Saturation Mechanism and Improvement of Conversion Efficiency of the Free-Electron Laser

Abstract
Saturation mechanisms of free-electron lasers are investigated in the Compton regime. It is found that saturation occurs because of quasilinear energy spreading of the electron beam in the case of multimode excitation. The energy conversion efficiency remains low even if many modes are taken into account. To improve the conversion efficiency, the effect of reacceleration by a microwave is investigated and turns out to increase the efficiency to more than 50%.