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The refractive indices of ZnGeP2, point group 4̄2m, have been determined from 0.64 to 12 μ. ZnGeP2 has positive birefringence with reasonable temperature tunability and a band gap in the visible. Its nonlinear optical coefficient d14 for second harmonic generation (SHG) measured relative to d14 of GaAs is 0.83 ± 15%. The birefringence of ZnGeP2 is not large enough to allow phase-matched SHG, but nondegenerate phase-matched three-frequency mixing is possible and the parametric oscillator threshold power is calculated for several situations. A redetermination of the coefficient d31 in CdSe is made and the materials compared. It is concluded that ZnGeP2 may be a most promising material for parametric generation in the 0.8– to 12-μ region.
Boyd et al. (Thu,) studied this question.