Study of jump-like superfast domain kinetics in lithium niobate crystals by in situ in-bulk imaging in slanted-cut plate

We have investigated the jump-like domain kinetics after domain merging during polarization reversal by in situ in-bulk optical imaging with high temporal resolution in slanted 36° Y-cut congruent lithium niobate single crystals. The chosen switching pulse parameters allowed us to create a chain of isolated conical domains along the electrode edge to realize two variants of the domain merging: (i) a large domain with a small one and (ii) two large domains. The steps of the jump-like domain structure evolution after merging of a small and a large domain have been distinguished: (i) formation of a ledge at the wall of the large domain, (ii) fast motion of the ledge in the polar direction, leading to the formation of a domain terrace at the domain wall, and (iii) domain terrace growth in the Y direction. Merging of two large domains led to the formation of a short-lived superfast domain wall propagating in the Y+ direction. Optical imaging of the superfast domain wall kinetics allowed us to estimate the wall tilt from the polar axis as 1.3°. The kinetic approach to domain growth allowed us to estimate the kink motion velocity in the polar direction along the superfast wall. Finally, optical imaging of domain kinetics in a slanted-cut sample allowed us to measure the forward growth and motion velocities for (i) isolated conical domains, (ii) ledges on the slow domain wall, and (iii) kinks on the superfast wall. The results obtained are important for improving the methods for controlling forward domain growth in the development of the domain engineering in crystals of the LN family.