Coherent frequency combs from electrons colliding with a laser pulse

TL;DR

This paper derives analytical conditions for generating coherent soft x-ray frequency combs via electron-laser collisions, demonstrating that regular electron spacing and monoenergetic beams enable high-quality coherent emission, with potential applications across various frequency ranges.

Contribution

It provides the first analytical framework for coherent x-ray comb generation from electron-laser interactions, including conditions for beam properties and pulse duration.

Findings

Coherent soft x-ray frequency combs require regularly spaced, monoenergetic electrons.

Few-cycle laser pulses relax energy uniformity requirements for coherence.

Conditions can be adapted for terahertz frequency emission.

Abstract

Highly coherent and powerful light sources capable of generating soft x-ray frequency combs are essential for high precision measurements and rigorous tests of fundamental physics. In this work, we derive the analytical conditions required for the emission of coherent radiation from an electron beam colliding with a laser pulse, modeled as a plane wave. These conditions are applied in a series of numerical simulations, where we show that a soft x-ray frequency comb can be produced if the electrons are regularly spaced and sufficiently monoenergetic. High quality beams of this kind may be produced in the near future from laser-plasma interactions or linear accelerators. Furthermore, we highlight the advantageous role of employing few-cycle laser pulses in relaxing the stringent monoenergeticity requirements for coherent emission. The conditions derived here can also be used to optimize coherent emission in other frequency ranges, such as the terahertz domain.