Abstract: The influence of the position of acoustic-optic Q-switch on the output pulse stability is analyzed by calculating the misalignment sensitivity of cavity mirrors. The theoretical results show placing the acoustic-optic Q-switch crystal near the output mirror can improve the stability of pulse train. The peak power of several tens of kilo-watt is achieved in fundamental mode. Using BBO crystal for fourth harmonic generation, a laser power of 1.9 W in ultraviolet is experimentally realized.