Nonlinear Dynamics of Wave Beams and Packets in an Ionizable Medium

We present a review of the studies on nonlinear dynamics of the plasma–field system formed in the processes of breakdown of a gas by high-intensity laser or microwave radiation. The ionization instability dominating these processes significantly modifies the known effects of self-action of waves in a medium and gives rise to a number of new effects which are absent for other nonlinearity mechanisms. We describe the most important among these effects, such as the ionization–field instability of a plane wave, the self-channeling of radiation in the form of surface or leaky waves, and the self-conversion of the spectrum of the ionizing radiation. The results of numerical simulations of the dynamics of nonequilibrium freely-localized discharges created by focused microwave and laser pulses are presented.