Three Dimensional Effects on Proton Acceleration with Grooved Hydrocarbon Targets

TL;DR

This study uses three-dimensional simulations to compare cylindrical and cuboidal grooves on targets for laser-driven proton acceleration, revealing significant differences in proton energies and the impact of laser polarization.

Contribution

It provides the first three-dimensional analysis of how groove geometry and laser polarization affect proton acceleration, highlighting the complex interplay between symmetry and polarization.

Findings

Cylindrical and cuboidal grooves exhibit distinct behaviors in proton acceleration.

Circular polarization reduces proton cut-off energy by up to 15% compared to linear polarization.

Three-dimensional effects are crucial for accurate modeling of structured target proton acceleration.

Abstract

Recently, using two-dimensional particle-in-cell simulations, it has been demonstrated that in laser based proton acceleration with micro-structured targets, a single rectangular groove on the target front offers significant proton cut-off enhancement with linearly polarised laser pulses. In the present work, three-dimensional investigations are carried out to identify notable differences between cylindrical and cuboidal groove geometries both of which correspond to a rectangular groove in a two-dimensional case. In particular, a waveguide model is employed to analyse the effect of the groove geometry and extensive three-dimensional particle-in-cell simulations are performed to demonstrate the distinct behaviour of laser pulse and electrons for cylindrical and cuboidal grooves. Further, the effect of a circular polarisation of the incident laser pulse on the spectra of accelerated protons is studied. It is shown that contrary to our initial expectations, cylindrical symmetry and circular polarisation do not play well together and cause as much as 15$\%$ decay in proton cut-off energies as compared to the case of cylindrical symmetry and linear polarisation.