Efficiency of radiation friction losses in laser-driven "hole boring" of dense targets

TL;DR

This paper investigates how radiation friction affects energy conversion in laser-driven hole boring of dense targets at ultra-high intensities, combining analytical modeling with 3D simulations to understand energy losses.

Contribution

It provides a new analytical model accounting for radiation losses in thick plasma targets, validated by 3D simulations, enhancing understanding of laser-plasma interactions at extreme intensities.

Findings

Radiation losses are significant in thick targets at >10^{23} W/cm^2.

Collective effects reduce radiation losses compared to electrons in vacuum.

Classical models remain valid at higher intensities due to collective effects.

Abstract

In the interaction of laser pulses of extreme intensity ($>10^{23}~{\rm W cm}^{-2}$) with high-density, thick plasma targets, simulations show significant radiation friction losses, in contrast to thin targets for which such losses are negligible. We present an analytical calculation, based on classical radiation friction modeling, of the conversion efficiency of the laser energy into incoherent radiation in the case when a circularly polarized pulse interacts with a thick plasma slab of overcritical initial density. By accounting for three effects including the influence of radiation losses on the single electron trajectory, the global `hole boring' motion of the laser-plasma interaction region under the action of radiation pressure, and the inhomogeneity of the laser field in both longitudinal and transverse direction, we find a good agreement with the results of three-dimensional particle-in-cell simulations. Overall, the collective effects greatly reduce radiation losses with respect to electrons driven by the same laser pulse in vacuum, which also shift the reliability of classical calculations up to higher intensities.