Record-power picosecond optical parametric oscillator delivering >240 mW at 6.2 µm through thermal control

We report a high-power, high-repetition-rate picosecond optical parametric oscillator (OPO) based on cadmium silicon phosphide CdSiP₂ (CSP) nonlinear crystal, synchronously pumped by a Yb-fiber laser at ~78 MHz, delivering record idler average power in the deep-infrared (deep-IR). The OPO generates 243 mW at 6249 nm, maintaining >150 mW across nearly 75% of the idler tuning range from 6199 to 6760 nm, along with simultaneous signal tuning from 1262 to 1284 nm. The generated idler exhibits an excellent passive power stability better than 1.3% rms over 6 h, while the near-IR signal shows <0.5% rms stability with 6.2 ps pulses centered at 1281 nm. The unprecedented output power in deep-IR is achieved by the systematic investigation and careful optimization to minimize thermal effects through focusing relaxation and efficient cavity design. This is the highest, to the best of our knowledge, deep-IR average power ever achieved in the 6-7 µm wavelength range.