Coherent conditions of electron–photon backscattering light in a wiggle magnetic field

In order to get a γ-laser by the backscattering of electron–photons in a wiggle magnetic field, the length of an effective backscattering region is postulated to be small enough. The paper demonstrates that the condition is only a sufficient one; it is not a necessary condition. The necessary condition is given. The backscattering of electron–photons in a wiggle magnetic field can produce a γ-laser. It is possible that the amplitude of the γ-laser is small. The amplitude can be significantly increased by increasing the magnetic induction of the wiggle magnetic field, by reducing the wavelength of the wiggle magnetic field, and by making the monochromaticity of an incident electron beam better. In a laser standing wave field or a superposition field of a wiggle magnetic field and a laser standing wave field, the backscattering of electron–photons can produce a quasi-laser with a shorter wavelength. (paper)