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 wavelengt hs 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 lo w-loss dielectric multilayer mirrors optimized at 300 and 240 nm, resp ectively, for the laser cavity. The wavelength of 228 nm is shorter th an the former record for FELs by more than 10 nm. Suppression of the b eam instability led to a drastic enhancement of the laser gain which e nabled us to achieve the FEL oscillation at such short wavelengths eve n in a small-scale storage ring.