A unified theory of magnetic bremsstrahlung, electrostatic bremsstrahlung, Compton-Raman scattering, and Cerenkov-Smith-Purcell free-electron lasers

This paper discusses in a comparative way the main operating parameters of various free-electron lasers (FEL\´s), providing a useful tool for laser design and a comparative evaluation of the various lasers. We show that the various kinds of FEL\´s satisfy the same gain-dispersion relation and differ only in a single coupling parameter . The different gain regimes which are common to all FEL\´s are delineated. We find the small signal gain in all the gain regimes (warm and cold beam, low- or high-gain, single electron, collective or strong coupling interaction). The laser gain parameter, radiation extraction efficiency, maximum power generation, and spectral width are given and compared in the various kinds of FEL\´s and gain regimes. The maximum power generation of all FEL\´s (except Compton-Raman scattering) is shown to be limited by an interaction region width parameter. This parameter and, consequently, the laser power are larger in the highly relativistic limit by a factor in all bremsstrahlung FEL\´s, in comparison to Cerenkov-Smith-Purcell FEL\´s. Some expressions which were derived earlier for the magnetic bremsstrahlung FEL, like the expression for gain in the low-gain regime with the space charge effect correction and the low-gain expression for efficiency, are shown to be special cases of more general expressions.