Laser-accelerated, low divergence 15 MeV quasi-monoenergetic electron bunches at 1 kHz

TL;DR

This paper reports the generation of 15 MeV quasi-monoenergetic electron bunches at 1 kHz with low divergence using laser wakefield acceleration driven by ultrashort laser pulses in a hydrogen gas jet, highlighting improved beam quality and stability.

Contribution

The study introduces a method to produce low-divergence, quasi-monoenergetic electron bunches at high repetition rate using laser polarization and gas jet control, with unique electron energy distribution observations.

Findings

Electron bunches up to 15 MeV at 1 kHz achieved.

Beam divergence less than 7 mrad.

Electron energy distribution exhibits 2D Lorentzian shape.

Abstract

We demonstrate laser wakefield acceleration of quasi-monoenergetic electron bunches up to 15 MeV at 1 kHz repetition rate with 2.5 pC charge per bunch and a core with < 7 mrad beam divergence. Acceleration is driven by 5 fs, < 2.7 mJ laser pulses incident on a thin, near-critical density hydrogen gas jet. Low beam divergence is attributed to reduced sensitivity to laser carrier envelope phase slip, achieved in two ways using laser polarization and gas jet control: (1) electron injection into the wake on the gas jet's plasma density downramp, and (2) use of circularly polarized drive pulses. Under conditions of mild wavebreaking in the downramp, electron beam profiles have a 2D Lorentzian shape consistent with a kappa electron energy distribution. Such distributions had previously been observed only in space or dusty plasmas. We attribute this shape to the strongly correlated collisionless bunch confined by the quadratic wakefield bubble potential, where transverse velocity space diffusion is imparted to the bunch by the red-shifted laser field in the bubble.