Self-Seeding XFELs: Operation Principle and Challenges

Abstract

A high-gain free electron laser gradually became one of the most promising hard X-ray sources after its experimental demonstration in 1997. The baseline mode of operation since then remains the self-amplified spontaneous emission (SASE), which is based on the shot noise amplification. Numerous statistically independent modes emerge in the electron density modulation of the electron beam and, as a result, in the temporal structure of the pulse. In a radiation spectrum, the same number of modes would be present (Figure 1(a)). In this way, SASE radiation has a poor temporal coherence.