Self-focusing of a light beam in an absorbing medium moving at near-sonic velocity

Linearized equation of hydrodynamics are used in a calculation of the perturbation of the density in a gaseous medium moving relative to a light beam at a near-sonic velocity. For Mach numbers M > 1, where (M²–1) ≪ 1, the density perturbations are such that a focusing dielectric waveguide forms in the medium and the focusing occurs mainly in a plane parallel to the direction of motion of the medium. Estimates of the critical powers needed for self-focusing indicate that the predicted effects should be important in the propagation of laser radiation in the atmosphere.