Strong Interference Effects in Surface Brillouin Scattering from a Supported Transparent Film

A measurement of surface Brillouin scattering from a 2250-Å film of silica grown on (001) silicon is presented. The spectrum shows many structures related to Rayleigh, Sezawa, and Lamb waves. We calculate the Brillouin cross section taking the ripple and the elasto-optic coupling mechanisms into account in the two media. Both the mechanisms are found to be important and there is evidence of strong interference effects between the ripple and the elasto-optic contributions to the scattering amplitude.