Q-switched Ho3+:YAG Porro resonators with improved alignment stability

We present a crossed-Porro prism resonator with a Ho3+:YAG crystal and investigate it with a focus on the alignment stability. Furthermore, we show a single-Porro-ended resonator optimized for Q-switched operation. Both resonators are compared to corresponding mirror resonators. In the crossed-Porro prism resonator, a maximum output power of 30.7 W is reached with a high slope efficiency of 67.4 %. By tilting each of the prism axes one by one and measuring the entailed drop in output power, the alignment sensitivity is determined. In comparison to a corresponding mirror resonator, it is improved by a factor of up to 200. With this design, 170 ns Q-switched pulses with an energy of 0.51 mJ are generated at a repetition rate of 50 kHz. In the single-Porroended resonator significantly shorter pulses with a duration of 55 ns and a maximum pulse energy of 0.8 mJ were achieved.