Simultaneous measurements on the electron and X-ray spectra from laser-irradiated near-critical-density double-layer targets at relativistic intensity

TL;DR

This study experimentally investigates electron and X-ray emissions from laser-irradiated near-critical-density double-layer targets, revealing optimal conditions for high-energy electron acceleration and bright X-ray generation through combined mechanisms.

Contribution

It provides new experimental data on electron and X-ray spectra dependence on target parameters and confirms acceleration mechanisms via 2D particle-in-cell simulations.

Findings

Electrons with 5.5 MeV temperature achieved

X-rays with 5 keV critical energy produced

Electron acceleration occurs through direct laser acceleration in plasma channels

Abstract

We report the experimental results of simultaneous measurements on the electron and X-ray spectra from near-critical-density (NCD) double-layer targets irradiated by relativistic femtosecond pulses at the intensity of 5E19 W/cm^2. The dependence of the electron and X-ray spectra on the density and thickness of the NCD layer was studied. For the optimal targets, electrons with temperature of 5.5 MeV and X-rays with critical energy of 5 keV were obtained. 2D particle-in-cell simulations based on the experimental parameters confirm the electrons are accelerated in the plasma channel through direct laser acceleration, resulting in temperature significantly higher than the pondermotive temperature. Bright X-rays are generated from betatron emission and Thomson backscattering before the electrons leave the double-layer targets.