS with Microresonator in the Open Environment

NASA Astrophysics Data System (ADS)

Lin, Cheng; Zhu, Yong; Wei, Wei; Wang, Ning; Bao, Weiyi

2013-09-01

An improved quartz-enhanced photoacoustic spectroscopy (QEPAS) sensing system for trace gas detection is proposed. The optical fiber Fabry-Perot (F-P) demodulation method is used to replace the conventional electrical one in the QEPAS system. The experimental QEPAS system, which has a microresonator consisting of two stainless steel tubes with a length of 2.3 mm and an inner diameter of 0.9 mm, is implemented to detect the absorption of water vapor in the open environment. The structure parameters of the quartz tuning fork (QTF) are optimized in order to make the sensing system work more stably and reliably. Demonstration experiments are carried out. The vibration signal of the QTF was picked up by the optical fiber F-P demodulator and the conventional electrical scheme at the same time. Normalized noise equivalent absorption coefficients of and are obtained, respectively. The experimental result demonstrates that the sensitivity of the improved QEPAS sensing system with an optical fiber F-P demodulator is about 5.9 times higher than that of the conventional QEPAS system.

Extracting third order optical nonlinearities of Mn(III)-Phthalocyanine chloride using high repetition rate femtosecond pulses

NASA Astrophysics Data System (ADS)

Makhal, Krishnandu; Mathur, Paresh; Maurya, Sidharth; Goswami, Debabrata

2017-02-01

Third order nonlinearities of Mn(III)-Phthalocyanine chloride in dimethyl-sulphoxide under 50 fs pulses, operating at 94 MHz, by eliminating cumulative thermal effects have been investigated and reported by us. Modifications were done in data acquisition during Z-scan experiment, which included recording of time evolution waveform traces in an oscilloscope and not collection of Z versus transmission and utilization of a chopper of a suitable duty cycle. Time evolution traces were further processed analytically through MatLab® programming, which yielded Z-scan traces similar to what was obtained with single shot 50 fs pulse. We observed reverse saturable absorption at 800 nm owing to excited state absorption. We show that the nonlinear refractive index (γ) and nonlinear absorption coefficient (β) are over estimated almost 100 times, when MHz pulses are used compared to a situation, where thermo-optical nonlinearities are accounted. Illumination and dark periods are carefully set in a way, so that the sample is able to completely recover its initial temperature before arrival of the next pulse. Magnitudes of γ and β were found to be -(6.5-4.9) × 10-16 m2/W and (5.4-6.2) × 10-10 m/W under the MHz condition, whereas they were -(0.18-2.2) × 10-18 m2/W and (9.5-15) × 10-12 m/W under the thermally managed condition, respectively. To reveal the associated fast nonlinearity, femtosecond transient absorption experiment was performed, which inferred excited state absorption and ground state bleaching across the 450-780 nm region. Dynamics associated with these processes are reported along with fluorescence lifetime obtained through the TCSPC technique. Structure optimization using TDDFT calculations and HOMO-LUMO gaps with orbital pictures are also shown.

Fine-Structure Measurements of Oxygen A Band Absorbance for Estimating the Thermodynamic Average Temperature of the Earth's Atmosphere: An Experiment in Physical and Environmental Chemistry

ERIC Educational Resources Information Center

Myrick, M. L.; Greer, A. E.; Nieuwland, A.; Priore, R. J.; Scaffidi, J.; Andreatta, Daniele; Colavita, Paula

2006-01-01

The experiment describe the measures of the A band transitions of atmospheric oxygen, a rich series of rotation-electronic absorption lines falling in the deep red portion of the optical spectrum and clearly visible owing to attenuation of solar radiation. It combines pure physical chemistry with analytical and environmental science and provides a…

Microscopic theory of optical absorption in graphene enhanced by lattices of plasmonic nanoparticles

NASA Astrophysics Data System (ADS)

Mueller, Niclas S.; Reich, Stephanie

2018-06-01

We present a microscopic description of plasmon-enhanced optical absorption in graphene, which is based on perturbation theory. We consider the interaction of graphene with a lattice of plasmonic nanoparticles, as was previously realized experimentally. By using tight-binding wave functions for the electronic states of graphene and the dipole approximation for the plasmon, we obtain analytic expressions for the coupling matrix element and enhanced optical absorption. The plasmonic nanostructure induces nonvertical optical transitions in the band structure of graphene with selection rules for the momentum transfer that depend on the periodicity of the plasmonic lattice. The plasmon-mediated optical absorption leads to an anisotropic carrier population around the K point in phase space, which depends on the polarization pattern of the plasmonic near field in the graphene plane. Using Fourier optics, we draw a connection to a macroscopic approach, which is independent from graphene-specific parameters. Each Fourier component of the plasmonic near field corresponds to the momentum transfer of an optical transition. Both approaches lead to the same expression for the integrated optical absorption enhancement, which is relevant for the photocurrent enhancement in graphene-based optoelectronic devices.

Enhanced optical limiting effect in fluorine-functionalized graphene oxide

NASA Astrophysics Data System (ADS)

Zhang, Fang; Wang, Zhengping; Wang, Duanliang; Wang, Shenglai; Xu, Xinguang

2017-09-01

Nonlinear optical absorption of fluorine-functionalized graphene oxide (F-GO) solution was researched by the open-aperture Z-scan method using 1064 and 532 nm lasers as the excitation sources. The F-GO dispersion exhibited strong optical limiting property and the fitted results demonstrated that the optical limiting behavior was the result of a two-photon absorption process. For F-GO nanosheets, the two-photon absorption coefficients at 1064 nm excitation are 20% larger than the values at 532 nm excitation and four times larger than that of pure GO nanosheets. It indicates that the doping of fluorine can effectively improve the nonlinear optical property of GO especially in infrared waveband, and fluorine-functionalized graphene oxide is an excellent nonlinear absorption material in infrared waveband.

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.

X-ray absorption and reflection as probes of the GaN conduction bands: Theory and experiments

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

Lambrecht, W.R.L.; Rashkeev, S.N.; Segall, B.

1997-04-01

X-ray absorption measurements are a well-known probe of the unoccupied states in a material. The same information can be obtained by using glancing angle X-ray reflectivity. In spite of several existing band structure calculations of the group III nitrides and previous optical studies in UV range, a direct probe of their conduction band densities of states is of interest. The authors performed a joint experimental and theoretical investigation using both of these experimental techniques for wurtzite GaN.

Gold nanoparticles: enhanced optical trapping and sensitivity coupled with significant heating.

PubMed

Seol, Yeonee; Carpenter, Amanda E; Perkins, Thomas T

2006-08-15

Gold nanoparticles appear to be superior handles in optical trapping assays. We demonstrate that relatively large gold particles (R(b)=50 nm) indeed yield a sixfold enhancement in trapping efficiency and detection sensitivity as compared to similar-sized polystyrene particles. However, optical absorption by gold at the most common trapping wavelength (1064 nm) induces dramatic heating (266 degrees C/W). We determined this heating by comparing trap stiffness from three different methods in conjunction with detailed modeling. Due to this heating, gold nanoparticles are not useful for temperature-sensitive optical-trapping experiments, but may serve as local molecular heaters. Also, such particles, with their increased detection sensitivity, make excellent probes for certain zero-force biophysical assays.

Effect of erythrocyte aggregation on optical transmission of blood

NASA Astrophysics Data System (ADS)

Shvartsman, L. D.; Fine, I.

2007-02-01

We present here a bird-eye view of time-dependent optical transmission of blood in red-near infrared spectral range. This issue is of the key importance both for fundamental understanding and for various applications connected with non-invasive optical blood analysis. A number of experiments measuring kinetics of blood transmission in the case of natural heart pulsations and of artificial kinetics following over-systolic occlusion is reviewed. The comprehensive theoretical approach has to consider scattering-associated mechanism rather than the widely accepted absorption-associated one. Light scattering occurs on RBC aggregates. The size of aggregates and their shape change in time due to blood flow variations. It results in the corresponding changes of optical transmission.

On the sub-band gap optical absorption in heat treated cadmium sulphide thin film deposited on glass by chemical bath deposition technique

NASA Astrophysics Data System (ADS)

Chattopadhyay, P.; Karim, B.; Guha Roy, S.

2013-12-01

The sub-band gap optical absorption in chemical bath deposited cadmium sulphide thin films annealed at different temperatures has been critically analyzed with special reference to Urbach relation. It has been found that the absorption co-efficient of the material in the sub-band gap region is nearly constant up to a certain critical value of the photon energy. However, as the photon energy exceeds the critical value, the absorption coefficient increases exponentially indicating the dominance of Urbach rule. The absorption coefficients in the constant absorption region and the Urbach region have been found to be sensitive to annealing temperature. A critical examination of the temperature dependence of the absorption coefficient indicates two different kinds of optical transitions to be operative in the sub-band gap region. After a careful analyses of SEM images, energy dispersive x-ray spectra, and the dc current-voltage characteristics, we conclude that the absorption spectra in the sub-band gap domain is possibly associated with optical transition processes involving deep levels and the grain boundary states of the material.

Suppressed power saturation due to optimized optical confinement in 9xx nm high-power diode lasers that use extreme double asymmetric vertical designs

NASA Astrophysics Data System (ADS)

Kaul, T.; Erbert, G.; Maaßdorf, A.; Knigge, S.; Crump, P.

2018-03-01

Broad area lasers with novel extreme double asymmetric structure (EDAS) vertical designs featuring increased optical confinement in the quantum well, Γ, are shown to have improved temperature stability without compromising series resistance, internal efficiency or losses. Specifically, we present here vertical design considerations for the improved continuous wave (CW) performance of devices operating at 940 nm, based on systematically increasing Γ from 0.26% to 1.1%, and discuss the impact on power saturation mechanisms. The results indicate that key power saturation mechanisms at high temperatures originate in high threshold carrier densities, which arise in the quantum well at low Γ. The characteristic temperatures, T 0 and T 1, are determined under short pulse conditions and are used to clarify the thermal contribution to power limiting mechanisms. Although increased Γ reduces thermal power saturation, it is accompanied by increased optical absorption losses in the active region, which has a significant impact on the differential external quantum efficiency, {η }{{diff}}. To quantify the impact of internal optical losses contributed by the quantum well, a resonator length-dependent simulation of {η }{{diff}} is performed and compared to the experiment, which also allows the estimation of experimental values for the light absorption cross sections of electrons and holes inside the quantum well. Overall, the analysis enables vertical designs to be developed, for devices with maximized power conversion efficiency at high CW optical power and high temperatures, in a trade-off between absorption in the well and power saturation. The best balance to date is achieved in devices using EDAS designs with {{Γ }}=0.54 % , which deliver efficiencies of 50% at 14 W optical output power at an elevated junction temperature of 105 °C.

Tunable emission and excited state absorption induced optical limiting in Tb2(MoO4)3: Sm3+/Eu3+ nanophosphors

NASA Astrophysics Data System (ADS)

Mani, Kamal P.; Sreekanth, Perumbilavil; Vimal, G.; Biju, P. R.; Unnikrishnan, N. V.; Ittyachen, M. A.; Philip, Reji; Joseph, Cyriac

2016-12-01

Photoluminescence properties and optical limiting behavior of pure and Sm3+/Eu3+ doped Tb2(MoO4)3 nanophosphors are investigated. The prepared nanophosphors exhibit excellent emission when excited by UV light. Color-tunable emissions in Tb2-xSmx(MoO4)3 and Tb2-xEux(MoO4)3 are realized by employing different excitation wavelengths or by controlling the doping concentration of Sm3+ and Eu3+. Luminescence quantum yield and CIE chromatic coordinates of the prepared phosphors were also presented. Optical limiting properties of the samples are investigated by open aperture Z-scan technique using 5 ns laser pulses at 532 nm. Numerical fitting of the measured Z-scan data to the relevant nonlinear transmission equations reveals that the nonlinear absorption is arising from strong excited state absorption, along with weak absorption saturation and it is found that the optical nonlinearity of Tb2(MoO4)3 increases with Sm3+/Eu3+doping. Parameters such as saturation fluence, excited state absorption cross section and ground state absorption cross section of the samples have been determined numerically, from which the figure of merit for nonlinear absorption is calculated. The excited state absorption cross-section of the samples is found to be one order of magnitude higher than that of the ground state absorption cross-section, indicating strong reverse saturable absorption. These results indicate that Sm3+/Eu3+ doped Tb2(MoO4)3 nanophosphors are efficient media for UV/n-UV pumped LEDs, and are also potential candidates for designing efficient optical limiting devices for the protection of human eyes and sensitive optical detectors from harmful laser radiation.

Highly specific spectroscopic photoacoustic molecular imaging of dynamic optical absorption shifts of an antibody-ICG contrast agent (Conference Presentation)

NASA Astrophysics Data System (ADS)

Wilson, Katheryne E.; Bachawal, Sunitha; Abou-Elkacem, Lotfi; Jensen, Kristen C.; Machtaler, Steven; Tian, Lu; Willmann, Juergen K.

2017-03-01

Improved techniques for breast cancer screening are critically needed as current methods lack diagnostic accuracy. Using spectroscopic photoacoustic (sPA) molecular imaging with a priori knowledge of optical absorption spectra allows suppression of endogenous background signal, increasing the overall sensitivity and specificity of the modality to exogenous contrast agents. Here, sPA imaging was used to monitor antibody-indocyanine green (ICG) conjugates as they undergo optical absorption spectrum shifts after cellular endocytosis and degradation to allow differentiation between normal murine mammary glands from breast cancer by enhancing molecular imaging signal from target (B7-H3)-bound antibody-ICG. First, B7-H3 was shown to have highly specific (AUC of 0.93) expression on both vascular endothelium and tumor stroma in malignant lesions through quantitative immunohistochemical staining of B7-H3 on 279 human samples (normal (n=53), benign lesions (11 subtypes, n=182), breast cancers (4 subtypes, n=97)), making B7-H3 a promising target for sPA imaging. Second, absorption spectra of intracellular and degraded B7-H3-ICG and Isotype control (Iso-ICG) were characterized through in vitro and in vivo experiments. Finally, a transgenic murine breast cancer model (FVB/N-Tg(MMTVPyMT)634Mul) was imaged, and sPA imaging in found a 3.01 (IQR 2.63, 3.38, P<0.001) fold increase in molecular B7-H3-ICG signal in tumors (n=80) compared to control conditions (B7-H3-ICG in tumor negative animals (n=60), Iso-ICG (n=30), blocking B7-H3+B7-H3-ICG (n=20), and free ICG (n=20)) despite significant tumor accumulation of Iso-ICG, confirmed through ex vivo histology. Overall, leveraging anti-B7-H3 antibody-ICG contrast agents, which have dynamic optical absorption spectra representative of molecular interactions, allows for highly specific sPA imaging of murine breast cancer.

All-optical laser spectral narrowing and line fixing at atomic absorption transition by injection competition and gain knock-down techniques

NASA Astrophysics Data System (ADS)

Gacheva, Lazarina I.; Deneva, Margarita A.; Kalbanov, Mihail H.; Nenchev, Marin N.

2008-12-01

We present two original, all optical techniques, to produce a narrowline laser light, fixed at the frequency of a chosen reference atomic absorption transition. The first type of systems is an essential improvement of our method 3,4 for laser spectral locking using a control by two frequency scanned, competitive injections with disturbed power ratio by the absorption at the reference line. The new development eliminates the narrowing limiting problem, related with the fixed laser longitudinal mode structure. We have proposed an original new technique for continuously tunable single mode laser operation in combination with synchronously and equal continuous tuning of the modes of the amplifier. By adapting the laser differential rate equations, the system is analyzed theoretically in details and is shown its feasibility. The results are in agreement with previous our experiments. The essential advantage, except simplicity of realization, is that the laser line can be of order of magnitude and more narrowed than the absorption linewidth. The second system is based of the laser amplifier arrangement with a gain knock-down from the competitive frequency scanned pulse, except at the wavelength of the desired absorption reference line. The essential advantages of the last system are that the problem of fixing laser mode presence is naturally avoided. The theoretical modeling and the numerical investigations show the peculiarity and advantages of the system proposed. The developed approaches are of interest for applications in spectroscopy, in DIAL monitoring of the atmospheric pollutants, in isotope separation system and potentially - for creation of simple, all optical, frequency standards for optical communications. Also, the continuously tunable single mode laser (and the combination with the simultaneously tunable amplifier) presents itself the interest for many practical applications in spectroscopy, metrology, and holography. We compare the action and the advantages of the two systems proposed.

Hyperspectral photoacoustic spectroscopy of highly-absorbing samples for diagnostic ocular imaging applications

NASA Astrophysics Data System (ADS)

Lim, Hoong-Ta; Murukeshan, Vadakke Matham

2017-01-01

Photoacoustic spectroscopy has been used to measure optical absorption coefficient and the application of tens of wavelength bands in photoacoustic spectroscopy was reported. Using optical methods, absorption-related information is, generally, derived from reflectance or transmittance values. Hence measurement accuracy is limited for highly absorbing samples where the reflectance or transmittance is too low to give reasonable signal-to-noise ratio. In this context, this paper proposes and illustrates a hyperspectral photoacoustic spectroscopy system to measure the absorption-related properties of highly absorbing samples directly. The normalized optical absorption coefficient spectrum of the highly absorbing iris is acquired using an optical absorption coefficient standard. The proposed concepts and the feasibility of the developed diagnostic medical imaging system are demonstrated using fluorescent microsphere suspensions and porcine eyes as test samples.

Quantification of optical absorption coefficient from acoustic spectra in the optical diffusive regime using photoacoustic microscopy

NASA Astrophysics Data System (ADS)

Guo, Zijian; Favazza, Christopher; Wang, Lihong V.

2012-02-01

Photoacoustic (PA) tomography (PAT) can image optical absorption contrast with ultrasonic spatial resolution in the optical diffusive regime. Multi-wavelength PAT can noninvasively monitor hemoglobin oxygen saturation (sO2) with high sensitivity and fine spatial resolution. However, accurate quantification in PAT requires knowledge of the optical fluence distribution, acoustic wave attenuation, and detection system bandwidth. We propose a method to circumvent this requirement using acoustic spectra of PA signals acquired at two optical wavelengths. With the acoustic spectral method, the absorption coefficients of an oxygenated bovine blood phantom at 560 and 575 nm were quantified with errors of ><5%.

Absorption properties of metal-semiconductor hybrid nanoparticles.

PubMed

Shaviv, Ehud; Schubert, Olaf; Alves-Santos, Marcelo; Goldoni, Guido; Di Felice, Rosa; Vallée, Fabrice; Del Fatti, Natalia; Banin, Uri; Sönnichsen, Carsten

2011-06-28

The optical response of hybrid metal-semiconductor nanoparticles exhibits different behaviors due to the proximity between the disparate materials. For some hybrid systems, such as CdS-Au matchstick-shaped hybrids, the particles essentially retain the optical properties of their original components, with minor changes. Other systems, such as CdSe-Au dumbbell-shaped nanoparticles, exhibit significant change in the optical properties due to strong coupling between the two materials. Here, we study the absorption of these hybrids by comparing experimental results with simulations using the discrete dipole approximation method (DDA) employing dielectric functions of the bare components as inputs. For CdS-Au nanoparticles, the DDA simulation provides insights on the gold tip shape and its interface with the semiconductor, information that is difficult to acquire by experimental means alone. Furthermore, the qualitative agreement between DDA simulations and experimental data for CdS-Au implies that most effects influencing the absorption of this hybrid system are well described by local dielectric functions obtained separately for bare gold and CdS nanoparticles. For dumbbell shaped CdSe-Au, we find a shortcoming of the electrodynamic model, as it does not predict the "washing out" of the optical features of the semiconductor and the metal observed experimentally. The difference between experiment and theory is ascribed to strong interaction of the metal and semiconductor excitations, which spectrally overlap in the CdSe case. The present study exemplifies the employment of theoretical approaches used to describe the optical properties of semiconductors and metal nanoparticles, to achieve better understanding of the behavior of metal-semiconductor hybrid nanoparticles.

Nonlinearities of polymethine and squarylium molecules for optical limiting

NASA Astrophysics Data System (ADS)

Lim, Jin Hong

Optical limiting, a process that reduces transmittance at high laser input energies (irradiance, fluence), is of interest in applications where sensitive optical components, e.g. detectors, are vulnerable to damage by the laser beam. Polymethine and squarylium dyes show strong reverse saturable absorption (RSA) at 532 nm. RSA is a process by which weak linear absorption populates excited states which subsequently absorb strongly. Thus, low inputs are transmitted while high inputs are absorbed. This nonlinear absorption is determined by the ground and excited-state absorption cross sections as well as excited state lifetimes of the molecular system. We characterized a series of polymethine and squarine molecules in ethanol and polyurethane acrylate polymeric host (PUA) using Z-scan and pump-probe techniques at the second harmonic of the Nd:YAG laser system. A comparison of the properties in these two hosts is made. Some of these dyes show a large ratio of excited to ground state absorption cross section, ~200, which is larger than any previously reported values. In order to determine the wavelength dependence of the nonlinearities of these molecules, we also performed Z-scan and pump-probe experiments at wavelengths from 440 to 650 nm using a picosecond optical parametric oscillator (OPO) which is synchronously pumped by the third-harmonic of a modelocked train of Nd:YAG laser pulses. The OPO is continuously tunable from 400 to 700 nm using two critically phase-matched BBO crystals mounted for walkoff compensation. A polymethine dye in PUA (PD #3), which is one of the best polymethine dyes at 532 nm, shows strong RSA over a broad spectral range from 480 to 620 nm. while a squarylium dye shows RSA over a relatively narrow spectral range from 500 to 560 nm. However, the excited state lifetimes (~2.5 ns in PUA) are shorter than desirable for good nanosecond optical limiting (10 ns) and at high inputs (>=0.36 J/cm2) the limiting properties are reduced. Extensive measurements of these molecules along with computer modeling indicate that the reduced limiting at high inputs is due to molecular degradation induced after a trans-cis conformational change. Evidence for this and possible methods to eliminate this problem are presented.

Effects of nanomaterial saturable absorption on gain-guide soliton in a positive group-dispersion fiber laser: Simulations and experiments

NASA Astrophysics Data System (ADS)

Du, Tuanjie; Wan, Xiaojiao; Yang, Runhua; Li, Weiwei; Ruan, Qiujun; Chen, Nan; Luo, Zhengqian

2018-01-01

In recent years, several kinds of nanomaterials have been discovered, and successfully used as saturable absorbers (SAs) for passively mode-locked fiber lasers. However, it is found that most of nanomaterials-based SAs cannot stably generate gain-guide solitons in positive group-dispersion fiber lasers, which is urgently expected to fully understand the inherent reasons. In this paper, we numerically and experimentally investigate the effects of nanomaterial saturable absorption (e.g. modulation depth and saturation optical power) on gain-guide soliton in positive group-dispersion Er3+-doped fiber laser (PGD-EDFL). By numerically solving the Ginzburg-Landau equation, the evolutions of both the mode-locked optical spectrum and pulse duration as a function of modulation depth and saturation optical power are analyzed, respectively. In experiment, we firstly prepare five nanomaterial SAs with the similar insertion loss, which have the different modulation depth from 1.80% to 23.36%, and the different saturation optical power from 8.8 to 536 W. We then perform the experimental comparison by incorporating the five SAs in a same PGD-EDFL cavity, respectively. The experimental results are in good agreement with the numerical ones. Our result reveals that: (1) a low modulation depth cannot support the formation of gain-guide soliton, (2) as the modulation depth increases, the spectral bandwidth of gain-guide soliton increases, the pulse duration decreases and the pulse chirp becomes large, (3) the saturation optical power has the weak influences on the gain-guide soliton performances.

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.

Quantitative absorption data from thermally induced wavefront distortions on UV, Vis, and NIR optics

NASA Astrophysics Data System (ADS)

Mann, Klaus; Schäfer, Bernd; Leinhos, Uwe; Lübbecke, Maik

2017-11-01

A photothermal absorption measurement system was set up, deploying a Hartmann-Shack wavefront sensor with extreme sensitivity to accomplish spatially resolved monitoring of thermally induced wavefront distortions. Photothermal absorption measurements in the near-infrared and deep ultra-violet spectral range are performed for the characterization of optical materials, utilizing a Yb fiber laser (λ = 1070 nm) and an excimer laser (193nm, 248nm) to induce thermal load. Wavefront deformations as low as 50pm (rms) can be registered, allowing for a rapid assessment of material quality. Absolute calibration of the absorption data is achieved by comparison with a thermal calculation. The method accomplishes not only to measure absorptances of plane optical elements, but also wavefront deformations and focal shifts in lenses as well as in complex optical systems, such as e.g. F-Theta objectives used in industrial high power laser applications. Along with a description of the technique we present results from absorption measurements on coated and uncoated optics at various laser wavelengths ranging from deep UV to near IR.

Fast wavelength calibration method for spectrometers based on waveguide comb optical filter

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

Yu, Zhengang; Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240; Huang, Meizhen, E-mail: mzhuang@sjtu.edu.cn

2015-04-15

A novel fast wavelength calibration method for spectrometers based on a standard spectrometer and a double metal-cladding waveguide comb optical filter (WCOF) is proposed and demonstrated. By using the WCOF device, a wide-spectrum beam is comb-filtered, which is very suitable for spectrometer wavelength calibration. The influence of waveguide filter’s structural parameters and the beam incident angle on the comb absorption peaks’ wavelength and its bandwidth are also discussed. The verification experiments were carried out in the wavelength range of 200–1100 nm with satisfactory results. Comparing with the traditional wavelength calibration method based on discrete sparse atomic emission or absorption lines,more » the new method has some advantages: sufficient calibration data, high accuracy, short calibration time, fit for produce process, stability, etc.« less

A modeling-based assessment of acousto-optic sensing for monitoring high-intensity focused ultrasound lesion formation

NASA Astrophysics Data System (ADS)

Adams, Matthew Tyler

Real-time acousto-optic (AO) sensing---a dual-wave modality that combines ultrasound with diffuse light to probe the optical properties of turbid media---has been demonstrated to non-invasively detect changes in ex vivo tissue optical properties during high-intensity focused ultrasound (HIFU) exposure. The AO signal indicates the onset of lesion formation and predicts resulting lesion volumes. Although proof-of-concept experiments have been successful, many of the underlying parameters and mechanisms affecting thermally induced optical property changes and the AO detectability of HIFU lesion formation are not well understood. In thesis, a numerical simulation was developed to model the AO sensing process and capture the relevant acoustic, thermal, and optical transport processes. The simulation required data that described how optical properties changed with heating. Experiments were carried out where excised chicken breast was exposed to thermal bath heating and changes in the optical absorption and scattering spectra (500 nm--1100 nm) were measured using a scanning spectrophotometer and an integrating sphere assembly. Results showed that the standard thermal dose model currently used for guiding HIFU treatments needs to be adjusted to describe thermally induced optical property changes. To model the entire AO process, coupled models were used for ultrasound propagation, tissue heating, and diffusive light transport. The angular spectrum method was used to model the acoustic field from the HIFU source. Spatial-temporal temperature elevations induced by the absorption of ultrasound were modeled using a finite-difference time-domain solution to the Pennes bioheat equation. The thermal dose model was then used to determine optical properties based on the temperature history. The diffuse optical field in the tissue was then calculated using a GPU-accelerated Monte Carlo algorithm, which accounted for light-sound interactions and AO signal detection. The simulation was used to determine the optimal design for an AO guided HIFU system by evaluating the robustness of the systems signal to changes in tissue thickness, lesion optical contrast, and lesion location. It was determined that AO sensing is a clinically viable technique for guiding the ablation of large volumes and that real-time sensing may be feasible in the breast and prostate.

Remote sensing of atmospheric chemistry; Proceedings of the Meeting, Orlando, FL, Apr. 1-3, 1991

NASA Technical Reports Server (NTRS)

Mcelroy, James L. (Editor); Mcneal, Robert J. (Editor)

1991-01-01

The present volume on remote sensing of atmospheric chemistry discusses special remote sensing space observations and field experiments to study chemical change in the atmosphere, network monitoring for detection of stratospheric chemical change, stratospheric chemistry studies, and the combining of model, in situ, and remote sensing in atmospheric chemistry. Attention is given to the measurement of tropospheric carbon monoxide using gas filter radiometers, long-path differential absorption measurements of tropospheric molecules, air quality monitoring with the differential optical absorption spectrometer, and a characterization of tropospheric methane through space-based remote sensing. Topics addressed include microwave limb sounder experiments for UARS and EOS, an overview of the spectroscopy of the atmosphere using an FIR emission experiment, the detection of stratospheric ozone trends by ground-based microwave observations, and a FIR Fabry-Perot spectrometer for OH measurements.

Optical Properties of the Organic Semiconductor Polyacetylene.

NASA Astrophysics Data System (ADS)

Feldblum, Avinoam Y.

Polyacetylene is the prototype conducting organic polymer. In its pristine form, it exhibits physical properties closely resembling those of a conventional inorganic semiconductor. When chemically or electrochemically doped, the polymer undergoes a semiconductor-metal transition. The nature of lightly doped polyacetylene, prior to the metallic transition, is not well understood. In addition, there still remain questions as to the nature of the pristine film itself. In this thesis, optical absorption experiments were performed in order to gain a clearer understanding of the electronic structure of polyacetylene. To attain this understanding, opto-electrochemical spectroscopy (OES), a new technique combining optical measurements with in situ electrochemical doping was developed. Optical absorption measurements were performed on cis-(CH)(,x) in order to examine doping induced isomerization. When doped to metallic levels followed by compensation or undoping, cis-(CH)(,x) isomerizes to trans-(CH)(,x). Using OES, one finds that with light doping, the main contribution to the midgap transition comes from the small trans content in the film. Electrochemical cycling shows isomerization beginning below y = 0.01 and repeated cycling to different concentrations indicate that the total isomerization depends on the value of the highest dopant level. These results suggest that upon light doping, the trans-(CH)(,x) dopes first, followed by enough cis-(CH)(,x) isomerizing to accomodate the injected charge. A quantitative study of the effects of doping on the absorption coefficient of trans-(CH)(,x) was carried out using OES. Upon doping, the interband absorption uniformly decreases over an extremely wide range. A strong absorbtion appeared at mid-gap; its oscillator strength increasing linearly with dopant concentration. A weak shoulder is observed on the interband edge which grows at low concentrations and then decreases to zero by 4%. These results agree with the predictions of the soliton model--the midgap absorption is identified as a soliton level and the shoulder as a transition between localized polaron levels. The pressure dependence of the photoabsorption of cis- and trans-(CH)(,x) has been measured. In both cases the bandedge shifted to a lower energy, and the value of the peak absorption coefficient decreased. These results suggest that the observed bandwidth is due primarily to the transverse transfer integral.

Electronic structure and optical properties of CdSxSe1-x solid solution nanostructures from X-ray absorption near edge structure, X-ray excited optical luminescence, and density functional theory investigations

NASA Astrophysics Data System (ADS)

Murphy, M. W.; Yiu, Y. M.; Ward, M. J.; Liu, L.; Hu, Y.; Zapien, J. A.; Liu, Yingkai; Sham, T. K.

2014-11-01

The electronic structure and optical properties of a series of iso-electronic and iso-structural CdSxSe1-x solid solution nanostructures have been investigated using X-ray absorption near edge structure, extended X-ray absorption fine structure, and X-ray excited optical luminescence at various absorption edges of Cd, S, and Se. It is found that the system exhibits compositions, with variable local structure in-between that of CdS and CdSe accompanied by tunable optical band gap between that of CdS and CdSe. Theoretical calculation using density functional theory has been carried out to elucidate the observations. It is also found that luminescence induced by X-ray excitation shows new optical channels not observed previously with laser excitation. The implications of these observations are discussed.

Universal modal radiation laws for all thermal emitters

PubMed Central

Zhu, Linxiao; Fan, Shanhui

2017-01-01

We derive four laws relating the absorptivity and emissivity of thermal emitters. Unlike the original Kirchhoff radiation law derivations, these derivations include diffraction, and so are valid also for small objects, and can also cover nonreciprocal objects. The proofs exploit two recent approaches. First, we express all fields in terms of the mode-converter basis sets of beams; these sets, which can be uniquely established for any linear optical object, give orthogonal input beams that are coupled one-by-one to orthogonal output beams. Second, we consider thought experiments using universal linear optical machines, which allow us to couple appropriate beams and black bodies. Two of these laws can be regarded as rigorous extensions of previously known laws: One gives a modal version of a radiation law for reciprocal objects—the absorptivity of any input beam equals the emissivity into the “backward” (i.e., phase-conjugated) version of that beam; another gives the overall equality of the sums of the emissivities and the absorptivities for any object, including nonreciprocal ones. The other two laws, valid for reciprocal and nonreciprocal objects, are quite different from previous relations. One shows universal equivalence of the absorptivity of each mode-converter input beam and the emissivity into its corresponding scattered output beam. The other gives unexpected equivalences of absorptivity and emissivity for broad classes of beams. Additionally, we prove these orthogonal mode-converter sets of input and output beams are the ones that maximize absorptivities and emissivities, respectively, giving these beams surprising additional physical meaning. PMID:28396436

Optical properties and aging of light-absorbing secondary organic aerosol

DOE PAGES

Liu, Jiumeng; Lin, Peng; Laskin, Alexander; ...

2016-10-14

The light-absorbing organic aerosol (OA) commonly referred to as “brown carbon” (BrC) has attracted considerable attention in recent years because of its potential to affect atmospheric radiation balance, especially in the ultraviolet region and thus impact photochemical processes. A growing amount of data has indicated that BrC is prevalent in the atmosphere, which has motivated numerous laboratory and field studies; however, our understanding of the relationship between the chemical composition and optical properties of BrC remains limited. We conducted chamber experiments to investigate the effect of various volatile organic carbon (VOC) precursors, NO x concentrations, photolysis time, and relative humidity (RH) on the lightmore » absorption of selected secondary organic aerosols (SOA). Light absorption of chamber-generated SOA samples, especially aromatic SOA, was found to increase with NO x concentration, at moderate RH, and for the shortest photolysis aging times. The highest mass absorption coefficient (MAC) value is observed from toluene SOA products formed under high-NO x conditions at moderate RH, in which nitro-aromatics were previously identified as the major light-absorbing compounds. BrC light absorption is observed to decrease with photolysis time, correlated with a decline of the organic nitrate fraction of SOA. SOA formed from mixtures of aromatics and isoprene absorb less visible (Vis) and ultraviolet (UV) light than SOA formed from aromatic precursors alone on a mass basis. However, the mixed SOA absorption was underestimated when optical properties were predicted using a two-product SOA formation model, as done in many current climate models. Further investigation, including analysis on detailed mechanisms, are required to explain the discrepancy.« less

Optical transmission radiation damage and recovery stimulation of DSB: Ce3+ inorganic scintillation material

NASA Astrophysics Data System (ADS)

Borisevich, A.; Dormenev, V.; Korjik, M.; Kozlov, D.; Mechinsky, V.; Novotny, R. W.

2015-02-01

Recently, a new scintillation material DSB: Ce3+ was announced. It can be produced in a form of glass or nano-structured glass ceramics with application of standard glass production technology with successive thermal annealing. When doped with Ce3+, material can be applied as scintillator. Light yield of scintillation is near 100 phe/MeV. Un-doped material has a wide optical window from 4.5eV and can be applied to detect Cherenkov light. Temperature dependence of the light yield LY(T) is 0.05% which is 40 times less than in case of PWO. It can be used for detectors tolerant to a temperature variation between -20° to +20°C. Several samples with dimensions of 15x15x7 mm3 have been tested for damage effects on the optical transmission under irradiation with γ-quanta. It was found that the induced absorption in the scintillation range depends on the doping concentration and varies in range of 0.5-7 m-1. Spontaneous recovery of induced absorption has fast initial component. Up to 25% of the damaged transmission is recuperated in 6 hours. Afterwards it remains practically constant if the samples are kept in the dark. However, induced absorption is reduced by a factor of 2 by annealing at 50°C and completely removed in a short time when annealing at 100°C. A significant acceleration of the induced absorption recovery is observed by illumination with visible and IR light. This effect is observed for the first time in a Ce-doped scintillation material. It indicates, that radiation induced absorption in DSB: Ce scintillation material can be retained at the acceptable level by stimulation with light in a strong irradiation environment of collider experiments.

Fjord light regime: Bio-optical variability, absorption budget, and hyperspectral light availability in Sognefjord and Trondheimsfjord, Norway

NASA Astrophysics Data System (ADS)

Mascarenhas, V. J.; Voß, D.; Wollschlaeger, J.; Zielinski, O.

2017-05-01

Optically active constituents (OACs) in addition to water molecules attenuate light via processes of absorption and scattering and thereby determine underwater light availability. An analysis of their optical properties helps in determining the contribution of each of these to light attenuation. With an aim to study the bio-optical variability, absorption budget and 1% spectral light availability, hydrographical (temperature and salinity), and hyperspectral optical (downwelling irradiance and upwelling radiance) profiles were measured along fjord transects in Sognefjord and Trondheimsfjord, Norway. Optical water quality observations were also performed using Secchi disc and Forel-Ule scale. In concurrence, water samples were collected and analyzed via visible spectrophotometry, fluorometry, and gravimetry to quantify and derive inherent optical properties of the water constituents. An absorption model (R2 = 0.91, n = 36, p < 0.05) as a function of OACs is developed for Sognefjord using multiple regression analysis. Influenced by glacial meltwater, Sognefjord had higher concentration of inorganic suspended matter, while Trondheimsfjord had higher concentrations of CDOM. Increase in turbidity caused increased attenuation of light upstream, as a result of which the euphotic depth decreased from outer to inner fjord sections. Triangular representation of absorption budget revealed dominant absorption by CDOM at 443-555 nm, while that by phytoplankton at 665 nm. Sognefjord however exhibited much greater optical complexity. A significantly strong correlation between salinity and acdom440 is used to develop an algorithm to estimate acdom440 using salinity in Trondheimsfjord.

Optical band gap of thermally deposited Ge-S-Ga thin films

NASA Astrophysics Data System (ADS)

Rana, Anjli; Heera, Pawan; Singh, Bhanu Pratap; Sharma, Raman

2018-05-01

Thin films of Ge20S80-xGax glassy alloy, obtained from melt quenching technique, were deposited on the glass substrate by thermal evaporation technique under a high vacuum conditions (˜ 10-5 Torr). Absorption spectrum fitting method (ASF) is employed to obtain the optical band gap from absorption spectra. This method requires only the measurement of the absorption spectrum of the sample. The width of the band tail was also determined. Optical band gap computed from absorption spectra is found to decrease with an increase in Ga content. The evaluated optical band gap (Eg) is in well agreement with the theoretically predicted Eg and obtained from transmission spectra.

Optical nonlinear absorption characteristics of Sb2Se3 nanoparticles

NASA Astrophysics Data System (ADS)

Muralikrishna, Molli; Kiran, Aditha Sai; Ravikanth, B.; Sowmendran, P.; Muthukumar, V. Sai; Venkataramaniah, Kamisetti

2014-04-01

In this work, we report for the first time, the nonlinear optical absorption properties of antimony selenide (Sb2Se3) 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 Sb2Se3 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.

Compensation of strong thermal lensing in high-optical-power cavities.

PubMed

Zhao, C; Degallaix, J; Ju, L; Fan, Y; Blair, D G; Slagmolen, B J J; Gray, M B; Lowry, C M Mow; McClelland, D E; Hosken, D J; Mudge, D; Brooks, A; Munch, J; Veitch, P J; Barton, M A; Billingsley, G

2006-06-16

In an experiment to simulate the conditions in high optical power advanced gravitational wave detectors, we show for the first time that the time evolution of strong thermal lenses follows the predicted infinite sum of exponentials (approximated by a double exponential), and that such lenses can be compensated using an intracavity compensation plate heated on its cylindrical surface. We show that high finesse approximately 1400 can be achieved in cavities with internal compensation plates, and that mode matching can be maintained. The experiment achieves a wave front distortion similar to that expected for the input test mass substrate in the Advanced Laser Interferometer Gravitational Wave Observatory, and shows that thermal compensation schemes are viable. It is also shown that the measurements allow a direct measurement of substrate optical absorption in the test mass and the compensation plate.

Effect of ladder diagrams on optical absorption spectra in a quasiparticle self-consistent GW framework

NASA Astrophysics Data System (ADS)

Cunningham, Brian; Grüning, Myrta; Azarhoosh, Pooya; Pashov, Dimitar; van Schilfgaarde, Mark

2018-03-01

We present an approach to calculate the optical absorption spectra that combines the quasiparticle self-consistent GW method [Phys. Rev. B 76, 165106 (2007), 10.1103/PhysRevB.76.165106] for the electronic structure with the solution of the ladder approximation to the Bethe-Salpeter equation for the macroscopic dielectric function. The solution of the Bethe-Salpeter equation has been implemented within an all-electron framework, using a linear muffin-tin orbital basis set, with the contribution from the nonlocal self-energy to the transition dipole moments (in the optical limit) evaluated explicitly. This approach addresses those systems whose electronic structure is poorly described within the standard perturbative GW approaches with density-functional theory calculations as a starting point. The merits of this approach have been exemplified by calculating optical absorption spectra of a strongly correlated transition metal oxide, NiO, and a narrow gap semiconductor, Ge. In both cases, the calculated spectrum is in good agreement with the experiment. It is also shown that for systems whose electronic structure is well-described within the standard perturbative GW , such as Si, LiF, and h -BN , the performance of the present approach is in general comparable to the standard GW plus Bethe-Salpeter equation. It is argued that both vertex corrections to the electronic screening and the electron-phonon interaction are responsible for the observed systematic overestimation of the fundamental band gap and spectrum onset.

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.

Effect of the concentration of magnetic grains on the linear-optical-absorption coefficient of ferrofluid-doped lyotropic mesophases: deviation from the Beer-Lambert law.

PubMed

Cuppo, F L S; Gómez, S L; Figueiredo Neto, A M

2004-04-01

In this paper is reported a systematic experimental study of the linear-optical-absorption coefficient of ferrofluid-doped isotropic lyotropic mixtures as a function of the magnetic-grains concentration. The linear optical absorption of ferrolyomesophases increases in a nonlinear manner with the concentration of magnetic grains, deviating from the usual Beer-Lambert law. This behavior is associated to the presence of correlated micelles in the mixture which favors the formation of small-scale aggregates of magnetic grains (dimers), which have a higher absorption coefficient with respect to that of isolated grains. We propose that the indirect heating of the micelles via the ferrofluid grains (hyperthermia) could account for this nonlinear increase of the linear-optical-absorption coefficient as a function of the grains concentration.

Noninvasive photoacoustic measurement of absorption coefficient using internal light irradiation of cylindrical diffusing fiber

NASA Astrophysics Data System (ADS)

Peng, Dong-qing; Zhu, Li-li; Li, Zhi-fang; Li, Hui

2017-09-01

Absorption coefficient of biological tissue is an important parameter in biomedicine, but its determination remains a challenge. In this paper, we propose a method using focusing photoacoustic imaging technique and internal light irradiation of cylindrical diffusing fiber (CDF) to quantify the target optical absorption coefficient. Absorption coefficients for ink absorbers are firstly determined through photoacoustic and spectrophotometric measurements at the same excitation, which demonstrates the feasibility of this method. Also, the optical absorption coefficients of ink absorbers with several concentrations are measured. Finally, the two-dimensional scanning photoacoustic image is obtained. Optical absorption coefficient measurement and simultaneous photoacoustic imaging of absorber non-invasively are the typical characteristics of the method. This method can play a significant role for non-invasive determination of blood oxygen saturation, the absorption-based imaging and therapy.

Correction to the Beer-Lambert-Bouguer law for optical absorption.

PubMed

Abitan, Haim; Bohr, Henrik; Buchhave, Preben

2008-10-10

The Beer-Lambert-Bouguer absorption law, known as Beer's law for absorption in an optical medium, is precise only at power densities lower than a few kW. At higher power densities this law fails because it neglects the processes of stimulated emission and spontaneous emission. In previous models that considered those processes, an analytical expression for the absorption law could not be obtained. We show here that by utilizing the Lambert W-function, the two-level energy rate equation model is solved analytically, and this leads into a general absorption law that is exact because it accounts for absorption as well as stimulated and spontaneous emission. The general absorption law reduces to Beer's law at low power densities. A criterion for its application is given along with experimental examples. (c) 2008 Optical Society of America

Water-based metamaterial absorbers for optical transparency and broadband microwave absorption

NASA Astrophysics Data System (ADS)

Pang, Yongqiang; Shen, Yang; Li, Yongfeng; Wang, Jiafu; Xu, Zhuo; Qu, Shaobo

2018-04-01

Naturally occurring water is a promising candidate for achieving broadband absorption. In this work, by virtue of the optically transparent character of the water, the water-based metamaterial absorbers (MAs) are proposed to achieve the broadband absorption at microwave frequencies and optical transparence simultaneously. For this purpose, the transparent indium tin oxide (ITO) and polymethyl methacrylate (PMMA) are chosen as the constitutive materials. The water is encapsulated between the ITO backed plate and PMMA, serving as the microwave loss as well as optically transparent material. Numerical simulations show that the broadband absorption with the efficiency over 90% in the frequency band of 6.4-30 GHz and highly optical transparency of about 85% in the visible region can be achieved and have been well demonstrated experimentally. Additionally, the proposed water-based MA displays a wide-angle absorption performance for both TE and TM waves and is also robust to the variations of the structure parameters, which is much desired in a practical application.

