SPIRALING BRIGHT SPATIAL SOLITONS FORMED BY THE BREAKUP OF AN OPTICALVORTEX IN A SATURABLE SELF-FOCUSING MEDIUM

We report the generation of three-dimensional bright spatial solitary waves by the breakup of an optical vortex in a saturable self-focusing nonlinear medium. An elliptical Gaussian beam from a Ti:sapphire lase r containing a singly charged on-axis vortex was passed through a nonl inear medium consisting of rubidium vapor at low concentrations. The m odulational instability resulted in the formation of a pair of out-of- phase solitonlike beams, which spiraled away from each other during pr opagation as a result of the repulsive nature of their interaction. Th e rate of rotation and separation of the two soliton beams could be co ntrolled by the parameters of the medium and the laser intensity. Nume rical analysis of the propagation based on a model nonlinearity corres ponding to a strongly saturated two-level system showed good quantitat ive agreement with the experimental data. (C) 1995 Optical Society of America