Showing papers on "Brillouin scattering published in 1976"
TL;DR: In this paper, the Brillouin scattering measurements on transparent single crystals at hydrostatic pressures up to 35 kilobars in a gasketed diamond anvil cell were performed.
Abstract: Instrumentation has been developed to conduct Brillouin scattering measurements on small (0.15 mm) transparent single crystals at hydrostatic pressures up to 35 kilobars in a gasketed diamond anvil cell. Phonon velocities obtained this way can be used to calculate elastic moduli as a function of pressure. Results of measurements made on NaCl yield zero‐pressure values of c11=4.82×1011 dyn cm−2, c12=1.28×1011 dyn cm−2, and c44=1.27×1011 dyn cm−2. The plots of the elastic moduli versus pressure are fitted with straight lines with the following slopes: ∂c11/∂P=11.62, ∂c12/∂P=3.05, and ∂c44/∂P=0.759.
277 citations
TL;DR: In this article, the intensity, frequency shift, and linewidth of the longitudinal Brillouin lines have been measured from 4 to 300 K in crystal quartz, fused quartz, and borosilicate glass.
Abstract: The intensity, frequency shift, and linewidth of the longitudinal Brillouin lines have been measured from 4 to 300 K in crystal quartz, fused quartz, and borosilicate glass. Differences in intensity between Stokes and anti-Stokes components have been found, extending to low temperatures the observation of long-lived vibrational states with occupation numbers equal to $({{e}^{\frac{h\ensuremath{
u}}{\mathrm{kT}}}\ensuremath{-}1)}^{\ensuremath{-}1}$. Some anomalies in the frequency dependence of the elastic properties of fused quartz are eliminated. The measurements of the attenuation, which modify previous results between 77 and 300 K, are in good agreement with stimulated Brillouin scattering measurements below 10 K.
74 citations
TL;DR: In this paper, the authors applied the dielectric method to the more concentrated (100, 80, 60%, by volume) solutions over a wide temperature and frequency range (30 Hz to 8 GHz) in order that the variation in activation energy characteristic of a glass-forming substance could be delineated.
Abstract: Dielectric relaxation and Brillouin scattering are jointly used in studying molecular relaxation in poly(propylene oxide) (PPO) and its solutions in methylcyclohexane. The dielectric method was applied to the more concentrated (100%, 80%, 60%, by volume) solutions over a wide temperature and frequency range (30 Hz to 8 GHz) in order that the variation in activation energy characteristic of a glass-forming substance could be delineated. The present work extends previous work on the undiluted polymer to higher frequencies so that range of 12 decades in the dielectric loss maximum fmax as a function of temperature is now available. The “Antoine” equation is found to represent the behavior of log fmax, of the bulk concentrated solutions very well. The more dilute (40%, 20%) solutions were studied only in the high-frequency (GHz) region since phase separation occurred at low temperatures. Both the temperature and dilution effects were interpreted in terms of free-volume theory. Brillouin scattering spectra were obtained at several scattering angles and a wide range of temperatures. A maximum in the curve of hypersonic attenuation versus temperature was observed in each polymer solution. The attenuation maximum shifts toward lower temperature upon dilution, in agreement with the dielectric relaxation result. The Brillouin scattering follows different activation parameters and evidences a more rapid process than does the dielectric relaxation. It is speculated that it monitors a secondary or subglass relaxation, due perhaps, to damped torsional oscillations.
54 citations
TL;DR: In this paper, the authors used a simple relaxation model similar to that used by Boon and Fleury in the case of rare gas liquids, and found a small correction term to the expression of the Landau-Placzek ratio for water near 4°C.
Abstract: High frequency sound propagation in water has been studied by Brillouin scattering in the entire temperature range of −9°C⩽t⩽100°C. Sound speeds deduced from the data show a peak at t≃70°C in agreement with previous ultrasonic results. Damping constants measured in a temperature range −9°C⩽t⩽20°C are also consistent with the ultrasonic values whenever available. A small negative dispersion of sound velocity is found however in the range 0°C⩽t⩽15°C. We explain this by a simple relaxation model similar to that used by Boon and Fleury in the case of rare gas liquids. We also use a theory of Brillouin scattering which takes into account the temperature fluctuation, and find a small correction term to the expression of the Landau–Placzek ratio. The correction term is calculated and is shown to be nonnegligible for water near 4°C. We believe the data taken in the supercooled regime are reported for the first time and their steep temperature dependence is as yet to be understood theoretically.