Photoacoustic absorption spectroscopy of single optically trapped aerosol droplets

NASA Astrophysics Data System (ADS)

Covert, Paul A.; Cremer, Johannes W.; Signorell, Ruth

2017-08-01

Photoacoustics have been widely used for the study of aerosol optical properties. To date, these studies have been performed on particle ensembles, with minimal ability to control for particle size. Here, we present our singleparticle photoacoustic spectrometer. The sensitivity and stability of the instrument is discussed, along with results from two experiments that illustrate the unique capabilities of this instrument. In the first experiment, we present a measurement of the particle size-dependence of the photoacoustic response. Our results confirm previous models of aerosol photoacoustics that had yet to be experimentally tested. The second set of results reveals a size-dependence of photochemical processes within aerosols that results from the nanofocusing of light within individual droplets.

Optical absorption in planar graphene superlattice: The role of structural parameters

NASA Astrophysics Data System (ADS)

Azadi, L.; Shojaei, S.

2018-04-01

We theoretically studied the optically driven interband transitions in a planar graphene superlattices (PGSL) formed by patterning graphene sheet on laterally hetrostructured substrate as Sio2/hBN. A tunable optical transitions between minibands is observed based on engineering structural parameters. We derive analytically expression for optical absorption from two-band model. Considerable optical absorption is obtained for different ratios between widths of heterostructured substrate and is explained analytically from the view point of wavefunction engineering and miniband dispersion, in details. The role of different statuses of polarization as circular and linear are considered. Our study paves a way toward the control of optical properties of PGSLs to be implemented in optoelectronics devices.

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

NASA Technical Reports Server (NTRS)

Neeley, Aimee Renee

2014-01-01

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

CW laser damage testing of RAR nano-textured fused silica and YAG

NASA Astrophysics Data System (ADS)

MacLeod, Bruce D.; Hobbs, Douglas S.; Manni, Anthony D.; Sabatino, Ernest; Bernot, David M.; DeFrances, Sage; Randi, Joseph A.; Thomas, Jeffrey

2017-11-01

A study of the continuous wave (CW) laser induced damage threshold (LiDT) of fused silica and yttrium aluminum garnet (YAG) optics was conducted to further illustrate the enhanced survivability within high power laser systems of an anti-reflection (AR) treatment consisting of randomly distributed surface relief nanostructures (RAR). A series of three CW LiDT tests using the 1070nm wavelength, 16 KW fiber laser test bed at Penn State Electro-Optic Center (PSEOC) were designed and completed, with improvements in the testing protocol, areal coverage, and maximum exposure intensities implemented between test cycles. Initial results for accumulated power, stationary site exposures of RAR nano-textured optics showed no damage and low surface temperatures similar to the control optics with no AR treatment. In contrast, optics with thin-film AR coatings showed high surface temperatures consistent with absorption by the film layers. Surface discriminating absorption measurements made using the Photothermal Common-path Interferometry (PCI) method, showed zero added surface absorption for the RAR nanotextured optics, and absorption levels in the 2-5 part per million range for thin-film AR coated optics. In addition, the surface absorption of thin-film AR coatings was also found to have localized absorption spikes that are likely pre-cursors for damage. Subsequent CW LiDT testing protocol included raster scanning an increased intensity focused beam over the test optic surface where it was found that thin-film AR coated optics damaged at intensities in the 2 to 5 MW/cm2 range with surface temperatures over 250C during the long-duration exposures. Significantly, none of the 10 RAR nano-textured fused silica optics tested could be damaged up to the maximum system intensity of 15.5 MW/cm2, and surface temperatures remained low. YAG optics tested during the final cycle exhibited a similar result with RAR nano-textured surfaces surviving intensities over 3 times higher than thin-film AR coated surfaces. This result was correlated with PCI measurements that also show zero-added surface absorption for the RAR nano-textured YAG optics.

Two-photon absorption in conjugated energetic molecule

DOE PAGES

Bjorgaard, Josiah August; Sifain, Andrew; Nelson, Tammie Renee; ...

2016-06-03

Time-dependent density functional theory (TD-DFT) is used to investigate the relationship between molecular structure and one- and two-photon absorption (OPA and TPA, respectively) properties in novel and recently synthesized conjugated energetic molecules (CEMs). The molecular structure of CEMs can be strategically altered to influence the heat of formation and oxygen balance, two factors that can contribute to the sensitivity and strength of an explosive material. OPA and TPA are sensitive to changes in molecular structure as well, influencing optical range of excitation. We find calculated vertical excitation energies in good agreement with experiment for most molecules. Peak TPA intensities aremore » significant and on the order of 102 GM. Natural transition orbitals for essential electronic states defining TPA peaks of relatively large intensity to examine the character of relevant transitions. Minor modification of molecular substituents, such as additional oxygen and other functional groups, produces significant changes in electronic structure, OPA, TPA, and improves the oxygen balance. Results show that select molecules are apt to nonlinear absorption, opening the possibility for controlled, direct optical initiation of CEMs through photochemical pathways.« less

Apparatus and method for quantitative measurement of small differences in optical absorptivity between two samples using differential interferometry and the thermooptic effect

DOEpatents

Cremers, David A.; Keller, Richard A.

1984-01-01

An apparatus and method for the measurement of small differences in optical absorptivity of weakly absorbing solutions using differential interferometry and the thermooptic effect has been developed. Two sample cells are placed in each arm of an interferometer and are traversed by colinear probe and heating laser beams. The interrogation probe beams are recombined forming a fringe pattern, the intensity of which can be related to changes in optical pathlength of these laser beams through the cells. This in turn can be related to small differences in optical absorptivity which results in different amounts of sample heating when the heating laser beams are turned on, by the fact that the index of refraction of a liquid is temperature dependent. A critical feature of this invention is the stabilization of the optical path of the probe beams against drift. Background (solvent) absorption can then be suppressed by a factor of approximately 400. Solute absorptivities of about 10.sup.-5 cm.sup.-1 can then be determined in the presence of background absorptions in excess of 10.sup.-3 cm.sup.-1. In addition, the smallest absorption measured with the instant apparatus and method is about 5.times. 10.sup.-6 cm.sup.-1.

Apparatus and method for quantitative measurement of small differences in optical absorptivity between two samples using differential interferometry and the thermooptic effect

DOEpatents

Cremers, D.A.; Keller, R.A.

1982-06-08

An apparatus and method for the measurement of small differences in optical absorptivity of weakly absorbing solutions using differential interferometry and the thermooptic effect has been developed. Two sample cells are placed in each arm of an interferometer and are traversed by colinear probe and heating laser beams. The interrogation probe beams are recombined forming a fringe pattern, the intensity of which can be related to changes in optical pathlength of these laser beams through the cells. This in turn can be related to small differences in optical absorptivity which results in different amounts of sample heating when the heating laser beams are turned on, by the fact that the index of refraction of a liquid is temperature dependent. A critical feature of this invention is the stabilization of the optical path of the probe beams against drift. Background (solvent) absorption can then be suppressed by a factor of approximately 400. Solute absorptivities of about 10/sup -5/ cm/sup -1/ can then be determined in the presence of background absorptions in excess of 10/sup -3/ cm/sup -1/. In addition, the smallest absorption measured with the instant apparatus and method is about 5 x 10/sup -6/ cm/sup -1/.

Optical band gap studies on lithium aluminum silicate glasses doped with Cr3+ ions

NASA Astrophysics Data System (ADS)

El-Diasty, Fouad; Abdel Wahab, Fathy A.; Abdel-Baki, Manal

2006-11-01

Lithium aluminum silicate glass system (LAS) implanted with chromium ions is prepared. The reflectance and transmittance measurements are used to determine the dispersion of absorption coefficient. The optical data are explained in terms of the different oxidation states adopted by the chromium ions into the glass network. It is found that the oxidation state of the chromium depends on its concentration. Across a wide spectral range, 0.2-1.6μm, analysis of the fundamental absorption edge provides values for the average energy band gaps for allowed direct and indirect transitions. The optical absorption coefficient just below the absorption edge varies exponentially with photon energy indicating the presence of Urbach's tail. Such tail is decreased with the increase of the chromium dopant. From the analysis of the optical absorption data, the absorption peak at ground state exciton energy, the absorption at band gap, and the free exciton binding energy are determined. The extinction coefficient data are used to determine the Fermi energy level of the studied glasses. The metallization criterion is obtained and discussed exploring the nature of the glasses. The measured IR spectra of the different glasses are used to throw some light on the optical properties of the present glasses correlating them with their structure and composition.

High-frame-rate imaging of biological samples with optoacoustic micro-tomography

NASA Astrophysics Data System (ADS)

Deán-Ben, X. Luís.; López-Schier, Hernán.; Razansky, Daniel

2018-02-01

Optical microscopy remains a major workhorse in biological discovery despite the fact that light scattering limits its applicability to depths of ˜ 1 mm in scattering tissues. Optoacoustic imaging has been shown to overcome this barrier by resolving optical absorption with microscopic resolution in significantly deeper regions. Yet, the time domain is paramount for the observation of biological dynamics in living systems that exhibit fast motion. Commonly, acquisition of microscopy data involves raster scanning across the imaged volume, which significantly limits temporal resolution in 3D. To overcome these limitations, we have devised a fast optoacoustic micro-tomography (OMT) approach based on simultaneous acquisition of 3D image data with a high-density hemispherical ultrasound array having effective detection bandwidth around 25 MHz. We performed experiments by imaging tissue-mimicking phantoms and zebrafish larvae, demonstrating that OMT can provide nearly cellular resolution and imaging speed of 100 volumetric frames per second. As opposed to other optical microscopy techniques, OMT is a hybrid method that resolves optical absorption contrast acoustically using unfocused light excitation. Thus, no penetration barriers are imposed by light scattering in deep tissues, suggesting it as a powerful approach for multi-scale functional and molecular imaging applications.

Traveling-wave photodetector

DOEpatents

Hietala, V.M.; Vawter, G.A.

1993-12-14

The traveling-wave photodetector of the present invention combines an absorptive optical waveguide and an electrical transmission line, in which optical absorption in the waveguide results in a photocurrent at the electrodes of the electrical transmission line. The optical waveguide and electrical transmission line of the electrically distributed traveling-wave photodetector are designed to achieve matched velocities between the light in the optical waveguide and electrical signal generated on the transmission line. This velocity synchronization provides the traveling-wave photodetector with a large electrical bandwidth and a high quantum efficiency, because of the effective extended volume for optical absorption. The traveling-wave photodetector also provides large power dissipation, because of its large physical size. 4 figures.

Traveling-wave photodetector

DOEpatents

Hietala, Vincent M.; Vawter, Gregory A.

1993-01-01

The traveling-wave photodetector of the present invention combines an absorptive optical waveguide and an electrical transmission line, in which optical absorption in the waveguide results in a photocurrent at the electrodes of the electrical transmission line. The optical waveguide and electrical transmission line of the electrically distributed traveling-wave photodetector are designed to achieve matched velocities between the light in the optical waveguide and electrical signal generated on the transmission line. This velocity synchronization provides the traveling-wave photodetector with a large electrical bandwidth and a high quantum efficiency, because of the effective extended volume for optical absorption. The traveling-wave photodetector also provides large power dissipation, because of its large physical size.

Radiometric observations of the 752.033-GHz rotational absorption line of H2O from a laboratory jet. [simulation of rocket plumes

NASA Technical Reports Server (NTRS)

Dionne, G. F.; Fitzgerald, J. F.; Chang, T.-S.; Fetterman, H. R.; Litvak, M. M.

1980-01-01

With the aid of a high-resolution two-stage heterodyne radiometer, spectral absorption measurements of the 752.033 GHz line of water vapor were carried out, using a blackbody continuum as a background radiation source for investigating the absorptive properties of the H2O content of high altitude rocket plumes. To simulate this physical situation in a laboratory environment, a small steam jet was operated within a large high-vacuum chamber, with the H2O jet plume traversing the radiometer line of sight. The experiments verified that this rotational line is optically thick, with excitation temperatures below 100 K, in the downstream part of the plume, as predicted by theoretical modelling.

AERONET derived (BC) aerosol absorption

NASA Astrophysics Data System (ADS)

Kinne, S.

2015-12-01

AERONET is a ground-based sun-/sky-photometer network with good annual statistics at more than 400 sites worldwide. Inversion methods applied to these data define all relevant column aerosol optical properties and reveal even microphysical detail. The extracted data include estimates for aerosol size-distributions and for aerosol refractive indices at four different solar wavelengths. Hereby, the imaginary parts of the refractive indices define the aerosol column absorption. For regional and global averages and radiative impact assessment with off-line radiative transfer, these local data have been extended with distribution patterns offered by AeroCom modeling experiments. Annual and seasonal absorption distributions for total aerosol and estimates for component contributions (such as BC) are presented and associated direct forcing impacts are quantified.

[Construction and application of an onboard absorption analyzer device for CDOM].

PubMed

Lin, Jun-Fang; Sun, Zhao-Hua; Cao, Wen-Xi; Hu, Shui-Bo; Xu, Zhan-Tang

2013-04-01

Colored dissolved organic matter (CDOM) plays an important role in marine ecosystems. In order to solve the current problems in measurement of CDOM absorption, an automated onboard analyzer based on liquid core waveguides (Teflon AF LWCC/LCW) was constructed. This analyzer has remarkable characteristics including adjusted optical pathlength, wide measurement range, and high sensitivity. The model of filtration and injection can implement the function of automated filtration, sample injection, and LWCC cleaning. The LabVIEW software platform can efficiently control the running state of the analyzer and acquire real time data including light absorption spectra, GPS data, and CTW data. By the comparison experiments and shipboard measurements, it was proved that the analyzer was reliable and robust.

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

NASA Astrophysics Data System (ADS)

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

2017-06-01

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

Ultrafast Spectroscopic Studies of Two-Photon States in Third Order Optical Processes of Dye Chromophores.

NASA Astrophysics Data System (ADS)

Yu, Yi-Zhong

1995-01-01

Conjugated organic and polymeric materials usually have large, nonresonant third order optical nonlinearity due to correlations of their delocalized pi -electrons. Most materials studied so far show positive values of third order nonlinear susceptibility when all frequencies that generate the third order effect are below any optical transition. A new class of organic molecules, namely indole squarylium (ISQ) and anilinium squarylium (BSQ), exhibit negative < gamma(-omega_4;omega_1, omega_2,omega_3)> when all three frequencies, omega_1, omega_2 and omega_3, lie below the first electronic transition. Although quantum many-electron calculations based on multiple-excitation configuration interaction have shown that the negative third order coefficient is essentially due to the contribution from high-lying two-photon states, the field of experimental studies exploring the microscopic origins of the negative squaraines remains uncultivated. The work presented in this thesis involves extensive experimental investigation of squaraines using techniques such as time-resolved transit absorption spectroscopy and saturable absorption. Theoretical simulations studying nonlinear absorption behavior of a simplified two-level system with ultrashort pulses are also presented. Part of the thesis is dedicated to the development, fabrication and characterization of our ultrafast laser system which offers tunable femtosecond pulses at wavelengths from UV to IR and served as a major tool in the experimental measurements. The dynamics of the population inversion between the ground state and the first excited state was also investigated through time-resolved experiments. The experiment results agree well with the theoretical predictions. Strong couplings between the gateway state and high-lying two-photon states were observed in BSQ squarylium molecules, which suggested a complete quantum calculation with multiple energy levels is required to correctly describe the negative third order effect.

Energy-gap reduction in heavily doped silicon: Causes and consequences

NASA Astrophysics Data System (ADS)

Pantelides, Sokrates T.; Selloni, Annabella; Car, Roberto

1985-02-01

The authors review briefly the existing theoretical treatments of the various effects that contribute to the reduction of the energy gap in heavily doped Si, namely electron-electron and electron-impurity interactions and the effect of disorder in the impurity distribution. They then turn to the longstanding question why energy-gap reductions extracted from three different types of experiments have persistently produced values with substantial discrepancies, making it impossible to compare with theoretical values. First, they demonstrate that a meaningful comparison between theory and experiment can indeed be made if theoretical calculations are carried out for actual quantities that experiments measure, e.g. luminescence spectra, as recently done by Selloni and Pantelides. Then, they demonstrate that, independent of any theoretical calculations, the optical absorption spectra are fully consistent with the luminescence spectra and that the discrepancies in the energy-gap reductions extracted from the two sets of spectra are caused entirely by the curve-fitting procedures used in analyzing optical-absorption data. Finally, they show explicitly that, as already believed by many authors, energy-gap reductions extracted from electrical measurements on transistors do not correspond to true gap reductions. They identify two corrections that must be added to the values extracted from the electrical data in order to arrive at the true gap reductions and show that the resulting values are in good overall agreement with luminescence and absorption data. They, therefore, demonstrate that the observed reduction in emitter injection efficiency in bipolar transistors is not strictly due to a gap reduction, as generally believed, but to three very different effects.

Simultaneous high crystallinity and sub-bandgap optical absorptance in hyperdoped black silicon using nanosecond laser annealing

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

Franta, Benjamin, E-mail: bafranta@gmail.com; Pastor, David; Gandhi, Hemi H.

2015-12-14

Hyperdoped black silicon fabricated with femtosecond laser irradiation has attracted interest for applications in infrared photodetectors and intermediate band photovoltaics due to its sub-bandgap optical absorptance and light-trapping surface. However, hyperdoped black silicon typically has an amorphous and polyphasic polycrystalline surface that can interfere with carrier transport, electrical rectification, and intermediate band formation. Past studies have used thermal annealing to obtain high crystallinity in hyperdoped black silicon, but thermal annealing causes a deactivation of the sub-bandgap optical absorptance. In this study, nanosecond laser annealing is used to obtain high crystallinity and remove pressure-induced phases in hyperdoped black silicon while maintainingmore » high sub-bandgap optical absorptance and a light-trapping surface morphology. Furthermore, it is shown that nanosecond laser annealing reactivates the sub-bandgap optical absorptance of hyperdoped black silicon after deactivation by thermal annealing. Thermal annealing and nanosecond laser annealing can be combined in sequence to fabricate hyperdoped black silicon that simultaneously shows high crystallinity, high above-bandgap and sub-bandgap absorptance, and a rectifying electrical homojunction. Such nanosecond laser annealing could potentially be applied to non-equilibrium material systems beyond hyperdoped black silicon.« less

Theoretical model for optical properties of porphyrin

NASA Astrophysics Data System (ADS)

Phan, Anh D.; Nga, Do T.; Phan, The-Long; Thanh, Le T. M.; Anh, Chu T.; Bernad, Sophie; Viet, N. A.

2014-12-01

We propose a simple model to interpret the optical absorption spectra of porphyrin in different solvents. Our model successfully explains the decrease in the intensity of optical absorption at maxima of increased wavelengths. We also prove the dependence of the intensity and peak positions in the absorption spectra on the environment. The nature of the Soret band is supposed to derive from π plasmon. Our theoretical calculations are consistent with previous experimental studies.

Excitonic Transitions and Off-resonant Optical Limiting in CdS Quantum Dots Stabilized in a Synthetic Glue Matrix

PubMed Central

2007-01-01

Stable films containing CdS quantum dots of mean size 3.4 nm embedded in a solid host matrix are prepared using a room temperature chemical route of synthesis. CdS/synthetic glue nanocomposites are characterized using high resolution transmission electron microscopy, infrared spectroscopy, differential scanning calorimetry and thermogravimetric analysis. Significant blue shift from the bulk absorption edge is observed in optical absorption as well as photoacoustic spectra indicating strong quantum confinement. The exciton transitions are better resolved in photoacoustic spectroscopy compared to optical absorption spectroscopy. We assign the first four bands observed in photoacoustic spectroscopy to 1se–1sh, 1pe–1ph, 1de–1dhand 2pe–2phtransitions using a non interacting particle model. Nonlinear absorption studies are done using z-scan technique with nanosecond pulses in the off resonant regime. The origin of optical limiting is predominantly two photon absorption mechanism.

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

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

Vishalli,, E-mail: vishalli-2008@yahoo.com; Dharamvir, Keya, E-mail: keya@pu.ac.in; Kaur, Ramneek

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 themore » 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.« less

Relative optical absorption of metallic and semiconducting single-walled carbon nanotubes.

PubMed

Huang, Houjin; Kajiura, Hisashi; Maruyama, Ryuichiro; Kadono, Koji; Noda, Kazuhiro

2006-03-16

While it is well-known that tube-tube interaction causes changes (peak red-shift and suppression) in the optical absorption of single-walled carbon nanotubes (SWNTs), we found in this work that, upon bundling, the optical absorption of metallic SWNTs (M11) is less affected compared to their semiconducting counterparts (S11 or S22), resulting in enhanced absorbance ratio of metallic and semiconducting SWNTs (A(M)/A(S)). Annealing of the SWNTs increases this ratio due to the intensified tube-tube interaction. We have also found that the interaction between SWNTs and the surfactant Triton X-405 has a similar effect. The evaluation of SWNT separation by types (metallic or semiconducting) based on the optical absorption should take these effects into account.

[Signal analysis and spectrum distortion correction for tunable diode laser absorption spectroscopy system].

PubMed

Bao, Wei-Yi; Zhu, Yong; Chen, Jun; Chen, Jun-Qing; Liang, Bo

2011-04-01

In the present paper, the signal of a tunable diode laser absorption spectroscopy (TDLAS) trace gas sensing system, which has a wavelength modulation with a wide range of modulation amplitudes, is studied based on Fourier analysis method. Theory explanation of spectrum distortion induced by laser intensity amplitude modulation is given. In order to rectify the spectrum distortion, a method of synchronous amplitude modulation suppression by a variable optical attenuator is proposed. To validate the method, an experimental setup is designed. Absorption spectrum measurement experiments on CO2 gas were carried out. The results show that the residual laser intensity modulation amplitude of the experimental system is reduced to -0.1% of its original value and the spectrum distortion improvement is 92% with the synchronous amplitude modulation suppression. The modulation amplitude of laser intensity can be effectively reduced and the spectrum distortion can be well corrected by using the given correction method and system. By using a variable optical attenuator in the TDLAS (tunable diode laser absorption spectroscopy) system, the dynamic range requirements of photoelectric detector, digital to analog converter, filters and other aspects of the TDLAS system are reduced. This spectrum distortion correction method can be used for online trace gas analyzing in process industry.

Nonlinear optical transmittance of semiconductors in the presence of high-intensity radiation fields

NASA Astrophysics Data System (ADS)

Dong, H. M.; Han, F. W.; Duan, Y. F.; Huang, F.; Liu, J. L.

2018-04-01

We developed a systematic theoretical study of nonlinear optical properties of semiconductors. The eight-band kṡp model and the energy-balance equation are employed to calculate the transmission and optical absorption coefficients in the presence of both the linear one-photon absorption and the nonlinear two-photon absorption (TPA) processes. A substantial reduction of the optical transmittance far below the band-gap can be observed under relatively high-intensity radiation fields due to the nonlinear TPA. The TPA-induced optical transmittance decreases with increasing intensity of the radiation fields. Our theoretical results are in line with those observed experimentally. The theoretical approach can be applied to understand the nonlinear optical properties of semiconductors under high-field conditions.

Optical limiting properties of optically active phthalocyanine derivatives

NASA Astrophysics Data System (ADS)

Wang, Peng; Zhang, Shuang; Wu, Peiji; Ye, Cheng; Liu, Hongwei; Xi, Fu

2001-06-01

The optical limiting properties of four optically active phthalocyanine derivatives in chloroform solutions and epoxy resin thin plates were measured at 532 nm with 10 ns pulses. The excited state absorption cross-section σex and refractive-index cross-section σr were determined with the Z-scan technique. These chromophores possess larger σex than the ground state absorption cross-section σ0, indicating that they are the potential materials for reverse saturable absorption (RSA). The negative σr values of these chromophores add to the thermal contribution, producing a larger defocusing effect, which may be helpful in further enhancing their optical limiting performance. The optical limiting responses of the thin plate samples are stronger than those of the chloroform solutions.

On the possibility of laser cooling of Cr3+ ions doped crystals

NASA Astrophysics Data System (ADS)

Feofilov, S. P.; Kulinkin, A. B.

2018-01-01

The fluorescence of Cr3+ ions doped insulating crystals was studied under the excitation in the long-wavelength tail of the absorption spectrum ("laser cooling regime"). The 4T2 - 4A2 and 2E - 4A2 fluorescence spectra with a dominant anti-Stokes component were observed. Though no optical refrigeration was detected in the presented experiments, the spectroscopic results suggest that electron-phonon bands of Cr3+ ions are of interest for further investigations from the point of view of achieving optical refrigeration.

Optical interference fringe reduction in frequency-modulation spectroscopy experiments

NASA Astrophysics Data System (ADS)

Hjelme, Dag Roar; Neegard, Steinar; Vartdal, Erling

1995-08-01

We show both theoretically and experimentally that interference fringe signals can always be suppressed to improve the signal-to-noise ratio, provided that the modulation frequency is of the order of the absorption linewidth or higher. Suppression of optical interference fringes by more than 1 order of magnitude and signal-to-noise ratio enhancement of more than 13 dB is demonstrated by use of a proper choice of laser modulation frequency. A further fringe reduction of 10 dB is possible by adjustment of the local oscillator phase.

Sensing nitrous oxide with QCL-coupled silicon-on-sapphire ring resonators.

PubMed

Smith, Clinton J; Shankar, Raji; Laderer, Matthew; Frish, Michael B; Loncar, Marko; Allen, Mark G

2015-03-09

We report the initial evaluation of a mid-infrared QCL-coupled silicon-on-sapphire ring resonator gas sensor. The device probes the N(2)O 2241.79 cm(-1) optical transition (R23 line) in the ν(3) vibrational band. N(2)O concentration is deduced using a non-linear least squares fit, based on coupled-mode theory, of the change in ring resonator Q due to gas absorption losses in the evanescent portion of the waveguide optical mode. These early experiments demonstrated response to 5000 ppmv N(2)O.

Nuclear fragmentation energy and momentum transfer distributions in relativistic heavy-ion collisions

NASA Technical Reports Server (NTRS)

Khandelwal, Govind S.; Khan, Ferdous

1989-01-01

An optical model description of energy and momentum transfer in relativistic heavy-ion collisions, based upon composite particle multiple scattering theory, is presented. Transverse and longitudinal momentum transfers to the projectile are shown to arise from the real and absorptive part of the optical potential, respectively. Comparisons of fragment momentum distribution observables with experiments are made and trends outlined based on our knowledge of the underlying nucleon-nucleon interaction. Corrections to the above calculations are discussed. Finally, use of the model as a tool for estimating collision impact parameters is indicated.

Preparation, optical and non-linear optical power limiting properties of Cu, CuNi nanowires

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

Udayabhaskar, R.; Karthikeyan, B., E-mail: bkarthik@nitt.edu; Ollakkan, Muhamed Shafi

2014-01-06

Metallic nanowires show excellent Plasmon absorption which is tunable based on its aspect ratio and alloying nature. We prepared Cu and CuNi metallic nanowires and studied its optical and nonlinear optical behavior. Optical properties of nanowires are theoretically explained using Gans theory. Nonlinear optical behavior is studied using a single beam open aperture z-scan method with the use of 5 ns Nd: YAG laser. Optical limiting is found to arise from two-photon absorption.

Preparation, optical and non-linear optical power limiting properties of Cu, CuNi nanowires

NASA Astrophysics Data System (ADS)

Udayabhaskar, R.; Ollakkan, Muhamed Shafi; Karthikeyan, B.

2014-01-01

Metallic nanowires show excellent Plasmon absorption which is tunable based on its aspect ratio and alloying nature. We prepared Cu and CuNi metallic nanowires and studied its optical and nonlinear optical behavior. Optical properties of nanowires are theoretically explained using Gans theory. Nonlinear optical behavior is studied using a single beam open aperture z-scan method with the use of 5 ns Nd: YAG laser. Optical limiting is found to arise from two-photon absorption.

Interpreting measurements obtained with the cloud absorption radiometer

NASA Technical Reports Server (NTRS)

1988-01-01

The software developed for the analysis of data from the Cloud Absorption Radiometer (CAR) is discussed. The CAR is a multichannel radiometer designed to measure the radiation field in the middle of an optically thick cloud (the diffusion domain). It can also measure the surface albedo and escape function. The instrument currently flies on a C-131A aircraft operated by the University of Washington. Most of this data was collected during the First International satellite cloud climatology project Regional Experiment (FIRE) Marine Stratocumulus Intensive Field Observation program off San Diego during July 1987. Earlier flights of the CAR have also been studied.

Nonreciprocal optical properties based on magneto-optical materials: n-InAs, GaAs and HgCdTe

NASA Astrophysics Data System (ADS)

Wang, Han; Wu, Hao; Zhou, Jian-qiu

2018-02-01

Compared with reciprocal optical materials, nonreciprocal materials can break the time reversal and detailed balance due to special nonreciprocal effect, while how its characteristics performing on infrared wavelength have not been paid enough attention. In this paper, the optical properties of three magneto-optical materials was investigated in infrared band, that are n-InAs, GaAs, HgCdTe, based on Finite Difference Time Domain (FDTD) method. The equations of dielectric constant tensor are present and the effect of magnetic field intensity and frequency has been studied in detail. Additionally, the effect of incidence angle at positive and negative directions to the nonreciprocal absorptivity is also investigated. It is found that the nonreciprocal effect is obvious in infrared wavelength, and the nonreciprocal effect could adjust the absorption characteristic, thus be able to tune the absorption for the specific frequency of incident light. In addition to modeling the directional radiative properties at various angles of incidence, the absorption peaks of three materials under different incident angles are also calculated to understand the light absorption and to facilitate the optimal design of high-performance photovoltaic and optical instrument.

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

NASA Astrophysics Data System (ADS)

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

2014-03-01

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

Biogeochemical and Optical Analysis of Coastal DOM for Satellite Retrieval of Terrigenous DOM in the U.S. Middle Atlantic Bight

NASA Technical Reports Server (NTRS)

Mannino, A.; Dyda, R. Y.; Hernes, P. J.; Hooker, Stan; Hyde, Kim; Novak, Mike

2012-01-01

Estuaries and coastal ocean waters experience a high degree of variability in the composition and concentration of particulate and dissolved organic matter (DOM) as a consequence of riverine/estuarine fluxes of terrigenous DOM, sediments, detritus and nutrients into coastal waters and associated phytoplankton blooms. Our approach integrates biogeochemical measurements (elemental content, molecular analyses), optical properties (absorption) and remote sensing to examine terrestrial DOM contributions into the U.S. Middle Atlantic Bight (MAB). We measured lignin phenol composition, DOC and CDOM absorption within the Chesapeake and Delaware Bay mouths, plumes and adjacent coastal ocean waters to derive empirical relationships between CDOM and biogeochemical measurements for satellite remote sensing application. Lignin ranged from 0.03 to 6.6 ug/L between estuarine and outer shelf waters. Our results demonstrate that satellite-derived CDOM is useful as a tracer of terrigenous DOM in the coastal ocean

Real-structure effects: Band gaps of Mg_xZn_{1-x}O, Cd_xZn_{1-x}O, and n-type ZnO from ab-initio calculations

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

Schleife, A; Bechstedt, F

2012-02-15

Many-body perturbation theory is applied to compute the quasiparticle electronic structures and the optical-absorption spectra (including excitonic effects) for several transparent conducting oxides. We discuss HSE+G{sub 0}W{sub 0} results for band structures, fundamental band gaps, and effective electron masses of MgO, ZnO, CdO, SnO{sub 2}, SnO, In{sub 2}O{sub 3}, and SiO{sub 2}. The Bethe-Salpeter equation is solved to account for excitonic effects in the calculation of the frequency-dependent absorption coefficients. We show that the HSE+G{sub 0}W{sub 0} approach and the solution of the Bethe-Salpeter equation are very well-suited to describe the electronic structure and the optical properties of various transparentmore » conducting oxides in good agreement with experiment.« less

Picosecond cubic and quintic nonlinearity of lithium niobate at 532 nm

NASA Astrophysics Data System (ADS)

Wang, Hongzhen; Boudebs, Georges; de Araújo, Cid B.

2017-08-01

The nonlinear (NL) optical response of bulk lithium niobate (LiNbO3) was investigated at 532 nm using the second harmonic of a Nd:YAG laser delivering pulses of 12 ps. The experiments were performed using the D4σ method combined with the conventional Z-scan technique. Two- and three-photon absorption coefficients equal to 0.27 c m /G W and 2.5 ×10-26 m3/W2, respectively, were determined. The NL absorption processes were due to transitions from the valence to the conduction band and to free-carrier absorption. The third- and fifth-order NL refractive indices were n2=(2.5 ±0.6 )×10-19 m2/W and n4<5.5 ×10-36 m4/W2. The present results give the support for previous experiments that indicate possible fifth-order processes in bulk samples and channel waveguides fabricated with LiNbO3.

Random-hole optical fiber evanescent-wave gas sensing.

PubMed

Pickrell, G; Peng, W; Wang, A

2004-07-01

Research on development of optical gas sensors based on evanescent-wave absorption in random-hole optical fibers is described. A process to produce random-hole optical fibers was recently developed that uses a novel in situ bubble formation technique. Gas molecules that exhibit characteristic vibrational absorption lines in the near-IR region that correspond to the transmission window for silica optical fiber have been detected through the evanescent field of the guided mode in the pore region. The presence of the gas molecules in the holes of the fiber appears as a loss at wavelengths that are characteristic of the particular gas species present in the holes. An experimental setup was constructed with these holey fibers for detection of acetylene gas. The results clearly demonstrate the characteristic absorptions in the optical spectra that correspond to the narrow-line absorptions of the acetylene gas, and this represents what is to our knowledge the first report of random-hole fiber gas sensing in the literature.

Characterization of laser damage performance of fused silica using photothermal absorption technique

NASA Astrophysics Data System (ADS)

Wan, Wen; Shi, Feng; Dai, Yifan; Peng, Xiaoqiang

2017-06-01

The subsurface damage and metal impurities have been the main laser damage precursors of fused silica while subjected to high power laser irradiation. Light field enhancement and thermal absorption were used to explain the appearance of damage pits while the laser energy is far smaller than the energy that can reach the intrinsic threshold of fused silica. For fused silica optics manufactured by magnetorheological finishing or advanced mitigation process, no scratch-related damage site occurs can be found on the surface. In this work, we implemented a photothermal absorption technique based on thermal lens method to characterize the subsurface defects of fused silica optics. The pump beam is CW 532 nm wavelength laser. The probe beam is a He-Ne laser. They are collinear and focused through the same objective. When pump beam pass through the sample, optical absorption induces the local temperature rise. The lowest absorptance that we can detect is about the order of magnitude of 0.01 ppm. When pump beam pass through the sample, optical absorption induces the local temperature rise. The photothermal absorption value of fused silica samples range from 0.5 to 10 ppm. The damage densities of the samples were plotted. The damage threshold of samples at 8J/cm2 were gived to show laser damage performance of fused silica.The results show that there is a strong correlation between the thermal absorption and laser damage density. The photothermal absorption technique can be used to predict and evaluate the laser damage performance of fused silica optics.

Assessment of using ultrasound images as prior for diffuse optical tomography regularization matrix

NASA Astrophysics Data System (ADS)

Althobaiti, Murad; Vavadi, Hamed; Zhu, Quing

2017-02-01

Imaging of tissue with Ultrasound-guided diffuse optical tomography (DOT) is a rising imaging technique to map hemoglobin concentrations within tissue for breast cancer detection and diagnosis. Near-infrared optical imaging received a lot of attention in research as a possible technique to be used for such purpose especially for breast tumors. Since DOT images contrast is closely related to oxygenation and deoxygenating of the hemoglobin, which is an important factor in differentiating malignant and benign tumors. One of the optical imaging modalities used is the diffused optical tomography (DOT); which probes deep scattering tissue (1-5cm) by NIR optical source-detector probe and detects NIR photons in the diffusive regime. The photons in the diffusive regime usually reach the detector without significant information about their source direction and the propagation path. Because of that, the optical reconstruction problem of the medium characteristics is ill-posed even with the tomography and Back-projection techniques. The accurate recovery of images requires an effective image reconstruction method. Here, we illustrate a method in which ultrasound images are encoded as prior for regularization of the inversion matrix. Results were evaluated using phantom experiments of low and high absorption contrasts. This method improves differentiation between the low and the high contrasts targets. Ultimately, this method could improve malignant and benign cases by increasing reconstructed absorption ratio of malignant to benign. Besides that, the phantom results show improvements in target shape as well as the spatial resolution of the DOT reconstructed images.

pH-Induced Modulation of One- and Two-Photon Absorption Properties in a Naphthalene-Based Molecular Probe.

PubMed

Murugan, N Arul; Kongsted, Jacob; Ågren, Hans

2013-08-13

Presently, there is a great demand for small probe molecules that can be used for two-photon excitation microscopy (TPM)-based monitoring of intracellular and intraorganelle activity and pH. The candidate molecules should ideally possess a large two-photon absorption cross section with optical properties sensitive to pH changes. In the present work, we investigate the potential of a methoxy napthalene (MONAP) derivative for its suitability to serve as a pH sensor using TPM. Using an integrated approach rooted in hybrid quantum mechanics/molecular mechanics, the structures, dynamics, and the one- and two-photon properties of the probe in dimethylformamide solvent are studied. It is found that the protonated form is responsible for the optical property of MONAP at moderately low pH, for which the calculated pH-induced red shift is in good agreement with experiments. A 2-fold increase in the two-photon absorption cross section in the IR region of the spectrum is predicted for the moderately low pH form of the probe, suggesting that this can be a potential probe for pH monitoring of living cells. We also propose some design principles aimed at obtaining control of the absorption spectral range of the probe by structural tuning. Our work indicates that the integrated approach employed is capable of capturing the pH-induced changes in structure and optical properties of organic molecular probes and that such in silico tools can be used to draw structure-property relationships to design novel molecular probes suitable for a specific application.

Estimates of the Spectral Aerosol Single Sea Scattering Albedo and Aerosol Radiative Effects during SAFARI 2000

NASA Technical Reports Server (NTRS)

Bergstrom, Robert W.; Pilewskie, Peter; Schmid, Beat; Russell, Philip B.

2003-01-01

Using measurements of the spectral solar radiative flux and optical depth for 2 days (24 August and 6 September 2000) during the SAFARI 2000 intensive field experiment and a detailed radiative transfer model, we estimate the spectral single scattering albedo of the aerosol layer. The single scattering albedo is similar on the 2 days even though the optical depth for the aerosol layer was quite different. The aerosol single scattering albedo was between 0.85 and 0.90 at 350 nm, decreasing to 0.6 in the near infrared. The magnitude and decrease with wavelength of the single scattering albedo are consistent with the absorption properties of small black carbon particles. We estimate the uncertainty in the single scattering albedo due to the uncertainty in the measured fractional absorption and optical depths. The uncertainty in the single scattering albedo is significantly less on the high-optical-depth day (6 September) than on the low-optical-depth day (24 August). On the high-optical-depth day, the uncertainty in the single scattering albedo is 0.02 in the midvisible whereas on the low-optical-depth day the uncertainty is 0.08 in the midvisible. On both days, the uncertainty becomes larger in the near infrared. We compute the radiative effect of the aerosol by comparing calculations with and without the aerosol. The effect at the top of the atmosphere (TOA) is to cool the atmosphere by 13 W/sq m on 24 August and 17 W/sq m on 6 September. The effect on the downward flux at the surface is a reduction of 57 W/sq m on 24 August and 200 W/sq m on 6 September. The aerosol effect on the downward flux at the surface is in good agreement with the results reported from the Indian Ocean Experiment (INDOEX).

Near-infrared voltage-sensitive fluorescent dyes optimized for optical mapping in blood-perfused myocardium.

PubMed

Matiukas, Arvydas; Mitrea, Bogdan G; Qin, Maochun; Pertsov, Arkady M; Shvedko, Alexander G; Warren, Mark D; Zaitsev, Alexey V; Wuskell, Joseph P; Wei, Mei-de; Watras, James; Loew, Leslie M

2007-11-01

Styryl voltage-sensitive dyes (e.g., di-4-ANEPPS) have been used successfully for optical mapping in cardiac cells and tissues. However, their utility for probing electrical activity deep inside the myocardial wall and in blood-perfused myocardium has been limited because of light scattering and high absorption by endogenous chromophores and hemoglobin at blue-green excitation wavelengths. The purpose of this study was to characterize two new styryl dyes--di-4-ANBDQPQ (JPW-6003) and di-4-ANBDQBS (JPW-6033)--optimized for blood-perfused tissue and intramural optical mapping. Voltage-dependent spectra were recorded in a model lipid bilayer. Optical mapping experiments were conducted in four species (mouse, rat, guinea pig, and pig). Hearts were Langendorff perfused using Tyrode's solution and blood (pig). Dyes were loaded via bolus injection into perfusate. Transillumination experiments were conducted in isolated coronary-perfused pig right ventricular wall preparations. The optimal excitation wavelength in cardiac tissues (650 nm) was >70 nm beyond the absorption maximum of hemoglobin. Voltage sensitivity of both dyes was approximately 10% to 20%. Signal decay half-life due to dye internalization was 80 to 210 minutes, which is 5 to 7 times slower than for di-4-ANEPPS. In transillumination mode, DeltaF/F was as high as 20%. In blood-perfused tissues, DeltaF/F reached 5.5% (1.8 times higher than for di-4-ANEPPS). We have synthesized and characterized two new near-infrared dyes with excitation/emission wavelengths shifted >100 nm to the red. They provide both high voltage sensitivity and 5 to 7 times slower internalization rate compared to conventional dyes. The dyes are optimized for deeper tissue probing and optical mapping of blood-perfused tissue, but they also can be used for conventional applications.

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.

The energy spectrum and the optical absorption spectrum of C{sub 60} fullerene within the Hubbard model

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

Silant’ev, A. V., E-mail: kvvant@rambler.ru

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.

Thermal, mechanical, optical and conductivity studies of a novel NLO active L-phenylalanine L-phenylalaninium dihydrogenphosphate single crystal

NASA Astrophysics Data System (ADS)

Sujatha, T.; Cyrac Peter, A.; Vimalan, M.; Merline Shyla, J.; Madhavan, J.

2010-08-01

An efficient, novel, semi-organic, nonlinear optical (NLO) material L-phenylalanine L-phenylalaninium dihydrogenphosphate (LPADHP), single crystal of dimension 11×5×2 mm 3, has been grown by the slow evaporation solution growth technique. Single crystal X-ray diffraction studies confirm that the grown crystal belongs to monoclinic system with the space group P2 1. The functional groups present in the crystal were confirmed by the Fourier transform infrared technique. Optical absorption spectrum shows that the material possesses very low absorption in the entire visible region. Thermal analysis confirmed that the crystal is thermally stable up to 161 °C. The frequency dependent dielectric properties of the grown crystal were studied for various temperatures. The second harmonic generation (SHG) efficiency of the grown crystal is 1.2 times greater than that of the potassium dihydrogenphosphate (KDP) single crystal. The laser induced surface damage threshold for the grown crystal was found to be 6.3 GW cm -2 with Nd:YAG laser assembly AC and DC conductivity and photoconductivity experiments are also carried out and the results are discussed.

Exciton self-trapping and Stark effect in the optical response of pentacene crystals from first principles

NASA Astrophysics Data System (ADS)

Strubbe, David A.; Sharifzadeh, Sahar; Neaton, Jeffrey B.; Louie, Steven G.

2012-02-01

Pentacene is a prototypical organic semiconductor with optoelectronic and photovoltaic applications. It is known that the lowest-energy singlet excitation has a Stokes shift between absorption and emission of about 0.14 eV, but the deformation associated with this self-trapped exciton remains unknown. We begin with a calculation of the optical properties via the first-principles GW/Bethe-Salpeter (BSE) theory [ML Tiago, JE Northrup, and SG Louie, Phys. Rev. B 67, 115212 (2003); S Sharifzadeh, A Biller, L Kronik, and JB Neaton, arXiv:1110.4928 (2011)]. We then study the self-trapping phenomenon via our reformulation of the Bethe-Salpeter excited-state forces approximation of Ismail-Beigi and Louie [Phys. Rev. Lett. 90, 076401 (2003)], which can describe the structural relaxation after optical excitation. Whether excitons in pentacene have charge-transfer character has been controversial in electro-absorption experiments. We use the same BSE analytic derivatives approach to calculate the changes in excitation energies due to an applied electric field to understand this experimental controversy.

Optical remote measurement of toxic gases

NASA Technical Reports Server (NTRS)

Grant, W. B.; Kagann, R. H.; McClenny, W. A.

