Upgrade of the A0 Photoinjector laser system for NML accelerator test facility at Fermilab

The current Fermilab A0 Photoinjector laser system includes a seed laser, a flashlamp pumped multipass amplifier cavity, a flashlamp pumped 2-pass amplifier system followed by an infra-red (IR) to ultra-violet (UV) conversion stage. However the current system can only deliver up to 800 pulses due to the low efficiency of Nd:glass used inside the multi-pass cavity. In this paper we will report the effort to develop a new multi-pass cavity based on Nd:YLF crystal end-pumped by a diode laser. We will also discuss the foreseen design of the laser system for the NML accelerator test facility at Fermilab.