Widely Tunable (2.2 – 10.4 μm) BaGa₄Se₇ Optical Parametric Oscillator Pumped by a Q-switched Nd:YLiF₄ Laser

We report on the first BaGa₄Se₇ nanosecond optical parametric oscillator pumped by Q-switched Nd:YLiF₄ laser at 1053 nm. Mid-infrared (MIR) idler wave tuning from 2.2 μm to 10.4 μm is demonstrated with an angle-tuned type-I (o-ee) y-cut sample, highlighting the superior performance of this novel large bandgap chalcogenide nonlinear crystal to generate tunable coherent radiation over its full MIR transparency range (0.47 – 18 μm). The phase-matching data are used to identify the most accurate dispersion relations of this compound among three recently published Sellmeier equations. Damage threshold measurements yielded values as high as 2.04 J/cm² at 100 Hz pulse repetition rate, one of the largest among existing MIR Χ⁽²⁾ nonlinear materials.