Abstract

Direct-field electron acceleration using radially polarized (TM₀₁) laser beams has recently been demonstrated experimentally using two-cycle laser pulses and a gas target [1]. Recent theoretical work has shown that this scheme could be used to generate quasi-monoenergetic electron pulses suitable for ultrafast electron diffraction with unprecedented time resolution [2]. The acceleration occurs when relativistic electrons move in phase with the longitudinal electric field component E_z of the TM₀₁ laser beam over a sizable length. In order to optimize the duration, energy, angular spread, and flux of the electron beams produced by direct-field acceleration, we have investigated how the introduction of frequency chirp in the pulse shape would affect the acceleration process. It has been reported in the literature that the use of chirped pulses can produce more energetic electrons in the context of other laser acceleration schemes [3,4].

© 2015 IEEE