Langevin description of speckle dynamics in nonlinear disordered media

Abstract

We formulate a Langevin description of dynamics of a speckle pattern resulting from the multiple scattering of a coherent wave in a nonlinear disordered medium. The speckle pattern exhibits instability with respect to periodic excitations at frequencies [Formula presented] below some [Formula presented] provided that the nonlinearity exceeds some [Formula presented]-dependent threshold. A transition of the speckle pattern from a stationary state to the chaotic evolution is predicted upon increasing nonlinearity. The shortest typical time scale of chaotic intensity fluctuations is of the order of [Formula presented] © 2003 The American Physical Society.