In this paper, we present the electric field controllable diffractive optical elements in strontium-barium niobate single crystals with stable tailored spiral-shaped domain structure and demonstrate the generation of optical beam with orbital angular momentum. The required domain pattern was created in the sample with initial domain structure by electric field application using the photolithographically defined liquid electrode. A series of bipolar triangular electric field pulses were applied to the sample for determination of the optimal parameters for complete polarization switching under the electrode. The stable tailored domain pattern of the spiral shape was created by the application of the unipolar pulse of a special shape. The complete switching under the electrode and partial switching under the photoresist layer have been revealed. The imaging by Cherenkov-type second harmonic generation microscopy confirmed that the created domain structure reaches the opposite polar surface. The imaging of the diffraction pattern of the laser beam passing through a voltage-biased DOE confirmed the formation of the beam with orbital angular momentum. The half-wave voltages of 237V and 302V for wavelength 632.8nm and 532nm, respectively, for 2-mm-thick sample were measured. The obtained knowledge can be used for the development of domain engineering methods in strontium-barium niobate single crystals for the creation of tailored domain structures for manufacturing of electric field controllable diffractive optical elements.

The evolution of as-grown domain structure under the action of the series of rectangular electric field pulses at the elevated temperature was studied by in situ optical imaging in calcium orthovanadate single crystals. It was revealed that the domain switching was accompanied by formation of the holes in the electrodes stimulated by conical domains reaching the surface. The multistage scenario of the domain kinetics was considered. It was shown that the evolution of the domain structure represented the independent growth of few large domains by motion of the smooth domain walls in the bulk and at the surface.

Abstract The temperature behavior of the hysteresis loops and switching current parameters measured in the increasing field have been studied in single crystals of deuterated triglycine sulfate. We have revealed the hysteresis loops doubling leading to appearance of additional maxima at the field/time dependence of the switching current during cooling from 59.3 to 51.4°С. This effect was attributed to the bias fields arising as a result of bulk screening of depolarization field. Different current maxima corresponded to the switching in the areas with different values of bias field.

Formation of the circular-shaped isolated domains surrounded by broad domain boundary (BDB) during dot ion beam irradiation in SBN:Ni crystals with submicron domain structure was studied. It was shown that domain and BDB sizes and depths increased proportionally to a square root of the irradiation dose. The radius decreased and BDB width increased with depth for dot and 2 D array exposure. The observed abnormal domain structure evolution was attributed to equiprobable positions of the steps due to merging with nanodomains. BDB increase with depth was explained by the features of spatial distribution of field polar component in the bulk.

Formation of nanodomain structure after linear scanning by IR laser beam in congruent lithium niobate crystal was attributed to switching under the action of pyroelectric field. The complicated domain patterns consisted of strictly oriented narrow stripe domains (width about 200 nm and depth about 20 mu m) arising in a wide switched band. Width of the switched band and domain length density at different distances from the center of the irradiated zone depend on the scanning velocity v (s). Relevance of the used model was supported by similarity of the experimental and calculated dependences.

1D domain patterning by electron beam in potassium titanyl phosphate crystals covered by an artificial dielectric layer were studied. The polygonal shape of the switched domains elongated along Y-crystallographic direction was obtained. The linear dose dependence of the domain size was attributed to screening of the depolarization field by injected charge. The domain size increase with electron energy is caused by increase in the electron penetration into the resist layer. Formation of an array of nanodomain streamers at the domain wall was observed. Creation of a through 1 D periodical domain pattern with a 10 mu m period was demonstrated.

Abstract Domain structure arising as a result of surface polishing in the bulk of barium titanate BaTiO3 single crystal was imaged by polarized optical microscopy and Čerenkov-type second harmonic generation (ČSHG) microscopy, which allowed distinguishing between 90° and 180° domain walls. 3D-morphology of different domain patterns in the bulk was recovered using ČSHG images. The domain structure represented the stack of the intermitting needlelike a-domains with charged domain walls rarely crossed by the zigzag domain patterns with 180° walls. The used experimental technique can be used for understanding the domain kinetics in the multiaxial crystals.

