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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Microstructure and Raman Scattering of Cu{sub 2}ZnSnSe{sub 4} Thin Films Deposited onto Flexible Metal Substrates

Cu{sub 2}ZnSnSe{sub 4} thin films are produced by selenizing electrochemically layer-by-layer deposited and preliminarily annealed Cu–Zn–Sn precursors. For flexible metal substrates, Mo and Ta foils are used. The morphology, elemental and phase compositions, and crystal structure of Cu{sub 2}ZnSnSe{sub 4} films are studied by scanning electron microscopy, X-ray spectral microanalysis, X-ray phase analysis, and Raman spectroscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Features of Defect Formation in Nanostructured Silicon under Ion Irradiation

Nanostructured silicon is irradiated by Si{sup +} and He{sup +} ions with energies of 200 and 150 keV, respectively. Destruction of the structure of irradiated samples and the accumulation of defects at different irradiation fluences are investigated by Raman scattering. It is shown that single-crystal silicon films are amorphized under irradiation at 0.7 displacements per atom. However, at 0.5 displacements per atom, porous silicon does not completely amorphize and the Raman spectra contain a weak signal of the amorphous silicon phase along with a pronounced signal of the crystalline silicon phase. The size of nanocrystals in the structure of porous silicon at different irradiation fluences is estimated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Raman Scattering in AlN Crystals Grown by Sublimation on SiC and AlN Seeds

The Raman-scattering technique is used to analyze the structural quality of bulk AlN crystals grown by sublimation on SiC and AlN seeds. Growth on SiC seeds is conducted with retention of the SiC seed during growth (type 1) and with total evaporation of the SiC seed (type 2). Growth on AlN seeds is conducted in tungsten containers with no graphite parts (type 3). According to the analysis of Raman spectra, the highest quality is inherent in type-3 crystals that exhibit minimal full widths at half maximum of Raman lines. The experimentally observed specific features are defined by differences in the mechanism of growth and by the content of dopant impurities in the crystals grown.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Raman Scattering by Crystals of Rare-Earth Hexaborides with Different Isotopes of Boron

Monocrystals of lanthanum hexaboride LaB{sub 6} containing both natural boron and its isotopes {sup 10}B and {sup 11}B have been produced using the solution-melt method. Polyelement hexaboride rare-earths have been grown and the corresponding ceramics have been synthesized for the first time. All these crystals have been studied by means of various techniques, generally using Raman scattering. The Raman spectra attributed to various spectral lines corresponding to nonanalyzable representations have been obtained and interpreted. Frequencies and half-widths of spectral lines have been obtained, the removal of degeneracy and the development of respective splitting of degenerate oscillations induced by defects, mainly by boron isotope inclusions, have been identified. The influence of defects on the Raman spectra has been determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Energy Structure of an Individual Mn Acceptor in GaAs : Mn

The energy structure of the Mn acceptor, which is a complex of Mn{sup 2+} ion plus valence band hole, is investigated in the external magnetic field and under presence of an uniaxial stress has been studied. The spin-flip Raman spectra are studied under resonant excitation of exciton bound to the Mn acceptor. The gfactors of the ground F = 1 and the first excited F = 2 states are determined and selection rules for the optical transitions between the acceptor states are described. The value of the random field (stress or electric field) acting on manganese acceptor and the deformation potential for the exchange interaction constant of the Mn{sup 2+} + hole complex are obtained. A theoretical model is developed that takes into account the influence of random internal and uniaxial external stress and magnetic field. The proposed model describes well the lines of spin-flip Raman scattering of Mn acceptor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ab initio Calculations of Phonon Dispersion in CdGa{sub 2}S{sub 4}

Abstract—The phonon spectrum of CdGa{sub 2}S{sub 4} has been experimentally investigated by Raman spectroscopy and theoretically analyzed using the density functional theory (DFT). Eleven active Raman modes (at 83, 135, 165, 219, 243, 260, 310, 322, 352, 361, and 392 cm{sup –1}) have been detected and identified. The identification of all vibrational modes is based on consideration of the point symmetry group. The results are compared with the existing experimental IR spectroscopy and Raman scattering data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Spatiotemporal imaging and manipulation of surface plasmons

