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 mo des in a two-dimensional Cartesian geometry has been studied for the f irst time by avoiding the paraxial optics approximation. This model al lows investigation of the competition between forward, sideward, and b ackward 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, an d their temporal dependence are governed mainly by two control paramet ers: the backward SBS gain coefficient G, and the ratio alpha(s)f of t he incident beam power to its critical value for the onset of self-foc using. In the case of large values of G greater than or similar to 15, backward SBS dominates and prevents both self-focusing and forward SB S. For smaller values of G, the interaction exhibits a complex oscilla tory behavior, which corresponds to the competition between backward a nd forward SBS for alpha(sf) less than or similar to 1, and involves a lso self-focusing for higher beam intensities.