摘要:

The phenomenological theory of light scattering by optical and acoustical phonons is reviewed. The resonance enhancement of Brillouin scattering by acoustical phonons in the vicinity of the intrinsic absorption edge is related to the enhancement of the elasto‐optical and electro‐optical constants. A macroscopic theory of resonance‐enhanced Brillouin scattering by acoustical phonons analogous to that of resonance‐enhanced Raman scattering by optical phonons is formulated in terms of the scattering of polaritons by the acoustic phonons via the exciton and continuum electron‐hole pair excitation parts of the incident and scattered polaritons.

ISSN:0001-4966    

DOI:10.1121/1.1912443

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

We have observed a splitting in the Brillouin spectrum of the two shear waves that propagate along thecaxis in α quartz. This is a consequence of a phase‐velocity dispersion linear in phonon wave vector.

ISSN:0001-4966    

DOI:10.1121/1.1912444

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Using techniques described by Ford, Langley, and Puglielli, we have observed Brillouin scattering from SF6near its critical point for two scattering angles, 166° and 45°. Sound velocities deduced from these measurements atT−Tc=0.5°CareCs=112±1 m/secfor a sound frequency of 370 MHz andCs=95±2 m/secfor a frequency of 130 MHz. The dispersion in the sound velocity of about 15% atT−Tc=0.5°Cdecreases as the temperature is increased to about 1% atT−Tc=40°C, where the sound velocity has increased to 160 m/sec. These data are compared with existing ultrasonic data and discussed in the light of a dynamical model considered by Mountain.

ISSN:0001-4966    

DOI:10.1121/1.1912445

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Brillouin scattering is used to study very small changes produced in the distribution of thermal phonons by the acoustoelectric interaction. Perturbation in the thermal acoustic flux has been observed with carrier drift velocity less than the sound velocity.

ISSN:0001-4966    

DOI:10.1121/1.1912446

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Brillouin‐scattering studies of acoustoelectric interactions CdS and ZnO are reviewed. The important characteristics of amplified acoustic shear‐wave noise as determined by Brillouin scattering is summarized. Data on acoustic parametric amplification is also given.

ISSN:0001-4966    

DOI:10.1121/1.1912447

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The recent observation of soft optic modes which trigger structural phase transitions of several different kinds leads naturally to the suggestion that the anomalous acoustic behavior near these phase transitions might arise from interactions between acoustic phonons and the soft optic modes. In this paper we explore this suggestion from both theoretical and experimental points of view. The concept of the soft mode is explained for both phonon and tunneling modes whose instabilities may occur at the center (q=0) or the boundary (q≈π/a) of the Brillouin zone. Illustrative experimental results from infrared absorption, light scattering, and neutron scattering techniques are presented. We review and compare several theories of the interaction between acoustic phonons and soft optic modes and cite appropriate experimental evidence, where available, for comparison. Among the crystals discussed areSrTiO3, KDP,KTaO3, andNH4Cl. We conclude that basically two types of optic‐acoustic interactions are sufficient to describe most structure transitions. However, to date, a complete microscopic description in quantitative agreement with experiment, both above and belowTc, has yet to appear. Nevertheless, the explanation of acoustic anomalies in terms of soft optic mode behavior is essentially correct and will prove quite fruitful.

ISSN:0001-4966    

DOI:10.1121/1.1912448

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Paramagnetic spins, which interact primarily with the resonant phonons in a dielectric crystal and show large magneto‐optical properties, can be used as a tunable and sensitive probe of acoustic waves and phonons in a dielectric crystal. The technique works at a few degrees Kelvin and at frequencies from 10 to 300 GHz or more. A variety of experiments demonstrating uses of the spectrometer are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1912449

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

This paper shows, by means of a ray‐tracing method, the existence of two orthogonal line foci in the scattered light arising from the interaction of a Huyghens' sound source and a converging fan of light. It extends to a higher degree of approximation the ray theory of Bragg diffraction imaging in three dimensions.

ISSN:0001-4966    

DOI:10.1121/1.1912450

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

This paper presents the results of experiment and theory concerning the resolution capabilities of a Bragg diffracting system which uses a cylindrically convergent laser beam for imaging objects which scatter sound. The derived theory predicts that thin wires, oriented parallel to the convergence line of the light beam and separated by one wire diameter, will just be resolved if the wire diameter is equal to (Λ/2)/sinαm, where Λ is the sound wavelength and αmis the semiangle of the light convergence. For wire orientation at right angles to this direction, the resolution is of quite a different character. The predicted wire diameter is then (Λ/2)/sinθm, where θmis half the angle subtending the light beam in the direction perpendicular to the wire axes. Copper wires as small as 10 sound wavelengths in diameter could be experimentally resolved in our system when the wires were oriented parallel to the convergence line of the light beam. When oriented at right angles, wires as small as23of a sound wavelength could be resolved. These figures demonstrate good experimental verification of the theory.

ISSN:0001-4966    

DOI:10.1121/1.1912451

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP