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Results for “Optical Absorption”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,711 records · Page 95
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

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

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.

Bair, C. H.↗
DOE OSTI2015

Specific features of the optical and photoelectric properties of nanocrystalline indium oxide

The spectral dependences of the absorption coefficient and steady-state photoconductivity and the relaxation of photoconductivity (after illumination switch off) in nanocrystalline indium oxide (In{sub 2}O{sub 3}) films synthesized by the sol–gel method are investigated. The mean nanocrystal size varies from 7–8 to 39–41 nm, depending on the sample-preparation conditions. The optical band gap of nanocrystalline In{sub 2}O{sub 3} is determined as a result of combined analysis of the optical absorption spectra and the spectral dependence of the photoconductivity. The optical band gap in nanocrystalline In{sub 2}O{sub 3} is found to be much narrower than the optical band gap in In{sub 2}O{sub 3} single crystals. The photoconductivity decay kinetics in nanocrystalline In{sub 2}O{sub 3} in air, vacuum, and argon at room temperature are studied. A model explaining the observed photoconductivity decay is proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Tracking Optical Phonon Dynamics in InP Nanocrystals via Transient Absorption and Femtosecond Stimulated Raman Spectroscopy

Semiconductor nanocrystals (NCs) offer actualized and prospective utility in optoelectronic technologies, yet key aspects of their thermal and vibrational behaviors remain unresolved. Compared with bulk crystals, heat dissipation involving NCs can differ substantially owing to pervasiveness of interfacial scattering, phonon confinement, and relaxed phonon momentum selection rules, as well as influences of ligands. Here, in addition to transient absorption, we use femtosecond stimulated Raman spectroscopy to track nonequilibrium optical-phonon dynamics in InP NCs capped with myristic acid ligands and compare the same particles coated with a ZnS shell. We identify distinct phonon decay pathways in ligand-capped versus ZnS-shelled NCs. Increasing the excitation density and introducing the ZnS shell measurably modify optical-phonon lifetimes, whereas phonon formation times remain largely unchanged. In addition, we observe phonon mode softening in ligand-capped nanocrystals, consistent with lattice expansion. Together, these results demonstrate that core–shell structures can strongly govern nanocrystal thermal dissipation pathways and should be considered a key design parameter for optoelectronic operation.

dissipation↗
DOE OSTI2015

Au-Cu{sub 2}O core-shell nanowire photovoltaics

Semiconductor nanowires are among the most promising candidates for next generation photovoltaics. This is due to their outstanding optical and electrical properties which provide large optical cross sections while simultaneously decoupling the photon absorption and charge carrier extraction length scales. These effects relax the requirements for both the minority carrier diffusion length and the amount of semiconductor needed. Metal-semiconductor core-shell nanowires have previously been predicted to show even better optical absorption than solid semiconductor nanowires and offer the additional advantage of a local metal core contact. Here, we fabricate and analyze such a geometry using a single Au-Cu{sub 2}O core-shell nanowire photovoltaic cell as a model system. Spatially resolved photocurrent maps reveal that although the minority carrier diffusion length in the Cu{sub 2}O shell is less than 1 μm, the radial contact geometry with the incorporated metal electrode still allows for photogenerated carrier collection along an entire nanowire. Current-voltage measurements yield an open-circuit voltage of 600 mV under laser illumination and a dark diode turn-on voltage of 1 V. This study suggests the metal-semiconductor core-shell nanowire concept could be extended to low-cost, large-scale photovoltaic devices, utilizing for example, metal nanowire electrode grids coated with epitaxially grown semiconductor shells.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Extended cavity laser absorption spectroscopy

Technologies for detecting absorption of electromagnetic radiation traveling through a measurement volume of interest are described herein. In a general embodiment, a laser is used to emit electromagnetic radiation through the measurement volume where absorption is desirably detected. An optical collector receives a portion of the radiation and directs a first fraction of the portion back to a gain medium of the laser, where the radiation is amplified and emitted again, and directs a second fraction to an optical sensor that can detect absorption in the measurement volume based upon attenuation of energy of the radiation. As the radiation feeds back to the gain medium and is emitted again, energy at attenuated wavelengths is amplified less than at other wavelengths. Thus, attenuation of energy of the radiation due to absorption in the measurement volume is cumulative, and relatively small absorptions are amplified, allowing smaller absorptions to be detected more easily.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Systematic DFT study of the impact of anionic variations on the physical properties of Cd1-xMnxX (XS, Se, Te; x = 6.25%)

