The optical path within the amplifier would be <5 m long.

A proposed high-gain free-electron laser (FEL) amplifier, conceived primarily for use in a maritime environment, would be capable of average output power of the order of a megawatt at one or more of several infrared wavelengths (1.045, 1.625, or 2.141 μm) for which propagation through air is minimally adversely affected by water vapor and aerosols. The conceptual design of this FEL amplifier provides for a combination of conventional and unconventional characteristics that, taken together, would be advantageous in the intended power and wavelength regime.

The High-Gain FEL Amplifier would accept input from a low-average-power FEL. The optical beam would be optically guided in the wiggler and optically pinched at the output end of the wiggler. Pinching of the optical beam would reduce its Rayleigh length and cause it to undergo rapid diffraction upon leaving the wiggler. Orienting the first relay mirror for grazing incidence would prevent damage to the mirror by spreading the beam power over a large mirror area.

The gain length, efficiency, electronpulse slippage, and distance between the wiggler and the first relay mirror have been calculated for the conceptual design. Of particular concern in the design is the overall length of the amplifier optical system; that is, the length of the wiggler and the distance from the wiggler to the first relay mirror. The wiggler would be about 1.5 m long. The distance from the wiggler to the first relay mirror would be chosen so that the threshold intensity for damage to the mirror would not be exceeded, as described next.