INFLUENCE OF THE DEFECT STRUCTURE ON THE REFRACTIVE-INDEXES OF UNDOPED AND MG-DOPED LITHIUM-NIOBATE

We measured the refractive indices of undoped and Mg-doped lithium nio bate by an interferometric technique in a wavelength range from 400 to 1200 nm. The composition of the undoped samples varied between 47 and 50 mol% Li2O in the crystal whereas the Mg-doped samples were grown f rom congruent melt with up to 9 mol% Mg. Our results can be excellentl y described by a generalized Sellmeier equation which takes into accou nt the defect structure of Li-deficient and Mg-doped lithium niobate. Calculations of the phase-matching conditions of several nonlinear eff ects in Mg-doped lithium niobate reveal good correspondence with the r espective experimental results in a temperature range from -50 to 250- degrees-C.