Narrow-linewidth BaGa4Se7 optical parametric oscillator

The linewidth of the BaGa 4 Se 7 (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 1.27-2.05nm.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.