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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Mapping Organic-Mineral Associations in Jezero crater

The search for potential signs of life on Mars, a primary aim of the Mars 2020 mission, is greatly informed by the detection of organic matter1. The presence of organic matter also provides key information about the habitability and biological potential of the planet throughout its history. The Perseverance rover was designed for in situ science with the ability to collect a suite of promising samples for eventual return to Earth. One of its instruments, Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC), is a deep ultraviolet (DUV) Raman and fluorescence spectrometer designed to map the distribution of organic molecules and minerals on rock surfaces at a resolution of 100 μm2. With its unique spectral mapping capabilities, SHERLOC enables a novel understanding of organic-mineral relationships on Mars to better determine their formation, deposition, and preservation mechanisms. The rover’s landing site within Jezero crater combines a high potential for past habitability as the site of an ancient lake basin with a diverse set of minerals, including carbonates and clays, that may preserve organic materials and potential biosignatures. The Jezero crater floor includes three formations (fm); two of these, Máaz and Séítah, were explored as part of the mission’s first campaign. Here, we report the detection of multiple species of aromatic organic molecules using Raman and fluorescence spectroscopy across ten targets in the two formations. This is the first evidence of organic molecules in Martian materials obtained using Raman spectroscopy, and among the first using fluorescence spectroscopy, beyond Earth3. We report specific spatial patterns and classes of organic molecules in these compositionally distinct formations, potentially indicating different fates of carbon in these environments. Our findings indicate that there is a diversity of aromatic molecules prevalent on the Martian surface and these materials persist despite exposure to surface conditions. These organic molecules are largely found within minerals linked to aqueous processes, suggesting that these processes may have had a key role in organic synthesis, transport from their point of origin, or preservation.

Sunanda Sharma↗
NASA NTRS2007

Ring-Down Spectroscopy for Characterizing a CW Raman Laser

.A relatively simple technique for characterizing an all-resonant intracavity continuous-wave (CW) solid-state Raman laser involves the use of ring-down spectroscopy. As used here, characterizing signifies determining such parameters as threshold pump power, Raman gain, conversion efficiency, and quality factors (Q values) of the pump and Stokes cavity modes. Heretofore, in order to characterize resonant-cavity-based Raman lasers, it has usually been necessary to manipulate the frequencies and power levels of pump lasers and, in each case, to take several sets of measurements. In cases involving ultra-high-Q resonators, it also has been desirable to lock pump lasers to resonator modes to ensure the quality of measurement data. Simpler techniques could be useful. In the present ring-down spectroscopic technique, one infers the parameters of interest from the decay of the laser out of its steady state. This technique does not require changing the power or frequency of the pump laser or locking the pump laser to the resonator mode. The technique is based on a theoretical analysis of what happens when the pump laser is abruptly switched off after the Raman generation reaches the steady state. The analysis starts with differential equations for the evolution of the amplitudes of the pump and Stokes electric fields, leading to solutions for the power levels of the pump and Stokes fields as functions of time and of the aforementioned parameters. Among other things, these solutions show how the ring-down time depends, to some extent, on the electromagnetic energy accumulated in the cavity. The solutions are readily converted to relatively simple equations for the parameters as functions of quantities that can be determined from measurements of the time-dependent power levels. For example, the steady-state intracavity conversion efficiency is given by G1/G2 1 and the threshold power is given by Pin(G2/G1)2, where Pin is the steady-state input pump power immediately prior to abrupt switch-off, G1 is the initial rate of decay of the pump field, and G2 is the final rate of decay of the pump field. Hence, it is possible to determine all the parameters from a single ring-down scan, provided that the measurements taken in that scan are sufficiently accurate and complete.

Matsko, Andrey↗
NASA NTRSDate not supplied

Algorithmic Classification of Raman Spectra Biosignatures: Improving Life Detection Confidence

