# Effects of hole-boring and relativistic transparency on particle acceleration in overdense plasma irradiated by short multi-PW laser pulses

## TL;DR

This paper investigates how relativistic transparency and hole-boring influence particle acceleration in overdense plasma under ultra-intense laser pulses, revealing conditions for proton energies up to 20 GeV.

## Contribution

It provides new insights into the interplay of transparency and hole-boring regimes affecting particle acceleration at multi-PW laser intensities.

## Key findings

- Protons can reach 10-20 GeV energies.
- Acceleration efficiency depends on initial plasma density and laser intensity.
- Relativistic transparency and hole-boring regimes are sensitive to plasma and laser parameters.

## Abstract

Propagation of short and ultra-intense laser pulses in a semi-infinite space of overdense hydrogen plasma is analyzed via fully-relativistic, real geometry particle-in-cell (PIC) simulations including radiation friction. The relativistic transparency and hole-boring regimes are found to be sensitive to the transverse plasma field, backward light reflection, and laser pulse filamentation. For laser intensities approaching $I\sim10^{24}$ W/cm$^2$ the direct laser acceleration of protons, along with ion Coulomb explosion, results in their injection into the acceleration phase of the compressed electron wave at the front of the laser pulses. The protons are observed to be accelerated up to 10-20 GeV with densities around a few times the critical density. The effect strongly depends on initial density and laser intensity disappearing with initial density increase and intensity decrease.