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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Observations and Laboratory Data of Planetary Organics

Many efforts are underway to search for evidence of prebiotic materials in the outer solar system. Current and planned Mars missions obtain remote sensing observations that can be used to address the potential presence of prebiotic materials. Additional missions to, and continuing earth-based observations of, more distant solar system objects will also provide remote sensing observations that can be used to address the potential presence of prebiotic materials. I will present an overview of on-going observations, associated laboratory investigations of candidate materials, and theoretical modeling of observational data. In the past the room temperature reflectance spectra of many residues created from HC-bearing gases and solids have been reported. The results of an investigation of what effect temperatures more representative of outer solar system surfaces (50-140K) have on the reflectance spectra of these residues, and the associated interpretations, will be presented. The relatively organic-rich Tagish Lake Meteorite has been suggested as a spectral analog for Dtype asteroids. Using a new approach that relies upon iterative use of Hapke theory and Kraniers-Kronig analysis the optical constants of TLM were estimated. The approach and results of the analysis will be presented. Use of optical constants in scattering theories, such as the Hapke theory, provide the ability to determine quantitative estimates of the relative abundances and grain sizes of candidate surface components. This approach has been applied to interpret the reflectance spectra of several outer solar system surfaces. A summary will be provided describing the results of such modeling efforts.

Roush, Ted L.↗
NASA NTRS1972

Reflectance of aqueous solutions

The optical properties and optical constants of water and aqueous solutions were studied to develop an accurate tabulation of graphical representations of the optical constants through a broad spectrum. Manuscripts of articles are presented concerning extinction coefficients, relative specular reflectance, and temperature effect on the water spectrum. Graphs of absolute reflectance, phase shifts, index of refraction, and extinction coefficients for water, heavy water and aqueous solutions are included.

Querry, M. R.↗
NASA NTRS1976

Study of Al with a combined Auger electron spectrometer-ellipsometer system

Auger electron spectroscopy and ellipsometry were applied in order to measure the optical constants and study the surface chemistry of vapor-deposited Al films and high-purity bulk Al surfaces in situ under vacuum. The optical constants measured were compared with the extinction coefficient computed by the free-electron theory. The contamination of the clean Al surface was in the form of a metal oxide film. Auger electron spectroscopic measurements were used to establish the relationship between the Auger peaks of O (513 eV) and aluminum oxide (53 eV) and changes in the measured optical phase and film thickness. The free path length of the Al Auger electrons (67 eV) in the oxide film was determined, and it was shown that the amplitude of these peaks is a linear function of film thickness down to 0.6 A.

Allen, T. H.↗
NASA NTRS1988

The problem of clustering in laboratory studies of cometary dust

In trying to understand the nature of interstellar or interplanetary dust grains it is tempting to simply rely on direct lab measurements of grain properties such as extinction. However, until agreement is achieved between directly measured extinction and the same property calculated from measured optical constants of the solid, application to astronomical observations is questionable. There are two major problems which are discussed: the problem of what optical constants to use in the calculation, and the almost unavoidable problem of particle clustering in lab studies. Regarding small particle measurements, a problem afflicting almost all lab measurements is the clustering of particles. Having failed in efforts to isolate particles, the solution to the problem was attempted with a simple theory which seems to adequately describe the extinction by small, clustered particles in many cases. The theory is briefly explained.

Huffman, Donald R.↗
NASA NTRS2011

Laboratory Spectra of Mixtures of CH4, C2H6, and CH3OH

Infrared spectroscopy is commonly used as a tool for identifying the composition of objects in the Solar System and beyond. Using laboratory spectra, optical constants can be calculated and used to create model spectra for comparison to spectra obtained from infrared telescopes. In this study, the optical constants of mixtures of simple organics, including CH4, C2H6, and CH3OH were calculated from 15 to 70 K, in the frequency range of 9000-500 cm(sup -1) (1.1-20 micrometers), at a spectral resolution of 1 cm(sup -1).

Mastrapa, Rachel↗
NASA NTRS1988

Extreme ultraviolet reflectivity studies of gold on glass and metal substrates

The paper reports measurements of the extreme ultraviolet reflectivity of gold from 44 to 920 A at grazing incidence. Gold was deposited using vacuum evaporation and electroplating on substrates of glass and polished nickel, respectively. Measurements are also presented of the extreme ultraviolet reflectivity of electroless nickel in the same wavelength region, where one of the polished nickel substrates was used as a sample. Derived optical constants for evaporated and electroplated gold and electroless nickel are presented. Additional studies of the effects of various contaminants on the EUV reflectivity are also reported. The variations of the optical constants are discussed in terms of density variations, surface roughness and contamination effects. These results ae reported as part of studies for the Extreme Ultraviolet Explorer satellite program to determine acceptance criteria for the EUV optics, contamination budgets and calibration plans.

