On the material response in stimulated Brillouin scattering

We re-examine behavior of the material response in stimulated Brillouin scattering and from this revise its theoretical formalism. We show that the response out of exact Brillouin resonance splits into two processes: one is the induction of a moving density grating, propagation characteristics of which follow these of the beat pattern of pump and Stokes fields, and the other is the induction of an acoustic wave, frequency of which coincides with that of the beat pattern but which propagates at the acoustic velocity in the medium. The resulting equations for the response amplitudes are solved analytically in several representative cases.