Quantum effects in high-gain free-electron lasers.

A many-particle fully quantized theory for a free-electron laser which is valid in the high-gain regime is presented. We examine quantum corrections for the high-gain single-pass free-electron laser. It is shown that quantum effects become significant when the photon energy becomes comparable to the gain bandwidth. The initiation of the free-electron laser process from quantum fluctuations in the position and momentum of the electrons is considered, and the parameter regime for enhanced start-up is identified. Photon statistics of the free-electron laser radiation are discussed, and the photon number statistics for the self-amplified spontaneous emission are calculated.