Free electron laser oscillation down to the deep UV range using a small-scale storage ring

A free electron laser (FEL) based on the small-scale storage-ring NIJI-IV at the Electrotechnical Laboratory (ETL) was operated at wavelengths down to the deep ultraviolet (UV) range. The laser oscillation was obtained at regions from 315 to 287 nm and from 253 to 228 nm using low-loss dielectric multilayer mirrors optimized at 300 and 240 nm, respectively, for the laser cavity. The wavelength of 228 nm is shorter than the former record for FELs by more than 10 nm. Suppression of the beam instability led to a drastic enhancement of the laser gain which enabled us to achieve the FEL oscillation at such short wavelengths even in a small-scale storage ring. (author)