Asymmetric two-bunch operation of free-electron laser and generation of inverse Compton photons

Yield enhancement of high-energy photon pulses, which were generated via inverse Compton scattering of free-electron laser (FEL) pulses with electron pulses in relativistic motion, was achieved by an asymmetric two-bunch method. This method involves the use of two electron bunches recirculating in an electron storage ring for FEL oscillation with asymmetric bunch filling, and the generation of inverse Compton photon pulses at two collision points. The effects of the magnetic field of an undulator for FEL oscillation on the photon energy spectrum and photon yield were analyzed by Monte Carlo simulations and experiments. -- Highlights: ► Yield enhancement of inverse Compton γ rays is achieved. ► Effects of magnetic field on the γ rays are analyzed by theory and experiments. ► The energy spread of the γ ray increases and the intensity decreases.