Abstract Surface plasmon polaritons (SPPs) are travelling surface waves that have shown promise for applications in nanophotonics as they provide a direct route toward photon-mediated electrical signal generation – a central paradigm for speeding up and scaling down photonic elements. SPP waves have also generated fundamental interest due to their high-field strength and sub-wavelength confinement, properties that have enabled the surface-enhanced Raman effect. Over the last decade, photoemission electron microscopy (PEEM) has emerged as a pioneering technique for imaging surface electric fields through ultrashort laser pulse mediated electron emission and has therefore become an indispensable tool for characterizing plasmonic phenomena at interfaces in a variety of materials. PEEM offers nanometer spatial resolution and femtosecond temporal resolution, allowing SPPs to be prepared, monitored, and manipulated on the nanometer-femtosecond scale. Through a brief review of recent reports, we aim to introduce PEEM-based SPP imaging and manipulation modalities and highlight their utility in the context of emerging nanoscale and quantum materials science advancements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

A PROFILE ANALYSIS OF RAMAN-SCATTERED O VI BANDS AT 6825 Å AND 7082 Å IN SANDULEAK’S STAR

We present a detailed modeling of the two broad bands observed at 6825 and 7082 Å in Sanduleak’s star, a controversial object in the Large Magellanic Cloud. These bands are known to originate from Raman scattering of O vi λ λ 1032 and 1038 photons with atomic hydrogen and are only observed in bona fide symbiotic stars. Our high-resolution spectrum obtained with the Magellan Inamori Kyocera Echelle spectrograph at the Magellan-Clay Telescope reveals, quite surprisingly, that the profiles of the two bands look very different: while the Raman 6825 Å band shows a single broad profile with a redward extended bump, the Raman 7082 Å band exhibits a distinct triple-peak profile. Our model suggests that the O vi emission nebula can be decomposed into a red, blue, and central emission region from an accretion disk, a bipolar outflow, and a further compact, optically thick region. We also perform Monte Carlo simulations with the aim of fitting the observed flux ratio F (6825)/ F (7082) ∼ 4.5, which indicates that the neutral region in Sanduleak’s star is characterized by the column density N{sub Hi} ∼ 1 × 10{sup 23} cm{sup −2}.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1974

Instrumentation for airbreathing propulsion; Proceedings of the Symposium, U.S. Naval Postgraduate School, Monterey, Calif., September 19-21, 1972

New developments and refinements in measuring techniques used for both ground testing and in-flight control, diagnosis, and monitoring of airbreathing combustors are analyzed in a number of papers. Some of the techniques studied include the application of laser velocimeters for flow measurements; on-the-shaft data systems for rotating engine components; total pressure averaging in pulsating flows; fiber optic and laser digital pressure transducers; holography of nozzles, jets, and spraying systems; application of the Raman effect fo flowfield diagnostics; holography of JP-4 droplets and combusting boron particles; the use of a laser-powered optical proximity probe in advanced turbofan engine development; pyrometry for measurement of surface temperature distribution on a rotating turbine blade; an ultrasonic turbine inlet gas temperature sensor; automatic detection and suppression of inlet buzz; and electrostatic probes for sensing incipient engine failure. Individual items are announced in this issue.

Fuhs, A. E.↗
NASA NTRS1981

On the Rayleigh-scattering optical depth of the atmosphere

It is pointed out that revised Rayleigh-scattering optical depths published by Hoyt (1977) are not correct, because King's (1923) formula, which was used by Hoyt, requires that the rotational lines be included in the polarization measurement. To exclude them is to exclude the contribution of the Raman-shifted photons to the total molecular extinction. Hoyt's error was repeated by Froehlich and Shaw (1980), who also confused the depolarization for natural light with that for (polarized) laser light. In an effort to clarify basic concepts, attention is given to the origin of the depolarization correction, depolarization ratios, vibrational Raman effects, and extinction measurements.

Young, A. T.↗
NASA NTRS1990

Progress of research on water vapor lidar

Research is described on several aspects of stimulated Raman scattering (SRS) of 532 nm laser light in H2, D2, and CH4. The goals of this work are to develop a more thorough understanding of nonlinear processes involving the Raman effect and four-wave mixing, and to find the best way to generate radiation at several wavelengths simultaneously, for lidar applications. Issues addressed are conversion efficiency, optimization of operating conditions (gas pressure, confocal parameter, etc.) and the distribution of output pulse energy over three Stokes components, the first anti-Stokes component, and the zeroth order (pump) wavelength. The described research and results constitute another step in the development of SRS applications for NASA's atmospheric lidar program.

