Generation of ultrafast electrons by simultaneous stimulated Raman backward and forward scattering

Fast electron generation in stimulated Raman forward and backward scattering is investigated. The simultaneous forward and backward scattering is shown to create an electrostatic Geld structure which is exceptionally efBcient in producing highly relativistic electrons. The Vlasov-Maxwell simulations reveal that the two plasma wave packets generated by the backward and forward scattering are spatially separated, and thus form a two-staged electron "accelerator. " The bulk electrons are accelerated from the lower boundary of the trapping region of the slower wave to the upper boundary of the trapping region of the faster wave. The mechanism of the electron acceleration is analyzed by Vlasov-Maxwell simulations with self-consistent fields and by test particle calculations with prescribed electrostatic fields.