Narrow-linewidthBaGa4Se7opticalparametricoscillator

The linewidth of the BaGa4Se7（BGSe） optical parametric oscillator（OPO） was narrowed for the first time, to the best of our knowledge, by inserting a Fabry–Perot（FP） etalon into an L-shaped cavity. When a 15 mm long BGSe（56.3°, 0°） was pumped by a 1064 nm laser, the peak wavelength was ～3529 nm, and the linewidth was 4.53 nm(3.64 cm-1) under type I phase matching. After inserting a 350 μm thick FP etalon, the linewidth was decreased to 1.27–2.05 nm. When the tilt angle of the etalon was 2.34°, the linewidth was 2.05 nm(1.65 cm-1), and the peak wavelength was still ～3529 nm. When the tilt angle of the etalon was 3.90°, the peak wavelength was 3534.9 nm, and the linewidth was 1.27 nm(1.02 cm-1), which was the narrowest linewidth of a BGSe OPO, to the best of our knowledge. The beam quality was also improved after inserting the FP etalon.