Lithium tantalate LiTaO3 (LT) plates with various composition gradient along the polar axis were produced by partial vapor transport equilibration (VTE) with annealing temperature above phase transition. The proper annealing parameters allow creating a charged domain wall (CDW) in the center of the plate. The CDW morphology depends on the spatial distribution of stoichiometry deviation. The bidomain actuators manufactured from the LT plates after partial VTE procedure possess a linear voltage dependence of the displacement of the free end without any hysteresis. It is shown that increase in CDW roughness leads to a noticeable decrease in the effective piezoelectric coefficient.

The increase of the domain shape dimensionality from one-dimensional (1D) to two-dimensional (2D) representing creation of the magnetic bubbles by application of the uniform magnetic field to the stripe domain structure is a well-known effect used for the magnetic memory. The analogy between ferromagnetic and ferroelectric domains stimulates a search of a similar effect in ferroelectrics. Here, we present the discovered 1D to 2D transformation of the domain shape under the action of pyroelectric field appeared in lithium niobate crystal as a result of irradiation by IR laser pulses. The imaging at the surface reveals the transformation of the stripe domains appeared after the first pulse into the regular arrays of isolated circular domains after the second pulse, whereas the imaging in the bulk reveals the transformation of the comb-like domain to array of isolated conical domains. The process was considered in terms of the kinetic approach. The mechanism of the comb-like domain formation by continuous tooth generation during domain elongation is proposed. The 1D to 2D transformation is attributed to the domain splitting due to the backward motion of the charged domain wall. The proposed mechanisms are confirmed by computer simulation of the temporal dependence of the pyroelectric field excess over the threshold value.

A transformation of the initial three-layer domain structure in lithium tantalate with composition gradient and formation of charged domain wall (CDW) under application of ac electric field have been studied on the surface and in the bulk. We have demonstrated the abilities to produce several types of domain structure by ac field treatment: (1) a layer of the maze structure in the bulk with lower thickness and domain wall concentration, (2) a CDW situated just in the center of the plate, and (3) a decay of the initial domain structure leading to formation of large through domains.

В работе использовалось оборудование Уральского центра коллективного пользования «Современные нанотехнологии». Исследование выполнено при финансовой поддержке РНФ в рамках научного проекта 19-12-00210.

Formation of the domain structure by ion beam irradiation was studied in thermally depolarized Ce-doped strontium barium niobate single crystals covered by a dielectric layer. Three types of irradiation regimes were used: dot exposure, stripe exposure, and line exposure. The dependences of the domain size and depth on the irradiated dose were measured. The circular shape of the isolated domains with partially switched broad domain boundary was obtained. Isotropic domain growth was attributed to the step generation at the wall by merging with the residual nanodomains that appeared after thermal depolarization. The obtained linear dose dependence of the switched area was attributed to the screening of the depolarization field by the injected charge. The shape distortion of the domains growing in the neighborhood with already created ones was attributed to the electrostatic interaction of the approaching charged domain walls. The obtained results can be applied for the creation of precise domain patterns with arbitrary orientation and shape to produce nonlinear optical devices with improved characteristics, including electrically tunable diffractive optical elements.

The evolution of the domain structure during polarization reversal in single crystals of a relaxor ferroelectric strontium-barium niobate (Sr0.61Ba0.39Nb2O6) doped with 0.05 wt.% Ni2O3 was investigated. The domains in the crystal bulk were imaged by Cerenkov-type second harmonic generation microscopy. Three types of domains were revealed: (1) domains with a broad boundary, (2) cylindrical domains, and (3) conical domains. Three stages of the domain shape evolution were distinguished in the domain with a broad boundary. The velocities of the sideways wall motion and forward domain growth were measured for all the domain types.

LaBGeO5 crystals emerged as the most promising candidates for UV laser sources based on a frequency conversion. Creation of periodical domain structures in LaBGeO5 for frequency conversion requires control of domains merging. Here, we studied domain structure evolution during domain merging with Cherenkov-type SHG microscopy. In low fields, two scenarios of domain merging were distinguished: "shape stability effect" and "jerky wall motion effect". The formation of concave angles after merging led to appearance of fast domain walls. In high fields, the difference between slow and fast wall velocities diminished and merging did not result in domain wall acceleration.

