Three-dimensional instabilities of counterpropagating light waves in homogeneous plasma

Abstract

A study is made of the three-dimensional instabilities of two light waves counterpropagating in homogeneous plasma. Such instabilities involve from one to four near-resonant electromagnetic sidebands, which interact with each other and the pump waves by scattering from four different ion-acoustic gratings. These gratings can be driven either resonantly, as in stimulated Brillouin scattering (SBS), or nonresonantly, as in filamentation. No restrictions are placed on the instability geometry. Within the framework of an infinite-medium analysis, the only four-sideband instability is the cooperative filamentation of both light waves, which is absolute in nature. SBS involves a single Stokes sideband and is usually convective. With the sole exception of sideward SBS, each light wave scatters independently. For parameters typical of current inertial-confinement-fusion experiments, the cooperative filamentation of both light waves should be dominant when the light waves have comparable intensities and the ion-acoustic wave damping is strong, while the SBS of the more intense light wave should be dominant when the light waves have disparate intensities and the ion-acoustic wave damping is weak.