We report a pulsed optical parametric generator (OPG) and optical parametric oscillator (OPO) based on the newly developed semiconductor nonlinear crystal, orientation-patterned gallium phosphide (OP-GaP), pumped by a Q-switched Nd:YAG laser at 25 kHz repetition rate. Using a 40-mm-long OP-GaP crystal under temperature tuning, we have generated signal and idler output tunable across 1721-1850 nm and 2504-2787 nm, respectively, with a single grating period of 15.5 μm. For a pump power of 2 W, a total output power of up to 18 mW was obtained. Transmission measurements of pump polarized along  axis of the OP-GaP crystal show a drop in transmission with increasing temperature. The OPG threshold increased from 0.6 W at 25 kHz to 4.7 W at 90 kHz. In the singly-resonant OPO operation, a higher idler power of 12.7 mW at 2670 nm was generated for a pump power of 2.2 W. The OPO idler power varied from 9.1 mW at 2530 nm to 7.9 mW at 2752 nm, with a highest power of 10.9 mW obtained at 2626 nm. For a fixed pump pulse energy of 88 μJ, when increasing the repetition rate from 25 kHz to 65 kHz, the OPO idler power at 2670 nm dropped from 12.3 mW to 0.7 mW. The OPG total output power exhibited a passive stability of 0.9% rms with mean values of 18.15 mW whereas the OPO idler exhibited a passive power stability of 1.2% rms with a mean value of 12.68 mW at 2670 nm.
Orientation-patterned gallium phosphide (OP-GaP) is a recently developed nonlinear material with wide transparency across 0.8-12 μm and high nonlinearity (d14∼70 pm/V), which is a promising candidate material for mid-infrared generation. Here we report the full performance characterization of a tunable single-pass nanosecond difference frequency generation (DFG) source based on OP-GaP by mixing the output of a Q-switched Nd:YAG laser at 1.064 μm with the signal from a pulsed MgO:PPLN OPO pumped by the same laser. Using the longest OP-GaP crystal (40 mm) deployed to date, the DFG source provides up to ∼14 mW of average output power at 2719 nm at 80 kHz repetition rate, with >6 mW across 2492-2782 nm, in TEM00 spatial profile. By performing relevant measurements, detrimental issues such as residual absorption and thermal effects have been studied and confirmed. The temperature and spectral acceptance bandwidths for DFG in the 40-mm-log OP-GaP are measured to be 18 °C and 17 nm, respectively, at 1766 nm. The DFG beam exhibits passive power stability better than 1.7% rms over 1.4 hours at 2774 nm, compared to 1.6% and 0.1% rms for the signal and pump, respectively. The polarization dependence of the input beams on the DFG power has also been systematically investigated, for the first time to our knowledge. Further, we have measured the damage threshold of the OP-GaP crystal to be 0.8 J/cm2 at 1064 nm.