Mechanisms to control laser-plasma coupling in laser wakefield electron acceleration

TL;DR

This paper demonstrates optimized laser-plasma coupling in laser wakefield acceleration through experimental and modeling techniques, improving electron bunch quality, energy, and alignment by tailoring plasma density and laser focus.

Contribution

It introduces novel control mechanisms for laser-plasma coupling, including tailored plasma density profiles and adaptive laser wavefront shaping, to enhance electron acceleration performance.

Findings

Enhanced electron bunch quality and energy with density downramp extension

Reduced electron bunch angular deviation through focal position optimization

Validated PIC simulations accurately predict bunch properties

Abstract

Experimental results, supported by precise modelling, demonstrate optimisation of a plasma-based injector with intermediate laser pulse energy ($<1$ J), corresponding to a normalised vector potential $a_0 = 2.15$, using ionisation injection in a tailored plasma density profile. An increase in electron bunch quality and energy is achieved experimentally with the extension of the density downramp at the plasma exit. Optimisation of the focal position of the laser pulse in the tailored plasma density profile is shown to efficiently reduce electron bunch angular deviation, leading to a better alignment of the electron bunch with the laser axis. Single peak electron spectra are produced in a previously unexplored regime by combining an early focal position and adaptive optic control of the laser wavefront through optimising the symmetry of the pre-focal laser energy distribution. Experimental results have been validated through particle-in-cell simulations using realistic laser energy, phase distribution, and temporal envelope, allowing for accurate predictions of difficult to model parameters, such as total charge and spatial properties of the electron bunches, opening the way for more accurate modelling for the design of plasma-based accelerators.