1992-01-01

Enactment of the Clean Air Act Amendments (CAAA) of 1990 has resulted in increased ambient air monitoring needs for industry, some of which may be met efficiently using open-path optical remote sensing techniques. These techniques include Fourier transform spectroscopy, differential optical absorption spectroscopy, laser long-path absorption, differential absorption lidar, and gas cell correlation spectroscopy. With this regulatory impetus, it is an opportune time to consider applying these technologies to the remote and/or path-averaged measurement and monitoring of toxic gases covered by the CAAA. This article reviews the optical remote sensing technology and literature for that application.

Double-pulse 1.57  μm integrated path differential absorption lidar ground validation for atmospheric carbon dioxide measurement.

PubMed

Du, Juan; Zhu, Yadan; Li, Shiguang; Zhang, Junxuan; Sun, Yanguang; Zang, Huaguo; Liu, Dan; Ma, Xiuhua; Bi, Decang; Liu, Jiqiao; Zhu, Xiaolei; Chen, Weibiao

2017-09-01

A ground-based double-pulse integrated path differential absorption (IPDA) instrument for carbon dioxide (CO 2 ) concentration measurements at 1572 nm has been developed. A ground experiment was implemented under different conditions with a known wall located about 1.17 km away acting as the scattering hard target. Off-/offline testing of a laser transmitter was conducted to estimate the instrument systematic and random errors. Results showed a differential absorption optical depth (DAOD) offset of 0.0046 existing in the instrument. On-/offline testing was done to achieve the actual DAOD resulting from the CO 2 absorption. With 18 s pulses average, it demonstrated that a CO 2 concentration measurement of 432.71±2.42  ppm with 0.56% uncertainty was achieved. The IPDA ranging led to a measurement uncertainty of 1.5 m.

Measurements of ionization states in warm dense aluminum with betatron radiation

NASA Astrophysics Data System (ADS)

Mo, M. Z.; Chen, Z.; Fourmaux, S.; Saraf, A.; Kerr, S.; Otani, K.; Masoud, R.; Kieffer, J.-C.; Tsui, Y.; Ng, A.; Fedosejevs, R.

2017-05-01

Time-resolved measurements of the ionization states of warm dense aluminum via K-shell absorption spectroscopy are demonstrated using betatron radiation generated from laser wakefield acceleration as a probe. The warm dense aluminum is generated by irradiating a free-standing nanofoil with a femtosecond optical laser pulse and was heated to an electron temperature of ˜20 -25 eV at a close-to-solid mass density. Absorption dips in the transmitted x-ray spectrum due to the Al4 + and Al5 + ions are clearly seen during the experiments. The measured absorption spectra are compared to simulations with various ionization potential depression models, including the commonly used Stewart-Pyatt model and an alternative modified Ecker-Kröll model. The observed absorption spectra are in approximate agreement with these models, though indicating a slightly higher state of ionization and closer agreement for simulations with the modified Ecker-Kröll model.

Apparatus and method for quantitative measurement of small differences in optical absorptivity between two samples using differential interferometry and the thermooptic effect

DOEpatents

Cremers, D.A.; Keller, R.A.

1984-05-08

An apparatus and method for the measurement of small differences in optical absorptivity of weakly absorbing solutions using differential interferometry and the thermooptic effect have been developed. Two sample cells are placed in each arm of an interferometer and are traversed by colinear probe and heating laser beams. The interrogation probe beams are recombined forming a fringe pattern, the intensity of which can be related to changes in optical path length of these laser beams through the cells. This in turn can be related to small differences in optical absorptivity which results in different amounts of sample heating when the heating laser beams are turned on, by the fact that the index of refraction of a liquid is temperature dependent. A critical feature of this invention is the stabilization of the optical path of the probe beams against drift. Background (solvent) absorption can then be suppressed by a factor of approximately 400. Solute absorptivities of about 10[sup [minus]5] cm[sup [minus]1] can then be determined in the presence of background absorptions in excess of 10[sup [minus]3] cm[sup [minus]1]. In addition, the smallest absorption measured with the instant apparatus and method is about 5 [times] 10[sup [minus]6] cm[sup [minus]1]. 6 figs.

Subgap Absorption in Conjugated Polymers

DOE R&D Accomplishments Database

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

1991-01-01

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

Analysis of diffential absorption lidar technique for measurements of anhydrous hydrogen chloride from solid rocket motors using a deuterium fluoride laser

NASA Technical Reports Server (NTRS)

Bair, C. H.; Allario, F.

1977-01-01

An active optical technique (differential absorption lidar (DIAL)) for detecting, ranging, and quantifying the concentration of anhydrous HCl contained in the ground cloud emitted by solid rocket motors (SRM) is evaluated. Results are presented of an experiment in which absorption coefficients of HCl were measured for several deuterium fluoride (DF) laser transitions demonstrating for the first time that a close overlap exists between the 2-1 P(3) vibrational transition of the DF laser and the 1-0 P(6) absorption line of HCl, with an absorption coefficient of 5.64 (atm-cm) to the -1 power. These measurements show that the DF laser can be an appropriate radiation source for detecting HCl in a DIAL technique. Development of a mathematical computer model to predict the sensitivity of DIAL for detecting anhydrous HCl in the ground cloud is outlined, and results that assume a commercially available DF laser as the radiation source are presented.

Decrease and enhancement of third-order optical nonlinearity in metal-dielectric composite films

NASA Astrophysics Data System (ADS)

Ning, Tingyin; Lu, Heng; Zhou, Yueliang; Man, Baoyuan

2018-04-01

We investigate third-order optical nonlinearity in gold nanoparticles embedded in CaCu3Ti4O12 (CCTO) films using the Z-scan method. We observe that the effective third-order nonlinear optical susceptibilities in such composite films can not only be enhanced, in line with the conventional behavior, but also be decreased, depending on the volume concentration of gold. In particular, the nonlinear absorption behavior can be changed from saturable absorption in pure CCTO films to reversed saturable absorption in composite films, and theoretically, even zero nonlinear absorption could be obtained. These results indicate that it should be possible to tune the third-order optical nonlinearity in Au:CCTO composite films by altering the gold concentration, thus making them suitable for applications in photonic devices.

Third-order nonlinear optical properties of organic azo dyes by using strength of nonlinearity parameter and Z-scan technique

NASA Astrophysics Data System (ADS)

Motiei, H.; Jafari, A.; Naderali, R.

2017-02-01

In this paper, two chemically synthesized organic azo dyes, 2-(2,5-Dichloro-phenyazo)-5,5-dimethyl-cyclohexane-1,3-dione (azo dye (i)) and 5,5-Dimethyl-2-tolylazo-cyclohexane-1,3-dione (azo dye (ii)), have been studied from optical Kerr nonlinearity point of view. These materials were characterized by Ultraviolet-visible spectroscopy. Experiments were performed using a continous wave diode-pumped laser at 532 nm wavelength in three intensities of the laser beam. Nonlinear absorption (β), refractive index (n2) and third-order susceptibility (χ (3)) of dyes, were calculated. Nonlinear absorption coefficient of dyes have been calculated from two methods; 1) using theoretical fits and experimental data in the Z-scan technique, 2) using the strength of nonlinearity curves. The values of β obtained from both of the methods were approximately the same. The results demonstrated that azo dye (ii) displays better nonlinearity and has a lower two-photon absorption threshold than azo dye (i). Calculated parameter related to strength of nonlinearity for azo dye (ii) was higher than azo dye (i), It may be due to presence of methyl in azo dye (ii) instead of chlorine in azo dye (i). Furthermore, The measured values of third order susceptibility of azo dyes were from the order of 10-9 esu . These azo dyes can be suitable candidate for optical switching devices.

Optical detection of tracer species in strongly scattering media.

PubMed

Brauser, Eric M; Rose, Peter E; McLennan, John D; Bartl, Michael H

2015-03-01

A combination of optical absorption and scattering is used to detect tracer species in a strongly scattering medium. An optical setup was developed, consisting of a dual-beam scattering detection scheme in which sample scattering beam overlaps with the characteristic absorption feature of quantum dot tracer species, while the reference scattering beam is outside any absorption features of the tracer. This scheme was successfully tested in engineered breakthrough tests typical of wastewater and subsurface fluid analysis, as well as in batch analysis of oil and gas reservoir fluids and biological samples. Tracers were detected even under highly scattering conditions, conditions in which conventional absorption or fluorescence methods failed.

Quantification of Absorption Due to Black and Brown Carbon from Biomass Burning and Parameterizations for Comparison to Climate Models Result

NASA Astrophysics Data System (ADS)

Pokhrel, Rudra Prasad

This dissertation examines the optical properties of fresh and aged biomass burning aerosols, parameterization of these properties, and development of new instrumentation and calibration techniques to measure aerosol optical properties. Data sets were collected from the fourth Fire Lab at Missoula Experiment (FLAME-4) that took place from October 15 to November 16, 2012. Biomass collected from the various parts of the world were burned under controlled laboratory conditions and fresh emissions from different stages of burning were measured and analyzed. Optical properties of aged aerosol under different conditions was also explored. A photoacoustic absorption spectrometer (PAS) was built and integrated with a newly designed thermal denuder to improve upon observations made during Flame-4. A novel calibration technique for the PAS was developed. Single scattering albedo (SSA) and absorption Angstrom exponent (AAE) from 12 different fuels with 41 individual burns were estimated and parameterized with modified combustion efficiency (MCE) and the ratio of elemental carbon (EC) to organic carbon (OC) mass. The EC / OC ratio has better capability to parameterize SSA and AAE than MCE. The simple linear regression model proposed in this study accurately predicts SSA during the first few hours of plume aging with the ambient data from a biomass burning event. In addition, absorption due to brown carbon (BrC) can significantly lower the SSA at 405 nm resulting in a wavelength dependence of SSA. Furthermore, smoldering dominated burns have larger AAE values while flaming dominated burns have smaller AAE values indicating a large fraction of BrC is emitted during the smoldering stage of the burn. Enhancement in BC absorption (EAbs) due to coating by absorbing and non-absorbing substances is estimated at 405 nm and 660 nm. Relatively smaller values of EAbs at 660 nm compared to 405 nm suggests lensing is a less important contributor to biomass burning aerosol absorption at lower wavelengths. Multiple burns of the same fuel produced significantly different EAbs values at 405 nm, but show good correlation with the EC/OC ratio indicating less dependency on fuel type and more dependency on burn conditions. In addition, absorption due to BrC can contribute up to 92 % of the total biomass burning aerosol absorption at 405 nm and up to 58 % of the total absorption at 532 nm. Indicating BrC absorption in biomass burning emissions is equally or more important than the absorption due to BC at short wavelengths. Furthermore, fractional absorption due to BrC shows reasonably good correlation with EC/OC ratio and AAE. Primary organic aerosol is found to be more volatile than secondary organic aerosol and it is found that the thermal denuder deployed in this study removes less organic aerosol if secondary organic aerosol is present. SSA at 532 nm remains constant during different conditions of aging while SSA at 405 nm increases under certain conditions suggesting the degradation of BrC. Decreases in AAE under the same experiment further support the proposed BrC degradation. The novel thermal denuder designed completely removes non-refractory material and can be used under higher flow rates (maximum of 5 LPM) than the most commercially available thermal denuders. The new calibration techniques proposed for the photoacousitc absorption spectrometer will reduce uncertainty during calibration compared to the conventional calibration methods.

Optical switching property of electromagnetically induced transparency in a Λ system

NASA Astrophysics Data System (ADS)

Zhang, Lianshui; Wang, Jian; Feng, Xiaomin; Yang, Lijun; Li, Xiaoli; Zhao, Min

2008-12-01

In this paper we study the coherent transient property of a Λ-three-level system (Ωd = 0) and a quasi- Λ -four-level system (Ωd>0). Optical switching of the probe field can be achieved by applying a pulsed coupling field or rf field. In Λ -shaped three-level system, when the coupling field was switched on, there is a almost total transparency of the probe field and the time required for the absorption changing from 90% to 10% of the maximum absorption is 2.9Γ0 (Γ0 is spontaneous emission lifetime). When the coupling field was switched off, there is an initial increase of the probe field absorption and then gradually evolves to the maximum of absorption of the two-level absorption, the time required for the absorption of the system changing from 10% to 90% is 4.2Γ0. In four-level system, where rf driving field is used as switching field, to achieve the same depth of the optical switching, the time of the optical switching is 2.5Γ0 and 6.1Γ0, respectively. The results show that with the same depth of the optical switching, the switch-on time of the four-level system is shorter than that of the three-level system, while the switch-off time of the four-level system is longer. The depth of the optical switching of the four-level system was much larger than that of the three-level system, where the depth of the optical switching of the latter is merely 14.8% of that of the former. The speed of optical switching of the two systems can be increased by the increase of Rabi frequency of coupling field or rf field.

Morphology and Optical Properties of Mixed Aerosol Particles

NASA Astrophysics Data System (ADS)

Fard, Mehrnoush M.; Krieger, Ulrich; Rudich, Yinon; Marcolli, Claudia; Peter, Thomas

2015-04-01

Experiments and modeling studies have shown that deliquesced aerosols can be present not only as one-phase system containing organics, inorganic salts and water, but often as two-phase systems consisting of a predominantly organic and a predominantly inorganic aqueous phase 1,2. Recent laboratory studies conducted with model mixtures representing tropospheric aerosols1,2,3, secondary organic aerosol (SOA) from smog chamber experiments4, and field measurements5 suggest that liquid- liquid phase separations (LLPS) is indeed a common phenomenon in mixed organic/ ammonium sulfate (AS) particles. During LLPS, particles may adopt different morphologies mainly core- shell and partially engulfed. A core- shell configuration will have consequences for heterogeneous chemistry and hygroscopicity and as a result will alter the optical properties of the particles since the aqueous inorganic-rich phase will be totally enclosed by a probably highly viscous organic coating with low diffusivity for reactants and water. The primary objective of this project is to establish a method for investigating the morphology of mixed inorganic and absorbing organic compounds of atmospheric relevance and study their radiative properties before, during, and after phase transitions mainly during LLPS. This will be the first study looking into the radiative effect of LLPS in detail. In this first experiment, the behavior of single droplets of carminic acid (CA)/ AS/ H2O mixture was monitored during relative humidity (RH) cycles using optical microscopy. The same mixture particle was levitated in an electrodynamic balance (EDB) and the change in its absorption properties was measured at varying RH. We also intend to determine the occurrence of LLPS in accumulation- sized particles and the change in their absorption using a cavity ring down aerosol spectrometer. If LLPS alters the absorptive properties of the suggested model aerosols significantly, absorption measurements of accumulation mode particles of the same composition would allow proving that LLPS indeed occurs in particles of atmospheric relevant size ranges. Up to now this prove is missing. References: 1. Bertram, et al. Atmos. Chem & Phys, 11(21), 10995-11006, 2011. 2. Krieger, et al. Chemical Society Reviews, 41(19), 6631-6662, 2012 3. Song, M. et al. Geophys Res Lett, 39(19), 2012b 4. Smith et al. Atmos Chem & Phys, 12(20), 9613- 9628, 2012. 5. You, Y. et al. Proceedings of the National Academy of Sciences, 109(33), 13188-13193, 2012.

Electromagnetically induced transparency in a multilayered spherical quantum dot with hydrogenic impurity

NASA Astrophysics Data System (ADS)

Pavlović, Vladan; Šušnjar, Marko; Petrović, Katarina; Stevanović, Ljiljana

2018-04-01

In this paper the effects of size, hydrostatic pressure and temperature on electromagnetically induced transparency, as well as on absorption and the dispersion properties of multilayered spherical quantum dot with hydrogenic impurity are theoretically investigated. Energy eigenvalues and wavefunctions of quantum systems in three-level and four-level configurations are calculated using the shooting method, while optical properties are obtained using the density matrix formalism and master equations. It is shown that peaks of the optical properties experience a blue-shift with increasing hydrostatic pressure and red-shift with increasing temperature. The changes of optical properties as a consequence of changes in barrier wells widths are non-monotonic, and these changes are discussed in detail.

Spatial frequency domain spectroscopy of two layer media

NASA Astrophysics Data System (ADS)

Yudovsky, Dmitry; Durkin, Anthony J.

2011-10-01

Monitoring of tissue blood volume and oxygen saturation using biomedical optics techniques has the potential to inform the assessment of tissue health, healing, and dysfunction. These quantities are typically estimated from the contribution of oxyhemoglobin and deoxyhemoglobin to the absorption spectrum of the dermis. However, estimation of blood related absorption in superficial tissue such as the skin can be confounded by the strong absorption of melanin in the epidermis. Furthermore, epidermal thickness and pigmentation varies with anatomic location, race, gender, and degree of disease progression. This study describes a technique for decoupling the effect of melanin absorption in the epidermis from blood absorption in the dermis for a large range of skin types and thicknesses. An artificial neural network was used to map input optical properties to spatial frequency domain diffuse reflectance of two layer media. Then, iterative fitting was used to determine the optical properties from simulated spatial frequency domain diffuse reflectance. Additionally, an artificial neural network was trained to directly map spatial frequency domain reflectance to sets of optical properties of a two layer medium, thus bypassing the need for iteration. In both cases, the optical thickness of the epidermis and absorption and reduced scattering coefficients of the dermis were determined independently. The accuracy and efficiency of the iterative fitting approach was compared with the direct neural network inversion.

Changes in the optical absorption induced by sequential exposition to short- and long-wavelength radiation in the BTO:Al crystal

NASA Astrophysics Data System (ADS)

Shandarov, S. M.; Dyu, V. G.; Kisteneva, M. G.; Khudyakova, E. S.; Smirnov, S. V.; Akrestina, A. S.; Kargin, Yu F.

2017-02-01

Modifications of the spectral dependences of the optical absorption induced in the Bi12TiO20:Al crystal as a result of sequential exposition to cw laser radiation first with the wavelength λ g = 532 nm and then with the longer wavelength λ l,n = 588, 633, 655, 658, 663, 700, 780, 871, or 1064 nm are investigated. We revealed that after the short-wavelength exposition to radiation with λg = 532 nm, the optical absorption in the crystal increases, and in the range 470-1000 nm, yields the spectrum whose form is independent of a prehistory. The subsequent exposition to longer-wavelength radiation leads to bleaching of the crystal in the examined spectral range. A maximum diminishing of the optical absorption in the crystal is observed upon exposure to radiation with the wavelength λ l,5 = 663 nm. To describe the experimentally observed reversible changes in the optical absorption spectrum in the Bi12TiO20:Al we use the impurity absorption model that takes into account the photoinduced transitions between two metastable states of a deep defect center leading to the change of its position in the crystal lattice under conditions of strong lattice relaxation.

Shuttle Contamination And Experimentation: DoD Implications

NASA Astrophysics Data System (ADS)

Barnhart, B. J.; Baker, J. C.

1981-07-01

As the DOD makes the transition into the Shuttle era, experimenters are becoming more concerned about the environmental contamination of the Shuttle Orbiter. Their concern is that Shuttle contamination could prevent major planned experiments from obtaining required data, particularly sensitive infrared systems (e.g., Talon Gold, SIRE, STMP). The performance of optical experiments could be limited by the natural background, by light scattering and emissions from particulates and molecules, and by molecular absorption. Deposition and optical surface degradation may prove to be extensive problems, particularly for cryogenic optics. Other experiments such as communications and space environment tests may also be affected by deposition as well as electromagnetic interference. It has been known that the Shuttle's environment could cause contamination problems during water dumps, thruster firings, paint outgassing and other sources. Predictions have been made, but the contamination species and extent of these problems will not be known definitely until space measurements are made. This paper identifies the contamination types, sources, and their possible effect on particular types of space experiments. The paper also discusses NASA's plans for contamination measurements and the Space Test experiments which could contribute to early resolution of the contamination questions.

Shuttle Contamination And Experimentation: DoD Implications

NASA Astrophysics Data System (ADS)

Barnhart, B. J.; Baker, J. C.

1982-02-01

As the DOD makes the transition into the Shuttle era, experimenters are becoming more concerned about the environmental contamination of the Shuttle Orbiter. Their concern is that Shuttle contamination could prevent major planned experiments from obtaining required data, particularly sensitive infrared systems (e.g., Talon Gold, SIRE, STMP). The performance of optical experiments could be limited by the natural background, by light scattering and emissions from particulates and molecules, and by molecular absorption. Deposition and optical surface degradation may prove to be extensive problems, particularly for cryogenic optics. Other experiments such as communications and space environment tests may also be affected by deposition as well as electromagnetic interference. It has been known that the Shuttle's environment could cause contamination problems during water dumps, thruster firings, paint outgassing and other sources. Predictions have been made, but the contamination species and extent of these problems will not be known definitely until space measurements are made. This paper identifies the contamination types, sources, and their possible effect on particular types of space experiments. The paper also discusses NASA's plans for contamination measurements and the Space Test experiments which could contribute to early resolution of the contamination questions.

Light transport in turbid media with non-scattering, low-scattering and high absorption heterogeneities based on hybrid simplified spherical harmonics with radiosity model

PubMed Central

Yang, Defu; Chen, Xueli; Peng, Zhen; Wang, Xiaorui; Ripoll, Jorge; Wang, Jing; Liang, Jimin

2013-01-01

Modeling light propagation in the whole body is essential and necessary for optical imaging. However, non-scattering, low-scattering and high absorption regions commonly exist in biological tissues, which lead to inaccuracy of the existing light transport models. In this paper, a novel hybrid light transport model that couples the simplified spherical harmonics approximation (SPN) with the radiosity theory (HSRM) was presented, to accurately describe light transport in turbid media with non-scattering, low-scattering and high absorption heterogeneities. In the model, the radiosity theory was used to characterize the light transport in non-scattering regions and the SPN was employed to handle the scattering problems, including subsets of low-scattering and high absorption. A Neumann source constructed by the light transport in the non-scattering region and formed at the interface between the non-scattering and scattering regions was superposed into the original light source, to couple the SPN with the radiosity theory. The accuracy and effectiveness of the HSRM was first verified with both regular and digital mouse model based simulations and a physical phantom based experiment. The feasibility and applicability of the HSRM was then investigated by a broad range of optical properties. Lastly, the influence of depth of the light source on the model was also discussed. Primary results showed that the proposed model provided high performance for light transport in turbid media with non-scattering, low-scattering and high absorption heterogeneities. PMID:24156077

Light transport in turbid media with non-scattering, low-scattering and high absorption heterogeneities based on hybrid simplified spherical harmonics with radiosity model.

PubMed

Yang, Defu; Chen, Xueli; Peng, Zhen; Wang, Xiaorui; Ripoll, Jorge; Wang, Jing; Liang, Jimin

2013-01-01

Modeling light propagation in the whole body is essential and necessary for optical imaging. However, non-scattering, low-scattering and high absorption regions commonly exist in biological tissues, which lead to inaccuracy of the existing light transport models. In this paper, a novel hybrid light transport model that couples the simplified spherical harmonics approximation (SPN) with the radiosity theory (HSRM) was presented, to accurately describe light transport in turbid media with non-scattering, low-scattering and high absorption heterogeneities. In the model, the radiosity theory was used to characterize the light transport in non-scattering regions and the SPN was employed to handle the scattering problems, including subsets of low-scattering and high absorption. A Neumann source constructed by the light transport in the non-scattering region and formed at the interface between the non-scattering and scattering regions was superposed into the original light source, to couple the SPN with the radiosity theory. The accuracy and effectiveness of the HSRM was first verified with both regular and digital mouse model based simulations and a physical phantom based experiment. The feasibility and applicability of the HSRM was then investigated by a broad range of optical properties. Lastly, the influence of depth of the light source on the model was also discussed. Primary results showed that the proposed model provided high performance for light transport in turbid media with non-scattering, low-scattering and high absorption heterogeneities.

TOPICAL REVIEW: Electron small polarons and bipolarons in LiNbO3

NASA Astrophysics Data System (ADS)

Schirmer, O. F.; Imlau, M.; Merschjann, C.; Schoke, B.

2009-03-01

An overview of the properties of electron small polarons and bipolarons is given, which can occur in the congruently melting composition of LiNbO3 (LN). Such polarons influence the performance of this important optical material decisively. Since coupling to the lattice strongly quenches the tunnelling of free small polarons in general, they are easily localized at one site even by weak irregularities of a crystal. The mechanism of their optical absorptions is thus shared with those of small polarons localized by binding to selected defects. It is shown that the optical properties of free electrons in LN as well as those bound to NbLi antisite defects can be attributed consistently to small polarons. This is extended to electron pairs forming bipolarons bound to NbLi-NbNb nearest neighbours in the LN ground state. On the basis of an elementary phenomenological approach, relying on familiar concepts of defect physics, the peak energies, lineshapes, widths of the related optical absorption bands as well as the defect binding energies induced by lattice distortion are analysed. A criterion universally identifying small polaron absorption bands in oxide materials is pointed out. For the bipolarons, the dissociation energy, 0.27 eV, derived from a corresponding study of the mass action behaviour, is shown to be consistent with the data on isolated polarons. Based on experience with simple O- hole small polaron systems, a mechanism is proposed which explains why the observed small polaron optical absorptions are higher above the peak energies of the bands than those predicted by the conventional theory. The parameters characterizing the optical absorptions are seen to be fully consistent with those determining the electrical conductivity, i.e. the bipolaron dissociation energy and the positions of the defect levels as well as the activation energy of mobility. A reinterpretation of previous thermopower data of reduced LN on the basis of the bipolaron model confirms that the mobility of the free polarons is activated by 0.27 eV. On the basis of the level scheme of the bipolarons as well as the bound and free polarons the temperature dependence of the electronic conductivity is explained. The polaron/bipolaron concept also allows us to account for the concentrations of the various polaron species under the combined influence of illumination and heating. The decay of free and bound polarons dissociated from bipolarons by intense short laser pulses of 532 nm light is put in the present context. A critical review of alternative models, being proposed to explain the mentioned absorption features, is given. These proposals include: single free polarons in the (diamagnetic) LN ground state, oxygen vacancies in their various conceivable charge states, quadpolarons, etc. It is shown why these models cannot explain the experimental findings consistently.

Comparison of experimental and modeled absorption enhancement by black carbon (BC) cored polydisperse aerosols under hygroscopic conditions.

PubMed

Shamjad, P M; Tripathi, S N; Aggarwal, S G; Mishra, S K; Joshi, Manish; Khan, Arshad; Sapra, B K; Ram, Kirpa

2012-08-07

The quantification of the radiative impacts of light absorbing ambient black carbon (BC) particles strongly depends on accurate measurements of BC mass concentration and absorption coefficient (β(abs)). In this study, an experiment has been conducted to quantify the influence of hygroscopic growth of ambient particles on light absorption. Using the hygroscopic growth factor (i.e., Zdanovskii-Stokes-Robinson (ZSR) approach), a model has been developed to predict the chemical composition of particles based on measurements, and the absorption and scattering coefficients are derived using a core-shell assumption with light extinction estimates based on Mie theory. The estimated optical properties agree within 7% for absorption coefficient and 30% for scattering coefficient with that of measured values. The enhancement of absorption is found to vary according to the thickness of the shell and BC mass, with a maximum of 2.3 for a shell thickness of 18 nm for the particles. The findings of this study underline the importance of considering aerosol-mixing states while calculating their radiative forcing.

Enhancement of broadband optical absorption in photovoltaic devices by band-edge effect of photonic crystals.

PubMed

Tanaka, Yoshinori; Kawamoto, Yosuke; Fujita, Masayuki; Noda, Susumu

2013-08-26

We numerically investigate broadband optical absorption enhancement in thin, 400-nm thick microcrystalline silicon (µc-Si) photovoltaic devices by photonic crystals (PCs). We realize absorption enhancement by coupling the light from the free space to the large area resonant modes at the photonic band-edge induced by the photonic crystals. We show that multiple photonic band-edge modes can be produced by higher order modes in the vertical direction of the Si photovoltaic layer, which can enhance the absorption on multiple wavelengths. Moreover, we reveal that the photonic superlattice structure can produce more photonic band-edge modes that lead to further optical absorption. The absorption average in wavelengths of 500-1000 nm weighted to the solar spectrum (AM 1.5) increases almost twice: from 33% without photonic crystal to 58% with a 4 × 4 period superlattice photonic crystal; our result outperforms the Lambertian textured structure.

Spectral Absorption Properties of Atmospheric Aerosols

NASA Technical Reports Server (NTRS)

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

2007-01-01

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

Surface plasmon-enhanced optical absorption in monolayer MoS2 with one-dimensional Au grating

NASA Astrophysics Data System (ADS)

Song, Jinlin; Lu, Lu; Cheng, Qiang; Luo, Zixue

2018-05-01

The optical absorption of a composite photonic structure, namely monolayer molybdenum disulfide (MoS2)-covered Au grating, is theoretically investigated using a rigorous coupled-wave analysis algorithm. The enhancement of localized electromagnetic field due to surface plasmon polaritons supported by Au grating can be utilized to enhance the absorption of MoS2. The remarkable enhancement of absorption due to exciton transition can also be realized. When the period of grating is 600 nm, the local absorption of the monolayer MoS2 on Au grating is nearly 7 times higher than the intrinsic absorption due to B exciton transition. A further study reveals that the absorption properties of Au grating can be tailored by altering number of MoS2 layers, changing to a MoS2 nanoribbon array, and inserting a hafnium dioxide (HfO2) spacer. This work will contribute to the design of MoS2-based optical and optoelectronic devices.

Aqueous glucose measurement using differential absorption-based frequency domain optical coherence tomography at wavelengths of 1310 nm and 1625 nm

NASA Astrophysics Data System (ADS)

John, Pauline; Manoj, Murali; Sujatha, N.; Vasa, Nilesh J.; Rao, Suresh R.

2015-07-01

This work presents a combination of differential absorption technique and frequency domain optical coherence tomography for detection of glucose, which is an important analyte in medical diagnosis of diabetes. Differential absorption technique is used to detect glucose selectively in the presence of interfering species especially water and frequency domain optical coherence tomography (FDOCT) helps to obtain faster acquisition of depth information. Two broadband super-luminescent diode (SLED) sources with centre wavelengths 1586 nm (wavelength range of 1540 to 1640 nm) and 1312 nm (wavelength range of 1240 to 1380 nm) and a spectral width of ≍ 60 nm (FWHM) are used. Preliminary studies on absorption spectroscopy using various concentrations of aqueous glucose solution gave promising results to distinguish the absorption characteristics of glucose at two wavelengths 1310 nm (outside the absorption band of glucose) and 1625 nm (within the absorption band of glucose). In order to mimic the optical properties of biological skin tissue, 2% and 10% of 20% intralipid with various concentrations of glucose (0 to 4000 mg/dL) was prepared and used as sample. Using OCT technique, interference spectra were obtained using an optical spectrum analyzer with a resolution of 0.5 nm. Further processing of the interference spectra provided information on reflections from the surfaces of the cuvette containing the aqueous glucose sample. Due to the absorption of glucose in the wavelength range of 1540 nm to 1640 nm, a trend of reduction in the intensity of the back reflected light was observed with increase in the concentration of glucose.

Z-scan measurement for nonlinear absorption property of rGO/ZnO:Al thin film

NASA Astrophysics Data System (ADS)

Sreeja, V. G.; Anila, E. I.

2018-04-01

We report the fabrication of reduced graphene oxide integrated aluminium doped zinc oxide (rGO/ZnO:Al) composite thin film on a glass substrate by spin coating technique. The effect of rGO on structural and linear optical properties of rGO/ZnO:Al composite thin film was explored with the help of X-Ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and UV-Vis absorption spectroscopy. Structural studies reveals that the composite film has hexagonal wurtzite structure with a strong bonding between rGO and ZnO:Al material. The band gap energy of ZnO:Al thin film was red shifted by the addition of rGO. The Nonlinear absorption property was investigated by open aperture Z-scan technique by using Q switched Nd-YAG laser at 532nm. The Z-scan results showed that the composite film demonstrates reverse saturable absorption property with a nonlinear absorption coefficient, β, of 12.75×10-7m/w. The results showed that investigated rGO/ZnO:Al thin film is a promising material suitable for the applications in absorbing type optical devices such as optical limiters, optical switches and protection of the optical sensors in the field of nonlinear optics.

Giant optical field enhancement in multi-dielectric stacks by photon scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Ndiaye, C.; Zerrad, M.; Lereu, A. L.; Roche, R.; Dumas, Ph.; Lemarchand, F.; Amra, C.

2013-09-01

Dielectric optical thin films, as opposed to metallic, have been very sparsely explored as good candidates for absorption-based optical field enhancement. In such materials, the low imaginary part of the refractive index implies that absorption processes are usually not predominant. This leads to dielectric-based optical resonances mainly via waveguiding modes. We show here that when properly designed, a multi-layered dielectric thin films stack can give rise to optical resonances linked to total absorption. We report here, on such dielectric stack designed to possess a theoretical optical field enhancement above 1000. Using photon scanning tunneling microscopy, we experimentally evaluate the resulting field enhancement of the stack as well as the associated penetration depth. We thus demonstrate the capability of multi-dielectric stacks in generating giant optical field with tunable penetration depth (down to few dozens of nm).

Effects of polarization and absorption on laser induced optical breakdown threshold for skin rejuvenation

NASA Astrophysics Data System (ADS)

Varghese, Babu; Bonito, Valentina; Turco, Simona; Verhagen, Rieko

2016-03-01

Laser induced optical breakdown (LIOB) is a non-linear absorption process leading to plasma formation at locations where the threshold irradiance for breakdown is surpassed. In this paper we experimentally demonstrate the influence of polarization and absorption on laser induced breakdown threshold in transparent, absorbing and scattering phantoms made from water suspensions of polystyrene microspheres. We demonstrate that radially polarized light yields a lower irradiance threshold for creating optical breakdown compared to linearly polarized light. We also demonstrate that the thermal initiation pathway used for generating seed electrons results in a lower irradiance threshold compared to multiphoton initiation pathway used for optical breakdown.

Electronic absorption spectrum of copper-doped magnesium potassium phosphate hexahydrate

NASA Astrophysics Data System (ADS)

Rao, S. N.; Sivaprasad, P.; Reddy, Y. P.; Rao, P. S.

1992-04-01

The optical absorption and EPR spectra of magnesium potassium phosphate hexahydrate (MPPH) doped with copper ions are recorded both at room and liquid nitrogen temperatures. The spectrum is characteristic of Cu2+ in tetragonal symmetry. The spin-Hamiltonian parameters and molecular orbital coefficients are evaluated. A correlation between EPR and optical absorption studies is drawn.

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

NASA Astrophysics Data System (ADS)

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

2017-08-01

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

Investigation of change of tumor optical properties after laser-induced plasmon-resonant photothermal treatment of transplanted tumors in rats

NASA Astrophysics Data System (ADS)

Genin, Vadim D.; Genina, Elina A.; Bucharskaya, Alla B.; Tuchin, Valery V.; Khlebtsov, Nikolay G.; Terentyuk, Georgy S.; Bashkatov, Alexey N.

2018-04-01

The paper presents the investigation of change of tumor optical properties of the rat tumor doped by gold nanoparticles after laser-induced plasmon-resonant photothermal treatment. To obtain the model tumors the rats have been implanted by suspension of alveolar kidney cancer cells. An hour before the experiment the animals have been injected by the suspension of gold nanorods intratumorally. For irradiation a diode laser with wavelength 808 nm has been used. After the irradiation the tumor has been removed and sliced. Spectra of total and collimated transmission and diffuse reflectance of the samples of different layers of the tumors have been measured in the wavelength range 350-2500 nm. Absorption, scattering, reduced scattering coefficients and scattering anisotropy factor of tumor tissues have been calculated with inverse adding-doubling method. The results of the experiment have shown that after doping the tumor tissue by the plasmon resonant nanoparticles and NIR laser irradiating, there is the decreases of absorption as well as scattering properties of the tumor and surrounding tissues. However, despite the sufficiently high temperature on the surface (about 80°C), the changes in the center of the tumor are insignificant.

Investigations on optimizing the energy transmission of ultrafast optical pulses in pure water

NASA Astrophysics Data System (ADS)

Lukofsky, David

Many of today's communication and imaging technologies share the common challenge of signal deterioration due to water's large absorption coefficient. As an example, it is water molecules that contaminate the fused silica of optical fibers and account for most of the absorption they exhibit at communication wavelengths. It is also water (in the form of vapor) that makes it challenging to devise practical THz spectroscopic systems. As such, this thesis examines how the transmission of electromagnetic radiation through water could be improved as a stepping stone towards bettering a wide array of communication and imaging applications. Recent time-domain approaches have noted the connection between pulse rise-time and precursor waveform absorption. This thesis represents the first in-depth analysis of precursors using an intuitive frequency-domain approach. It was shown with well-known physical metrics that precursors are a linear effect resulting from the temporal representation of a Beer's law of absorption for broadband pulses. Experimental validation was achieved with a spatial light modulator used in conjunction with Frequency-Resolved-Optical-Gating (FROG) to obtain the first measurement of the amplitude and phase of an optical precursor. The semi-classical two-level atom model was used to infer the transitional dipole moments of the 1447 nm and 2:94 mum vibrational resonances of the medium. These values supported finite-difference-time-domain simulations suggesting how 52 fs sech2 pulses of 220 GW/cm2 peak intensity could propagate with negligible attenuation over 15 absorption lengths when tuned to the 2:94 mum transition of water. Extensive use of 1550 nm lasers in communication systems and the presence of the second vibrational overtone resonance of water at 1447 nm were the motivation for transmission experiments completed at the Naval Research Laboratory (Washington, DC) at this transition. As much as a 500% increase in absolute transmission was observed in a 5 mm sample of distilled water when compared to steady-state transmission. Different causes for this increase in transmission were examined, including coherent and incoherent bleaching effects. Overall, this study reveals that efficient propagation of optical pulses in water requires pulses of near single-cycle duration and large intensities and/or fluence. While these large intensities would make it difficult to apply this work to medical imaging applications, there remains a window of opportunity for efficient underwater communication. Indeed, assuming a channel of water with few physical obstructions, the advent of sufficiently intense, robust, and high repetition-rate laser technology might one day lead to the implementation of a practical underwater communication link at optical wavelengths.

Bilayered Hybrid Perovskite Ferroelectric with Giant Two-Photon Absorption.

PubMed

Li, Lina; Shang, Xiaoying; Wang, Sasa; Dong, Ningning; Ji, Chengmin; Chen, Xueyuan; Zhao, Sangen; Wang, Jun; Sun, Zhihua; Hong, Maochun; Luo, Junhua

2018-06-06

Perovskite ferroelectrics with prominent nonlinear optical absorption have attracted great attention in the field of photonics. However, they are traditionally dominated by inorganic oxides and exhibit relatively small nonlinear optical absorption coefficients, which hinder their further applications. Herein, we report a new organic-inorganic hybrid bilayered perovskite ferroelectric, (C 4 H 9 NH 3 ) 2 (NH 2 CHNH 2 )Pb 2 Br 7 (1), showing an above-room-temperature Curie temperature (∼322 K) and notable spontaneous polarization (∼3.8 μC cm -2 ). Significantly, the unique quantum-well structure of 1 results in intriguing two-photon absorption properties with a giant nonlinear optical absorption coefficient as high as 5.76 × 10 3 cm GW -1 , which is almost two-orders of magnitude larger than those of mostly traditional all-inorganic perovskite ferroelectrics. To our best knowledge, 1 is the first example of hybrid ferroelectrics with giant two-photon absorption coefficient. The mechanisms for ferroelectric and two-photon absorption are revealed. This work will shed light on the design of new ferroelectrics with two-photon absorption and promote their potentials in the photonic application.

Nonlinear pulse propagation in InAs/InP quantum dot optical amplifiers: Rabi oscillations in the presence of nonresonant nonlinearities

NASA Astrophysics Data System (ADS)

Karni, O.; Mishra, A. K.; Eisenstein, G.; Reithmaier, J. P.

2015-03-01

We study the interplay between coherent light-matter interactions and nonresonant pulse propagation effects when ultrashort pulses propagate in room-temperature quantum dot (QD) semiconductor optical amplifiers (SOAs). The signatures observed on a pulse envelope after propagating in a transparent SOA, when coherent Rabi oscillations are absent, highlight the contribution of two-photon absorption (TPA), and its accompanying Kerr-like effect, as well as of linear dispersion, to the modification of the pulse complex electric field profile. These effects are incorporated into our previously developed finite-difference time-domain comprehensive model that describes the interaction between the pulses and the QD SOA. The present generalized model is used to investigate the combined effect of coherent and nonresonant phenomena in the gain and absorption regimes of the QD SOA. It confirms that in the QD SOA we examined, linear dispersion in the presence of the Kerr-like effect causes pulse compression, which counteracts the pulse peak suppression due to TPA, and also modifies the patterns which the coherent Rabi oscillations imprint on the pulse envelope under both gain and absorption conditions. The inclusion of these effects leads to a better fit with experiments and to a better understanding of the interplay among the various mechanisms so as to be able to better analyze more complex future experiments of coherent light-matter interaction induced by short pulses propagating along an SOA.

Bulk damage and absorption in fused silica due to high-power laser applications

NASA Astrophysics Data System (ADS)

Nürnberg, F.; Kühn, B.; Langner, A.; Altwein, M.; Schötz, G.; Takke, R.; Thomas, S.; Vydra, J.

2015-11-01

Laser fusion projects are heading for IR optics with high broadband transmission, high shock and temperature resistance, long laser durability, and best purity. For this application, fused silica is an excellent choice. The energy density threshold on IR laser optics is mainly influenced by the purity and homogeneity of the fused silica. The absorption behavior regarding the hydroxyl content was studied for various synthetic fused silica grades. The main absorption influenced by OH vibrational excitation leads to different IR attenuations for OH-rich and low-OH fused silica. Industrial laser systems aim for the maximum energy extraction possible. Heraeus Quarzglas developed an Yb-doped fused silica fiber to support this growing market. But the performance of laser welding and cutting systems is fundamentally limited by beam quality and stability of focus. Since absorption in the optical components of optical systems has a detrimental effect on the laser focus shift, the beam energy loss and the resulting heating has to be minimized both in the bulk materials and at the coated surfaces. In collaboration with a laser research institute, an optical finisher and end users, photo thermal absorption measurements on coated samples of different fused silica grades were performed to investigate the influence of basic material properties on the absorption level. High purity, synthetic fused silica is as well the material of choice for optical components designed for DUV applications (wavelength range 160 nm - 260 nm). For higher light intensities, e.g. provided by Excimer lasers, UV photons may generate defect centers that effect the optical properties during usage, resulting in an aging of the optical components (UV radiation damage). Powerful Excimer lasers require optical materials that can withstand photon energy close to the band gap and the high intensity of the short pulse length. The UV transmission loss is restricted to the DUV wavelength range below 300 nm and consists of three different absorption bands centered at 165 nm (peroxy radicals), 215 nm (E'-center), and 265 nm (non-bridging oxygen hole center (NBOH)), which change the transmission behavior of material.

Study the effects of varying interference upon the optical properties of turbid samples using NIR spatial light modulation

NASA Astrophysics Data System (ADS)

Shaul, Oren; Fanrazi-Kahana, Michal; Meitav, Omri; Pinhasi, Gad A.; Abookasis, David

2018-03-01

Optical properties of biological tissues are valuable diagnostic parameters which can provide necessary information regarding tissue state during disease pathogenesis and therapy. However, different sources of interference, such as temperature changes may modify these properties, introducing confounding factors and artifacts to data, consequently skewing their interpretation and misinforming clinical decision-making. In the current study, we apply spatial light modulation, a type of diffuse reflectance hyperspectral imaging technique, to monitor the variation in optical properties of highly scattering turbid media in the presence varying levels of the following sources of interference: scattering concentration, temperature, and pressure. Spatial near-infrared (NIR) light modulation is a wide-field, non-contact emerging optical imaging platform capable of separating the effects of tissue scattering from those of absorption, thereby accurately estimating both parameters. With this technique, periodic NIR illumination patterns at alternately low and high spatial frequencies, at six discrete wavelengths between 690 to 970 nm, were sequentially projected upon the medium while a CCD camera collects the diffusely reflected light. Data analysis based assumptions is then performed off-line to recover the medium's optical properties. We conducted a series of experiments demonstrating the changes in absorption and reduced scattering coefficients of commercially available fresh milk and chicken breast tissue under different interference conditions. In addition, information on the refractive index was study under increased pressure. This work demonstrates the utility of NIR spatial light modulation to detect varying sources of interference upon the optical properties of biological samples.

Single-shot measurement of nonlinear absorption and nonlinear refraction.

PubMed

Jayabalan, J; Singh, Asha; Oak, Shrikant M

2006-06-01

A single-shot method for measurement of nonlinear optical absorption and refraction is described and analyzed. A spatial intensity variation of an elliptical Gaussian beam in conjugation with an array detector is the key element of this method. The advantages of this single-shot technique were demonstrated by measuring the two-photon absorption and free-carrier absorption in GaAs as well as the nonlinear refractive index of CS2 using a modified optical Kerr setup.

Long-range parametric amplification of THz wave with absorption loss exceeding parametric gain.

