Showing papers on "Brillouin scattering published in 1984"
TL;DR: In this article, it was shown that an irreversible change in the longitudinal sound velocity takes place between 10 and 17 GPa and that this change is stable at atmospheric pressure, and the Raman spectra of the retrieved sample indicate that it is also amorphous but differ noticeably from that of the original sample.
Abstract: Brillouin scattering from $a$-Si${\mathrm{O}}_{2}$ up to 17 GPa shows that an irreversible change in the longitudinal sound velocity takes place between 10 and 17 GPa and that this change is stable at atmospheric pressure. Raman spectra of the retrieved sample indicate that it is also amorphous but differ noticeably from that of the original sample.
255 citations
TL;DR: In this article, the refractive index of BP was measured in the visible spectral range by means of the Brewster angle method, and the elastic constants were determined by Brillouin scattering.
120 citations
TL;DR: Brillouin scattering is used to determine the speed of sound in (and hence longitudinal modulus of) A‐ and B‐DNA fibers to show a small anisotropy with sound speeds along the fiber axis higher by up to 10% B‐ DNA fibers appear to be isotropic.
Abstract: We have used Brillouin scattering to determine the speed of sound in (and hence longitudinal modulus of) A- and B-DNA fibers. The speed of sound is very sensitive to the degree of hydration of the fibers, and measurements have to be made at laser powers below 5 mW to avoid local heating and dehydration. Under those conditions, we obtain sound speed perpendicular to the fiber axis of about 2.2 and 1.9 km/s in A- and B-DNA fibers, respectively. A-DNA fibers show a small anisotropy with sound speeds along the fiber axis higher by up to 10% B-DNA fibers appear to be isotropic.
109 citations
TL;DR: In this paper, Thomson scattering was used to identify electron plasma waves driven by stimulated Raman scattering in a low-density preformed plasma, and the plasma waves were observed in a Gaussian-shaped plasma whose peak density was in the range $(0.01\ensuremath{-}0.05){n}_{c}), in qualitative agreement with threshold calculations using a convective amplification model.
Abstract: We have used temporally and spectrally resolved Thomson scattering in a C${\mathrm{O}}_{2}$-laser-plasma interaction experiment to identify electron plasma waves driven by stimulated Raman scattering in a low-density preformed plasma. Plasma waves were observed in a Gaussian-shaped plasma whose peak density was in the range $(0.01\ensuremath{-}0.05){n}_{c}$, in qualitative agreement with threshold calculations using a convective amplification model. The plasma waves were observed only during the early part of the pump pulse, and disappea\ifmmode \acute{r}\else \'{r}\fi{}ed coincidentally with the onset of ion waves driven by stimulated Brillouin scattering.
79 citations
TL;DR: In this paper, the elastic constants of CeB6 were determined by ultrasonic and Brillouin scattering measurements, and all elastic constants were found to be positive, especially c12.
Abstract: Elastic constants of CeB6 were redetermined by ultrasonic and Brillouin scattering measurements. We found all elastic constants to be positive, especiallyc12. The temperature and magnetic field dependence of the elastic modesc44 and (c11-c12)/2 is explained on the basis of the newly proposed crystalline-electric-field level scheme for CeB6 with theΓ7 level 545 K above theΓ8 ground state. The deduced quadrupolar coupling constants give an antiferroquadrupolar ordering temperature of 3.3 K in agreement with experiment.
67 citations
TL;DR: A method is described to measure the speed of sound and the temperature in the sea as functions of depth using backscattered laser light with an interferometric spectrometer.
Abstract: A method is described to measure the speed of sound and the temperature in the sea as functions of depth. Backscattered laser light is analyzed with an interferometric spectrometer. The speed of sound at very short acoustic wavelengths is obtained directly from the wavelength shift of the Brillouin scattered light, and the temperature is deduced from the speed of sound together with auxiliary information on depth and salinity. Experiments are described.
59 citations
TL;DR: In this article, the authors performed a study of magnons in Mo/Ni metallic superlattices with the use of Brillouin scattering and found that the magnetic field and modulation wavelength dependence of the magnon frequencies were in reasonable agreement with theoretical predictions.
