Corrections to refractive index data of stoichiometric lithium tantalate in the 5-6 μm range

We propose corrections to the coefficients in the published Sellmeier equation for stoichiometric LiTaO₃ [Opt. Lett. 28, 194 (2003)] that allow the extension of the wavelength range within the region of midinfrared absorption edge up to 6 μm. The required extraordinary refractive index data for this range were obtained using single-pass optical parametric fluorescence measurements with a pump wavelength of 1064.4 nm. We also observed efficient parasitic second-harmonic generation that could affect some quasi-phase-matching interactions. The corrected Sellmeier equation improves the accuracy of poling period calculations where the idler wavelength is within the region.