INTERACTION OF AN ULTRASHORT, RELATIVISTICALLY STRONG LASER-PULSE WITH AN OVERDENSE PLASMA

The results of an analytical description and of a particle-in-cell sim ulation of the interaction of an ultrashort, relativistically intense laser pulse, obliquely incident on a nonuniform overdense plasma, are presented and several novel features are identified. The absorption an d reflection of the ultraintense electromagnetic laser radiation from a sharp-boundary plasma, high harmonic generation, and the transformat ion into low-frequency radiation are discussed. In the case of weak pl asma nonuniformity the excitation of nonlinear Langmuir oscillations i n the plasma resonance region and the resulting electron acceleration are investigated. The vacuum heating of the electrons and the self-int ersection of the electron trajectories are also studied. In the case o f a sharp-boundary plasma, part of the energy of the laser pulse is fo und to be converted into a localized, relativistically strong, nonline ar electromagnetic pulse propagating into the plasma. The expansion of the hot electron cloud into the vacuum region and the action of the p onderomotive force of the laser pulse in the localized longitudinal el ectric field of the Langmuir oscillations lead to ion acceleration. Th e energy increase of a minority population of multicharged ions is fou nd to be much greater than that of the ambient ions.