Development of multi-bunch laser system for photocathode RF gun in KU-FEL

We have been developing mid-infrared FEL (MIR-FEL) system, KU-FEL (Kyoto University-FEL), which utilizes a 4.5 cell S-band thermionic RF gun, in Institute of Advanced Energy, Kyoto University. We plan to introduce a BNL-type 1.6-cell photocathode RF gun to generate higher peak power MIR-FEL. The purpose of this work is to develop the 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 μJ in the wavelength of 266 nm. The laser system consists of a mode-locked Nd: YVO4 laser as the oscillator, an acousto-optic modulator, a laser beam pointing stabilization system, a diode pumped Nd: YAG amplifier and 4th harmonic generation crystals.