Refractive indices of orthorhombic KNbO_3 I Dispersion and temperature dependence

Abstract

We have measured the refractive indices of potassium niobate in the orthorhombic phase at six different temperatures between 22 and 180°C in the wavelength range 400–3400 nm. Sellmeier coefficients are determined by using a two-term oscillator model with an IR correction term. The temperature-dependent spontaneous polarization and the quadratic polarization optical coefficients are obtained from the index data. For practical purposes the temperature dependence can be well approximated by a polynomial expansion of degree 2.