Analysis of the stimulated Raman effects in an anisotropic crystal KDP.
Stimulated Raman effects in anisotropic crystal potassium dihydrogen phosphate with Stokes generations
ANISOTROPIC MATERIAL↗
SEARCH · Search NASA
Results for “RAMAN EFFECT”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
First-principles study of the magneto-Raman effect in van der Waals layered magnets
Magneto-Raman spectroscopy has been used to study spin-phonon coupling in two-dimensional (2D) magnets. Raman spectra of CrI 3 show a strong dependence on the magnetic order within a layer and between the layers. Here we carry out the first systematic theoretical investigation of the magneto-Raman effect in 2D magnets by performing density functional theory calculations and developing a generalized polarizability model. Our first-principles simulations well reproduce experimental Raman spectra of CrI 3 with different magnetic states. The model reveals how the change of spin orientation in each layer is coupled to the layer’s vibration to induce or eliminate the spin-dependent anti-symmetric off-diagonal terms in the Raman tensor for altering the selection rules. We also uncover that the correlation between phonon modes and magnetic orders is a universal phenomenon, which should exist in other phonon modes and 2D magnets. Our predictive simulations and modeling are expected to guide the research in 2D magnets.
36 MATERIALS SCIENCE↗
On probing the outer planets with the Raman effect
The paper examines the feasibility of using the H2 rotational Raman spectrum to study the physical structure of the atmospheres of the outer planets. Computations of the strengths of the S(0) and S(1) lines are made for a wide range of physical conditions on the basis of a semi-infinite homogeneous pure H2 atmospheric model. Initial applications of the Raman probe technique to Jupiter and Uranus are reported.
Price, M. J.↗
Calculating the true line contour of the Raman effect based on the observable line contour
Calculation method for true profile of Raman lines
SPECTRAL LINE↗
Preventing Raman Lasing in High-Q WGM Resonators
A generic design has been conceived to suppress the Raman effect in whispering- gallery-mode (WGM) optical resonators that have high values of the resonance quality factor (Q). Although it is possible to exploit the Raman effect (even striving to maximize the Raman gain to obtain Raman lasing), the present innovation is intended to satisfy a need that arises in applications in which the Raman effect inhibits the realization of the full potential of WGM resonators as frequency-selection components. Heretofore, in such applications, it has been necessary to operate high-Q WGM resonators at unattractively low power levels to prevent Raman lasing. (The Raman-lasing thresholds of WGM optical resonators are very low and are approximately proportional to Q(sup -2)). Heretofore, two ways of preventing Raman lasting at high power levels have been known, but both entail significant disadvantages: A resonator can be designed so that the optical field is spread over a relatively large mode volume to bring the power density below the threshold. For any given combination of Q and power level, there is certain mode volume wherein Raman lasing does not start. Unfortunately, a resonator that has a large mode volume also has a high spectral density, which is undesirable in a typical photonic application. A resonator can be cooled to the temperature of liquid helium, where the Raman spectrum is narrower and, therefore, the Raman gain is lower. However, liquid-helium cooling is inconvenient. The present design overcomes these disadvantages, making it possible to operate a low-spectral-density (even a single-mode) WGM resonator at a relatively high power level at room temperature, without risk of Raman lasing.
Savchenkov, Anatoliy↗
Electron and solid state physics
Electron and solid state physics - reflected light, Raman effects, solid and liquid optical properties, spectroscopy, Brillouin effects, and carbon dioxide laser
BRILLOUIN EFFECT↗
Effects of Raman scattering on the water-leaving radiance
The contribution of Raman scattering to the water-leaving radiance is examined using Monte Carlo simulations. Exit angle information is retained, allowing a comparison of different satellite viewing directions. Chlorophyll values of 0.0, 0.01, 0.1, and 1.0 mg Chl/cu m are simulated. Little directional variability is found, with the exception of the direct solar backscatter direction. The wavelength variability is greatest for low chlorophyll concentrations and is negligible for 1.0 mg Chl/cu m. At 550 nm the Raman contribution ranges from approximately 18% of the total water-leaving radiance for pure water to 3% for 1.0 mg Chl/cu m. At 440 nm the range is from 6% to 2%, indicating that Raman scattering will impact radiance ratios for ocean color satellite algorithms.
Waters, Kirk J.↗
Near-octave lithium niobate soliton microcomb
Thin film lithium niobate (LN) is bringing renewed potential to the realm of integrated photonics. Its strong quadratic and cubic nonlinearities as well as wide transparency window are ideal for realizing on-chip self-referenced soliton microcombs. However, broadband Kerr cavity soliton generation in LN thin films remains challenging due to limited dispersion control and competition from strong stimulated Raman scattering (SRS). Here, we demonstrate the generation of soliton microcombs in LN thin films featuring broad spectral spans up to 4/5 octaves with the emission of dual dispersion waves (2/3 octaves apart) and sub-terahertz repetition rates (down to 335 GHz) by suppressing strong SRS. Numerical simulations based on coupled-mode equations that incorporate Raman effects further elucidate the soliton dynamics in this highly Raman-active material system.
Gong, Zheng (ORCID:0000000301704870)↗
A combined Raman lidar for low tropospheric studies
One of the main goals of laser sensing of the atmosphere was the development of techniques and facilities for remote determination of atmospheric meteorological and optical parameters. Of lidar techniques known at present the Raman-lidar technique occupies a specific place. On the one hand Raman lidar returns due to scattering on different molecular species are very simple for interpretation and for extracting the information on the atmospheric parameters sought, but, on the other hand, the performance of these techniques in a lidar facility is overburdened with some serious technical difficulties due to extremely low cross sections of Raman effect. Some results of investigations into this problem is presented which enables the construction of a combined Raman lidar capable of acquiring simultaneously the profiles of atmospheric temperature, humidity, and some optical characteristics in the ground atmospheric layer up to 1 km height. The operation of this system is briefly discussed.
Arshinov, Y. F.↗
High-Temperature Raman Scattering Study of the Li{sub 2}O–B{sub 2}O{sub 3}–MoO{sub 3} System: I. Detailed Comparison of the Structures of Molten Lithium and Potassium Molybdates
The structure and polymerization behavior of molybdenum–oxygen groups in molten lithium and potassium molybdates with different alkali-metal oxide to molybdenum oxide ratios have been studied by high-temperature Raman spectroscopy. The results are analyzed in comparison with the structural units of pure molybdenum oxide.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
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↗
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↗
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↗
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↗
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↗
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.↗
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.↗