SPIRALING BRIGHT SPATIAL SOLITONS FORMED BY THE BREAKUP OF AN OPTICAL VORTEX 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 laser containing a singly charged on-axis vortex was passed through a nonlinear medium consisting of rubidium vapor at low concentrations. The modulational instability resulted in the formation of a pair of out-of-phase solitonlike beams, which spiraled away from each other during propagation as a result of the repulsive nature of their interaction. The rate of rotation and separation of the two soliton beams could be controlled by the parameters of the medium and the laser intensity. Numerical analysis of the propagation based on a model nonlinearity corresponding to a strongly saturated two-level system showed good quantitative agreement with the experimental data. (C) 1995 Optical Society of America