Betatron radiation emitted during the direct laser acceleration of electrons in underdense plasmas

TL;DR

This paper demonstrates through simulations that direct laser acceleration in underdense plasmas can produce high-brightness, high-energy betatron radiation with potential applications in gamma-ray sources, highlighting the importance of plasma density and laser focusing.

Contribution

The study provides the first detailed analysis combining PIC simulations and analytical estimates of betatron radiation in DLA, emphasizing low plasma density and optimal laser focusing for enhanced brightness.

Findings

DLA can emit ~10^{10} photons at hundreds of MeV energies.

Low plasma density improves radiation collimation and brightness.

Conversion efficiency can reach a few percent with optimal focusing.

Abstract

Relativistic laser pulses can accelerate electrons up to energies of several GeV during the interaction with gaseous targets through the direct laser acceleration (DLA) mechanism. While the electrons are accelerated to high energies, they oscillate transversely to the laser propagation direction, emitting radiation. We demonstrate using particle-in-cell (PIC) simulations that the high accelerated electron charge enables DLA sources to emit $\sim 10^{10}~\rm{photons}/0.1\%\rm{BW}$ at energies of hundreds MeV when interacting with multi-petawatt laser pulses. We provide an analytical estimate of the expected critical frequency for the DLA betatron spectrum which is in strong agreement with PIC simulations. We also show that using gas jets of low density ($\sim 10^{19}~\rm{cm^{-3}}$) is beneficial for the brightness of the source, since low plasma density produces collimated radiation. If the laser pulse is focused to an optimal spot size that results in the highest cut-off energies, conversion efficiency from laser to radiation can reach up to a few percent, which makes the DLA a promising high-brilliance source of gamma-ray radiation.