Measurement of laser-induced refractive index changes of Mg-doped congruent and stoichiometric LiNbO3

Abstract

Light-induced refractive index changes and nonlinear absorption of undoped and Mg-doped LiNbO3 with congruent and stoichiometric composition were investigated by the Z-scan method using an all-visible argon-ion laser with intensities up to the MW/cm2 level. Charge coupled device recordings demonstrate that the Z-scan method is suitable for quantitative study of Mg-doped samples, while it can be used only for qualitative measurements of undoped samples because of beam fanning in the latter case. Stoichiometric LiNbO3 doped with 5 mol % Mg shows positive refractive index changes opposite to those in cases of undoped congruent, undoped stoichiometric and 5 mol % Mg-doped congruent LiNbO3. The refractive index change of Δne=2.5×10−5 measured at 0.37 MW/cm2 light intensity for stoichiometric LiNbO3:Mg is six times smaller than that of congruent LiNbO3:Mg at 0.1 MW/cm2.