Mutual coherence of the components of a stimulated emission spectrum under self-focusing and self-switching conditions

An analysis is made of the stability of a plane monochromatic wave in a transparent isotropic dispersive medium exhibiting a cubic nonlinear polarizability. The frequencies of growing perturbations are obtained in the first approximation. In the second approximation, these perturbations acquire additional harmonics. Exact periodic solutions are obtained in the form of amplitude- and phase-modulated waves of the envelope curve. In the first approximation the period of these waves is equal to the fundamental period of the space–time instability. It is concluded that a plane monochromatic wave is transformed in such a medium into a periodic amplitude- and phase-modulated wave. It follows from the theoretical model that under self-focusing conditions the scattered-light spectrum should consist of equidistant frequency–angular components observed in earlier experiments and the radiation should be spatially coherent. The spatial coherence is supported by interference experiments.