Enhancing proton acceleration by using composite targets

TL;DR

This paper demonstrates that using composite targets with a thin foil and a near-critical density slab enhances laser-driven proton acceleration by guiding the laser pulse and mitigating foil transparency, leading to higher ion energies.

Contribution

The study introduces composite targets as a novel approach to relax fundamental acceleration limits and significantly increase ion energies in laser-driven acceleration.

Findings

Composite targets guide laser pulses effectively.

Maximum ion energy is substantially increased.

Transverse expansion and transparency limits are mitigated.

Abstract

Efficient laser ion acceleration requires high laser intensities, which can only be obtained by tightly focusing laser radiation. In the radiation pressure acceleration regime, where the tightly focused laser driver leads to the appearance of the fundamental limit for the maximum attainable ion energy, this limit corresponds to the laser pulse group velocity as well as to another limit connected with the transverse expansion of the accelerated foil and consequent onset of the foil transparency. These limits can be relaxed by using composite targets, consisting of a thin foil followed by a near critical density slab. Such targets provide guiding of a laser pulse inside a self-generated channel and background electrons, being snowplowed by the pulse, compensate for the transverse expansion. The use of composite targets results in a significant increase in maximum ion energy, compared to a single foil target case.