Propagation of Gaussian beams in a nonlinear saturable medium.

A variational procedure is implemented to investigate the propagation of cw Gaussian beams in a saturable medium with and without loss. The saturation is modeled by taking into account higher-order terms in the intensity-dependent refractive index. In the lossless case, exact analytical expressions for the behavior of the spot width are determined, along with the condition for steady-state propagation. Gaussian beams under dissipation are also considered, and the results agree with recent numerical simulations.