Highlights: • The structural and electronic properties are investigated with most accurate mBJ potential. • The FM state stability is illustrated for Cd{sub 0.9375}Mn{sub 0.0625}S/Se/Te DMSs. • The FM semiconducting nature depicts potential applications in magneto-optic applications. • The absorption shifts within the visible range with S to Te variation that is verified by E{sub g}. • Thermoelectric properties indicate dominant hole-carriers and suitability at high temperatures. - Abstract: The structural and electronic properties are theoretically investigated for Cd{sub 1-x}Mn{sub x}X (XS, Se, Te; x = 6.25%) diluted magnetic semiconductors, which are further employed for extracting the magnetic, optical and thermoelectric properties using modified-Becke-Johnson (mBJ) potential. Ferromagnetic state stability is confirmed through the computed enthalpy of formation and the cohesive energies. The electronic properties elucidate Cd{sub 1-x}Mn{sub x}X (XS, Se, Te; x = 6.25%) as ferromagnetic semiconductors because both spin channels have Fermi energy level (E{sub F}) within the band gap, depicting potential applications in spintronic devices. The calculated optical response indicates shifts in the absorption within the visible energy that is consistent with the computed direct band gap values (1.9 eV–3.1 eV). Thermoelectric properties observed within 200 K–800 K show positive Seebeck coefficient indicating holes as majority charge carriers. Although Mn-doping suppresses the power factor, however, it improves with temperature, showing a potential for optimizing the thermoelectric performance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1990

Probing the Interstellar Medium of External Galaxies Using Quasar Absorption Lines: the 3C 232/NGC 3067 System

Quasar absorption lines offer unique opportunities to probe the interstellar medium of external galaxies. Researchers present new optical and UV absorption line spectroscopy of the quasar 3C232 (z=0.55) revealing new detail in the foreground absorption system due to the bright, spiral galaxy NGC 3067 (cz=1420 km/s). Specifically, the spectra show evidence for two and possibly three separate absorption components in CaII and Na I spanning approx. 150 km/s. The original HI detection of Haschick and Burke (1975) corresponds to the strongest of these metal systems which exhibits doublet ratios consistent with saturation in both CaII and Na I. Due to the recent detection in HI emission of a tidal tail or finger of HI extending from the western edge of NGC 3067 through the position of 3C 232 (Carilli, van Gorkom and Stocke, 1989), the morphology of the HI absorber is now known and is not either a warped disk nor a spherical halo as had been proposed. New deep continuum and H alpha imaging provides a sensitive upper limit on the the ionizing continuum impinging upon this cloud (and thus a limit on the intensity of the extragalactic ionizing radiation field). Together with the observed UV spectrum of 3C 232, the optical emission line ratios and the deep H alpha imaging set a minimum distance between the quasar and the HI cloud disregarding redshift information. This limit strains the non-cosmological redshift interpretation for 3C 232 -- and this quasar is one of the original 5 3C quasars found to be too close to NGC galaxies as if by chance (Burbidge, Burbidge, Solomon and Strittmatter, 1972).

Stocke, John T.↗
DOE OSTI2024

Microwave-Absorbing Foams with Adjustable Absorption Frequency and Structural Coloration

Microwave-absorbing materials with regulatable absorption frequency and optical camouflage hold great significance in intelligent electronic devices and advanced stealth technology. Herein, we present an innovative microwave-absorbing foam that can dynamically tune microwave absorption frequencies via a simple mechanical compression while in parallel enabling optical camouflage over broad spectral ranges by adjusting the structural colors. In this study, the vivid colors spanning different color categories generated from thin-film interference can be precisely regulated by adjusting the thickness of the conformal TiO 2 coatings on Ni/melamine foam. Enhanced interfacial and defect-induced polarizations resulting from the introduction of TiO 2 coating synergistically contribute to the dielectric attenuation performance. Consequently, such a foam exhibits exceptional microwave absorption capabilities, and the absorption frequency can be dynamically tuned from the S band to the Ku band by manipulating its compression ratio. Additionally, simulation calculations validate the adjustable electromagnetic wave loss behavior, offering valuable insights for the development of next-generation intelligent electromagnetic devices across diverse fields.

