Exponential Gain and Saturation of a Self-Amplified Spontaneous Emission Free-Electron Laser

TLDR

Self‑amplified spontaneous emission in a free‑electron laser has been proposed to generate very high‑brightness coherent X‑rays. The process employs a high‑energy, high‑charge, short‑pulse, low‑emittance electron beam passing through a long series of high‑quality undulator magnets, causing the emitted radiation to grow exponentially until saturation. The experiment demonstrated exponential gain and saturation of self‑amplified spontaneous emission at 530 nm and 385 nm, with theory and simulation in good agreement, confirming the underlying physics and supporting the development of operational X‑ray free‑electron lasers.

Abstract

Self-amplified spontaneous emission in a free-electron laser has been proposed for the generation of very high brightness coherent x-rays. This process involves passing a high-energy, high-charge, short-pulse, low-energy-spread, and low-emittance electron beam through the periodic magnetic field of a long series of high-quality undulator magnets. The radiation produced grows exponentially in intensity until it reaches a saturation point. We report on the demonstration of self-amplified spontaneous emission gain, exponential growth, and saturation at visible (530 nanometers) and ultraviolet (385 nanometers) wavelengths. Good agreement between theory and simulation indicates that scaling to much shorter wavelengths may be possible. These results confirm the physics behind the self-amplified spontaneous emission process and forward the development of an operational x-ray free-electron laser.