Low-threshold, self-frequency-stabilized AgGaS₂ continuous-wave subharmonic optical parametric oscillator

We report the demonstration of a cw AgGaS₂ optical parametric oscillator (OPO). The subharmonic (3ω → 2ω + ω) 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 λ_p ≈ 845 nm. Oscillation at λ_s ≈ 1267 nm and λ_i ≈ 2535 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.