The physical mechanisms that contribute to harmonic radiation in free-electron laser systems are examined.
Mathematical models for the spontaneous and coherent-spontaneous emission in plane-polarized
wigglers are given. How these models are used to perform numerical simulations is discussed. Modifications
of the models to incorporate non-ideal free-electron laser effects are reviewed.
Mark J. Schmitt, Mark J. Schmitt,
"Harmonic generation mechanisms in short-wavelength free-electron lasers", Proc. SPIE 1227, Free-Electron Lasers and Applications, (1 May 1990); doi: 10.1117/12.18620; https://doi.org/10.1117/12.18620