Theory of Brillouin scattering from an isotropic elastic film

Abstract

In the elastic plate limit of thickness L much less than the acoustic wavelength lambda a, the description of the propagating modes simplifies to a bending, or undulation, mode and a longitudinal, or peristaltic, mode. Green functions and fluctuation spectra for these modes are derived by linear response theory. The differential cross sections for Brillouin scattering off these modes by the surface ripple mechanism are calculated. For the bending mode the power spectrum increases strongly and the cross section increases with decreasing L. For the longitudinal mode both the power spectrum and the cross section decrease with decreasing L.