LETTERS TO THE EDITOR: Optically pumped x-ray free-electron laser as a two-level quantum oscillator with a completely inverted active medium
A laser with a sufficiently monoenergetic free-electron beam pumped by a counterpropagating optical wave can exhibit quantum effects. The threshold of appearance of these effects for the beam parameters attainable at present lies in the x-ray emission range where an optically pumped free-electron laser becomes a two-level quantum oscillator with a completely inverted active medium. It is shown that 100% utilization of the inversion in each pass is possible in such a laser. Estimates of the output radiation and optical pump powers are obtained.