Continuous-wave difference-frequency generation based on BaGa4Se7 crystal

A continuous-wave mid-infrared radiation from difference frequency generation by mixing a continuous-wave Ti: sapphire laser and a continuous-wave YAG laser in a 15 mm long BaGa₄Se₇ crystal is demonstrated for the first time. The tunable range from 3.15 to 7.92 μm was achieved by rotating the crystal to fulfill the type I phase-matching condition. A maximum DFG power of 1.41 μW was obtained at 5 μm. Meanwhile the experimental DFG power conversion efficiency was 20.2 μW/W², with a length-normalized slope efficiency of 15.5 μW/cmW². The conversion efficiency decreases rapidly from 50 μW/cmW² at 3.15 μm to 1 μW/cmW² at 7.92 μm. The wavelength acceptance bandwidth and the angular acceptance bandwidth were measured to be 16.4 cm^-1 and 44' for DFG at 5.1 μm, respectively.