Dielectric matrices with air cavities as a waveguide photonic crystal

Frequency dependences of the transmission coefficient of a microwave photonic crystal that represents a structure containing alternating layers of ceramic material (Al₂O₃) with a relatively large number of cavities and foam plastic are studied in the presence and absence of distortions of the periodicity of a photonic structure. The frequency dependences of the transmission coefficient can be analyzed using a model of effective medium that makes it possible to consider the interaction of electromagnetic wave and photonic crystal using a transfer matrix of a 1D photonic crystal. The band character of the frequency dependence of the transmission coefficient of the photonic crystal related to the periodicity of the photonic crystal in the transverse plane for the waveguide with a standard cross section is not manifested in a certain range of material permittivities.     

Oxidizing agent concentration effect on metal-assisted electroless etching mechanism in HF-oxidizing agent-H2O solutions

The mechanism of metal-assisted electroless etching of silicon in HF-oxidizing agent-H₂O etching system as a function of oxidizing agent concentration was studied. Three types of oxidizing agent were experimented namely Na₂S₂O₈, K₂Cr₂O₇ and KMnO₄. Their concentrations were varied from 0.05 M to 0.3 M. The layers formed on silicon were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray (EDX). It is shown that an insoluble solid-phase film (K₂SiF₆) form on silicon surface when concentration of K₂Cr₂O₇ or KMnO₄ increases in chemical solutions. On other hand, when Na₂S₂O₈ concentration increases, the surface roughness decreases without any chemical complex formation.     

Enhancement of Faraday effect in one-dimensional magneto-optical photonic crystal including a magnetic layer with wavelength dependent off-diagonal elements of dielectric constant tensor

Optical and magneto-optical properties of one-dimensional magneto-optical photonic crystal (1-D MPC) prepared by the sol–gel dip-coating method, including a magnetic defect layer composed of mixture of CoFe₂O₄ and SiO₂, are investigated from both the experimental and theoretical standpoints. The resonant transmission of light was observed around 570 nm in the photonic band gap. The Faraday rotation angle θ_F showed two maxima at 490 and 640 nm, and the wavelength dependence of θ_F above 760 nm was similar to that of the CoFe₂O₄+SiO₂ single-layer film. The two maxima of θ_F are attributed to the enhanced Faraday rotation of nonmagnetic TiO₂ layers in the cavity structure and that in magnetic CoFe₂O₄+SiO₂ layer through the light localization in MPC. The maximum value of θ_F due to the magnetic CoFe₂O₄+SiO₂ layer in the MPC was 22-times larger than that in the single-layer film. The simulation study of MPC with CoFe₂O₄+SiO₂ magnetic defect layer, based on the matrix approach method, showed that the resonant light transmission was accompanied by the localization of electric field, and large enhancement of θ_F appeared at different wavelengths so as to agree with the experimental features. This can be explained in terms of the wavelength dependent off-diagonal components of the dielectric constant tensor in addition to the large extinction coefficient in the CoFe₂O₄+SiO₂ magnetic defect layer.     

Ta2O5/MgF2异质结构三维光子晶体的偏振性

为了在可见及近红外波段得到具有良好带隙结构的三维光子晶体,利用传输矩阵法分析了MgF₂、Ta₂O₅ 以及Ta₂O₅/MgF₂异质结构三维光子晶体的带隙性质.结果表明：Ta₂O₅/MgF₂异质结构三维光子晶体在820~1 020 nm的近红外波段TM模式下具有不受入射光方向影响的全方位光子带隙.该结构有望用于制作近红外光波段的偏振器件.     

