Thermal effects limitations in mid-infrared continuous wave optical parametric oscillators

Continuous-wave (cw) optical parametric oscillation (OPO) is a stringent test for the assessment of optical quality of nonlinear mid-infrared materials, because of the low intracavity loss (less than or equal to1% per round-trip) required to balance the weak cw parametric gain. We observed for the first time parametric oscillation at 2.53 mum (idler) and 1.265 mum (signal) using chalcopyrite AgGaS2 in a triply resonant configuration leading to a pump threshold of 90 mW at lambda (p)similar to 845nm. Strong thermal effects induced by the residual absorption of the crystal are reported and analyzed. In particular, long-term (> 30 min) stable single mode-pair operation is observed owing to a passive thermal servo of the cavity optical path length. The effect of thermal lensing under cw operation is also analyzed. We compare the performance of the AgGaS2-TRO with those of a periodically poled lithium niobate (PPLN) OPO, subject to weaker thermal effects.