PubMed

Wang, Tsong-Dong; Huang, Yen-Chieh; Chuang, Ming-Yun; Lin, Yen-Hou; Lee, Ching-Han; Lin, Yen-Yin; Lin, Fan-Yi; Kitaeva, Galiya Kh

2013-01-28

Optical parametric mixing is a popular scheme to generate an idler wave at THz frequencies, although the THz wave is often absorbing in the nonlinear optical material. It is widely suggested that the useful material length for co-directional parametric mixing with strong THz-wave absorption is comparable to the THz-wave absorption length in the material. Here we show that, even in the limit of the absorption loss exceeding parametric gain, the THz idler wave can grows monotonically from optical parametric amplification over a much longer distance in a nonlinear optical material until pump depletion. The coherent production of the non-absorbing signal wave can assist the growth of the highly absorbing idler wave. We also show that, for the case of an equal input pump and signal in difference frequency generation, the quick saturation of the THz idler wave predicted from a much simplified and yet popular plane-wave model fails when fast diffraction of the THz wave from the co-propagating optical mixing waves is considered.

Graphene-based ultrasonic detector for photoacoustic imaging

NASA Astrophysics Data System (ADS)

Yang, Fan; Song, Wei; Zhang, Chonglei; Fang, Hui; Min, Changjun; Yuan, Xiaocong

2018-03-01

Taking advantage of optical absorption imaging contrast, photoacoustic imaging technology is able to map the volumetric distribution of the optical absorption properties within biological tissues. Unfortunately, traditional piezoceramics-based transducers used in most photoacoustic imaging setups have inadequate frequency response, resulting in both poor depth resolution and inaccurate quantification of the optical absorption information. Instead of the piezoelectric ultrasonic transducer, we develop a graphene-based optical sensor for detecting photoacoustic pressure. The refractive index in the coupling medium is modulated due to photoacoustic pressure perturbation, which creates the variation of the polarization-sensitive optical absorption property of the graphene. As a result, the photoacoustic detection is realized through recording the reflectance intensity difference of polarization light. The graphene-based detector process an estimated noise-equivalentpressure (NEP) sensitivity of 550 Pa over 20-MHz bandwidth with a nearby linear pressure response from 11.0 kPa to 53.0 kPa. Further, a graphene-based photoacoustic microscopy is built, and non-invasively reveals the microvascular anatomy in mouse ears label-freely.

Remarkable optical red shift and extremely high optical absorption coefficient of V-Ga co-doped TiO2

NASA Astrophysics Data System (ADS)

Deng, Quanrong; Han, Xiaoping; Gao, Yun; Shao, Guosheng

2012-07-01

A first attempt has been made to study the effect of codoping of transition metal and sp metal on the electronic structure and associated optical properties of TiO2, through V-Ga codoped thin films. V-Ga codoped rutile TiO2 films were fabricated on fused quartz substrates using pulsed laser ablation, followed by heat treatment at high temperatures. Gigantic redshift in the optical absorption edge was observed in V-Ga co-doped TiO2 materials, from UV to infrared region with high absorption coefficient. Through combined structural characterization and theoretical modeling, this is attributed to the p-d hybridization between the two metals. This leads to additional energy bands to overlap with the minimum of the conduction band, leading to remarkably narrowed band gap free of mid-gap states. The direct-gap of the co-doped phase is key to the remarkably high optical absorption coefficient of the coped titania.

E-beam deposited Ag-nanoparticles plasmonic organic solar cell and its absorption enhancement analysis using FDTD-based cylindrical nano-particle optical model.

PubMed

Kim, Richard S; Zhu, Jinfeng; Park, Jeung Hun; Li, Lu; Yu, Zhibin; Shen, Huajun; Xue, Mei; Wang, Kang L; Park, Gyechoon; Anderson, Timothy J; Pei, Qibing

2012-06-04

We report the plasmon-assisted photocurrent enhancement in Ag-nanoparticles (Ag-NPs) embedded PEDOT:PSS/P3HT:PCBM organic solar cells, and systematically investigate the causes of the improved optical absorption based on a cylindrical Ag-NPs optical model which is simulated with a 3-Dimensional finite difference time domain (FDTD) method. The proposed cylindrical Ag-NPs optical model is able to explain the optical absorption enhancement by the localized surface plasmon resonance (LSPR) modes, and to provide a further understanding of Ag-NPs shape parameters which play an important role to determine the broadband absorption phenomena in plasmonic organic solar cells. A significant increase in the power conversion efficiency (PCE) of the plasmonic solar cell was experimentally observed and compared with that of the solar cells without Ag-NPs. Finally, our conclusion was made after briefly discussing the electrical effects of the fabricated plasmonic organic solar cells.

Optical mechanisms for detection of lipid-rich atherosclerotic plaques by near-infrared spectroscopy

NASA Astrophysics Data System (ADS)

Hull, Edward L.; Gardner, Craig M.; Muller, James E.; Muller, Vianna J.; Salvato, Christopher V.; Lisauskas, Jennifer B.; Caplan, Jay D.

2008-02-01

InfraReDx has developed a spectroscopic cardiac catheter system capable of acquiring near-infrared (NIR) reflectance spectra from coronary arteries in vivo for identification of lipid-rich plaques of interest (LRP). The spectral data are analyzed with a chemometric model, producing a hyperspectral image (a chemogram) used to identify LRP in the interrogated region. In this paper, we describe a FT-IR microscopy system for measurement of the NIR scattering and absorption properties of healthy and diseased regions of human coronary arteries in small volumes (~10 μl). Scattering and absorption coefficients are obtained from sequential 140 um x 140 um regions of interest across the face of 500-micron thick, saline-irrigated fresh coronary artery sections. A customized FTIR microscope, measurement protocol, and inversion algorithm are used for optical property determination, and the system is calibrated using measurements of tissue-simulating phantoms having well-characterized optical properties. Tissue optical properties are co-registered with brightfield transmission images as well as with stained histologic thin sections (H&E, Movat Pentachrome, and Oil Red O) acquired from an immediately-adjacent section. The ultimate goal of these experiments is to establish a mechanistic link between the multivariate model predictions displayed on the InfraReDx chemogram and the light-tissue interactions that govern the measured NIR reflectance spectra.

Application of Cavity Enhanced Absorption Spectroscopy to the Detection of Nitric Oxide, Carbonyl Sulphide, and Ethane—Breath Biomarkers of Serious Diseases

PubMed Central

Wojtas, Jacek

2015-01-01

The paper presents one of the laser absorption spectroscopy techniques as an effective tool for sensitive analysis of trace gas species in human breath. Characterization of nitric oxide, carbonyl sulphide and ethane, and the selection of their absorption lines are described. Experiments with some biomarkers showed that detection of pathogenic changes at the molecular level is possible using this technique. Thanks to cavity enhanced spectroscopy application, detection limits at the ppb-level and short measurements time (<3 s) were achieved. Absorption lines of reference samples of the selected volatile biomarkers were probed using a distributed feedback quantum cascade laser and a tunable laser system consisting of an optical parametric oscillator and difference frequency generator. Setup using the first source provided a detection limit of 30 ppb for nitric oxide and 250 ppb for carbonyl sulphide. During experiments employing a second laser, detection limits of 0.9 ppb and 0.3 ppb were obtained for carbonyl sulphide and ethane, respectively. The conducted experiments show that this type of diagnosis would significantly increase chances for effective therapy of some diseases. Additionally, it offers non-invasive and real time measurements, high sensitivity and selectivity as well as minimizing discomfort for patients. For that reason, such sensors can be used in screening for early detection of serious diseases. PMID:26091398

Application of Cavity Enhanced Absorption Spectroscopy to the Detection of Nitric Oxide, Carbonyl Sulphide, and Ethane--Breath Biomarkers of Serious Diseases.

PubMed

Wojtas, Jacek

2015-06-17

The paper presents one of the laser absorption spectroscopy techniques as an effective tool for sensitive analysis of trace gas species in human breath. Characterization of nitric oxide, carbonyl sulphide and ethane, and the selection of their absorption lines are described. Experiments with some biomarkers showed that detection of pathogenic changes at the molecular level is possible using this technique. Thanks to cavity enhanced spectroscopy application, detection limits at the ppb-level and short measurements time (<3 s) were achieved. Absorption lines of reference samples of the selected volatile biomarkers were probed using a distributed feedback quantum cascade laser and a tunable laser system consisting of an optical parametric oscillator and difference frequency generator. Setup using the first source provided a detection limit of 30 ppb for nitric oxide and 250 ppb for carbonyl sulphide. During experiments employing a second laser, detection limits of 0.9 ppb and 0.3 ppb were obtained for carbonyl sulphide and ethane, respectively. The conducted experiments show that this type of diagnosis would significantly increase chances for effective therapy of some diseases. Additionally, it offers non-invasive and real time measurements, high sensitivity and selectivity as well as minimizing discomfort for patients. For that reason, such sensors can be used in screening for early detection of serious diseases.

Laser generated gold nanocorals with broadband plasmon absorption for photothermal applications

NASA Astrophysics Data System (ADS)

Poletti, Annamaria; Fracasso, Giulio; Conti, Giamaica; Pilot, Roberto; Amendola, Vincenzo

2015-08-01

Gold nanoparticles with efficient plasmon absorption in the visible and near infrared (NIR) regions, biocompatibility and easy surface functionalization are of interest for photothermal applications. Herein we describe the synthesis and photothermal properties of gold ``nanocorals'' (AuNC) obtained by laser irradiation of Au nanospheres (AuNS) dispersed in liquid solution. AuNC are formed in two stages: by photofragmentation of AuNS, followed by spontaneous unidirectional assembly of gold nanocrystals. The whole procedure is performed without chemicals or templating compounds, hence the AuNC can be coated with thiolated molecules in one step. We show that AuNC coated with thiolated polymers are easily dispersed in an aqueous environment or in organic solvents and can be included in polymeric matrixes to yield a plasmonic nanocomposite. AuNC dispersions exhibit flat broadband plasmon absorption ranging from the visible to the NIR and unitary light-to-heat conversion. Besides, in vitro biocompatibility experiments assessed the absence of cytotoxic effects even at a dose as high as 100 μg mL-1. These safe-by-designed AuNC are promising for use in various applications such as photothermal cancer therapy, light-triggered drug release, antimicrobial substrates, optical tomography, obscurant materials and optical coatings.

Spatial effects in intrinsic optical bistability

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

Haus, J.W.; Wang, L.; Scalora, M.

Using the nonlinear oscillator model as a prototype medium exhibiting intrinsic optical bistability, we investigate the inhomogeneous absorption of the electromagnetic field. The forward- and backward-field amplitudes and diffraction effects are retained in the mathematical description. Analytic results are given in the limit of plane-wave propagation under steady-state conditions. The transmitted and reflected intensity exhibit a structure that is determined by the spatial inhomogeneity of the absorption in the longitudinal direction. The transmitted intensity has a structure that is dependent on the length of the medium. The reflected intensity has an interference structure from light reflected at the front surfacemore » and the internal boundary separating a high-polarization from a low-polarization branch. A degenerate-four-wave-mixing experiment is predicted to be a very sensitive probe of the internal boundary and the interference between the forward and backward field. The phase-conjugate signal develops large oscillations as the input field is varied. Numerical results for diffraction effects are also given, and we find that the plane-wave results for the center of the beam remain reliable down to Fresnel numbers of order unity and in media that are smaller than the linear absorption length.« less

Atomic scale origins of sub-band gap optical absorption in gold-hyperdoped silicon

NASA Astrophysics Data System (ADS)

Ferdous, Naheed; Ertekin, Elif

2018-05-01

Gold hyperdoped silicon exhibits room temperature sub band gap optical absorption, with potential applications as infrared absorbers/detectors and impurity band photovoltaics. We use first-principles density functional theory to establish the origins of the sub band gap response. Substitutional gold AuSi and substitutional dimers AuSi - AuSi are found to be the energetically preferred defect configurations, and AuSi gives rise to partially filled mid-gap defect bands well offset from the band edges. AuSi is predicted to offer substantial sub-band gap absorption, exceeding that measured in prior experiments by two orders of magnitude for similar Au concentration. This suggests that in experimentally realized systems, in addition to AuSi, the implanted gold is accommodated by the lattice in other ways, including other defect complexes and gold precipitates. We further identify that it is energetically favorable for isolated AuSi to form AuSi - AuSi, which by contrast do not exhibit mid-gap states. The formation of dimers and other complexes could serve as nuclei in the earliest stages of Au precipitation, which may be responsible for the observed rapid deactivation of sub-band gap response upon annealing.

Absorption bleaching of squarylium dye J aggregates via a two-photon excitation process

NASA Astrophysics Data System (ADS)

Furuki, Makoto; Tian, Minquan; Sato, Yasuhiro; Pu, Lyong Sun; Tatsuura, Satoshi; Abe, Shuji

2001-08-01

Squarylium dye J aggregates exhibit ultrafast nonlinear optical response of absorption saturation at the resonant wavelength of 770 nm. We studied the two-photon excitation process of J aggregates. By fluorescence measurement, we found the two-photon absorption band at 1.3 μm, which was different from that of the dye solution at 1.2 μm. Absorption saturation at 770 nm via a two-photon excitation process was observed by two-photon resonant excitation at 1.3 μm and also by off-resonant excitation at 1.55 μm, suggesting the possibility of J aggregates for optical switching materials working at the wavelength used in optical communications.

All-optical switch consisting of two-stage interferometers controlled by using saturable absorption of monolayer graphene.

PubMed

Oya, Masayuki; Kishikawa, Hiroki; Goto, Nobuo; Yanagiya, Shin-ichiro

2012-11-19

At routing nodes in future photonic networks, pico-second switching will be a key function. We propose an all-optical switch consisting of two-stage Mach-Zehnder interferometers, whose arms contain graphene saturable absorption films. Optical amplitudes along the interferometers are controlled to perform switching between two output ports instead of phase control used in conventional switches. Since only absorption is used for realizing complete switching, insertion loss of 10.2 dB is accompanied in switching. Picosecond response can be expected because of the fast response of saturable absorption of graphene. The switching characteristics are theoretically analyzed and numerically simulated by the finite-difference beam propagation method (FD-BPM).

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

PubMed

In, Sungjun; Park, Namkyoo

2016-02-23

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.

Nonlinear Optical Interactions in Plasmas at JILA

NASA Astrophysics Data System (ADS)

Dollar, F.; Hickstein, D. D.; Popmintchev, D.; Becker, A.; Ellis, J.; Hernandez-Garcia, C.; Jaron-Becker, A.; Popmintchev, T.; Xiong, W.; Murnane, M. M.; Kapteyn, H. C.; Dukovic, G.; Jimenez, J.; Palm, B.; Schnitzenbaumer, K.; Perez-Hernandez, J.; Gaeta, A.; Gao, X.; Shim, B.; Plaja, L.; Levis, R.; Tarazkar, M.; Foord, M. E.; Gaffney, J. A.; Libby, S. B.

2014-10-01

We present data from two recent experiments. First, we demonstrate direct observations of localized light absorption in a single nanoparticle irradiated by a strong femtosecond laser field. By imaging the photoion momentum distribution resulting from plasma formation in a laser-irradiated nanostructure, we map the spatial location of the highly localized plasma and thereby image the nanoscale light absorption. Secondly, we show the high linear and nonlinear UV refractive indices of both neutral atoms and ions compensate for plasma dispersion, even in multiply-ionized gases. The experimental work was primarily funded by DOE Grant Number: DE-SC0008803, the DARPA PULSE program, and ARO W911NF-12-1-0436.

Application of the Tauc-Lorentz formulation to the interband absorption of optical coating materials

NASA Astrophysics Data System (ADS)

von Blanckenhagen, Bernhard; Tonova, Diana; Ullmann, Jens

2002-06-01

Recent progress in ellipsometry instrumentation permits precise measurement and characterization of optical coating materials in the deep-UV wavelength range. Dielectric coating materials exhibit their first electronic interband transition in this spectral range. The Tauc-Lorentz model is a powerful tool with which to parameterize interband absorption above the band edge. The application of this model for the parameterization of the optical absorption of TiO2, Ta2O5, HfO2, Al2O3, and LaF3 thin-film materials is described.

Photoacoustic spectral characterization of perfluorocarbon droplets

NASA Astrophysics Data System (ADS)

Strohm, Eric; Gorelikov, Ivan; Matsuura, Naomi; Kolios, Michael

2012-02-01

Perfluorocarbon droplets containing optical absorbing nanoparticles have been developed for use as theranostic agents (for both imaging and therapy) and as dual-mode contrast agents. Droplets can be used as photoacoustic contrast agents, vaporized via optical irradiation, then the resulting bubbles can be used as ultrasound imaging and therapeutic agents. The photoacoustic signals from micron-sized droplets containing silica coated gold nanospheres were measured using ultra-high frequencies (100-1000 MHz). The spectra of droplets embedded in a gelatin phantom were compared to a theoretical model which calculates the pressure wave from a spherical homogenous liquid undergoing thermoelastic expansion resulting from laser absorption. The location of the spectral features of the theoretical model and experimental spectra were in agreement after accounting for increases in the droplet sound speed with frequency. The agreement between experiment and model indicate that droplets (which have negligible optical absorption in the visible and infrared spectra by themselves) emitted pressure waves related to the droplet composition and size, and was independent of the physical characteristics of the optical absorbing nanoparticles. The diameter of individual droplets was calculated using three independent methods: the time domain photoacoustic signal, the time domain pulse echo ultrasound signal, and a fit to the photoacoustic model, then compared to the diameter as measured by optical microscopy. It was found the photoacoustic and ultrasound methods calculated diameters an average of 2.6% of each other, and 8.8% lower than that measured using optical microscopy. The discrepancy between the calculated diameters and the optical measurements may be due to the difficulty in resolving the droplet edges after being embedded in the translucent gelatin medium.

Absorption characterization of immersion medium for multiphoton microscopy at the 1700nm window

NASA Astrophysics Data System (ADS)

Wen, Wenhui; Qiu, Ping

2017-02-01

Larger imaging depth is the quest of almost all the imaging modalities, including multiphoton microscopy (MPM). Recently, it has been domonstrated that excitation at the 1700-nm helps extending imaging depth in MPM, optical coherence tomography, as well as photoacoustic imaging compared with excitation at other wavelengths. In MPM, immersion objective lenses with high numerical aperture (NA) are typically used to achieve better signal resolution, higer signal collection efficiency, and stronger signal generation. Although physically short ( mm), this extra optical path length traversed by the excitation light inevitably introduces absorption of the excitation light, and as a result leads to a decrease in the signal generation. Here we demonstrate experimental characterization of absorption spectrum of various immersion media at the 1700-nm window, including water (H2O), deuterium oxide (D2O), and several brands of immersion oil. Our results identify either the best immersion medium for a specific wavelength, or the best wavelength for a specific immersion medium at the 1700-nm window. Furthermore, through quantitative MPM experiments comparing different immersion media, we show that the MPM signal levels can be enhanced by more than ten fold simply by selecting the proper immersion medium, in good agreement with theoretical expectation based on the absorption measurement. Our results will offer guidelines for signal optimization in MPM at the 1700-nm window.

Laser-induced micro-plasmas in air for incoherent broadband cavity-enhanced absorption spectroscopy

NASA Astrophysics Data System (ADS)

Ruth, Albert; Dixneuf, Sophie; Orphal, Johannes

2016-04-01

Incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) is an experimentally straightforward absorption method where the intensity of light transmitted by an optically stable (high finesse) cavity is measured. The technique is realized using broadband incoherent sources of radiation and therefore the amount of light transmitted by a cavity consisting of high reflectance mirrors (typically R > 99.9%) can be low. In order to find an alternative to having an incoherent light source outside the cavity, an experiment was devised, where a laser-induced plasma in ambient air was generated inside a quasi-confocal cavity by a high-power femtosecond laser. The emission from the laser-induced plasma was utilized as pulsed broadband light source. The time-dependent spectra of the light leaking from the cavity were compared with those of the laser-induced plasma emission without the cavity. It was found that the light emission was sustained by the cavity despite the initially large optical losses caused by the laser-induced plasma in the cavity. The light sustained by the cavity was used to measure part of the S1 ← S0 absorption spectrum of gaseous azulene at its vapour pressure at room temperature in ambient air, as well as the strongly forbidden γ-band in molecular oxygen (b1Σ(2,0) ← X3Σ(0,0)).

Optical absorption properties of Ge 2–44 and P-doped Ge nanoparticles

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

Qin, Wei; Lu, Wen-Cai; Zhao, Li-Zhen

The optical absorption properties of non-crystalline and crystalline Ge nanoparticles with the sizes from ~ 2.5 to 15 Å have been studied at the B3LYP/6-31G level using time-dependent density functional theory. Hydrogen passivation and phosphorus doping on some selected Ge nanoparticles were also calculated. With the increase of cluster size, the optical absorption spectra of the non-crystalline Ge nanoparticles change from many peaks to a continuous broad band and at the same time exhibit a systematic red-shift. Doping phosphorus also causes the absorption spectra to shift toward the lower energy region for both non-crystalline and crystalline Ge nanoparticles. The non-crystallinemore » Ge nanoparticles are found to have stronger absorption in the visible region in comparison with the crystalline ones, regardless phosphorus doping.« less

Optical absorption properties of Ge 2–44 and P-doped Ge nanoparticles

DOE PAGES

Qin, Wei; Lu, Wen-Cai; Zhao, Li-Zhen; ...

2017-09-15

The optical absorption properties of non-crystalline and crystalline Ge nanoparticles with the sizes from ~ 2.5 to 15 Å have been studied at the B3LYP/6-31G level using time-dependent density functional theory. Hydrogen passivation and phosphorus doping on some selected Ge nanoparticles were also calculated. With the increase of cluster size, the optical absorption spectra of the non-crystalline Ge nanoparticles change from many peaks to a continuous broad band and at the same time exhibit a systematic red-shift. Doping phosphorus also causes the absorption spectra to shift toward the lower energy region for both non-crystalline and crystalline Ge nanoparticles. The non-crystallinemore » Ge nanoparticles are found to have stronger absorption in the visible region in comparison with the crystalline ones, regardless phosphorus doping.« less

Tuning the nonlinear optical absorption of reduced graphene oxide by chemical reduction.

PubMed

Shi, Hongfei; Wang, Can; Sun, Zhipei; Zhou, Yueliang; Jin, Kuijuan; Redfern, Simon A T; Yang, Guozhen

2014-08-11

Reduced graphene oxides with varying degrees of reduction have been produced by hydrazine reduction of graphene oxide. The linear and nonlinear optical properties of both graphene oxide as well as the reduced graphene oxides have been measured by single beam Z-scan measurement in the picosecond region. The results reveal both saturable absorption and two-photon absorption, strongly dependent on the intensity of the pump pulse: saturable absorption occurs at lower pump pulse intensity (~1.5 GW/cm2 saturation intensity) whereas two-photon absorption dominates at higher intensities (≥5.7 GW/cm2). Intriguingly, we find that the two-photon absorption coefficient (from 1.5 cm/GW to 4.5cm/GW) and the saturation intensity (from 1 GW/cm2 to 2 GW/cm2) vary with chemical reduction, which is ascribed to the varying concentrations of sp2 domains and sp2 clusters in the reduced graphene oxides. Our results not only provide an insight into the evolution of the nonlinear optical coefficient in reduced graphene oxide, but also suggest that chemical engineering techniques may usefully be applied to tune the nonlinear optical properties of various nano-materials, including atomically thick graphene sheets.

Cavity ring-down spectroscopy in the liquid phase

NASA Astrophysics Data System (ADS)

Xu, Shucheng; Sha, Guohe; Xie, Jinchun

2002-02-01

A new application for cavity ring-down spectroscopic (CRDS) technique using a pulsed polarized light source has been developed in the absorption measurement of liquids for "colorless" organic compounds using both a single sample cell and double sample cells inserted in an optical cavity at Brewster angle. At present an experimental capability of measuring absorption coefficients as small as 2-5×10-7 cm-1 has been demonstrated by measurement of the absorption baselines. The first spectra for CRDS in the liquid phase, the C-H stretching fifth vibrational overtones of benzene in the pure liquid and hexane solution are obtained. The optical absorption length for liquids in both a single sample cell and double sample cells of 1 cm length is up to 900 cm due to multipass of light within an optical cavity. Compared to the thermal lens and optoacoustic spectroscopic techniques, the sensitivity for CRDS mainly depends on the optical absorption path of the sample (single passing path of the sample times multipass times), is not determined by the laser power and the length of the sample cell. The absolute absorption coefficient and band intensity for the sample are determined directly by the spectroscopy.

Semi-analytical Model for Estimating Absorption Coefficients of Optically Active Constituents in Coastal Waters

NASA Astrophysics Data System (ADS)

Wang, D.; Cui, Y.

2015-12-01

The objectives of this paper are to validate the applicability of a multi-band quasi-analytical algorithm (QAA) in retrieval absorption coefficients of optically active constituents in turbid coastal waters, and to further improve the model using a proposed semi-analytical model (SAA). The ap(531) and ag(531) semi-analytically derived using SAA model are quite different from the retrievals procedures of QAA model that ap(531) and ag(531) are semi-analytically derived from the empirical retrievals results of a(531) and a(551). The two models are calibrated and evaluated against datasets taken from 19 independent cruises in West Florida Shelf in 1999-2003, provided by SeaBASS. The results indicate that the SAA model produces a superior performance to QAA model in absorption retrieval. Using of the SAA model in retrieving absorption coefficients of optically active constituents from West Florida Shelf decreases the random uncertainty of estimation by >23.05% from the QAA model. This study demonstrates the potential of the SAA model in absorption coefficients of optically active constituents estimating even in turbid coastal waters. Keywords: Remote sensing; Coastal Water; Absorption Coefficient; Semi-analytical Model

Methods for estimating the optical constants of atmospheric hazes based on complex optical measurements

NASA Technical Reports Server (NTRS)

Zuev, V. E.; Kostin, B. S.; Naats, I. E.

1986-01-01

The methods of multifrequency laser sounding (MLS) are the most effective remote methods for investigating the atmospheric aerosols, since it is possible to obtain complete information on aerosol microstructure and the effective methods for estimating the aerosol optical constants can be developed. The MLS data interpretation consists in the solution of the set of equations containing those of laser sounding and equations for polydispersed optical characteristics. As a rule, the laser sounding equation is written in the approximation of single scattering and the equations for optical characteristics are written assuming that the atmospheric aerosol is formed by spherical and homogeneous particles. To remove the indeterminacy of equations, the method of optical sounding of atmospheric aerosol, consisting in a joint use of a mutifrequency lidar and a spectral photometer in common geometrical scheme of the optical experiment was suggested. The method is used for investigating aerosols in the cases when absorption by particles is small and indicates the minimum necessary for interpretation of a series of measurements.

Properties of optical breakdown in BK7 glass induced by an extended-cavity femtosecond laser oscillator.

PubMed

Do, Binh T; Phillips, Mark C; Miller, Paul A; Kimmel, Mark W; Britsch, Justin; Cho, Seong-Ho

2009-02-16

Using an extended-cavity femtosecond oscillator, we investigated optical breakdown in BK7 glass caused by the accumulated action of many laser pulses. By using a pump-probe experiment and collecting the transmitted pump along with the reflected pump and the broadband light generated by the optical breakdown, we measured the build-up time to optical breakdown as a function of the pulse energy, and we also observed the instability of the plasma due to the effect of defocusing and shielding created by the electron gas. The spectrum of the broadband light emitted by the optical breakdown and the origin of the material modification in BK7 glass was studied. We developed a simple model of electromagnetic wave propagation in plasma that is consistent with the observed behavior of the reflection, absorption, and transmission of the laser light.

Polymethine and squarylium molecules with large excited-state absorption

NASA Astrophysics Data System (ADS)

Lim, Jin Hong; Przhonska, Olga V.; Khodja, Salah; Yang, Sidney; Ross, T. S.; Hagan, David J.; Van Stryland, Eric W.; Bondar, Mikhail V.; Slominsky, Yuriy L.

1999-07-01

We study nonlinear absorption in a series of ten polymethine dyes and two squarylium dyes using Z-scan, pump-probe and optical limiting experiments. Both picosecond and nanosecond characterization were performed at 532 nm, while picosecond measurements were performed using an optical parametric oscillator (OPO) from 440 to 650 nm. The photophysical parameters of these dyes including cross sections and excited-state lifetimes are presented both in solution in ethanol and in an elastopolymeric material, polyurethane acrylate (PUA). We determine that the dominant nonlinearity in all these dyes is large excited-state absorption (ESA), i.e. reverse saturable absorption. For several of the dyes we measure a relatively large ground-state absorption cross section, σ01, which effectively populates an excited state that possesses an extremely large ESA cross section, σ12. The ratios of σ12/ σ01 are the largest we know of, up to 200 at 532 nm, and lead to very low thresholds for optical limiting. However, the lifetimes of the excited state are of the order of 1 ns in ethanol, which is increased to up to 3 ns in PUA. This lifetime is less than optimum for sensor protection applications for Q-switched inputs, and intersystem crossing times for these molecules are extremely long, so that triplet states are not populated. These parameters show a significant improvement over those of the first set of this class of dyes studied and indicate that further improvement of the photophysical parameters may be possible. From these measurements, correlations between molecular structure and nonlinear properties are made. We propose a five-level, all-singlet state model, which includes reorientation processes in the first excited state. This includes a trans- cis conformational change that leads to the formation of a new state with a new molecular configuration which is also absorbing but can undergo a light-induced degradation at high inputs.

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.

Charge-transfer optical absorption mechanism of DNA:Ag-nanocluster complexes.

PubMed

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:Ag_{4}. In all 23 different complexes investigated, we obtain new absorption peaks in the visible region that are not found in either the isolated Ag_{4} or isolated DNA base pairs. Absorption from red to green are predominantly of charge-transfer character, from the Ag_{4} to the DNA fragment, while absorption in the blue-violet range are mostly associated to electronic transitions of a mixed character, involving either DNA-Ag_{4} 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.

Influence of the light propagation models on a linearized photoacoustic image reconstruction of the light absorption coefficient

NASA Astrophysics Data System (ADS)

Okawa, Shinpei; Hirasawa, Takeshi; Kushibiki, Toshihiro; Ishihara, Miya

2015-03-01

Quantification of the optical properties of the tissues and blood by noninvasive photoacoustic (PA) imaging may provide useful information for screening and early diagnosis of diseases. Linearized 2D image reconstruction algorithm based on PA wave equation and the photon diffusion equation (PDE) can reconstruct the image with computational cost smaller than a method based on 3D radiative transfer equation. However, the reconstructed image is affected by the differences between the actual and assumed light propagations. A quantitative capability of a linearized 2D image reconstruction was investigated and discussed by the numerical simulations and the phantom experiment in this study. The numerical simulations with the 3D Monte Carlo (MC) simulation and the 2D finite element calculation of the PDE were carried out. The phantom experiment was also conducted. In the phantom experiment, the PA pressures were acquired by a probe which had an optical fiber for illumination and the ring shaped P(VDF-TrFE) ultrasound transducer. The measured object was made of Intralipid and Indocyanine green. In the numerical simulations, it was shown that the linearized image reconstruction method recovered the absorption coefficients with alleviating the dependency of the PA amplitude on the depth of the photon absorber. The linearized image reconstruction method worked effectively under the light propagation calculated by 3D MC simulation, although some errors occurred. The phantom experiments validated the result of the numerical simulations.

Effect of idler absorption in pulsed optical parametric oscillators.

PubMed

Rustad, Gunnar; Arisholm, Gunnar; Farsund, Øystein

2011-01-31

Absorption at the idler wavelength in an optical parametric oscillator (OPO) is often considered detrimental. We show through simulations that pulsed OPOs with significant idler absorption can perform better than OPOs with low idler absorption both in terms of conversion efficiency and beam quality. The main reason for this is reduced back conversion. We also show how the beam quality depends on the beam width and pump pulse length, and present scaling relations to use the example simulations for other pulsed nanosecond OPOs.

Photovoltaic device with increased light absorption and method for its manufacture

DOEpatents

Glatfelter, Troy; Vogeli, Craig; Call, Jon; Hammond, Ginger

1993-07-20

A photovoltaic cell having a light-directing optical element integrally formed in an encapsulant layer thereof. The optical element redirects light to increase the internal absorption of light incident on the photovoltaic device.

Deep seawater inherent optical properties in the Southern Ionian Sea

NASA Astrophysics Data System (ADS)

Riccobene, G.; Capone, A.; Aiello, S.; Ambriola, M.; Ameli, F.; Amore, I.; Anghinolfi, M.; Anzalone, A.; Avanzini, C.; Barbarino, G.; Barbarito, E.; Battaglieri, M.; Bellotti, R.; Beverini, N.; Bonori, M.; Bouhadef, B.; Brescia, M.; Cacopardo, G.; Cafagna, F.; Caponetto, L.; Castorina, E.; Ceres, A.; Chiarusi, T.; Circella, M.; Cocimano, R.; Coniglione, R.; Cordelli, M.; Costa, M.; Cuneo, S.; D'Amico, A.; de Bonis, G.; de Marzo, C.; de Rosa, G.; de Vita, R.; Distefano, C.; Falchini, E.; Fiorello, C.; Flaminio, V.; Fratini, K.; Gabrielli, A.; Galeotti, S.; Gandolfi, E.; Grimaldi, A.; Habel, R.; Leonora, E.; Lonardo, A.; Longo, G.; Lo Presti, D.; Lucarelli, F.; Maccioni, E.; Margiotta, A.; Martini, A.; Masullo, R.; Megna, R.; Migneco, E.; Mongelli, M.; Montaruli, T.; Morganti, M.; Musumeci, M.; Nicolau, C. A.; Orlando, A.; Osipenko, M.; Osteria, G.; Papaleo, R.; Pappalardo, V.; Petta, C.; Piattelli, P.; Raffaelli, F.; Raia, G.; Randazzo, N.; Reito, S.; Ricco, G.; Ripani, M.; Rovelli, A.; Ruppi, M.; Russo, G. V.; Russo, S.; Russo, S.; Sapienza, P.; Sedita, M.; Schuller, J.-P.; Shirokov, E.; Simeone, F.; Sipala, V.; Spurio, M.; Taiuti, M.; Terreni, G.; Trasatti, L.; Urso, S.; Valente, V.; Vicini, P.

2007-02-01

The NEMO (NEutrino Mediterranean Observatory) Collaboration has been carrying out since 1998 an evaluation programme of deep sea sites suitable for the construction of the future Mediterranean km3 Čerenkov neutrino telescope. We investigated the seawater optical and oceanographic properties of several deep sea marine areas close to the Italian Coast. Inherent optical properties (light absorption and attenuation coefficients) have been measured as a function of depth using an experimental apparatus equipped with standard oceanographic probes and the commercial transmissometer AC9 manufactured by WETLabs. This paper reports on the visible light absorption and attenuation coefficients measured in deep seawater of a marine region located in the Southern Ionian Sea, 60 100 km SE of Capo Passero (Sicily). Data show that blue light absorption coefficient is about 0.015 m-1 (corresponding to an absorption length of 67 m) close to the one of optically pure water and it does not show seasonal variation.

Design of near-infrared dyes for nonlinear optics: toward optical limiting applications at telecommunication wavelengths

NASA Astrophysics Data System (ADS)

Bellier, Quentin; Bouit, Pierre-Antoine; Kamada, Kenji; Feneyrou, Patrick; Malmström, E.; Maury, Olivier; Andraud, Chantal

2009-09-01

The rapid development of frequency-tunable pulsed lasers up to telecommunication wavelengths (1400-1600 nm) led to the design of new materials for nonlinear absorption in this spectral range. In this context, two families of near infra-red (NIR) chromophores, namely heptamethine cyanine and aza-borondipyrromethene (aza-bodipy) dyes were studied. In both cases, they show significant two-photon absorption (TPA) cross-sections in the 1400-1600 nm spectral range and display good optical power limiting (OPL) properties. OPL curves were interpreted on the basis of TPA followed by excited state absorption (ESA) phenomena. Finally these systems have several relevant properties like nonlinear absorption properties, gram scale synthesis and high solubility. In addition, they could be functionalized on several sites which open the way to numerous practical applications in biology, solid-state optical limiting and signal processing.

Synthesis, spectral and third-order nonlinear optical properties of terpyridine Zn(II) complexes based on carbazole derivative with polyether group

NASA Astrophysics Data System (ADS)

Kong, Ming; Liu, Yanqiu; Wang, Hui; Luo, Junshan; Li, Dandan; Zhang, Shengyi; Li, Shengli; Wu, Jieying; Tian, Yupeng

2015-01-01

Four novel Zn(II) terpyridine complexes (ZnLCl2, ZnLBr2, ZnLI2, ZnL(SCN)2) based on carbazole derivative group were designed, synthesized and fully characterized. Their photophysical properties including absorption and one-photon excited fluorescence, two-photon absorption (TPA) and optical power limiting (OPL) were further investigated systematically and interpreted on the basis of theoretical calculations (TD-DFT). The influences of different solvents on the absorption and One-Photon Excited Fluorescence (OPEF) spectral behavior, quantum yields and the lifetime of the chromophores have been investigated in detail. The third-order nonlinear optical (NLO) properties were investigated by open/closed aperture Z-scan measurements using femtosecond pulse laser in the range from 680 to 1080 nm. These results revealed that ZnLCl2 and ZnLBr2 exhibited strong two-photon absorption and ZnLCl2 showed superior optical power limiting property.

Optical evidence of strong coupling between valence-band holes and d -localized spins in Zn1-xMnxO

NASA Astrophysics Data System (ADS)

Sokolov, V. I.; Druzhinin, A. V.; Gruzdev, N. B.; Dejneka, A.; Churpita, O.; Hubicka, Z.; Jastrabik, L.; Trepakov, V.

2010-04-01

We report on optical-absorption study of Zn1-xMnxO (x=0-0.06) films on fused silica substrates taking special attention to the spectral range of the fundamental absorption edge (3.1-4 eV). Well-pronounced excitonic lines observed in the region 3.40-3.45 eV were found to shift to higher energies with increasing Mn concentration. The optical band-gap energy increases with x too, reliably evidencing strong coupling between oxygen holes and localized spins of manganese ions. In the 3.1-3.3 eV region the optical-absorption curve in the manganese-contained films was found to shift to lower energies with respect to that for undoped ZnO. The additional absorption observed in this range is interpreted as a result of splitting of a localized Zhang-Rice-type state into the band gap.

Resonant indirect optical absorption in germanium

NASA Astrophysics Data System (ADS)

Menéndez, José; Noël, Mario; Zwinkels, Joanne C.; Lockwood, David J.

2017-09-01

The optical absorption coefficient of pure Ge has been determined from high-accuracy, high-precision optical measurements at photon energies covering the spectral range between the indirect and direct gaps. The results are compared with a theoretical model that fully accounts for the resonant nature of the energy denominators that appear in perturbation-theory expansions of the absorption coefficient. The model generalizes the classic Elliott approach to indirect excitons, and leads to a predicted optical absorption that is in excellent agreement with the experimental values using just a single adjustable parameter: the average deformation potential DΓ L coupling electrons at the bottom of the direct and indirect valleys in the conduction band. Remarkably, the fitted value, DΓ L=4.3 ×108eV /cm , is in nearly perfect agreement with independent measurements and ab initio predictions of this parameter, confirming the validity of the proposed theory, which has general applicability.

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 and the proportionality to Tl concentration. The ionic model satisfactorily explains the observed concentration and temperature dependence of the absorption. It also provides for the first time, a universal explanation of the exponential edge in liquid semiconductors where charged defects are present, and provides a means of measuring the concentration of ions when the absorption can be calibrated.

Fabrication of a Quartz-Crystal-Microbalance/Optical-Waveguide Hybrid Sensor and In situ Evaluation of Vacuum-Evaporated Lead Phthalocyanine Thin Film

NASA Astrophysics Data System (ADS)

Shinbo, Kazunari; Uno, Akihiro; Hirakawa, Ryo; Baba, Akira; Ohdaira, Yasuo; Kato, Keizo; Kaneko, Futao

2013-05-01

In this study, we fabricated a novel quartz-crystal-microbalance (QCM)/optical-waveguide hybrid sensor. An in situ observation of a lead phthalocyanine (PbPc) thin-film deposition was conducted during vacuum evaporation, and the effectiveness of the sensor was demonstrated. The film thickness was obtained from the QCM frequency, and the optical absorption of the film was observed by optical waveguide spectroscopy using part of the QCM substrate without the electrode. The film absorption depends on the polarization direction, substrate temperature and deposition rate, owing to aggregate formation. The thickness dependence of the absorption property was also investigated.

A diode laser-based velocimeter providing point measurements in unseeded flows using modulated filtered Rayleigh scattering (MFRS)

NASA Astrophysics Data System (ADS)

Jagodzinski, Jeremy James

2007-12-01

The development to date of a diode-laser based velocimeter providing point-velocity-measurements in unseeded flows using molecular Rayleigh scattering is discussed. The velocimeter is based on modulated filtered Rayleigh scattering (MFRS), a novel variation of filtered Rayleigh scattering (FRS), utilizing modulated absorption spectroscopy techniques to detect a strong absorption of a relatively weak Rayleigh scattered signal. A rubidium (Rb) vapor filter is used to provide the relatively strong absorption; alkali metal vapors have a high optical depth at modest vapor pressures, and their narrow linewidth is ideally suited for high-resolution velocimetry. Semiconductor diode lasers are used to generate the relatively weak Rayleigh scattered signal; due to their compact, rugged construction diode lasers are ideally suited for the environmental extremes encountered in many experiments. The MFRS technique utilizes the frequency-tuning capability of diode lasers to implement a homodyne detection scheme using lock-in amplifiers. The optical frequency of the diode-based laser system used to interrogate the flow is rapidly modulated about a reference frequency in the D2-line of Rb. The frequency modulation is imposed on the Rayleigh scattered light that is collected from the probe volume in the flow under investigation. The collected frequency modulating Rayleigh scattered light is transmitted through a Rb vapor filter before being detected. The detected modulated absorption signal is fed to two lock-in amplifers synchronized with the modulation frequency of the source laser. High levels of background rejection are attained since the lock-ins are both frequency and phase selective. The two lock-in amplifiers extract different Fourier components of the detected modulated absorption signal, which are ratioed to provide an intensity normalized frequency dependent signal from a single detector. A Doppler frequency shift in the collected Rayleigh scattered light due to a change in the velocity of the flow under investigation results in a change in the detected modulated absorption signal. This change in the detected signal provides a quantifiable measure of the Doppler frequency shift, and hence the velocity in the probe volume, provided that the laser source exhibits acceptable levels of frequency stability (determined by the magnitude of the velocities being measured). An extended cavity diode laser (ECDL) in the Littrow configuration provides frequency tunable, relatively narrow-linewidth lasing for the MFRS velocimeter. Frequency stabilization of the ECDL is provided by a proportional-integral-differential (PID) controller based on an error signal in the reference arm of the experiment. The optical power of the Littrow laser source is amplified by an antireflection coated (AR coated) broad stripe diode laser. The single-mode, frequency-modulatable, frequency-stable O(50 mW) of optical power provided by this extended cavity diode laser master oscillator power amplifier (ECDL-MOPA) system provided sufficient scattering signal from a condensing jet of CO2 to implement the MFRS technique in the frequency-locked mode of operation.

Theory of absorption integrated optical sensor of gaseous materials

NASA Astrophysics Data System (ADS)

Egorov, A. A.

2010-10-01

The eigen and noneigen (leaky) modes of a three-layer planar integrated optical waveguide are described. The dispersion relation of a three-layer planar waveguide and other dependences are derived, and the cutoff conditions are analyzed. The diagram of propagation constants of the guided and radiation modes of an irregular asymmetric three-layer waveguide and the dependence of the electric field amplitudes of radiation modes of substrate on vertical coordinate in a tantalum integrated optical waveguide are presented. The operating principles of an absorption integrated optical waveguide sensor are investigated. The dependences of sensitivity of an integrated optical waveguide sensor on the sensory cell length, the coupling efficiency of the laser radiation into the waveguide, the absorption cross-section of the studied material, and the level of additive statistical noise are investigated. Some of the prospective areas of application of integrated-optical waveguide sensors are outlined.

Static and dynamic optical properties of La 1-xSr xFeO 3-δ: The effects of A-site and oxygen stoichiometry

DOE PAGES

Sergey Y. Smolin; Sfeir, Matthew Y.; Scafetta, Mark D.; ...

2015-12-09

Perovskite oxides are a promising material class for photovoltaic and photocatalytic applications due to their visible band gaps, nanosecond recombination lifetimes, and great chemical diversity. However, there is limited understanding of the link between composition and static and dynamic optical properties, despite the critical role these properties play in the design of light-harvesting devices. To clarify these relationships, we systemically studied the optoelectronic properties in La 1-xSr xFeO 3-δ epitaxial films, uncovering the effects of A-site cation substitution and oxygen stoichiometry. Variable-angle spectroscopic ellipsometry was used to measure static optical properties, revealing a linear increase in absorption coefficient at 1.25more » eV and a red-shifting of the optical absorption edge with increasing Sr fraction. The absorption spectra can be similarly tuned through the introduction of oxygen vacancies, indicating the critical role that nominal Fe valence plays in optical absorption. Dynamic optoelectronic properties were studied with ultrafast transient reflectance spectroscopy, revealing similar nanosecond photoexcited carrier lifetimes for oxygen deficient and stoichiometric films with the same nominal Fe valence. Furthermore, these results demonstrate that while the static optical absorption is strongly dependent on nominal Fe valence tuned through cation or anion stoichiometry, oxygen vacancies do not appear to play a significantly detrimental role in the recombination kinetics.« less

Geometrical-optics code for computing the optical properties of large dielectric spheres.

