Laser-driven plasma acceleration in a regime of strong-mismatch between the incident laser envelope and the nonlinear plasma response

TL;DR

This paper investigates a strongly mismatched laser-plasma acceleration regime, revealing new dynamics and the potential for higher electron energies than traditional matched regimes, through a novel adjusted-a0 model.

Contribution

It introduces a new adjusted-a0 model for the strongly mismatched regime and uncovers novel interaction dynamics and enhanced electron acceleration capabilities.

Findings

Laser pulse transforms into an optical shock in the mismatched regime.

The strongly mismatched regime can produce higher electron energies than matched regimes.

New self-injection mechanisms are identified in the elongated bubble shape.

Abstract

We explore a regime of laser-driven plasma acceleration of electrons where the radial envelope of the laser-pulse incident at the plasma entrance is strongly mismatched to the nonlinear plasma electron response excited by it. This regime has been experimentally studied with the gemini laser using f/40 focusing optics in August 2015 and f/20 in 2008. The physical mechanisms and the scaling laws of electron acceleration achievable in a laser-plasma accelerator have been studied in the radially matched laser regime and thus are not accurate in the strongly mismatched regime explored here. In this work, we show that a novel adjusted-a0 model applicable over a specific range of densities where the laser enters the state of a strong optical shock, describes the mismatched regime. Beside several novel aspects of laser-plasma interaction dynamics relating to an elongating bubble shape and the corresponding self-injection mechanism, importantly we find that in this strongly mismatched regime when the laser pulse transforms into an optical shock it is possible to achieve beam-energies that significantly exceed the incident intensity matched regime scaling laws.