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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Infrared thermometry in high temperature materials processing: influence of liquid water and steam

Here, the capability of four infrared thermometry techniques (2-colour and 1-colour pyrometers, Pyrolaser and IR camera) was evaluated with respect to the impact of water or steam in the line of sight to determine temperature from two heat sources (blackbody calibration source and steel block inside the furnace). The influence of liquid water on the temperature readings was minimal when using 2-colour pyrometry due to comparable absorption coefficients of water for the measured wavelengths. The signals measured using both the Pyrolaser and the 1-colour pyrometer were decreased due to the partial absorption and resulted in an apparent temperature lower than the actual. Water readily absorbed the IR signal in the range of the IR camera operation, resulting in no signal whenever liquid water was present in the line of sight. Steam caused the most deviation and fluctuation of temperature readings for all techniques due to the large level of light scattering in addition to the absorption of the radiant energy. A technique was developed to determine the transmissivity (apparent emissivity) when water or steam is in the line of sight of measurement. An approximate correction to the measurements based on Planck’s law is discussed for both 2-colour and 1-colour pyrometers.

2-colour and 1-colour pyrometry↗
NASA NTRS1986

Parameterization of near infrared absorption by atmospheric gases

An absorption coefficient (k) distribution model is presented for fast calculation of atmospheric transmittances based solely on essential data from line-by-line (LBL) calculations. The absorption at any site is summed over the spectra obtained by LBL calculations. Application of the scaling model is illustrated with sample calculations for 0.72 micron emissions and the 1.36 micron water vapor band. LBL absorption spectra are calculated for the pressure levels 260 mb, 400 mb and 1000 mb.

Ridgway, W. L.↗
DOE OSTI2022

Ab initio theory of free-carrier absorption in semiconductors

The absorption of light by free carriers in semiconductors results in optical loss for all photon wavelengths. Since free-carrier absorption competes with optical transitions across the band gap, it also reduces the efficiency of optoelectronic devices such as solar cells because it does not generate electron-hole pairs. In this work, we develop a first-principles theory of free-carrier absorption taking into account both single-particle excitations and the collective Drude term, and we demonstrate its application to the case of doped Si. Here, we determine the free-carrier absorption coefficient as a function of carrier concentration and we obtain excellent agreement with experimental data. We identify the dominant processes that contribute to free-carrier absorption at various photon wavelengths, and analyze the results to evaluate the impact of this loss mechanism on the efficiency of Si-based optoelectronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1975

Empirical relation between interstellar X-ray absorption and optical extinction

An empirical relation between interstellar X-ray absorption and optical extinction is derived from the correlation of measurements made on objects of large intrinsic diameter. The result is Av = 4.5 times 10 to the -22nd power N(H) mag, with the principal error being largely systematic in origin, where N(H) represents the column density of interstellar matter in the Brown and Gould model for the X-ray absorption coefficient. Applying this ratio to optically identified compact sources, it is concluded that sources in binary systems showing pronounced X-ray occultations have an intrinsic absorption equivalent to about 10 to the 22-nd power atoms per sq cm of interstellar matter and that there are a few compact sources where the absorption seems to be primarily interstellar in origin. The interstellar absorption expected in Cyg X-1 from the extinction of its optical counterpart is much greater than that suggested by X-ray spectra, which may be due to a soft X-ray component greater than that predicted by the power law fitted to higher energy data.

Gorenstein, P.↗
DOE OSTI2021

Solvated Electron in Acetonitrile: Radiation Yield, Absorption Spectrum, and Equilibrium between Cavity- and Solvent-Localized States

The equilibrium between a solvent cavity-localized electron, ecav-, and a dimeric solvent anion, (CH 3 CN)$_{2}^{•-}$, which are the two lowest energy states of the solvated electron in acetonitrile, has been investigated by pulse radiolysis at 233-353 K. The enthalpy and entropy for the e$_{cav}^{-}$ to (CH 3 CN)$_{2}^{•-}$ conversion amount to -11.2 ± 0.3 kcal/mol and -39.3 ± 1.2 cal/(mol K), corresponding to a 0.44 ± 0.35 equilibrium constant at 25 °C. The radiation yield of the solvated electron has been quantified using a Co(II) macrocycle that scavenges electrons with a 1.55 × 10 11 M -1 s -1 rate constant. The apparent yield increases without saturation over the attainable scavenger concentration range, reaching 2.8 per 100 eV; this value represents the lower limit for the acetonitrile ionization yield in pulse radiolysis. The apparent molar absorption coefficient of (20.8 ± 1.5) × 10 3 M -1 cm -1 at 1450 nm and 20 °C for the solvated electron and individual vis-near-infrared (NIR) absorption spectra of e$_{cav}^{-}$ and (CH 3 CN)$_{2}^{•-}$ are derived from the data. Variances with previous reports are thoroughly discussed. All together, these results resolve several controversies concerning the solvated electron properties in acetonitrile and furnish requisite data for quantitative pulse radiolysis investigations in this commonly used solvent.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
NASA NTRS1972

Comparison of measured and theoretical inverse bremsstrahlung and photoionization absorption of infrared radiation in a H-He plasma.

