Compact and fault-tolerant photonic crystal add-drop filter

We propose an add-drop filter consisting of two adjacent waveguides carved into a two-dimensional photonic crystal that is etched through a standard guiding structure. This filter is based on distributed energy transfer via the frequency-selective intermediate conversion of the fundamental guided mode to a high-order low-group-velocity mode. This geometry circumvents the fabrication sensitivity on the single-hole scale of previous cavity-based designs. Combining distributed energy transfer and reduced group velocity preserves compactness. The design is analytically optimized with a coupled-mode approach.     

Geometry of crystal structure with defects. II. Non-Euclidean picture

The following point of view is geometrically formulated and its consequences examined: the lattice of a crystalline body with a continuous distribution of dislocations can be locally described as an ideal lattice in non-Euclidean space. The types of distribution of dislocations are described by the classification of three-dimensional real Lie algebras. The influence of point defects and the elastic deformation field on the geometry of the material structure of a crystalline body with dislocations is examined. The case where a crystal with dislocations reacts as a body with internal rotational degrees of freedom is discussed.     

Kinematics of edge dislocations. I. Involutive distributions of local slip planes

The geometry of continuous distributions of dislocations and secondary point defects created by these distributions is considered. Particularly, the dependence of a distribution of dislocations on the existence of secondary point defects is modeled by treating dislocations as those located in a time-dependent Riemannian material space describing, in a continuous limit, the influence of these point defects on metric properties of a crystal structure. The notions of local glide systems and involutive distributions of local slip planes are introduced in order to describe, in terms of differential geometry, some aspects of the kinematics of the motion of edge dislocations. The analysis leads, among others, to the definition of a class of distributions of dislocations with a distinguished involutive distribution of local slip planes and such that a formula of mesoscale character describing the influence of edge dislocations on the mean curvature of glide surfaces is valid.     

Study of the In2O3 molecule in the free state and in the crystal

ABSTRACT

The nanomaterials based on the In₂O₃ molecule are widely used as catalysts and sensors among other applications. In the present study, we discuss the possibility of using nanoclusters of In₂O₃ as molecular photomotors. A comparative analysis of the electronic structure of the In₂O₃ molecule in the free state and in the crystal is performed. For the free In₂O₃ molecule the geometry of its lowest structures, V-shape and linear, was optimised at the CCSD(T) level, which is the most precise computational method applied up to date to study In₂O₃. Using experimental crystallographic data, we determined the geometry of In₂O₃ in the crystal. It has a zigzag, not symmetric structure and possesses a dipole moment with magnitude slightly smaller than that of the V-structure of the free molecule (the linear structure due to its symmetry has no dipole moment). According to the Natural Atomic population analysis, the chemical structure of the linear In₂O₃ can be represented as O = In?O?In = O; the V-shaped molecule has the similar double- and single-bond structure. The construction of nanoclusters from ?bricks? of In₂O₃ with geometry extracted from crystal (or nanoclusters extracted directly from crystal) and their use as photo-driven molecular motors are discussed.     

Mixed valency and phase transitions at the (001) SmS surface

A model for mixed valency and phase transitions at (001) SmS is suggested. Focussing on the electron-lattice coupling as a mechanism potentially responsible for both phenomena, the problem of the semi-infinite crystal is factorized and reduced to the investigation of a low-dimensional effective Hamiltonian matrix. Surface geometry and electronic structure are obtained simultaneously by numerical minimization of the free energy. The possible appearance of mixed valency and of phase transitions confined to the surface region and involving relaxed or reconstructed geometry is demonstrated.     

Geometry of etched charged particle tracks in crystalline detectors

Studies on the shape of etched fission tracks in crystalline detectors show that the track geometry carries valuable information on the crystal structure of the detector involved. The geometry of the etched tracks in crystalline detectors is a prism formed of certain crystal planes. In mica detectors, for given etching conditions the type and number of the planes depend on the incident angle and the extent of the radiation damage along the track. In a single track the type of crystal planes forming the track prism may change along the track resulting in dramatic variations of the track geometry at certain depth of focus.     