36 MATERIALS SCIENCE↗
NASA NTRS1990

Ultraviolet observations of the enigmatic bipolar nebula M1-92

IUE observations of the bipolar nebula M1-92 indicate that this object is an evolved object and possibly a preplanetary nebula. Data acquired in the SWP camera clearly show a flat UV continuum indicative of a relatively unobscured O subdwarf. Data acquired in the long wavelength region of the SWP and in the LWP camera reveal an object which mimics the characteristics of an F2 supergiant. These results, combined with other data at visual and infrared wavelengths, strongly favor that the central object of M1-92 is an evolved binary system. The He I 5876 and 6678 A absorption seen in optical spectra is extremely problematic. This, plus the presence of Fe II, Mg II, and Mg I absorption arising from resonance transitions and transitions from low-lying metastable levels, leads to the suggestion that the object resembling an F2 star is actually an early-type subdwarf cloaked in a thick circumstellar nebula. This interpretation and the similarities of the IR flux distribution to Vy 2-2, a preplanetary prototype, is consistent with M1-92 being in the process of forming a planetary nebula. The bipolar flow, the optical Fe II and ultraviolet Mg II emission of M1-92 are also characteristics of T Tauri stars. Although constraints definitely rule out that M1-92 is a pre-main-sequence object, these similarities imply that in many cases it may be difficult to distinguish between T Tauri stars and protoplanetary nebulae.

Feibelman, Walter A.↗
DOE OSTI2017

Controlling the magnetic and optical responses of a MoS 2 monolayer by lanthanide substitutional doping: a first-principles study

Here, the electronic, magnetic and optical properties of lanthanide substitutional doping (~2% concentration) on the MoS 2 monolayer have been investigated within the density functional theory formalism together with the Hubbard correction (DFT+U). The dopants investigated include Ce, Eu, Gd, Lu and Tm. The calculated dopant substitutional energies under both Mo-rich and S-rich conditions suggest that it is possible to experimentally realize the lanthanide doped MoS 2 monolayer systems. The Eu, Gd and Tm dopants induce strong magnetization in the host lattice. The electronic structure calculations reveal that the dopants have a p-type character and they exhibit a half-metallic behavior in the Gd and Eu doped systems. A dilute magnetic semiconducting behavior can also be realized in Gd, Eu and Tm doped systems by slightly tuning the Fermi level. All the dopants refine the optical responses of the host system with the onset of the optical absorption edge shifting to lower energies within the visible range (red shift phenomenon). We observe an optical anisotropy for two different directions of the electric field (E) polarizations, i.e. parallel, E∥, and perpendicular, E⊥, to the xy-plane. Lanthanide substitutional doping significantly influences the electron energy loss spectra (EELS), absorption spectra, and dielectric properties of the host MoS 2 monolayer. Furthermore, we notice that lanthanide substitutional doping could enhance the photocatalytic properties of the MoS 2 monolayer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Accurate measurements and temperature dependence of the water vapor self-continuum absorption in the 2.1 μm atmospheric window