The absorption coefficients of 1.15- and 3.39-micrometer radiation for a homogeneous H-He plasma have been measured in a temperature and electron density range where the major absorption mechanisms are electron-ion inverse bremsstrahlung and neutral-atom photoionization. Measurements were made behind both the incident and reflected shock waves in a driven tube by recording the laser intensity transmitted along the tube diameter as a function of time. The measured values compare well with those obtained from theoretical calculations for a gas in thermodynamic equilibrium.

Billman, K. W.↗
NASA NTRS1973

The emission coefficient of uranium plasmas

The emission coefficient for uranium plasmas (Temperature: 8000 K) was measured for the wavelength range (200 A - 6000 A). The results are compared to theory and other measurements. The absorption coefficient for the same wavelength interval is also given.

Schneider, R. T.↗
NASA NTRS1999

A Solar Radiation Parameterization for Atmospheric Studies

The solar radiation parameterization (CLIRAD-SW) developed at the Goddard Climate and Radiation Branch for application to atmospheric models are described. It includes the absorption by water vapor, O3, O2, CO2, clouds, and aerosols and the scattering by clouds, aerosols, and gases. Depending upon the nature of absorption, different approaches are applied to different absorbers. In the ultraviolet and visible regions, the spectrum is divided into 8 bands, and single O3 absorption coefficient and Rayleigh scattering coefficient are used for each band. In the infrared, the spectrum is divided into 3 bands, and the k-distribution method is applied for water vapor absorption. The flux reduction due to O2 is derived from a simple function, while the flux reduction due to CO2 is derived from precomputed tables. Cloud single-scattering properties are parameterized, separately for liquid drops and ice, as functions of water amount and effective particle size. A maximum-random approximation is adopted for the overlapping of clouds at different heights. Fluxes are computed using the Delta-Eddington approximation.

Chou, Ming-Dah↗
NASA NTRS1988

High-resolution spectra and photoabsorption coefficients for carbon monoxide absorption bands between 94.0 nm and 100.4 nm

Photoabsorption coefficients have been measured for the CO in interstellar clouds at a resolving power more than 20 times greater than previously obtainable. In order to facilitate comparisons, these data have been integrated over the same wavelength ranges as used in Letzelter et al. (1987). It is found that most of the results obtained for bands between 94.0 and 100.4 nm are larger than those of Letzelter; the discrepancy may be attributable to the difference between the resolving powers of the spectrometers used, because the saturation effects associated with low resolution can underestimate absorption coefficient values.

Yoshino, K.↗
NASA NTRS1989

Stoichiometric effects on the optical properties of LiInSe(2)

The diffuse reflectance of LiInSe(2) between 0.67 and 3.54 eV have been measured and the Kubelka-Munk theory was used to obtain the absorption coefficient from the data. The band gap in the samples is located at approximately 1.6 eV. The In and Se content of the samples was determined from atomic absorption measurements. Absorption peaks at 0.890 and 0.896 eV have been observed which are correlated, respectively, to the selenium and indium deficiencies in the samples.

Smith, Cecily J.↗
NASA NTRS2002

Thermophysics Characterization of Multiply Ionized Air Plasma Absorption of Laser Radiation

The impact of multiple ionization of air plasma on the inverse Bremsstrahlung absorption of laser radiation is investigated for air breathing laser propulsion. Thermochemical properties of multiply ionized air plasma species are computed for temperatures up to 200,000 deg K, using hydrogenic approximation of the electronic partition function; And those for neutral air molecules are also updated for temperatures up to 50,000 deg K, using available literature data. Three formulas for absorption are calculated and a general formula is recommended for multiple ionization absorption calculation. The plasma composition required for absorption calculation is obtained by increasing the degree of ionization sequentially, up to quadruple ionization, with a series of thermal equilibrium computations. The calculated second ionization absorption coefficient agrees reasonably well with that of available data. The importance of multiple ionization modeling is demonstrated with the finding that area under the quadruple ionization curve of absorption is found to be twice that of single ionization. The effort of this work is beneficial to the computational plasma aerodynamics modeling of laser lightcraft performance.

Wang, Ten-See↗
NASA NTRS2005

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

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.

