Stimulated emission from a "hot" electron beam in an undulator with a transverse magnetic field

An analysis is made of the amplification and stimulated emission of coherent radiation by an electron beam having an appreciable angular and energy spread in an undulator with a transverse magnetostatic field. It is found that the amplification mechanism is due to the inhomogeneity of the electron phase distribution as the resonance point is approached. As a result, the efficiency is almost insensitive to the initial spread. The optimal "nondipolarity" parameter for an undulator giving the maximum efficiency is determined. Under lasing conditions, it is possible to achieve an appreciably higher radiation power than that in a traditional free-electron laser system due to a shift of the saturation level toward higher powers.