Free electron laser small signal gain measurement at 10.6 µm

Small signal gain has been observed for 10.6 μm radiation using a constant (untapered) wiggler. The permanent magnet wiggler was 2.65 m long, had a period of 3.56 cm (75 periods) and a magnetic field on axis of 2.67 kG. The gain measured was 1.5 ± 0.4 percent agreeing well with the predicted gain corresponding to the experimental electron beam conditions ( E = 25 MeV, \DeltaE/E = 0.75 percent, \epsilon = 8\pi mm . mrad, and I = 10 A).