Non-stoichiometric control of LiNbO₃ and LiTaO₃ in ferroelectric domain engineering for optical devices

Photorefractive damage, photoconductivity, and photogalvanic currents of stoichiometry controlled LiNbO3 and LiTaO3 have been investigated. A nearly stoichiometric LiNbO3 single crystal shows a lower photorefractive damage resistance than congruent LiNbO3, however, crystals doped with a small amount of MgO (> 0.78 mol.%) exhibit no measurable photorefractive damage at 532 nm up to intensities of 2 MW/cm2. In the case of LiTaO3, it turned out that nearly stoichiometric crystals exhibit considerably high damage resistivity even without MgO doping. Green-induced infrared absorption (GRIIRA) in the crystals was also investigated by a photothermal technique. The GRIIRA in nearly stoichiometric LiNbO3 is found to be remarkably decreased by a small amount of MgO. GRIIRA in nearly stoichiometric LiTaO3 was strongly suppressed even without MgO doping.