Study on the Drive Laser System of the Photocathode-injector Used in High Gain FEL

High gain FEL requires high quality electron beam which can be provided only by the RF photocathode gun.The drive laser for electron source plays the key role. In Institute of Heavy Ion Physics of Peking University, the laser system is required to deliver a 500 μJ, 6～8 ps pulse of UV photons (260 nm) to the cathode. This system mainly consists of a CW, frequency-doubled,diode-pumped Nd∶YAG laser, which provides energy to pump a CW mode-locked Ti∶sapphire oscillator, Q -switched Nd∶YAG pump lasers, a regenerative amplifier and harmonics crystals. To meet the low jitters of pulses (1.0 ps), cavity length of the oscillator should be adjustable to lock the pulse frequency with external RF reference, and a phase stability feedback system is also used.