Periodic Domain Structure Research Articles

Effect of impurity iron ions on the formation of photoinduced lattices and domain structures in lithium niobate

Processes and mechanisms of the formation of lattices and periodic domain structures in iron-doped lithium niobate monocrystals under the effect of laser beams are examined. The role of Jahn-Teller Fe2+ ions in the formation of photoinduced periodic structures is demonstrated.

Difference-frequency generation in the field of a few-cycle laser pulse propagating in a GaAs crystal with a domain structure

Difference-frequency generation in a GaAs crystal with a periodic domain structure in the field of a few-cycle laser pulse is considered for the case of weakly pronounced material dispersion. The straight-line method is used to solve numerically the system of coupled nonlinear partial differential equations describing the evolution of the electric field of this laser pulse in GaAs crystals with periodic and chirped domain structures. It is shown that application of a GaAs crystal with a chirped domain structure makes it possible to control the frequency-modulation law for a broadband difference-frequency pulse.

Frequency Dependence of the Dielectric Permittivity in Ferroelectric Thin Films with 180° Domain Structure

We have studied the dynamical permittivity in ferroelectric nanometricaly-thin films with 180° periodic domain structure, sandwiched between two paraelectric layers. The domain walls were assumed to interact with an atmosphere of mobile defects that provides the domain walls energy dissipation. The resulting frequency-dependent permittivity demonstrates the Debye-like relaxation behavior at ω∼104 Hz and a sharp collective resonance mode at ω∼5·1011 Hz

Surface periodic domain structures for waveguide applications

We report the results of fabrication and investigations of surface periodic domain structures created by a set of quasi-point e-beam irradiations both on the Y- and X-cuts of LiNbO(3), and on Ti:LiNbO(3) and Zn:LiNbO(3) planar waveguides. Domain gratings with spatial periods from 4.75 to 7.25 μm were formed by a 25-keV e-beam. Doses from 500 to 2000 μC/cm(2) were used for different structures to estimate optimal fabrication conditions. The investigations allowed the visualization of the formed surface domain structures, estimation of their uniformity, and determination of waveguide generation of the second optical harmonic. The surface structures can be used in optical devices for the realization of quasi-phase-matched frequency conversion, which includes the creation of compact radiation sources based on waveguides.

Spatially Periodic Domain Structure in Coupled Reaction–Diffusion Equations for Segment Formation

Segment formation is an important process of pattern formation in the developing vertebrate embryo. The mechanism of such pattern formation is considered to be different from that of Turing instability. We propose reaction–diffusion equations generating traveling pulses and coupled reaction–diffusion equations for two genes that generate a domain structure. Next, we construct a synthetic model for segment formation by combining the coupled reaction–diffusion equations. A spatially periodic domain structure is found in the numerical simulation of the model equation. It is shown that the wavelength of the spatially periodic pattern and the proportion of the sizes of the anterior and posterior domains in each segment can be controlled by adjusting some system parameters.

Synthesis and laser patterning of ferroelastic β′-RE2(MoO4)3 crystals (RE: Sm, Gd, Tb, Dy) in rare-earth molybdenum borate glasses

The glasses with the compositions of 22.5RE2O3–47.5MoO3–30B2O3 (RE: Sm, Gd, Tb, and Dy) (mol%) were prepared by a conventional melt quenching method, and the formation and laser patterning of ferroelastic β′-RE2(MoO4)3 crystals were examined. The initial crystalline phase was β′-RE2(MoO4)3 in all the glasses, and the second crystalline phases were rare-earth borates such as Gd(BO2)3, Tb(BO2)3, and DyBO3, and α-RE2(MoO4)3 in the glass with Sm2O3. It was confirmed from polarized optical microscope observations and micro-Raman scattering spectra that β′-RE2(MoO4)3 crystal lines having periodic refractive index changes were patterned by irradiations of continuous wave Yb:YVO4 fiber laser (wavelength:1080nm, power: 0.5–2.0W, scanning speed: 8–20μms−1). It was found that the periodic degree of refractive index changes depends on the kind of RE3+ ions. The present study demonstrates that the appearance of periodic domain structures is an intrinsic feature in the laser patterning of ferroelastic β′-RE2(MoO4)3 crystals.

