THEORY OF BRILLOUIN-SCATTERING FROM CORRUGATED SURFACES

The phonon-surface-polariton (SP) interaction in addition to the phonon-phonon mixing is accounted for in order to get the Brillouin scattering cross section from an optical bigrating or from a rough surface of a metal. We limit our attention to nontransparent media, thus neglecting from the start the elasto-optic effect and linearize the ripple contribution in the extinction-theorem equations. We compare these results with the experimental data. In a silver grating the Rayleigh peak shows a "replica" in the frequency spectrum due to phonon-SP coupling. On the contrary, in a Si grating phonon-phonon mixing is responsible for the observed gaps in the second- and higher-order Brillouin zones. © 1995 The American Physical Society.