Electron acceleration by an intense laser pulse with echelon phase modulation

Abstract

Electron acceleration, in vacuum, mediated by an intense echelon phase-modulated long Gaussian laser pulse, is investigated here. Theoretical and numerical analyses show that this pulse can accelerate an electron to much higher energies than an unmodulated pulse. The staircase-like phase structure of the laser field encourages electron trapping in the favorable wave phase, greatly increasing the effective acceleration distance. Also, the electron motion is now more in the laser propagation direction. The conditions for efficient acceleration are obtained. Since the slower electrons can also be efficiently accelerated to high energies and the accelerated electrons are more axially oriented, the average energy gain by an initially Maxwellian electron bunch can be more than 13 times that obtained without the echelon phase modulation. This is at the expense of somewhat increased spatial and thermal spread, and the accelerated bunch is also more collimated.