Showing papers on "Brillouin scattering published in 1972"
TL;DR: In this paper, a linear temperature dependence of the specific heat in amorphous solids at very low temperatures is shown to follow from an ionic tunneling model, which predicts both the observed temperature dependence and the magnitude of the thermal conductivity.
Abstract: A linear temperature dependence of the specific heat in amorphous solids at very low temperatures is shown to follow from an ionic tunneling model. Moreover, this model predicts both the observed temperature dependence and the magnitude of the thermal conductivity and also explains the anomalous results obtained for the phonon free path by means of stimulated Brillouin scattering.
1,953 citations
TL;DR: These effects of stimulated Raman and Brillouin scattering must be considered in the design of optical communication systems using low loss fibers especially when low loss optical fibers are used.
Abstract: The effect of stimulated Raman and Brillouin scattering on the power handling capacity of optical fibers is considered and found to be important especially when low loss optical fibers are used. A critical power below which stimulated effects may be neglected is defined for forward and backward Raman scattering and for backward Brillouin scattering. This critical power is determined by the effective core area A, the small signal attenuation constant of the fiber alpha, and the gain coefficient for the stimulated scattering process (gamma0), by the approximate relation P(crit) approximately 20Aalpha/(gamma0). For a fiber with 20-dB/km attenuation and an area of 10(-7) cm(2)P(crit) approximately 35 mW for stimulated Brillouin scattering. For stimulated Raman scattering P(crit) is approximately two orders of magnitude higher. It is concluded that these effects must be considered in the design of optical communication systems using low loss fibers.
1,080 citations
TL;DR: In this article, backward stimulated Brillouin scattering (SBS) in glass optical fibers has been observed with less than 1 W of input power at 5355 A. Experimental results are compared with theory, and the implied limitation to optical fiber transmission is discussed.
Abstract: Observations of backward stimulated Brillouin scattering (SBS) in glass optical fibers are reported. Threshold for SBS has been achieved with less than 1 W of input power at 5355 A. Relaxation behavior in the SBS signal has also been observed and is attributed to finite‐cell‐length oscillation. Experimental results are compared with theory, and the implied limitation to optical fiber transmission is discussed.
655 citations
TL;DR: In this paper, the Brillouin-line intensities for scattering angles of 90, 120, and 180 degrees for all crystal systems, except for the monoclinic and triclinic ones, and for the low-symmetry classes of the rhombohedric system.
Abstract: After an outline of the Brillouin effect and of elastic waves in crystals, a method for the determination of elastic and photoelastic constants is analyzed. The authors propose a set of conditions with a view to obtaining accurately the numerical values of elastic and photoelastic constants and to ascertain their sign. The Brillouin-line intensities for scattering angles of 90\ifmmode^\circ\else\textdegree\fi{} and 180\ifmmode^\circ\else\textdegree\fi{} are presented for all crystal systems, except for the monoclinic and triclinic ones, and for the low-symmetry classes of the rhombohedric system.
244 citations
01 Feb 1972
156 citations
TL;DR: The first Brillouin scattering measurements on silicon and germanium were reported in this paper, where the optical absorption lies in the range of 10.4 to 6.5 GHz.
Abstract: This is a report of the first Brillouin scattering measurements on silicon and germanium. The measurements were made at $\ensuremath{\lambda}=6328 \mathrm{and} 4880$ \AA{} at which frequencies the optical absorption lies in the range ${10}^{4}$ to 6\ifmmode\times\else\texttimes\fi{}${10}^{5}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. As a result of the high absorption, the light sees only a few wavelengths' extent of the phonon, and so from the uncertainty principle the Brillouin peaks become very broad. The measured linewidths have been analyzed to give the real and imaginary part of the refractive indices. Good agreement is obtained with the values reported in the literature.
119 citations
TL;DR: Within the framework of the Wang Chang-Uhlenbeck kinetic equation, the authors proposed a model description of molecular gases, which is related to the models earlier discussed by Hanson and Morse.
Abstract: Within the framework of the Wang Chang–Uhlenbeck kinetic equation, we propose a model description of molecular gases. The model is related to the models earlier discussed by Hanson and Morse. In ou...
