Recent progress in short wavelength free-electron lasers extending from the extreme ultraviolet through the x-ray regime have opened new avenues for industrial and research applications. A high-gain/low-Q oscillator, i.e., a regenerative amplifier free-electron laser (RAFEL), is one possible concept. In this paper, we present the first analysis of efficiency enhancement in a RAFEL with a long, tapered undulator line. For the present analysis, we consider a high average power EUV RAFEL at 13.5 nm and show that the performance exceeds that of single-pass, tapered self-amplified spontaneous emission. This points the way to high power tapered undulator x-ray RAFELs.
@article{arxiv.2501.01911,
title = {Efficiency enhancement in regenerative amplifier free-electron lasers using a tapered undulator},
author = {Henry Freund and Peter van der Slot and Patrick O'Shea},
journal= {arXiv preprint arXiv:2501.01911},
year = {2025}
}