TRANSVERSE INSTABILITIES OF 2 INTERSECTING LASER-BEAMS IN A NONLINEARKERR MEDIUM

We develop a detailed theory of the transverse instabilities that can occur as two laser beams intersect in a nonlinear Kerr medium. Our ana lysis of the interaction includes all the various sources of nonlinear phase shifts of the interacting fields as well as the mutual interact ion of the two pump waves. In general, the interaction gives rise to a four-sidemode process. The couplings among the sidemodes arise from t hree distinct interactions of modulational instability, two-beam-excit ed (TBE) conical emission, and nonlinear Bragg diffraction. Modulation al instability and TBE conical emission are shown to exhibit exponenti al spatial gain. The value of this gain is higher for the case in whic h both processes contribute than in the cases in which the two process es occur singly. Nonlinear Bragg diffraction is shown to be a spatiall y stable process by itself. However, in the presence of the other two processes this process provides an additional nonlinear phase shift th at changes the direction of maximum growth of the instability. In none of the cases does the maximum growth occur for perfect linear phase m atching.