Enhancing extinction ratio of polarization and pulse stability simultaneously from passively Q-switched [100]-Nd:YAG/[110]-Cr4+:YAG laser

Depolarization is one of important factor limits the output extinction ratio of polarization, pulse stability and energy of passively Q-switched Nd:YAG/Cr4+:YAG laser, especially in high pump energy regime. We experimentally investigate the output extinction ratio of polarization, pulse stability and energy with different crystal cuts of Nd:YAG and Cr4+:YAG. We demonstrate that linearly polarized, highly stable passively Q-switched output can be greatly enhanced by adopting [100]-cut Nd:YAG crystal as the gain medium and [110]-cut Cr4+:YAG crystal as the saturable absorber. The output pulse energy is 8.5 mJ, repetition frequency is 100 Hz, pulse duration is 13 ns, extinction ratio of polarization is higher than 800:1 and pulse amplitude instability is 2.8%.