Enhanced laser-driven proton acceleration via improved fast electron heating in a controlled pre-plasma

TL;DR

This paper demonstrates that creating a controlled pre-plasma with a femtosecond pre-pulse significantly enhances laser-driven proton acceleration by increasing the energy of fast electrons, confirmed through experiments and simulations.

Contribution

It provides experimental evidence and numerical validation that a micrometer scale-length pre-plasma improves proton acceleration efficiency by enhancing fast electron heating.

Findings

Three-fold increase in proton cut-off energy with pre-plasma

Numerical simulations confirm stochastic electron heating role

Pre-plasma creation via femtosecond pre-pulse enhances acceleration

Abstract

The interaction of ultraintense laser pulses with solids is largely affected by the plasma gradient at the vacuum-solid interface, which modifies the absorption and ultimately, controls the energy distribution function of heated electrons. A micrometer scale-length plasma has been predicted to yield a significant enhancement of the energy and weight of the fast electron population and to play a major role in laser-driven proton acceleration with thin foils. We report on recent experimental results on proton acceleration from laser interaction with foil targets at ultra-relativistic intensities. We show a three-fold increase of the proton cut-off energy when a micrometer scale-length pre-plasma is introduced by irradiation with a low energy femtosecond pre-pulse. Our realistic numerical simulations agree with the observed gain of the proton cut-off energy and confirm the role of stochastic heating of fast electrons in the enhancement of the accelerating sheath field.