Coherent radiation of an electron bunch colliding with an intense laser pulse

TL;DR

This paper investigates the conditions under which an electron bunch colliding with an intense laser pulse emits coherent radiation, revealing a backward emission with narrow angular spread and extending to high frequencies, supported by analytical and simulation results.

Contribution

It provides a theoretical framework for coherent radiation emission in laser-electron interactions and validates it with 3D particle-in-cell simulations, highlighting potential for high-frequency radiation.

Findings

Coherent radiation is emitted backwards with narrow angular spread.

The spectrum extends to hundreds of keV frequencies.

Simulations confirm the analytical predictions of coherence effects.

Abstract

We study the conditions for coherent radiation of an electron bunch driven by a counterpropagating strong pulsed electromagnetic plane wave. We derive the spectrum of the coherent radiation and show that it is emitted backwards with respect to the laser propagation direction and has a very narrow angular spread. We demonstrate that for a solid density plasma coherent radiation extends to frequencies up to hundreds of keV thereby enhancing the low-frequency part of the spectrum by many orders of magnitude. Our analytical findings are tested with 3D particle-in-cell simulations of an electron bunch passing through a laser pulse, clearly demonstrating how the coherence can essentially modify the observed radiation spectrum.