Role of ultrashort trapezoidal temporal pulse profile in laser wakefield acceleration in bubble regime

Abstract

A computational study is presented on laser wakefield acceleration (LWFA) in bubble regime with the use of ultrashort laser pulse propagating in an under‐dense plasma. The Particle‐In‐Cell simulations are performed to investigate the bubble wakefield acceleration of electrons realized by the incidence of an intense laser beam on cold, under‐dense plasma in two‐dimensional geometry. Different simulations are carried out and the results are compared for the beams with trapezoidal and Gaussian temporal pulse profiles having almost equal but slightly different energy contents. Focus is given to plasma density modulation, wakefield strength, electrons self‐injection, energy spectrum of accelerated electrons, the effect of an external longitudinal magnetic field and the study of pump depletion length and dephasing length in bubble regime with respect to these laser pulse profiles. Two limiting cases of the trapezoidal pulse, that is, triangular and rectangular pulses, are also discussed for better understanding of the role of steepness and plateau region in the laser pulse profile to the bubble wakefield acceleration. Since down ramp density gradient plays a crucial role for the generation of high‐quality electron beam in plasma wakefield acceleration as well as in LWFA, three different adjustments on the down ramp length determining three different density gradients are discussed for uncovering the role of trapezoidal laser pulse in LWFA.