INDUCED SELF-FOCUSING AND CROSS-FOCUSING (DEFOCUSING) IN SELF-DEFOCUSING (FOCUSING) MEDIA INTERACTING WITH A BICHROMATIC FIELD

We discuss the nonlinear refractive index cross-modulation produced by an intense laser beam at frequency omega(L) and a second moderately s trong laser whose frequency is near the Rabi sideband omega(L)+/-Omega (L) where Omega(L) is the generalized Rabi frequency associated with t he first laser. As a consequence, depending on the transverse profiles of the two lasers, self-focusing (defocusing) may be induced in self- defocusing (focusing) nonlinear media. Recently observed anomalies in conical emission can be understood qualitatively by these effects.