Stability of vortex solitons in thermal nonlinear media with cylindrical symmetry

We analyze the salient features of vortex- ring solitons supported by cylindrically symmetric media with nonlocal thermal nonlinearity. We discover the existence of a maximum allowed topological charge for such vortex solitons to be stable on propagation: Only vortex- ring solitons with topological charge 2 m <= are found to be stable. This remarkable result holds independently of the radius of the sample. (c) 2007 Optical Society of America.