Research on defects and domain characteristics of MgO-doped near-stoichiometric lithium tantalate in room-temperature polarization process

Abstract

MgO-doped congruent and near-stoichiometric lithium tantalate single crystals were grown by Czochralski technique and flux method respectively. Optical absorption studies showed that the UV absorption edge was very sensitive to the composition of the crystals and the decrease in defects led to the blue-shift of the UV-edge. The unit domain shape also related to the composition, and the observed results of the crystal wafers that etched by hydrofluoric acid indicate that the domain structure of nearstoichiometric lithium tantalate is hexagonal. Domain movement characteristics in the room-temperature polarization process and the asymmetry between the domain walls of periodically poled lithium tantalate crystals are discussed in detail. Room-temperature polarization experiment of the grown crystal wafers with 1.8 mm thickness was carried out and periodical structures were obtained. near-stoichiometric lithium tantalate, defects, domain characteristics, room-temperature polarization Citation:Jia B S, Zhao Y Q, Zhang X F. Research on defects and domain characteristics of MgO-doped near-stoichiometric lithium tantalate in room-temperature polarization process.Lithium tantalate (LiTaO 3 , LT) is a well-known ferroelectric material for surface acoustic wave, piezo-electric, electrooptic, waveguide, integrated optics and nonlinear optical devices. In nonlinear optical applications, periodically poled LiTaO 3 is the most attractive material for frequency conversion, because of its wide transparency range, large nonlinear coefficients, and high resistance to optical damage [1]. Owing to its lower defect density, coercive field in stoichiometric lithium tantalate (SLT) is one order of magnitude lower than that in the congruent type (CLT) [2], thus greatly facilitating the electrical poling of long and thick crystals with good uniformity of domain structures for high-power quasiphase-matched (QPM) frequency conversion. Kitamura et al. developed double-crucible Czochralski technique to grow stoichiometric lithium tantalate [3-5] and fabricated QPM devices with the grown crystals [6-8]. However, the growth equipment used in this method is sophisticated, and the process is complicated. Compared with doublecrucible Czochralski technique, flux method is much easier.Moreover, MgO-doped SLT crystals have the advantage of almost zero photorefractive damage, which guarantees the frequency conversion with high beam quality even at room temperature. Nevertheless, up to now pretty rare reports about flux growth of SLT have been published. In this work, MgO-doped near stoichiometric lithium tantalate (Mg:SLT) crystals were grown with flux method. The absorption in the UV region was characterized using UV-visible spectrophotometry and its relationship with the defects was discussed. Despite the growing importance of SLT as a device material and the success in obtaining rather perfect crystals, the nature and behavior of non-stoichiometric defects and characteristics of domain movement in this material have received only limited attention c...