In spite of its importance for the evaluation of the Earth radiative budget, thus for climate change, very few measurements of the water vapor continuum are available in the near infrared atmospheric windows especially at temperature conditions relevant for our atmosphere. In addition, as a result of the difficulty to measure weak broadband absorption signals, the few available measurements show large disagreements. We report here accurate measurements of the water vapor self-continuum absorption in the 2.1 μm window by Optical Feedback Cavity Enhanced Absorption Spectroscopy (OF-CEAS) for two spectral points located at the low energy edge and at the center of the 2.1 μm transparency window, at 4302 and 4723 cm{sup −1}, respectively. Self-continuum cross sections, C{sub S}, were retrieved with a few % relative uncertainty, from the quadratic dependence of the spectrum base line level measured as a function of water vapor pressure, between 0 and 16 Torr. At 296 K, the C{sub S} value at 4302 cm{sup −1} is found 40% higher than predicted by the MT-CKD V2.5 model, while at 4723 cm{sup −1}, our value is 5 times larger than the MT-CKD value. On the other hand, these OF-CEAS C{sub S} values are significantly smaller than recent measurements by Fourier transform spectroscopy at room temperature. The temperature dependence of the self-continuum cross sections was also investigated for temperatures between 296 K and 323 K (23-50 °C). The derived temperature variation is found to be similar to that derived from previous Fourier transform spectrometer (FTS) measurements performed at higher temperatures, between 350 K and 472 K. The whole set of measurements spanning the 296-472 K temperature range follows a simple exponential law in 1/T with a slope close to the dissociation energy of the water dimer, D{sub 0} ≈ 1100 cm{sup −1}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2005

Protection of Conductive and Non-conductive Advanced Polymer-based Paints from Highly Aggressive Oxidative Environments

Research has been continued to further improve the space durability of conductive and non-conductive polymer-based paints and of conductive thermal control paints for space applications. Efforts have been made to enhance the space durability and stability of functional Characteristics in ground-based space environment imitating conditions, using specially developed surface modification treatment. The results of surface modification of new conductive paints, including the ground-based testing in aggressive oxidative environments, such as atomic oxygen/UV and oxygen plasma, and performance evaluation are presented. Functional properties and performance characteristics, such as thermal optical properties (differential solar absorptance and thermal emittance representing the thermal optical performance of thermal control paints) and surface resistivity characteristics of pristine, surface modified, and tested materials were verified. Extensive surface analysis studies have been performed using complementary surface analyses including SEM/EDS and XPS. Test results revealed that the successfully treated materials exhibit reduced mass loss and no surface morphology change, thus indicating good protection from the severe oxidative environment. It was demonstrated that the developed surface modification treatment could be applied successfully to charge dissipative and conductive paints.

Gudimenko, Y.↗
DOE OSTI2016

Controlling the size of gold nanoparticles grown on indium tin oxide substrates prepared by seed mediated growth method

One of the unique optical properties of gold nanoparticles is the enhanced absorption and scattering light around metal nanoparticles commonly called the Localized Surface Plasmon Resonance (LSPR) effect of gold nanoparticles. This property is determined by the shape and size of gold nanoparticles. In this work, we observed the role of three materials used in synthesis process on the morphology and the LSPR effect of gold nanoparticles. The gold nanoparticles were directly grown on indium tin oxide (ITO) coated glass substrates using the seed mediated growth method with three different concentrations of trisodium citrate (Na{sub 3}C{sub 6}H{sub 5}O{sub 7}), C{sub 16}TAB and ascorbic acid (C{sub 6}H{sub 8}O{sub 6}). Based on the FESEM image and optical absorption spectrum of gold nanoparticles, it was found that the higher concentration of those materials has decreased the size of gold nananoparticles and shifted the LSPR peaks to lower wavelength.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1994

Optical remote sensing for measurement of toxic gases

There is renewed interest in using optical remote sensing techniques for measuring and monitoring airborne toxins. Many instruments have been used to measure traces of atmospheric molecular species. Some optical remote sensing technology is in use for measuring or monitoring toxic or pollutant gases. The examples in this article provide a number of lessons that may be of use in the new field of optical remote sensing of toxic gases. Topics covered include the following: atmospheric properties, Fourier transform spectrometry, gas-filter correlation, differential absorption laser systems, aircraft missions, laser long-path instruments, differential optical absorption spectrometry, and ozone measurement.