Magneto-optical activity of a one-dimensional photonic crystal with a magnetic defect

The influence of a magnetic defect on the field distribution and magneto-optical properties of a one-dimensional photonic crystal has been investigated. It has been shown that the maximum localization of the wave field in the defect layer is achieved in an asymmetric photonic crystal structure. A greater Faraday rotation, which significantly exceeds the angle of rotation of the polarization plane in an isolated magnetized layer, and a higher degree of localization of the wave field can be achieved when the magnetic layer is surrounded by layers of photonic crystal mirrors with a lower refractive index. An increase in the Faraday rotation angle is determined not only by an increase in the thickness of the magnetic defect but also by a symmetric increase in the number of periods in the photonic crystal mirrors.     

Optical properties of a stack of right- and left-handed layers of a cholesteric liquid crystal

We have studied the optical properties of a stack that consists of right- and left-handed layers of a cholesteric liquid crystal (CLC). The problem has been solved using the modified Ambartsumyan layer-summation method. We have examined particular features of the reflection spectra of this system and have shown that, as distinct from a single CLC layer, this system has multiple photonic band gaps. Particular features of the spectra of the photonic density of states have been considered. We have shown that this system has unique polarization characteristics; thus, in particular, if the number of sublayers is even, the eigenpolarizations of the system are degenerate (both eigenpolarizations coincide) and, as distinct from ordinary gyrotropic media, the rotation of the plane of polarization can decrease with increasing thickness of the system, the sign of the rotation depends on the sign of the chirality of the first sublayer of the system, the system is very sensitive to the variation in the number of sublayers, etc. We have investigated how the sublayer thickness, the angle of incidence, the local dielectric anisotropy, and the pitch of helix of sublayers affect the reflection spectra and other optical characteristics of the system.     

铁电晶体(K0.20Na0.20Sr0.60Ba0.20)Nb2O6全部电弹常数的测定

本文讨论了由作者首次人工合成的新的钨青铜结构铁电单晶(K_0.20Na_0.20Sr_0.60Ba_0.20)Nb₂O₆全部电弹常数的测量方法和测量程序。第一次发表了该晶体的全部电弹常数及电-机耦合系数等共53个数据。绝大多数的数据是按IRE标准进行测量的。采用了(zxl)45°切片的厚度切变振动模式和(xzt)45°棒的长度扩张模式来测定弹性系数s₆₆^D和s₁₃^D。对实验过程引起的测量误差进行了讨论。 关键词：     

Magnetische struktur von columbiten MnTa2O6 und CoNb2O6

By means of neutron diffraction we found for MnTa₂O₆S₁S₂ S₃S₄ with a magnetic unit which is the same as the chemical. Whereas the chemical unit of CoNb₂O₆ is doubled in c-direction; all spins in the chemical unit are parallel. Therefore the orthorhombic symmetry of the crystal structure cannot be maintained. In both compositions are the spins parallel to the a-axis.     

Synthesis and structure of the monolayer hydrate K0.3CoO2·0.4H2O

The monolayer hydrate (MLH) K_0.3CoO₂·0.4H₂O was synthesized from K_0.6CoO₂ by extracting K⁺ cations using K₂S₂O₈ as an oxidant and the subsequent intercalation of water between the layers of edge-sharing CoO₆ octahedra. A hexagonal structure (space group P6₃/mmc) with lattice parameters a=2.8262(1) Å, c=13.8269(6) Å similar to the MLH Na_0.36CoO₂·0.7H₂O was established using high-resolution synchrotron X-ray powder diffraction data. The K/H₂O layer in the K-MLH is disordered, which is in contrast to the Na-MLH. At low temperatures metallic and paramagnetic behavior was found.     

Structural,electronic and elastic properties of potassium hexatitanate crystal from first-principles calculations

The structural, electronic and elastic properties of potassium hexatitanate (K₂Ti₆O₁₃) whisker were investigated using first-principles calculations. The calculated cell parameters of K₂Ti₆O₁₃ including lattice constants and atomic positions are in good agreement with the experimental data. The obtained formation enthalpy (−61.1535 eV/atom) and cohesive energy (−137.4502 eV/atom) are both negative, showing its high structural stability. Further analysis of the electronic structures shows that the potassium hexatitanate is a wide-band semiconductor. Within K₂Ti₆O₁₃ crystal, the TiO bonding interactions are stronger than that of KO, while no apparent KTi bonding interactions can be observed. The structural stability of K₂Ti₆O₁₃ was closely associated with the covalent bond interactions between Ti (d) and O (p) orbits. Further calculations on elastic properties show that K₂Ti₆O₁₃ is a high stiffness and brittle material with small anisotropy in shear and compression.     

