Sellmeier coefficients for the birefringence and refractive indices of ZnGeP_2 nonlinear crystal at different temperatures

Abstract

Birefringence (B(f)), refractive indices, and their temperature derivatives (dB(f)/dT) determine the temperature characteristics of nonlinear-optical laser devices. The birefringences at different temperatures are analyzed critically by use of a new physically meaningful Sellmeier equation for what is to the author's knowledge the first time the birefringences at different operating temperature from 14 to 500 K and wavelength for ZnGeP(2) nonlinear crystal have been found. This equation is based on the average electronic absorption gap in the UV region and the lattice absorption gap at the IR region. In this model the fitting accuracy is better than the experimental accuracy of ?0.0001 at different temperatures. The refractive indices are estimated at different temperatures from the room-temperature values, the thermo-optic coefficients, and the smoothed values of birefringence. The Sellmeier coefficients for refractive indices that are used to characterize the currently available nonlinear-optical devices satisfactorily are then evaluated. These optical constants are essential in characterizing the parametric short-pulse generation in the mid-IR region.