Vladimir Ya. Shur

Backswitch poling in lithium niobate for high-fidelity domain patterning and efficient blue light generation

In nonlinear optics applications employing quasiphase matching, short-pitch domain gratings are generally required for the efficient generation of visible and ultraviolet light. Here we introduce an improved electric-field poling technique, which incorporates spontaneous backswitching and leads to uniform short-pitch domain structures. The total volume of backswitched material, and hence the duty cycle of the backswitched domain grating, can be accurately controlled. First-order single-pass continuous-wave second harmonic generation of 60 mW at 460 nm is achieved at 6.1%/W efficiency in 0.5-mm-thick 4-μm-period backswitch-poled lithium niobate.

Kinetics of phase transformations in real finite systems: Application to switching in ferroelectrics

The modification of Kolmogorov–Avrami theory for real objects accounting for the finiteness of the transformed object/media is proposed. It takes into account the changing of the domain growth dimensionality (“geometrical catastrophe”) during the switching process. The validity of the proposed approach has been confirmed by model experiments and computer simulation. By this approach we have obtained the essential information about phase kinetics concealed in integrated experimental data. The method has been successfully used for the description of domain kinetics during the fast switching in ferroelectric single crystals and thin films. The scenario of domain evolution and voltage dependence of the main kinetic parameters have been discussed.

Continuous-wave quasi-phase-matched generation of 60 mW at 465 nm by single-pass frequency doubling of a laser diode in backswitch-poled lithium niobate

We report continuous-wave single-pass second-harmonic generation (SHG) in 4-mum -period 0.5-mm-thick backswitch-poled lithium niobate. Pump sources at 920-930 nm include both Ti:sapphire and diode-oscillator-amplifier lasers. SHG of a Ti:sapphire laser at 6.1%/W efficiency, producing 61 mW of power at 460 nm, is demonstrated in 50-mm-long periodically poled lithium niobate samples with a nonlinear coefficient d(eff) approximately 9pm/V, and 60 mW at 465 nm and 2.8%/W efficiency is obtained by SHG of a laser-diode source.

PHYSICAL BASIS OF THE DOMAIN ENGINEERING IN THE BULK FERROELECTRICS

We present a review of our theoretical and experimental investigations of the domain engineering aspects of domain structure development. Particular attention is paid to the processes governing the fabrication of periodic domain patterns.

Finite size and intrinsic field effect on the polar-active properties of ferroelectric-semiconductor heterostructures

Using Landau-Ginzburg-Devonshire approach we calculated the equilibrium distributions of electric field, polarization and space charge in the ferroelectric-semiconductor heterostructures containing proper or incipient ferroelectric thin films. The role of the polarization gradient and intrinsic surface energy, interface dipoles and free charges on polarization dynamics are specifically explored. The intrinsic field effects, which originated at the ferroelectric-semiconductor interface, lead to the surface band bending and result into the formation of depletion space-charge layer near the semiconductor surface. During the local polarization reversal (caused by the electric field of the nanosized tip of the Scanning Probe Microscope) the thickness and charge of the interface layer drastically changes, in particular the sign of the screening carriers is determined by the polarization direction. Obtained analytical solutions could be extended to analyze polarization-mediated electronic transport.

Kinetic approach to fatigue phenomenon in ferroelectrics

We propose an approach to the explanation of the fatigue effect as an evolution of the switching area during cyclic switching as a result of self-organized domain kinetics due to retardation of bulk screening of the depolarization field. The formation of spatially nonuniform internal bias field during cycling (kinetic imprint effect) slows the domain kinetics in some regions leading to formation of the kinetically frozen domains. Presented fatigue and rejuvenation experimental data measured in sol-gel PbZrxTi1−xO3 thin films are in accordance with the results of computer simulation.

DOMAIN STRUCTURE OF LEAD GERMANATE

With the help of selective etchants as-grown domain structure arising as a result of the phase transition and its restruction in electric field is investigated in lead germanate single crystals. It is shown that this structure consists of small counter domains which are enlarged in electric field. By the use of stroboscopic lighting the domain dynamics under applied electric field is studied. It is shown that the influence of growth layers upon forward domain growth can be explained by the relative variation of the spontaneous polarization in the layers of the order of 0,1%. The observed peculiarities of sidewise motion of plane domain wall are explained by the presence of dielectric gap and by the influence of bulk screening. It is supposed that in low-field region domain wall motion occurs through the one-dimensional nucleation at the wall. Within this model it is possible to qualitatively explain the domain shape dependence on the switching conditions.

Kinetics of ferroelectric domain structure during switching: Theory and experiment

Abstract Some trends in modern research of domain kinetics during switching are reviewed. The importance of the complex investigations of model crystals by local and integral experimental methods simultaneously with computer simulation of domains evolution is stressed. Some new experimental results conserning superfast switching are presented. It is shown that the momentary domain patterns are defined by kinetics of switching process. The general theoretical approach based on nucleation theory in analogy with any phase transformations is used for explanation of all observed effects. The influence of geometrical transformations occuring during domain evolution on transient current shape is confirmed by computer simulation.

Comparative in Vivo Assessment of Some Adverse Bioeffects of Equidimensional Gold and Silver Nanoparticles and the Attenuation of Nanosilver’s Effects with a Complex of Innocuous Bioprotectors

Stable suspensions of nanogold (NG) and nanosilver (NS) with mean particle diameter 50 and 49 nm, respectively, were prepared by laser ablation of metals in water. To assess rat’s pulmonary phagocytosis response to a single intratracheal instillation of these suspensions, we used optical, transmission electron, and semi-contact atomic force microscopy. NG and NS were also repeatedly injected intraperitoneally into rats at a dose of 10 mg/kg (0.5 mg per mL of deionized water) three times a week, up to 20 injections. A group of rats was thus injected with NS after oral administration of a “bioprotective complex” (BPC) comprised of pectin, multivitamins, some amino acids, calcium, selenium, and omega-3 PUFA. After the termination of the injections, many functional and biochemical indices and histopathological features of the spleen, kidneys and liver were evaluated for signs of toxicity, and accumulation of NG or NS in these organs was measured. From the same rats, we obtained cell suspensions of different tissues for performing the RAPD test. It was demonstrated that, although both nanometals were adversely bioactive in all respects considered in this study, NS was more noxious as compared with NG, and that the BPC tested by us attenuated both the toxicity and genotoxicity of NS.

Evolution of bias field and offset piezoelectric coefficient in bulk lead zirconate titanate with fatigue

Hysteresis loops of the piezoelectric coefficient, d33=f(E3), are measured on virgin and fatigued lead zirconate titanate ceramics. Four parameters are directly extracted from the measurements: internal bias field Eb, offset piezoelectric coefficient doffset, coercive field Ec, and remnant piezoelectric coefficient dr. The reduction in dr displays the decreasing switchable polarization with fatigue cycling. Eb and doffset are found to be linearly related. After thermal annealing, both offsets disappear, while the increase in Ec and the reduction in dr withstand annealing. The microscopic entities responsible for the offsets are less stable than those for reduced switching.