Vacuum acceleration of electrons by a diffracted laser beam

To be effective, electron acceleration by a laser beam in vacuum requires efficient electron injection into the beam and a mechanism for counteracting transverse expulsion. These requirements are hard to satisfy with a conventional laser beam. However, recent experiments using the high-contrast 20 TW laser system at Tel-Aviv University have revealed that a conventional laser beam diffracted by a wavelength-scale rod can generate well-directed bunches of energetic electrons. We have performed two-dimensional kinetic simulations and test particle calculations to investigate the impact of the field topology in the diffracted beam on electron acceleration. Our simulations results reproduce the formation of the forward-directed electron bunches seen in the experiment. This suggests that the considered setup has the potential to solve the injection and the expulsion problems.