Showing papers on "Brillouin scattering published in 1977"
TL;DR: In this article, the elastic constants of SiO2, coesite (monoclinic, C2/c), have been determined from Brillouin scattering measurements on a 100-μm crystal.
Abstract: The single-crystal elastic constants of SiO2, coesite (monoclinic, C2/c), have been determined from Brillouin scattering measurements on a 100-μm crystal. The elastic constants inferred from acoustic velocities for 80 different propagation directions are (in units of Mbar) c11 = 1.608, c22 = 2.304, c33 = 2.316, c44 = 0.678, c55 = 0.733, c66 = 0.588, c12 = 0.821, c13 = 1.029, c15 = −0.362, c23 = 0.356, c25 = 0.026, c35 = −0.393, and c46 = 0.099. This experimental technique provides a method of determining single-crystal elastic properties for materials such as high-pressure phases that are not available in sufficiently large sizes for ultrasonic measurements.
224 citations
TL;DR: The first experimental observation of resonant Brillouin scattering of excitonic polaritons in a semiconductor was reported in this paper, where the incident light energy was scanned through the $n=1$ exciton resonance and allowed a direct measurement of the polariton dispersion curve.
Abstract: We report the first experimental observation of resonant Brillouin scattering of excitonic polaritons in a semiconductor The usual symmetric Brillouin doublet becomes an asymmetric multiplet when the incident light energy is scanned through the $n=1$ exciton resonance and allows a direct measurement of the polariton dispersion curve In GaAs we determine a longitudinal-transverse splitting of 008 \ifmmode\pm\else\textpm\fi{} 002 meV and a translational mass ${M}_{\mathrm{ex}}=(06\ifmmode\pm\else\textpm\fi{}01){m}_{0}$ for the [100] heavy exciton The excitions couple preferentially to LA phonons
121 citations
TL;DR: In this paper, a narrow-band cw dye laser through the A-exciton transition at helium temperatures was tuned for resonance enhancement, and the authors observed a pronounced asymmetry of the Stokes and anti-Stokes shift and a dramatic increase of the Brillouin shifts as a function of laser frequency.
56 citations
TL;DR: In this article, the absorption of intense laser light is reduced when targets are irradiated by 1.06-m light with long pulse widths (150-400 ps) and large focal spots (100-250 m).
Abstract: The absorption of intense laser light is found to be reduced when targets are irradiated by 1.06-\ensuremath{\mu} m light with long pulse widths (150-400 ps) and large focal spots (100-250 \ensuremath{\mu}m). Estimates of Brillouin scatter which account for the finite heat capacity of the underdense plasma predict this reduction. Spectra of the back-reflected light show red shifts indicative of Brillouin scattering.
50 citations
39 citations
TL;DR: In this paper, a condition for the frequency shift which ensures that the reproduction effect occurs also in stimulated Raman scattering was derived, and the condition was shown to be applicable to the case of a relatively large frequency shift.
Abstract: Wavefront reproduction or reversal, observed earlier experimentally and interpreted for stimulated Brillouin scattering, is considered now in the case of stimulated Raman scattering, i.e., for the scattering accompanied by a relatively large frequency shift. A condition is derived for the frequency shift which ensures that the reproduction effect occurs also in stimulated Raman scattering.
38 citations
01 Jan 1977
TL;DR: In this article, the authors used a very small (0.15 mm) single-crystal sample to measure the velocities of thermal phonons in a transparent sample.
Abstract: Laser light scattered from thermal phonons in a transparent sample undergoes frequency shifts from which phonon velocities in the sample can be calculated. Elastic moduli of the sample can then be calculated from the phonon velocities. Since no mechanical or electrical coupling to the sample is necessary, very small (0.15 mm), single-crystal samples can be used. It is possible to place these samples under hydrostatic pressure in a gasketed diamond-anvil cell and to pass the laser light through the transparent diamond anvils. Measurements on NaCl have yielded data that are in good agreement with measurements by ultrasonic techniques, and with the Hildebrand and Decker equations of state.
36 citations
TL;DR: In this paper, the authors discuss the possibility of obtaining stimulated backscattering from the ionosphere using the Eiscat radar and find that stimulated Brillouin scattering off ion modes and quasi modes may be possible with the signal power that is planned for the EISCat radar.
Abstract: We discuss the possibility of obtaining stimulated backscattering from the ionosphere. It is found that stimulated Brillouin scattering off ion modes and quasi modes may be possible with the signal power that is planned for the Eiscat radar.