Abstract: We have performed a study of magnons in Mo/Ni metallic superlattices with the use of Brillouin scattering. The magnetic field and modulation wavelength dependence of the magnon frequencies are found to be in reasonable agreement with theoretical predictions. Certain features in the spectra which are characteristic of a superlattice and cannot be expalined by a trivial superposition of the spectra of the individual constituent layers are presented and discussed.
56 citations
TL;DR: Etude des spectres de diffusion Brillouin dans l'etat normal et dans leetat surfondu metastable jusqu'a −27,0°C.
Abstract: Etude des spectres de diffusion Brillouin dans l'etat normal et dans l'etat surfondu metastable jusqu'a −27,0°C. Deduction de l'absorption et de la vitesse d'hypersons
51 citations
47 citations
TL;DR: In this article, the authors measured the frequency and damping of the longitudinal (LA) and transverse (TA) acoustic modes propagating along the X, Y, Z directions with a temperature resolution better than 0.02 K. This anomalous damping was interpreted as a consequence of the anisotropic coupling of the soft mode with TA modes which was invoked by Aslanyan and Levanyuk to explain the occurrence of the incommensurate phase.
Abstract: The recently discovered incommensurate phase of quartz close to the α-β transition has been investigated using Brillouin scattering. The frequency and the damping of the longitudinal (LA) and transverse (TA) acoustic modes propagating along the X, Y and Z directions have been measured as a function of the temperature in the range 845 K-860 K with a temperature resolution better than 0.02 K. The frequency of the TA modes is practically temperature independent but the damping of the TA mode propagating along the Y direction and polarized along the X direction shows an increase near the incommensurate transition point T i . This anomalous damping which is not observed for TA modes propagating along the X axis, is interpreted as a consequence of the anisotropic coupling of the soft mode with TA modes which was invoked by Aslanyan and Levanyuk to explain the occurrence of the incommensurate phase. The temperature dependence of the LA modes is very strong and exhibits a change of slope at T i . This temperature dependence can be attributed to third order anharmonic interactions between the LA modes and the soft mode Mesure de la frequence et de l'amortissement des modes LA et TA se propageant selon les directions X, Y, Z, en fonction de la temperature (845-860 K) avec une resolution d'au moins 0,02 K: variation thermique pratiquement nulle pour la frequence des modes T-A, mais augmentation de l'amortissement du mode TA se propageant suivant Y et polarise suivant X a l'approche de la temperature de la transition incommensurable T i (couplage anisotrope entre mode mou et modes TA). Forte variation thermique des modes LA, avec rupture de pente a T i (termes anharmoniques du 3eme ordre)
45 citations
TL;DR: In this article, a practical stimulated Brillouin-scattering method for spectroscopic characterization of low-frequency excitations is extended to permit optical generation and detection of phase-coherent transverse, longitudinal, and mixed polarization acoustic phonons, tunable over a wide frequency range, in solid media.
TL;DR: In this paper, the authors analyzed the effect of the Brillouin scattering in finite systems which have a boundary reflective to light and showed that in the nonlinear regime the scattered light intensity may behave chaotically in time and exhibit rich frequency spectra including shifts corresponding to fractional harmonics of the fundamental acoustic wave.
Abstract: Stimulated Brillouin scattering is analyzed in finite systems which have a boundary reflective to light. The linear instability is considerably altered from that for the usual transmitting boundaries. In the nonlinear regime the scattered light intensity may behave chaotically in time and exhibit rich frequency spectra including shifts corresponding to fractional harmonics of the fundamental acoustic wave. Simulation results compare favorably with data from laser-plasma-interaction experiments.
TL;DR: In this article, a theory model for the reduction of stimulated Brillouin scattering by the generation of higher ion wave harmonics is derived, and a simplified model based on the truncation to second harmonic ion waves reveals several interesting features.