“Agnostic” biosignatures – indicators of life (or the absence of life), independent of a particular biochemistry – are increasingly considered a high standard for life detection. The Ladder of Life Detection (2018) called for investigating how combinations of independent and different potential biosignatures affect confidence. To address this gap, statistical classification of elemental abundances, isotopic fractionation, and reflectance spectroscopy (VNIR) has been implemented. Raman spectroscopy, highly desirable due to its wide availability, has the potential to improve this predictive power. This work implemented biosignature classification algorithms on Raman data alone, in preparation for combination with the other data types. Raman spectroscopy data was collected from published databases and papers as part of a manually curated dataset of “indicative” and “non-indicative of life” samples. These currently include 61 non-indicative samples (meteorites, magnetite); 3 indicative living samples (bacteria); 20 indicative non-living samples (chalk, bone); and 12 indicative mixed (with non-indicative material) samples (soil, microbial mats). Laboratory work is ongoing to characterize additional samples, particularly a greater breadth of mixed systems. Spectra were interpolated, filtered with the Savitzsky-Golay filter, and de-noised. For a preliminary examination, agnostic features were manually extracted including mean intensity, number of peaks, and mean peak width. Different peak prominences and filtering polynomials were used to refine features. Classification algorithms were implemented: k-nearest neighbors (KNN), logistic regression (LR), linear support vector machines (SVM), random forest (RF), Gaussian naïve bayes (GNB). Lastly, Monte Carlo simulations on 1,000 50%-train-test-splits were used to validate classification performance and feature significance. The preliminary feature set achieved its highest AUC of 0.52 with LR, with no strongly discriminatory features. Work to improve feature extraction, such as through deep learning with back propagation, is planned. In future work, the Raman data will be combined with the other data types, and potentially new data types such as enantiomeric excess. This project was partially supported through the NASA Ames Project EXcellence (APEX) incubator program.

Astrobiology↗
NASA NTRS2005

Analysis of Black Bearing Balls from a Space Shuttle Body Flap Actuator

A significantly deteriorated ball bearing mechanism from a body flap actuator on Space Shuttle OV-103 was disassembled and the balls submitted for analysis in conjunction with Return to Flight activities. The OV-103 balls, referred to as the "black balls", were subjected to X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) and Raman micro spectroscopy, surface profilometry, and optical and electron microscopy. The spectroscopic results in combination with microscopy analysis allowed a determination of the lubricant degradation pathway. The chemical attack mechanism does not adequately explain the unique visual appearance of the black balls. Numerous efforts have unsuccessfully focused on duplication of the phenomena causing this unique surface structure and appearance of the black balls. Further detail will be presented supporting these conclusions along with plausible explanations of the unique black appearance to the balls.

Sovinski, Marjorie F.↗
NASA NTRS1988

Laser Diagnostics for combustion temperature and species measurements

Laser optical diagnostic techniques for the measurement of combustion gaseous-phase temperatures and, or species concentrations are discussed. The techniques fall into two classes: incoherent (Rayleigh scattering, spontaneous Raman scattering, laser induced fluorescence spectroscopy) and coherent (coherent anti-Stokes Raman spectroscopy). The advantages, disadvantages and applicability of each method are outlined.

Eckbreth, Alan C.↗
NASA NTRS2017

Rotational Raman-Based Temperature Measurements in a High-Velocity Turbulent Jet

Spontaneous rotational Raman scattering spectroscopy is used to acquire the first ever high quality, spatially-resolved measurements of the mean and root mean square (rms) temperature fluctuations in turbulent, high-velocity heated jets. Raman spectra in air were obtained across a matrix of radial and axial locations downstream from a 50 mm diameter nozzle operating from subsonic to supersonic conditions over a wide range of temperatures and Mach numbers, in accordance with the Tanna matrix frequently used in jet noise studies. These data were acquired in the hostile, high noise (115 dB) environment of a large scale open air test facility at NASA Glenn Research Center (GRC). Temperature estimates were determined by performing nonlinear least squares fitting of the single shot spectra to the theoretical rotational Stokes spectra of N2 and O2, using a custom in-house code developed specifically for this investigation. The laser employed in this study was a high energy, long-pulsed, frequency doubled Nd:YAG laser. One thousand single-shot spectra were acquired at each spatial coordinate. Mean temperature and rms temperature variations were calculated at each measurement location. Excellent agreement between the averaged and single-shot temperatures was observed with an accuracy better than 2.5 percent for temperature, and rms variations in temperature between +/-2.2 percent at 296 K and +/-4.5 percent at 850 K. The results of this and planned follow-on studies will support NASA GRC's development of physics-based jet noise prediction, turbulence modeling and aeroacoustic source modeling codes.

Randy J Locke↗
NASA NTRS2017

Rotational Raman-Based Temperature Measurements in a High-Velocity Turbulent Jet

Spontaneous rotational Raman scattering spectroscopy is used to acquire the first ever high quality, spatially-resolved measurements of the mean and root mean square (rms) temperature fluctuations in turbulent, high-velocity heated jets. Raman spectra in air were obtained across a matrix of radial and axial locations downstream from a 50 mm diameter nozzle operating from subsonic to supersonic conditions over a wide range of temperatures and Mach numbers, in accordance with the Tanna matrix frequently used in jet noise studies. These data were acquired in the hostile, high noise (115 dB) environment of a large scale open air test facility at NASA Glenn Research Center (GRC). Temperature estimates were determined by performing nonlinear least squares fitting of the single shot spectra to the theoretical rotational Stokes spectra of N2 and O2, using a custom in-house code developed specifically for this investigation. The laser employed in this study was a high energy, long-pulsed, frequency doubled Nd:YAG laser. One thousand single-shot spectra were acquired at each spatial coordinate. Mean temperature and rms temperature variations were calculated at each measurement location. Excellent agreement between the averaged and single-shot temperatures was observed with an accuracy better than 2.5 percent for temperature, and rms variations in temperature between +/-2.2 percent at 296 K and +/-4.5 percent at 850 K. The results of this and planned follow-on studies will support NASA GRC's development of physics-based jet noise prediction, turbulence modeling and aeroacoustic source modeling codes.

