Engineering Papers⌕ Search

SEARCH · Engineering Papers

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.

At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Optical Properties of Copper-Doped Lithium Niobate Crystals

We have studied the optical properties of copper-doped lithium niobate crystals using semiconductor light-emitting diodes and lasers emitting in the visible and ultraviolet spectral regions as excitation sources. The results demonstrate that, at an excitation frequency approaching the frequency of electronic absorption in copper ions, there is discrete resonance Raman scattering in the form of a frequency comb. The observed Raman satellites of discrete light scattering are due to polar longitudinal A{sub 1} optical modes of the lithium niobate single crystal. Under excitation by a light-emitting diode with a wavelength of 520 nm, we observe a sharp increase in discrete light scattering intensity in comparison with the photoluminescence excited by shorter wavelength excitation sources.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Remote Sensing of Hydrogen Sulfide Molecules in the Atmosphere by a Raman Lidar from Space

The results of numerical solution of the lidar equation for Raman scattering of light by molecules of hydrogen sulphide in the direction of 180° under detecting molecules of hydrogen sulfide in the atmosphere with concentration at a level of 1016 cm{sup –3} from a platform in space at heights of the order of hundreds of kilometers in the synchronous photon counting mode have been presented. It is shown that, for such a variant of a lidar and level of concentration of the investigated molecules, the duration of measurement at a wavelength of the laser radiation of 405 nm and altitude range of 100–600 km lies in the range of 0.14–4.9 s. The development of new schemes of lidars opens up additional possibilities for remote detection of low concentrations of hydrogen sulfide molecules from space.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Thermalization of Photons in a Microcavity

A theoretical interpretation of the spectral condensation of photons in a microcavity based on solution of kinetic equations describing photon-gas thermalization as a result of Raman scattering from an atomic-gas thermostat is proposed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

On Precision Measurement of the Frequency of the 1{sup 1}S–2{sup 3}S Forbidden Transition of a Helium Atom

The possibility is demonstrated of a precision frequency measurement for the 1{sup 1}S{sub 0}−2{sup 3}S{sub 1} forbidden transition (at 62.6 nm) of a helium atom using the stimulated Raman scattering method. The 1{sup 1}S{sub 0} singlet state is the ground state of {sup 4}He, while the metastable 2{sup 3}S{sub 1} state has the lowest energy in the triplet part of the spectrum ({sup 4}He*). The transition has a very small natural width, which allows us to consider it as a possible reference for creation of a frequency standard in the vacuum ultraviolet region.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Enhancement of Fluorescence and Raman Scattering in Cyanine-Dye Molecules on the Surface of Silicon-Coated Silver Nanoparticles

A method of formation of a composite structure based on silver nanoparticles and a thin protective silicon film (AgNPs/Si) is developed. Enhancement of the fluorescence and Raman scattering in cyaninedye molecules deposited onto the formed nanostructure is observed. The optical properties and morphology stability of particles that are in contact with cyanine-dye solutions in organic solvents are studied. It is shown that the AgNPs/Si composite structure can be multiply used as an SERS-active surface.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Withdrawal of Electrodynamical Forbiddance and Peculiarities of the SERS Spectra in Fullerene C{sub 70}

It is demonstrated that in fullerene C{sub 70}, which can be considered as a deformed fullerene C{sub 60} in some mean sense there is a withdrawal of an Electrodynamical forbiddance of a strong quadrupole light-molecule interaction, which is realized in the fullerene C{sub 60}. This situation occurs because of the reduction of symmetry of C{sub 60} from the icosahedral symmetry group Y{sub h} to the group D{sub 5h}. The withdrawal results in appearance of the lines in the SERS spectra of C{sub 60}, which are forbidden in usual Raman scattering and are active in the infrared absorption spectra. The experimentally measured SERS spectra of C{sub 70} demonstrates existence of such lines that strongly confirms our ideas about the dipole-quadrupole SERS mechanism.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Optical Properties of Nonstoichiometric Tantalum Oxide TaO{sub x} (x < 5/2) According to Spectral-Ellipsometry and Raman-Scattering Data

