High-charge relativistic electrons by vacuum laser acceleration from plasma mirrors using flying focus pulses

TL;DR

This paper demonstrates that flying focus laser pulses significantly enhance the charge yield of relativistic electrons in vacuum laser acceleration from plasma mirrors, overcoming velocity mismatch issues.

Contribution

The study introduces the use of flying focus lasers to improve electron acceleration efficiency and charge yield in vacuum laser acceleration from plasma mirrors.

Findings

Flying focus lasers increase relativistic electron charge yield.

Enhanced synchronization of electrons within the acceleration region.

Prolonged longitudinal ponderomotive force in flying focus lasers.

Abstract

Relativistic electron beams produced by intense lasers over short distances have important applications in high energy density physics and medical technologies. Vacuum laser acceleration with plasma mirrors injectors has garnered substantial research interest recently. However, a persistent challenge remains unresolved that electrons inevitably detach from the laser acceleration phase due to velocity mismatch. Here, we employ flying focus lasers to address this limitation. Through three-dimensional particle-in-cell simulations, we demonstrate that flying focus lasers can achieve a substantial enhancement in relativistic electron charge yield compared to conventional Gaussian lasers. This improvement stems from two key attributes: (1) The subluminal propagation velocity of the peak intensity keeps a larger electron population synchronized within the longitudinal ponderomotive acceleration region, and (2) Flying focus lasers sustain higher magnitudes of the longitudinal ponderomotive force over longer distances in comparison to Gaussian lasers. This approach offers high-charge relativistic electron sources ideal for demanding applications such as high-flux Thomson scattering and radiography.