Free electron laser small signal gain measurement at 10.6 microns

A free electron laser (FEL) generates stimulated radiation by the interaction of a relativistic electron beam with a periodic transverse planar magnetic field (wiggler). The experimental layout used in the present investigation consists of three major components, including electron beam, photon beam, and magnetic wiggler. The wiggler is a planar permanent magnet design with a wavelength of 3.56 cm. The optical system consists of a low-pressure single line CO2 laser, laser beam transport optics, and a gain measurement system. The CO2 laser was employed directly as input to the free electron laser. The laser signal was varied from 1 to 10 mW. The energy beam of the electron beam was varied about 25 MeV. The gain was invariant over the range of input powers, and scaled with current over the range from 5 A to 10 A. The results demonstrate that the small signal gain of a FEL agrees well with theory even when corrections due to finite energy spread and emittance must be employed.