Difference frequency generation in the mid-infrared with orientation-patterned gallium phosphide crystals

We report on the generation of coherent mid-infrared radiation around 5.85 μm by difference frequency generation (DFG) of a continuous-wave Nd:YAG laser at 1064 nm and a diode laser at 1301 nm in an orientation-patterned gallium phosphide (OP-GaP) crystal. We provide the first characterization of the linear, thermo-optic, and nonlinear properties of OP-GaP in a DFG configuration. Moreover, by comparing the experimental efficiency to Gaussian beam DFG theory, we derive an effective nonlinear coefficient d=17(3)  pm/V for first-order quasi-phase-matched OP-GaP. The temperature and signal wavelength tuning curves are in qualitative agreement with theoretical modeling.