Experiments with the free-electron laser

Experiments conducted at the Electron Laser Facility (ELF) and the Paladin Experimental Facility (PEF) in order to evaluate the capabilities of FELs are discussed. For the ELF investigations the experimental test accelerator, which has an electron beam of 4.5 MeV and is applicable in the microwave regime, was utilized. At the PEF, the advanced test accelerator with a 50-MeV electron beam at IR wavelengths was employed. The experimental conditions at the two facilities and the composition of the wigglers are described. The high-gain and high-efficiency of FELs operating in the visible wavelength, the spatial mode purity of the amplified signals, frequency harmonics associated with the FEL, evolution of the phase of the radiation along the interaction region, and the effects of beam current and input power on FEL performance are evaluated in the ELF. The optical guiding of the electromagnetic wave and the horizontal focusing of the electron beam without quadrupoles are demonstrated in the PEF.