Stochastic heating of electrons in focused multimode laser fields

Abstract

A direct relativistic electron-acceleration-simulation model with a given electromagnetic field, which is determined by the wave-packet parameters, is considered. The multimode time-spatial structure of a focused Nd-laser beam with stochastic phase disturbances of each spectral components is taken into account as a source of random forces. The electron energies of more than 10 MeV are derived even at moderate flux densities of 1016 W/cm2. The numerical code developed makes it possible to obtain a quantitative energy-distribution function with respect to both the field intensities and the temporal U-shaped laser pulse. An efficient heating of electrons can be triggered in the presence of a counter-propagating wave reflected from the critical plasma area with a varied reflection coefficient. The heating mechanism occurs with a delay with respect to the beginning of a pulse when the laser fields exceed certain threshold amplitudes. A qualitative comparison of the results of simulation with the experimental data is given to justify this mechanism.