LaBGeO5 (LBGO) crystals are unique ferroelectric materials for manufacturing highly efficient UV laser sources based on frequency conversion. This is due to their low cut-off wavelength, high nonlinear-optical coefficients, and non-hygroscopicity. Periodical poling requires a deep study of domain kinetics in these crystals. Domain imaging by Cherenkov second harmonic generation microscopy was used to reveal the main processes of domain structure evolution: (1) growth and merging of isolated domains, (2) growth of stripe domains formed on the artificial linear surface defects, and (3) domain shrinkage. In a low field, growth of triangular domains and fast shape recovery after merging were observed, while in a high field, the circular domains grew independently after merging. The revealed essential wall motion anisotropy decreased with the field. The anisotropy led to significant shape transformations during domain shrinkage in low field. The formation of short-lived triangular domains rotated by 180 degrees with respect to the growing isolated domains was observed. The obtained results were explained within the kinetic approach to domain structure evolution based on the analogy between the growth of crystals and ferroelectric domains, taking into account the gradual transition from determined nucleation in low field to the stochastic one in high field.

We present the results of approaching domain walls merging in lithium niobate single crystals with artificial surface dielectric layer produced by proton exchange. It was shown that existence of dielectric layer led to formation of quasi-regular chain of residual rounded domains near Z + polar surface. The residual comb-like domain was formed near Z-polar surface. The tilt angle of charged domain wall was 5 degrees. The formation of chain of isolated rounded domains was attributed to splitting instability of residual stripe domain. The formation of comb-like domain was related to the cyclic formation and termination of growing dents.

The morphology of a single charged domain wall, appeared under the action of composition gradients produced by partial VTE procedure by Cherenkov-type second harmonic generation microscopy, was observed in detail. The width of the charged domain wall was estimated as 70 μm. Non-through and through narrow domains, grown from the charged domain wall, were revealed. The maximum length of non-through domains with submicron diameter was about 100 μm. The growth of narrow domains from the charged domain wall was demonstrated and attributed to the action of pyroelectric field. The widening of domains occurred after achieving the polar surface.

The formation of the domain structure by electron beam irradiation in thermally depolarized Ce-doped strontium barium niobate single crystals with free surface and surface covered by a dielectric layer has been studied. The dependences of the domain sizes and domain depth on the irradiated dose have been measured. The circular shape of the isolated domains was obtained. The isotropic domain growth was attributed to step generation at the wall as a result of merging with the residual nanodomains which existed after thermal depolarization. The linear dose dependence of the switched area was attributed to the screening of the depolarization field by the injected charge. The electrostatic interaction of the approaching charged domain walls was revealed. The better quality of the domain patterns was achieved in the samples with electron localization in the dielectric layer. The obtained results can be applied for the creation of precise domain patterns with arbitrary orientation and shape to produce nonlinear optical devices with improved characteristics.

The initial domain structure was investigated in Z-cut plates of lithium tantalate crystal with various spatially nonuniform distributions of Li concentration along the polar axis formed by VTE annealing of different durations. The composition gradient resulted in formation of single domain layers near the polar surfaces. The single tail-to-tail charged domain wall formed in the center of the sample, where the composition gradient changed its sign. Nonuniform shape of the charged domain wall was attributed to the pyroelectric field. It was demonstrated that the shape of isolated domains changed with depth depending on the composition variation.

The active substrates with rings of silver nanoparticles arising by drying of sessile colloid drops were used for realization of the surface-enhanced Raman scattering. The colloids have been produced by laser ablation in water using pulse Yb fiber laser. The droplets with diameter down to 10 mu m were dispensed by electrohydrodynamic technique by means of pyroelectric field produced by lithium tantalate plate. The optimal spatial distribution of hotspots was obtained for substrate covered by the micron-size rings of silver nanoparticles. The method was applied for various organic molecules rhodamine 6G, thymine, and RNA with enhancement factor up to 10(5).