X-Ray Free-Electron Lasers and Self-Amplified Spontaneous Emission (SASE)

Abstract

In this chapter, we consider X-ray free-electron lasers and self-amplified spontaneous radiation (SASE). Because there are no suitable seed lasers at these wavelengths and because the development of X-ray optics has not reached a point which makes oscillator configurations robust, the development of X-ray free-electron lasers has relied on SASE where shot noise on the electron beam grows to saturation in a single pass through a long undulator. Because this requires extremely high peak currents in order to enhance the exponential gain, extreme bunch compression is required prior to the injection of the electron beam into the wiggler. Also, since long wigglers are needed, the wiggler line is composed of multiple wiggler segments separated by quadrupoles to provide for strong focusing of the electron beam. In this chapter, we discuss the equivalent noise power for the start-up of SASE, magnetic chicanes for bunch compression, focusing/defocusing (FODO) lattices, simulation of shot noise, comparison between SASE and master oscillator power amplifiers (MOPAs), phase matching between wiggler segments, and phase shifters, and we give comparisons between the simulation procedures discussed in Chap. 6 with SASE experiments.