Self-amplified stimulated emission
Self-amplified stimulated (or spontaneous) emission (SASE) is a process within a free-electron laser (FEL) by which a laser beam is created by the high-energy electron beam. The lasing starts up from the random microbunching (i.e., shot noise) on the electron beam instead of being coherently produced by an input seed laser source. This source is fully transversely coherent at saturation, but, because the radiation starts from random noise at many radiation wavelengths, the longitudinal coherence of the radiation is less than that of the amplifier case but better than that of spontaneous radiation.
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