Tomasz Błachowicz

Application of Laser Light for Solid State Elastic Features Investigations

in a Hypersonic Range of Frequencies

Silesian University of Technology Press, Gliwice 1999, ISBN 83-88000-25-X

OUTLINE

The main purpose of the monograph rely on description of an experimental arrangement, presentation of theoretical calculations of acoustic wave propagation parameters and mesurements of elastic constants in the LiTaO₃ crystal in the hypersonic range of frequencies from 20.9 GHz to 38.5 GHz in order to test dispersion dependencies in respect to ultrasonic range. All the measurements were performed using Brillouin laser light scattering method. This method consists of evidence for changes of photon frequencies nonelastically influenced by acoustical phonons lying at the beginning of first Brillouin zone. In quantum picture, annihilation and creation processes were responsible for typical Brillouin spectrum view, where lines of lowered and increased frequency were visible.

The measurement were done on the equipment, which main elements were as follows: single mode ion argon laser working at 514.5 nm with 100 mW power, designed and constructed single-pass pressure scanned Fabry-Perot interferometer, and PMT unit for single photon counting method. PMT unit was coupled with digital counter sensitive for TTL standard signal and then connected with parallel port of PC computer by constructed interface. A systematic error of phonon frequencies measurement was induced by experimental arrangement and numerical treatment of data and was equal to about 0.15 GHz. Statistical error of measurements was equal to (0.04 GHz - 0.27 GHz) range, but in most cases was equal to 0.08 GHz. All the measurements were performed at three cubic samples prepared with known crystallographic directions with accuracy equal to 20 angle minutes. In all cases the angle between direction of incident and scattered light was equal to 90 angle degrees.

Before the measurement theoretical calculations of frequency, velocity and kind of polarization of an acoustic wave were done. Piezoelectricity of LiTaO₃ crystal was taken into account. The calculations were based on eigen-value problem formalism. Useful configuration for purposes of the work were determined and scattering efficiencies (cross sections) for different cases were calculated.

The whole work has also didactic character. Essential look on theories for bulk and surface phonons were prowided. Informations of different materials investigated by Brillouin scattering were reviewed. The book in 11 chapters possesses 72 tables and 36 figures.