THE RESPONSE OF THE SHORT-PULSE FREE-ELECTRON LASER-OSCILLATOR TO PERIODIC PERTURBATION OF THE CAVITY SYNCHRONISM

The detailed optical pulse structure of the short pulse free-electron laser depends on the synchronism between optical and electron pulses i n the cavity. For certain cavity detuning a regular train of optical p ulses are produced and the macroscopic energy of the optical pulses ex hibits a limit cycle. We show that the instabilities associated with t he limit cycle and chaotic behaviour can be examined by periodically a djusting the cavity desynchronism. Resonances have been observed at th e limit cycle, the period doubled, etc. frequencies. Moreover, the opt ical power close to these resonances is enhanced and the frequency of the optical pulse microstructure in the cavity is locked to the pertur bing frequency leading to possible new methods of synchronising extern al lasers to the free-electron laser. (C) 1998 Elsevier Science B.V. A ll rights reserved.