On the physics of electron ejection from laser-irradiated overdense plasmas

TL;DR

This paper investigates how intense laser pulses cause electron bunch ejection from overdense plasmas, revealing the role of plasma capacitors and gradient scale lengths, and linking the process to high-harmonic generation.

Contribution

It introduces a model explaining electron ejection dynamics and their dependence on laser intensity and plasma gradient scale length, connecting it to high-harmonic generation mechanisms.

Findings

Electron bunch ejection is maximized for short gradient scale lengths.

A plasma capacitor forms during each laser cycle, accelerating electrons.

The process is linked to high-harmonic generation via the Relativistic Oscillating Mirror mechanism.

Abstract

Using 1D and 2D PIC simulations, we describe and model the backward ejection of electron bunches when a laser pulse reflects off an overdense plasma with a sharp density gradient on its front side. The dependence on the laser intensity and gradient scale length is studied. It is found that during each laser period the incident laser pulse generates a large charge-separation field, or plasma capacitor, which accelerates an attosecond bunch of electrons towards vacuum. This process is maximized for short gradient scale lengths and collapses when the gradient scale length is comparable to the laser wavelength. We develop a model that reproduces the electron dynamics and the dependence on laser intensity and gradient scale length. This process is shown to be strongly linked with high-harmonics generation via the Relativistic Oscillating Mirror mechanism.