Enhanced laser-driven electron beam acceleration due to ionization-induced injection

TL;DR

This paper demonstrates enhanced laser wakefield acceleration using ionization injection in a helium-nitrogen mixture, achieving higher energy electron beams with improved quality compared to pure helium, and discusses potential for ultra-compact free-electron lasers.

Contribution

The study introduces ionization injection in a helium-nitrogen mixture as a method to improve electron beam quality and energy in laser wakefield acceleration.

Findings

Generated > 300 MeV electron beams at specific plasma densities.

Ionization injection yields higher charge and energy, with narrower energy spread.

Reduced dark current and multiple bunches compared to pure helium.

Abstract

We report an overall enhancement of a laser wakefield acceleration (LWFA) using the ionization injection in a mixture of 0.3 % nitrogen gas in 99.7 % helium gas. Upon the interaction of 30 TW, 30 fs laser pulses with a gas jet of the above gas mixture, > 300 MeV electron beams were generated at a helium plasma densities of 3.3-8.5*10^18 cm^{-3}. Compared with the electron self-injection in pure helium gas jet, the ionization injection has led to the generation of electron beams with higher energies, higher charge, lower density threshold for trapping, and a narrower energy spread without dark current (low energy electrons) or multiple bunches. It is foreseen that further optimization of such a scheme is expected to bring the electron beam energy-spread down to 1 %, making them suitable for driving ultra-compact free-electron lasers