Robust self-trapping of vortex beams in a saturable optical medium

We report on the observation of robust self-trapping of vortex beams propagating in a uniform condensed medium featuring local saturable self-focusing nonlinearity. Optical vortices with topological charge m=1, that remain self-trapped over approximately five Rayleigh lengths, are excited in carbon disulfide using a helical light beam at 532 nm and intensities from 8 to 10GW/cm2. At larger intensities, the vortex beams lose their stability, spontaneously breaking into two fragments. Numerical simulations based on the nonlinear Schrödinger equation, including the three-photon absorption and nonpolynomial saturation of the refractive nonlinearity, demonstrate close agreement with the experimental findings.