112 citations
TL;DR: In this article, the elastic constants of DyVO4 and TbVO4 were measured at 14 and 34 K respectively and anomalously at the transition temperature TD, and the frequency dependence of these elastic constants was explained using both thermodynamic and microscopic theories.
Abstract: DyVO4 and TbVO4 undergo a Jahn-Teller induced crystallographic phase change at 14 and 34 K respectively, and elastic constants of these materials behave anomalously at the transition temperature TD. Brillouin scattering measurements on DyVO4 show that the elastic constant (c11 - c12) falls to zero at TD. The electron lattice interaction which drives the transition in this material is predominantly of short range and a cluster theory is used to interpret the measurements. The elastic constant c66 of TbVO4 also has an anomaly. It falls to zero at TD when measured at ultrasonic frequencies but only falls to a finite value when measured at the higher frequencies used in Brillouin scattering. This frequency dependence of the elastic constants is explained using both thermodynamic and microscopic theories.
92 citations
01 Jan 1972
TL;DR: The theory and applications of these low-frequency change (or quasi-elastic) light-scattering experiments to the study of macromolecules in solution are reviewed, with emphasis on biological molecules.
Abstract: Light-scattering spectroscopy has recently undergone a revival because of the development of lasers and their associated detection techniques. Raman and Brillouin scattering studies (which have frequency changes ;::: 107 Hz) could be done only with great difficulty using prelaser sources (usually mercury). These studies can now be performed easily with laser sources combined with much improved versions of classical predetection filters (interferometers and diffraction gratings). On the other hand, the Rayleigh scattered light from dilute macromo lecular solutions exhibits frequency broadening of only about 10-108 Hz, an impossible region for experiments using prelaser sources or even for those using laser sources combined with filter methods (except at frequencies greater than about 107 Hz). However, a newly developed nonlinear detection technique known as optical mixing has made measurement of these small frequency changes a relatively routine matter over most of the range between 10-106 Hz. Thus, while studies of the Rayleigh scattered light from macromolecular solutions were formerly con fined to the measurement of frequency-integrated intensities, optical-mixing spectroscopy allows measurements of the frequency distribution of the scattered intensity to be made. The frequency-integrated scattering intensity provides information only on "equilibrium" properties of dilute macromolecular solutions (molecular weights, radii of gyration, optical anisotropies, etc), while the fre quency distribution of this scattered intensity provides, in addition, information about dynamic properties (translationaland rotational-diffusion coefficients, intramolecular relaxation times, etc). Optical mixing (or beating) methods, usually subdivided into homodyning and heterodyning techniques, are essentially ex tensions into the optical region of nonlinear detection methods long used in the radio region of the spectrum. This article reviews the theory and applications of these low-frequency change (or quasi-elastic) light-scattering experiments to the study of macromolecules in solution, with emphasis on biological molecules. Raman and Brillouin scattering
80 citations
TL;DR: In this article, the Brillouin shift and extra lines are predicted with intensities comparable to the usual lines, and they form an octet instead of the familiar doublet.
Abstract: Inelastic scattering of light near an exciton resonance is considered, using a polariton description of the scattering process. We obtain the following results: for incident frequency approaching the resonance from below, the Brillouin shift increases; very near and above resonance, extra lines are predicted with intensities comparable to the usual lines. They form an octet instead of the familiar Brillouin doublet. Numerical calculations of the Brillouin scattering for CdS are given: The shifts and extra lines seem to be observable.
66 citations
TL;DR: In this article, a comparative Brillouin scattering (reference scatterer: toluene) was used to measure the photoelastic tensor elements of calcite (eight elastically symmetric, one elastically anti-symmetric) in both magnitude and sign.