Gyrotropic Features of a Nonideal Optically Active 1D Photonic Orientationally Disordered Crystal

Journal of Applied Spectroscopy - The gyrotropic characteristics of a nonideal unidimensional photonic crystal with an arbitrary number of sublattices (one of which, potassium dithionate K2S2O6, is...     

Optical interconnection between different spatial modes using double phase conjugate mirror with polarization alignment system

We propose a fundamental interconnection method using a polarization alignment system for waveguides having different spatial modes. In addition, as an example for the verification of the fundamental operation, we demonstrate an interconnection between a photonic crystal fiber and a laser that have obviously different spatial modes. The polarization alignment system operates synergistically with a self-written waveguide formed with a double phaseconjugate mirror. This technique enables us to interconnect a photonic crystal fiber with a laser source without complicated and time-consuming optical alignment. In this method, although it is not necessary to perform an external control for interconnection, the waveguide most suitable for connection is formed autonomously in a Sn₂P₂S₆:Sb crystal developed for this purpose. There was a marked reduction in the polarization dependence of coupling efficiency, compared with that observed using a stand-alone double phase-conjugate mirror.     

Influence of K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript> on dielectric and barrier properties of polymer

Polymer composite comprising polyvinylidene fluoride (PVDF) and potassium hexatitante (K₂Ti₆O₁₃) was synthesized by solution casting. The effect of K₂Ti₆O₁₃ on surface, thermal, and electrical properties of polymer composite were investigated. The addition of K₂Ti₆O₁₃ with polymer leads to thermal degradation and transition of polymer composite from semi-crystalline to amorphous phase. The optimum results of contact angle for different loading wt% of K₂Ti₆O₁₃ were directly correlated with the surface morphology. Our experimental results confirmed the incorporation of K₂Ti₆O₁₃ in polymer by SEM micrographs. The evaluated dielectric properties (ε' = 424; tan δ = 2.14 at 130 °C and 100 Hz frequency for 20 wt% loading of K₂Ti₆O₁₃) for polymer composite are higher in compared to pure polymer. The enhancement in dielectric constant and changing the surface properties of polymer composite can be used for the development of electrochemical storage device applications.     

Investigation of temperature dependence of surface anisotropy field and constant in the system of BaFe12O19 nanocrystals

We show a possibility to determine the parameters characterizing surface magnetic anisotropy of platelet BaFe₁₂O₁₉ nanocrystals with thickness comparable to the magnetoperturbed surface layer of high-anisotropic hexagonal crystal. Taking into account the above-mentioned specific character of the particles, we introduce the constant K_S as the surface anisotropy energy per unit volume of near-surface layer. Temperature dependence of the surface anisotropy field as one of the components of effective anisotropy was corrected taking into account the thermal fluctuations. Discovered anomaly initiated calculation of the surface anisotropy constant with different approaches for two different temperature ranges. Analyzing the K_S sign changes with temperature, we conclude about the transformation of surface anisotropy from plane to axis type.     

双包层大模场面积保偏掺镱光子晶体光纤研究

采用改进的化学气相沉积法和溶液掺杂法制备出掺镱石英光纤预制棒,以该预制棒为有源纤芯制备芯区直径约为30μm的双包层保偏掺镱光子晶体光纤.模拟计算得到该保偏光纤的模场面积约232μm2,双折射系数B为5×10-5.利用该光纤分别进行了脉冲激光和连续激光的放大测试实验,在国内首次实现了高效率的飞秒激光放大,2 m长的光子晶体光纤可得到1.64 W的激光输出,激光放大斜率效率为49.8%.同时5 m长的光纤还能够实现8.12 W的连续激光放大输出,斜率效率达到55.9%,具有较高的斜率效率.此外,该光纤消光比约10 dB,具有良好的保偏特性.     

