High-performance UV/VUV optics for the storage ring FEL at ELETTRA

Going to shorter wavelengths beyond the deep ultraviolet involves the development of dedicated optics for FEL with devoted coating techniques and characterizations. Low loss, high reflectivity dielectric mirrors with a long lifetime in a strongly harsh synchrotron radiation environment are required. In February 2001, lasing at 189.7 nm was obtained with Al/sub 2/O/sub 3//SiO/sub 2/ Ion Beam Sputtering mirrors, the shortest wavelength obtained so far with FEL oscillators. In July 2001, 330 mW extracted power was measured with optimized transmission mirrors. Coating research and development correlated to lasing performance obtained so far is reported.