Refractive indices of lithium niobate as a function of temperature, wavelength, and composition: A generalized fit

An interferometric method is applied to determine the refractive indices of litihum niobate single crystals over a wide wavelength and composition range. In combination with a careful review of the literature data, a temperature-dependent generalized Sellmeier equation is derived which takes into account the defect structure of Li-deficient ${\mathrm{LiNbO}}_3$. On the basis of this generalized Sellmeier equation, all refractive-index-dependent effects in lithium niobate can be calculated in the wavelength range 400–1200 nm, the composition range 47–50 mol % ${\mathrm{Li}}_2$O, and the temperature range 50–600 K. The parameters of several optical-characterization methods are computed to state calibration curves in the respective composition range. The calculations of the phase matching conditions for nonlinear effects, such as second-harmonic generation and optical parametric oscillation, show excellent agreement with the respective experimental values.