摘要： We present the recent achievements in periodical poling in MgO doped single crystals of lithium niobate (LN), lithium tantalate (LT) and potassium titanyl phosphate (KTP) based on the experimental study of the domain structure evolution by the complementary high-resolution domain visualization methods [1]. The crystals with tailored periodically poled domain structures (PPLN and PPLT) produced with nano-scale period reproducibility have been used for Second Harmonic Generation (SHG) and Optical Parametric Oscillation (OPO) based on quasi-phase-matched nonlinear optical wavelength conversion. The periodical poling techniques were based on the deep experimental and theoretical study of the mechanisms of domain growth and domain wall motion in these crystals. The wide range of wall velocities with two orders of magnitude difference was observed for switching in a uniform electric field [2,3]. The kinetic maps allowed analyzing the spatial distribution of the wall motion velocities and classifying the walls by velocity ranges. The distinguished slow, fast, and superfast types of domain walls in KTP differed by their orientation. The revealed increase in the wall velocity with deviation from low-index crystallographic planes for slow and fast walls was considered in terms of determined step generation and anisotropic kink motion. It was shown that the polarization reversal in KTP with artificial surface dielectric layer leads to formation and growth of the large number of narrow domain streamers oriented strictly along [010] direction with about ten times higher velocity (6-60 mm/s) than the domain walls (2-5.5 mm/s). Study of the static domain structures demonstrated that the streamers are formed by [100] and [010]-oriented domain walls. The streamer width was about 500 nm and the distance between the neighboring streamers – about 100 nm. The global domain kinetics during the poling process at elevated temperatures has been studied by in situ optical observation which allowed us to reveal the main characteristics of the poling process at elevated temperatures. It has been shown that the periodically poled area propagates from the edges to the middle of the electrode pattern. The interfering effect of essential increasing of the bulk conductivity during poling has been studied and several ways to overcome this problem have been proposed. The static domain images revealed by chemical etching were visualized by optical and scanning probe microscopy. The influence of the spatially nonuniform electric field on the domain kinetics has been studied for finite-size electrodes of various shapes. The key role of the field anomalies at the electrode corners, ends, and edges in the nucleation process has been revealed by computer simulations and confirmed experimentally. Essential acceleration of the switching at the boundaries of the electrode patterns (so called “pattern effect”) has been explained. The optimized design of the electrode pattern was based on experimental results and computer simulation. The fan-out periodical domain structures created in 3-mm-thick MgO:LN wafers allowed us to realize the widely tunable OPO generation with the signal wave from 2.5 to 4.5 μm using the 1.053 μm pump. The possibility of producing the elements with thickness up to 10 mm for high-power application has been discussed. The peridical domain struture with period of 40 μm was created in KTP single crystals for OPO generation at 2.4 μm using the 1.053 μm pump. The abilities and perspectives of producing the elements with submicron periods has been discussed. The optimized periodical poling techniques have been used for creation of ridge waveguides in periodically poled MgOLN single crystals. The high-index contrast of obtained multi-mode waveguides allowed tuning of the SHG wavelength from 510 to 570 nm using the 1.064 μm pump. The deep knowledge of the domain structure evolution at elevated temperatures and relaxation of the high bulk conductivity along the charged domain walls MgO:LN and MgO:LT allowed us to optimize the periodical poling technique and to produce high-fidelity domain patterns.