Low-threshold, self-frequency-stabilized AgGaS_2 continuous-wave subharmonic optical parametric oscillator

We report the demonstration of a cw ${\mathrm{AgGaS}}_2$ optical parametric oscillator (OPO). The subharmonic $\left(3\omega \to 2\omega +\omega \right)$ OPO is configured as a doubly resonant oscillator with weak pump enhancement. The temperature-tuned, noncritically phase-matched crystal is pumped by a diode laser at ${\lambda }_p\approx 845 \mathrm{nm}$. Oscillation at ${\lambda }_s\approx 1267 \mathrm{nm}$ and ${\lambda }_i\approx 2535 \mathrm{nm}$ is observed at an input threshold power of 60 mW. Crystal thermal loading induces a robust passive self-frequency stabilization of any single-axial-mode pair to the OPO cavity resonance. The conversion efficiency is limited by thermal effects to 2% for a 200-mW pump input.