Search

The experimental results on laser beam guiding by a self-tightening lattice photo induced in a strontium barium niobate (SBN) photorefractive crystal is reported. The gradual transformation of the optical lattice into array of weakly coupled ones revealed significant role of induced modulation instability in the strong laser beam guiding.

Optical nonlinearities of periodically poled LiNb[O.sub.3] crystals were investigated by the single beam Z-scan technique with a continuous wave (cw) laser beam at 532 nm. The nonlinear optical absorption coefficient and refractive index change are determined to be 8.1 x [10.sup-6] cm/W and 2.6 X [10.sup.-4] at 0.5 MW/[cm.sup.2] light intensity, respectively. Both sign and magnitude of the measured refractive nonlinearity are considerably different from the Z-scan results in congruent LiNb[O.sub.3]. The nonlinearities in the periodically poled LiNb[O.sub.3] induced by 532 nm continuous waves are believed to be mainly due to the photorefractive effect. OCIS codes: 190.5330, 160.2260.

A two-dimensional square lattice photonic crystal (PC) constructed with ferroelectric cylinder rods is proposed to demonstrate the tunable negative refraction based on the Pockels effect in visible region. The refractive indices of rods can be changed linearly along with applied electric field and the refractive angle could vary from negative to positive depending on intensity of electric field at a certain incident angle.

The evolution of polarization with time is studied to give rise to a nonlinear Duffing oscillator equation as the governing equation, taking the ferroelectric material as a Hamiltonian system and using the equation of motion of Euler-Lagrange. A detailed theoretical analysis is presented in order to elucidate different stability pictures and present some ideas on the onset of chaos with the help of the Duffing oscillator equation.

A polarimeter to be mounted on the Yunnan solar tower is described. It features the ability to simultaneously measure the magnetic fields of the solar photosphere and chromosphere by analyzing the Stokes spectra of those magnetosensitive lines forming in the two regions with very high efficiency of polarization measurement. The polarimeter consists of two ferroelectric liquid crystals and one [lambda]/4 wave plate before a polarizing beam splitter. The achromatism of the design is emphasized to get the maximum combination efficiency over a spectral range from 5000 to 6000 A. For the used solar absorption lines MgI517.27, FeI525.06, FeI630.15, and FeI630.25 nm, the design gives theoretical efficiencies of polarization measurements, which are 0.999, 1.0, 0.943, and 0.943, respectively. A comparison with other reference polarimeters, such as the Synoptic Optical Long-term Investigation of the Sun, the Tenerife infrared polarimeter, and the La Palma Stokes Polarimeter, is carried out.

Application of near-field optical second harmonic microscopy to nanometer scale crystal and strain analysis of thin polycrystalline ferroelectric films is described. The technique provides a tool for nanometer scale crystal and strain analysis of polycrystalline samples.

The optic tensor configurations in surface stabilized ferroelectric liquid crystal cells with homeotropic alignment are considerably simpler than in cells with the more conventional homogeneous alignment. Combined analysis of angle dependent reflectivity and transmissivity data enhances the sensitivity of the original half-leaky guided mode (HLGM) technique enabling the director profile in cells with hoeotropic alignment to be explored in detail.

Strong Stark splitting, which is independent of the R-ions replacement, is observed through the photoluminescence investigation of electronic ferroelectric [Er.sub.1][Yb.sub.x][Fe.sub.2][O.sub.4]. The unusually large Stark splitting at visible range has shown the existence of strong local field originated from the W-layer in the charge-frustrated Er[Fe.sub.2][O.sub.4].

A new methodology for producing the single ferroelectric domain nanoparticles of BaTi[O.sub.3] compounds from a group of other nanoparticles is discussed. The nanoparticles thus harvested are shown to be extreme significance in the different disparate liquid crystal systems.

The [Ba.sub.1-x][Ca.sub.x]Zr[O.sub.3] solid solution is examined by structural and dielectric measurements on pulsed laser deposition grown films and by first principles calculations. The results have shown the important interplay between unit cell volume and ferroelectricity arising from off-centered ions.

First-principles density functional theory calculations are used for studying the structural, electronic, and ferroelectric properties of [La.sub.2][Ti.sub.2][O.sub.7] (LTO) and [Nd.sub.2][Ti.sub.2][O.sub.7] (NTO). Density of states analysis has shown that the localized Nd 4f levels has acted as charge-trapping sites, which has explained the reduced photocatalytic activity of NTO.

The nucleation limited switching model is employed to explain the ferroelectric polarization switching of the different ferroelectric [(N[H.sub.4]).sub.0.39][K.sub.0.61]N[O.sub.3] films.

Several studies are conducted to explain the synthesis and the different dielectric and electro-optical properties of the ferroelectric liquid crystals. The various effects of the polymeric nanoparticles on these properties are also analyzed.

Several studies are conducted to explain the relationship existing between the short-circuit photocurrent, imprint and the polarization observed in the ferroelectric thin films. The results demonstrate the presence of a strange dependence between the photocurrent and polarization imprint.

Photocurrent system of the ferroelectric nanocylinder (FNC), including nanodisks, nanorods, and nanowires, sandwiched between metal electrodes with the short-circuit boundary conditions is examined. The results have shown that the photocurrent of the FNC can be controlled by adjusting its size and states of the polarization up and down.

The trapping properties of the ferroelectric LiNb[O.sub.3]/AlGaN/GaN heterostructure capacitors are studied by using temperature dependent capacitance and conductance measurements. The measured time constant of bulk traps is almost independent of bias, which is different from that of interface traps.

