Abstract We present an overview of the regimes in which operation

Prospects for an X -Ray Free- Electron LaserJulio Gea- Banacloche, Gerald T. Moore and Marlan O. ScullyInstitute for Modern Optics, Department of Physics and AstronomyUniversity of New Mexico, Albuquerque, New Mexico 87131AbstractWe present an overview of the regimes in which operation of an x -ray free -electron laser(FEL) may be feasible, including discussion of static and electromagnetic wigglers, quantumrecoil, high -gain operation, mass -shift broadening, and electron beam quality.IntroductionThe free -electron laser is a swept -gain laser which offers unique possibilities forscaling to short -wavelength operation. Atomic charge- exchange swept -gain devices' 2 whichhave been proposed for operation at x -ray wavelengths are limited by rapid spontaneous decayof the upper lasing level. By contrast, energy input to the FEL is in the stable form ofelectron kinetic energy, and the electrons themselves (not just the gain) propagate atnearly the speed of light. No atomic nuclei or bound electrons are present to complicatethe physics (except in the resonator materials).We shall consider here possible regimes for an x -ray FEL lasing at the fundamentalfrequency