Refractive index changes in Mg-doped LiNbO3caused by photorefraction and thermal effects

Abstract

The origin of light-induced refraction changes in Mg-doped congruent and stoichiometric LiNbO3 (LN) has been investigated using the Z-scan method. The limitations of this method are discussed. We showed that in 5 mol% Mg-doped congruent LN photorefraction (PR) dominates among the nonlinear effects at the MW cm−2 light intensity level. For 2–5 mol% Mg-doped stoichiometric samples at the same intensity level PR are absent as shown by CCD recordings of the beam cross section, the sign of the changes and the excellent fitting of the Z-scan curves. From the magnitude and the intensity dependence of the measured nonlinear refraction of the Mg-doped stoichiometric crystals we concluded that a thermal effect is responsible for the changes observed. The thermally induced refractive index changes are associated with nonlinear absorption.