2-DIMENSIONAL STUDIES OF STIMULATED BRILLOUIN-SCATTERING, FILAMENTATION, AND SELF-FOCUSING INSTABILITIES OF LASER-LIGHT IN PLASMAS

The parametric interaction of an intense laser beam with ion plasma modes in a two-dimensional Cartesian geometry has been studied for the first time by avoiding the paraxial optics approximation. This model allows investigation of the competition between forward, sideward, and backward stimulated Brillouin scattering (SBS) along with filamentation and self-focusing instabilities. It is shown that the SBS saturation level, the angular distribution of transmitted and scattered light, and their temporal dependence are governed mainly by two control parameters: the backward SBS gain coefficient G, and the ratio alpha(s)f of the incident beam power to its critical value for the onset of self-focusing. In the case of large values of G greater than or similar to 15, backward SBS dominates and prevents both self-focusing and forward SBS. For smaller values of G, the interaction exhibits a complex oscillatory behavior, which corresponds to the competition between backward and forward SBS for alpha(sf) less than or similar to 1, and involves also self-focusing for higher beam intensities.