Stimulated emission from relativistic electrons passing through a spatially periodic longitudinal magnetic field

Stimulated emission in the high-gain regime from a cold, relativistic beam of electrons gyrating in a combined solenoidal and longitudinally polarized periodic wiggler magnetic field is considered as a source of short-wavelength radiation. The emitted wave frequency is Doppler upshifted in proportion to the wave number of the wiggler magnetic field. Amplification is due to a ponderomotive bunching force acting on the electrons in either the transverse or axial directions. Expressions for the linear growth rate are obtained; conditions for their validity and estimates for the saturated efficiency are given.