Optical performance of the Los Alamos free-electron laser

During a year of oscillator experiments, the Los Alamos free-electron laser has demonstrated high-power and diffraction-limited output capabilities with a factor-of-4 wavelength tunability in the infrared. A conventional,
L
-band RF linear accelerator produced a 100 μs long, 2000 pulse train of 35 ps wide electron-beam pulses with peak currents to 50 A and nominal energy of 20 MeV. Small-signal gain in excess of 40 percent was generated in a 1 m, plane-polarized, uniform-period undulator for wavelengths between 9 and 11 μm. Best performance included an electron-energy extraction efficiency of 1 percent, 10 MW peak output power, and a corresponding average power of 6 kW over a 90 μs pulse train. A Strehl ratio of 0.9 characterized the output spatial beam quality. By reducing the electron energy by a factor of 2, the wavelength was tuned continuously from 9 to 35 μm.