2117 Nm pumped Long-Wavelength tunable optical parametric oscillator in a long BGSe crystal

In this paper, we demonstrate a temperature-tunable long-wave infrared optical parametric oscillator (OPO) based on a 76 mm BaGa₄Se₇ (BGSe) crystal pumped by a 2117.4 nm Ho:YAP laser. To the best of our knowledge, this is the first demonstration of BGSe-OPO pumped at this wavelength. The 76 mm BGSe crystal is the longest single crystal ever used in OPO. At 33 °C, the OPO delivers a maximum output power of 300 mW at 9976 nm, with a slope efficiency of 2.71 % and beam quality factors of 2.0 and 2.3. By tuning the crystal temperature from 14 °C to 33 °C, the wavelength is continuously tuned from 9976 nm to 10937 nm with a high tuning efficiency of 50.6 nm/°C. Compared with the 2090 nm pumping scheme, the output wavelength is extended by up to ∼ 1 μm at 14 °C, verifying that a longer pump wavelength can effectively broaden the long-wave infrared output range.