Grant, William B.↗
NASA NTRSDate not supplied

Thermal Materials and Coatings for Near Rectilinear Halo Orbit (NRHO)

Passive thermal control of a spacecraft is reliant on external surface optical properties (solar absorptivity and IR emissivity), which degrade over time depending on length of mission, material or coating, and natural and induced environments. Understanding the degradation and resulting End of Life (EOL) optical properties enables optimization of the thermal performance and reduces risk. The environmental factors that affect degradation of materials and coatings include UV, solar wind, vacuum, contamination, lunar dust, atomic oxygen, and more. Future spacecraft such as Gateway will be flying in the Near Rectilinear Halo Orbit (NRHO), an environment that has not been flown before and environmental factors are different from Low Earth Orbit. There is no on orbit data for materials in this environment, and optical property data from on-orbit and ground experiments for other environments is of limited use. This 1.5 hour short course will explore optical properties and degradation by introducing the expected environment of NRHO, types of materials and coatings that could be used, how to estimate their EOL properties, and future work. This course will focus on the NRHO environment, but it will be beneficial for anyone interested in optical property degradation in the space environment.

Optics↗
NASA NTRS1994

Hubble Space Telescope faint object spectrograph Quasar Absorption System Snapshot Survey (AbSnap). 1: Astrometric optical positions and finding charts of 269 bright QSO

We present finding charts and optical positions accurate to less than 1 arcsec for 269 bright (V less than or = 18.5) Quasi-Stellar Objects (QSOs). These objects were selected as candidates for the Hubble Space Telescope (HST) Quasar Absorption System Snapshot Survey (AbSnap), a program designed to use the Faint Object Spectrograph (FOS) to obtain short exposure ultraviolet (UV) spectra of bright QSOs. Many quasars were included because of their proximity to bright, low redshift galaxies and positions of these QSOs are measured accurately for the first time. Data were obtained using the digitized sky survey produced by the Space Telescope Science Institute's Guide Stars Selection System Astrometric Support Program.

Bowen, David V.↗
DOE OSTI2017

X-ray and optical pulse interactions in GaAs

Absorption of hard x-rays in GaAs creates excitations that can dramatically alter the propagation of optical laser pulses with photon energies near the bandgap. Measurements of optical transmission through a thin crystalline wafer of GaAs after absorption of an intense x-ray synchrotron pulse demonstrate how x-ray induced optical transparency depends on the recombination of excited conduction band electrons and valence band holes via Auger, spontaneous emission, and especially stimulated emission processes. The x-ray induced band fluorescence spectrum also reveals amplified spontaneous emission at the high x-ray fluences used, confirming the importance of stimulated emission. Finally, for laser pulses with sufficiently high fluence, the interaction of optically excited electrons with x-ray excited electrons can quench the enhanced laser transmission.

36 MATERIALS SCIENCE↗
DOE OSTI2014

MAGNETOHYDRODYNAMIC MODELING OF THE ACCRETION SHOCKS IN CLASSICAL T TAURI STARS: THE ROLE OF LOCAL ABSORPTION IN THE X-RAY EMISSION

We investigate the properties of X-ray emission from accretion shocks in classical T Tauri stars (CTTSs), generated where the infalling material impacts the stellar surface. Both observations and models of the accretion process reveal several aspects that are still unclear: the observed X-ray luminosity in accretion shocks is below the predicted value, and the density versus temperature structure of the shocked plasma, with increasing densities at higher temperature, deduced from the observations, is at odds with that proposed in the current picture of accretion shocks. To address these open issues, we investigate whether a correct treatment of the local absorption by the surrounding medium is crucial to explain the observations. To this end, we describe the impact of an accretion stream on a CTTS by considering a magnetohydrodynamic model. From the model results, we synthesize the X-ray emission from the accretion shock by producing maps and spectra. We perform density and temperature diagnostics on the synthetic spectra, and we directly compare the results with observations. Our model shows that the X-ray fluxes inferred from the emerging spectra are lower than expected because of the complex local absorption by the optically thick material of the chromosphere and of the unperturbed stream. Moreover, our model, including the effects of local absorption, explains in a natural way the apparently puzzling pattern of density versus temperature observed in the X-ray emission from accretion shocks.

79 ASTRONOMY AND ASTROPHYSICS↗