Investigation on repetition rate stability of Cr4+:YAG passively Q-switched microchip laser

Repetition rate stability of CW LD-pumped Nd:YVO4/Cr4+:YAG passively Q-switched microchip laser is investigated theoretically and experimentally. The results show that there is an optimal net gain in the cavity, which can make the laser work in the stable area. By optimizing the net gain in the cavity, the laser can work in stable area with coupled output mirror reflectivity of 85%, small-signal transmission of saturable absorber of 70%, and pump power from 1.05 W to 1.20 W. As the pump power is 1.16 W, high repetition rate output laser with repetition rate of 19.48 kHz and RMS jitter less than 0.68% is obtained. Moreover, the effects of the jitter of pump power on the repetition rate stability are studied. It is shown that jitter of pump power is the dominant factor after working in stable area. The pre-pumping technology is introduced and discussed, for reducing jitter of repetition rate from jitter of pump power.