GENERATION OF DIFFERENCE FREQUENCY RADIATION IN THE FIELD OF FEW-CYCLE LASER PULSE PROPAGATING IN GaAs CRYSTAL WITH PERIODIC AND APERIODIC DOMAIN STRUCTURE

We consider process of generation of difference frequency in a GaAs crystal with periodic domain structure during propagation of a few-cycle laser pulse in the crystal in the regime when chromatic dispersion is expressed weakly. Method of lines is used to obtain numerical solution to the system of coupled nonlinear differential equations in partial derivatives describing the evolution of the electric field of a few-cycle laser pulse in GaAs crystal both with periodic and aperiodic domain structure. Time-frequency distribution is obtained, with use of Wigner transformation, for linearly-polarized femtosecond laser pulse and for orthogonally polarized difference-frequency pulse generated via filtration of the orthogonally-polarized pulse at the crystal output.

Theoretical Analysis of the Difference-Frequency Generation of Terahertz Radiation in Lithium Niobate with Regular Domain Structure

The difference-frequency generation of terahertz (THz) radiation in single crystalline lithium niobate with periodic domain structure has been studied theoretically. The quadratic nonlinear dielectric with lithium niobate parameters has been considered in collinear geometry of wave interaction and absence of absorption for several types of the regular domain structures. The features of the generated THz and their dependence on the domain structure have been revealed.

Formation of submicron partially ordered domain structures in ferroelectric and magnetic materials

Formation of domains and partially ordered periodic domain structures in ferroelectric and magnetic oxides of metals of transition groups has been investigated. Physical features of appearance of submicron periodic domain structures and possibilities of their use for the control over the parameters of high-frequency acoustic waves have been considered using the example of single crystals of lithium niobate and lanthanum-strontium manganites.

Multiheterodyne Detection for Spectral Compression and Downconversion of Arbitrary Periodic Optical Signals

Optical frequency combs are used as local oscillators for the measurement and analysis of unknown optical waveforms with periodic time domain structures. Experimental results obtained by heterodyning pulsed and phase-modulated laser sources are presented. The analysis is then extended to the heterodyning and sampling of bandlimited incoherent light sources. It is shown theoretically and experimentally that the correlations between photodetected white light at different times can generate RF interference that is sensitive to the optical phase.

Efficient Photovoltaic Current Generation at Ferroelectric Domain Walls

We elucidate the mechanism of a newly observed photovoltaic effect which occurs in ferroelectrics with periodic domain structures. Under sufficiently strong illumination, domain walls function as nanoscale generators of the photovoltaic current. The steps in the electrostatic potential function to accumulate electrons and holes on opposite sides of the walls while locally reducing the concentration of the oppositely charged carriers. As a result, the recombination rate adjacent to the walls is reduced, leading to a net diffusion current. In open circuit, photovoltages for periodically ordered domain walls are additive and voltages much larger than the band gap can be generated. The internal quantum efficiency for individual domain walls can be surprisingly high, approaching 10% for above band-gap photons. Although we have found the effect in BiFeO(3) films, it should occur in any system with a similar periodic potential.

MgO:LiNbO$_{3}$ Waveguide Quasi-Phase-Matched Second-Harmonic Generation Devices Fabricated by Two-Step Voltage Application Under UV Light

A new simple method for formation of MgO:LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> domain inverted gratings is demonstrated. Periodic domain structure was formed on - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> face by first voltage application under ultraviolet (UV) light with periodic intensity distribution. Following second voltage application without UV resulted in periodic structure continuing through crystal thickness. A waveguide quasi-phase-matched (QPM) nonlinear-optic device was fabricated by the method and characterized. The device performance agreed with approximate theoretical prediction, and high applicability of the method to QPM device fabrication was demonstrated.

Ferroelectric domains in near-stoichiometric LiNbO3 by e-beam polarization reversal

Local polarization reversal and periodical domain structure engineering by an electron beam in the Z-cut of near-stoichiometric LiNbO3 crystal (NSLN) was investigated. The NSLN was grown from a congruent composition containing 6%wt. K2O flux by top-seeded solution growth method. The 0.75 mm thick Z-cut samples were irradiated in the SEM with a lithography system. Both −z and +z crystal sides were studied after selective etching using an optical microscope. The sideways and frontal domain wall motions at different densities of introduced e-beam charges were analyzed. Irradiation conditions for long triangular string-like domain reversal in the crystal plates of 750 µm thickness were determined. The domain gratings were fabricated in the same crystal plates by e-beam. In the bulk crystal, domain gratings (Λ = 10 µm) transformed to the 2D structure. The NSLN crystals hold promise for thick periodical domain structure engineering by e-beam technique.