Randy J Locke↗
NASA NTRS1995

Aggregation-Enhanced Raman Scattering by a Water-Soluble Porphyrin

Much interest in our laboratory has focused on aggregation of organic compounds, particularly cyanine dyes and porphyrins. For this discussion we have applied absorption and Raman scattering spectroscopies to characterize aggregated TSPP (tetrakis-(p-sulfonatophynyl) porphyrin) in aqueous solution. Based on concentration, pH and ionic strength dependence of TSPP absorption, we deduce that aggregation evolves through the formation of TSPP diacid and that the diacid is the repeating unit in the aggregate. The Raman bands of TSPP in strongly acidic solution lead us further to conclude that vibrations of adjacent molecules are perturbed in a fashion that is consistent with the pyrrolic ring in the porphinato macrocycle being ruffled, and that two aggregate arrangements occur: specifically J- and H-type aggregates. Furthermore, aggregation enhancement is advanced as a viable mechanism to explain enhanced Raman Scattering for homogeneous aqueous phase TSPP, where the surface-enhancement mechanism is not applicable.

Akins, Daniel L.↗
NASA NTRS2001

Versatile Vials

Advanced Fuel Research, Inc. (AFR) developed a new sol-gel material coating for sample vials to be used in surface-enhanced Raman (SER) spectroscopy. In the fields of biomedical and forensic science, the coated vials are used to identify physiological chemicals present in blood and urine. The vials are used in the pharmaceutical industry in the area of drug development and discovery. In the drug enforcement field, using the vials helps with detection of trace amounts of drugs on surfaces. The SER vials will also help to identify contaminants in water sources, such as various inorganics and pesticides. The new vials have advantages over other SER materials. Former products required that samples be pre-mixed or dissolved into specific solvents or reagents. The SER vials do not have these limitations, and measurements can be performed using any solvent. Furthermore, the signal appears in less than one second. The sol-gel material will stay active for at least one year and the vials are compatible with any Raman spectrometer. Most importantly, the SER activity can be duplicated from vial-to-vial, allowing for reproducible results.

Source record↗
NASA NTRS1990

Study of diamond film growth and properties

The objective was to study diamond film growth and its properties in order to enhance the laser damage threshold of substrate materials. Calculations were performed to evaluate laser induced thermal stress parameter, R(sub T) of diamond. It is found that diamond has several orders of magnitude higher in value for R(sub T) compared to other materials. Thus, the laser induced damage threshold (LIDT) of diamond is much higher. Diamond films were grown using a microwave plasma enhanced chemical vapor deposition (MPECVD) system at various conditions of gas composition, pressure, temperature, and substrate materials. A 0.5 percent CH4 in H2 at 20 torr were ideal conditions for growing of high quality diamond films on substrates maintained at 900 C. The diamond films were polycrystalline which were characterized by scanning electron microscopy (SEM) and Raman scattering spectroscopy. The top surface of the growing film is always rough due to the facets of polycrystalline film while the back surface of the film replicates the substrate surface. An analytical model based on two dimensional periodic heat flow was developed to calculate the effective in-plane (face parallel) diffusivity of a two layer system. The effective diffusivity of diamond/silicon samples was measured using a laser pulse technique. The thermal conductivity of the films was measured to be 13.5 W/cm K, which is better than that of a type Ia natural diamond. Laser induced damage experiments were performed on bare Si substrates, diamond film coated Si, and diamond film windows. Significant improvements in the LIDT were obtained for diamond film coated Si compared to the bare Si.

Albin, Sacharial↗
NASA NTRS1993

Raman scattering measurements of vibrational and rotational distributions in expanding nitrogen

Vibrational and rotational population distributions in expanding nitrogen in the supersonic nozzle of a reflected shock tunnel were investigated using spontaneous Raman scattering spectroscopy. The experimental data are compared with two multitemperature nonequilibrium calculations, one based on the Landau-Teller model for vibrational relaxation, the other on the solution of the vibrational master equations. Good agreement was found between both the Landau-Teller and the master equation solutions for the vibrational energy mode, but the experimentally inferred rotational temperatures were found to be systematically low, due to collisional narrowing. The dramatic increase in vibrational relaxation rates for a cooling flowfield reported in most previous studies was not reproduced by the present experiments.