PubMed

Zhou, Xiaobing; Li, Shusun; Stamnes, Knut

2003-07-20

Absorption of electromagnetic radiation by absorptive dielectric spheres such as snow grains in the near-infrared part of the solar spectrum cannot be neglected when radiative properties of snow are computed. Thus a new, to our knowledge, geometrical-optics code is developed to compute scattering and absorption cross sections of large dielectric particles of arbitrary complex refractive index. The number of internal reflections and transmissions are truncated on the basis of the ratio of the irradiance incident at the nth interface to the irradiance incident at the first interface for a specific optical ray. Thus the truncation number is a function of the angle of incidence. Phase functions for both near- and far-field absorption and scattering of electromagnetic radiation are calculated directly at any desired scattering angle by using a hybrid algorithm based on the bisection and Newton-Raphson methods. With these methods a large sphere's absorption and scattering properties of light can be calculated for any wavelength from the ultraviolet to the microwave regions. Assuming that large snow meltclusters (1-cm order), observed ubiquitously in the snow cover during summer, can be characterized as spheres, one may compute absorption and scattering efficiencies and the scattering phase function on the basis of this geometrical-optics method. A geometrical-optics method for sphere (GOMsphere) code is developed and tested against Wiscombe's Mie scattering code (MIE0) and a Monte Carlo code for a range of size parameters. GOMsphere can be combined with MIE0 to calculate the single-scattering properties of dielectric spheres of any size.

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

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

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

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

Effects of γ-ray irradiation on optical absorption and laser damage performance of KDP crystals containing arsenic impurities.

PubMed

Guo, D C; Jiang, X D; Huang, J; Wang, F R; Liu, H J; Xiang, X; Yang, G X; Zheng, W G; Zu, X T

2014-11-17

The effects of γ-irradiation on potassium dihydrogen phosphate crystals containing arsenic impurities are investigated with different optical diagnostics, including UV-VIS absorption spectroscopy, photo-thermal common-path interferometer and photoluminescence spectroscopy. The optical absorption spectra indicate that a new broad absorption band near 260 nm appears after γ-irradiation. It is found that the intensity of absorption band increases with the increasing irradiation dose and arsenic impurity concentration. The simulation of radiation defects show that this absorption is assigned to the formation of AsO₄⁴⁻ centers due to arsenic ions substituting for phosphorus ions. Laser-induced damage threshold test is conducted by using 355 nm nanosecond laser pulses. The correlations between arsenic impurity concentration and laser induced damage threshold are presented. The results indicate that the damage performance of the material decreases with the increasing arsenic impurity concentration. Possible mechanisms of the irradiation-induced defects formation under γ-irradiation of KDP crystals are discussed.

Pure optical photoacoustic microscopy

PubMed Central

Xie, Zhixing; Chen, Sung-Liang; Ling, Tao; Guo, L. Jay; Carson, Paul L.; Wang, Xueding

2011-01-01

The concept of pure optical photoacoustic microscopy(POPAM) was proposed based on optical rastering of a focused excitation beam and optically sensing the photoacoustic signal using a microring resonator fabricated by a nanoimprinting technique. After the refinements of the microring’s working wavelength and in the resonator structure and mold fabrication, an ultrahigh Q factor of 3.0×105 was achieved which provided high sensitivity with a noise equivalent detectable pressure(NEDP) value of 29Pa. This NEDP is much lower than the hundreds of Pascals achieved with existing optical resonant structures such as etalons, fiber gratings and dielectric multilayer interference filters available for acoustic measurement. The featured high sensitivity allowed the microring resonator to detect the weak photoacoustic signals from micro- or submicroscale objects. The inherent superbroad bandwidth of the optical microring resonator combined with an optically focused scanning beam provided POPAM with high resolution in the axial as well as both lateral directions while the axial resolution of conventional photoacoustic microscopy (PAM) suffers from the limited bandwidth of PZT detectors. Furthermore, the broadband microring resonator showed similar sensitivity to that of our most sensitive PZT detector. The current POPAM system provides a lateral resolution of 5 μm and an axial resolution of 8 μm, comparable to that achieved by optical microscopy while presenting the unique contrast of optical absorption and functional information complementing other optical modalities. The 3D structure of microvasculature, including capillary networks, and even individual red blood cells have been discerned successfully in the proof-of-concept experiments on mouse bladders ex vivo and mouse ears in vivo. The potential of approximately GHz bandwidth of the microring resonator also might allow much higher resolution than shown here in microscopy of optical absorption and acoustic propagation properties at depths in unfrozen tissue specimens or thicker tissue sections, which is not now imageable with current optical or acoustic microscopes of comparable resolution. PMID:21643156

Origin of optical non-linear response in TiN owing to excitation dynamics of surface plasmon resonance electronic oscillations

NASA Astrophysics Data System (ADS)

Divya, S.; Nampoori, V. P. N.; Radhakrishnan, P.; Mujeeb, A.

2014-08-01

TiN nanoparticles of average size 55 nm were investigated for their optical non-linear properties. During the experiment the irradiated laser wavelength coincided with the surface plasmon resonance (SPR) peak of the nanoparticle. The large non-linearity of the nanoparticle was attributed to the plasmon resonance, which largely enhanced the local field within the nanoparticle. Both open and closed aperture Z-scan experiments were performed and the corresponding optical constants were explored. The post-excitation absorption spectra revealed the interesting phenomenon of photo fragmentation leading to the blue shift in band gap and red shift in the SPR. The results are discussed in terms of enhanced interparticle interaction simultaneous with size reduction. Here, the optical constants being intrinsic constants for a particular sample change unusually with laser power intensity. The dependence of χ(3) is discussed in terms of the size variation caused by photo fragmentation. The studies proved that the TiN nanoparticles are potential candidates in photonics technology offering huge scope to study unexplored research for various expedient applications.

Estimation of elasticity map of soft biological tissue mimicking phantom using laser speckle contrast analysis

NASA Astrophysics Data System (ADS)

Suheshkumar Singh, M.; Rajan, K.; Vasu, R. M.

2011-05-01

Scattering of coherent light from scattering particles causes phase shift to the scattered light. The interference of unscattered and scattered light causes the formation of speckles. When the scattering particles, under the influence of an ultrasound (US) pressure wave, vibrate, the phase shift fluctuates, thereby causing fluctuation in speckle intensity. We use the laser speckle contrast analysis (LSCA) to reconstruct a map of the elastic property (Young's modulus) of soft tissue-mimicking phantom. The displacement of the scatters is inversely related to the Young's modulus of the medium. The elastic properties of soft biological tissues vary, many fold with malignancy. The experimental results show that laser speckle contrast (LSC) is very sensitive to the pathological changes in a soft tissue medium. The experiments are carried out on a phantom with two cylindrical inclusions of sizes 6mm in diameter, separated by 8mm between them. Three samples are made. One inclusion has Young's modulus E of 40kPa. The second inclusion has either a Young's modulus E of 20kPa, or scattering coefficient of μs'=3.00mm-1 or absorption coefficient of μa=0.03mm-1. The optical absorption (μa), reduced scattering (μs') coefficient, and the Young's modulus of the background are μa=0.01mm-1, μs'=1.00mm-1 and 12kPa, respectively. The experiments are carried out on all three phantoms. On a phantom with two inclusions of Young's modulus of 20 and 40kPa, the measured relative speckle image contrasts are 36.55% and 63.72%, respectively. Experiments are repeated on phantoms with inclusions of μa=0.03mm-1, E =40kPa and μs'=3.00mm-1. The results show that it is possible to detect inclusions with contrasts in optical absorption, optical scattering, and Young's modulus. Studies of the variation of laser speckle contrast with ultrasound driving force for various values of μa, μs', and Young's modulus of the tissue mimicking medium are also carried out.

Double-pulse 2-μm integrated path differential absorption lidar airborne validation for atmospheric carbon dioxide measurement.

PubMed

Refaat, Tamer F; Singh, Upendra N; Yu, Jirong; Petros, Mulugeta; Remus, Ruben; Ismail, Syed

2016-05-20

Field experiments were conducted to test and evaluate the initial atmospheric carbon dioxide (CO₂) measurement capability of airborne, high-energy, double-pulsed, 2-μm integrated path differential absorption (IPDA) lidar. This IPDA was designed, integrated, and operated at the NASA Langley Research Center on-board the NASA B-200 aircraft. The IPDA was tuned to the CO₂ strong absorption line at 2050.9670 nm, which is the optimum for lower tropospheric weighted column measurements. Flights were conducted over land and ocean under different conditions. The first validation experiments of the IPDA for atmospheric CO₂ remote sensing, focusing on low surface reflectivity oceanic surface returns during full day background conditions, are presented. In these experiments, the IPDA measurements were validated by comparison to airborne flask air-sampling measurements conducted by the NOAA Earth System Research Laboratory. IPDA performance modeling was conducted to evaluate measurement sensitivity and bias errors. The IPDA signals and their variation with altitude compare well with predicted model results. In addition, off-off-line testing was conducted, with fixed instrument settings, to evaluate the IPDA systematic and random errors. Analysis shows an altitude-independent differential optical depth offset of 0.0769. Optical depth measurement uncertainty of 0.0918 compares well with the predicted value of 0.0761. IPDA CO₂ column measurement compares well with model-driven, near-simultaneous air-sampling measurements from the NOAA aircraft at different altitudes. With a 10-s shot average, CO₂ differential optical depth measurement of 1.0054±0.0103 was retrieved from a 6-km altitude and a 4-GHz on-line operation. As compared to CO₂ weighted-average column dry-air volume mixing ratio of 404.08 ppm, derived from air sampling, IPDA measurement resulted in a value of 405.22±4.15  ppm with 1.02% uncertainty and 0.28% additional bias. Sensitivity analysis of environmental systematic errors correlates the additional bias to water vapor. IPDA ranging resulted in a measurement uncertainty of <3  m.

Role of Quantum Vibrations on the Structural, Electronic, and Optical Properties of 9-Methylguanine.

PubMed

Law, Yu Kay; Hassanali, Ali A

2015-11-05

In this work, we report theoretical predictions of the UV-absorption spectra of 9-methylguanine using time dependent density functional theory (TDDFT). Molecular dynamics simulations of the hydrated DNA base are peformed using an empirical force field, Born-Oppenheimer ab initio molecular dynamics (AIMD), and finally path-integral AIMD to understand the role of the underlying electronic potential, solvation, and nuclear quantum vibrations on the absorption spectra. It is shown that the conformational distributions, including hydrogen bonding interactions, are perturbed by the inclusion of nuclear quantum effects, leading to significant changes in the total charge and dipole fluctuations of the DNA base. The calculated absorption spectra using the different sampling protocols shows that the inclusion of nuclear quantum effects causes a significant broadening and red shift of the spectra bringing it into closer agreement with experiments.

Nonlinear absorption and optical limiting in gold-precipitated glasses induced by a femtosecond laser

NASA Astrophysics Data System (ADS)

Qu, Shiliang; Gao, Yachen; Jiang, Xiongwei; Zeng, Huidan; Song, Yinglin; Qiu, Jianrong; Zhu, Congshan; Hirao, K.

2003-09-01

Nonlinear absorptions of Au nanoparticles precipitated silicate glasses by irradiation of a focused femtosecond pulsed laser were investigated using Z-scan technique with 8 ns pulses at 532 nm. Optical limiting (OL) effects in such glasses have been also measured. It is observed that the behaviors of transition from saturable absorption to reverse saturable absorption and the OL performances for different samples are significantly different, which depend drastically on the irradiation power density of the femtosecond laser used for the Au nanoparticles precipitation in the glass. Strong nonlinear absorptions in these samples are mainly attributed to the surface plasmon resonance (SPR) and free carrier absorptions of the precipitated Au nanoparticles.

The cloud radiation impact from optics simulation and airborne observation

NASA Astrophysics Data System (ADS)

Melnikova, Irina; Kuznetsov, Anatoly; Gatebe, Charles

2017-02-01

The analytical approach of inverse asymptotic formulas of the radiative transfer theory is used for solving inverse problems of cloud optics. The method has advantages because it does not impose strict constraints, but it is tied to the desired solution. Observations are accomplished in extended stratus cloudiness, above a homogeneous ocean surface. Data from NASA`s Cloud Absorption Radiometer (CAR) during two airborne experiments (SAFARI-2000 and ARCTAS-2008) were analyzed. The analytical method of inverse asymptotic formulas was used to retrieve cloud optical parameters (optical thickness, single scattering albedo and asymmetry parameter of the phase function) and ground albedo in all 8 spectral channels independently. The method is free from a priori restrictions and there is no links to parameters, and it has been applied to data set of different origin and geometry of observations. Results obtained from different airborne, satellite and ground radiative experiments appeared consistence and showed common features of values of cloud parameters and its spectral dependence (Vasiluev, Melnikova, 2004; Gatebe et al., 2014). Optical parameters, retrieved here, are used for calculation of radiative divergence, reflected and transmitted irradiance and heating rates in cloudy atmosphere, that agree with previous observational data.

Field Studies of Broadband Aerosol Optical Extinction in the Ultraviolet Spectral Region

NASA Astrophysics Data System (ADS)

Washenfelder, R. A.; Attwood, A.; Brock, C. A.; Brown, S. S.

2013-12-01

Aerosols influence the Earth's radiative budget by scattering and absorbing incoming solar radiation. The optical properties of aerosols vary as a function of wavelength, but few measurements have reported the wavelength dependence of aerosol extinction cross sections and complex refractive indices. In the case of brown carbon, its wavelength-dependent absorption in the ultraviolet spectral region has been suggested as an important component of aerosol radiative forcing. We describe a new field instrument to measure aerosol optical extinction as a function of wavelength, using cavity enhanced spectroscopy with a broadband light source. The instrument consists of two broadband channels which span the 360-390 and 385-420 nm spectral regions using two light emitting diodes (LED) and a grating spectrometer with charge-coupled device (CCD) detector. We deployed this instrument during the Fire Lab at Missoula Experiment during Fall 2012 to measure biomass burning aerosol, and again during the Southern Oxidant and Aerosol Study in summer 2013 to measure organic aerosol in the Southeastern U.S. In both field experiments, we determined aerosol optical extinction as a function of wavelength and can interpret this together with size distribution and composition measurements to characterize the aerosol optical properties and radiative forcing.

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 absorption in the a-Si thin-film using advanced thin-film metrology methods, including spectroscopic ellipsometry and Fourier transform infrared (FTIR) spectroscopy. The resulting analysis identifies a fundamental mechanism contributing to this absorption and a method for minimizing and accounting for the unwanted absorption in the thin-film such that the exact optical response function can be achieved.

Two schemes for quantitative photoacoustic tomography based on Monte Carlo simulation

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

Liu, Yubin; Yuan, Zhen, E-mail: zhenyuan@umac.mo

Purpose: The aim of this study was to develop novel methods for photoacoustically determining the optical absorption coefficient of biological tissues using Monte Carlo (MC) simulation. Methods: In this study, the authors propose two quantitative photoacoustic tomography (PAT) methods for mapping the optical absorption coefficient. The reconstruction methods combine conventional PAT with MC simulation in a novel way to determine the optical absorption coefficient of biological tissues or organs. Specifically, the authors’ two schemes were theoretically and experimentally examined using simulations, tissue-mimicking phantoms, ex vivo, and in vivo tests. In particular, the authors explored these methods using several objects withmore » different absorption contrasts embedded in turbid media and by using high-absorption media when the diffusion approximation was not effective at describing the photon transport. Results: The simulations and experimental tests showed that the reconstructions were quantitatively accurate in terms of the locations, sizes, and optical properties of the targets. The positions of the recovered targets were accessed by the property profiles, where the authors discovered that the off center error was less than 0.1 mm for the circular target. Meanwhile, the sizes and quantitative optical properties of the targets were quantified by estimating the full width half maximum of the optical absorption property. Interestingly, for the reconstructed sizes, the authors discovered that the errors ranged from 0 for relatively small-size targets to 26% for relatively large-size targets whereas for the recovered optical properties, the errors ranged from 0% to 12.5% for different cases. Conclusions: The authors found that their methods can quantitatively reconstruct absorbing objects of different sizes and optical contrasts even when the diffusion approximation is unable to accurately describe the photon propagation in biological tissues. In particular, their methods are able to resolve the intrinsic difficulties that occur when quantitative PAT is conducted by combining conventional PAT with the diffusion approximation or with radiation transport modeling.« less

Electrically tunable coherent optical absorption in graphene with ion gel.

PubMed

Thareja, Vrinda; Kang, Ju-Hyung; Yuan, Hongtao; Milaninia, Kaveh M; Hwang, Harold Y; Cui, Yi; Kik, Pieter G; Brongersma, Mark L

2015-03-11

We demonstrate electrical control over coherent optical absorption in a graphene-based Salisbury screen consisting of a single layer of graphene placed in close proximity to a gold back reflector. The screen was designed to enhance light absorption at a target wavelength of 3.2 μm by using a 600 nm-thick, nonabsorbing silica spacer layer. An ionic gel layer placed on top of the screen was used to electrically gate the charge density in the graphene layer. Spectroscopic reflectance measurements were performed in situ as a function of gate bias. The changes in the reflectance spectra were analyzed using a Fresnel based transfer matrix model in which graphene was treated as an infinitesimally thin sheet with a conductivity given by the Kubo formula. The analysis reveals that a careful choice of the ionic gel layer thickness can lead to optical absorption enhancements of up to 5.5 times for the Salisbury screen compared to a suspended sheet of graphene. In addition to these absorption enhancements, we demonstrate very large electrically induced changes in the optical absorption of graphene of ∼3.3% per volt, the highest attained so far in a device that features an atomically thick active layer. This is attributable in part to the more effective gating achieved with the ion gel over the conventional dielectric back gates and partially by achieving a desirable coherent absorption effect linked to the presence of the thin ion gel that boosts the absorption by 40%.

Measurement of optical blurring in a turbulent cloud chamber

NASA Astrophysics Data System (ADS)

Packard, Corey D.; Ciochetto, David S.; Cantrell, Will H.; Roggemann, Michael C.; Shaw, Raymond A.

2016-10-01

Earth's atmosphere can significantly impact the propagation of electromagnetic radiation, degrading the performance of imaging systems. Deleterious effects of the atmosphere include turbulence, absorption and scattering by particulates. Turbulence leads to blurring, while absorption attenuates the energy that reaches imaging sensors. The optical properties of aerosols and clouds also impact radiation propagation via scattering, resulting in decorrelation from unscattered light. Models have been proposed for calculating a point spread function (PSF) for aerosol scattering, providing a method for simulating the contrast and spatial detail expected when imaging through atmospheres with significant aerosol optical depth. However, these synthetic images and their predicating theory would benefit from comparison with measurements in a controlled environment. Recently, Michigan Technological University (MTU) has designed a novel laboratory cloud chamber. This multiphase, turbulent "Pi Chamber" is capable of pressures down to 100 hPa and temperatures from -55 to +55°C. Additionally, humidity and aerosol concentrations are controllable. These boundary conditions can be combined to form and sustain clouds in an instrumented laboratory setting for measuring the impact of clouds on radiation propagation. This paper describes an experiment to generate mixing and expansion clouds in supersaturated conditions with salt aerosols, and an example of measured imagery viewed through the generated cloud is shown. Aerosol and cloud droplet distributions measured during the experiment are used to predict scattering PSF and MTF curves, and a methodology for validating existing theory is detailed. Measured atmospheric inputs will be used to simulate aerosol-induced image degradation for comparison with measured imagery taken through actual cloud conditions. The aerosol MTF will be experimentally calculated and compared to theoretical expressions. The key result of this study is the proposal of a closure experiment for verification of theoretical aerosol effects using actual clouds in a controlled laboratory setting.

The Optical Properties of Ion Implanted Silica

NASA Technical Reports Server (NTRS)

Smith, Cydale C.; Ila, D.; Sarkisov, S.; Williams, E. K.; Poker, D. B.; Hensley, D. K.

1997-01-01

We will present our investigation on the change in the optical properties of silica, 'suprasil', after keV through MeV implantation of copper, tin, silver and gold and after annealing. Suprasil-1, name brand of silica glass produced by Hereaus Amerisil, which is chemically pure with well known optical properties. Both linear nonlinear optical properties of the implanted silica were investigated before and after thermal annealing. All implants, except for Sn, showed strong optical absorption bands in agreement with Mie's theory. We have also used Z-scan to measure the strength of the third order nonlinear optical properties of the produced thin films, which is composed of the host material and the metallic nanoclusters. For implants with a measurable optical absorption band we used Doyle's theory and the full width half maximum of the absorption band to calculate the predicted size of the formed nanoclusters at various heat treatment temperatures. These results are compared with those obtained from direct observation using transmission electron microscopic techniques.

Structural and optical properties of co-precipitated copper doped zinc oxide

NASA Astrophysics Data System (ADS)

Pandey, Devendra K.; Modi, Anchit; Pandey, Padmini; Gaur, N. K.

2018-05-01

We have synthesized pure and copper doped zinc oxide Zn1-xO:Cux (x = 0, 0.03) powder by wet chemical co-precipitation method followed by sintering of the co-precipitated amorphous phase powder at 450°C for 4 hours. The experiment is performed to recognize the effect of nominal doping of transition metal over the structural, morphological and optical properties. The structural parameters are observed by using Rietveld refinement of X-ray diffraction data which clearly represents that Cu ion is perfectly incorporated at the Zn site with minimal distortions within the lattice. The crystallite size is estimated by Debye-Scherrer and Hall-Williamson formulation. The particle morphology and size is determined with scanning electron microscopic (SEM) technique. The band gap and optical measurements are carried out with UV-visible absorption and photoluminescence (PL) spectroscopic technique, respectively. Enhanced PL spectral response is observed for ZnO:Cu along with non-radiative transitions from conduction band to valence band. The energy levels near the conduction band that are commonly involved in the optoelectronic transitions in the UV-region are traced by using absorption and luminescence spectral graphs.

Absorption line metrology by optical feedback frequency-stabilized cavity ring-down spectroscopy

NASA Astrophysics Data System (ADS)

Burkart, Johannes; Kassi, Samir

2015-04-01

Optical feedback frequency-stabilized cavity ring-down spectroscopy (OFFS-CRDS) is a near-shot-noise-limited technique combining a sensitivity of with a highly linear frequency axis and sub-kHz resolution. Here, we give an in-depth review of the key elements of the experimental setup encompassing a highly stable V-shaped reference cavity, an integrated Mach-Zehnder modulator and a tightly locked ring-down cavity with a finesse of 450,000. Carrying out a detailed analysis of the spectrometer performance and its limitations, we revisit the photo-electron shot-noise limit in CRDS and discuss the impact of optical fringes. We demonstrate different active schemes for fringe cancelation by varying the phase of parasitic reflections. The proof-of-principle experiments reported here include a broadband high-resolution spectrum of carbon dioxide at 1.6 µm and an isolated line-shape measurement with a signal-to-noise ratio of 80,000. Beyond laboratory-based absorption line metrology for fundamental research, OFFS-CRDS holds a considerable potential for field laser measurements of trace gas concentrations and isotopic ratios by virtue of its small sample volume and footprint, the robust cavity-locking scheme and supreme precision.

Morphology and Optical Properties of Mixed Aerosol Particles

NASA Astrophysics Data System (ADS)

Fard, Mehrnoush M.; Krieger, Ulrich; Rudich, Yinon; Marcolli, Claudia; Peter, Thomas

2016-04-01

Experiments and modeling studies have shown that deliquesced aerosols can exist not only as one-phase system containing organics, inorganic salts and water, but often as two-phase systems consisting of a predominantly organic and a predominantly inorganic aqueous phase (1,2). Recent laboratory studies conducted with model mixtures representing tropospheric aerosols (1,2,3), secondary organic aerosol (SOA) from smog chamber experiments (4), and field measurements (5) suggest that liquid-liquid phase separations (LLPS) is indeed a common phenomenon in mixed organic/ inorganic particles. During LLPS, particles may adopt different morphologies mainly core-shell and partially engulfed. A core-shell configuration will have consequences for heterogeneous chemistry and hygroscopicity and as a result will alter the optical properties of the particles in particular for organic phases containing absorbing molecules, e.g. brown carbon. The primary objective of this project is to establish a method for investigating the morphology of mixed inorganic and absorbing organic compounds of atmospheric relevance and study their radiative properties before, during, and after phase transitions mainly during LLPS. This will be the first study looking into the radiative effect of LLPS in detail. Our ternary model system consist of ammonium sulfate (AS)/ Polyethylene Glycol (PEG)/ and water (H2O). Carminic acid (CA) was added as a proxy for an absorbing organic compound to the system. The behavior of single droplets of above ternary mixture was monitored during relative humidity (RH) cycles using optical microscopy. The same ternary mixture particle was levitated in an electrodynamic balance (EDB) and the change in its absorption properties was measured at varying RH. In addition, Mie-code modeling is used to predict the absorption efficiency of the same ternary system and the result will be compared with the data obtained from EDB experiment. We also intend to determine the occurrence of LLPS in accumulation-sized particles and the change in their absorption using a cavity ring down aerosol spectrometer. If LLPS alters the absorptive properties of the suggested model aerosols significantly, absorption measurements of accumulation mode particles of the same composition would allow proving that LLPS indeed occurs in particles of accumulation mode size. Up to now LLPS has not been studied for particles in this size range. References: 1. Bertram, et al. Atmos. Chem & Phys, 11(21), 10995-11006, 2011.
 2. Krieger, et al. Chemical Society Reviews, 41(19), 6631-6662, 2012 
3. Song, M. et al. Geophys Res Lett, 39(19), 2012b 4. Smith et al. Atmos Chem & Phys, 12(20), 9613- 9628, 2012.
 5. You, Y. et al. Proceedings of the National Academy of Sciences, 109(33), 13188-13193, 2012.

Rich magneto-absorption spectra of AAB-stacked trilayer graphene.

PubMed

Do, Thi-Nga; Shih, Po-Hsin; Chang, Cheng-Peng; Lin, Chiun-Yan; Lin, Ming-Fa

2016-06-29

A generalized tight-binding model is developed to investigate the feature-rich magneto-optical properties of AAB-stacked trilayer graphene. Three intragroup and six intergroup inter-Landau-level (inter-LL) optical excitations largely enrich magneto-absorption peaks. In general, the former are much higher than the latter, depending on the phases and amplitudes of LL wavefunctions. The absorption spectra exhibit single- or twin-peak structures which are determined by quantum modes, LL energy spectra and Fermion distribution. The splitting LLs, with different localization centers (2/6 and 4/6 positions in a unit cell), can generate very distinct absorption spectra. There exist extra single peaks because of LL anti-crossings. AAB, AAA, ABA, and ABC stackings considerably differ from one another in terms of the inter-LL category, frequency, intensity, and structure of absorption peaks. The main characteristics of LL wavefunctions and energy spectra and the Fermi-Dirac function are responsible for the configuration-enriched magneto-optical spectra.

Paper area density measurement from forward transmitted scattered light

DOEpatents

Koo, Jackson C.

2001-01-01

A method whereby the average paper fiber area density (weight per unit area) can be directly calculated from the intensity of transmitted, scattered light at two different wavelengths, one being a non-absorpted wavelength. Also, the method makes it possible to derive the water percentage per fiber area density from a two-wavelength measurement. In the optical measuring technique optical transmitted intensity, for example, at 2.1 microns cellulose absorption line is measured and compared with another scattered, optical transmitted intensity reference in the nearby spectrum region, such as 1.68 microns, where there is no absorption. From the ratio of these two intensities, one can calculate the scattering absorption coefficient at 2.1 microns. This absorption coefficient at this wavelength is, then, experimentally correlated to the paper fiber area density. The water percentage per fiber area density can be derived from this two-wavelength measurement approach.

Reflectance-mode interferometric near-infrared spectroscopy quantifies brain absorption, scattering, and blood flow index in vivo.

PubMed

Borycki, Dawid; Kholiqov, Oybek; Srinivasan, Vivek J

2017-02-01

Interferometric near-infrared spectroscopy (iNIRS) is a new technique that measures time-of-flight- (TOF-) resolved autocorrelations in turbid media, enabling simultaneous estimation of optical and dynamical properties. Here, we demonstrate reflectance-mode iNIRS for noninvasive monitoring of a mouse brain in vivo. A method for more precise quantification with less static interference from superficial layers, based on separating static and dynamic components of the optical field autocorrelation, is presented. Absolute values of absorption, reduced scattering, and blood flow index (BFI) are measured, and changes in BFI and absorption are monitored during a hypercapnic challenge. Absorption changes from TOF-resolved iNIRS agree with absorption changes from continuous wave NIRS analysis, based on TOF-integrated light intensity changes, an effective path length, and the modified Beer-Lambert Law. Thus, iNIRS is a promising approach for quantitative and noninvasive monitoring of perfusion and optical properties in vivo.

Nanopillar Optical Antenna Avalanche Detectors

DTIC Science & Technology

2014-08-30

tuning and hybridization of the optical absorption via Surface Plasmon Polariton Bloch Waves (SPP-BWs) and Localized Surface Plasmon Resonances (LSPRs...of the optical absorption via Surface Plasmon Polariton Bloch Waves (SPP-BWs) and Localized Surface Plasmon Resonances (LSPRs) will be discussed...Surface Plasmon Polariton Bloch wave (SPP-BW) 36, 40. Also, resonant-field enhancement occurs in bounded metallic/dielectric structures that support

Miniaturized differential optical absorption spectroscopy (DOAS) system for the analysis of NO2

NASA Astrophysics Data System (ADS)

Morales, J. Alberto; Walsh, James E.; Treacy, Jack E.; Garland, Wendy E.

2003-03-01

Current trends in optical design engineering are leading to the development of new systems which can analyze atmospheric pollutants in a fast and easy way, allowing remote-sensing and miniaturization at a low cost. A small portable fiber-optic based system is presented for the spectroscopic analysis of a common gas pollutant, NO2. The novel optical set-up described consists of a small telescope that collects ultraviolet-visible light from a xenon lamp located 600 m away. The light is coupled into a portable diode array spectrometer through a fiber-optic cable and the system is controlled by a lap-top computer where the spectra are recorded. Using the spectrum of the lamp as a reference, the absorption spectrum of the open path between the lamp and the telescope is calculated. Known absorption features in the NO2 spectrum are used to calculate the concentration of the pollutant using the principles of Differential Optical Absorption Spectroscopy (DOAS). Calibration is carried by using sample gas bags of known concentration of the pollutant. The results obtained demonstrate that it is possible to detect and determine NO2 concentrations directly from the atmosphere at typical environment levels by using an inexpensive field based fiber-optic spectrometer system.

Optical properties of embedded metal nanoparticles at low temperatures

NASA Astrophysics Data System (ADS)

Heilmann, A.; Kreibig, U.

2000-06-01

Metal nanoparticles (gold, silver, copper) that are embedded in an insulating organic host material exhibit optical plasma resonance absorption in the visible and near-infrared region. The spectral position, the half width and the intensity of the plasma resonance absorption all depend on the particle size, the particle shape, and the optical behavior of the cluster and the host material. The optical extinction of various gold, silver or copper particle assemblies embedded in plasma polymer or gelatin was measured at 4.2 K and 1.2 K as well as at room temperature. The packing density of several samples was high enough to resolve a reversible increase of the plasma resonance absorption intensity towards lower temperatures. Additionally, at larger silver particles D_m > 50 nm a significant blue shift of the plasma resonance absorption was measured. Particle size and shape distribution were determined by transmission electron microscopy (TEM). For the first time, simultaneous measurements of the electrical and optical properties at one and the same particle assembly were performed at low temperatures. Contrary to the increasing optical extinction, the d.c. conductivity decreased to two orders of magnitude. At silver particles embedded in a plasma polymer made from thiophene a significant photocurrent was measured.

Materials for Digital Optical Design:. a Survey Study

NASA Astrophysics Data System (ADS)

Ismail, Ayman Abdel Khader; Ismail, Imane Aly Saroit; Ahmed, S. H.

2010-04-01

In the last few years digital optical design had major attention in research fields. Many researches were published in the fields of optical materials, instruments, circuit design and devices. This is considered to be the most multidisciplinary field and requires for its success collaborative efforts of many disciplines, ranging from device and optical engineers to computer architects, chemists, material scientists, and optical physicists. In this study we will introduce a survey of the latest papers in the field of optical materials and its properties for light; this paper is organized in three major sections, optical glasses, compound materials and nonlinear absorption (multi photon absorption) and up-conversion.

Investigating the Spectral Dependence of Biomass Burning Aerosol Optical Properties

NASA Astrophysics Data System (ADS)

Odwuor, A.; Corr, C.; Pusede, S.

2016-12-01

Aerosol optical properties, such as light absorption and scattering, are important for understanding how aerosols affect the global radiation budget and for comparison with data gathered from remote sensing. It has been established that the optical properties of aerosols are wavelength dependent, although some remote sensing measurements do not consider this. Airborne measurements of these optical properties were used to calculate the absorption Angstrom exponent, a parameter that characterizes the wavelength dependence of light absorption by aerosols, and single scattering albedo, which measures the relative magnitude of light scattering to total extinction (scattering and absorption combined). Aerosols produced by biomass burning in Saskatchewan, Canada in July 2008 and a forest fire in Southern California, U.S. in June 2016 were included in this analysis. These wildfires were sampled by the NASA DC-8 aircraft during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) and NASA Student Airborne Research Program (SARP) missions, respectively. Aerosol absorption was measured using a particle soot photometer (PSAP) at 470, 532 and 660 nm. Scattering was measured using a 3-wavelength (450, 550 and 700 nm) nephelometer. Absorption Angstrom exponents were calculated at 470 and 660 nm and single scattering albedos were calculated at 450 and 550 nm. Results of this study indicate that disregarding the wavelength dependence of organic aerosol can understate the positive radiative forcing (warming) associated with aerosol absorption.

The optical absorption of triatomic carbon C3 for the wavelength range 260 to 560 nm

NASA Technical Reports Server (NTRS)

Jones, J. J.

1978-01-01

The spectral absorption properties of C3 have been measured in a shock tube containing a test gas mixture of acetylene diluted with argon. The absorption of a pulsed xenon light source was measured by means of eight photomultiplier channels to a spectrograph and an accompanying drum camera. The postshock test gas temperature and pressure were varied over the range 3240 to 4300 K and 37 to 229 kPa, respectively. The results showed appreciable absorption by C3 for the wavelength range 300 to 540 nm. The various reported measurements of the heat of formation of C3 which are available in the open literature were reviewed, and a value of 198 kcal/mol is recommended. This value, along with best available values for other species, was used to calculate the number density of C3 for the conditions of the present experiments in order to compute absorption cross section or electronic oscillator strength. The computed electronic oscillator strength varied from a high of 0.062 at 3300 K to a low of 0.036 at 3900 K.

Experimental technique for simultaneous measurement of absorption-, emission cross-sections, and background loss coefficient in doped optical fibers

NASA Astrophysics Data System (ADS)

Karimi, M.; Seraji, F. E.

2010-01-01

We report a new simple technique for the simultaneous measurements of absorption-, emission cross-sections, background loss coefficient, and dopant density of doped optical fibers with low dopant concentration. Using our proposed technique, the experimental characterization of a sample Ge-Er-doped optical fiber is presented, and the results are analyzed and compared with other reports. This technique is suitable for production line of doped optical fibers.

Measurements of the intrinsic quantum efficiency and absorption length of tetraphenyl butadiene thin films in the vacuum ultraviolet regime

NASA Astrophysics Data System (ADS)

Benson, Christopher; Gann, Gabriel Orebi; Gehman, Victor

2018-04-01

A key enabling technology for many liquid noble gas (LNG) detectors is the use of the common wavelength shifting medium tetraphenyl butadiene (TPB). TPB thin films are used to shift ultraviolet scintillation light into the visible spectrum for detection and event reconstruction. Understanding the wavelength shifting efficiency and optical properties of these films are critical aspects in detector performance and modeling and hence in the ultimate physics sensitivity of such experiments. This article presents the first measurements of the room-temperature microphysical quantum efficiency for vacuum-deposited TPB thin films - a result that is independent of the optics of the TPB or substrate. Also presented are measurements of the absorption length in the vacuum ultraviolet regime, the secondary re-emission efficiency, and more precise results for the "black-box" efficiency across a broader spectrum of wavelengths than previous results. The low-wavelength sensitivity, in particular, would allow construction of LNG scintillator detectors with lighter elements (Ne, He) to target light mass WIMPs.

All-Optical Cantilever-Enhanced Photoacoustic Spectroscopy in the Open Environment

NASA Astrophysics Data System (ADS)

Wei, Wei; Zhu, Yong; Lin, Cheng; Tian, Li; Xu, Zhuwen; Nong, Jinpeng

2015-06-01

A novel all-optical cantilever-enhanced photoacoustic spectroscopy technique for trace gas detection in the open environment is proposed. A cantilever is set off-beam to "listen to" the photoacoustic signal, and an improved quadrature-point stabilization Fabry-Perot demodulation unit is used to pick up the vibration signal of the acoustic transducer instead of a complicated Michelson interferometer. The structure parameters of the cantilever are optimized to make the sensing system work more stably and reliably using a finite element method, which is then fabricated by surface micro-machining technology. Finally, related experiments are carried out to detect the absorption of water vapor at one atmosphere in the open environment. It was found that the normalized noise-equivalent absorption coefficient obtained by a traditional Fabry-Perot demodulation unit is , while that by a quadrature- point stabilization Fabry-Perot demodulation unit is , which indicates that the sensitivity is increased by a factor of 3.1 using improved cantilever-enhanced photoacoustic spectroscopy.

Observation of soliton compression in silicon photonic crystals

PubMed Central

Blanco-Redondo, A.; Husko, C.; Eades, D.; Zhang, Y.; Li, J.; Krauss, T.F.; Eggleton, B.J.

2014-01-01

Solitons are nonlinear waves present in diverse physical systems including plasmas, water surfaces and optics. In silicon, the presence of two photon absorption and accompanying free carriers strongly perturb the canonical dynamics of optical solitons. Here we report the first experimental demonstration of soliton-effect pulse compression of picosecond pulses in silicon, despite two photon absorption and free carriers. Here we achieve compression of 3.7 ps pulses to 1.6 ps with <10 pJ energy. We demonstrate a ~1-ps free-carrier-induced pulse acceleration and show that picosecond input pulses are critical to these observations. These experiments are enabled by a dispersion-engineered slow-light photonic crystal waveguide and an ultra-sensitive frequency-resolved electrical gating technique to detect the ultralow energies in the nanostructured device. Strong agreement with a nonlinear Schrödinger model confirms the measurements. These results further our understanding of nonlinear waves in silicon and open the way to soliton-based functionalities in complementary metal-oxide-semiconductor-compatible platforms. PMID:24423977

An optically transparent metasurface for broadband microwave antireflection

NASA Astrophysics Data System (ADS)

Zhao, Jie; Zhang, Cheng; Cheng, Qiang; Yang, Jin; Cui, Tie Jun

2018-02-01

Metamaterial absorbers and diffusers provide powerful routes to decrease the backward reflection significantly with advantages of ultrathin profile and customized bandwidth. Simultaneous control of the absorption and scattering behaviors of the metamaterials which helps to improve the suppression capabilities of backward reflection, however, still remains a challenge. Aiming at this goal, we propose a metasurface constituted by two kinds of elements in a pseudorandom arrangement. By the use of indium tin oxide with moderate sheet resistance in the meta-atoms, enhanced absorption of energy can be achieved in a broad spectrum when interacted with illuminated waves. In the meanwhile, electromagnetic diffusion will be invoked from the destructive interference among the elements, giving rise to significant reduction of specular reflection as a result. Excellent agreements are observed between simulation and experiment with pronounced reflection suppression from 6.8 GHz to 19.4 GHz. In addition, the optical transparence of the patterns and substrates makes the proposed metasurface a promising candidate for future applications like photovoltaic solar cells and electromagnetic shielding glasses.

First principles study of electronic properties, interband transitions and electron energy loss of α-graphyne

NASA Astrophysics Data System (ADS)

Behzad, Somayeh

2016-04-01

The electronic and optical properties of α-graphyne sheet are investigated by using density functional theory. The results confirm that α-graphyne sheet is a zero-gap semimetal. The optical properties of the α-graphyne sheet such as dielectric function, refraction index, electron energy loss function, reflectivity, absorption coefficient and extinction index are calculated for both parallel and perpendicular electric field polarizations. The optical spectra are strongly anisotropic along these two polarizations. For (E ∥ x), absorption edge is at 0 eV, while there is no absorption below 8 eV for (E ∥ z).

Temperature dependence of the fundamental optical absorption edge in crystals and disordered semiconductors

NASA Astrophysics Data System (ADS)

Grein, C. H.; John, Sajeev

1989-04-01

We present a first principles theory of the temperature dependence of the Urbach optical absorption edge in crystals and disordered semiconductors which incorporates the effects of short range correlated static disorder and the non-adiabatic quantum dynamics of the coupled electron-phonon system. At finite temperatures the dominant features of the Urbach tail are accounted for by multiple phonon absorption and emission side bands which accompany the optically induced electronic transition and which provide a dynamic polaronic potential well that localizes the electron. Excellent agreement is found with experimental data on both crystalline and amorphous silicon.

Terahertz optical properties of nonlinear optical CdSe crystals

NASA Astrophysics Data System (ADS)

Yan, Dexian; Xu, Degang; Li, Jining; Wang, Yuye; Liang, Fei; Wang, Jian; Yan, Chao; Liu, Hongxiang; Shi, Jia; Tang, Longhuang; He, Yixin; Zhong, Kai; Lin, Zheshuai; Zhang, Yingwu; Cheng, Hongjuan; Shi, Wei; Yao, Jianquan; Wu, Yicheng

2018-04-01

We investigate the optical properties of cadmium selenide (CdSe) crystals in a wide terahertz (THz) range from 0.2 to 6 THz by THz time-domain spectroscopy (THz-TDS) and Fourier transform infrared spectroscopy (FTIR). The refractive index, absorption coefficient and transmittance are measured and analyzed. The properties are characterized by several absorption peaks which represent the relevant phonon vibrations modes. The experimental results are in agreement with the theoretical results. The dispersion and absorption properties of CdSe crystal are analyzed in THz range. These properties indicate a good potential for THz sources and THz modulated devices.

The electronic and optical properties of amorphous silica with hydrogen defects by ab initio calculations

NASA Astrophysics Data System (ADS)

Ren, Dahua; Xiang, Baoyan; Hu, Cheng; Qian, Kai; Cheng, Xinlu

2018-04-01

Hydrogen can be trapped in the bulk materials in four forms: interstitial molecular H2, interstitial atom H, O‑H+(2Si=O–H)+, Si‑H‑( {{4O}}\\bar \\equiv {{Si&x2212H}})‑ to affect the electronic and optical properties of amorphous silica. Therefore, the electronic and optical properties of defect-free and hydrogen defects in amorphous silica were performed within the scheme of density functional theory. Initially, the negative charged states hydrogen defects introduced new defect level between the valence band top and conduction band bottom. However, the neutral and positive charged state hydrogen defects made both the valence band and conduction band transfer to the lower energy. Subsequently, the optical properties such as absorption spectra, conductivity and loss functions were analyzed. It is indicated that the negative hydrogen defects caused the absorption peak ranging from 0 to 2.0 eV while the positive states produced absorption peaks at lower energy and two strong absorption peaks arose at 6.9 and 9.0 eV. However, the neutral hydrogen defects just improved the intensity of absorption spectrum. This may give insights into understanding the mechanism of laser-induced damage for optical materials. Project supported by the Science and Technology of Hubei Provincial Department of Education (No. B2017098).

