Stabilization of transverse solitary waves by a nonlocal response of the nonlinear medium.

Optical pumping of atomic vapors can lead to self-focusing of resonant laser beams. The saturation of the optical pumping process at low intensity allows the study of transverse solitons in the form of selftrapped laser beams, using low-power cw lasers. The long lifetime of the optically pumped atoms allows the atomic diffusion to transport the excitation away from the interaction region. Numerical simulations show that the resulting nonlocal response of the medium represents an important mechanism that stabilizes the self-trapped beam. The theoretical predictions are confirmed by experimental results from sodium vapor.