Wilkerson, T. D.↗
DOE OSTI2015

Raman parametric excitation effect upon the third harmonic generation by a metallic nanoparticle lattice

This work is a theoretical study on third harmonic generation in the nonlinear propagation of an intense laser pulse through a periodic three-dimensional lattice of nanoparticles. Using a perturbative method, the nonlinear equations that describe the laser–nanoparticle interaction in the weakly relativistic regime are derived. Additionally, the nonlinear dispersion relation and the amplitude of the third harmonic are obtained. Finally, the effects of the nanoparticle radius and separation length, the distribution of the nanoparticle electron density, and the laser frequency upon the third harmonic efficiency are investigated. In addition to the expected resonance that occurs when the third harmonic resonates with the plasmon wave, another resonance appears when the nonlinear interaction of the fundamental mode with the third harmonic excites a longitudinal collective plasmon wave via the parametric Raman mechanism.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Thermal effects on the Raman phonon of few-layer phosphorene

Two-dimensional phosphorene is a promising channel material for next generation transistor applications due to its superior carrier transport property. Here, we report the influence of thermal effects on the Raman phonon of few-layer phosphorene formed on hafnium-dioxide (HfO{sub 2}) high-k dielectric. When annealed at elevated temperatures (up to 200 °C), the phosphorene film was found to exhibit a blue shift in both the out-of-plane (A{sup 1}{sub g}) and in-plane (B{sub 2g} and A{sup 2}{sub g}) phonon modes as a result of compressive strain effect. This is attributed to the out-diffusion of hafnium (Hf) atoms from the underlying HfO{sub 2} dielectric, which compresses the phosphorene in both the zigzag and armchair directions. With a further increase in thermal energy beyond 250 °C, strain relaxation within phosphorene eventually took place. When this happens, the phosphorene was unable to retain its intrinsic crystallinity prior to annealing, as evident from the broadening of full-width at half maximum of the Raman phonon. These results provide an important insight into the impact of thermal effects on the structural integrity of phosphorene when integrated with high-k gate dielectric.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effects of large laser bandwidth on stimulated Raman scattering instability in underdense plasma

The effects of laser bandwidth on stimulated Raman scattering (SRS) instability in underdense plasma are studied by particle-in-cell simulations. In the simulations, sinusoidal frequency modulation of the incident laser pulse is used. By changing the size of bandwidth, it is shown that the linear growth of SRS can be suppressed considerably, provided the laser bandwidth is much larger than the SRS linear growth rate. Simulations also show that by choosing the proper frequency modulation parameters or decreasing the linear growth rate of SRS, the inhibitory effects become more obvious. The plasma electron temperature tends to weaken the bandwidth effects especially when it is over a keV level. The laser bandwidth can only increase the time duration for linear growth but cannot diminish the instability completely.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Nonlinear models for coupling the effects of stimulated Raman scattering to inertial confinement fusion codes

Laser plasma instabilities (LPI) reduce driver-target coupling, alter implosion symmetry, and therefore can fundamentally limit fusion performance in inertial confinement fusion (ICF). Developing a predictive modeling capability for LPI effects can critically advance the success of the field. We perform vector particle-in-cell simulations of multi-speckled laser beams undergoing stimulated Raman scattering (SRS) at various densities and intensities relevant to mainly indirectly driven and a subset of parameter space for directly driven ICF systems, focusing on the regimes with intensities above the onset of electron trapping. Based on the wavenumber of the SRS daughter electron plasma wave, we identify several regions with underpinning SRS saturation physics: the electron-trapping dominated region with intermediate kλD values, the strong Landau damping region at larger kλD values, and the region where the Langmuir decay instability arises at lower kλD values. We develop a nonlinear SRS reflectivity model that features the base trapping-dominated scaling of (kλD)−4 and its modifications. Electron trapping deforms the initialized electron distribution functions, and we have developed a new δf-Gaussian-mixture algorithm for an accurate characterization of the trapped hot electron population. With this SRS hot electron description, we construct a nonlinear energy deposition model and a hot electron source model—based on a modified Manley–Rowe relation—suitable for including SRS effects as a sub-grid module in a high-fidelity ICF design code.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1984

Collisional narrowing effects in the Raman Q-branch spectral profiles of N2, CO, and NO

A description is presented of coherent Raman spectroscopic studies of N2, CO, and NO molecules. It is pointed out that the Q-branch Raman spectra of these simple diatomics are characterized by lines which overlap with increasing pressure as a result of collisional line broadening. Attention is given to Q-branch vibrational spectra and their determination, the spectral line shape of isolated lines, the line overlap regime, fitting laws, and the isotropic Raman spectrum of NO. It is found that the room temperature spectra of the considered molecules at low pressure (approximately 0.2 atm) may be treated as a sum of isolated lines. It is possible to extract J-dependent pressure-broadening coefficients. With increasing pressure, collisional narrowing occurs and the description of the spectrum must include the effects of interference among neighboring lines.

Hurst, W. S.↗