Coherent ultra-broadband laser-assisted injection radiation from a laser plasma accelerator

TL;DR

This paper reports the observation of an intense, coherent, ultra-broadband, ultrashort radiation flash generated during electron injection in a laser wakefield accelerator, revealing detailed injection dynamics and high brightness.

Contribution

It provides the first detailed measurements of the spectral, coherence, and polarization properties of the injection radiation in LWFA, highlighting laser-assisted off-axis electron injection mechanisms.

Findings

Generation of a bright, coherent ultra-broadband radiation flash.

Spectral, coherence, and polarization characteristics of the flash analyzed.

Electron injection dynamics preserve wake coherence.

Abstract

The injection of electrons into a laser wakefield accelerator (LWFA) is observed to generate an intense coherent ultra-broadband and ultrashort pulse radiation flash, consistent with the acceleration of electrons from rest to nearly the speed of light in a distance < ~ 1 $\mu$m. The flash is sufficiently bright to induce large nonlinear refractive index shifts in optical materials; we estimate a source brightness temperature of ~$10^{18}$ K. We present measurements of the flash spectra, coherence, pulse duration, polarization and angular distribution, providing a detailed picture of electron injection dynamics in LWFA. These are characteristic of laser-assisted injection of off-axis electrons, which preserves wake coherence.