KDP晶体拉曼散射角度特性

利用群理论详细分析了磷酸二氢钾(KDP)晶体的拉曼振动模式,得出了其拉曼振动模的归类。并采用拉曼光谱仪测量了Z切退火KDP晶体X(ZZ)珡X,Z(XY)珚Z和Y(XY)X三种散射配置和未退火KDP晶体Z(XY)珚Z配置下的拉曼光谱。根据拉曼选择定则得出X(ZZ)珡X,Z(XY)珚Z和Y(XY)X散射配置下的拉曼峰分别对应A1,B2(LO),B2(TO)对称类振动模,但在Z(XY)珚Z配置下的拉曼光谱中除了B2模,还观察到了A1模,而在Y(XY)X配置下的拉曼光谱中只有B2模,且退火和未退火晶体Z(XY)珚Z配置下的拉曼光谱无明显差别,此结果表明KDP晶体的对称性降低,在背向散射时A1模也具有角度特性,但与晶体的内应力无关,这是由KDP晶体内部结构决定的。     

Two-dimensional hexagonal photonic crystal with new element geometry

A new type of the geometry of the elements of hexagonal-lattice photonic crystal shaped as the Wigner-Seitz cell is proposed. Dispersion curves of electromagnetic waves are calculated and the photonic crystal band gap characteristics are determined using the plane wave expansion technique. It is shown that the proposed geometry of the photonic crystal element leads to band gap widening. A simple method for fabricating prototypes using negative electron lithography is proposed.     

First-principles study on the optical properties for CsI crystal with a pair of V_(Cs)~(1-)-V_I~(1+)

The electronic structures and optical properties of both the perfect CsI crystal and the crystal containing a pair of V_(Cs)~1-V_1~(1+) are calculated using CASTEP code with the lattice structure optimized.The calculated results indicate that the optical symmetry of the CsI crystal coincides with the lattice structure geometry of the CsI crystal.The absorption spectrum of the CsI crystal containing a pair of V_(Cs)~(1-)-V_1~(1+) also does not occur in the visible and near-ultraviolet range.It reveals tha...     

光子晶体光纤拉制中工艺参数的控制

分析了光子晶体光纤拉制中各工艺参数之间的相互影响,建立了工艺参数与最终光纤结构之间的对应关系.在温度和送料速度的协调控制下,通过调节气压参数可有效控制气孔结构.实验拉制出孔径孔距比分别为0.45和0.8的单模以及高占空比光子晶体光纤.在制备非均匀孔径光子晶体光纤时,仅靠调控工艺参数往往难以拉制出理想结构,本文以一种单偏振单模PCF结构为例,对预制棒结构进行了优化设计.计算表明可由此拉制出满足要求的光子晶体光纤. 关键词： 光子晶体光纤 工艺参数 气压控制 气孔结构     

Dislocations and internal length measurement in continuized crystals. I. Riemannian material space

Distributions of dislocations creating point defects are considered. These point defects are described by a metric tensor, which supplements a Burgers field responsible for dislocations. The metric tensor depends on the distribution of dislocations and defines a Riemannian geometry of the material space of a continuized crystal and thus an internal length measurement in this crystal. The dependence of the distribution of dislocations on the existence of point defects created by these dislocations is modeled by treating the Burgers field as a field defined on the Riemannian material space. Field equations, following from geometric identities, are formulated as balance equations on this Riemannian space and their source terms, responsible for interactions of dislocations and point defects, are identified.     

Structure in LEED Bragg reflexes of spherical Ag crystals

LEED at room temperature is performed on spherically-shaped silver crystals grown by solidification of a drop of melt. The domains of intensity in the reciprocal lattice, which are usually rodlike, change to double cones caused by the crystal sphere. The size and the structure of Bragg reflexes were studied as a function of primary electron energy and diffraction geometry. The influence of impurities on the diffraction patterns is examined.     

