An X-ray free-electron laser loaded with a periodic dielectric

When a periodic medium is inserted along the axis of a free-electron laser (FEL), the synchronism condition between the electron beam and the electromagnetic wave is changed. This alteration permits a wider parameter selection than the conventional FEL, and provides for the possibility of X-ray operation. The device is a hybridization of the FEL and the stimulated-transition-radiation laser. Photon absorption by the periodic medium and scattering of the electrons limit the interaction length, but calculated gains are still high enough for oscillation. The analysis shows that ultrarelativistic electron beams and low-density foil materials give the most physically realizable parameters. Higher order resonant transition modes (r>1) should be used to maximize gain