Free-electron dynamics and gain in a free-electron laser based on the laser-pumped wiggler

Relativistic electron dynamics and gain of a free-electron laser with a counter propagating linearly polarized laser wiggler embedded in a uniform guide magnetic field have been studied. This scheme enables to produce very short wavelengths via Thomson backscattering; it can be considered in principle as a source of X-ray pulses which is easily tunable and highly monochromatic. The developing of laser wiggler shortens the period lengths to micrometer level, and therefore reduces the electron beam energy required by the X-ray sources from several GeV to multi-MeV range. A fourth-order Runge–Kutta method has been employed to simulate the electron trajectories. Furthermore, the gain function of the laser-pumped FEL has been presented, in detail. Numerical solutions showed that by enhancing the cyclotron frequency (or axial magnetic field), the gain for group I orbits increased, while a gain decrement was obtained for group II orbits.