Surface acoustic waves in thin films of barium strontium titanate on magnesium oxide substrates

It is established that, using a thin barium strontium titanate (BST) film as the active element in a surface acoustic wave (SAW) device, it possible to double the working frequency of the converter due to the formation of a periodic domain structure in the BST film. A thin ferroelectric film device with a standard electrode structure is capable of effectively exciting the SAW second harmonic. Variation of the external polarizing voltage applied to the electrodes ensures field-controlled electromechanical feedback in the converter.

Nonlinear optical detection of terahertz-frequency radiation in crystals with periodic domain structure

The temporal and spectral characteristics of the terahertz response are measured for crystals of doped lithium niobate with an as-grown domain structure. It is shown that the crystals can be used for narrow-band generation and detection of terahertz waves in the processes of nonlinear-optical conversion of the laser radiation frequency. Frequency tuning in the range from 0.5 to 2.5 THz can be performed, due to both variations in the domain structure period and changes in the nonlinear-optical interaction geometry.

Laser patterning and morphology of two-dimensional planar ferroelastic rare-earth molybdate crystals on the glass surface

The laser-induced crystallization method is applied to pattern two-dimensional planar crystals consisting of ferroelastic β′-(Sm,Gd) 2(MoO 4) 3 crystals (designated here as SGMO crystals) on the surface of Sm 2O 3–Gd 2O 3–MoO 3–B 2O 3 glass. By scanning Yb:YVO 4 fiber lasers (wavelength: 1080 nm) continuously with a small pitch (0.7 μm) between laser irradiated parts, planar SGMO crystals with periodic domain structures showing different refractive indices are patterned successfully, and a high orientation of SGMO crystals is confirmed from micro-Raman scattering spectrum and second harmonic intensity measurements. It is found that the crystal growth direction is perpendicular to the laser scanning direction. This relation, i.e., the perpendicular relation, is a different from the behavior in discrete crystal line patterning, where the crystal growth direction is consistent with the laser scanning direction. The present study proposes the possibility of the control of crystal growth direction in laser-induced crystallization in glasses.

Controlling quasi-relativistic dynamics of domain walls in the regime of self-phasing

Quasi-relativistic nonlinear dynamics of domain walls in a plate of an orthorhombic magnet with a plane-parallel periodic domain structure in an external field with a slowly changing frequency has been investigated. It has been found that, in the regime of self-phasing, large-amplitude oscillations of a domain wall with a quasi-relativistic effective mass can be generated. It is shown that by modulating field frequency it is possible to transfer a system of domain walls from an equilibrium (or close to equilibrium) state into a stationary nonlinear regime of oscillations and to control the quasi-relativistic nonlinear dynamics of the walls under the conditions of self-phasing.

Anisotropic Superconductivity and Vortex Dynamics in Magnetically Coupled F/S and F/S/F Hybrids

Magnetically coupled superconductor–ferromagnet hybrids offer advanced routes for nanoscale control of superconductivity. Magnetotransport characteristics and scanning tunneling microscopy images of vortex structures in superconductor–ferromagnet hybrids reveal rich superconducting phase diagrams. Focusing on a particular combination of a ferromagnet with a well-ordered periodic magnetic domain structure with alternating out-of-plane component of magnetization, and a small coherence length superconductor, we find directed nucleation of superconductivity above the domain wall boundaries. We show that near the superconductor-normal state phase boundary the superconductivity is localized in narrow mesoscopic channels.

Periodic domain structures obtained by growth of LiNbO3 crystals doped with gadolinium

The growth of a periodic domain structure in LiNbO3 crystals doped with gadolinium (Gd, 0.44 wt %) was investigated by special electron beam surface charging in a scanning electron microscope and on a atomic force microscope. Ferroelectric domain boundaries with "tailtotail" and "headtohead" Ps orientations were comparatively analyzed. The domain boundaries had different forms and differed by their physical properties. Micronsize surface crystal regions close to the "tailtotail" boundaries were charged slower by electron irradiation and had modified elastic properties. This region was detected by using the lat� eral force mode of atomic force microscopy. The observed morphology and property features were supposed to be due to different concentration gradients of the Gd impurity and different width of its distribution close to the domain boundaries of different types.

Formation of photon ferroelectric crystals with the use of quasi-standing acoustic waves

An acoustic-interference method of formation of photon ferroelectric crystals is investigated. The method does not necessitate photolithography. Schemes of formation of periodic domain structures with the use of elastic waves that interfere in the ferroelectric volume are considered. It is shown that this technology is the most efficient for the creation of photon crystals based on high-coercitivity ferroelectrics, for example, pure congruent-composition LiNbO3.