Multi-level quantum electrodynamic calculation of spontaneous emission and small signal gain in high voltage free electron lasers

Abstract

Abstract Using the Weisskopf-Wigner technique, a self consistent quantum electrodynamic (SCQED) theory of spontaneous emission of radiation and single photon small signal gain is developed for high voltage free electron lasers (FEL). Excellent agreement is obtained simultaneously to our knowledge for the first time between the predictions and the experimental observations for lineshift, linewidth and gain. The SCQED theory predicts lineshift and broadening due to quantum mechanical effects for linear, helical and tapered undulator FELs which are not predicted by the classical/conventional FEL theories, but which have been observed 4,5,18,22,23,45,46. Excellent agreement is obtained between the SCQED theory predicted spontaneous emission spectra and the 1980–81 ACO FEL4,18, ACO Optical Klystron FEL45,46, Stanford 10.6 μm FEL22 and Stanford 3.4 μm FEL23 experimental spectra. This agreement is much better than the prediction from the classical/conventional FEL theory which gives errors of many tens of percen...