33 citations
32 citations
TL;DR: In this article, the growth rate of thermally stimulated Brillouin scattering was calculated for a uniform magnetoplasma and it was concluded that this new instability is probably responsible for the generation of large-scale field-aligned irregularities associated with artificial spread-F produced by ionospheric heating.
Abstract: The threshold and growth rate of conventional stimulated Brillouin scattering are first calculated for a uniform magnetoplasma. Approximate calculations of the threshold and growth rate are then carried out for a new instability which could be termed thermally stimulated Brillouin scattering: in this instability the nonlinear Lorentz force (ponderomotive force) is replaced by a pressure force due to differential heating in the interference pattern of the pump wave and the generated electromagnetic wave. The threshold for this new instability in a uniform medium is much lower than for conventional Brillouin scattering if the low-frequency wavelength measured along the magnetic field is much longer than the electron mean free path. The threshold is then calculated for the purely growing version of the new instability numerically, taking both the inhomogeneity of the medium and the effect of the geomagnetic field on wave propagation into account. The growth rate is also calculated and it is concluded that this new instability is probably responsible for the generation of large-scale field-aligned irregularities associated with artificial spread-F produced by ionospheric heating.
32 citations
TL;DR: These calculations are valid for well aligned etalons when the phonon lineshape is Lorentzian and cover a wide range of instrumental and phonon spectral widths.
Abstract: The sharper instrumental profile of the multipassed Fabry-Perot etalon introduces distortions to Brillouin spectra which may differ considerably from those introduced by the single-pass etalon. The half-width at half-height of the observed profile is calculated for five-pass and three-pass spectrometers. Phonon spectral widths may be extracted from the graphs and appropriate relationships are presented. These calculations are valid for well aligned etalons when the phonon lineshape is Lorentzian and cover a wide range of instrumental and phonon spectral widths.
TL;DR: In this paper, the hypersonic loss tan δ was determined as a function of temperature for amorphous polyisobutylene (PIB), atactic polypropylene (PP), PP, PVA, PS, and bisphenol-A polycarbonate (PC) by Brillouin scattering.
Abstract: Hypersonic relaxation was studied in amorphous polyisobutylene (PIB), atactic polypropylene (PP), atactic poly(vinyl acetate) (PVA), atactic polystyrene (PS), and bisphenol-A polycarbonate (PC) by Brillouin scattering. The hypersonic loss tan δ was determined as a function of temperature. Only a single loss maximum was observed for the polymers studied in this work. The temperatures of maximum loss are 200°C at 4.95 GHz for PIB, 180°C at 4.11 GHz for PP, 200°C at 4.50 GHz for PVA, 240°C at 5.50 GHz for PS, and 280°C at 5.43 GHz for PC. The present results agree very well with the extrapolated secondary glass-rubber transition lines above the temperature where the primary and secondary lines have merged. The loss process is proposed to be local torsional motions of the polymer backbone which lead to structural relaxation of the fluid.
TL;DR: In this article, self-focusing of light in the liquid crystalline mediump-ethoxybenzyldine-p-butylaniline (EBBA) was studied experimentally.
Abstract: We have studied experimentally self-focusing of light in the liquid crystalline mediump-ethoxybenzyldine-p-butylaniline (EBBA). By variation of temperature, the response time of the field-induced refractive index was adjusted from larger than to smaller than theQ-switched laser pulsewidth. Accordingly, self-focusing varied from transient to quasi-steady-state. The results agree well with existing theoretical predictions and can be qualitatively understood from a simple physical description. The induced stimulated Brillouin scattering was also measured and was shown to be responsible for the limiting diameter of the self-focused beam in the present case.
TL;DR: In this article, the phonon frequencies have been determined as a function of temperature and the integrated intensities of the shear modes in KCN and NaCN were also measured as the temperature increases.
Abstract: Brillouin spectra of acoustic phonons in the orientationally disordered phase in KCN and NaCN have been studied. The phonon frequencies have been determined as a function of temperature. The frequency of the transverse acoustic phonon propagating along (110) and polarized along (001) corresponds well with mean field theory for the phase transition for the two cyanide crystals. The elastic constants C11, C12,, and C44 have been determined as a function of temperature in the cubic disordered phase. The Cauchy relation for cubic crystals is found to be invalid in KCN and NaCN. The two types of phase transitions in KCN and NaCN are discussed in terms of the vanishing shear modulii C44 and (C11−C12)/2, each of which induces lattice instability when it becomes small. The integrated intensities of the shear modes in KCN and NaCN were also measured as a function of temperature. The intensity enhancement upon approaching the phase transition temperature has been found to be due to the decrease of C44. The relative...
