Photoelastic and surface-corrugation contributions to Brillouin scattering from an opaque crystal

Abstract

We present a theory of the Brillouin scattering of light from long-wavelength acoustical phonons in an opaque crystal which takes into account the effects associated with a finite skin depth. The theory incorporates the photoelastic back scattering of the penetrating light, the effect of the thermal elastic strain induced surface corruga ion on the reflected light, as well as the interference between the two scattering processes. We relate the scattering cross section to the spectral density of the elastic-strain fluctuations in the materials, which we construct from the relevant classical elastic Green's functions for a semi-infinite elastic medium bounded by a stress-free surface. We present representative computed line shapes and compare the relative strengths of the different contributions to the spectra for various angles of incidence.