Spectrally peaked proton beams shock accelerated from an optically shaped overdense gas jet by a near-infrared laser

TL;DR

This study demonstrates the generation of impurity-free proton beams via collisionless shock acceleration from an optically shaped overdense gas jet driven by a near-infrared laser, with significant control over beam properties.

Contribution

It introduces optical shaping of the gas profile to control proton acceleration modes, achieving shock-accelerated proton beams with narrow energy spread and high charge, advancing laser-driven ion acceleration techniques.

Findings

Optical shaping suppresses radial proton emission.

Forward-going protons exhibit narrow energy spread (~7%).

Proton beams are consistent with collisionless shock acceleration.

Abstract

We report on the generation of impurity-free proton beams from an overdense gas jet driven by a near-infrared laser ($\lambda_L=1.053$ $\mathrm{\mu} m$). The gas profile was shaped prior to the interaction using a controlled prepulse. Without this optical shaping, a 30$\pm$4 nCsr$^{-1}$ thermal spectrum was detected transversely to the laser propagation direction with a high energy 8.27$\pm$7 MeV, narrow energy spread (6$\pm$2 %) bunch containing 45$\pm$7 pCsr$^{-1}$. In contrast, with optical shaping the radial component was not detected and instead forward going protons were detected with energy 1.32$\pm$2 MeV, 12.9$\pm$3 % energy spread, and charge 400$\pm$30 pCsr$^{-1}$. Both the forward going and radial narrow energy spread features are indicative of collisionless shock acceleration of the protons.