Accurate measurements of refractive indices of undoped and Mg-doped stoichiometric LiNbO3 and LiTaO3

Stoichiometric LiNbO₃ (SLN) and LiTaO₃ (SLT), the high-quality crystals of which have been recently grown, are intensively investigated as next-generation nonlinear-optical materials because they have several superior properties to conventional congruent LiNbO₃ (CLN) and LiTaO₃ (CLT). However, the refractive indices of SLN and SLT, which are essential for accurately designing and evaluating nonlinear-optical devices, have been measured only with an accuracy of 10^-3. In this paper, we report on the measurements of the refractive indices of undoped and Mg-doped SLN and SLT with an accuracy of better than 1 x 10^-4 at the wavelengths from 398 to 1064 nm by using the minimum deviation method.