Jelinsky, Sharon R.↗
NASA NTRS2006

Molecular Substrate Alteration by Solar Wind Radiation Documented on Flown Genesis Mission Array Materials

The Genesis spacecraft sampling arrays were exposed to various regimes of solar wind during flight that included: 313.01 days of high-speed wind from coronal holes, 335.19 days of low-speed inter-stream wind, 191.79 days of coronal mass ejections, and 852.83 days of bulk solar wind at Lagrange 1 orbit. Ellipsometry measurements taken at NASA s Johnson Space Center show that all nine flown array materials from the four Genesis regimes have been altered by solar wind exposure during flight. These measurements show significant changes in the optical constant for all nine ultra-pure materials that flew on Genesis when compared with their non-flight material standard. This change in the optical constant (n and k) of the material suggests that the molecular structure of the all nine ultra-pure materials have been altered by solar radiation. In addition, 50 samples of float-zone and czochralski silicon bulk array ellipsometry results were modeled with an effective medium approximation layer (EMA substrate layer) revealing a solar radiation molecular damage zone depth below the SiO2 native oxide layer ranging from 392 to 613 . This bulk solar wind radiation penetration depth is comparable to the depth of solar wind implantation depth of Mg measured by SIMS and SARISA.

Calaway, Michael J.↗
NASA NTRS1997

Titan haze: structure and properties of cyanoacetylene and cyanoacetylene-acetylene photopolymers

The structure and morphological properties of polymers produced photochemically from the UV irradiation of cyanoacetylene and cyanoacetylene mixtures have been examined to evaluate their possible contribution to the haze layers found on Titan. A structural analysis of these polymers may contribute to our understanding of the data returned from the Huygens probe of the Cassini mission that will pass through the atmosphere of Titan in the year 2004. Infrared analysis, elemental analysis, and thermal methods (thermogravimetric analysis, thermolysis, pyrolysis) were used to examine structures of polycyanoacetylenes produced by irradiation of the gas phase HC3N at 185 and 254 nm. The resulting brown to black polymer, which exists as small particles, is believed to be a branched chain of conjugated carbon-carbon double bonds, which, on exposure to heat, cyclizes to form a graphitic structure. Similar methods of analysis were used to show that when HC3N is photolyzed in the presence of Titan's other atmospheric constituents (CH4, C2H6, C2H2, and CO), a copolymer is formed in which the added gases are incorporated as substituents on the polymer chain. Of special significance is the copolymer of HC3N and acetylene (C2H2). Even in experiments where C2H2 was absorbing nearly all of the incident photons, the ratio of C2H2 to HC3N found in the resulting polymer was only 2:1. Scanning electron microscopy was used to visually examine the polymer particles. While pure polyacetylene particles are amorphous spheres roughly 1 micrometer in diameter, polycyanoacetylenes appear to be strands of rough, solid particles slightly smaller in size. The copolymer of HC3N and C2H2 exhibits characteristics of both pure polymers. This is particularly important as pure polyacetylenes do not match the optical constants measured for Titan's atmospheric hazes. The copolymers produced by the incorporation of other minor atmospheric constituents, like HC3N, into the polyacetylenes are expected to have optical constants more comparable to those of the Titan haze.

Non-NASA Center↗
NASA NTRS1994

Visual-Motion Cueing in Altitude and Yaw Control

Research conducted using the Vertical Motion Simulator at the NASA Ames Research Center examined the contributions of platform motion and visual level-of-detail (LOD) cueing to tasks that required altitude and/or yaw control in a simulated AH-64 Apache helicopter. Within the altitude control tasks the LOD manipulation caused optical density to change across altitudes by a small, moderate, or large amount; while platform motion was either present or absent. The results from these tasks showed that both constant optical density and platform motion improved altitude awareness in an altitude repositioning task, while the presence of platform motion also led to improved performance in a vertical rate control task. The yaw control tasks had pilots'sit 4.5 ft in front of the center of rotation, thus subjecting them to both rotational and lateral motions during a yaw. The pilots were required to regulate their yaw, while the platform motion was manipulated in order to present all combinations of the resulting rotational and lateral motion components. Ratings of simulation fidelity and sensed platform motion showed that the pilots were relatively insensitive to the rotational component, but highly aware of the lateral component. Together these findings show that: 1) platform motion cues are important when speed regulation is required during altitude change; 2) platform motion contributes to the perception of movement amplitude; 3) lateral, but not rotational, motion cues are essential to the perception of vehicle yaw; and 4) LOD management yielding constant optical density across altitudes improves altitude awareness.