Structural and optical properties of thin films porous amorphous silicon carbide formed by Ag-assisted photochemical etching

In this work, we present the formation of porous layers on hydrogenated amorphous SiC (a-SiC: H) by Ag-assisted photochemical etching using HF/K₂S₂O₈ solution under UV illumination at 254 nm wavelength. The amorphous films a-SiC: H were elaborated by d.c. magnetron sputtering using a hot pressed polycrystalline 6H-SiC target. Because of the high resistivity of the SiC layer, around 1.6 MΩ cm and in order to facilitate the chemical etching, a thin metallic film of high purity silver (Ag) has been deposited under vacuum onto the thin a-SiC: H layer. The etched surface was characterized by scanning electron microscopy, secondary ion mass spectroscopy, infrared spectroscopy and photoluminescence. The results show that the morphology of etched a-SiC: H surface evolves with etching time. For an etching time of 20 min the surface presents a hemispherical crater, indicating that the porous SiC layer is perforated. Photoluminescence characterization of etched a-SiC: H samples for 20 min shows a high and an intense blue PL, whereas it has been shown that the PL decreases for higher etching time. Finally, a dissolution mechanism of the silicon carbide in 1HF/1K₂S₂O₈ solution has been proposed.     

Linear optical properties of γ-modification of bismuth borate BiB3O6

The refractive index dispersion of the ??-BiB₃O₆ crystal in the wavelength range 0.43?C0.81 ??m has been measured. It has been shown that the principal refractive indices n ₁, n ₂, and n ₃ are on average higher than those of ??-BiB₃O₆, but are slightly lower than those of ??-BiB₃O₆. The temperature dependences of the rotation angle ??(T) of the optical indicatrix and birefringence ??n ₂(T) = (n ₁ ? n ₃)(T) have been studied in the temperature range 100?C963 K. It has been shown that the ??-BiB₃O₆ crystal is stable in this temperature region.     

Radiolytic formation of plutonium (VII)

Abstract

Radiolytic oxidation of Pu(VI) to Pu(VII) in 1M NaOH solution has been investigated in presence of K₂S₂O₈. The radiolytic yield of Pu(VII), G[Pu(VTI)], has been found to depend both on the concentrations of Pu(VI) and K₂ S₂O₈., The maximum value of G [Pu(VII)] =4.0 has been obtained in solution containing 5.1 × 10^?4 M Pu(VI) and 7. 0 × 10^?2 M K₂S₂O₈.     

空气包层大模场面积掺镱光子晶体光纤研究

采用改进的化学气相沉积法和气相液相混合掺杂技术制备大芯径掺镱石英光纤预制棒, 以此作为有源纤芯制备了纤芯直径约90 μm的掺镱双包层光子晶体光纤, 纤芯组分为镱铝磷共掺.双包层光子晶体光纤的模场面积约1330 μm², 纤芯数值孔径0.065,包层数值孔径0.5.首次实现了国产掺镱光子晶体光纤的高功率高效率激光输出, 1 m长的光子晶体光纤激光器实现102 W 激光输出,斜率效率76%.     

Splitting of defect-mode in one-dimensional magnetic photonic crystal

Using the 4×4 transfer matrix method, we investigate the splitting of defect-modes in one-dimensional magnetic photonic crystal. Numerical results exhibit defect-mode splitting in the presence of external magnetic fields. The splitting condition has been examined. The results show that defect-mode splitting critically depends on the magneto-optical gyrotropy factor and number of layers. We predict theoretically that magnetic photonic crystal consisting of gyrotropic material can be used as a tunable filter.