Nonlinear absorption on the front of relativistically strong electromagnetic pulse in an underdense plasma

The recent progress in producing extremely strong laser pulses has made available for investigators the relativistically strong laser pulses in the field of which the energy of oscillating electron can exceed their rest energy mc2. In the ultrarelativistic limit the matter of primary interest is to study the nonlinear interaction on the pulse edges, since inside the main body of the pulse the interaction is suppressed due to the relativistic electron mass growth. As it was shown the sharp leading edge of the pulse generates an intense electron plasma wave. For the smooth pulses the leading part of the pulse can undergo steepening as a result of various nonlinear processes, for example, it can be initiated by the stimulated backward Raman scattering. Once the steepening has appeared the excitation of the plasma wake is switched on and we again return to the case of a sharp leading edge. In the present paper the propagation of a relativistically strong electromagnetic pulse in an underdense homogeneous plasma is considered with the focus on the possible existence of stationary structure of a pulse front. (author) 6 refs., 2 figs