Growth of large size near-stoichiometric lithium niobate single crystals with low coercive field for manufacturing high quality periodically poled lithium niobate

Periodically poled lithium niobate is an important component in mid-infrared lasers due to its perfect nonlinear optical property. However, fabrication of high-power laser based on periodically poled lithium niobate is still a great challenge, because lithium niobate crystal wafer with large thickness for large clear aperture periodically poled lithium niobate is hard to be completely poled due to the high coercive field of commercial congruent lithium niobate (LiNbO3). In this work, we have successfully grown 3-inch near-stoichiometric LiNbO3 by efficiently regulation of temperature gradient with the aid of thermal field simulation. Characteristics on the as-grown large size near-stoichiometric LiNbO3 proved that the [Li]/[Nb] of crystal is around 1:1, and the crystal possesses a typical single domain with high optical homogeneity. Compared with congruent and Mg-doped LiNbO3, the near-stoichiometric LiNbO3 crystal has better piezoelectric performance. The forward and backward coercive fields of the near-stoichiometric LiNbO3 crystal were 2.90 kV/mm and 2.43 kV/mm, respectively, which were approximately 8 times lower than that for CLN (21 kV/mm). The periodically polarization experiments proved that only 1.36 kV can realize the complete polarization for a 1 mm thick near-stoichiometric LiNbO3 wafer. The mass-productive near-stoichiometric LiNbO3 crystals grown in this work will have great applications in high-power mid-infrared solid-state laser.