SMALL SIGNAL THEORY FOR THE BACKWARD WAVE FREE ELECTRON LASERS

A detailed analysis for the backward wave free electron laser (FEL) in small signal regime is conducted, following the single partical approach. By the use of a modified factor Fm, the formulas resulted are similar to those of normal FELs. To compare with normal FELs, these formulas show that the backward wave FELs have two main features: the high energy conversion! effeciency and the loose e-beam quality requirement. So it is suitable to be one stage of the two-stage FEL.