LASING IN THE ULTRAVIOLET REGION WITH THE NIJI-IV STORAGE-RING FREE-ELECTRON LASER

Lasing at around 352 nm of the NIJI-IV storage-ring free-electron lase r (FEL) was successfully achieved in April 1994, and the tunable wavel ength region of the system is now 350-595 nm. The electron-beam energy was 311 MeV, and the beam current was 6-10 mA/bunch, The peak output power was estimated roughly to be higher than 50 mW. After the first l asing at 595 nm and 488 nm with the present system in 1992, the storag e ring NIJI-IV was modified to realize the lower-emittance mode, which proved to be quite effective for FEL, experiments in the ultraviolet region. The radio-frequency knockout system has been modified to impro ve the purity of the single bunch. The gain of the 6.3-m optical klyst ron (ETLOK-II) is about 3.2 times that of a normal undulator of the sa me length. The optical cavity consists of dielectric multilayer mirror s made of Ta2O5/SiO2. The initial cavity loss was about 5 X 10(-4), bu t it increased rapidly with ultraviolet and vacuum-ultraviolet irradia tion.