Optical properties of amorphous nonstoichiometric tantalum-oxide films of variable composition (TaO{sub x}, x = 1.94–2.51) in the spectral range of 1.12–4.96 eV, obtained by ion-beam sputtering-deposition of metallic tantalum at different partial oxygen pressures (0.53–9.09 × 10{sup –3} Pa), have been investigated. It is shown by spectral ellipsometry that the character of dispersion of the absorption coefficient and refractive index in TaO{sub x} of variable composition suggests that light-absorbing films with dispersion similar to that in metals are formed at oxygen pressures in the growth chamber below 2.21 × 10{sup –3} Pa, whereas transparent films with dielectric dispersion are formed at pressures above 2.81 × 10{sup –3} Pa. According to the data of quantumchemical simulation, the absorption peak at a photon energy of 4.6 eV in TaO{sub x} observed in the absorptioncoefficient dispersion spectrum is due to oxygen vacancy. The peak in the Raman-scattering spectra of TaO{sub x} films with metallic dispersion at frequencies of 200–230 cm{sup –1} is presumably related to tantalum nanoclusters.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Photochromic Properties and Surface Enhanced Raman Scattering Spectra of Indoline Spiropyran in Silver-Based Nanocomposite Films

The structure and photochromic transformations of composite organometallic nanosystems composed of Ag nanoparticles covered with a layer of indoline-spiropyran (ISP) molecules from solutions were studied by spectrophotometry, surface Raman scattering spectroscopy (SERS) and quantum chemistry. Analysis of experimental data showed that studied nanostructured systems have photochromic properties, manifested in the reversible photo-induced changes both of the electronic-absorption spectra and of the relative intensity of the SERS bands. The open form of ISP, formed in the organometallic nanostructured film as a result of photochromic transformations, has an adsorption geometry, and, possibly, a conformation different from that formed as a result of chemisorption of ISP molecules on silver colloids.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Quasi-Elastic Light Scattering in Congruent Lithium Niobate Crystals

Raman scattering spectra in the frequency range of 5–75 cm{sup –1} in lithium niobate samples with various structural imperfections were obtained. It is shown that the intensity of quasi-elastic light scattering on the wing of the Rayleigh line demonstrates an exponential dependence on the concentration of large-scale defects in the samples. Calibration curves for the intensity of quasi-elastic scattering dependence at low frequencies on the acoustic quality factor are constructed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Polarized Raman Scattering in Silicon Layers on Sapphire

The intensities of polarized components of Raman light scattering are measured for different crystallographic directions in epitaxial layers of silicon on sapphire. The experiment shows that the scattered radiation has a strong depolarized component, which is directly related to the occurrence of defects in the epitaxial layer. A model of an ensemble of crystallites is proposed to describe a defect crystal silicon layer on sapphire. It is shown that the characteristic value of disordering of crystalline domains in the epitaxial layer can be determined from the ratio between the intensities of the polarized and depolarized components. From measurements of the Raman scattering intensity as a function of the crystallographic direction, the anisotropy of the Raman scattering tensor is determined. Numerical values for two samples are obtained.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Rapid Preparation of Large-Area Densely Packed Plasmonic Hot-Spots for Reliable Sers Sensing

A facile, efficient and time-saving strategy is proposed to obtain large-area and reliable surface-enhanced Raman scattering (SERS) substrates via artificial heat-treatment of Au nanoparticles or ultrathin Au films sputtered on the silica substrates. Excellent Raman enhancements with the detection limitation down to 10{sup –9} mol/L are obtained due to the highly-dense plasmonic hot-spots and strong plasmons near-field coupling. Decreased intensity of Raman peaks with the increased sputtering time of Au nanoparticles or ultrathin films mainly originates from the excited and hybridized coupling of multiple surface plasmons. The simple fabrication strategy and superior performance make these substrates promising candidates for the development of inexpensive and reliable SERS substrates.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Dependence of the surface topology and raman scattering spectra of Ge{sub x}Si{sub 1-x}/Si films on the composition variation over the layer thickness

The surface topology and Raman scattering spectra of Ge{sub x}Si{sub 1-x}/Si(100) films are investigated in dependence of the composition variation over the film thickness. It is shown that the character of the Ge content variation in the Ge{sub x}Si{sub 1-x} alloy at the constant cumulative Ge fraction in the film (x{sub int} = 0.5) affects the surface morphology of the grown Ge{sub x}Si{sub 1-x}/Si layer. The heterostructures were grown by molecular-beam epitaxy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Computer simulation of surface-enhanced Raman scattering in nanostructured metamaterials

