REFRACTIVE-INDEXES 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 lithium 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 LiNbO3. 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 % Li2O, 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.