Abstract: Reduction of stimulated Brillouin scattering by the generation of higher ion wave harmonics is investigated. A theory model is derived which includes all harmonics. A simplified model based on the truncation to second harmonic ion waves reveals several interesting features. When damping and detuning are neglected the reflectivity is drastically reduced in a low‐density plasma (ne<0.25ncr), but the solution turns phase unstable at low reflectivity levels. Finite damping of ion waves extends the range of validity of the model. Still nonlinear damping of the primary decay may considerably exceed the linear damping, rendering the generation of the second harmonic an important mechanism. A large detuning of the second harmonic is required before it can be considered decoupled. The strong interaction between the ion waves introduces a power shift which is able to dynamically reduce the Brillouin reflectivity. Undersone parameter conditions the reflectivity approaches an oscillatory steady state. The accuracy of...
27 Sep 1984
TL;DR: In this paper, the use of Brillouin and Raman scattering for the measurement of temperature and salinity in the ocean is described, together with the results of recent experiments and an assessment of the errors to be expected.
Abstract: Recent progress is described in the use of Brillouin and Raman scattering for the measurement of temperature and salinity in the ocean. The use of Brillouin scattering is described for the measurement of the sound velocity, and the use of Raman scattering is described for the independent measurement of the temperature and salinity. Coupling these techniques permits the assessment of both temperature and salinity. The experimental techniques are described together with the results of recent experiments and an assessment of the errors to be expected.
TL;DR: Stimulated Brillouin scattering of KrF laser radiation focused in SF(6) gas at pressures of 1.4 to 9.8 atm has been studied experimentally and pulse compression up to peak intensities of two times the pump intensity has been achieved.
Abstract: Stimulated Brillouin scattering of KrF laser radiation focused in SF6 gas at pressures of 1.4 to 9.8 atm has been studied experimentally. For an input linewidth of 0.08 cm−1 and focal lengths of 1 and 2 m, reflectivities of 80% have been measured. Pulse compression up to peak intensities of two times the pump intensity has been achieved in a pulse that is partially phase conjugate to the pump pulse. At high pressures a short backward Raman spike was observed preceding the Brillouin backscattered signal.
TL;DR: Narrow-linewidth radiation has been used to generate pulses of ~200-psec duration by the combined effects of stimulated Brillouin scattering and competing nonlinear processes.
Abstract: Narrow-linewidth radiation has been used to generate pulses of ∼200-psec duration by the combined effects of stimulated Brillouin scattering and competing nonlinear processes.
TL;DR: In this article, polarized photon correlation measurements of bulk poly(phenylmethyl siloxane) (PPMS) with a molecular weight of about 2500 at different pressures from 1 to 1750 bar and temperatures between 269 and 308 K.
Abstract: We report polarized photon correlation measurements of bulk poly(phenylmethyl siloxane) (PPMS) with a molecular weight of about 2500 at different pressures from 1 to 1750 bar and temperatures between 269 and 308 K. In the Frequency range accessible by present-day digital correlators, the time correlation function can measure a slow q2-dependent diffusional process due to local concentration fluctuations and a fast α-mode structural relaxation process. The mean characteristic times of the two processes approach each other at low temperatures and high pressures, in contrast to the behavior of the α- and β-relaxation times. We should be cautious in relating the mean characteristic times for the structural relaxation process obtained by different experimental techniques, such as Brillouin scattering and photon correlation spectroscopy, because of the differnces in the probe emphasis and the extremely broad frequency distribution of such relaxation processes.
TL;DR: In this paper, a phase-conjugating Brillouin mirror was used for regenerative amplification in a XeCl excimer laser with a phaseconjugation beam.
TL;DR: In this article, the Brillouin scattering from surface-wave excitations of metals by means of a tandem Fabry-Perot interferometer according to Sandercock allows reliable determination of bulk elastic moduli and elastic constants, respectively, of polycrystals and single crystals.
Abstract: Measurements of Brillouin scattering from surface-wave excitations of metals by means of a tandem Fabry-Perot interferometer according to Sandercock allow the reliable determination of bulk elastic moduli and elastic constants, respectively, of polycrystals and single crystals. This determination is independent of Cauchy's relation (cL=3cT, or c12=c44). The accuracy of the method of 5-10% (depending on the penetration depth of the light) has been demonstrated for cubic rare-earth (R) compounds with known elastic constants, such as CePd3 (polycrystal) and CeAl2 (single crystal). The method has been applied to determine the bulk moduli cB of polycrystalline tetragonal RCu2Si2 at 300K with an accuracy of better than 10%. The stable-valent compounds follow cB varies as Q/V (Q=valence of the R ion, V=unit cell volume). With respect to this behaviour, valence instabilities are identified by the softening of cB of EuCu2Si (32%) and YbCu2Si2 (43%). The 'heavy-fermion' superconductor CeCu2Si2 shows a 14% softening of cB with respect to the reference compounds.
