Fully quantized many-particle theory of a free-electron laser

Publisher Website
Google Scholar
Abstract
A fully quantized many-particle theory of the standard free-electron laser in the small-signal, cold-beam regime is presented. The approach is based on an evaluation of the time-evolution operator in the interaction picture to first order in the quantum-mechanical recoil. For algebraic convenience we use the moving (Bambini-Renieri) frame, in which resonance occurs for zero electron momentum. Though we neglect space-charge effects, genuine many-particle contributions still show up, because the radiation emitted by one electron can be amplified by another electron. Our main results are gross features of the amplification, such as gain and spread, are virtually without many-particle effects. These effects are mainly important in the case of spontaneous emission. For a sufficiently high current, the buildup of the laser field from vacuum is enhanced by amplified spontaneous emission. Incoherence of the spontaneous radiation from several electrons induces deviations from Poisson statistics even if gain is neglected. For a dilute electron beam, spontaneous radiation is slightly antibunched for negative gain. Squeezing is obtained for positive gain independent of the number of electrons. However, owing to some idealizations used in the model, it is uncertain whether this applies to a physically realizable situation.