Two Photon Absorption And Refraction in Bulk of the Semiconducting Materials

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

Kumari, Vinay; Department of Physics, DCRUST Murthal, Haryana; Kumar, Vinod

2011-10-20

Fast electronic detection systems have opened up a number of new fields like nonlinear optics, optical communication, coherent optics, optical bistability, two/four wave mixing. The interest in this field has been stimulated by the importance of multiphoton processes in many fundamental aspects of physics. It has proved to be an invaluable tool for determining the optical and electronic properties of the solids because of the fact that one gets the information about the bulk of the material rather than the surface one. In this paper we report, the measurement of the nonlinear absorption and refraction from the band gap tomore » half-band gap region of bulk of semiconductors in the direct and indirect band gap crystals with nanosecond laser. The measured theoretical calculated values of two-photon absorption coefficients ({beta}) and nonlinear refraction n{sub 2}({omega}) of direct band gap crystal match the earlier reported theoretical predictions. By making use of these theoretical calculated values, we have estimated {beta} and n{sub 2}({omega}) in the case of indirect band gap crystals. Low value of absorption coefficient in case of indirect band gap crystals have been attributed to phonon assisted transition while reduction in nonlinear refraction is due to the rise in saturation taking place in the absorption.« less

Quantum size and magnesium composition effects on the optical absorption in the MgxZn(1-x)O/ZnO quantum well

NASA Astrophysics Data System (ADS)

Dakhlaoui, Hassen ben Bechir; Mouna, Nefzi

2018-02-01

In this work, we investigated the effects of polarizations and structural parameters on the optical absorption coefficient (OAC) and the intersubband transition between the three lowest energy levels E1,E2 , and E3 in the MgxZn(1-x)O/ZnO single quantum well. The energy of the electron in each level and its respective wavefunction are calculated by the numerical solution of Schrödinger and Poisson equations self-consistently using an effective mass approximation. Our findings exhibit that the intersubband transitions, ΔE12 and ΔE13 , can be altered and controlled by varying the quantum well width and the magnesium composition, x. Moreover, our results suggest that the optical absorption coefficients, α12 and α13 , can be modulated principally by adjusting the quantum well width, especially the optical absorption coefficient (α12), which presents a red shift by raising the quantum well thickness. Contrary to α12 , the optical absorption coefficient, α13 , can present either a red or a blue shift by increasing the quantum well width. The process responsible for this behavior, which can be suitable for optoelectronic device applications, is discussed here in detail.

O2 adsorbed on Ptn clusters: Structure and optical absorption

NASA Astrophysics Data System (ADS)

Wang, Ruiying; Zhao, Liang; Jia, Jianfeng; Wu, Hai-Shun

2018-03-01

The interaction of O2 with Ptn and the optical absorption properties of PtnO2 were explored under the framework of density functional theory. The Ptn (n= 2, 4, 6, 9, 10, 14, 18, 22, and 27) clusters were selected, which were reported as magnetic number Ptn clusters in reference (V. Kumar and Y. Kawazoe, Phys. Rev. B 77(20), 205418 (2008)). The single Pt atom was also considered. The longest O2 bonds were found for Pt27O2, Pt6O2 and Pt14O2, while PtO2 and Pt2O2 have the shortest O2 bonds. This result showed that the single Pt atom was not preferred for O2 activation. The O2 bond length was closely related to the electron transfer from Ptn to O2. The optical absorptions of PtnO2 were investigated with time-dependent density functional theory method. A new term of charge transfer strength was defined to estimate the further electron transfer from Ptn to O2 caused by the optical absorption in the visible light range. Our calculations showed that with the increasing n, the further electron transfer from Ptn to O2 caused by optical absorption will become very weak.

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

Li, H.; Chang, C.; Cheng, H. H., E-mail: hhcheng@ntu.edu.tw

We report an investigation on the absorption mechanism of a GeSn photodetector with 2.4% Sn composition in the active region. Responsivity is measured and absorption coefficient is calculated. Square root of absorption coefficient linearly depends on photon energy indicating an indirect transition. However, the absorption coefficient is found to be at least one order of magnitude higher than that of most other indirect materials, suggesting that the indirect optical absorption transition cannot be assisted only by phonon. Our analysis of absorption measurements by other groups on the same material system showed the values of absorption coefficient on the same ordermore » of magnitude. Our study reveals that the strong enhancement of absorption for the indirect optical transition is the result of alloy disorder from the incorporation of the much larger Sn atoms into the Ge lattice that are randomly distributed.« less

Theoretical Prediction of Si 2–Si 33 Absorption Spectra

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

Zhao, Li -Zhen; Lu, Wen -Cai; Qin, Wei

Here, the optical absorption spectra of Si 2–Si 33 clusters were systematically studied by a time-dependent density functional theory approach. The calculations revealed that the absorption spectrum becomes significantly broad with increasing cluster size, stretching from ultraviolet to the infrared region. The absorption spectra are closely related to the structural motifs. With increasing cluster size, the absorption intensity of cage structures gradually increases, but the absorption curves of the prolate and the Y-shaped structures are very sensitive to cluster size. If the transition energy reaches ~12 eV, it is noted that all the clusters have remarkable absorption in deep ultravioletmore » region of 100–200 nm, and the maximum absorption intensity is ~100 times that in the visible region. Further, the optical responses to doping in the Si clusters were studied.« less

Theoretical Prediction of Si 2–Si 33 Absorption Spectra

DOE PAGES

Zhao, Li -Zhen; Lu, Wen -Cai; Qin, Wei; ...

2017-07-07

Here, the optical absorption spectra of Si 2–Si 33 clusters were systematically studied by a time-dependent density functional theory approach. The calculations revealed that the absorption spectrum becomes significantly broad with increasing cluster size, stretching from ultraviolet to the infrared region. The absorption spectra are closely related to the structural motifs. With increasing cluster size, the absorption intensity of cage structures gradually increases, but the absorption curves of the prolate and the Y-shaped structures are very sensitive to cluster size. If the transition energy reaches ~12 eV, it is noted that all the clusters have remarkable absorption in deep ultravioletmore » region of 100–200 nm, and the maximum absorption intensity is ~100 times that in the visible region. Further, the optical responses to doping in the Si clusters were studied.« less

Ultrasonic modulation of tissue optical properties in ex vivo porcine skin to improve transmitted transdermal laser intensity.

PubMed

Whiteside, Paul J D; Qian, Chenxi; Golda, Nicholas; Hunt, Heather K

2017-09-01

Applications of light-based energy devices involving optical targets within the dermis frequently experience negative side-effects resultant from surface scattering and excess optical absorption by epidermal melanin. As a broadband optical absorber, melanin decreases the efficacy of light-based treatments throughout the ultraviolet, visible, and near-infrared spectra while also generating additional heat within the surface tissue that can lead to inflammation or tissue damage. Consequently, procedures may be performed using greater energy densities to ensure that the target receives a clinically relevant dose of light; however, such practices are limited, as doing so tends to exacerbate the detrimental complications resulting from melanin absorption of treatment light. The technique presented herein represents an alternative method of operation aimed at increasing epidermal energy fluence while mitigating excess absorption by unintended chromophores. The approach involves the application of continuously pulsed ultrasound to modulate the tissue's optical properties and thereby improve light transmission through the epidermis. To demonstrate the change in optical properties, pulsed light at a wavelength of 532 nm from a Q-switched Nd:YAG laser was transmitted into 4 mm thick samples of porcine skin, comprised of both epidermal and dermal tissue. The light was transmitted using an optical waveguide, which allowed for an ultrasonic transducer to be incorporated for simultaneous paraxial pulsation in parallel with laser operation. Light transmitted through the tissue was measured by a photodiode attached to an integrating sphere. Increasing the driving voltage of ultrasonic pulsation resulted in an increase in mean transmitted optical power of up to a factor of 1.742 ± 0.0526 times the control, wherein no ultrasound was applied, after which the optical power increase plateaued to an average amplification factor of 1.733 ± 0.549 times the control. The increase implies a reduction in light either back-scattered or absorbed within the tissue, which would allow for a greater proportion of incident energy to be delivered to the clinical target, thereby improving procedural efficacy and potentially reducing the severity of detrimental side-effects. Apparatus Lasers Surg. Med. 49:666-674, 2017. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Evaluation of polymer based third order nonlinear integrated optics devices

NASA Astrophysics Data System (ADS)

Driessen, A.; Hoekstra, H. J. W. M.; Blom, F. C.; Horst, F.; Krijnen, G. J. M.; van Schoot, J. B. P.; Lambeck, P. V.; Popma, Th. J. A.; Diemeer, M. B.

1998-01-01

Nonlinear polymers are promising materials for high speed active integrated optics devices. In this paper we evaluate the perspectives polymer based nonlinear optical devices can offer. Special attention is directed to the materials aspects. In our experimental work we applied mainly Akzo Nobel DANS side-chain polymer that exhibits large second and third order coefficients. This material has been characterized by third harmonic generation, z-scan and pump-probe measurements. In addition, various waveguiding structures have been used to measure the nonlinear absorption (two photon absorption) on a ps time-scale. Finally an integrated optics Mach Zehnder interferometer has been realized and evaluated. It is shown that the DANS side-chain polymer has many of the desired properties: the material is easily processable in high-quality optical waveguiding structures, has low linear absorption and its nonlinearity has a pure electronic origin. More materials research has to be done to arrive at materials with higher nonlinear coefficients to allow switching at moderate light intensity ( < 1 W peak power) and also with lower nonlinear absorption coefficients.

Measurements of ionization states in warm dense aluminum with betatron radiation

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

Mo, M. Z.; Chen, Z.; Fourmaux, S.

Time-resolved measurements of the ionization states of warm dense aluminum via K-shell absorption spectroscopy are demonstrated using betatron radiation generated from laser wakefield acceleration as a probe. The warm dense aluminum is generated by irradiating a free-standing nanofoil with a femtosecond optical laser pulse and was heated to an electron temperature of ~20–25 eV at a close-to-solid mass density. Absorption dips in the transmitted x-ray spectrum due to the Al 4+ and Al 5+ ions are clearly seen during the experiments. The measured absorption spectra are compared to simulations with various ionization potential depression models, including the commonly used Stewart-Pyattmore » model and an alternative modified Ecker-Kröll model. Furthermore, the observed absorption spectra are in approximate agreement with these models, though indicating a slightly higher state of ionization and closer agreement for simulations with the modified Ecker-Kröll model.« less

Measurements of ionization states in warm dense aluminum with betatron radiation

DOE PAGES

Mo, M. Z.; Chen, Z.; Fourmaux, S.; ...

2017-05-19

Time-resolved measurements of the ionization states of warm dense aluminum via K-shell absorption spectroscopy are demonstrated using betatron radiation generated from laser wakefield acceleration as a probe. The warm dense aluminum is generated by irradiating a free-standing nanofoil with a femtosecond optical laser pulse and was heated to an electron temperature of ~20–25 eV at a close-to-solid mass density. Absorption dips in the transmitted x-ray spectrum due to the Al 4+ and Al 5+ ions are clearly seen during the experiments. The measured absorption spectra are compared to simulations with various ionization potential depression models, including the commonly used Stewart-Pyattmore » model and an alternative modified Ecker-Kröll model. Furthermore, the observed absorption spectra are in approximate agreement with these models, though indicating a slightly higher state of ionization and closer agreement for simulations with the modified Ecker-Kröll model.« less

Excited-state absorption and fluorescence dynamics of Er3+:KY3F10

NASA Astrophysics Data System (ADS)

Labbé, C.; Doualan, J. L.; Moncorgé, R.; Braud, A.; Camy, P.

2018-05-01

We report here on a complete investigation of the excited-state absorption and fluorescence dynamics of Er3+ doped KY3F10 single crystals versus dopant concentrations and optical excitation conditions. Radiative and effective (including non-radiative relaxations) emission lifetimes and branching ratios are determined from a Judd-Ofelt analysis of the absorption spectra and via specific fluorescence experiments using wavelength selective laser excitations. Excited-state absorption and emission spectra are registered within seven spectral domains, i.e. 560 nm, 650 nm, 710 nm, 810 nm, 970 nm, 1550 nm and 2750 nm. A maximum gain cross-section of 0.93 × 10-21 cm2 is determined at the potential laser wavelength of 2.801 μm for a population ratio of 0.48. Saturation of fluorescence intensities and variations of population ratios versus pumping rates are registered and confronted with a rate equation model to derive the rates of the most important up-conversion and cross-relaxation energy transfers occurring at high dopant concentrations.

Optical effect of the contamination of infrared windows by the outgassing of materials in outer space

NASA Technical Reports Server (NTRS)

Silberman, E.

1975-01-01

The products and kinetics of outgassing from S13G paint were studied by using infrared absorption measurements of the material outgassed (using an evaporation cell and vacuum chamber). Two separate long-term experimental depositions from heated samples of the S13G paint were made. Before each experiment, the vacuum chamber and sample holder were carefully cleaned and outgassed to ensure that subsequent deposits on the colled-window were due only to the products evaporated from the sample. Results of experiments are listed and discussed.

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

NASA Astrophysics Data System (ADS)

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

2017-02-01

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

Linear and nonlinear magneto-optical absorption in a triangular quantum well

NASA Astrophysics Data System (ADS)

Tung, Luong V.; Vinh, Pham T.; Dinh, Le; Phuc, Huynh V.

2018-05-01

In this work, we study the linear and nonlinear magneto-optical absorption spectrum in a triangular quantum well (TrQW) created by the applied electric field via investigating the phonon-assisted cyclotron resonance (PACR) effect. The results are calculated for a specific Ga0.7Al0.3As/GaAs quantum well. The magneto-optical absorption coefficient (MOAC) and the full width at half maximum (FWHM) are found to be significantly dependent on the magnetic field, the electric field and the temperature. Our results showed that the MOAC and FWHM increase with the magnetic, electric fields and temperature. The obtained results also suggest a useful way to control the magneto-optical properties of TrQW by changing these parameters.

Investigation of quadratic electro-optic effects and electro-absorption process in GaN/AlGaN spherical quantum dot

PubMed Central

2014-01-01

Quadratic electro-optic effects (QEOEs) and electro-absorption (EA) process in a GaN/AlGaN spherical quantum dot are theoretically investigated. It is found that the magnitude and resonant position of third-order nonlinear optical susceptibility depend on the nanostructure size and aluminum mole fraction. With increase of the well width and barrier potential, quadratic electro-optic effect and electro-absorption process nonlinear susceptibilities are decreased and blueshifted. The results show that the DC Kerr effect in this case is much larger than that in the bulk case. Finally, it is observed that QEOEs and EA susceptibilities decrease and broaden with the decrease of relaxation time. PMID:24646318

A High Spectral Resolution Lidar Based on Absorption Filter

NASA Technical Reports Server (NTRS)

Piironen, Paivi

1996-01-01

A High Spectral Resolution Lidar (HSRL) that uses an iodine absorption filter and a tunable, narrow bandwidth Nd:YAG laser is demonstrated. The iodine absorption filter provides better performance than the Fabry-Perot etalon that it replaces. This study presents an instrument design that can be used a the basis for a design of a simple and robust lidar for the measurement of the optical properties of the atmosphere. The HSRL provides calibrated measurements of the optical properties of the atmospheric aerosols. These observations include measurements of aerosol backscatter cross sections, optical depth, backscatter phase function depolarization, and multiple scattering. The errors in the HSRL data are discussed and the effects of different errors on the measured optical parameters are shown.

Determination of optical band gap of powder-form nanomaterials with improved accuracy

NASA Astrophysics Data System (ADS)

Ahsan, Ragib; Khan, Md. Ziaur Rahman; Basith, Mohammed Abdul

2017-10-01

Accurate determination of a material's optical band gap lies in the precise measurement of its absorption coefficients, either from its absorbance via the Beer-Lambert law or diffuse reflectance spectrum via the Kubelka-Munk function. Absorption coefficients of powder-form nanomaterials calculated from absorbance spectrum do not match those calculated from diffuse reflectance spectrum, implying the inaccuracy of the traditional optical band gap measurement method for such samples. We have modified the Beer-Lambert law and the Kubelka-Munk function with proper approximations for powder-form nanomaterials. Applying the modified method for powder-form nanomaterial samples, both absorbance and diffuse reflectance spectra yield exactly the same absorption coefficients and therefore accurately determine the optical band gap.

The saturable absorption and reverse saturable absorption properties of Cu doped zinc oxide thin films

NASA Astrophysics Data System (ADS)

Yao, Cheng-Bao; Wen, Xin; Li, Qiang-Hua; Yan, Xiao-Yan; Li, Jin; Zhang, Ke-Xin; Sun, Wen-Jun; Bai, Li-Na; Yang, Shou-Bin

2017-03-01

We present the structure and nonlinear absorption (NLA) properties of Cu-doped ZnO (CZO) films prepared by magnetron sputtering. The films were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results show that the CZO films can maintain a wurtzite structure. Furthermore, the open-aperture (OA) Z-scan measurements of the film were carried out by nanosecond laser pulse. A transition from saturable absorption (SA) to reverse saturable absorption (RSA) was observed as the excitation intensity increasing. With good excellent nonlinear optical coefficient, the samples were expected to be the potential applications in optical devices.

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

PubMed

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

2016-07-08

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

Polarization-controlled optimal scatter suppression in transient absorption spectroscopy

PubMed Central

Malý, Pavel; Ravensbergen, Janneke; Kennis, John T. M.; van Grondelle, Rienk; Croce, Roberta; Mančal, Tomáš; van Oort, Bart

2017-01-01

Ultrafast transient absorption spectroscopy is a powerful technique to study fast photo-induced processes, such as electron, proton and energy transfer, isomerization and molecular dynamics, in a diverse range of samples, including solid state materials and proteins. Many such experiments suffer from signal distortion by scattered excitation light, in particular close to the excitation (pump) frequency. Scattered light can be effectively suppressed by a polarizer oriented perpendicular to the excitation polarization and positioned behind the sample in the optical path of the probe beam. However, this introduces anisotropic polarization contributions into the recorded signal. We present an approach based on setting specific polarizations of the pump and probe pulses, combined with a polarizer behind the sample. Together, this controls the signal-to-scatter ratio (SSR), while maintaining isotropic signal. We present SSR for the full range of polarizations and analytically derive the optimal configuration at angles of 40.5° between probe and pump and of 66.9° between polarizer and pump polarizations. This improves SSR by (or compared to polarizer parallel to probe). The calculations are validated by transient absorption experiments on the common fluorescent dye Rhodamine B. This approach provides a simple method to considerably improve the SSR in transient absorption spectroscopy. PMID:28262765

Optical properties of armchair (7, 7) single walled carbon nanotubes

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

Gharbavi, K.; Badehian, H., E-mail: hojatbadehian@gmail.com

2015-07-15

Full potential linearized augmented plane waves method with the generalized gradient approximation for the exchange-correlation potential was applied to calculate the optical properties of (7, 7) single walled carbon nanotubes. The both x and z directions of the incident photons were applied to estimate optical gaps, dielectric function, electron energy loss spectroscopies, optical conductivity, optical extinction, optical refractive index and optical absorption coefficient. The results predict that dielectric function, ε (ω), is anisotropic since it has higher peaks along z-direction than x-direction. The static optical refractive constant were calculated about 1.4 (z-direction) and 1.1 (x- direction). Moreover, the electron energymore » loss spectroscopy showed a sharp π electron plasmon peaks at about 6 eV and 5 eV for z and x-directions respectively. The calculated reflection spectra show that directions perpendicular to the tube axis have further optical reflection. Moreover, z-direction indicates higher peaks at absorption spectra in low range energies. Totally, increasing the diameter of armchair carbon nanotubes cause the optical band gap, static optical refractive constant and optical reflectivity to decrease. On the other hand, increasing the diameter cause the optical absorption and the optical conductivity to increase. Moreover, the sharp peaks being illustrated at optical spectrum are related to the 1D structure of CNTs which confirm the accuracy of the calculations.« less

Silver nanocube aggregation gradient materials in search for total internal reflection with high phase sensitivity

NASA Astrophysics Data System (ADS)

König, Tobias A. F.; Ledin, Petr A.; Russell, Michael; Geldmeier, Jeffrey A.; Mahmoud, Mahmoud. A.; El-Sayed, Mostafa A.; Tsukruk, Vladimir V.

2015-03-01

We fabricated monolayer coatings of a silver nanocube aggregation to create a step-wise optical strip by applying different surface pressures during slow Langmuir-Blodgett deposition. The varying amount of randomly distributed nanocube aggregates with different surface coverages in gradient manner due to changes in surface pressure allows for continuous control of the polarization sensitive absorption of the incoming light over a broad optical spectrum. Optical characterization under total internal reflection conditions combined with electromagnetic simulations reveal that the broadband light absorption depends on the relative orientation of the nanoparticles to the polarization of the incoming light. By using computer simulations, we found that the electric field vector of the s-polarized light interacts with the different types of silver nanocube aggregations to excite different plasmonic resonances. The s-polarization shows dramatic changes of the plasmonic resonances at different angles of incidence (shift of 64 nm per 10° angle of incidence). With a low surface nanocube coverage (from 5% to 20%), we observed a polarization-selective high absorption of 80% (with an average 75%) of the incoming light over a broad optical range in the visible region from 400 nm to 700 nm. This large-area gradient material with location-dependent optical properties can be of particular interest for broadband light absorption, phase-sensitive sensors, and imaging.We fabricated monolayer coatings of a silver nanocube aggregation to create a step-wise optical strip by applying different surface pressures during slow Langmuir-Blodgett deposition. The varying amount of randomly distributed nanocube aggregates with different surface coverages in gradient manner due to changes in surface pressure allows for continuous control of the polarization sensitive absorption of the incoming light over a broad optical spectrum. Optical characterization under total internal reflection conditions combined with electromagnetic simulations reveal that the broadband light absorption depends on the relative orientation of the nanoparticles to the polarization of the incoming light. By using computer simulations, we found that the electric field vector of the s-polarized light interacts with the different types of silver nanocube aggregations to excite different plasmonic resonances. The s-polarization shows dramatic changes of the plasmonic resonances at different angles of incidence (shift of 64 nm per 10° angle of incidence). With a low surface nanocube coverage (from 5% to 20%), we observed a polarization-selective high absorption of 80% (with an average 75%) of the incoming light over a broad optical range in the visible region from 400 nm to 700 nm. This large-area gradient material with location-dependent optical properties can be of particular interest for broadband light absorption, phase-sensitive sensors, and imaging. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr06430e

Semiconductor Optical Nonlinearities in the IR

DTIC Science & Technology

2007-09-01

study of the nonlinear properties of semiconductors in the infrared spectral region to develop a fundamental understanding of their optical... infrared countermeasures. 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF RESPONSIBLE PERSON a. REPORT b...absorption [I] B. S. Wherrett, "Scaling rules for multiphoton interband absorption in semiconductors", Journal of Optical Society ofAmerica B, 1, 67 (1984) [2

Magneto-optical properties of semi-parabolic plus semi-inverse squared quantum wells

NASA Astrophysics Data System (ADS)

Tung, Luong V.; Vinh, Pham T.; Phuc, Huynh V.

2018-06-01

We theoretically study the optical absorption in a quantum well with the semi-parabolic potential plus the semi-inverse squared potential (SPSIS) in the presence of a static magnetic field in which both one- and two-photon absorption processes have been taken into account. The expression of the magneto-optical absorption coefficient (MOAC) is expressed by the second-order golden rule approximation including the electron-LO phonon interaction. We also use the profile method to obtain the full width at half maximum (FWHM) of the absorption peaks. Our numerical results show that either MOAC or FWHM strongly depends on the confinement frequency, temperature, and magnetic field but their dependence on the parameter β is very weak. The temperature dependence of FWHM is consistent with the previous theoretical and experimental works.

Radiation effects on beta /10.6/ of pure and europium doped KCl

NASA Technical Reports Server (NTRS)

Grimes, H. H.; Maisel, J. E.; Hartford, R. H.

1975-01-01

Changes in the optical absorption coefficient as the result of X-ray and electron bombardment of pure monocrystalline and polycrystalline KCl and of divalent europium doped polycrystalline KCl were determined. A constant heat flow calorimetric method was used to measure the optical absorption coefficients. Both 300 kV X-ray irradiation and 2 MeV electron irradiation produced increases in the optical absorption coefficient at room temperature. X-ray irradiation produced more significant changes in pure monocrystalline KCl than equivalent amounts of electron irradiation. Electron irradiation of pure and Eu-doped polycrystalline KCl produced increases in the absorption by as much as a factor of 20 over untreated material. Bleaching of the electron-irradiated doped KCl with 649 millimicron light produced a further increase.

Optical absorption enhancement in silicon nanowire arrays with a large lattice constant for photovoltaic applications.

PubMed

Lin, Chenxi; Povinelli, Michelle L

2009-10-26

In this paper, we use the transfer matrix method to calculate the optical absorptance of vertically-aligned silicon nanowire (SiNW) arrays. For fixed filling ratio, significant optical absorption enhancement occurs when the lattice constant is increased from 100 nm to 600 nm. The enhancement arises from an increase in field concentration within the nanowire as well as excitation of guided resonance modes. We quantify the absorption enhancement in terms of ultimate efficiency. Results show that an optimized SiNW array with lattice constant of 600 nm and wire diameter of 540 nm has a 72.4% higher ultimate efficiency than a Si thin film of equal thickness. The enhancement effect can be maintained over a large range of incidence angles.

Enhancement of optical absorption of Si (100) surfaces by low energy N+ ion beam irradiation

NASA Astrophysics Data System (ADS)

Bhowmik, Dipak; Karmakar, Prasanta

2018-05-01

The increase of optical absorption efficiency of Si (100) surface by 7 keV and 8 keV N+ ions bombardment has been reported here. A periodic ripple pattern on surface has been observed as well as silicon nitride is formed at the ion impact zones by these low energy N+ ion bombardment [P. Karmakar et al., J. Appl. Phys. 120, 025301 (2016)]. The light absorption efficiency increases due to the presence of silicon nitride compound as well as surface nanopatterns. The Atomic Force Microscopy (AFM) study shows the formation of periodic ripple pattern and increase of surface roughness with N+ ion energy. The enhancement of optical absorption by the ion bombarded Si, compared to the bare Si have been measured by UV - visible spectrophotometer.

Coherent perfect rotation

NASA Astrophysics Data System (ADS)

Crescimanno, Michael; Dawson, Nathan J.; Andrews, James H.

2012-09-01

Two classes of conservative, linear, optical rotary effects (optical activity and Faraday rotation) are distinguished by their behavior under time reversal. Faraday rotation, but not optical activity, is capable of coherent perfect rotation, by which we mean the complete transfer of counterpropagating coherent light fields into their orthogonal polarization. Unlike coherent perfect absorption, however, this process is explicitly energy conserving and reversible. Our study highlights the necessity of time-reversal-odd processes (not just absorption) and coherence in perfect mode conversion and thus informs the optimization of active multiport optical devices.

Models of filter-based particle light absorption measurements

NASA Astrophysics Data System (ADS)

Hamasha, Khadeejeh M.

Light absorption by aerosol is very important in the visible, near UN, and near I.R region of the electromagnetic spectrum. Aerosol particles in the atmosphere have a great influence on the flux of solar energy, and also impact health in a negative sense when they are breathed into lungs. Aerosol absorption measurements are usually performed by filter-based methods that are derived from the change in light transmission through a filter where particles have been deposited. These methods suffer from interference between light-absorbing and light-scattering aerosol components. The Aethalometer is the most commonly used filter-based instrument for aerosol light absorption measurement. This dissertation describes new understanding of aerosol light absorption obtained by the filter method. The theory uses a multiple scattering model for the combination of filter and particle optics. The theory is evaluated using Aethalometer data from laboratory and ambient measurements in comparison with photoacoustic measurements of aerosol light absorption. Two models were developed to calculate aerosol light absorption coefficients from the Aethalometer data, and were compared to the in-situ aerosol light absorption coefficients. The first is an approximate model and the second is a "full" model. In the approximate model two extreme cases of aerosol optics were used to develop a model-based calibration scheme for the 7-wavelength Aethalometer. These cases include those of very strong scattering aerosols (Ammonium sulfate sample) and very absorbing aerosols (kerosene soot sample). The exponential behavior of light absorption in the strong multiple scattering limit is shown to be the square root of the total absorption optical depth rather than linear with optical depth as is commonly assumed with Beer's law. 2-stream radiative transfer theory was used to develop the full model to calculate the aerosol light absorption coefficients from the Aethalometer data. This comprehensive model allows for studying very general cases of particles of various sizes embedded on arbitrary filter media. Application of this model to the Reno Aerosol Optics Study (Laboratory data) shows that the aerosol light absorption coefficients are about half of the Aethalometer attenuation coefficients, and there is a reasonable agreement between the model calculated absorption coefficients at 521 nm and the measured photoacoustic absorption coefficients at 532 nm. For ambient data obtained during the Las Vegas study, it shows that the model absorption coefficients at 521 nm are larger than the photoacoustic coefficients at 532 nm. Use of the 2-stream model shows that particle penetration depth into the filter has a strong influence on the interpretation of filter-based aerosol light absorption measurements. This is likely explanation for the difference found between model results for filter-based aerosol light absorption and those from photoacoustic measurements for ambient and laboratory aerosol.

Naphtyl- and pyrenyl-flavylium dyads: Synthesis, DFT and optical properties

NASA Astrophysics Data System (ADS)

Aguilar-Castillo, Bethsy Adriana; Sánchez-Bojorge, Nora Aydee; Chávez-Flores, David; Camacho-Dávila, Alejandro A.; Pasillas-Ornelas, Eddie; Rodríguez-Valdez, Luz-María; Zaragoza-Galán, Gerardo

2018-03-01

A one-step preparation of flavylium salts containing naphtyl and pyrenyl moieties is described hereafter. Flavylium salts were successfully characterized by 1H NMR spectroscopy and ESI-MS spectrometry. Theoretical calculations were carried out by means of Density Functional Theory in order to simulate flavylium cation electronic transitions. Molecular simulation of -naphtyl derivatives displayed a coplanar conformation between naphthalene and benzopyrylium moieties. In contrast, DFT analysis exhibited a non-coplanar arrangement of pyrene and benzopyrylium units. These former statements in coherence with the absorption experiments where the naphtyl-flavylium dyads shows a red-shifted maximum absorption band with respect to pyrene dyads, led us to conclude that these bathochromic effects are associated with a more planar conformation.

Optical properties of soot particles: measurement - model comparison

NASA Astrophysics Data System (ADS)

Forestieri, S.; Lambe, A. T.; Lack, D.; Massoli, P.; Cross, E. S.; Dubey, M.; Mazzoleni, C.; Olfert, J.; Freedman, A.; Davidovits, P.; Onasch, T. B.; Cappa, C. D.

2013-12-01

Soot, a product of incomplete combustion, plays an important role in the earth's climate system through the absorption and scattering of solar radiation. In order to accurately model the direct radiative impact of black carbon (BC), the refractive index and shape dependent scattering and absorption characteristics must be known. At present, the assumed shape remains highly uncertain because BC particles are fractal-like, being agglomerates of smaller (20-40 nm) spherules, yet traditional optical models such as Mie theory typically assume a spherical particle morphology. To investigate the ability of various optical models to reproduce observed BC optical properties, we measured light absorption and extinction coefficients of methane and ethylene flame soot particles. Optical properties were measured by multiple instruments: absorption by a dual cavity ringdown photoacoustic spectrometer (CRD-PAS), absorption and scattering by a 3-wavelength photoacoustic/nephelometer spectrometer (PASS-3) and extinction and scattering by a cavity attenuated phase shift spectrometer (CAPS). Soot particle mass was quantified using a centrifugal particle mass analyzer (CPMA) and mobility size was measured with a scanning mobility particle sizer (SMPS). Measurements were made for nascent soot particles and for collapsed soot particles following coating with dioctyl sebacate or sulfuric acid and thermal denuding to remove the coating. Wavelength-dependent refractive indices for the sampled particles were derived by fitting the observed absorption and extinction cross-sections to spherical particle Mie theory and Rayleigh-Debye-Gans theory. The Rayleigh-Debye-Gans approximation assumes that the absorption properties of soot are dictated by the individual spherules and neglects interaction between them. In general, Mie theory reproduces the observed absorption and extinction cross-sections for particles with volume equivalent diameters (VED) < ~160 nm, but systematically predicts lower absorption cross-sections relative to observations for larger particles with VED > ~160 nm. The discrepancy is most pronounced for measurements made at shorter wavelengths. In contrast, Rayleigh-Debye-Gans theory, which does not assume spherical particle morphology, exhibited good agreement with the observations for all particle diameters and wavelengths. These results indicate that the use of Mie theory to describe the absorption behavior of particles >160 nm VED will underestimate the absorption by these particles. Concurrent measurements of the absorption Angstrom exponent and the single scattering albedo, and their dependence on particle size, will also be discussed.

Measurement of nanoparticle size, suspension polydispersity, and stability using near-field optical trapping and light scattering (Conference Presentation)

NASA Astrophysics Data System (ADS)

Schein, Perry; O'Dell, Dakota; Erickson, David

2017-02-01

Nanoparticles are becoming ubiquitous in applications including diagnostic assays, drug delivery and therapeutics. However, there remain challenges in the quality control of these products. Here we present methods for the orthogonal measurement of these parameters by tracking the motion of the nanoparticle in all three special dimensions as it interacts with an optical waveguide. These simultaneous measurements from a single particle basis address some of the gaps left by current measurement technologies such as nanoparticle tracking analysis, ζ-potential measurements, and absorption spectroscopy. As nanoparticles suspended in a microfluidic channel interact with the evanescent field of an optical waveguide, they experience forces and resulting motion in three dimensions: along the propagation axis of the waveguide (x-direction) they are propelled by the optical forces, parallel to the plane of the waveguide and perpendicular to the optical propagation axis (y-direction) they experience an optical gradient force generated from the waveguide mode profile which confines them in a harmonic potential well, and normal to the surface of the waveguide they experience an exponential downward optical force balanced by the surface interactions that confines the particle in an asymmetric well. Building on our Nanophotonic Force Microscopy technique, in this talk we will explain how to simultaneously use the motion in the y-direction to estimate the size of the particle, the comparative velocity in the x-direction to measure the polydispersity of a particle population, and the motion in the z-direction to measure the potential energy landscape of the interaction, providing insight into the colloidal stability.

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

PubMed Central

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

2014-01-01

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

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

PubMed

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

2014-05-27

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

Measuring and Modeling the Effect of Surface Moisture on the Spectral Reflectance of Coastal Beach Sand

PubMed Central

Nolet, Corjan; Poortinga, Ate; Roosjen, Peter; Bartholomeus, Harm; Ruessink, Gerben

2014-01-01

Surface moisture is an important supply limiting factor for aeolian sand transport, which is the primary driver of coastal dune development. As such, it is critical to account for the control of surface moisture on available sand for dune building. Optical remote sensing has the potential to measure surface moisture at a high spatio-temporal resolution. It is based on the principle that wet sand appears darker than dry sand: it is less reflective. The goals of this study are (1) to measure and model reflectance under controlled laboratory conditions as function of wavelength () and surface moisture () over the optical domain of 350–2500 nm, and (2) to explore the implications of our laboratory findings for accurately mapping the distribution of surface moisture under natural conditions. A laboratory spectroscopy experiment was conducted to measure spectral reflectance (1 nm interval) under different surface moisture conditions using beach sand. A non-linear increase of reflectance upon drying was observed over the full range of wavelengths. Two models were developed and tested. The first model is grounded in optics and describes the proportional contribution of scattering and absorption of light by pore water in an unsaturated sand matrix. The second model is grounded in soil physics and links the hydraulic behaviour of pore water in an unsaturated sand matrix to its optical properties. The optical model performed well for volumetric moisture content 24% ( 0.97), but underestimated reflectance for between 24–30% ( 0.92), most notable around the 1940 nm water absorption peak. The soil-physical model performed very well ( 0.99) but is limited to 4% 24%. Results from a field experiment show that a short-wave infrared terrestrial laser scanner ( = 1550 nm) can accurately relate surface moisture to reflectance (standard error 2.6%), demonstrating its potential to derive spatially extensive surface moisture maps of a natural coastal beach. PMID:25383709

Optical absorption in degenerately doped semiconductors: Mott transition or Mahan excitons?

NASA Astrophysics Data System (ADS)

Schleife, André.; Rödl, Claudia; Hannewald, Karsten; Bechstedt, Friedhelm

2012-02-01

In the exploration of material properties, parameter-free calculations are a modern, sophisticated complement to cutting-edge experimental techniques. Ab-initio calculations are now capable of providing a deep understanding of the interesting physics underlying the electronic structure and optical absorption, e.g., of the transparent conductive oxides. Due to electron doping, these materials are conductive even though they have wide fundamental band gaps. The degenerate electron gas in the lowest conduction-band states drastically modifies the Coulomb interaction between the electrons and, hence, the optical properties close to the absorption edge. We describe these effects by developing an ab-initio technique which captures also the Pauli blocking and the Fermi-edge singularity at the optical absorption onset, that occur in addition to quasiparticle and excitonic effects. We answer the question whether free carriers induce an excitonic Mott transition or trigger the evolution of Wannier-Mott excitons into Mahan excitons. The prototypical n-type zinc oxide is studied as an example.

Functionalizing a Tapered Microcavity as a Gas Cell for On-Chip Mid-Infrared Absorption Spectroscopy

PubMed Central

Mandon, Julien; Harren, Frans J. M.; Wolffenbuttel, Reinoud F.

2017-01-01

Increasing demand for field instruments designed to measure gas composition has strongly promoted the development of robust, miniaturized and low-cost handheld absorption spectrometers in the mid-infrared. Efforts thus far have focused on miniaturizing individual components. However, the optical absorption path that the light beam travels through the sample defines the length of the gas cell and has so far limited miniaturization. Here, we present a functionally integrated linear variable optical filter and gas cell, where the sample to be measured is fed through the resonator cavity of the filter. By using multiple reflections from the mirrors on each side of the cavity, the optical absorption path is elongated from the physical μm-level to the effective mm-level. The device is batch-fabricated at the wafer level in a CMOS-compatible approach. The optical performance is analyzed using the Fizeau interferometer model and demonstrated with actual gas measurements. PMID:28878167

Optical levitation of 10-ng spheres with nano-g acceleration sensitivity

NASA Astrophysics Data System (ADS)

Monteiro, Fernando; Ghosh, Sumita; Fine, Adam Getzels; Moore, David C.

2017-12-01

We demonstrate optical levitation of SiO2 spheres with masses ranging from 0.1 to 30 ng. In high vacuum, we observe that the measured acceleration sensitivity improves for larger masses and obtain a sensitivity of 0.4 ×10-6g /√{Hz } for a 12-ng sphere, more than an order of magnitude better than previously reported for optically levitated masses. In addition, these techniques permit long integration times and a mean acceleration of (-0.7 ±2.4 [stat] ±0.2 [syst] ) ×10-9g is measured in 1.4 ×104 s. Spheres larger than 10 ng are found to lose mass in high vacuum where heating due to absorption of the trapping laser dominates radiative cooling. This absorption constrains the maximum size of spheres that can be levitated and allows a measurement of the absorption of the trapping light for the commercially available spheres tested here. Spheres consisting of material with lower absorption may allow larger objects to be optically levitated in high vacuum.

Influence of Two-Photon Absorption Anisotropy on Terahertz Emission Through Optical Rectification in Zinc-Blende Crystals

NASA Astrophysics Data System (ADS)

Sanjuan, Federico; Gaborit, Gwenaël; Coutaz, Jean-Louis

2018-04-01

We report for the first time on the observation of an angular anisotropy of the THz signal generated by optical rectification in a < 111 > ZnTe crystal. This cubic (zinc-blende) crystal in the < 111 > orientation exhibits both transverse isotropy for optical effects involving the linear χ (1) and nonlinear χ (2) susceptibilities. Thus, the observed anisotropy can only be related to χ (3) effect, namely two-photon absorption, which leads to the photo-generation of free carriers that absorb the generated THz signal. Two-photon absorption in zinc-blende crystals is known to be due to a spin-orbit interaction between the valence and higher-conduction bands. We perform a couple of measurements that confirm our hypothesis, as well as we fit the recorded data with a simple model. This two-photon absorption effect makes difficult an efficient generation, through optical rectification in < 111 > zinc-blende crystals, of THz beams of any given polarization state by only monitoring the laser pump polarization.

Saturation spectroscopy of calcium atomic vapor in hot quartz cells with cold windows

NASA Astrophysics Data System (ADS)

Vilshanskaya, E. V.; Saakyan, S. A.; Sautenkov, V. A.; Murashkin, D. A.; Zelener, B. B.; Zelener, B. V.

2018-01-01

Saturation spectroscopy of calcium atomic vapor was performed in hot quartz cells with cold windows. The Doppler-free absorption resonances with spectral width near 50 MHz were observed. For these experiments and future applications long-lived quartz cells with buffer gas were designed and made. A cooling laser for calcium magneto-optical trap will be frequency locked to the saturation resonances in the long-lived cells.

Influence of carrier density on the electronic cooling channels of bilayer graphene

NASA Astrophysics Data System (ADS)

Limmer, T.; Houtepen, A. J.; Niggebaum, A.; Tautz, R.; Da Como, E.

2011-09-01

We study the electronic cooling dynamics in a single flake of bilayer graphene by femtosecond transient absorption probing the photon-energy range 0.25-1.3 eV. From the transients, we extract the carrier cooling curves for different initial temperatures and densities of the photoexcited electrons and holes. Two regimes of carrier cooling, dominated by optical and acoustic phonons emission, are clearly identified. For increasing carrier density, the crossover between the two regimes occurs at larger carrier temperatures, since cooling via optical phonons experiences a bottleneck. Acoustic phonons, which are less sensitive to saturation, show an increasing contribution at high density.

Hemodynamic analysis of patients in intensive care unit based on diffuse optical spectroscopic imaging system

NASA Astrophysics Data System (ADS)

Hsieh, Yao-Sheng; Wang, Chun-Yang; Ling, Yo-Wei; Chuang, Ming-Lung; Chuang, Ching-Cheng; Tsai, Jui-che; Lu, Chih-Wei; Sun, Chia-Wei

2010-02-01

Diffuse optical spectroscopic imaging (DOSI) is a technique to assess the spatial variation in absorption and scattering properties of the biological tissues and provides the monitoring of changes in concentrations of oxy-hemoglobin and deoxy-hemoglobin. In our preliminary study, the temporal tracings of hemodynamic oxygenation are measured with DOSI and venous occlusion test (VOT) from normal subjects, patients with heart failure and patients with sepsis in intensive care unit (ICU). In experiments, the obvious differences of hemodynamic signals can be observed among the three groups. The physiological relevance of VOT hemodynamics with respect to diseases is also discussed in this paper.

Optical scattering lengths in large liquid-scintillator neutrino detectors.

PubMed

Wurm, M; von Feilitzsch, F; Göger-Neff, M; Hofmann, M; Lachenmaier, T; Lewke, T; Marrodán Undagoitia, T; Meindl, Q; Möllenberg, R; Oberauer, L; Potzel, W; Tippmann, M; Todor, S; Traunsteiner, C; Winter, J

2010-05-01

For liquid-scintillator neutrino detectors of kiloton scale, the transparency of the organic solvent is of central importance. The present paper reports on laboratory measurements of the optical scattering lengths of the organic solvents phenylxylylethane, linear alkylbenzene (LAB), and dodecane, which are under discussion for next-generation experiments such as SNO+ (Sudbury Neutrino Observatory), HanoHano, or LENA (Low Energy Neutrino Astronomy). Results comprise the wavelength range of 415-440 nm. The contributions from Rayleigh and Mie scattering as well as from absorption/re-emission processes are discussed. Based on the present results, LAB seems to be the preferred solvent for a large-volume detector.

Optical scattering lengths in large liquid-scintillator neutrino detectors

NASA Astrophysics Data System (ADS)

Wurm, M.; von Feilitzsch, F.; Göger-Neff, M.; Hofmann, M.; Lachenmaier, T.; Lewke, T.; Undagoitia, T. Marrodán; Meindl, Q.; Möllenberg, R.; Oberauer, L.; Potzel, W.; Tippmann, M.; Todor, S.; Traunsteiner, C.; Winter, J.

2010-05-01

For liquid-scintillator neutrino detectors of kiloton scale, the transparency of the organic solvent is of central importance. The present paper reports on laboratory measurements of the optical scattering lengths of the organic solvents phenylxylylethane, linear alkylbenzene (LAB), and dodecane, which are under discussion for next-generation experiments such as SNO+ (Sudbury Neutrino Observatory), HanoHano, or LENA (Low Energy Neutrino Astronomy). Results comprise the wavelength range of 415-440 nm. The contributions from Rayleigh and Mie scattering as well as from absorption/re-emission processes are discussed. Based on the present results, LAB seems to be the preferred solvent for a large-volume detector.

Using carrier-depletion silicon modulators for optical power monitoring.

PubMed

Yu, Hui; Korn, Dietmar; Pantouvaki, Marianna; Van Campenhout, Joris; Komorowska, Katarzyna; Verheyen, Peter; Lepage, Guy; Absil, Philippe; Hillerkuss, David; Alloatti, Luca; Leuthold, Juerg; Baets, Roel; Bogaerts, Wim

2012-11-15

Defect-mediated subbandgap absorption is observed in ion-implanted silicon-on-oxide waveguides that experience a rapid thermal annealing at 1075°C. With this effect, general carrier-depletion silicon modulators exhibit the capability of optical power monitoring. Responsivity is measured to be 22 mA/W for a 3 mm long Mach-Zehnder modulator of 2×10(18) cm(-3) doping concentration at -7.1 V bias voltage and 5.9 mA/W for a ring modulator of 1×10(18) cm(-3) doping concentration at -10 V bias voltage. The former is used to demonstrate data detection of up to 35 Gbits/s.

