Light scattering cross section from surface acoustic phonons in multilayer films

We calculate the Brillouin cross section from surface and guided acoustic modes in opaque multilayer supported films by including the ripple scattering at all the interfaces. The results are compared with the usual approximate calculations. The superlattices Ag/Pd and Mo/Si are studied. We investigate in detail the dependence of the cross section on the top layer and the limit of validity of the effective-medium approximation. It is found that this approximation is no longer valid in case of a long-period metal-semiconductor superlattice such as Mo/Si.