GAIN MEASUREMENT OF A FREE-ELECTRON LASER WITH AN OPTICAL KLYSTRON ON THE UVSOR STORAGE RING

We have conducted experiments to measure the gain of a free electron laser (FEL) with an optical klystron (OK) on the UVSOR storage ring. A conventional undulator has been remodeled into the OK in order to increase the gain. The FEL gain at a wavelength of 488 nm has been measured as a function of N(d), which is the number of wavelengths of light passing over an electron in a dispersive section of the OK. The measured gain curve is in good agreement with that calculated according to Madey's theorem from a measured spectrum of spontaneous radiation. The measured instantaneous peak gain is 0.4% for an average beam current of 10 mA/bunch, which agrees well with the gain calculated theoretically. The gain with the OK is enhanced by a factor of five compared with that with the conventional undulator.