Gillespie, Walter D.↗
NASA NTRS1994

Pressure broadening of vibrational Raman lines in N2 at temperatures below 300 K

Using quasi-cw stimulated Raman gain spectroscopy, the pressure broadening coefficients for the N2 vibrational Q-branch transitions have been measured over the temperature range 113-297 K for the rotational components J = 4, 6, 8, 10, and 12. The experimental results are fit to a simple power law to give an empirical formula for the temperature dependence of the pressure broadening over the 100-300 K range. These results are also compared to previously published scaling laws that are based on collision induced rotational transition rates.

Herring, G. C.↗
NASA NTRS1995

Low temperature Zn diffusion for GaSb solar cell structures fabrication

Low temperature Zn diffusion in GaSb, where the minimum temperature was 450 C, was studied. The pseudo-closed box (PCB) method was used for Zn diffusion into GaAs, AlGaAs, InP, InGaAs and InGaAsP. The PCB method avoids the inconvenience of sealed ampoules and proved to be simple and reproducible. The special design of the boat for Zn diffusion ensured the uniformality of Zn vapor pressure across the wafer surface, and thus the uniformity of the p-GaSb layer depth. The p-GaSb layers were studied using Raman scattering spectroscopy and the x-ray rocking curve method. As for the postdiffusion processing, an anodic oxidation was used for a precise thinning of the diffused GaSb layers. The results show the applicability of the PCB method for the large-scale production of the GaSb structures for solar cells.

Sulima, Oleg V.↗
NASA NTRS1996

Trace Element Zoning and Incipient Metamictization in a Lunar Zircon: Application of Three Microprobe Techniques

We have determined major (Si, Zr, Hf), minor (Al, Y, Fe, P), and trace element (Ca, Sc, Ti, Ba, REE, Th, U) concentrations and Raman spectra of a zoned, 200 microns zircon grain in lunar sample 14161,7069, a quartz monzodiorite breccia collected at the Apollo 14 site. Analyses were obtained on a thin section in situ with an ion microprobe, an electron microprobe, and a laser Raman microprobe. The zircon grain is optically zoned in birefringence, a reflection of variable (incomplete) metamictization resulting from zo- nation in U and Th concentrations. Variations in the concentrations of U and Th correlate strongly with those of other high-field-strength trace elements and with changes in Raman spectral parameters. Concentrations of U and Th range from 21 to 55 ppm and 6 to 31 ppm, respectively, and correlate with lower Raman peak intensities, wider Raman peaks, and shifted Si-O peak positions. Concentrations of heavy rare earth elements range over a factor of three to four and correlate with intensities of fluorescence peaks. Correlated variations in trace element concentrations reflect the original magmatic differentiation of the parental melt approx. 4 b.y. ago. Degradation of the zircon structure, as reflected by the observed Raman spectral parameters, has occurred in this sample over a range of alpha-decay event dose from approx. 5.2 x 10(exp 14) to 1.4 x 10(exp 15) decay events per milligram of zircon, as calculated from the U and Th concentrations. This dose is well below the approx. 10(exp 16) events per milligram cumulative dose that causes complete metamictization and indicates that laser Raman microprobe spectroscopy is an analytical technique that is very sensitive to the radiation-induced damage in zircon.

Wopenka, Brigitte↗
NASA NTRS1998

Advanced Non-Intrusive Instrumentation for Propulsion Engines

Changes in engine technology such as higher temperatures, higher tip speeds, new metal/composite/ceramic materials together with radical changes in design philosophy will require amongst other prerequisites the ability to measure and to monitor key internal gas and structural characteristics. The symposium papers presented non-intrusive measurement and analysis technologies in the following categories: Laser Point Measurements (11); Absorption and Infrared Techniques (4); Paints - Surface Sensors (6); Laser Induced Fluorescence (6); Mechanical (7); Films (5); Laser Planar Measurement (9); and a Keynote Address.

Propulsion↗
NASA NTRS2003

Investigarion of the effects of a quantum dot crystal geometry on its brillouin spectrum

We develop a theoretical model and carry out simulation of Brillouin spectrum of three-dimensional (3D) quantum dot (QD) arrays with a high order of 3D periodicity, i.e. quantum dot crystals (QDC). The phonon spectrum of Ge/Si QDC is found from the numerical solution of the elasticity equation for the whole structure. The developed approach is valid for any QD shape and regimentation and allows to include disorder in consider at ion.

quantum dot arrays quantum dot crystal raman spect↗