Review of x-ray free-electron laser theory

TLDR

High‑gain free‑electron lasers are being developed as extremely bright sources for next‑generation x‑ray facilities. This paper reviews the basic theory of start‑up, exponential growth, and saturation in high‑gain FELs, focusing on self‑amplified spontaneous emission. The review covers radiation characteristics such as transverse coherence, temporal features, and harmonic content, examines performance under machine errors and undulator wakefields, and summarizes enhancement schemes via seeding and beam manipulations.

Abstract

High-gain free-electron lasers (FELs) are being developed as extremely bright sources for a next-generation x-ray facility. In this paper, we review the basic theory of the start-up, the exponential growth, and the saturation of the high-gain process, emphasizing the self-amplified spontaneous emission. The radiation characteristics of an x-ray FEL, including its transverse coherence, temporal characteristics, and harmonic content, are discussed. FEL performance in the presence of machine errors and undulator wakefields is examined. Various enhancement schemes through seeding and beam manipulations are summarized.