FEL technologies R&D and SASE gain enhancement observation at the BNL ATF

The research at the Brookhaven Accelerator Test Facility (ATF) covers all major aspects of the future light source (LS) technologies, from high-brightness electron beam source, beam diagnostics to FEL experiments. The ATF itself is the testing ground for photocathode RF gun technologies; it is the only multi-user facility based on the photocathode RF gun injection system. Using vacuum based laser-cleaning technique, 0.5 % quantum efficiency (QE) was measured for an Mg cathode. The best emittance (normalized rms) for a 0.5 nC charge with peak current 110 A is measured to be 1.5 mm-mrad. The ATF is the only facility where both laser seeded (HGHG) and SASE FEL experiments are performed, SASE was observed at the ATF from 5.3 µm to visible. A record of 7 orders of magnitude gain was observed at the ATF high-gain harmonic-generation (HGHG) experiment. An order of magnitude SASE gain enhancement by optical klystron was observed at the ATF.