TL;DR: In this paper, an extended hydrodynamic theory of birefringence induced by ultrasonic waves in liquids composed of rigid symmetric top molecules is presented, which is closely related to that for HH depolarized light scattering spectra and to that of sound absorption.
Abstract: An extended hydrodynamic theory of birefringence induced by ultrasonic waves in liquids composed of rigid symmetric top molecules is presented. This theory is closely related to that for HH depolarized light scattering spectra and to that of sound absorption. These phenomena involve the interactions of orientations with longitudinal or compressional modes, and the parameters that enter into the theory are the same as those involved in the corresponding theory of the interaction of orientations with shear modes, a theory which is applicable to flow birefringence and VH depolarized light scattering spectra. The theory predicts a linewidth expression for Brillouin scattering and a sound absorption coefficient for a liquid composed of anisometric molecules that differ from expressions previously derived; these expressions depend upon the frequency dependence of the rotational component of the shear viscosity but not upon the frequency dependence of the nonrotational component of the shear viscosity.
TL;DR: In this paper, two types of pump beam in the quasioptics approximation were used to investigate the spatial characteristics of the radiation in stimulated Brillouin scattering, and conditions were formulated under which the scattered radiation reproduces the amplitude and phase profiles of the pump beam.
Abstract: The example of two types of pump beam in the quasioptics approximation is used to investigate the spatial characteristics of the radiation in stimulated Brillouin scattering. The conditions are formulated under which the scattered radiation reproduces the amplitude and phase profiles of the pump beam.
TL;DR: In this article, it was shown that the effects of these asymmetries on the double-humped spectra of incoherent backscatter measured at Jicamarca and at Arecibo were probably much smaller.
Abstract: Stimulated Brillouin scattering can cause asymmetries of ± 25% and ± 1% in the double humped spectra of incoherent backscatter measured at Jicamarca and at Arecibo, respectively. Errors of 10-15 m/sec in the measured velocity could have been caused by ignoring the effects of these asymmetries at Arecibo but the typical errors were probably much smaller.
TL;DR: In this paper, a temperature study of viscoelastic relaxation in butanediol was made using digital correlation and Brillouin scattering spectroscopic methods, and it was concluded that the relaxations observed in the real and imaginary parts of the complex longitudinal modulus are the same.
Abstract: A temperature study of viscoelastic relaxation in butanediol‐1,3 was made using digital correlation and Brillouin scattering spectroscopic methods. The digital correlator provided measurement of the relaxation function from which average relaxation times were calculated. The Brillouin scattering method allows a more accurate determination of the high frequency longitudinal modulus than older ultrasonic methods that require extrapolation of data over a large temperature range for the determination of this modulus. From the light scattering data, it has been concluded that, contrary to previous studies, the relaxations observed in the real and imaginary parts of the complex longitudinal modulus are the same. Under these circumstances the use of a ’’hysteresis’’ effect to interpret the nature of the relaxation at high frequencies is unnecessary. A theoretical derivation has been given that allows the average relaxation time obtained via correlator studies to be compared directly to the measured shear viscosity.
TL;DR: In this article, the elastic constants of TGS are measured at room temperature and a Debye type relaxation of the dielectric constant with a single relaxation time occurs, which is the only relaxation known to date.
Abstract: The elastic constants of TGS are measured at room temperature. The study of the temperature dependence of shift and broadening of the Brillouin line which corresponds to a wave propagating along [0, 0, 1] gives information about the high frequency dielectric constant e22(ω). A Debye type relaxation of the dielectric constant with a single relaxation time occurs.
TL;DR: In this paper, the elastic and photoelastic constants of ZnTe crystals have been determined from Brillouin scattering spectra with 90 degrees -scattering geometry at room temperature.
Abstract: The elastic and photoelastic constants of ZnTe crystals have been determined from Brillouin scattering spectra with 90 degrees -scattering geometry at room temperature. From the measured frequency shifts of the Brillouin doublets, the following values are obtained for the elastic constants: C11=7.22+or-0.02, C12=4.09+or-0.06 and C44=3.080.03 in units of 1010 N m-2. From the comparison of the absolute intensities of the Brillouin doublets measured in ZnTe with that in fused quartz whose photoelastic constants are well-known, the following values are determined for the photoelastic constants: P11=0.144+or-0.007, P12=0.094+or-0.005 and P44=0.046+or-0.003.
