Thermal self-interaction, optical turbulence and self-excited oscillations of radiation in a medium moving along a beam

Analytic and numerical investigations are made of thermal self-defocusing of a radiation beam in a medium moving parallel or antiparallel to the beam. It is shown that a nonlinearity, which accumulates and becomes integrated along the beam either in space or in time, initiates various types of optical turbulence that determine the minimum nonlinear divergence of the beam and the optimal nonlinear coherence of the radiation. The relevant parameters are determined and maps of stable and unstable regimes, of growing space–time self-excited oscillations, and of the self-interaction of the radiation are established. Similar turbulent processes associated with other mechanisms of the refractive-index nonlinearity are pointed out.