Tapering Enhanced Stimulated Superradiant Amplification
  High conversion efficiency between electrical and optical power is highly desirable both for high peak and high average power radiation sources. In this paper, we discuss a new mechanism based on stimulated superradiant emission in a strongly tapered undulator whereby an optimal undulator tapering is calculated by dynamically matching the resonant energy variation to the ponderomotive decelerating gradient. The method has the potential to allow the extraction of a large fraction (~50%) of power from a relativistic electron beam and convert it into coherent narrow-band tunable radiation, and shows a clear path to very high average power radiation sources. 
Joseph Duris, Alex Murokh and Pietro Musumeci
physics.acc-ph