Role of Laser Pulse Shape Asymmetry in Electron Acceleration from Underdense Plasmas

Abstract

Temporal asymmetry in the shape of a linearly polarised laser pulse can influence electron acceleration during interaction with underdense plasmas. This study numerically investigates electron acceleration for Gaussian, positive-skew and negative-skew laser pulses using a one-dimensional fluid model. The positive-skew pulse is characterised by a sharp rise and slow fall, whereas the negative-skew pulse has a slow rise and sharp fall. The model solves Maxwell equations, the electron continuity equation and the electron momentum equations to compare laser propagation, wakefield generation, electron energy gain and harmonic production under different pulse-shape conditions. The results show that the positive-skew pulse generates a strong intensity gradient at the laser front, producing a strong ponderomotive force and an immediate increase in electron energy. However, the negative-skew pulse allows electron oscillations to persist for a longer duration near the laser pulse, resulting in a stronger wakefield of approximately 650 GV/m and the highest electron energy gain of approximately 0.25 MeV. During propagation through the plasma, the laser pulse splits into harmonic components, and odd harmonics up to the 29th order are observed. No substantial difference in spectral intensity is found among the Gaussian, positive-skew and negative-skew cases. These findings indicate that temporal pulse asymmetry can influence wakefield evolution and electron acceleration in underdense plasmas.