Conditions of Phase Matching for the Second Harmonic Generation with ZnGeP2 Crystals

The reasons for the discrepancy between the available experimental data on the phase-matching conditions for the second harmonic generation with nonlinear ZnGeP₂ crystals are elucidated. The calculated and experimental phase-matching angles agree for crystals at room temperature and low pumping radiation power. Simultaneous solution of the consistent shortened equations for the complex amplitudes and of the heat conductivity equation demonstrates that pumping by intense laser beams causes the angles phase-matching to decrease by 5–25° and the long-wavelength edge of phase matching for doubled frequency of CO₂-laser radiation to increase from 10.32 to 10.8 m. An excess decrease in the angles phase-matching by 1–3° is due to the asymmetry of the thermal processes caused by the birefringence.