  Photoinjectors are widely used for linear accelerators as electron sources to
generate high-brightness electron beam. Drive laser, which determines the
timing structure and quality of the electron beam, is a crucial device of
photoinjector. A new drive laser system has been designed and constructed for
the upgraded 3.5-cell DC-SRF photoinjector at Peking University. The drive
laser system consists of a 1064 nm laser oscillator, a four- stage amplifier,
the second and fourth harmonic generators, the optical system to transfer the
UV pulses to the photocathode, and the synchronization system. The drive laser
system has been successfully applied in the stable operation of DC-SRF
photoinjector and its performance meets the requirements. 266 nm laser with an
average power close to 1W can be delivered to illuminate the Cs2Te photocathode
and the instability is less than 5% for long time operation. The design
consideration for improving the UV laser quality, a detailed description of
laser system, and its performance are presented in this paper.