Johnson, Walter W.↗
NASA NTRS1985

Molybdenum-silicon multilayer mirrors for the extreme ultraviolet

Multilayer structures of molybdenum and silicon have been synthesized by sputter deposition onto flat silicon single-crystal silicon substrates and spherically ground (0.5and 22.0-m radii) fused silica substrates; and the reflectivities for 170.4-A (72.8-eV), 160.1-A (77.4-eV), and 228-A (54.4-eV) light measured at near normal incidence. Observed peak values ranged from 26.2 to 78 percent, the highest reflectivities occurring closest to normal incidence. Energy resolutions were about 10 in all cases. Model calculations were performed using optical constants and experimentally determined multilayer structural parameters. In all cases the measured reflectivities were equal to or larger (by up to a factor of 2) than the calculated values, a result attributed to uncertainty in the optical constants used in the calculations. Experimental and calculated angular-peak positions and energy resolutions were in good agreement. The high reflectivities of these molybdenum-silicon structures will make possible application of traditional optics approaches in the EUV and support new developments including free-electron lasers.

Barbee, T. W., Jr.↗
NASA NTRS2019

Estimated Refractive Indices of Calcite, Dolomite, and Magnesite: ~0.3-500 M.

Carbonate minerals are germane to questions involving volatile and climate history on Mars [e.g., 1-2]. In particular, the abundance of carbonate-bearing minerals can provide broad useful bounds on the amount of CO2 out-gassed into the atmosphere over its history and their spatial distribution and mineralogy can yield constraints on the environments in which they were produced. Earth-based, orbital, and landed spectral observations provide evidence for the presence of carbonates in the Martian environment [3-6]. Infrared observations made from spacecraft near Mars were interpreted to indicate the presence of carbonates. [6] associated the carbonates with the surface dust and interpreted the mineralogy as being consistent with magnesite (MgCO3). Near- infrared observations from Mars orbit have been interpreted to suggest magnesite outcrops in restricted locations [7-9]. Quantitative estimates of the abundance of carbonates on Mars range from 0-3% [3], 2-5% [6], less than a few percent [10], and <10% [8]. With the growing evidence for magnesite on Mars additional quantitative estimates can be provided via theoretical modeling of the reflectance from the Martian surface. Calcite (CaCO3) and dolomite ((Ca,Mg)CO3) are identified in Asian dust [2-17%], [10] and calcite in Saharan dust [~8-10% [12-15]. The importance of op- tical constants at visible and near-infrared wavelengths as proxies for estimating the effects at infrared wave- lengths, has been investigated [15]. The growing evidence for Mg-carbonates on Mars, the presence of calcite and dolomite in terrestrial aero- sols, and general lack of optical constants for these materials in the visible- to mid-infrared (VMIR, ~0.3-6 ❍m) has motivated the current effort to estimate the optical constants of calcite, dolomite, and magnesite in the VMIR.

Roush, T. L.↗
NASA NTRS1989

Optical properties of epitaxial CoSi2 and NiSi2 films on silicon

The optical constants of epitaxial films of CoSi2 and NiSi2, grown by molecular beam epitaxy on Si(111), in the energy range of 0.9-4.0 eV have been measured. The behavior of the optical constants is characteristic of metals. It is Drude-like in low energy region and deviates from Drude behavior as interband transitions set in. Interband transitions are found to have already set in at 1 eV. The absorption varies significantly with energy, which has implications for photoresponse studies of internal photoemission in these material systems.

Jimenez, J. R.↗
NASA NTRS1990

Optical constraints of kerogen from 0.15 to 40 microns: Comparison with meteoritic organics

Kerogens are dark, complex organic materials produced on the Earth primarily by geologic processing of biologic materials, but kerogens have chemical and spectral similarities to some classes of highly processed extraterrestrial organic materials. Kerogen-like solids were proposed as constitutents of the very dark reddish surfaces of some asteroids and are also spectrally similar to some carbonaceous organic residues and the Iapetus dark material. Kerogen can thus serve as a useful laboratory analog to very dark, spectrally red extraterrestrial materials; its optical constants can be used to investigate the effects of particle size, void space and mixing of bright and dark components in models of scattering by dark asteroidal, cometary, and satellite surfaces. Measurements of the optical constants of both Type 2 kerogen and of macromolecular organic residue from the Murchison carbonaceous chondrite via transmission and reflection measurements on thin films are reported. The real part of the refractive index, n, is determined by variable incidence-angle reflectance to be 1.60 + or - 0.05 from 0.4 to 2.0 micrometers wavelength. Work extending the measurement of n to longer wavelengths is in progress. The imaginary part of the refractive index, k, shows substantial structure from 0.15 to 40 micrometers. The values are accurate to + or - 20 percent in the UV and IR regions and to + or - 30 percent in the visible. The k values of organic residues were also measured from the Murchison meteorite. Comparison of the kerogen and Murchison data reveals that between 0.15 and 40 microns, Murchison has a similar structure but no bands as sharp as in kerogen, and that the k values for Murchison are significantly higher than those of kerogen.

