Abstract: Apparatus, and a related method for its operation, for producing a high-power optical beam from a free-electron laser, at a high overall efficiency. Electrons are accelerated in an electron acceleration system producing bunches of electrons having a narrow energy spread but relatively long time spread. A bunch compression technique converts each bunch to one having a narrow time spread and relatively wide energy spread, suitable for injection into the gain region of a free-electron laser. After exit from the gain region, each electron bunch is further processed to restore it to the same energy-phase distribution as electrons produced by the acceleration system. The restored bunches of electrons are decelerated in the acceleration system, to conserve energy and increase the overall efficiency of the system.

Abstract: A free-electron laser capable of operation at a shorter wavelength than the fundamental lasing wavelength, but without any increase in electron energy requirements. The laser includes a conventional high-energy electron beam source and a wiggler transverse magnetic field through which the beam is passed to produce lasing. Opposed optical mirrors are selected to be reflective at a selected harmonic wavelength as well as at the fundamental wavelength. Lasing is initiated at the fundamental wavelength, but is then supported at the selected harmonic wavelength as well. By appropriate design lasing at the fundamental wavelength may be subsequently terminated without affecting lasing at the harmonic wavelength, which continues at a substantially reduced energy cost than would have been incurred if lasing at the harmonic frequency been initiated in a fundamental mode.