NASA Discipline Life Sciences Technologies↗
DOE OSTI2022

A new route to obtain fluorescence X-ray absorption spectra of compounds and to remove the self-absorption induced nonlinearity in the spectra

A new route to obtain fluorescence X-ray absorption spectra of compounds and to remove the self-absorption induced nonlinearity in the spectra is described. The fluorescent intensity If is linearly proportional to the absorption coefficient μ. For studies of surface structures around an element (κ) the fluorescence detection is often the mode of choice. However, the measurement may suffer from a self-absorption (SA) effect which nonlinearly distorts the spectra. The effect is severe when κ is concentrated or the measurements are carried out in certain geometries. Here, the correlations among emission events in compounds are examined following resonance X-ray core-electron excitation within κ. Under conditions leading to SA, If emitted from κ apparently has a conjugated relationship with the fluorescent intensities simultaneously emitted from other elements (ξ). Normalizing the former (κ) by the latter (ξ) will largely remove SA effects and reduce this nonlinear problem to a tractable linear problem. This does result in a moderate reduction of the spectral amplitude due to the so-called secondary emission from ξ excited by the emission from κ. Nonetheless, the resulting spectra will allow one to accurately determine bond distances and disorder and, in some respects, can be superior to spectra obtained via the absorption channel. For μξ < μκ and grazing incidence geometry, the amplitude reduction can be small and simple normalization is sufficient to restore the spectral integrity with remarkable accuracy. This has been instrumental in unravelling the surface and subsurface structures around cations in amorphous Ga–In–O and Zn–Sn–O films which are otherwise inaccessible due to severe SA effects. This method has also been applied to several samples with μξ ≃ μκ to examine its applicability. For these samples, the amplitude reduction is 12 ± 4% versus their standards for the data measured with the classical 45°/45° geometry. This experimental method is easy to implement. Since If from κ and ξ are measured by the same detector system, it is also superior to other methods in removing systematic errors such as detector system nonlinearity, electronic noise, and some beam instabilities, and in removing spectral imperfections due to, for example, SA effects, diffraction effects and sample inhomogeneity. The distortions resulting from the latter can be severe in the spectra measured in transmission mode.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1974

Radiative transitions involving the /2p2/ 3Pe metastable autodetaching state of H-

A Hylleraas bound-state wave function and 1s-2s-2p close-coupling continuum wave functions are used to calculate the absorption coefficient for the free-bound transition of H(1s) + e + quantum to a H anion in (2p2,3Pe) and the differential emission rate for the inverse process. The absorption and emission spectral maximum is found to be at a photon wavelength of 1219.5 A, an improvement of 2 A on other calculations. This free-bound absorption process appears to be a significant source of continuous ultraviolet opacity.

Jacobs, V. L.↗
NASA NTRS1990

Intracavity Dye-Laser Absorption Spectroscopy (IDLAS) for application to planetary molecules

Time-resolved, quasi-continuous wave, intracavity dye-laser absorption spectroscopy is applied to the investigation of absolute absorption coefficients for vibrational-rotational overtone bands of water at visible wavelengths. Emphasis is placed on critical factors affecting detection sensitivity and data analysis. Typical generation-time dependent absorption spectra are given.

Lang, Todd M.↗
DOE OSTI2024

Structural, electronic, and optical-absorption properties of 2D Si thin films

Recent experimental studies highlighted the potential of thin-film crystalline silicon (Si) for high-efficiency solar cells. Using density functional theory, we investigated 2D Si thin films across various orientations, thicknesses, and surface structures to elucidate their structure–property relationships. Through surface-energy calculations and Wulff construction, we determined the crystal habit of Si, which aligns with available experimental observations. Electronic-structure calculations underscored the critical role of valence saturation on surfaces in enabling semiconducting behavior in Si thin films, essential for optical applications. From optical-absorption calculations, we identified the surface index exhibiting the highest absorption coefficients for thin films Si solar cell applications.

36 MATERIALS SCIENCE↗
NASA NTRS1977

Differential-optoacoustic absorption detector

Two-cell spectrophone detects trace amounts of atmospheric pollutants by measuring absorption coefficients of gases with various laser sources. Device measures pressure difference between two tapered cells with differential manometer. Background signal is reduced by balanced window heating and balanced carrier gas absorption in two cells.

Shumate, M. S.↗
NASA NTRS1993

One-parameter scaling and exponential-sum fitting for water vapor and CO2 infrared transmission functions

A medium-sized band model for water vapor and CO2 absorption is developed using the one-parameter scaling approximation. The infrared spectrum is divided into 10 bands. The Planck-weighted diffuse transmittance is reduced to a function dependent only upon the scaled absorber amount and fit by an exponential sum. By selecting specific sets of absorption coefficients for exponential-sum fitting, computations of fluxes and cooling rate are made very fast. Compared to a broadband model, the accuracy, speed, and versatility are all enhanced. With absorption due to water vapor line, continuum, CO2 as well as O3 included, the parameterization introduces an error of less than 1.5 W/sq m in fluxes and less than 0.15 C/day in the tropospheric and lower stratospheric cooling rates.

Chou, Ming-Dah↗