Rapid Annealing Of Amorphous Hydrogenated Carbon

NASA Technical Reports Server (NTRS)

Alterovitz, Samuel A.; Pouch, John J.; Warner, Joseph D.

1989-01-01

Report describes experiments to determine effects of rapid annealing on films of amorphous hydrogenated carbon. Study represents first efforts to provide information for applications of a-C:H films where rapid thermal processing required. Major finding, annealing causes abrupt increase in absorption and concomitant decrease in optical band gap. Most of change occurs during first 20 s, continues during longer annealing times. Extend of change increases with annealing temperature. Researchers hypothesize abrupt initial change caused by loss of hydrogen, while gradual subsequent change due to polymerization of remaining carbon into crystallites or sheets of graphite. Optical band gaps of unannealed specimens on silicon substrates lower than those of specimens on quartz substrates.

Synthesis, characterization and optical properties of novel star azo-oligomers containing well-defined oligo(ethylene glycol) segments

NASA Astrophysics Data System (ADS)

González-Gómez, Roberto; Vonlanthen, Mireille; Ortíz-Palacios, Jesús; Ruiu, Andrea; Valderrama-García, Bianca X.; Rivera, Ernesto

2018-05-01

In this work, the synthesis and characterization of a series of star azo-oligomers bearing amino, amino-methoxy, amino-nitro and amino-cyano substituted azobenzene units and oligo(ethylene glycol) segments is reported. The full characterization of the obtained compounds was achieved by FTIR, 1H and 13C NMR spectroscopies, and their molecular weights were determined by MALDI-TOF mass spectrometry. The optical properties of these compounds were studied by absorption spectroscopy in solution. Finally, light polarized microscopy experiments as a function of the temperature were performed in order to study the liquid-crystalline behavior of these star azo-oligomers.

Hierarchical clustering method for improved prostate cancer imaging in diffuse optical tomography

NASA Astrophysics Data System (ADS)

Kavuri, Venkaiah C.; Liu, Hanli

2013-03-01

We investigate the feasibility of trans-rectal near infrared (NIR) based diffuse optical tomography (DOT) for early detection of prostate cancer using a transrectal ultrasound (TRUS) compatible imaging probe. For this purpose, we designed a TRUS-compatible, NIR-based image system (780nm), in which the photo diodes were placed on the trans-rectal probe. DC signals were recorded and used for estimating the absorption coefficient. We validated the system using laboratory phantoms. For further improvement, we also developed a hierarchical clustering method (HCM) to improve the accuracy of image reconstruction with limited prior information. We demonstrated the method using computer simulations laboratory phantom experiments.

Colorado Ultraviolet Transit Experiment: a dedicated CubeSat mission to study exoplanetary mass loss and magnetic fields

NASA Astrophysics Data System (ADS)

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

2018-01-01

The Colorado Ultraviolet Transit Experiment (CUTE) is a near-UV (2550 to 3300 Å) 6U CubeSat mission designed to monitor transiting hot Jupiters to quantify their atmospheric mass loss and magnetic fields. CUTE will probe both atomic (Mg and Fe) and molecular (OH) lines for evidence of enhanced transit absorption, and to search for evidence of early ingress due to bow shocks ahead of the planet's orbital motion. As a dedicated mission, CUTE will observe ≳100 spectroscopic transits of hot Jupiters over a nominal 7-month mission. This represents the equivalent of >700 orbits of the only other instrument capable of these measurements, the Hubble Space Telescope. CUTE efficiently utilizes the available CubeSat volume by means of an innovative optical design to achieve a projected effective area of ˜28 cm2, low instrumental background, and a spectral resolving power of R˜3000 over the primary science bandpass. These performance characteristics enable CUTE to discern transit depths between 0.1% and 1% in individual spectral absorption lines. We present the CUTE optical and mechanical design, a summary of the science motivation and expected results, and an overview of the projected fabrication, calibration, and launch timeline.

Adipocyte property evaluation with photoacoustic spectrum analysis: a feasibility study on human tissues

NASA Astrophysics Data System (ADS)

Cao, Meng; Zhu, Yunhao; O'Rourke, Robert; Wang, Huaideng; Yuan, Jie; Cheng, Qian; Xu, Guan; Wang, Xueding; Carson, Paul

2017-03-01

Photoacoustic spectrum analysis (PASA) offers potential advantages in identifying optically absorbing microstructures in biological tissues. Working at high ultrasound frequency, PASA is capable of identifying the morphological features of cells based on their intrinsic optical absorption. Adipocyte size is correlated with metabolic disease risk in the form of diabetes mellitus, thus it can be adopted as a pathology predictor to evaluate the condition of obese patient, and can be helpful for assessing the patient response to bariatric surgery. In order to acquire adipocyte size, usually adipose tissue biopsy is performed and histopathology analysis is conducted. The whole procedure is not well tolerated by patients, and is also labor and cost intensive. An unmet need is to quantify and predict adipocyte size in a mild and more efficient way. This work aims at studying the feasibility to analyze the adipocyte size of human fat tissue using the method of PASA. PA measurements were performed at the optical wavelength of 1210 nm where lipid has strong optical absorption, enabling the study of adipocyte without need of staining. Both simulation and ex vivo experiments have been completed. Good correlation between the quantified photoacoustic spectral parameter slope and the average adipocyte size obtained by the gold-standard histology has been established. This initial study suggests the potential opportunity of applying PASA to future clinical management of obesity.

Interlaced spin grating for optical wave filtering

NASA Astrophysics Data System (ADS)

Linget, H.; Chanelière, T.; Le Gouët, J.-L.; Berger, P.; Morvan, L.; Louchet-Chauvet, A.

2015-02-01

Interlaced spin grating is a scheme for the preparation of spectrospatial periodic absorption gratings in an inhomogeneously broadened absorption profile. It relies on the optical pumping of atoms in a nearby long-lived ground state sublevel. The scheme takes advantage of the sublevel proximity to build large contrast gratings with unlimited bandwidth and preserved average optical depth. It is particularly suited to Tm-doped crystals in the context of classical and quantum signal processing. In this paper, we study the optical pumping dynamics at play in an interlaced spin grating and describe the corresponding absorption profile shape in an optically thick atomic ensemble. We show that, in Tm:YAG, the diffraction efficiency of such a grating can reach 18.3 % in the small-angle and 11.6 % in the large-angle configuration when the excitation is made of simple pulse pairs, considerably outperforming conventional gratings.

Valley- and spin-polarized oscillatory magneto-optical absorption in monolayer MoS2 quantum rings

NASA Astrophysics Data System (ADS)

Oliveira, D.; Villegas-Lelovsky, L.; Soler, M. A. G.; Qu, Fanyao

2018-03-01

Besides optical valley selectivity, strong spin-orbit interaction along with Berry curvature effects also leads to unconventional valley- and spin-polarized Landau levels in monolayer transition metal dichalcogenides (TMDCs) under a perpendicular magnetic field. We find that these unique properties are inherited to the magneto-optical absorption spectrum of the TMDC quantum rings (QRs). In addition, it is robust against variation of the magnetic flux and of the QR geometry. In stark contrast to the monolayer bulk material, the MoS2 QRs manifest themselves in both the optical valley selectivity and unprecedented size tunability of the frequency of the light absorbed. We also find that when the magnetic field setup is changed, the phase transition from Aharonov-Bohm (AB) quantum interference to aperiodic oscillation of magneto-optical absorption spectrum takes place. The exciton spectrum in a realistic finite thickness MoS2 QR is also discussed.

Optical and transient capacitance study of EL2 in the absence and presence of other midgap levels. [in gallium arsenide crystals

NASA Technical Reports Server (NTRS)

Skowronski, M.; Lagowski, J.; Gatos, H. C.

1986-01-01

A high-resolution optical study was carried out on GaAs crystals grown by horizontal Bridgman and liquid-encapsulated-Czochralski methods. An excellent correlation was found between the intensity of the 1.039-eV no-phonon line and the characteristic absorption of EL2, the major deep donor level in GaAs. A correlation was also found between the characteristic optical absorption of EL2 and its concentration as determined by junction capacitance measurements. The presence of EL0, another midgap level contained in heavily oxygen-doped crystals at concentration always less than those of EL2, had no effect on the optical spectra, but altered the capacitance measurements. Accordingly, an accurate calibration for the determination of EL2 by optical absorption was obtained from capacitance measurements on crystals containing only EL2; in this way the uncertainties introduced by other midgap levels were eliminated.

Properties of the 4.45 eV optical absorption band in LiF:Mg,Ti.

PubMed

Nail, I; Oster, L; Horowitz, Y S; Biderman, S; Belaish, Y

2006-01-01

The optical absorption (OA) and thermoluminescence (TL) of dosimetric LiF:Mg,Ti (TLD-100) as well as nominally pure LiF single crystal have been studied as a function of irradiation dose, thermal and optical bleaching in order to investigate the role of the 4.45 eV OA band in low temperature TL. Computerised deconvolution was used to resolve the absorption spectrum into individual gaussian bands and the TL glow curve into glow peaks. Although the 4.45 eV OA band shows thermal decay characteristics similar to the 4.0 eV band its dose filling constant and optical bleaching properties suggest that it cannot be associated with the TL of composite peaks 4 or 5. Its presence in optical grade single crystal LiF further suggests that it is an intrinsic defect or possibly associated with chance impurities other than Mg, Ti.

The influence of different alkaline earth oxides on the structural and optical properties of undoped, Ce-doped, Sm-doped, and Sm/Ce co-doped lithium alumino-phosphate glasses

NASA Astrophysics Data System (ADS)

Othman, H. A.; Arzumanyan, G. M.; Möncke, D.

2016-12-01

Undoped, singly Sm doped, Ce doped, and Sm/Ce co-doped lithium alumino-phosphate glasses with different alkaline earth modifiers were prepared by melt quenching. The structure of the prepared glasses was investigated by FT-IR and Raman, as well as by optical spectroscopy. The effect of the optical basicity of the host glass matrix on the added active dopants was studied, as was the effect doping had on the phosphate structural units. The optical edge shifts toward higher wavelengths with an increase in the optical basicity due to the increased polarizability of the glass matrix, but also with increasing CeO2 concentration as a result of Ce3+/Ce4+ inter valence charge transfer (IV-CT) absorption. The optical band gap for direct and indirect allowed transitions was calculated for the undoped glasses. The glass sample containing Mg2+ modifier ions is found to have the highest value (4.16 eV) for the optical band gap while Ba2+ has the lowest value (3.61 eV). The change in the optical band gap arises from the structural changes and the overall polarizability (optical basicity). Refractive index, molar refractivity Rm and molar polarizability αm values increase with increasing optical basicity of the glasses. The characteristic absorption peaks of Sm3+ were also investigated. For Sm/Ce co-doped glasses, especially at high concentration of CeO2, the absorption of Ce3+ hinders the high energy absorption of Sm3+ and this effect becomes more obvious with increasing optical basicity.

Hollow-core photonic-crystal-fiber-based optical frequency references

NASA Astrophysics Data System (ADS)

Holá, Miroslava; Hrabina, Jan; Mikel, Břetislav; Lazar, Josef; Číp, Ondřej

2016-12-01

This research deals with preparation of an optical frequency references based on hollow-core photonic crystal fibers (HC-PCF). This fiber-based type of absorption cells represents a effiecient way how to replace classic bulky and fragile glass made tubes references with low-weight and low-volume optical fibers. This approach allows not only to increase possible interaction length between incident light and absorption media but it also carries a possibility of manufacturing of easy-operable reference which is set up just by plugging-in of optical connectors into the optical setup. We present the results of preparation, manufacturing and filling of a set of fiber-based cells intended for lasers frequency stabilization. The work deals with setting and optimalization of HC-PCF splicing processes, minimalization of optical losses between HC-PCF and SMF fiber transitions and finishing of HC-PCF spliced ends with special care for optimal closing of hollow-core structure needed for avoiding of absorption media leakage.

Linear and Nonlinear Optical Properties of Spherical Quantum Dots: Effects of Hydrogenic Impurity and Conduction Band Non-Parabolicity

NASA Astrophysics Data System (ADS)

Rezaei, G.; Vaseghi, B.; Doostimotlagh, N. A.

2012-03-01

Simultaneous effects of an on-center hydrogenic impurity and band edge non-parabolicity on intersubband optical absorption coefficients and refractive index changes of a typical GaAs/AlxGa1-x As spherical quantum dot are theoretically investigated, using the Luttinger—Kohn effective mass equation. So, electronic structure and optical properties of the system are studied by means of the matrix diagonalization technique and compact density matrix approach, respectively. Finally, effects of an impurity, band edge non-parabolicity, incident light intensity and the dot size on the linear, the third-order nonlinear and the total optical absorption coefficients and refractive index changes are investigated. Our results indicate that, the magnitudes of these optical quantities increase and their peaks shift to higher energies as the influences of the impurity and the band edge non-parabolicity are considered. Moreover, incident light intensity and the dot size have considerable effects on the optical absorption coefficients and refractive index changes.

Nonlinear Optical Spectroscopy of Two-Dimensional Materials

NASA Astrophysics Data System (ADS)

Cui, Qiannan

Nonlinear optical properties of two-dimensional (2D) materials, such as transition metal dichalcogenides (TMDs), graphene, black phosphorus, and so on, play a key role of understanding nanoscale light-matter interactions, as well as developing nanophotonics applications from solar cells to quantum computation. With ultrafast lasers, we experimentally study nonlinear optical properties of 2D materials. Employing transient absorption microscopy, we study several members of 2D materials, such as WSe2, TiS3 and ReS2. The dynamical saturable absorption process of 2D excitons is spatiotemporally resolved. Intrinsic parameters of these 2D materials, such as exciton lifetime, exciton diffusion coefficient, and exciton mobility, are effectively measured. Especially, in-plane anisotropy of transient absorption and diffusive transport is observed for 2D excitons in monolayer ReS2, demonstrating the in-plane degree of freedom. Furthermore, with quantum interference and control nanoscopy, we all-optically inject, detect and manipulate nanoscale ballistic charge currents in a ReS2 thin film. By tuning the phase difference between one photon absorption and two photon absorption transition paths, sub-picosecond timescale of ballistic currents is coherently controlled for the first time in TMDs. In addition, the spatial resolution is two-order of magnitude smaller than optical diffraction limit. The second-order optical nonlinearity of 2D monolayers is resolved by second harmonic generation (SHG) microscopy. We measure the second-order susceptibility of monolayer MoS 2. The angular dependence of SHG in monolayer MoS2 shows strong symmetry dependence on its crystal lattice structure. Hence, second harmonic generation microscopy can serve as a powerful tool to noninvasively determine the crystalline directions of 2D monolayers. The real and imaginary parts of third-order optical nonlinearity of 2D monolayers are resolved by third harmonic generation (THG) microscopy and two-photon transient absorption microscopy, respectively. With third harmonic generation microscopy, we observe strong and anisotropic THG in monolayer and multilayer ReS2. Comparing with 2D materials with hexagonal lattice, such as MoS2, the third-order susceptibility is higher by one order of magnitude in ReS2 with a distorted 1T structure. The in-plane anisotropy of THG is attributed to the lattice distortion in ReS2 after comparing with a symmetry analysis. With two-photon transient absorption microscopy, we observe a giant two-photon absorption coefficient of monolayer WS2.

Optical properties of doped sol-gel silica glasses

NASA Astrophysics Data System (ADS)

King, Terence A.

1994-01-01

Sol-gel optical composites were developed and characterized for potential applications in optics, lasers, nonlinear optics, and optoelectronics. Post-doped xerogels were index matched by in-situ polymerization of monomers to form inorganic-organic composites of low scatter and high optical quality. Characterization of the microstructure was made by visible and IR absorption and Raman Spectroscopy and optical quality by attenuation and scatter measurement. Doping techniques were optimized using hypercritical drying and vacuum impregnation and doping distribution monitored by laser-induced fluorescence. One-tenth wavelength surfaces were formed by novel optical polishing. Organic molecular dopants were tested in laser and nonlinear systems. Initial third harmonic generation and Z-scan measurements have shown the potential for saturable absorption and optical limiting.

Gold nanorods-silicone hybrid material films and their optical limiting property

NASA Astrophysics Data System (ADS)

Li, Chunfang; Qi, Yanhai; Hao, Xiongwen; Peng, Xue; Li, Dongxiang

2015-10-01

As a kind of new optical limiting materials, gold nanoparticles have optical limiting property owing to their optical nonlinearities induced by surface plasmon resonance (SPR). Gold nanorods (GNRs) possess transversal SPR absorption and tunable longitudinal SPR absorption in the visible and near-infrared region, so they can be used as potential optical limiting materials against tunable laser pulses. In this letter, GNRs were prepared using seed-mediated growth method and surface-modified by silica coating to obtain good dispersion in polydimethylsiloxane prepolymers. Then the silicone rubber films doped with GNRs were prepared after vulcanization, whose optical limiting property and optical nonlinearity were investigated. The silicone rubber samples doped with more GNRs were found to exhibit better optical limiting performance.

Effect of size and indium-composition on linear and nonlinear optical absorption of InGaN/GaN lens-shaped quantum dot

NASA Astrophysics Data System (ADS)

Ahmed, S. Jbara; Zulkafli, Othaman; M, A. Saeed

2016-05-01

Based on the Schrödinger equation for envelope function in the effective mass approximation, linear and nonlinear optical absorption coefficients in a multi-subband lens quantum dot are investigated. The effects of quantum dot size on the interband and intraband transitions energy are also analyzed. The finite element method is used to calculate the eigenvalues and eigenfunctions. Strain and In-mole-fraction effects are also studied, and the results reveal that with the decrease of the In-mole fraction, the amplitudes of linear and nonlinear absorption coefficients increase. The present computed results show that the absorption coefficients of transitions between the first excited states are stronger than those of the ground states. In addition, it has been found that the quantum dot size affects the amplitudes and peak positions of linear and nonlinear absorption coefficients while the incident optical intensity strongly affects the nonlinear absorption coefficients. Project supported by the Ministry of Higher Education and Scientific Research in Iraq, Ibnu Sina Institute and Physics Department of Universiti Teknologi Malaysia (UTM RUG Vote No. 06-H14).

Nonlinear optical inves

NASA Astrophysics Data System (ADS)

Zidan, M. D.; Arfan, A.; Allahham, A.

2017-03-01

Z-scan technique was used to investigate the nonlinear optical properties of Quinine and 1-(carboxymethyl)-6-methoxy-4-(3-(3-vinylpiperidin-4-yl) propanoyl) quinolin-1-ium chloride (Quinotoxine) salts. The two salts were characterized using UV-visible, FTIR and NMR measurements. The characterization spectra confirm the expected molecular structure of the prepared ;Quinotoxine ; salt. The z-scan measurements were performed with a CW Diode laser at 635 nm wavelength and 26 mW power. The nonlinear absorption coefficient (β), nonlinear refractive index (n2), the ground-state absorption cross sections (σg), the excited-state absorption cross sections (σex) and thermo-optic coefficient of the samples were determined. Our results reveal that the σex is higher than the σg indicating that the reverse saturable absorption (RSA) is the dominating mechanism for the observed absorption nonlinearities. The results suggest that this material should be considered as a promising candidate for future optical devices applications.

Nonlinear optical study of 1-(carboxymethyl)-8-hydroxyquinolin-1-ium chloride and 1-(carboxymethyl)quinolin-1-ium chloride salts by Z-scan technique

NASA Astrophysics Data System (ADS)

Zidan, M. D.; Arfan, A.; Allahham, A.

2016-12-01

Z-scan technique was used to investigate the nonlinear optical properties of 1-(carboxymethyl)-8-hydroxyquinolin-1-ium chloride and 1-(carboxymethyl)quinolin-1-ium chloride salts. The new 1-(carboxymethyl)-8-hydroxyquinolin-1-ium chloride and 1-(carboxymethyl)quinolin-1-ium chloride salts were synthesized and characterized using UV-visible, FTIR and NMR measurements and the characterization spectra confirm the expected molecular structure of the prepared salts. Measurements were performed with a CW Diode laser at 635 nm wavelength and 26 mW power. The nonlinear optical absorption coefficient (β) and nonlinear refractive index (n2) of the 1-(carboxymethyl)-8-hydroxyquinolin-1-ium chloride was affected by OH group. The excited-state absorption cross sections (σex) and the ground -state absorption cross sections (σg) were calculated for the two studied compounds. It was found that the σex is larger than the σg, indicating that the reverse saturable absorption mechanism (RSA) is the dominating mechanism for the observed absorption nonlinearities. Our results suggest that this material should be considered as a promising candidate for future optical devices applications.

Optical absorption, electron spin resonance, and electron spin echo studies of the photoionization of tetramethylbenzidine in cationic and anionic synthetic vesicles: comparison with analogous micellar systems

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

Li, A.S.W.; Kevan, L.

1983-09-07

The photoionization of N,N,N',N'-tetramethylbenzidine (TMB) in dihexadecylphosphate anionic vesicles and in dioctadecyldimethylammonium chloride cationic vesicles has been studied by optical absorption and electron spin resonance in liquid and frozen solutions. The TMB cation has been observed to be stabilized in both types of vesicles. The photoionization efficiency is about twofold greater in the cationic vesicles compared to the anionic vesicles. Shifts in the optical absorption maximum between micellar and vesicle solutions indicate that TMB is in a less polar environment in the vesicle systems. Electron spin echo modulation spectrometry has been used to detect TMB cation-water interactions that are foundmore » to be weaker than in previously studied micellar solutions. This is consistent with the optical absorption results and with an asymmetric solubilization site for TMB and TMB/sup +/ within the vesicular structure. A new absorption in the photoionized vesicles is assigned to a nonparamagnetic diamine-diimine charge-transfer complex between two TMB cations in the same vesicle. This complex is not formed in micellar systems. 5 figures.« less

Selective sensitivity of Mueller imaging for tissue scattering over absorption changes in cancer mimicking phantoms

NASA Astrophysics Data System (ADS)

Fathima, Adeeba; Sharma B. S., Mahima; N., Sujatha

2018-03-01

Tissue characterization using optical polarimetry, especially Mueller imaging is receiving sustained interest due to its potential in achieving optical contrast between normal and malignant variations. This is particularly important in identifying the margin of malignant growth in suspected tissue regions for accurate surgical removal, or in aiding the sampling procedure during biopsy. The sensitivity of Mueller matrix derived depolarization index to the combined effects of changes in scattering and absorption occurring in a cancerous growth is illustrated in this study. Depolarization imaging is shown to be useful in demarcating the boundary of two regions of differing optical properties using a tissue phantom, modeled according to the changes expected during cancerous growth in tissue. Tissue scattering and absorption are expected to generally increase with the nuclear size change and crowding as well as angiogenesis associated with malignancy. We have observed that there is selective sensitivity for the Mueller elements and derived depolarization index to tissue scattering over absorption in the object field. Although the scattering and absorption are expected to increase and decrease depolarization respectively, the optical contrast of Mueller images and the derived depolarization index between normal and cancerous tissue is found appreciable in this region.

Characterization by optical and magnetic spectroscopy of a synthesized SiO2 thin film used for radiation detector

NASA Astrophysics Data System (ADS)

Abdelaziz, T. D.; Ezz-Eldin, F. M.

2017-09-01

This work reports the synthesis and characterization of silica glass prepared by sol-gel procedure and finds out the effects of doses of gamma irradiation on the steps route of the heat-treated sample at 600 and 1100 °C. Combined characterizations of the glassy samples have been carried out by optical absorption and electron paramagnetic resonance. Also, FT infrared absorption spectra have been measured for both the heat-treated samples before and after gamma irradiation. Optical absorption spectra have identified an absorption band at 212-215 nm beside a broad band at 230-265 nm and the correlation of E' center with heat-treatment and gamma irradiation have been followed. FT infrared absorption spectra indicate the bands within near IR region representing the vibrational modes due to water, OH and SiOH within the wavenumber range 2500-3700 cm-1 are affected by heat treatment due to the elimination of organic residue and amount of OH and water. ESR investigations confirm the results obtained from optical and FTIR measurements. It is concluded from the collective data that sol-gel silica glass can serve as acceptable candidate for gamma-rays irradiator and gamma chamber dosimetry.

Optical sensor system for time-resolved quantification of methane densities in CH4-fueled spark ignition engines.

PubMed

Golibrzuch, Kai; Digulla, Finn-Erik; Bauke, Stephan; Wackerbarth, Hainer; Thiele, Olaf; Berg, Thomas

2017-08-01

We present the development and the first application of an optical sensor system that allows single-cycle determination of methane (CH 4 ) concentration inside internal combustion (IC) engines. We use non-dispersive infrared absorption spectroscopy to detect the CH 4 density with a time resolution up to 33 μs at acquisition rates of 30 kHz. The measurement scheme takes advantage of the strong temperature dependence of the absorption band applying two detection channels for CH 4 that detect different spectral regions of the ν 3 anti-symmetric C-H-stretch absorption. The strategy allows the simultaneous determination of fuel concentration as well as gas temperature. We show the proof-of-concept by validation of the measurement strategy in static pressure cell experiments as well as its application to a methane-fueled IC engine using a modified spark plug probe. Our results clearly demonstrate that it is crucial to determine the CH 4 temperature in the probe volume. Due to thermal influences of the sensor probe, the temperature needed to calculate the desired quantities (fuel density, fuel concentration) significantly differs from the gas phase temperature in the rest of the combustion chamber and estimations from standard thermodynamic models, e.g., polytropic compression, will fail.

Two-photon absorption in SiO{sub 2}- and (SiO{sub 2} + GeO{sub 2})-based fibres at a wavelength of 349 nm

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

Chunaev, D S; Karasik, A Ya

2014-06-30

The nonlinear two-photon light absorption coefficients have been measured in an optical fibre with a quartz glass (SiO{sub 2}) core and in a fibre with a germanosilicate glass (SiO{sub 2} + GeO{sub 2}) core. The two-photon absorption coefficient β measured at a wavelength of 349 nm in the (SiO{sub 2} + GeO{sub 2})-based fibre (13.7 cm TW{sup -1}) multiply exceeds that for the pure quartz glass optical fibre (0.54 cm TW{sup -1}). (nonlinear optical phenomena)

Optical absorption spectra and energy band gap in manganese containing sodium zinc phosphate glasses

NASA Astrophysics Data System (ADS)

Sardarpasha, K. R.; Hanumantharaju, N.; Gowda, V. C. Veeranna

2018-05-01

Optical band gap energy in the system 25Na2O-(75-x)[0.6P2O5-0.4ZnO]-xMnO2 (where x = 0.5,1,5,10 and 20 mol.%) have been studied. The intensity of the absorption band found to increase with increase of MnO2 content. The decrease in the optical band gap energy with increase in MnO2 content in the investigated glasses is attributed to shifting of absorption edge to a longer wavelength region. The obtained results were discussed in view of the structure of phosphate glass network.

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.

Oil-based gel phantom for ultrasound and optical imaging

NASA Astrophysics Data System (ADS)

Cabrelli, Luciana C.; Pelissari, Pedro I. B. G. B.; Aggarwal, Lucimara P.; Deana, Alessandro M.; Carneiro, Antonio A. O.; Pavan, Theo. Z.

2015-06-01

Water-based materials are commonly used in phantoms for ultrasound and optical imaging techniques. However, these materials have disadvantages such as easy degradation and low temporal stability. In this study, we propose an oil-based new tissue mimicking material for ultrasound and optical imaging, with the advantage of presenting low temporal degradation. Styrene-Ethylene/Butylene-Styrene (SEBS) copolymer in mineral oil samples were made varying the SEBS concentration between 5-15%, and low-density polyethylene (LDPE) between 0-9%. Acoustic properties such as speed of sound and attenuation coefficient were obtained by the substitution technique with frequencies ranging from 2.25-10 MHz, and were consistent to that of soft tissue. These properties were controlled varying SEBS and LDPE concentration; speed of sound from 1445-1480 m/s, and attenuation from 0.86-11.31 dB/cm were observed. SEBS gels with 0% of LDPE were optically transparent, presenting low optical absorption and scattering coefficients in the visible region of the spectrum. In order to fully characterize the optical properties of the samples, the reflectances of the surfaces were measured, along with the absorption. Scattering and absorption coefficients ranging from 400 nm to 1200 nm were calculated for each compound. The results showed that the presence of LDPE increased absorption and scattering of the phantoms. The results suggest the copolymer gels are promising for ultrasound and optical imaging, what make them also potentially useful for photoacoustic imaging.

Quenching Mo optical losses in CIGS solar cells by a point contacted dual-layer dielectric spacer: a 3-D optical study.

PubMed

Rezaei, Nasim; Isabella, Olindo; Vroon, Zeger; Zeman, Miro

2018-01-22

A 3-D optical modelling was calibrated to calculate the light absorption and the total reflection of fabricated CIGS solar cells. Absorption losses at molybdenum (Mo) / CIGS interface were explained in terms of plasmonic waves. To quench these losses, we assumed the insertion of a lossless dielectric spacer between Mo and CIGS, whose optical properties were varied. We show that such a spacer with low refractive index and proper thickness can significantly reduce absorption in Mo in the long wavelength regime and improve the device's rear reflectance, thus leading to enhanced light absorption in the CIGS layer. Therefore, we optimized a realistic two-layer MgF 2 / Al 2 O 3 dielectric spacer to exploit (i) the passivation properties of ultra-thin Al 2 O 3 on the CIGS side for potential high open-circuit voltage and (ii) the low refractive index of MgF 2 on the Mo side to reduce its optical losses. Combining our realistic spacer with optically-optimized point contacts increases the implied photocurrent density of a 750 nm-thick CIGS layer by 10% for the wavelengths between 700 and 1150 nm with respect to the reference cell. The elimination of plasmonic resonances in the new structure leads to a higher electric field magnitude at the bottom of CIGS layer and justifies the improved optical performance.

Determining thin film properties by fitting optical transmittance

NASA Astrophysics Data System (ADS)

Klein, J. D.; Yen, A.; Cogan, S. F.

1990-08-01

The optical transmission spectra of rf sputtered tungsten oxide films on glass substrates were modeled to determine absorption edge behavior, film thickness, and index of refraction. Removal of substrate reflection and absorption phenomena from the experimental spectra allowed direct examination of thin film optical characteristics. The interference fringe pattern allows determination of the film thickness and the dependence of the real index of refraction on wavelength. Knowledge of the interference fringe behavior in the vicinity of the absorption edge was found essential to unambiguous determination of the optical band gap. In particular, the apparently random deviations commonly observed in the extrapolation of as-acquired data are eliminated by explicitly considering interference fringe phenomena. The multivariable optimization fitting scheme employed allows air-film-substrate reflection losses to be compensated without making reflectance measurements.

Impact of one-dimensional photonic crystal back reflector in thin-film c-Si solar cells on efficiency

NASA Astrophysics Data System (ADS)

Jalali, Tahmineh

2018-05-01

In this work, the effect of one-dimensional photonic crystal on optical absorption, which is implemented at the back side of thin-film crystalline silicon (c-Si) solar cells, is extensively discussed. The proposed structure acts as a Bragg reflector which reflects back light to the active layer as well as nanograting which couples the incident light to enhance optical absorption. To understand the optical mechanisms responsible for the enhancement of optical absorption, quantum efficiency and current density for all structures are calculated and the effect of influential parameters, such as grating period is investigated. The results confirm that our proposed structure have a great deal for substantial efficiency enhancement in a broad range from 400 to 1100 nm.

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.

Demonstration of an all-optical feed-forward delay line buffer using the quadratic Stark effect and two-photon absorption in an SOA.

PubMed

Soto, Horacio; Tong, Miriam A; Domínguez, Juan C; Muraoka, Ramón

2017-09-04

We have inserted into an unbiased semiconductor optical amplifier (SOA) a powerful control beam, with photon energy slightly smaller than that of the band-gap of its active region, for exciting two-photon absorption and the quadratic Stark effect. For the available SOA, we estimated these phenomena generated a nonlinear absorption coefficient β= -865 cm/GW and induced an appreciable birefringence inside the amplifier waveguide, which significantly modified the polarization-state of a probe beam. Based on these effects, we have experimentally demonstrated the operation of an all-optical buffer, using an 80 Gb/s optical pulse comb, as well as an unbiased SOA, which was therefore, devoid of amplified spontaneous emission and pattern effects.

Interfacial charge transfer absorption: Application to metal molecule assemblies

NASA Astrophysics Data System (ADS)

Creutz, Carol; Brunschwig, Bruce S.; Sutin, Norman

2006-05-01

Optically induced charge transfer between adsorbed molecules and a metal electrode was predicted by Hush to lead to new electronic absorption features, but has been only rarely observed experimentally. Interfacial charge transfer absorption (IFCTA) provides information concerning the barriers to charge transfer between molecules and the metal/semiconductor and the magnitude of the electronic coupling and could thus provide a powerful tool for understanding interfacial charge-transfer kinetics. Here, we utilize a previously published model [C. Creutz, B.S. Brunschwig, N. Sutin, J. Phys. Chem. B 109 (2005) 10251] to predict IFCTA spectra of metal-molecule assemblies and compare the literature observations to these predictions. We conclude that, in general, the electronic coupling between molecular adsorbates and the metal levels is so small that IFCTA is not detectable. However, few experiments designed to detect IFCTA have been done. We suggest approaches to optimizing the conditions for observing the process.

Coherent free space optics communications over the maritime atmosphere with use of adaptive optics for beam wavefront correction.

PubMed

Li, Ming; Cvijetic, Milorad

2015-02-20

We evaluate the performance of the coherent free space optics (FSO) employing quadrature array phase-shift keying (QPSK) modulation over the maritime atmosphere with atmospheric turbulence compensated by use of adaptive optics (AO). We have established a comprehensive FSO channel model for maritime conditions and also made a comprehensive comparison of performance between the maritime and terrestrial atmospheric links. The FSO links are modeled based on the intensity attenuation resulting from scattering and absorption effects, the log-amplitude fluctuations, and the phase distortions induced by turbulence. The obtained results show that the FSO system performance measured by the bit-error-rate (BER) can be significantly improved when the optimization of the AO system is achieved. Also, we find that the higher BER is observed in the maritime FSO channel with atmospheric turbulence, as compared to the terrestrial FSO systems if they experience the same turbulence strength.

The Diffuse Interstellar Cloud Experiment: a high-resolution far-ultraviolet spectrograph.

PubMed

Schindhelm, Eric; Beasley, Matthew; Burgh, Eric B; Green, James C

2012-03-01

We have designed, assembled, and launched a sounding rocket payload to perform high-resolution far-ultraviolet spectroscopy. The instrument is functionally a Cassegrain telescope followed by a modified Rowland spectrograph. The spectrograph was designed to achieve a resolving power (R=λ/δλ) of 60,000 in a compact package by adding a magnifying secondary optic. This is enabled by using a holographically ruled grating to minimize aberrations induced by the second optic. We designed the instrument to observe two stars on opposing sides of a nearby hot/cold gas interface. Obtaining spectra of the O VI doublet in absorption toward these stars can provide new insight into the processes governing hot gas in the local interstellar medium. Here we present the optical design and alignment of the telescope and spectrograph, as well as flight results. © 2012 Optical Society of America

Self-assembled materials and devices that process light

NASA Astrophysics Data System (ADS)

Zhu, Peiwang; Kang, Hu; van der Boom, Milko E.; Liu, Zhifu; Xu, Guoyang; Ma, Jing; Zhou, Delai; Ho, Seng-Tiong; Marks, Tobin J.

2004-12-01

Self-assembled superlattices (SASs) are intrinsically acentric and highly cross-linked structures. For organic electro-optics, they offer great advantages such as not requiring electric field poling for creating an acentric, EO-active microstructure and having excellent chemical, thermal, and orientational stabilities. In this paper, a greatly improved two-step all "wet-chemical" self-assembly (SA) approach is reported. Excellent radiation hardness of the SAS films is demonstrated by high-energy proton irradiation experiments. By introducing metal oxide nanolayers during SA, we show that the refractive indices of SAS films can be tuned over a wide range. Through special chromophore design, the optical absorption maxima of SAS films can also be greatly blue-shifted. Prototype waveguiding electro-optic modulators have been fabricated using the SAS films integrated with low-loss polymeric materials functioning as partial guiding and cladding layers. EO parameters such as the half-wave voltage and the effective electro-optic coefficient are reported.

Scale Closure in Upper Ocean Optical Properties: From Single Particles to Ocean Color

NASA Technical Reports Server (NTRS)

Green, Rebecca E.

2002-01-01

Predictions of chlorophyll concentration from satellite ocean color are an indicator of primary productivity, with implications for foodwebs, fisheries, and the global carbon cycle. Models describing the relationship between optical properties and chlorophyll do not account for much of the optical variability observed in natural waters, because of the presence of seawater constituents that do not covary with phytoplankton pigments. in order to understand variability in these models, the optical contributions of seawater constituents were investigated. A combination of Mie theory and flow cytometry was used to determine the diameter, complex refractive index, and optical cross-sections of individual particles. In New England continental shelf waters, eukaryotic phytoplankton were the main particle contributors to absorption and scaftering. Minerals were the main contributor to backscattering (bb) in the spring, whereas in the summer both minerals and detritus contributed to bb. Synechococcus and heterotrophic bacteria were relatively unimportant optically. Seasonal differences in the spectral shape of remote sensing reflectance, Rrs, were contributed to approximately equally by eukaryotic phytoplankton absorption, dissolved absorption, and non-phytoplankton bb. Differences between measurements of bb and Prs and modeled values based on chlorophyll concentration were caused by higher dissolved absorption and non-phytoplankton bb than were assumed by the model.

Emerging Low-Dimensional Materials for Nonlinear Optics and Ultrafast Photonics.

PubMed

Liu, Xiaofeng; Guo, Qiangbing; Qiu, Jianrong

2017-04-01

Low-dimensional (LD) materials demonstrate intriguing optical properties, which lead to applications in diverse fields, such as photonics, biomedicine and energy. Due to modulation of electronic structure by the reduced structural dimensionality, LD versions of metal, semiconductor and topological insulators (TIs) at the same time bear distinct nonlinear optical (NLO) properties as compared with their bulk counterparts. Their interaction with short pulse laser excitation exhibits a strong nonlinear character manifested by NLO absorption, giving rise to optical limiting or saturated absorption associated with excited state absorption and Pauli blocking in different materials. In particular, the saturable absorption of these emerging LD materials including two-dimensional semiconductors as well as colloidal TI nanoparticles has recently been utilized for Q-switching and mode-locking ultra-short pulse generation across the visible, near infrared and middle infrared wavelength regions. Beside the large operation bandwidth, these ultrafast photonics applications are especially benefit from the high recovery rate as well as the facile processibility of these LD materials. The prominent NLO response of these LD materials have also provided new avenues for the development of novel NLO and photonics devices for all-optical control as well as optical circuits beyond ultrafast lasers. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Single-shot terahertz time-domain spectroscopy in pulsed high magnetic fields.

PubMed

Noe, G Timothy; Katayama, Ikufumi; Katsutani, Fumiya; Allred, James J; Horowitz, Jeffrey A; Sullivan, David M; Zhang, Qi; Sekiguchi, Fumiya; Woods, Gary L; Hoffmann, Matthias C; Nojiri, Hiroyuki; Takeda, Jun; Kono, Junichiro

2016-12-26

We have developed a single-shot terahertz time-domain spectrometer to perform optical-pump/terahertz-probe experiments in pulsed, high magnetic fields up to 30 T. The single-shot detection scheme for measuring a terahertz waveform incorporates a reflective echelon to create time-delayed beamlets across the intensity profile of the optical gate beam before it spatially and temporally overlaps with the terahertz radiation in a ZnTe detection crystal. After imaging the gate beam onto a camera, we can retrieve the terahertz time-domain waveform by analyzing the resulting image. To demonstrate the utility of our technique, we measured cyclotron resonance absorption of optically excited carriers in the terahertz frequency range in intrinsic silicon at high magnetic fields, with results that agree well with published values.

Light Trapping for Silicon Solar Cells: Theory and Experiment

NASA Astrophysics Data System (ADS)

Zhao, Hui

Crystalline silicon solar cells have been the mainstream technology for photovoltaic energy conversion since their invention in 1954. Since silicon is an indirect band gap material, its absorption coefficient is low for much of the solar spectrum, and the highest conversion efficiencies are achieved only in cells that are thicker than about 0.1 mm. Light trapping by total internal reflection is important to increase the optical absorption in silicon layers, and becomes increasingly important as the layers are thinned. Light trapping is typically characterized by the enhancement of the absorptance of a solar cell beyond the value for a single pass of the incident beam through an absorbing semiconductor layer. Using an equipartition argument, in 1982 Yablonovitch calculated an enhancement of 4n2 , where n is the refractive index. We have extracted effective light-trapping enhancements from published external quantum efficiency spectra in several dozen silicon solar cells. These results show that this "thermodynamic" enhancement has never been achieved experimentally. The reasons for incomplete light trapping could be poor anti-reflection coating, inefficient light scattering, and parasitic absorption. We report the light-trapping properties of nanocrystalline silicon nip solar cells deposited onto two types of Ag/ZnO backreflectors at United Solar Ovonic, LLC. We prepared the first type by first making silver nanparticles onto a stainless steel substrate, and then overcoating the nanoparticles with a second silver layer. The second type was prepared at United Solar using a continuous silver film. Both types were then overcoated with a ZnO film. The root mean square roughness varied from 27 to 61 nm, and diffuse reflectance at 1000 nm wavelength varied from 0.4 to 0.8. The finished cells have a thin, indium-tin oxide layer on the top that acts as an antireflection coating. For both backreflector types, the short-circuit photocurrent densities J SC for solar illumination were about 25 mA/cm2 for 1.5 micron cells. We also measured external quantum efficiency spectra and optical reflectance spectra, which were only slightly affected by the back reflector morphology. We performed a thermodynamic calculation for the optical absorptance in the silicon layer and the top oxide layer to explain the experimental results; the calculation is an extension of previous work by Stuart and Hall that incorporates the antireflection properties and absorption in the top oxide film. From our calculations and experimental measurements, we concluded that parasitic absorption in this film is the prominent reason for incomplete light trapping in these cells. To reduce the optical parasitic loss in the top oxide layer, we propose a bilayer design, and show the possible benefits to the photocurrent density.

Multimodal hyperspectral optical microscopy

DOE PAGES

Novikova, Irina V.; Smallwood, Chuck R.; Gong, Yu; ...

2017-09-02

We describe a unique and convenient approach to multimodal hyperspectral optical microscopy, herein achieved by coupling a portable and transferable hyperspectral imager to various optical microscopes. The experimental and data analysis schemes involved in recording spectrally and spatially resolved fluorescence, dark field, and optical absorption micrographs are illustrated through prototypical measurements targeting selected model systems. Namely, hyperspectral fluorescence micrographs of isolated fluorescent beads are employed to ensure spectral calibration of our detector and to gauge the attainable spatial resolution of our measurements; the recorded images are diffraction-limited. Moreover, spatially over-sampled absorption spectroscopy of a single lipid (18:1 Liss Rhod PE)more » layer reveals that optical densities on the order of 10-3 may be resolved by spatially averaging the recorded optical signatures. We also briefly illustrate two applications of our setup in the general areas of plasmonics and cell biology. Most notably, we deploy hyperspectral optical absorption microscopy to identify and image algal pigments within a single live Tisochrysis lutea cell. Overall, this work paves the way for multimodal multidimensional spectral imaging measurements spanning the realms of several scientific disciples.« less

Multimodal hyperspectral optical microscopy

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

Novikova, Irina V.; Smallwood, Chuck R.; Gong, Yu

We describe a unique and convenient approach to multimodal hyperspectral optical microscopy, herein achieved by coupling a portable and transferable hyperspectral imager to various optical microscopes. The experimental and data analysis schemes involved in recording spectrally and spatially resolved fluorescence, dark field, and optical absorption micrographs are illustrated through prototypical measurements targeting selected model systems. Namely, hyperspectral fluorescence micrographs of isolated fluorescent beads are employed to ensure spectral calibration of our detector and to gauge the attainable spatial resolution of our measurements; the recorded images are diffraction-limited. Moreover, spatially over-sampled absorption spectroscopy of a single lipid (18:1 Liss Rhod PE)more » layer reveals that optical densities on the order of 10-3 may be resolved by spatially averaging the recorded optical signatures. We also briefly illustrate two applications of our setup in the general areas of plasmonics and cell biology. Most notably, we deploy hyperspectral optical absorption microscopy to identify and image algal pigments within a single live Tisochrysis lutea cell. Overall, this work paves the way for multimodal multidimensional spectral imaging measurements spanning the realms of several scientific disciples.« less

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.

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 attempted to examine the role of the optical absorption parameters on optical diffusion studies. A significant outcome of the present investigation was that the improvement of phosphor spatial resolution without decreasing the light collection efficiency too much can be better achieved by increasing the parameter [Formula: see text] rather than the parameter p%.