Abstract: We have used comparative Brillouin scattering (reference scatterer: toluene) to measure the nine photoelastic tensor elements of calcite (eight elastically symmetric, one elastically anti-symmetric) in both magnitude and sign. Our measurement of the recently predicted anti-symmetric component agrees in magnitude to 5% with that theoretically predicted. By adopting the theoretical sign for this component, the signs of all other components are determined from the data. The 5% agreement gives a measure of the absolute accuracy of the results. The presence of the antisymmetric component causes ${p}_{2323}$ and ${p}_{2332}$, previously believed to be equal, to differ by more than a factor of 10. The formulas needed to analyze Brillouin scattering in anisotropic media are derived using a new constitutive relation and a new Green's function for radiation in an anisotropic medium. Inclusion of boundary effects (solid angle expansion, scattering-volume demagnification, etc.) makes the formulas valid outside the scattering medium. The convenience of comparative Brillouin scattering for the numerical determination of the photoelastic tensor components, particularly in low-symmetry crystals, is emphasized.
TL;DR: The third ASTM symposium on damage in laser materials held at NBS in May 1971 is discussed, and the results are reviewed.
Abstract: The third ASTM symposium on damage in laser materials held at NBS in May 1971 is discussed, and the results are reviewed.
TL;DR: In this article, the dispersion of the Brillouin scattering cross section of fast-TA phonons in GaAs was measured in detail in the range 8850 to 11 500 ε at 295 ε ifmmode √ √ unless √ text degree √ K. The effect of increasing phonon intensity on dispersion curve was correlated with an associated broadening of the intrinsic absorption edge.
Abstract: The dispersion of the Brillouin-scattering cross section of fast-TA phonons in GaAs was measured in detail in the range 8850 to 11 500 \AA{} at 295\ifmmode^\circ\else\textdegree\fi{}K. Acoustoelectrically amplified domains supplied very intense acoustic flux in the range 0.2-1.0 GHz; this permitted a detailed study of the dispersion with a monochromator and a continuous light source. Close to the intrinsic absorption edge, we see a resonant contribution to the scattering cross section. Further from the edge, a deep minimum indicates that the contributions to the elasto-optic coefficient ${P}_{44}$ from resonant and nonresonant terms have opposite signs. At still longer wave-lengths, the dominant trend is determined by the expected ${\ensuremath{\lambda}}^{\ensuremath{-}4}$ dependence of the scattering cross section. The effect of increasing phonon intensity on the dispersion curve was studied and correlated with an associated broadening of the intrinsic absorption edge.
TL;DR: In this article, an elastic Bragg scattering in that region provides an explanation for the previously observed "coherent crystal radiation" and the possibility of studying phonon phenomena at momenta as small as Ω(10}^{4}$ \mathrm{cm}^{\ensuremath{-}1} ).
Abstract: An investigation of x-ray scattering, when the Bragg condition is nearly satisfied, reveals the possibility of studying phonon phenomena at momenta as small as ${10}^{4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. A closer study of elastic Bragg scattering in that region provides an explanation for the previously observed "coherent crystal radiation."
TL;DR: In this article, a theory of the Brillouin scattering of light by long wavelength acoustic phonons in a metal is presented, which incorporates the effects associated with a finite skin depth.
TL;DR: In this article, the thresholds of stimulated Brillouin scattering and the velocities of hypersound were determined experimentally for CH4, N2, Xe, and SF6.
Abstract: The thresholds of stimulated Brillouin scattering and the velocities of hypersound were determined experimentally for CH4, N2, Xe, and SF6. The instantaneous powers of a laser beam at the entry to a gas-filled cuvette and of the beam transmitted by the gap were recorded by two photocells. The signals from these photocells were applied to the horizontal and vertical deflection systems of a cathode-ray tube. Oscillograms obtained in this way were used to determine the threshold of stimulated Brillouin scattering. The threshold powers for different gases were compared with the corresponding value for methane at a pressure of 105 atm, for which the gain was calculated theoretically. The velocity of hypersound was deduced from the frequency shift between the spectra of the exciting and scattered radiation. The results of the measurements were used to calculate the linewidths and gains.
TL;DR: In this article, the velocity and attenuation of 35 GHz longitudinal $c$-axis acoustic phonons have been measured as a function of temperature and free-carrier concentration by high-resolution Brillouin spectroscopy.
Abstract: The velocity and attenuation of 35-GHz longitudinal $c$-axis acoustic phonons have been measured as a function of temperature and free-carrier concentration by high-resolution Brillouin spectroscopy. These measurements determine both the acoustoelectric and the anharmonic contributions to the phonon damping for comparison to theoretical models.
