Self-Amplified Spontaneous (or Stimulated) 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 up 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.
The SPring-8 FEL in Japan has demonstrated this concept and it is the principle that will be employed by the Linac Coherent Light Source (LCLS) and the European x-ray free electron laser.