Optical properties of mid-infrared FELs from the FELI Facility I

The FELI Facility I has succeeded in mid-infrared FEL oscillation at 6 μ m using a 30-MeV, 42-A electron beam from the FELI S-band linac in October 31, 1994. The FELI Facility I is composed of a 2-m vertical type undulator (λu=3.4cm, N=58, K m a x = 55, gap length≥14mm) and a 6.72-m optical cavity. It can cover the wavelength range of 5-20μm. The FELs can be delivered from the optical cavity to the diagnostics room through a 50-m evacuated optical pipeline. Wavelength and cavity length dependences of optical properties such as peak power, average power, spectrum width, subpulses in FEL macropulse, FEL transverse profile are reported