53 citations
TL;DR: In this article, the spatial distribution of the field in stimulated Brillouin scattering may be a complex conjugate of the laser radiation field, and conditions needed for experimental realization of this effect are given.
Abstract: Methods usually employed in the theory of volume holograms are used to show that the spatial distribution of the field in stimulated Brillouin scattering may be a complex conjugate of the laser radiation field. The conditions needed for experimental realization of this effect are given.
51 citations
TL;DR: In this paper, the Brillouin spectra of the ferroelectric triglycine sulfate (TGS) and its isomorphous selenate (TGSe) crystals have been observed in three cases of orientations of the longitudinal or quasi-longitudinal phonon vector q ; (1) q // c -axis, q // b -axis and q deviates 5° from b-axis in the (100) plane.
Abstract: The Brillouin spectra of the ferroelectric triglycine sulfate (TGS) and its isomorphous selenate (TGSe) crystals have been observed in three cases of orientations of the longitudinal or quasi-longitudinal phonon vector q ; (1) q // c -axis, (2) q // b -axis and (3) q deviates 5° from b -axis in the (100) plane. The temperature dependence of both the frequency shift and the spectral width shows a remarkable anisotropy near T c . In the case (1) the temperature at which the width becomes maximum shifts to the lower temperature than T c which has simultaneously been determined by an accompanied measurement of dielectric constant. The polarization relaxation time is determined from this temperature shift using the phenomenological relation. In the case (2) and the case (3), the decrease in the anomaly is explained as the depolarization field effect of the long range dipole-dipole interaction which is characteristic in the ferroelectric phase transition.
48 citations
43 citations
TL;DR: In this paper, a comparison between theory and experiment is made; the theory includes damping of the acoustic phonons, while the experiment only qualitatively describes the Brillouin scattering of light from highly opaque materials.
Abstract: Brillouin scattering from isotropic metals is investigated experimentally and theoretically. The observation of highly asymmetric Brillouin spectra from liquid mercury and liquid gallium is reported. A comparison is made between theory and experiment; the theory includes the damping of the acoustic phonons. It is found that the present state of the theory only qualitatively describes the Brillouin scattering of light from highly opaque materials. The velocities of sound of mercury and gallium deduced from the measurements are found to be 38% larger than the corresponding values determined by ultrasonic techniques. The observed intensity is at least an order of magnitude larger than the theory predicts, and the line shape, especially in the case of liquid gallium, differs appreciably from the theoretical line shape. The major origin of the discrepancy between theory and experiment is believed to be the simple model employed for the description of the dynamics of the density fluctuations near the surface. The spectra observed may therefore contribute to further understanding of the surface physics of liquid metals.
43 citations
TL;DR: In this paper, the generalized theory by Weinberg, Kapral, and Desai was applied for the first time to analyze the power spectra of C2F6 and C2H6, for which the Mountain theory was inadequate.
Abstract: We have measured the light scattering profiles of CO2, N2, C2F6, and C2H6 at 29 °C in both kinetic and hydrodynamic regimes. The generalized theory by Weinberg, Kapral, and Desai was applied for the first time, we believe, to analyze the power spectra of C2F6 and C2H6, for which the Mountain theory was inadequate. We have also observed the rotational relaxation times of C2H6 and C2F6 and the vibrational relaxation time of the latter.
42 citations
TL;DR: In this article, the temperature dependence of the elastic shear constant C44 of cubic potassium cyanide has been measured by optical Brillouin spectroscopy in the temperature range from 300-168 K.
42 citations
TL;DR: In this article, the effect of the macroscopic electric field on the coupled cage-liquid system was discussed. But the analysis was restricted to the case of a coupled cage liquid system.
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24 Nov 1976TL;DR: In this article, a stimulated Brillouin scattering (SBS) ring laser gyroscope is constructed from a single-mode optical fiber waveguide and is optically coupled to a laser to accommodate being pumped in two directions by laser radiation having sufficient energy to induce SBS.
Abstract: A stimulated Brillouin scattering (SBS) ring laser gyroscope. The SBS laser gyroscope is fabricated from a single-mode optical fiber waveguide and is optically coupled to a laser to accommodate being pumped in two directions by laser radiation having sufficient energy to induce stimulated Brillouin scattering radiation (SBS). The apparatus includes means for extracting a portion of each of the SBS radiation from the single-mode optical fiber waveguide and superimposing the extracted portions to permit detection of a beat frequency therebetween. The beat frequency detected is indicative of the rate of angular rotation of the area circumscribed by the single-mode optical fiber waveguide. Means are provided to accommodate a significant reduction in the required laser pumping power.
