Thermal defocusing and transformation of the statistics of a spatially noncoherent light beam

The Monte Carlo method is used to consider the problem of thermal self-interaction of a multimode light beam. A study is made of the transformation of the statistics of the distributions of the intensity and phase of the radiation, and also of the behavior of the average width and of the spatial coherence radius. It is shown that at distances of the order of the nonlinear thermal self-interaction length of coherent radiation a multimode beam splits into filaments and this results in deterioration of its spatial coherence and in a considerable change in the statistics of the radiation.