*Article* **High Repetition Rate, Tunable Mid-Infrared BaGa4Se7 Optical Parametric Oscillator Pumped by a 1** μ**m Nd:YAG Laser**

**Yixin He 1, Chao Yan 2,3, Kai Chen 2,3, Degang Xu 2,3,\*, Jining Li 2,3, Kai Zhong 2,3, Yuye Wang 2,3, Rui Yao 1, Jiyong Yao 4,\* and Jianquan Yao 2,3**


**Abstract:** A tunable and compact mid-infrared optical parametric oscillator (OPO) based on BaGa4Se7 (BGSe) crystal with a repetition rate up to 250 Hz was demonstrated. A high energy and more approachable side-pumped Q-switched Nd:YAG laser was employed as the pump for the BGSe OPO. Due to the pump double-pass single-resonant oscillator (DP-SRO) configuration, the maximum average power of 250 mW and the maximum pulse energy of 1.28 mJ at 4.06 μm was achieved with the repetition rate of 250 Hz and 100 Hz, respectively. The tunable mid-infrared output from 3.42–4.73 μm was obtained. The influence of repetition rate and cavity length was studied and the thermal effect was analyzed.

**Keywords:** optical parametric oscillator; BaGa4Se7; mid-infrared
