A Compact, Optically Guided, Megawatt Free-Electron Laser Amplifier for Maritime Propagation

Abstract

Abstract : In this paper, we present a conceptual design and parameters for a compact, megawatt-class, optically guided free-electron laser (FEL) amplifier. Full-scale laser propagation simulations, including the effects of aerosols, turbulence, and thermal blooming, indicate that operating the FEL in water-vapor transmission windows, i.e., 1.045, 1.625, and 2.141 micrometer, can result in high propagation efficiencies in a maritime environment (>50% over a 5 km range). In the present design we choose the FEL wavelength to be 2.141 micrometer because of propagation and generation advantages as well as for eye safety reasons. The average output power of this high gain FEL amplifier is approximately 1.5MW, and the input is provided by a low average power (<50 W) FEL oscillator. Diffractive spreading of the FEL output beam is sufficiently large to allow the first grazing angle relay mirror to be close to the exit of the wiggler without exceeding the mirror damage intensity threshold level, which is taken to be 50 kW/cm2. In this design the wiggler length is <2 m and, depending on the mirror grazing angle and the optical beam quality, the distance from the wiggler exit to the relay mirror can be <3 m.