TL;DR: In this paper, the authors compared experiment and theory of stimulated Brillouin scattering of high-intensity CO2 laser radiation from underdense hydrogen and helium plasmas, and confirmed the ion acoustic wave as responsible for the backscatter.
Abstract: Results of detailed measurements undertaken to compare experiment and theory of stimulated Brillouin scattering of high‐intensity CO2 laser radiation from underdense hydrogen and helium plasmas are reported. Spectral measurements confirm the ion acoustic wave as responsible for the backscatter. Ion Landau damping and collisions both contribute to spectral broadening. The maximum linear scattering growth rate γk was determined experimentally to be 6×1011 sec−1 in good agreement with a theoretical value calculated from random‐phase wave scattering. The value derived assuming coherent‐wave interaction was 1011 sec−1 which is a factor of 2 greater than the corresponding theoretical prediction. Temporal characteristics and reflectivity of the backscattered radiation are discussed.
TL;DR: In this paper, the authors derive an expression for the lineshape of the Brillouin spectrum of an acoustic phonon in an absorbing material taking account of phonon reflection at the sample boundary.
Abstract: Derives an expression for the lineshape of the Brillouin spectrum of an acoustic phonon in an absorbing material taking account of phonon reflection at the sample boundary. The shape is asymmetric and differs appreciably from that previously used to interpret experimental spectra.
TL;DR: In this article, the stimulated Brillouin scattering from an underdense plasma in a magnetic field was observed, and the observed shifts correspond to those expected from a plasma with the measured temperature.
Abstract: Observations of stimulated Brillouin scattering from an underdense plasma in a magnetic field are reported. The observed shifts correspond to those expected from a plasma with the measured temperature. Scattering with twice the Brillouin shift was observed when the fundamental Brillouin reflectivity approached 5%.
TL;DR: In this paper, the temperature dependence of the C 55 elastic constant of LaP 5 O 14 has been investigated, using Brillouin scattering, between room-temperature and 225°C, across the 126°C ferroelastic phase transition of this material.
TL;DR: In this article, the frequency shift and linewidth of longitudinal Brillouin scattering lines are given in the range of 20-1000°C and the critical index of damping is found equal to 0.8 in the α-phase and 1.9 in the β-phase, respectively.
TL;DR: In this article, the authors verify the finite interaction length threshold for stimulated Brillouin scattering in a plasma with no critical layers and use the time-dependent Stark effect to detect ion-frequency electric fields.
Abstract: Two new results are reported: (1) verification of the finite-interaction- length threshold for stimulated Brillouin scattering in a plasma with no critical layers, and (2) use of the time-dependent Stark effect to detect ion-frequency electric fields in a plasma. (AIP)
TL;DR: The Brillouin spectrum of gelatin gels has been recorded at room temperature as a function of concentration of gelatin, using a double passed Fabry-Perot spectrometer as discussed by the authors.
TL;DR: In this paper, a comprehensive Brillouin scattering experimental study of polypropylene glycol (PPG), average molecular weight of 1025, 2025, and 4000, has been carried out.
Abstract: A comprehensive Brillouin scattering experimental study of polypropylene glycol (PPG), average molecular weight of 1025, 2025, and 4000, has been carried out. The hypersonic velocity, attenuation coefficient, the modulus of elasticity, and the Landau–Placzek ratio have been obtained as a function of temperature for each polymer. The PPG 425 data reported earlier are also included for comparison. For all the quantities measured, only the Laudau–Placzek ratio (below ambient temperature) is molecular weight dependent; the hypersonic velocity, attenuation coefficient, and elastic modulus are found to be independent of molecular weight in the present 425–4000 weight range. The differences in the Landau–Placzek ratio between the different polymers are attributed to different degree of frozen‐in density fluctuations due to the difference in the medium’s viscosity; the mechanism of structural relaxation is not sufficient to explain the increase of the Landau–Placzek ratio of each polymer below ambient temperature...
TL;DR: In this article, nonlinear processes competing with hyper-Raman scattering are discussed and two lines corresponding to the transverse and longitudinal optic phonons at the centre of the Brillouin zone are clearly observed.
TL;DR: In this article, the authors measured the liquid crystal 5CB and determined the hypersonic speed and attenuation at the nematic-isotropic transition, and compared the results with available ultrasonic data.
TL;DR: In this paper, the behavior of Brillouin splittings, Δωl and Δωt, in the region of the glass-rubber relaxation was studied from amorphous bisphenol-A polycarbonate in the temperature interval 60-240°C.
