SPECTRUM, TEMPORAL STRUCTURE, AND FLUCTUATIONS IN A HIGH-GAIN FREE-ELECTRON LASER STARTING FROM NOISE

We study the time structure, the frequency composition, and the shot to shot fluctuations of the radiation emitted by a free-electron laser starting from shot noise in the electron beam longitudinal distribution, taking into account slippage and finite bunch length effects. We find a very different behavior when the bunch length, l(b), is much longer than the cooperation length, l(c), or of the order of a few l(c). The field evolution is dominated by slippage effects in both cases, and shows the presence of superradiant spikes.