TL;DR: In this article, a quantum-mechanical formulation of light scattering in a dielectric fluid is applied to liquid helium, and the resulting two-roton differential cross section is significantly smaller than Stephen's prediction, in good agreement with the experiments of Greytak and Yan.
Abstract: A quantum-mechanical formulation of light scattering in a dielectric fluid is applied to liquid helium. To lowest order in the (small) dielectric susceptibilitynα, the theory reproduces the usual expression for Brillouin scattering. Two-roton processes occur in both first and second order innα, and the relevant ground-state matrix elements are evaluated with Feynman wave functions in the convolution approximation. The resulting two-roton differential cross section is significantly smaller than Stephen's prediction, in good agreement with the experiments of Greytak and Yan. The depolarization is somewhat reduced from that of Stephen; present techniques should be able to detect this difference.
TL;DR: In this article, the absorption spectrum of iodine vapour in the neighbourhood of 5145 AA (Ar+ laser green line) has been examined to determine its usefulness as a filter to reduce parasitic light in Raman and Brillouin scattering experiments.
Abstract: The absorption spectrum of iodine vapour in the neighbourhood of 5145 AA (Ar+ laser green line) has been examined to determine its usefulness as a filter to reduce parasitic light in Raman and Brillouin scattering experiments. An absorption cell 100 mm in length containing iodine vapour at 50 degrees C attenuates laser light at 5145 AA by a factor of greater than 104. However, other absorption lines occur at -3 and +6 GHz from the laser frequency which limit the useful frequency range of the filter for Brillouin scattering. A large number of narrow, closely spaced absorption lines in the near frequency range (>or approximately=+or-100 AA) cause an irregular but relatively small distortion of Raman line shapes.
TL;DR: Sound speeds for gigahertz frequencies were measured as a function of temperature from 25 degrees C to 110 degrees C in clean samples of polystyrene by stimulated Brillouin scattering.
Abstract: Sound speeds for gigahertz frequencies were measured as a function of temperature from 25°C to 110°C in clean samples of polystyrene by stimulated Brillouin scattering. The effect on the sound speeds of annealing the polymer was shown. The glass transition temperature was determined to be 95°C from which the number averaged molecular weight was found. Damage observations were made on the prepared sample and compared with those made on commercial samples.
TL;DR: In this paper, the modified hydrodynamic equations describing the behavior of a fluid under the influence of an optical electric field are solved and the contributions to stimulated scattering arising from electrostriction, absorptive heating, and the electrocaloric effect are exactly described.
Abstract: The modified hydrodynamic equations describing the behavior of a fluid under the influence of an optical electric field are solved. The contributions to stimulated scattering arising from electrostriction, absorptive heating, and the electrocaloric effect are exactly described. Previously unreported terms are given which significantly modify both the Rayleigh and Brillouin scattering. In particular, the experimentally observed stimulated Rayleigh scattering in nonabsorbing media is shown to arise as much from electrostriction as from the electrocaloric effect, while anti-Stokes stimulated Brillouin scattering is predicted in a medium near its critical point. The possibility of observing additional scattering contributions proportional to ${(\frac{\ensuremath{\partial}\ensuremath{\epsilon}}{\ensuremath{\partial}T})}_{\ensuremath{\rho}}$ is also discussed.
TL;DR: In this article, the temperature dependence of the longitudinal sound velocities in the [100]- and [110]-directions has been measured in single crystals of argon in a temperature range from 4.2 k to 77 K by stimulated Brillouin scattering.
TL;DR: In this paper, the effects of annealing on the phonon lifetime and the power threshold for stimulated Brillouin scattering (SBS), steadystate and transient gains for SBS, and phonon lifetimes were investigated in polymethylmethacrylate and polyethylmethacetyl (PMT) as a function of temperature.
Abstract: Hypersound speeds, the power threshold for stimulated Brillouin scattering (SBS), steady‐state and transient gains for SBS, and the phonon lifetime have been studied in the plastics of polymethylmethacrylate and polyethylmethacrylate as a function of temperature. Damage thresholds were investigated and the effects of annealing are discussed. An extension of current theory allows a determination of phonon lifetimes and relative gains to be determined without absolute calibration of the laser power.