Generation of amplified picosecond square shaped pulses in ultraviolet region for an RF photocathode

Summary form only given. The photocathode RF gun can generate short pulse length electron bunches since the employed laser pulses in the RF gun are very short, such as in the picosecond or femtosecond region. It is considered that a picosecond square shaped pulse is one of the best candidates for low emittance electron beam generation. We have demonstrated the generation of square profile laser pulses in the ultraviolet region with durations up to 10 picoseconds. For this purpose, a pulse shaping apparatus was placed between a laser oscillator and an amplifier to avoid damage to the modulation devise. Since the spectral amplitude modulation of the laser pulses before the chirped pulse amplification may cause damage of optical elements in a regenerative amplifier, especially for a longer shaped pulse, a phase-only spectral filter, which does not cause damage in the process of the chirped pulse amplification, was used. Since the spectral phase-only filtering cannot be decided by any analytical method, we used a simulated annealing optimization algorithm to design the spectral phase-only modulation. The experimental system consists of a mode-locked Ti:sapphire laser oscillator, a pulse shaping apparatus, a pulse stretcher, a regenerative amplifier and a pulse compressor.