We present analytical results and computer simulations of the nonlinear evolution of wake field waves in inhomogeneous plasmas. The wake wave break that occurs due to the inhomogeneity of the Langmuir frequency makes it possible to inject electrons into the acceleration phase of the wave. Particle-in-cell simulations show that stable beams of energetic electrons are formed. These beams are well bunched in coordinate and velocity space and contain a considerable fraction of the pulse energy [S1063-651X(98)50311-X]

The results of an analytical description and of a particle-in-cell simulation 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 and reflection of the ultraintense electromagnetic laser radiation from a sharp-boundary plasma, high harmonic generation, and the transformation into low-frequency radiation are discussed. In the case of weak plasma nonuniformity the excitation of nonlinear Langmuir oscillations in the plasma resonance region and the resulting electron acceleration are investigated. The vacuum heating of the electrons and the self-intersection of the electron trajectories are also studied. In the case of a sharp-boundary plasma, part of the energy of the laser pulse is found to be converted into a localized, relativistically strong, nonlinear electromagnetic pulse propagating into the plasma. The expansion of the hot electron cloud into the vacuum region and the action of the ponderomotive force of the laser pulse in the localized longitudinal electric field of the Langmuir oscillations lead to ion acceleration. The energy increase of a minority population of multicharged ions is found to be much greater than that of the ambient ions.

An analytical description of the interaction of laser light with a foil, described as a thin slab of overdense plasma, is presented together with the results of multidimensional particle in cell simulations. The matching conditions at the foil result in nonlinear boundary conditions for the wave equation. The conditions for relativistic transparency are given. The interaction with the foil leads to shaping of the laser pulse. In the case of oblique incidence of a relativistically intense pulse, nonlinear coupling modifies the pulse polarization and causes emission of high harmonics and generation of an electric current. Strong focalization of the reflected pulse, in particular in three-dimensional simulations, is observed for normal and oblique incidence due to the induced distortion of the foil surface. (C) 1998 American Institute of Physics. [S1070-664X(98)03507-1]