Stimulated Brillouin scattering as a parametric interaction

In the stimulated Brillouin scattering of an intense laser beam, a forward-traveling coherent acoustic wave and a backward-traveling electromagnetic wave are produced. This interaction is studied from the coupled mode approach and shown to be describable as a parametric interaction. An inherent instability of this particular interaction is discussed. Frequencies of the interacting waves are calculated for quartz and cadmium sulfide. The non-linearity is shown to be due to the electrostrictive and photoelastic properties of the medium. By expressing the coupling coefficient as a tensor of rank four, selection rules for the interaction in isotropic and certain anisotropic media are derived. Finally the experimental approach for detection of the acoustic wave is discussed.