Temperature-dependent Sellmeier equation for the extraordinary refractive index of 5 mol. % MgO-doped LiNbO3 in the terahertz range

We present a Sellmeier equation for the temperature- and wavelength-dependent extraordinary refractive index of 5 mol. % MgO-doped congruent lithium niobate, which is valid for frequencies from 1 to 3 THz in a temperature range from 30°C to 200°C. The determination of the Sellmeier coefficients is based on the tuning behavior of a quasi-phase-matched, continuous-wave optical parametric oscillator with its idler wave in the terahertz regime.