First lasings at visible and IR range of linac-based FELs at the FELI

First lasings at 5.5 μm and 1.88 μm have been achieved in October 1994 and February 1995 at the FELI using two undulators installed at 30-MeV and 80-MeV undulator beam lines of the FELI S-band linac. Lasing on the third harmonics at 0.64 μm has been also observed. A thermionic triode gun of the linac emits 500 ps pulses of 2.3 A at 23.125 MHz. These pulses are compressed with a 714-MHz prebuncher, a 2856-MHz standing wave type buncher, and 3 m long accelerating waveguides to 42 A×10 ps. The 24-μs stable RF pulses can increase a conversion efficiency from electron beam power to FEL power at short wavelength FELs. At 5.5 μm, 1.88 μm and 0.63 μm, FEL peak power are 3 MW, 2 MW and 0.3 MW, and FEL spectral widths are 0.5%, 0.3% and 0.3%, respectively