LINEAR AND NONLINEAR OPTICAL PROPERTIES OF ZnGeP2 AND CdSe

Abstract
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 d 14 for second harmonic generation(SHG) measured relative to d 14 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 d 31 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.