High-pressure Brillouin and Raman scattering spectroscopy and x-ray diffraction measurements were performed on disordered Pb([Sc.sub.1/2][Nb.sub.1/2])[O.sub.3] to demonstrate its application as a model system for phase transitions in relaxor ferroelectrics and related materials. Both the temperature and pressure dependencies of the linewidth indicated that the longitudinal acoustic mode softening arises from electrostrictive coupling between polar nanoregions and acoustic modes.

Strong upconversion green luminescence is seen in [Er.sup.3+] and [Yb.sup.3+] codoped [Bi.sub.4][Ti.sub.3][O.sub.12] ferroelectric thin films, which are prepared by chemical solution deposition method. The upconversion emission mechanism of the thin films is discussed and the analysis has helped in constructing new integrated photoluminescent ferroelectric thin film devices.

The plasma formation on the surface of a ferroelectric sample is described based on assumptions about the electrodynamic evolution of the system along with the continuity equation for the current and the conversion of the ion flow impulse. Two models starting with these assumptions are capable of predicting the plasma density and temperature and plasma propagation velocity.

The tetracarboxylate organic linker and Zn(II) ions have assembled into chiral building blocks for a porous meal-organic framework with ferroelectric and second-order nonlinear optical properties.

The modified Ginzburg-Landau-Devonshire phenomenological theory is used to study the ferroelectric bilayer film with the transition layer within each constituent film and an interfacial coupling between two materials. The anomalous dielectric susceptibility behavior observed for the ferroelectric bilayer film is attributed to the competition of the transition layer and interfacial coupling deviated from this transition point.

The effect of thermal treatment on physical properties of ([Ba.sub.0.6],[Sr.sub.0.4])Ti[O.sub.3] (BST60) ferroelectric thick films deposited by aerosol deposition (AD) technique is examined by x-ray photoelectron spectroscopy (XPS and complex impedance spectroscopy (CIS) to describe the leakage current behavior of the films. The decrease in resistivity at the grain boundary regions and activation energy is caused by the diffusion from the highly conductive isolated areas present in the grain boundary toward the entire grain boundary area with increase in thermal treatment temperature.

Photovoltaic responses, including photovoltage, photocurrent, illuminated J-V curve, and light-to-electricity power conversion efficiency, are examined in chemical-solution-derived polycrystalline and epitaxial ([Pb.sub.0.97][La.sub.0.03])([Zr.sub.0.52][Ti.sub.0.48])[O.sub.3] (PLZT) thin films sandwiched between different metal and oxide electrodes. The studies have shown that photovoltage has linearly increased with film thickness while both photocurrent and efficiency have exponentially increased with the decrease in thickness.

Memory behavior in the ferroelectric liquid crystal (FLC) material (Felix 17/100) is examined by electro-optical, dielectric and hysteresis methods at different temperatures ranging from room temperature to near ferro-paraelectric phase transition. The electrical conductivity measurements have shown that the steep increase in the conductivity near the transition temperature in Sm C* phase has increased the motion of free ions and has weakened the depolarization field in the material, thus showing memory effect.

The static and dynamic magnetic properties of as-grown, epitaxial ferromagnetic properties of as-grown, epitaxial ferromagnetic Fe films on ferroelectric BaTi[O.sub.3]/SrTi[O.sub.3](001) buffer/substrates are studied. The dispersion curves have shown both optic and acoustic branches along the hard axis [110], with the optic branch resulting from resonance below saturation, which has indicated high quality Fe in these samples.

The first principles calculations within generalized gradient approximation are used for determining the structural, electronic and optical properties of three chemically ordered ferromagnetic K[Ta.sub.1/2][Nb.sub.1/2][O.sub.3] phases. The results have shown that the ferroelectric states are sensitive to the chemical ordering of B site cations and the long-range ordering has significant effect on the properties of K[Ta.sub.1/2][Nb.sub.1/2][O.sub.3] crystals.

Ferroelectric BaTi[O.sub.3] phase of a [P.sub.nma] orthorhombic crystal structure is prepared by using a chemical method that has used a polymer complex of [Ba.sup.2+] and [Ti.sup.4+] with polyvinyl alcohol (PVA). The low dissipation factor is useful for the low power loss devices, uncooled infrared (IR) detectors and thermal imaging applications.

The mesomorphic behavior and phase structure are examined in the mixture of two kinds of dimeric compounds, [alpha][omega]-bis(4-alkoxyanilinebenzylidene-4'-carbonyloxy)pentane (mOAM5AMOm), by optical microscopy, X-ray diffraction, polarization switching and second-harmonic generation measurements. The new appearances of these bilayer phases is discussed as a mixing effect of long and short tail groups and also in relation to the structural characteristics of a twin dimer molecule.

The comprehensive optical properties for tetragonal ferroelectric single crystal 0.65([Mg.sub.1/3][Nb.sub.2/3])O3-0.35PbTiO3 are characterized. The results have shown that the tetragonal lead magnesium niobate lead titanate single crystals are very promising candidate for a wide range of practical optical devices.

The equilibrium polarization states and the macroscopic dielectric response of nanocrystalline ferroelectric ceramics with single-domain grains are described. Calculations show that the dielectric properties of nanocrystalline ferroelectric ceramics may be very different from those of conventional materials due to the elastic clamping of single-domain crystallites.

A study investigated the generation of narrow-band, multifrequency terahertz (THz) radiation via optical rectification of femtosecond laser pulses in poled ferroelectric materials. A method is proposed based on simulated annealing algorithm to inversely determine the needed ferroelectric domain structure for generating the expected THz radiation.

Coexistence of ferroelectric ferroelastic domains in some materials plays an important role in practical area of domain engineering. Considering this, the problem is discussed theoretically from the point of view of elastic aspects.

The spectral properties of Yb(super 3+) ions in Strontium barium niobate (SBN ) nonlinear crystal were investigated and compared ytterbium doped crystals. The obtained results make this crystal a promising candidate for tunable laser generation in the visible domain.