He原子掺杂铝材料的第一性原理研究

采用基于第一性原理的平面波超软赝势方法,结合广义梯度近似(GGA),计算了铝及铝晶胞间隙位置掺入He原子后体系的几何结构、电子结构、总体能量和电荷布居值.计算结果表明:随着氦在金属铝中逐渐形成,铝晶胞体系会发生晶格畸变,但总的趋势是He在铝体系的八面体位置的晶格畸变小于其在四面体位置的晶格畸变.He在铝晶胞八面体和四面体间隙的杂质形成能分别为1.3367 eV和2.4411 eV.由此可知,He在铝晶胞中最稳定位置是八面体间隙位置.同时,文中还从原子尺度层面分析了He原子在铝晶胞中的占位及其键合性质,讨论 关键词： 铝材料 第一性原理 形成能     

Trifluoromethanesulfonamide: X‐ray single‐crystal determination and quantum chemical calculations

The X‐ray single‐crystal structure of 1,1,1‐trifluoromethanesulfonamide (triflamide) CF₃SO₂NH₂, which is the ancestor of a large family of its derivatives, has been determined. The crystal structure is composed of infinite layers with an interlayer distance of 3.4 Å. Geometry optimization at the Møller‐Plesset (MP2) and density functional theory (DFT) level showed the calculated bond distances to be, as a rule, longer than the experimental ones. A trial to simulate crystal packing effect on the geometrical parameters by calculating the dimer of triflamide in the gas phase failed – the starting X‐ray geometry of the ‘dimeric’ unit with one NH···O=S H‐bond – was optimized to the cyclic dimer with two H‐bonds. However, when the external (crystal) field effect was simulated using the polarizable continuum model, the experimental geometry of the ‘dimeric’ fragment was satisfactorily reproduced. Calculations of the heptamer cluster having the structure of the hexagon with six triflamide molecules in vertices and one in the middle nicely reproduce the X‐ray structure and brings the geometrical parameters closer to the experiment. Copyright © 2015 John Wiley & Sons, Ltd.     

Probability distribution of normalized structure factor magnitudes for a centrosymmetric crystal with planar molecules in the unit cell

The reasons and conditions for applicability of the Cauchy distribution law for crystal structure factor components are discussed. It is shown that the standardized structure factors of centrosymmetric crystals are quite prone to be Cauchy distributed for crystals having planar molecules in their unit cells.     

Multiwavelength fiber laser based on a photonic crystal fiber loop mirror with cooperative Rayleigh scattering

In this work, a multiwavelength fiber Raman laser based on a highly birefringent photonic crystal fiber loop mirror is presented. A laser resonator is formed when the Raman amplification with cooperative Rayleigh scattering in a dispersion-compensating fiber is used as a distributed mirror and combined with a photonic crystal fiber loop mirror filtering structure. Stable multiwavelength lasing at room temperature is achieved due to the low temperature sensitivity of the highly birefringent photonic crystal fiber.     

Coherent X-ray radiation generated by a relativistic electron in an artificial periodic structure

A theory of coherent X-ray radiation from a relativistic electron crossing an artificial periodic layered structure in the Laue scattering geometry is constructed. The expressions describing the spectral-angular radiation parameters are obtained. It is shown that the radiation yield in such a medium may substantially exceed the radiation yield in a crystal under analogous conditions.     

Investigation of ring resonators in photonic crystal circuits

In this paper, we propose the implementation of waveguide-coupled ring resonators in photonic crystal integrated circuits. Using two-dimensional finite difference time domain (2D FDTD) method, we study the spectral characteristics of a waveguide-coupled ring carved in two-dimensional photonic crystal of square lattice (2D SLPC) and based on the results, we suitably modify the structure geometry to establish its performance as a ring resonator. We further investigate the effects of ring dimension and crystal parameters on the resonance properties of the ring resonator.     

The electron-lattice interaction energy of strongly compressed matter

A crystal structure dependent term of strongly compressed matter is calculated. The correction is of the same order of magnitude as the terms calculated allready on an assumption of a uniformly distributed background of positive charge.     

Dynamic magnetic and hysteretic properties of the different type core/shell nanostructures: the effect of geometry of wire shape

In the present study, we examine by comparison the dynamic magnetic and hysteretic properties of nanostructures with different magnetic core/shell particles confined within a shape structure of the wire. The model of nanostructures with core?=?spin-1 and shell?=?spin-3/2, namely cylindrical, cubic and hexagonal nanowire, is proposed for studying the effect of the geometry of wire shape on the magnetic and hysteretic properties. The results were obtained by mean-field theory as well as Glauber-type stochastic dynamics, and focused the response to thermal and hysteretic behaviours of systems. All results display dynamic magnetic properties of the nanostructure strongly dependent on the geometry of wire shape. Moreover, temperature and crystal field are proposed as the important factors affecting the dynamic properties of wire systems.