DEVELOPMENT OF MULTI-BUNCH LASER SYSTEM FOR PHOTOCATHODE RF GUN IN KU-FEL

We have been developing mid-infrared FEL (MIRFEL) system, Kyoto University-FEL (KU-FEL), which utilizes a 4.5-cell S-band thermionic radio frequency (RF) gun, in Institute of Advanced Energy, Kyoto University. We plan to introduce a Brookhaven National Laboratory (BNL)-type 1.6-cell photocathode RF gun to generate higher peak power MIR-FEL. The purpose of this work is to develop a multi-bunch laser system which excites the photocathode in the RF gun. The target values of the system are bunch number of 300 and micro-pulse energy of 1 J in the wavelength of 266 nm. The laser system consists of a mode-locked Nd:YVO4 laser as the oscillator, an acousto-optic modulator (AOM), a beam alignment feedback system, a laser diode (LD) pumped Nd:YAG amplifier. We could stabilize the laser position within 1 m at the downstream of the AOM, and achieve to amplify the seed laser up to 1.2 J per micro-pulse.