Simulation of the thermo-optic coupling effect in mid-infrared second harmonic generation of ZnGeP₂ crystal

The thermo-optic coupling process of second harmonic generation was numerically simulated in ZnGeP₂ crystals pumped by a pulsed CO₂ laser at the wavelength of 9.6 μm, under the strong and weak cooling conditions. The conversion efficiencies, temperature distributions were calculated during the evolution of the thermo-optic coupling. The results showed that the thermooptic coupling was weak in the strong cooling condition, which nearly did not disturb the conversion processes and temperature distribution, while in the weak cooling case, the temperature distribution showed a great influence on the conversion efficiency and light intensity. Finally, it was found that compensation of the phase mismatch induced by the thermal effect can well recover the conversion efficiency.