DISPERSION OF THERMOOPTIC COEFFICIENTS IN A POTASSIUM NIOBATE NONLINEAR CRYSTAL

The thermo-optic coefficients, i.e., the variation of refractive index with temperature (dn/dT) for potassium niobate crystal, KNbO3, are analyzed critically by use of a physically meaningful model. This model is based on the thermal expansion coefficient, and the optical band gaps, such as excitonic and isentropic instead of the consideration of the spontaneous polarization as suggested earlier. The computed optical constants have been used to calculate refractive indices for any wavelength from 0.4 to 3.4 μm at any operating temperature within orthorhombic phase accurately. © 1994 American Institute of Physics.