TL;DR: In this article, the authors have studied the extent of the disorder in the fluorite sublattice using both Brillouin scattering and theoretical methods and they discuss the degree of disorder.
Abstract: Many crystals with the fluorite structure show a specific heat anomaly at a temperature Tc a few hundred degrees below the melting temperature. It is generally assumed that this anomaly is due to the development of extensive disorder in the anion sublattice. The authors have studied this disorder using both Brillouin scattering and theoretical methods and they discuss the extent of the disorder.
TL;DR: In this paper, the dispersion curves of the Brillouin scattering crosssections for both T 1 −slo... were investigated at room temperature by using injected acoustic domains, and the results showed that the crosssections of the scattering crosssection of the ZnTe crosssections are smooth and uniform.
Abstract: Resonant Brillouin scattering in ZnTe has been investigated at room temperature by using injected acoustic domains. The dispersion curves of the Brillouin scattering crosssections for both T 1-(slo...
TL;DR: In this paper, an experimental set-up was described for measuring, with high resolution, the hypersound-phase velocity and damping by means of Brillouin spectroscopy in the Giga-Hertz range.
Abstract: An experimental set-up is described for measuring, with high resolution, the hypersound-phase velocity and damping by means of Brillouin spectroscopy in the Giga-Hertz range. Measurements on water at 20°C between 3 and 6 GHz are presented showing no observable onset of dispersion in this region. Due to the high-power single-frequency HeNe-laser used and due to an effective collection of Brillouin-scattered light our experimental error is far smaller and the data are more reliable than in earlier investigations.
TL;DR: In this paper, a method of high-resolution Bragg reflection was used to measure ultrasonic velocity and absorption in liquid dichloromethane and dibromoethane near the room temperature, over the frequency range from 60 to 700 MHz.
Abstract: A method of high‐resolution Bragg reflection was utilized to measure ultrasonic velocity and absorption in liquid dichloromethane and dibromomethane near the room temperature, over the frequency range from 60 to 700 MHz. In both liquids, considerable velocity dispersion and decrease in α/f2 were observed and described with single relaxation frequencies, 192 MHz for dichloromethane and 393 MHz for dibromoethane at 20° C. The observed relaxation strengths were roughly consistent with the theoretical values calculated from the hypothesis of the vibrational relaxation associated with all but the lowest mode. The hypersonic velocities were measured in dichloromethane with the technique of Brillouin scattering. No dispersion was observed between 700‐MHz and gigahertz region. The second relaxation involved with the lowest mode was expected to be in the range higher than 10 GHz, and the volume viscosity was estimated to be ηv?3ηs, the shear viscosity.
TL;DR: In this paper, the rhombohedral primitive cell is presented as a slightly distorted ZB unit cell that is twice as long as the primitive cell in the [III] direction.
Abstract: The pressure-induced phase transitions: zinc-blende (ZB)-lfhombohedral--->tetragonal in CuI were studied by Raman scattering. The rhombohedral primitive cell is presented as a slightly distorted ZB unit cell that is twice as long as the primitive cell in the [III] direction. By folding back the ZB Brillouin zone, an approximation to the phonon dispersion curves of the rhombohedral structure in the [III] direction can be obtained. A comparison can then be made between the rhombohedral Raman frequencies and those obtained by neutron scattering at the ZB zone boundary at L. The agreement was found to be satisfactory. A similar analysis is made of the tetragonal phase; it can be related to the zinc-blende structure by means of a doubled primitive cell which involves a slight distortion of the iodine sublattice but a large rearrangement of the copper sublattice. The Brillouin zone must be folded along one cubic axis. The mode Griineisen parameters were calculated for the rhombohedral phase and all of them were found to be positive including that of the E mode that corresponds to TA(L) of the ZB structure.
TL;DR: In this article, the temperature dependence of the elastic constants of NaCN has been studied by propagation of ultrasonic waves at 15 MHz and by Brillouin scattering at 3 GHz over the temperature range from 287K to 355K.
TL;DR: In this paper, the authors show that Hg2Cl2 undergoes a second order phase transition around 185 K. The authors support the hypothesis that the transition is induced by the condensation of a transversal acoustical mode at an X point of the first Brillouin zone in the tetragonal phase.