Evolution of spatial solitons in quadratic media with fluctuating nonlinearity

The influence of a fluctuating nonlinearity on the propagation of spatial s olitons in quadratic media is studied. We derive mean field evolution equat ions for both frequency components and show that fluctuations of the nonlin earity induce effective nonlinear losses. The predictions of the mean field theory are in good agreement with numerical simulations of the full stocha stic system. We find an approximate analytical expression for the damping r ate of spatial solitons and show that the amplitude of the fundamental wave decreases more rapidly than the amplitude of the second harmonic. (C) 1999 Elsevier Science B.V. All rights reserved.