Dynamic Desynchronization of a Free-Electron Laser Resonator

In a free-electron laser oscillator operating with short electron bunches, the desynchronism between electron bunches and optical pulses resulting in the shortest buildup time to saturation is different from that giving the largest saturated power. In this Rapid Communication we present an experimental demonstration of the dynamic variation of the cavity desynchronism. This is achieved by ramping the electron-bunch repetition frequency during part of each 12-mus machine pulse. A high small-signal gain and a high saturated power are obtained simultaneously.