Development of optical coatings for 157-nm lithography. II. Reflectance, absorption, and scatter measurement

NASA Astrophysics Data System (ADS)

Otani, Minoru; Biro, Ryuji; Ouchi, Chidane; Hasegawa, Masanobu; Suzuki, Yasuyuki; Sone, Kazuho; Niisaka, Shunsuke; Saito, Tadahiko; Saito, Jun; Tanaka, Akira

2002-06-01

The total loss that can be suffered by an antireflection (AR) coating consists of reflectance loss, absorption loss, and scatter loss. To separate these losses we developed a calorimetric absorption measurement apparatus and an ellipsoidal Coblentz hemisphere based scatterometer for 157-nm optics. Reflectance, absorption, and scatter of AR coatings were measured with these apparatuses. The AR coating samples were supplied by Japanese vendors. Each AR coating as supplied was coated with the vendor's coating design by that vendor's coating process. Our measurement apparatuses, methods, and results for these AR coatings are presented here.

Optical losses in p-type layers of GaN ridge waveguides in the IR region

NASA Astrophysics Data System (ADS)

Westreich, Ohad; Katz, Moti; Atar, Gil; Paltiel, Yossi; Sicron, Noam

2017-07-01

Optical losses in c-plane (0001) GaN ridge waveguides, containing Mg-doped layers, were measured at 1064 nm, using the Fabry-Perot method. The losses increase linearly with the modal content of the p-layer, indicating that the absorption in these waveguides is dominated by p-layer absorption. The p-layer absorption is strongly anisotropic with E⊥c losses 4 times higher than E∥c. The absorption is temperature independent between 10 °C and 60 °C, supporting the possibility that it is related to Mg-bound holes.

Optical reading of field-effect transistors by phase-space absorption quenching in a single InGaAs quantum well conducting channel

NASA Astrophysics Data System (ADS)

Chemla, D. S.; Bar-Joseph, I.; Klingshirn, C.; Miller, D. A. B.; Kuo, J. M.

1987-03-01

Absorption switching in a semiconductor quantum well by electrically varying the charge density in the quantum well conducting channel of a selectively doped heterostructure transistor is reported for the first time. The phase-space absorption quenching (PAQ) is observed at room temperature in an InGaAs/InAlAs grown on InP FET, and it shows large absorption coefficient changes with relatively broad spectral bandwidth. This PAQ is large enough to be used for direct optical determination of the logic state of the FET.

Nonlinear optical and multi-photon absorption properties in graphene-ZnO nanocomposites

NASA Astrophysics Data System (ADS)

Tong, Qing; Wang, Yu-Hua; Yu, Xiang-Xiang; Wang, Bo; Liang, Zhuang; Tang, Meng; Wu, An-Shun; Zhang, Hai-Jun; Liang, Feng; Xie, Ya-Feng; Wang, Jun

2018-04-01

Graphene-ZnO (GZO) nanocomposites were synthesized by a modified solvothermal method, and characterized by transmission electron microscopy, x-ray diffraction, Raman spectra, and UV-vis absorption spectra. The controllable nonlinear optical (NLO) properties of as-prepared GZO nanocomposites were tested by an open-aperture Z-scan method with 1030 nm fs laser pulses; the tested results showed that there were five-photon absorption (5PA) at 46.8 GW cm-2, 3PA at 28.1 GW cm-2, 2PA at 18.7 GW cm-2, and a vital change from saturable absorption (SA) to reverse SA (RSA) with the increase of incident intensity. This was the first time that 5PA was found in GZO nanocomposites at such a low intensity, 46.8 GW cm-2. The tunable NLO property from SA to RSA and controllable multi-photon absorption provided a facile approach for their applications in optical, optoelectronic devices, and information storage.

Characterization of absorption and degradation on optical components for high power excimer lasers

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

Mann, K.; Eva, E.; Granitza, B.

1996-12-31

At Laser-Laboratorium Goettingen, the performance of UV optical components for high power excimer lasers is characterized, aiming to employ testing procedures that meet industrial conditions, i.e. very high pulse numbers and repetition rates. Measurements include determination of single and multiple pulse damage thresholds, absorption loss and degradation of optical properties under long-term irradiation. Absorption of excimer laser pulses is investigated by a calorimetric technique which provides greatly enhanced sensitivity compared to transmissive measurements. Thus, it allows determining both single and two photon absorption coefficients at intensities of standard excimer lasers. Results of absorption measurements at 248nm are presented for baremore » substrates (CaF{sub 2}, BaF{sub 2}, z-cut quartz and fused silica). UV calorimetry is also employed to investigate laser induced aging phenomena, e.g. color center formation in fused silica. A separation of transient and cumulative effects as a function of intensity is achieved, giving insight into various loss mechanisms.« less

Reflectance-mode interferometric near-infrared spectroscopy quantifies brain absorption, scattering, and blood flow index in vivo

PubMed Central

Borycki, Dawid; Kholiqov, Oybek; Srinivasan, Vivek J.

2017-01-01

Interferometric near-infrared spectroscopy (iNIRS) is a new technique that measures time-of-flight- (TOF-) resolved autocorrelations in turbid media, enabling simultaneous estimation of optical and dynamical properties. Here, we demonstrate reflectance-mode iNIRS for noninvasive monitoring of a mouse brain in vivo. A method for more precise quantification with less static interference from superficial layers, based on separating static and dynamic components of the optical field autocorrelation, is presented. Absolute values of absorption, reduced scattering, and blood flow index (BFI) are measured, and changes in BFI and absorption are monitored during a hypercapnic challenge. Absorption changes from TOF-resolved iNIRS agree with absorption changes from continuous wave NIRS analysis, based on TOF-integrated light intensity changes, an effective path length, and the modified Beer–Lambert Law. Thus, iNIRS is a promising approach for quantitative and non-invasive monitoring of perfusion and optical properties in vivo. PMID:28146535

Molecular design of TiO2 for gigantic red shift via sublattice substitution.

PubMed

Shao, Guosheng; Deng, Quanrong; Wan, Lin; Guo, Meilan; Xia, Xiaohong; Gao, Yun

2010-11-01

The effects of 3d transition metal doping in TiO2 phases have been simulated in detail. The results of modelling indicate that Mn has the biggest potential among 3d transition metals, for the reduction of energy gap and the introduction of effective intermediate bands to allow multi-band optical absorption. On the basis of theoretical formulation, we have incorporated considerable amount of Mn in nano-crystalline TiO2 materials. Mn doped samples demonstrate significant red shift in the optical absorption edge, with a secondary absorption edge corresponding to theoretically predicted intermediate bands/states. The gigantic red shift achievable in Mn-doped TiO2 is expected to extend the useful TiO2 functionalities well beyond the UV threshold via the optical absorption of both visible and infrared photon irradiance.

Broadband nonlinear optical response of monolayer MoSe2 under ultrafast excitation

NASA Astrophysics Data System (ADS)

Nie, Zhonghui; Trovatello, Chiara; Pogna, Eva A. A.; Dal Conte, Stefano; Miranda, Paulo B.; Kelleher, Edmund; Zhu, Chunhui; Turcu, Ion Crisitan Edmond; Xu, Yongbing; Liu, Kaihui; Cerullo, Giulio; Wang, Fengqiu

2018-01-01

Due to their strong light-matter interaction, monolayer transition metal dichalcogenides (TMDs) have proven to be promising candidates for nonlinear optics and optoelectronics. Here, we characterize the nonlinear absorption of chemical vapour deposition (CVD)-grown monolayer MoSe2 in the 720-810 nm wavelength range. Surprisingly, despite the presence of strong exciton resonances, monolayer MoSe2 exhibits a uniform modulation depth of ˜80 ± 3% and a saturation intensity of ˜2.5 ± 0.4 MW/cm2. In addition, pump-probe spectroscopy is performed to confirm the saturable absorption and reveal the photocarrier relaxation dynamics over hundreds of picoseconds. Our results unravel the unique broadband nonlinear absorptive behavior of monolayer MoSe2 under ultrafast excitation and highlight the potential of using monolayer TMDs as broadband ultrafast optical switches with customizable saturable absorption characteristics.

Influence of dose on particle size and optical properties of colloidal platinum nanoparticles.

PubMed

Gharibshahi, Elham; Saion, Elias

2012-11-12

Attempts to produce colloidal platinum nanoparticles by using steady absorption spectra with various chemical-based reduction methods often resulted in the fast disappearance of the absorption maxima leaving reduced platinum nanoparticles with little information on their optical properties. We synthesized colloidal platinum nanoparticles in an aqueous solution of polyvinyl pyrrolidone by gamma radiolytic reduction method, which produced steady absorption spectra of fully reduced and highly pure platinum nanoparticles free from by-product impurities or reducing agent contamination. The average particle size was found to be in the range of 3.4–5.3 nm and decreased with increasing dose due to the domination of nucleation over ion association in the formation of metal nanoparticles by the gamma radiolytic reduction method. The platinum nanoparticles exhibit optical absorption spectra with two absorption peaks centered at about 216 and 264 nm and the peaks blue shifted to lower wavelengths with decreasing particle size. The absorption spectra of platinum nanoparticles were also calculated using quantum mechanical treatment and coincidently a good agreement was obtained between the calculated and measured absorption peaks at various particle sizes. This indicates that the 216 and 264-nm absorption peaks of platinum nanoparticles conceivably originated from the intra-band transitions of conduction electrons of (n = 5, l = 2) and (n = 6, l = 0) energy states respectively to higher energy states. The absorption energies, i.e., conduction band energies of platinum nanoparticles derived from the absorption peaks increased with increasing dose and decreased with increasing particle size.

Influence of Dose on Particle Size and Optical Properties of Colloidal Platinum Nanoparticles

PubMed Central

Gharibshahi, Elham; Saion, Elias

2012-01-01

Attempts to produce colloidal platinum nanoparticles by using steady absorption spectra with various chemical-based reduction methods often resulted in the fast disappearance of the absorption maxima leaving reduced platinum nanoparticles with little information on their optical properties. We synthesized colloidal platinum nanoparticles in an aqueous solution of polyvinyl pyrrolidone by gamma radiolytic reduction method, which produced steady absorption spectra of fully reduced and highly pure platinum nanoparticles free from by-product impurities or reducing agent contamination. The average particle size was found to be in the range of 3.4–5.3 nm and decreased with increasing dose due to the domination of nucleation over ion association in the formation of metal nanoparticles by the gamma radiolytic reduction method. The platinum nanoparticles exhibit optical absorption spectra with two absorption peaks centered at about 216 and 264 nm and the peaks blue shifted to lower wavelengths with decreasing particle size. The absorption spectra of platinum nanoparticles were also calculated using quantum mechanical treatment and coincidently a good agreement was obtained between the calculated and measured absorption peaks at various particle sizes. This indicates that the 216 and 264-nm absorption peaks of platinum nanoparticles conceivably originated from the intra-band transitions of conduction electrons of (n = 5, l = 2) and (n = 6, l = 0) energy states respectively to higher energy states. The absorption energies, i.e., conduction band energies of platinum nanoparticles derived from the absorption peaks increased with increasing dose and decreased with increasing particle size. PMID:23203091

Eat-by-light fiber-optic and micro-optic devices for food quality and safety assessment

NASA Astrophysics Data System (ADS)

Mignani, A. G.; Ciaccheri, L.; Cucci, C.; Mencaglia, A. A.; Cimato, A.; Attilio, C.; Thienpont, H.; Ottevaere, H.; Paolesse, R.; Mastroianni, M.; Monti, D.; Buonocore, G.; Del Nobile, A.; Mentana, A.; Grimaldi, M. F.; Dall'Asta, C.; Faccini, A.; Galaverna, G.; Dossena, A.

2007-06-01

A selection is presented of fiber-optic and micro-optic devices that have been designed and tested for guaranteeing the quality and safety of typical foods, such as extra virgin olive oil, beer, and milk. Scattered colorimetry is used to authenticate various types of extra virgin olive oil and beer, while a fiber-optic-based device for UV-VIS-NIR absorption spectroscopy is exploited in order to obtain the hyperspectral optical signature of olive oil. This is done not only for authentication purposes, but also so as to correlate the spectral data with the content of fatty acids, which are important nutritional factors. A micro-optic sensor for the detection of olive oil aroma that is capable of distinguishing different ageing levels of extra virgin olive oil is also presented. It shows effective potential for acting as a smart cap of bottled olive oil in order to achieve a non-destructive olfactory perception of oil ageing. Lastly, a compact portable fluorometer for the rapid monitoring of the carcinogenic M1 aflatoxin in milk, is experimented.

Eat-by-light: fiber-optic and micro-optic devices for food safety and quality assessment

NASA Astrophysics Data System (ADS)

Mignani, A. G.; Ciaccheri, L.; Cucci, C.; Mencaglia, A. A.; Cimato, A.; Attilio, C.; Thienpont, H.; Ottevaere, H.; Paolesse, R.; Mastroianni, M.; Monti, D.; Buonocore, G.; Del Nobile, A.; Mentana, A.; Dall'Asta, C.; Faccini, A.; Galaverna, G.; Dossena, A.

2007-07-01

A selection of fiber-optic and micro-optic devices is presented designed and tested for monitoring the quality and safety of typical foods, namely the extra virgin olive oil, the beer, and the milk. Scattered colorimetry is used for the authentication of various types of extra virgin olive oil and beer, while a fiber-optic-based device for UV-VIS-NIR absorption spectroscopy is exploited in order to obtain the hyperspectral optical signature of olive oil. This is done not only for authentication purposes, but also so as to correlate the spectral data with the content of fatty acids that are important nutritional factors. A micro-optic sensor for the detection of olive oil aroma is presented. It is capable of distinguishing different ageing levels of extra virgin olive oil. It shows effective potential for acting as a smart cap of bottled olive oil in order to achieve a non-destructive olfactory perception of oil ageing. Lastly, a compact portable fluorometer is experimented for the rapid monitoring of the carcinogenic M1 aflatoxin in milk.

Non-destructive evaluation of UV pulse laser-induced damage performance of fused silica optics.

PubMed

Huang, Jin; Wang, Fengrui; Liu, Hongjie; Geng, Feng; Jiang, Xiaodong; Sun, Laixi; Ye, Xin; Li, Qingzhi; Wu, Weidong; Zheng, Wanguo; Sun, Dunlu

2017-11-24

The surface laser damage performance of fused silica optics is related to the distribution of surface defects. In this study, we used chemical etching assisted by ultrasound and magnetorheological finishing to modify defect distribution in a fused silica surface, resulting in fused silica samples with different laser damage performance. Non-destructive test methods such as UV laser-induced fluorescence imaging and photo-thermal deflection were used to characterize the surface defects that contribute to the absorption of UV laser radiation. Our results indicate that the two methods can quantitatively distinguish differences in the distribution of absorptive defects in fused silica samples subjected to different post-processing steps. The percentage of fluorescence defects and the weak absorption coefficient were strongly related to the damage threshold and damage density of fused silica optics, as confirmed by the correlation curves built from statistical analysis of experimental data. The results show that non-destructive evaluation methods such as laser-induced fluorescence and photo-thermal absorption can be effectively applied to estimate the damage performance of fused silica optics at 351 nm pulse laser radiation. This indirect evaluation method is effective for laser damage performance assessment of fused silica optics prior to utilization.

Circular dichroism and optical absorption spectra of mononuclear and trinuclear chiral Cu(II) amino-alcohol coordinated compounds: A combined theoretical and experimental study

NASA Astrophysics Data System (ADS)

Valencia, Israel; Ávila-Torres, Yenny; Barba-Behrens, Norah; Garzón, Ignacio L.

2015-04-01

Studies on the physicochemical properties of biomimetic compounds of multicopper oxidases are fundamental to understand their reaction mechanisms and catalytic behavior. In this work, electronic, optical, and chiroptical properties of copper(II) complexes with amino-alcohol chiral ligands are theoretically studied by means of time-dependent density functional theory. The calculated absorption and circular dichroism spectra are compared with experimental measurements of these spectra for an uncoordinated pseudoephedrine derivative, as well as for the corresponding mononuclear and trinuclear copper(II)-coordinated complexes. This comparison is useful to gain insights into their electronic structure, optical absorption and optical activity. The optical absorption and circular dichroism bands of the pseudoephedrine derivative are located in the UV-region. They are mainly due to transitions originated from n to π anti-bonding orbitals of the alcohol and amino groups, as well as from π bonding to π anti-bonding orbitals of carboxyl and phenyl groups. In the case of the mononuclear and trinuclear compounds, additional signals in the visible spectral region are present. In both systems, the origin of these bands is due to charge transfer from ligand to metal and d-d transitions.

Near-ideal optical metamaterial absorbers with super-octave bandwidth.

PubMed

Bossard, Jeremy A; Lin, Lan; Yun, Seokho; Liu, Liu; Werner, Douglas H; Mayer, Theresa S

2014-02-25

Nanostructured optical coatings with tailored spectral absorption properties are of interest for a wide range of applications such as spectroscopy, emissivity control, and solar energy harvesting. Optical metamaterial absorbers have been demonstrated with a variety of customized single band, multiple band, polarization, and angular configurations. However, metamaterials that provide near unity absorptivity with super-octave bandwidth over a specified optical wavelength range have not yet been demonstrated experimentally. Here, we show a broadband, polarization-insensitive metamaterial with greater than 98% measured average absorptivity that is maintained over a wide ± 45° field-of-view for mid-infrared wavelengths between 1.77 and 4.81 μm. The nearly ideal absorption is realized by using a genetic algorithm to identify the geometry of a single-layer metal nanostructure array that excites multiple overlapping electric resonances with high optical loss across greater than an octave bandwidth. The response is optimized by substituting palladium for gold to increase the infrared metallic loss and by introducing a dielectric superstrate to suppress reflection over the entire band. This demonstration advances the state-of-the-art in high-performance broadband metamaterial absorbers that can be reliably fabricated using a single patterned layer of metal nanostructures.

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

ABSORBANCE, ABSORPTION COEFFICIENT, AND APPARENT QUANTUM YIELD: A COMMENT ON AMBIGUITY IN THE USE OF THESE OPTICAL CONCEPTS

EPA Science Inventory

Several important optical terms such as "absorbance" and "absorption coefficient" are frequently used ambiguously in the current peer-reviewed literature. Since they are important terms that are required to derive other quantities such as the "apparent quantum yield" of photoprod...

A Single Optical Fiber Telephone System

DTIC Science & Technology

1984-09-06

the photophones developed by A. 0, sel1 and his oolleagues. The recent advent of light 30 generators in the form of light eAitthg diodee (ZED@) and... photophone . Such a photophone is shown in Figure 7. I1t comprises a small chamber Ill which is filed with an optically absorptive material 113, which may be...carbonized cotton fiber. A 1 photo-acoustic effect takes place when light interacts with absorptive material of this types The absorption raises the 30

Study of Photosensitive Dry Films Absorption for Printed Circuit Boards by Photoacoustic Technique

NASA Astrophysics Data System (ADS)

Hernández, R.; Zaragoza, J. A. Barrientos; Jiménez-Pérez, J. L.; Orea, A. Cruz; Correa-Pacheco, Z. N.

2017-08-01

In this work, the study of photosensitive dry-type films by photoacoustic technique is proposed. The dry film photoresist is resistant to chemical etching for printed circuit boards such as ferric chloride, sodium persulfate or ammonium, hydrochloric acid. It is capable of faithfully reproducing circuit pattern exposed to ultraviolet light (UV) through a negative. Once recorded, the uncured portion is removed with alkaline solution. It is possible to obtain good results in surface mount circuits with tracks of 5 mm. Furthermore, the solid resin films are formed by three layers, two protective layers and a UV-sensitive optical absorption layer in the range of 325 nm to 405 nm. By means of optical absorption of UV-visible rays emitted by a low-power Xe lamp, the films transform this energy into thermal waves generated by the absorption of optical radiation and subsequently no-radiative de-excitation occurs. The photoacoustic spectroscopy is a useful technique to measure the transmittance and absorption directly. In this study, the optical absorption spectra of the three layers of photosensitive dry-type films were obtained as a function of the wavelength, in order to have a knowledge of the absorber layer and the protective layers. These analyses will give us the physical properties of the photosensitive film, which are very important in curing the dry film for applications in printed circuit boards.

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

PubMed Central

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

2016-01-01

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

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

NASA Astrophysics Data System (ADS)

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

2016-07-01

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

L-Asparagine crystals with wide gap semiconductor features: optical absorption measurements and density functional theory computations.

PubMed

Zanatta, G; Gottfried, C; Silva, A M; Caetano, E W S; Sales, F A M; Freire, V N

2014-03-28

Results of optical absorption measurements are presented together with calculated structural, electronic, and optical properties for the anhydrous monoclinic L-asparagine crystal. Density functional theory (DFT) within the generalized gradient approximation (GGA) including dispersion effects (TS, Grimme) was employed to perform the calculations. The optical absorption measurements revealed that the anhydrous monoclinic L-asparagine crystal is a wide band gap material with 4.95 eV main gap energy. DFT-GGA+TS simulations, on the other hand, produced structural parameters in very good agreement with X-ray data. The lattice parameter differences Δa, Δb, Δc between theory and experiment were as small as 0.020, 0.051, and 0.022 Å, respectively. The calculated band gap energy is smaller than the experimental data by about 15%, with a 4.23 eV indirect band gap corresponding to Z → Γ and Z → β transitions. Three other indirect band gaps of 4.30 eV, 4.32 eV, and 4.36 eV are assigned to α3 → Γ, α1 → Γ, and α2 → Γ transitions, respectively. Δ-sol computations, on the other hand, predict a main band gap of 5.00 eV, just 50 meV above the experimental value. Electronic wavefunctions mainly originating from O 2p-carboxyl, C 2p-side chain, and C 2p-carboxyl orbitals contribute most significantly to the highest valence and lowest conduction energy bands, respectively. By varying the lattice parameters from their converged equilibrium values, we show that the unit cell is less stiff along the b direction than for the a and c directions. Effective mass calculations suggest that hole transport behavior is more anisotropic than electron transport, but the mass values allow for some charge mobility except along a direction perpendicular to the molecular layers of L-asparagine which form the crystal, so anhydrous monoclinic L-asparagine crystals could behave as wide gap semiconductors. Finally, the calculations point to a high degree of optical anisotropy for the absorption and complex dielectric function, with more structured curves for incident light polarized along the 100 and 101 directions.

Focusing Light Beams To Improve Atomic-Vapor Optical Buffers

NASA Technical Reports Server (NTRS)

Strekalov, Dmitry; Matsko, Andrey; Savchenkov, Anatoliy

2010-01-01

Specially designed focusing of light beams has been proposed as a means of improving the performances of optical buffers based on cells containing hot atomic vapors (e.g., rubidium vapor). There is also a companion proposal to improve performance by use of incoherent optical pumping under suitable conditions. Regarding the proposal to use focusing: The utility of atomic-vapor optical buffers as optical storage and processing devices has been severely limited by nonuniform spatial distributions of intensity in optical beams, arising from absorption of the beams as they propagate in atomic-vapor cells. Such nonuniformity makes it impossible to optimize the physical conditions throughout a cell, thereby making it impossible to optimize the performance of the cell as an optical buffer. In practical terms simplified for the sake of brevity, "to optimize" as used here means to design the cell so as to maximize the group delay of an optical pulse while keeping the absorption and distortion of the pulse reasonably small. Regarding the proposal to use incoherent optical pumping: For reasons too complex to describe here, residual absorption of light is one of the main impediments to achievement of desirably long group delays in hot atomic vapors. The present proposal is directed toward suppressing residual absorption of light. The idea of improving the performance of slow-light optical buffers by use of incoherent pumping overlaps somewhat with the basic idea of Raman-based slow-light systems. However, prior studies of those systems did not quantitatively answer the question of whether the performance of an atomic vapor or other medium that exhibits electromagnetically induced transparency (EIT) with Raman gain is superior to that of a medium that exhibits EIT without Raman gain.

Creation and validation of a visual macroscopic hematuria scale for optimal communication and an objective hematuria index.

PubMed

Wong, Lih-Ming; Chum, Jia-Min; Maddy, Peter; Chan, Steven T F; Travis, Douglas; Lawrentschuk, Nathan

2010-07-01

Macroscopic hematuria is a common symptom and sign that is challenging to quantify and describe. The degree of hematuria communicated is variable due to health worker experience combined with lack of a reliable grading tool. We produced a reliable, standardized visual scale to describe hematuria severity. Our secondary aim was to validate a new laboratory test to quantify hemoglobin in hematuria specimens. Nurses were surveyed to ascertain current hematuria descriptions. Blood and urine were titrated at varying concentrations and digitally photographed in catheter bag tubing. Photos were processed and printed on transparency paper to create a prototype swatch or card showing light, medium, heavy and old hematuria. Using the swatch 60 samples were rated by nurses and laymen. Interobserver variability was reported using the generalized kappa coefficient of agreement. Specimens were analyzed for hemolysis by measuring optical density at oxyhemoglobin absorption peaks. Interobserver agreement between nurses and laymen was good (kappa = 0.51, p <0.001). Subgroup analysis showed substantial agreement for light hematuria (kappa = 0.71). Overall agreement improved when the moderate (kappa = 0.28) and heavy (kappa = 0.53) hematuria categories were combined (kappa = 0.70). Compared to known blood concentrations the assay of optical density at oxyhemoglobin absorption peaks showed a linear trend. A simple visual scale to grade and communicate hematuria with adequate interobserver agreement is feasible. The test for optical density at oxyhemoglobin absorption peaks is a new method, validated in our study, to quantify hemoglobin in a hematuria specimen. Copyright (c) 2010 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.

Temporal Variations of Telluric Water Vapor Absorption at Apache Point Observatory

NASA Astrophysics Data System (ADS)

Li, Dan; Blake, Cullen H.; Nidever, David; Halverson, Samuel P.

2018-01-01

Time-variable absorption by water vapor in Earth’s atmosphere presents an important source of systematic error for a wide range of ground-based astronomical measurements, particularly at near-infrared wavelengths. We present results from the first study on the temporal and spatial variability of water vapor absorption at Apache Point Observatory (APO). We analyze ∼400,000 high-resolution, near-infrared (H-band) spectra of hot stars collected as calibration data for the APO Galactic Evolution Experiment (APOGEE) survey. We fit for the optical depths of telluric water vapor absorption features in APOGEE spectra and convert these optical depths to Precipitable Water Vapor (PWV) using contemporaneous data from a GPS-based PWV monitoring station at APO. Based on simultaneous measurements obtained over a 3° field of view, we estimate that our PWV measurement precision is ±0.11 mm. We explore the statistics of PWV variations over a range of timescales from less than an hour to days. We find that the amplitude of PWV variations within an hour is less than 1 mm for most (96.5%) APOGEE field visits. By considering APOGEE observations that are close in time but separated by large distances on the sky, we find that PWV is homogeneous across the sky at a given epoch, with 90% of measurements taken up to 70° apart within 1.5 hr having ΔPWV < 1.0 mm. Our results can be used to help simulate the impact of water vapor absorption on upcoming surveys at continental observing sites like APO, and also to help plan for simultaneous water vapor metrology that may be carried out in support of upcoming photometric and spectroscopic surveys.

The usefulness of optical analyses for detecting vulnerable plaques using rabbit models

NASA Astrophysics Data System (ADS)

Nakai, Kanji; Ishihara, Miya; Kawauchi, Satoko; Shiomi, Masashi; Kikuchi, Makoto; Kaji, Tatsumi

2011-03-01

Purpose: Carotid artery stenting (CAS) has become a widely used option for treatment of carotid stenosis. Although technical improvements have led to a decrease in complications related to CAS, distal embolism continues to be a problem. The purpose of this research was to investigate the usefulness of optical methods (Time-Resolved Laser- Induced Fluorescence Spectroscopy [TR-LIFS] and reflection spectroscopy [RS] as diagnostic tools for assessment of vulnerable atherosclerotic lesions, using rabbit models of vulnerable plaque. Materials & Methods: Male Japanese white rabbits were divided into a high cholesterol diet group and a normal diet group. In addition, we used a Watanabe heritable hyperlipidemic (WHHL) rabbit, because we confirmed the reliability of our animal model for this study. Experiment 1: TR-LIFS. Fluorescence was induced using the third harmonic wave of a Q switch Nd:YAG laser. The TR-LIFS was performed using a photonic multi-channel analyzer with ICCD (wavelength range, 200 - 860 nm). Experiment 2: RS. Refection spectra in the wavelength range of 900 to 1700 nm were acquired using a spectrometer. Results: In the TR-LIFS, the wavelength at the peak was longer by plaque formation. The TR-LIFS method revealed a difference in peak levels between a normal aorta and a lipid-rich aorta. The RS method showed increased absorption from 1450 to 1500 nm for lipid-rich plaques. We observed absorption around 1200 nm due to lipid only in the WHHL group. Conclusion: These methods using optical analysis might be useful for diagnosis of vulnerable plaques. Keywords: Carotid artery stenting, vulnerable plaque, Time-Resolved Laser-Induced Fluorescence

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).

Wide-area remote-sensing system of pollution and gas dispersal by near-infrared absorption based on low-loss optical fiber network

NASA Technical Reports Server (NTRS)

Inaba, H.

1986-01-01

An all optical remote sensing system utilizing long distance, ultralow loss optical fiber networks is studied and discussed for near infrared absorption measurements of combustible and/or explosive gases such as CH4 and C3H8 in our environment, including experimental results achieved in a diameter more than 20 km. The use of a near infrared wavelength range is emphasized.

Far-Field to Near-Field Coupling for Enhancing Light-Matter Interaction

NASA Astrophysics Data System (ADS)

Bonakdar, Alireza

This thesis reports on theoretical, modeling, and experimental research within the framework of a key scientific question, which is enhancing the coupling between diffraction-limited far-field and sub-wavelength quantum emitter/absorber. A typical optoelectronic device delivers an optical process such as light detection (e.g. photodetector) or light intensity modulation (e.g. electro-absorptive modulator). In conventional devices, optical process is in the form of far-field or guided wave modes. The main aim of this thesis is to show that converting these modes into near-field domain can enhance the performance of the optoelectronic device. Light in the form of far-field can be converted into near-field domain by the optical antenna. Among different optoelectronic devices, this thesis focuses mainly on integrating the optical antenna with infrared photodetectors. The available semiconductors have weak infrared absorption that reduces light detection efficiency. Integration of the optical antenna with infrared absorber (such as quantum wells in quantum well infrared photodetector (QWIP)) increases the infrared absorption. Particularly this integration is favorable as the optical antenna has low metallic loss in infrared region. The author of this thesis believes that optical antenna has unique properties in confining light on the scale of deep sub-wavelength, enhancing electric field intensity and delivering optical energy to semiconductor absorbers. These properties are reaching into practical applications only if overall optical performance is low loss, parameter free (independent of optical parameters such a polarization and angle of incident) and broadband. In this thesis, the integration of optical antenna with infrared photodetectors and thermophotovoltaic are researched and developed which satisfy the aforementioned criteria. In addition, several different optical antennas have been designed, fabricated and characterized in order to analyze and demonstrate the improvement of infrared absorption. In terms of design, novel optical antennas were simulated and proposed for a variety of infrared photodetectors such as a quantum well infrared photodetector, metal-insulator-metal detector, Schottky infrared photodetector, and two-photon absorption infrared detector. Antenna analyzes are not limited to light detection as a chapter of this thesis devoted on design and develop of a low power and ultrafast all-optical/optomechanical switchable antenna. The rest of the manuscript contains the novel lithography method in order to fabricate optical antennas with low cost and in cm-scale area. The method is based on the microsphere photolithography that expose photoresist underneath each microsphere with a focused intensive light -so called photonic nanojet. The developed lithography method takes advantage of microscopic range of optical path (micro-optics) in microsphere lenses that allows to push the exposure wavelength beyond deep UV region, where the refractive optics becomes impractical due to severe material absorption. The author believes that micro-optics lithography is an excellent candidate for large area and high throughput fabrication of sub-100-nm feature sizes in periodic array. In particular, this method facilitates the feasibility of metasurfaces and metamaterials, optical coating with efficient photon extraction/trapping, and highly sensitive bio-sensors in near IR and visible ranges of spectrum.

Improving Assessments of Chlorophyll Concentration From In Situ Optical Measurements

NASA Astrophysics Data System (ADS)

Nardelli, S.; Twardowski, M.

2016-02-01

Florescence as a chlorophyll proxy has poor accuracy because it is dependent on specific absorption (effective molar absorptivity of packaged chlorophyll in living cells) and fluorescence quantum yield, both of which are highly variable. Absorption is a better proxy, as it is only dependent on specific absorption for packaged chlorophyll, although excepted accuracy in using a nominal specific absorption for all phytoplankton is still about 50%. Bricaud et al. (1995), Ciotti et al. (2002), Mouw et al. (2010), etc. have shown, however, that specific absorption is closely related to the average size of phytoplankton due to the relative packaging effect. Through other methods that have been developed over the years (Morel 1973; Diehl and Haart 1980; Boss et al. 2001; Slade and Boss 2015), it has been shown that measurements of spectral particulate attenuation (i.e., light transmission), and perhaps spectral particulate backscattering, can be used as simple proxies for the average size of the particle field. We therefore test the hypothesis that information on average particle size may be used to better estimate specific absorption for packaged chlorophyll, possibly enabling more accurate retrievals of chlorophyll concentration from optical measurements. The required optical measurements can be made with compact commercial off-the-shelf sensors with high sampling frequency that can be operated from autonomous vehicles; as a result, derived chlorophyll concentration could be resolved at far higher temporal and spatial frequency than is currently possible through extracting chlorophyll from discretely collected samples. This study examines the relationship between specific absorption and the attenuation spectral slope in extensive datasets from Case I and Case II waters found globally in an attempt to assess the link between pigment packaging and phytoplankton size dynamics and the impact on improving the derivation of chlorophyll from in situ optical measurements.

Characterization by combined optical and FT infrared spectra of 3d-transition metal ions doped-bismuth silicate glasses and effects of gamma irradiation.

PubMed

ElBatal, F H; Abdelghany, A M; ElBatal, H A

2014-03-25

Optical and infrared absorption spectral measurements were carried out for binary bismuth silicate glass and other derived prepared samples with the same composition and containing additional 0.2% of one of 3d transition metal oxides. The same combined spectroscopic properties were also measured after subjecting the prepared glasses to a gamma dose of 8 Mrad. The experimental optical spectra reveal strong UV-near visible absorption bands from the base and extended to all TMs-doped samples and these specific extended and strong UV-near visible absorption bands are related to the contributions of absorption from both trace iron (Fe(3+)) ions present as contaminated impurities within the raw materials and from absorption of main constituent trivalent bismuth (Bi(3+)) ions. The strong UV-near visible absorption bands are observed to suppress any further UV bands from TM ions. The studied glasses show obvious resistant to gamma irradiation and only small changes are observed upon gamma irradiation. This observed shielding behavior is related to the presence of high Bi(3+) ions with heavy mass causing the observed stability of the optical absorption. Infrared absorption spectra of the studied glasses reveal characteristic vibrational bands due to both modes from silicate network and the sharing of Bi-O linkages and the presence of TMs in the doping level (0.2%) causes no distinct changes within the number or position of the vibrational modes. The presence of high Bi2O3 content (70 mol%) appears to cause stability of the structural building units towards gamma irradiation as revealed by FTIR measurements. Copyright © 2013 Elsevier B.V. All rights reserved.

Interstellar silicate dust in the z = 0.685 absorber toward TXS 0218+357

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

Aller, Monique C.; Kulkarni, Varsha P.; Liger, Nicholas

2014-04-10

We report the detection of interstellar silicate dust in the z {sub abs} = 0.685 absorber along the sightline toward the gravitationally lensed blazar TXS 0218+357. Using Spitzer Space Telescope Infrared Spectrograph data, we detect the 10 μm silicate absorption feature with a detection significance of 10.7σ. We fit laboratory-derived silicate dust profile templates obtained from the literature to the observed 10 μm absorption feature and find that the best single-mineral fit is obtained using an amorphous olivine template with a measured peak optical depth of τ{sub 10} = 0.49 ± 0.02, which rises to τ{sub 10} ∼ 0.67 ±more » 0.04 if the covering factor is taken into account. We also detected the 18 μm silicate absorption feature in our data with a >3σ significance. Due to the proximity of the 18 μm absorption feature to the edge of our covered spectral range, and associated uncertainty about the shape of the quasar continuum normalization near 18 μm, we do not independently fit this feature. We find, however, that the shape and depth of the 18 μm silicate absorption are well matched to the amorphous olivine template prediction, given the optical depth inferred for the 10 μm feature. The measured 10 μm peak optical depth in this absorber is significantly higher than those found in previously studied quasar absorption systems. However, the reddening, 21 cm absorption, and velocity spread of Mg II are not outliers relative to other studied absorption systems. This high optical depth may be evidence for variations in dust grain properties in the interstellar medium between this and the previously studied high redshift galaxies.« less

Spatio-Temporal Distribution of Particulate and Dissolved Organic Matter in the Mississippi River Bight From Optical Measurements

NASA Technical Reports Server (NTRS)

DSa, E. J.; Miller, R. L.; DelCastillo, C.

2003-01-01

The Mississippi River Bight is a highly dynamic region influenced by the seasonally variable outflow from the Mississippi River. In an effort to characterize the distribution of particulate and dissolved organic matter in the region, we conducted a two-year field program in the spring and fall (high and low flow river discharge) of 2000 and 2002. We collected a comprehensive set of bio-optical measurements consisting of vertical profiles (absorption, scattering, chlorophyll fluorescence and radiometry) and discrete measurements (pigment concentrations, particulate and CDOM absorption) that enabled us to obtain better insight into the seasonal and spatial variability of some important biogeochemical parameters. Our field measurements generally showed higher phytoplankton clorophyll concentrations in the plume waters (associated with lower surface salinities) and confirmed the high biological activity abserved in other studies. The seasonal flow of river discharge and advective currents due to wind forcing exerted a strong influence on the biological and optical properties of the region. An examination of absorption at 440 nm by the algal and non-algal fraction of the particulate pool and of CDOM revealed that at nearshore stations, contributions by the non-algal particles were high (about 40%) and decresed with increasing salinities. While CDOM absorption exhibited conservative mixing, its relative contribution to the total absorption was variable. Surface waters at most stations had lower salinities that generalliy increased with dept. Particulate matter and CDOM also decreased with depth as evidenced by absorption and scattering measurements. Good correlations in surface waters between concentrations of particulate and dissolved matter, the inherent optical properties of absorption and ackscattering and remote sensing reflectance values has allowed the development of robust empirical algorithms for phytoplankton chlorophyll and CDOM absorption.

Mahan excitons in Weyl semimetals

NASA Astrophysics Data System (ADS)

Garate, Ion; Bertrand, Simon; Côté, René

We report on a theoretical study of excitons in weakly doped Weyl semimetals. Solving a two-body Coulomb problem in the presence of a monopole Berry vector potential, we obtain the binding energies of electron-hole pairs and establish their dependence on the monopole charge and on the sign of the magnetic quantum number. We discuss the implications of our results for optical absorption experiments. This research has been supported by Canada's NSERC and Québec's RQMP.

Towards Resonant-State THz Laser Based on Strained p-Ge and SiGe QW Structures

DTIC Science & Technology

2006-07-01

used. The relaxed compositionally graded Si1-xGex/Si(001) buffer layer with low threading dislocations density have been grown by chemical vapour ...observe in absorption experiments. 5. Intracenter optical transitions between hydrogenic levels in doped silicon, germanium, and gallium arsenid [P...34, b. Critical magnetic field Hc vs valence band splitting Δ. Lines show the calculated Hc(Δ) dependence. 14. The gallium -doped Ge crystals with

Computational Analysis of Hybrid Two-Photon Absorbers with Excited State Absorption

DTIC Science & Technology

2007-03-01

level. This hybrid arrangement creates a complex dynamical system in which the electron carrier concentration of every photo-activated energy level...spatiotemporal details of the electron population densities of each photo-activated energy level as well as the pulse shape in space and time. The main...experiments at low input energy . However, further additions must be done to the calculation of the optical path for high input energy . 1 15. SUBJECT TERM

Enhanced Optical Properties of Germanate and Tellurite Glasses Containing Metal or Semiconductor Nanoparticles

PubMed Central

de Araujo, Cid Bartolomeu; Silvério da Silva, Diego; Alves de Assumpção, Thiago Alexandre; Kassab, Luciana Reyes Pires; Mariano da Silva, Davinson

2013-01-01

Germanium- and tellurium-based glasses have been largely studied due to their recognized potential for photonics. In this paper, we review our recent studies that include the investigation of the Stokes and anti-Stokes photoluminescence (PL) in different glass systems containing metallic and semiconductor nanoparticles (NPs). In the case of the samples with metallic NPs, the enhanced PL was attributed to the increased local field on the rare-earth ions located in the proximity of the NPs and/or the energy transfer from the metallic NPs to the rare-earth ions. For the glasses containing silicon NPs, the PL enhancement was mainly due to the energy transfer from the NPs to the Er3+ ions. The nonlinear (NL) optical properties of PbO-GeO2 films containing gold NPs were also investigated. The experiments in the pico- and subpicosecond regimes revealed enhanced values of the NL refractive indices and large NL absorption coefficients in comparison with the films without gold NPs. The reported experiments demonstrate that germanate and tellurite glasses, having appropriate rare-earth ions doping and NPs concentration, are strong candidates for PL-based devices, all-optical switches, and optical limiting. PMID:23710138

Nonlinear optical investigation of the Tris(2‧,2-bipyridyl)iron(II) tetrafluoroborate using z-scan technique

NASA Astrophysics Data System (ADS)

Zidan, M. D.; Al-Ktaifani, M. M.; Allahham, A.

2017-05-01

Z-scan measurements were performed with a CW diode laser at 635 nm to investigate the nonlinear optical properties of Tris(2‧,2-bipyridyl)iron(II) tetrafluoroborate in ethanol at two concentrations. Theoretical fit was carried out to evaluate the nonlinear absorption coefficient (β) and the negative nonlinear refractive index (n2) for the studied complex. Furthermore, the ground-state absorption cross sections (σg), the excited-state absorption cross sections (σex) and thermo-optic coefficient were also estimated. The investigations show large NLO response, which is predominantly associated with substantial conjugation between the aromatic ring π-electron system and d-electron set metal center. The obtained results give a strong indication that Tris(2‧,2-bipyridyl)iron(II) tetrafluoroborate have a potential application in optical domain.

Ab-initio calculations of structural, electronic, and optical properties of Zn3(VO4)2

NASA Astrophysics Data System (ADS)

Ahmed, Nisar; Mukhtar, S.; Gao, Wei; Zafar Ilyas, Syed

2018-03-01

The structural, electronic, and optical properties of Zn3(VO4)2 are investigated using full potential linearized augmented plane wave (FP-LAPW) method within the framework of density functional theory (DFT). Various approaches are adopted to treat the exchange and correlation potential energy such as generalized gradient approximation (GGA), GGA+U, and the Tran–Blaha modified Becke–Johnson (TB-mBJ) potential. The calculated band gap of 3.424 eV by TB-mBJ is found to be close to the experimental result (3.3 eV). The optical anisotropy is analyzed through optical constants, such as dielectric function and absorption coefficient along parallel and perpendicular crystal orientations. The absorption coefficient reveals high absorption (1.5× {10}6 {cm}}-1) of photons in the ultraviolet region.

Optical absorption by indirect excitons in a transition metal dichalcogenide/hexagonal boron nitride heterostructure

NASA Astrophysics Data System (ADS)

Brunetti, Matthew N.; Berman, Oleg L.; Kezerashvili, Roman Ya

2018-06-01

We study optical transitions in spatially indirect excitons in transition metal dichalcogenide (TMDC) heterostructures separated by an integer number of hexagonal boron nitride (h-BN) monolayers. By solving the Schrödinger equation with the Keldysh potential for a spatially indirect exciton, we obtain eigenfunctions and eigenenergies for the ground and excited states and study their dependence on the interlayer separation, controlled by varying the number of h-BN monolayers. The oscillator strength, optical absorption coefficient, and optical absorption factor, the fraction of incoming photons absorbed in the TMDC/h-BN/TMDC heterostructure, are evaluated and studied as a function of the interlayer separation. Using input parameters from the existing literature which give the largest and the smallest spatially indirect exciton binding energy, we provide upper and lower bounds on all quantities presented.

Measurement and compensation of wavefront deformations and focal shifts in high-power laser optics

NASA Astrophysics Data System (ADS)

Mann, K.; Schäfer, B.; Stubenvoll, M.; Hentschel, K.; Zenz, M.

2015-11-01

We demonstrate the feasibility of passive compensation of the thermal lens effect in fused silica optics, placing suitable optical materials with negative dn/dT in the beam path of a high power near IR fiber laser. Following a brief overview of the involved mechanisms, photo-thermal absorption measurements with a Hartmann-Shack sensor are described, from which coefficients for surface/coating and bulk absorption in various materials are determined. Based on comprehensive knowledge of the 2D wavefront deformations resulting from absorption, passive compensation of thermally induced aberrations in complex optical systems is possible, as illustrated for an F-Theta objective. By means of caustic measurements during high-power operation we are able to demonstrate a 60% reduction of the focal shift in F-Theta lenses through passive compensation.