Initial gain measurements of an 800 nm SASE FEL, VISA

Abstract The Visible to Infrared SASE Amplifier (VISA) FEL is designed to obtain high gain at a radiation wavelength of 800 nm. The FEL uses the high brightness electron beam of the Accelerator Test Facility (ATF), with energy of 72 MeV. VISA uses a novel, 4 m long, strong focusing undulator with a gap of 6 mm and a period of 1.8 cm. To obtain large gain the beam and undulator axis have to be aligned to better than 5 μm. Results from initial measurements on the alignment, gain, and spectrum will be presented and compared to theoretical calculations and simulations.