# Laser reflection as a catalyst for direct laser acceleration in multipicosecond laser-plasma interaction

## TL;DR

This paper reveals that laser reflection significantly enhances high-energy electron production in multipicosecond laser-plasma interactions, through a two-stage acceleration process involving stochastic and non-stochastic phases.

## Contribution

It introduces a new understanding of how laser reflection catalyzes direct laser acceleration, highlighting the two-stage process and its relevance to multipicosecond laser applications.

## Key findings

- Laser reflection acts as a catalyst for electron acceleration.
- High energy electrons are produced via a two-stage process.
- Electrostatic potential energy gain is secondary to laser reflection effects.

## Abstract

We demonstrate that laser reflection acts as a catalyst for superponderomotive electron production in the preplasma formed by relativistic multipicosecond lasers incident on solid density targets. In 1D particle-in-cell simulations, high energy electron production proceeds via two stages of direct laser acceleration, an initial stochastic backward stage, and a final non-stochastic forward stage. The initial stochastic stage, driven by the reflected laser pulse, provides the pre-acceleration needed to enable the final stage to be non-stochastic. Energy gain in the electrostatic potential, which has been frequently considered to enhance stochastic heating, is only of secondary importance. The mechanism underlying the production of high energy electrons by laser pulses incident on solid density targets is of direct relevance to applications involving multipicosecond laser-plasma interactions.