Physical mechanism of electron bunch generation by an ultrarelativistic-intensity laser pulse passing through a sharp plasma boundary

The physical mechanism of the interaction process of a laser pulse of ultrarelativistic intensity with semi-bounded plasma having a sharp boundary is studied in one-dimensional geometry. It is shown that electron bunches are generated by the laser pulse due to the multiflow motion of plasma electrons with crossing trajectories. An analytical relation that allows an electron bunch charge to be estimated as a function of plasma characteristics and electron trajectory parameters is derived and confirmed by the results of numerical simulations.