REFRACTIVE-INDEXES OF ORTHORHOMBIC KNBO3 .1. DISPERSION AND TEMPERATURE-DEPENDENCE

We have measured the refractive indices of potassium niobate in the orthorhombic phase at six different temperatures between 22 and 180-degrees-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.