Brillouin Scattering in Hexagonal Crystals: Calculation of Scattering Cross Section in CdS

Abstract

A generalized expression for the Brillouin-scattering cross-section is obtained by incorporating birefringence in hexagonal crystals. Scattering cross sections of any case can be calculated from the formula when the mode and propagation direction of the acoustic waves, and the polarization direction of the incident light are known. The formula derived in the present paper is very useful to analyze the spectrum of phonons amplified through acoustoelectric interactions in hexagonal crystals like CbS. The Brillouin cross sections are evaluated for the scattering by the transverse and longitudinal acoustic waves with the propagation directions parallel and perpendicular to the c -axis. The cross section is found to depend on the frequency of the acoustic waves for example in the case of the scattering by the transverse acoustic waves with the polarization vector parallel to the c -axis and the propagation direction perpendicular to the c -axis. The effect of multiple internal reflections is also taken into account.