The simulation of local field fluctuations and surface-enhanced Raman scattering in percolation systems at the percolation threshold is described. An approximate real-space renormalization group method was used in the simulation. It allows one to radically reduce the computation time compared to an exact calculation and to obtain detailed information about the electromagnetic field. The local fields in real macroscopic systems can be calculated by using this approximation. A computer simulation of the local fields in metal island (percolation) films has been performed by the developed method. The calculation has confirmed the existence of giant local field fluctuations. In turn, the local electric field excites Raman scattering. The local fields of surface-enhanced Raman scattering have been calculated for the first time. The dependence of the Raman scattering enhancement factor on the reference frequency and Stokes shift has been derived. An experimental observation of this dependence could be considered as a confirmation of the electromagnetic nature of the enhancement.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Dynamics of the order parameter and the potential of the hydrogen bond in a ferroelectric DKDP crystal

Within a pseudospin model of a KD{sub 2}PO{sub 4} crystal, the relaxation time of the average pseudospin (the order parameter) in the mean-field approximation depends on the activation energy of the jump of a deuteron between the minima of the hydrogen bond potential, the average equilibrium value of the pseudospin, and the dielectric susceptibility. Calculating the average equilibrium spin and the susceptibility within the four-particle cluster approximation and fitting the data for the width of the central peak from a Raman scattering experiment, we numerically estimate the activation energy. For the same values of the parameters of the cluster method, the calculated inverse relaxation time is in good agreement with the data of ultrasonic measurements.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Bistability of self-modulation of the GaAs intrinsic stimulated picosecond radiation spectrum

The bistability of self-modulation of the spectrum of the stimulated picosecond radiation that appears during picosecond optical pumping of GaAs is detected. The radiation is measured before it reaches the end faces of a sample. One set of equidistant modes occurs in the radiation spectrum at the radiation pulse front. A set of modes located at the center between the initial modes replaces the first set in the descending radiation branch. The intermode interval inside each set coincides with the calculated interval between the eigenmodes of the GaAs layer, which is an active cavity. The radiation rise time turns out to be an oscillating function of the photon energy. The spectrum evolution is self-consistent so that the time-integrated spectrum and the spectrum-integrated radiation pulse envelope have a smooth (without local singularities) shape. The revealed bistability explains the physical nature of the two radiation-induced states of population depletion between which subterahertz self-oscillations in the radiation field were detected earlier. The radiation spectrum self-modulation is assumed to be a variant of stimulated Raman scattering.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Stimulated Raman scattering in the approximation of unidirectional propagation in a medium with static dipole moments

The evolution equations of two-frequency stimulated Raman scattering in a molecular quasithree- level medium with static dipole moments have been derived in the approximations of the nondepletion of the pump field and the unidirectional propagation of the Stokes field. Completely integrable particular cases of the resulting system of equations have been found. New mechanisms of controlling the parameters of microwave pulses generated in such a system have been studied within this model. The numerical analysis and particular exact solutions demonstrate the possibility of switch between the regimes of generation of narrow Stokes field pulses and nearly rectangular pulses.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Angular dependence of Raman scattering selection rules for long-wavelength optical phonons in short-period GaAs/AlAs superlattices

The angular dependence of Raman scattering selection rules for optical phonons in short-period (001) GaAs/AlAs superlattices is calculated and experimentally studied. Experiments are performed using a micro-Raman setup, in the scattering geometry with the wavevectors of the incident and scattered light lying in the plane of superlattices (so-called in-plane geometry). Phonon frequencies are calculated using the Born model taking the Coulomb interaction into account in the rigid-ion approximation. Raman scattering spectra are calculated in the framework of the deformation potential and electro-optical mechanisms. Calculations show an angular dependence of the selection rules for optical phonons with different directions of the wavevectors. Drastic differences in the selection rules are found for experimental and calculated spectra. Presumably, these differences are due to the Fröhlich mechanism in Raman scattering for short-period superlattices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