X-ray free-electron lasing in a flying-focus undulator
Abstract
Laser-driven free-electron lasers (LDFELs) replace magnetostatic undulators with the electromagnetic fields of a laser pulse. Because the undulator period is half the wavelength of the laser pulse, LDFELs can amplify x rays using lower electron energies and over shorter interaction lengths than a traditional free-electron laser. In LDFELs driven by conventional laser pulses, the undulator uniformity required for high gain necessitates large laser-pulse energies. Here, we show that a flying-focus pulse provides the undulator uniformity required to reach high gain with a substantially lower energy than a conventional pulse. The flying-focus pulse features an intensity peak that travels in the opposite direction of its phase fronts. This enables an LDFEL configuration where an electron beam collides head-on with the phase fronts and experiences a near-constant undulator strength as it co-propagates with the intensity peak. Three-dimensional simulations of this configuration demonstrate the generation of megawatts of coherent x-ray radiation with 20 times less energy than a conventional laser pulse.
Cite
@article{arxiv.2410.12975,
title = {X-ray free-electron lasing in a flying-focus undulator},
author = {D. Ramsey and B. Malaca and T. T. Simpson and M. Formanek and L. S. Mack and J. Vieira and D. H. Froula and J. P. Palastro},
journal= {arXiv preprint arXiv:2410.12975},
year = {2025}
}