Khare, Bishun N.↗
NASA NTRS1990

Additions and corrections to the absorption coefficients of CO2 ice - Applications to the Martian south polar cap

Reflectance spectra of carbon dioxide frosts were calculated using the optical constants provided by Warren (1986) for the wavelength region 2-6 microns. In comparing these calculated spectra to spectra of frosts observed in the laboratory and on the surface of Mars, problems in the optical constants presented by Warren (1986) became apparent. Absorption coefficients for CO2 ice have been derived using laboratory reflectance measurements and the Hapke (1981) model for calculating diffuse reflectance. This provides approximate values in regions where no data were previously available and indicates where corrections to the compilation by Warren (1986) are required. Using these coefficients to calculate the reflectance of CO2 ice at varying grain sizes indicates that a typical Mariner polar cap spectrum is dominated by absorptions due to CO2 frost or ice at grain sizes that are quite large, probably of the order of millimeters to centimeters. There are indications of contamination of water frost or dust, but confirmation will require more precise absorption coefficients for solid CO2 than can be obtained from the method used here.

Calvin, Wendy M.↗
NASA NTRS1994

Optical properties of poly-HCN and their astronomical applications

Matthews (1992) has proposed that HCN "polymer" is ubiquitous in the solar system. We apply vacuum deposition and spectroscopic techniques previously used on synthetic organic heteropolymers (tholins), kerogens, and meteoritic organic residues to the measurement of the optical constants of poly-HCN in the wavelength range 0.05-40 micrometers. These measurements allow quantitative comparison with spectrophotometry of organic-rich bodies in the outer solar system. In a specific test of Matthews' hypothesis, poly-HCN fails to match the optical constants of the haze of the Saturnian moon, Titan, in the visible and near-infrared derived from astronomical observations and standard models of the Titan atmosphere. In contrast, a tholin produced from a simulated Titan atmosphere matches within the probable errors. Poly-HCN is much more N-rich than Titan tholin.

Optics↗
NASA NTRS1974

Techniques for carrying out radiative transfer calculations for the Martian atmospheric dust

A description is given of the modification of a theory on the reflectance of particulate media so as to apply it to analysis of the infrared spectra obtained by the IRIS instrument on Mariner 9. With the aid of this theory and the optical constants of muscovite mica, quartz, andesite, anorthosite, diopside pyroxenite, and dunite, modeling calculations were made to refine previous estimates of the mineralogical composition of the Martian dust particles. These calculations suggest that a feldspar rich mixture is a very likely composition for the dust particles. The optical constants used for anorthosite and diopside pyroxenite were derived during this program from reflectance measurements. Those for the mica were derived from literature reflectance data. Finally, a computer program was written to invert the measured radiance data so as to obtain the absorption coefficient spectrum which should then be independent of the temperature profile and gaseous component effects.

Aronson, J. R.↗
NASA NTRS2002

Toward an Improved Single-Particle Model for Large Irregular Grains

To interpret remote spectral observations, scattering and absorption in a particulate surface are simulated via radiative transfer models. The standard model for this purpose among the planetary science community is the Hapke model. This model (like many others) uses two parameters to characterize the optical behavior of individual grains in a particulate surface, the single-scattering albedo omega and phase function p(g). These terms describe, respectively, the quantity and the angular distribution of light scattered by an individual grain. Unfortunately, these parameters are strictly optical. They can be rather difficult to interpret in terms of more interesting particle properties such as grain sizes, shapes, and compositions, that a remote sensing experiment might seek to discover. An equivalent slab approximation is typically used to relate omega to the grain size and optical constants of the material. This approach can mimic the wavelength-dependent absorption behavior of irregular grains, as long as the imaginary index kappa is much less than 1, the shape is equant, and the grain size D is much larger than the wavelength lambda. Unfortunately, the equivalent slab approach provides no information about p(g), which also has a strong dependence on optical constants and particle form.

Grundy, W. M.↗
NASA NTRS1991

Temperature dependence of optical properties of GaAs

The effect of temperature on the optical properties of GaAs was investigated using spectroscopic ellipsometry measurements, between room temperature and about 610 C in increments of 50 C, of pseudodielectric functions and related optical constants of GaAs. A quantitative analysis of the pseudodielectric function spectrum was carried out using a harmonic-oscillator approximation (HOA) to fit the measured dielectric functions. Good fits were obtained with this model, which provides a convenient means of reproducing the GaAs dielectric function at any temperature, by using the temperature-dependent oscillator parameters. The HOA analysis also provides information about band-gap variation with temperature. Using the measured optical constants at a number of fixed temperatures, an algorithm was developed for computing the dielectric function spectrum at an arbitrary temperature in the range 22-610 C.

Yao, Huade↗