GAS-PLASMA AND SUPERLATTICE FREE-ELECTRON LASERS EXPLOITING A MEDIUM WITH PERIODICALLY MODULATED REFRACTIVE-INDEX

Free-electron lasers exploiting media with periodically modulated refr active indices are studied. The regime of large modulation is consider ed, and the conditions of its realization are discussed. Two types of media with periodically modulated refractive indices are analyzed: a g as-plasma medium with a periodically varying degree of ionization and a superlattice-like medium. The gain, saturation field, and efficiency of these free-electron lasers are found. For any given frequency, the gain is optimized with respect to the choice of electron energy, dire ction of motion, and other parameters. Its relationship with other typ es of free-electron lasers (e.g., the Cherenkov laser) is discussed.