Abstract: Brillouin scattering has been studied from amorphous bisphenol-A polycarbonate in the temperature interval 60–240°C. Both longitudinal and transverse Brillouin peaks are observed over the entire range. The behavior of both types of Brillouin splittings, Δωl and Δωt, in the region of the glass–rubber relaxation is typical of an amorphous polymer. Equilibrium values of Δωl and Δωt were obtained 20°C below the glass-transition temperature Tg determined at cooling rates of 20°C/hr. Comparison of the present results with previous ultrasonic data reveals a considerable dispersion in the longitudinal phonon velocity below Tg. The origin of the large transverse Brillouin intensities is related to the structure of polycarbonate.
26 Jan 1976
TL;DR: In this paper, the effect of Brillouin scattering on the R ayleigh spectra from nitrogen, oxygen, air and argon was analyzed using a trimodal Gaussian model convoluted with the instrument function for the spectrometer.
Abstract: The determination of the temperature of combustion gases from Rayleigh scattered laser light can be greatly simplified if the effect of Brillouin scattering is assumed to be negligible. To define precisely the regimes in which this assumption is applicable, measurements of the broadening effect of Brillouin scattering on the R ayleigh spectra from nitrogen, oxygen, air and argon have been made with a Fabry-Perot spectrometer. These spectra were analyzed using a trimodal Gaussian model convoluted with the instrument function for the spectrometer. The results of this investigation indicate that if the value of a parameter y, the ratio of the wavelength of the fluctuations producing the scattering divided by 2..pi.. to the collision mean free path, is less than 0.1, Brillouin scattering is negligible. This criterion is shown to be satisfied in the post flame zone of an atmospheric pressure premixed hydrogen air flame.
TL;DR: In this article, the frequency of the transverse acoustic wave with the wave vector q //[010] and the polarization ξ//[001] approaches to zero at the transition temperature with decreasing temperature.
Abstract: Brillouin scattering experiments have been made on KH 3 (SeO 3 ) 2 . The frequency of the transverse acoustic wave with the wave vector q //[010] and the polarization ξ//[001] approaches to zero at the transition temperature with decreasing temperature. The intensity of the Rayleigh line rapidly increases below about –50°C.
TL;DR: In this paper, the Brillouin displacements and the spectra of light scattered from CH4 in the density range from 2 to 20 amagat, y=2.1-21, have been measured and compared with hydrodynamic and kinetic theories.
Abstract: The Brillouin displacements and the spectra of light scattered from CH4 in the density range from 2 to 20 amagat, y=2.1–21, have been measured and compared with hydrodynamic and kinetic theories. Using hydrodynamic theory it was found necessary to include both Burnett corrections in the equations describing translational motion and the effects of diffusion on the rotational energy relaxation time. An extended hydrodynamic theory is proposed which includes not only these corrections but, in addition, makes provision for a second internal energy relaxation. Comparisons of experimental results with this extended theory over the entire density range, with a kinetic description at the lower densities, and with translational hydrodynamic theory at higher density are presented. Owing to the success of the extended theory, it is suggested that the use of frequency dependent thermodynamic and transport coefficients is not required. Further, re‐examinations of the kinetic and translational hydrodynamic formulations...
TL;DR: The Brillouin scattering measurement in KH3(SeO3)2 above the transition temperature shows a large anomaly in hypersonic velocity of the transverse wave with the wave vector q = [010] and the polarization ξ = [001], which indicates acoustic phonon softening as mentioned in this paper.
TL;DR: In this paper, the Brillouin scattering technique has been used to measure the velocity dispersion of hypersonic acoustic waves in the disordered cubic phase of adamantane, and the L -mode data have been correctly fitted.
TL;DR: In this article, the authors investigated Resonant Brillouin Scattering in semi-insulating ZnSe at room temperature by using two kinds of injected acoustic waves; fast transverse and slow transverse modes.
Abstract: Resonant Brillouin Scattering in semi-insulating ZnSe is investigated at room temperature by using two kinds of injected acoustic waves; fast transverse and slow transverse modes. The observed dispersions in scattering cross section show the resonant enhancement and cancellation near the fundamental absorption edge, which are explained by theoretical analyses based upon Loudon's theory. Calculated dispersions taking account of exciton virtual states agree well with the experimental results. Resonant cancellation is explained in terms of the relevant photoelastic constants undergoing a sign reversal near the band edge, which was confirmed by the analyses of piezobirefringence theory.