TL;DR: In this paper, it was shown that this is forced by the approach of the system to a thermodynamic limit where liquid and crystalline entropy contents would equalize: the limit falls only 26 K below Tg.
Abstract: Brillouin scattering, viscosity, and calorimetric studies of the congruently melting glass‐forming compound KCl⋅2BiCl3 have been made to clarify and extend a pattern of relaxation behavior seen over wide temperature ranges in a recent study of the simple ionic liquid system KNO3 +Ca(NO3)2. Viscosity data for the two systems covering nearly four orders of magnitude superimpose when scaled by the glass temperature Tg ratio, and comparable parallels are seen in the hypersonic absorption behavior. Sound velocity and absorption data are consistent with single relaxation time kinetics at high temperature in accordance with findings for the KNO3 +Ca(NO3)2 system. In each system high temperature Arrhenius behavior breaks down when τ>10−11s. It is shown in the present system that this is forced by the approach of the system to a thermodynamic limit where liquid and crystalline entropy contents would equalize: the limit falls only 26 K below Tg. A relationship to the behavior of argon is considered.
Abstract: The elastic properties of p‐terphenyl were studied in its high and low temperature phases. The 13 elastic constants were determined in the monoclinic phase, whereas 16 elastic constants were found sufficient to describe the elastic properties of the triclinic phase. In this phase the main change in the Brillouin spectra is a splitting of a quasilongitudinal line. This splitting varies like the square of the order parameter. A quasielastic component is observed in the vicinity of the transition temperature. Deuterated and hydrogenated samples revealed the same behavior. Elastic anomalies are tentatively interpreted inside the frame of the Landau theory.
TL;DR: In this article, the spatial and temporal development of the SBS ion wave was investigated extensively by ruby-laser light scattering techniques using a picosecond streak-camera for recording.
Abstract: The spatial and temporal development of the SBS ion wave was investigated extensively by ruby-laser light scattering techniques using a picosecond streak-camera for recording. The measurements performed for various levels of peak backscattering provide the ion wave energy density as a function of space, time and backscatter level, i.e. peak power density of CO2 laser radiation focussed into an underdense and homogeneous target plasma of large extent. In an attempt to understand the various experimental aspects, numerical solutions of respective theories were compared with observations. Whilst for backscatter levels below 5% the three-wave description of Forslund et al. [11] does suffice, it took an extensive review of nonlinear mechanisms to pin down harmonic production of the ion wave according to Karttunen and Salomaa [23] as the process governing SBS behaviour above 5% up to the Manley-Rowe limit. The corresponding system of four-wave equations is capable to explain reasonably well all the aspects observed; in particular, it shows, how it comes about that the dangerous Manley-Rowe limit is reached already at moderate power densities below 1013 W/cm2 such as in [1]. From this description, it is also evident that — by contrast to many other aspects of laser fusion — this is an effect which becomes the more serious theshorter the laser wavelength is.
TL;DR: In this article, the Schaefer-Bergmann scattering of sound velocity at 10 MHz in both liquid and crystal tetradeuteromethane (CD4) and cyclohexane (C6H12) is described.
Abstract: Measurements, by Schaefer–Bergmann scattering, of sound velocity at 10 MHz in both liquid and crystal tetradeuteromethane (CD4) and cyclohexane (C6H12) are described. The elastic constants of CD4 at 85.57 K are found to be C11=2.056±0.015, C12=1.542±0.015, and C44=0.939±0.005 GPa. For cyclohexane at 278.6 K the results are C11=2.580±0.015 and C12+2C44=2.97±0.03 GPa. It is argued that the separate elastic constants of cyclohexane are C12=2.25 and C44=0.36 GPa. By comparison with published Brillouin scattering data, the presence of dispersion in the case of cyclohexane and its absence in the case of methane is noted.