Mechanisms of self-focusing in the interaction of laser radiation with a gaseous medium

An analysis is made of the influence of changes in the density and polarizability of molecules in a medium on changes in the refractive index when the molecules in a gas absorb resonant radiation. The example of the absorption of HF laser radiation by atmospheric water vapor is used to show that the striction and a change in the resonant part of the polarizability on saturation of the absorbing transition, as well as kinetic cooling, may play an important role in the formation of a transient focusing lens.