Aperiodic birefringent photonic structures based on Kolakoski sequence

A novel type of aperiodic porous silicon-based multilayered structures which can be used for the electromagnetic radiation manipulation in the visible and infrared parts of spectrum are proposed in this paper. The one-dimensional aperiodic structures under consideration are arranged by stacking together two anisotropic layers according to the Kolakoski self-generation scheme. The spectral properties of the structures are theoretically investigated by using the electromagnetic field scalarization method in coupling with the finite-difference method. It is shown that the Kolakoski multilayers have both completely transparent states in the transmission spectra and pronounced omnidirectional reflectance which can used in integrated optics, optical fiber telecommunications, vertical cavity surface emitting lasers, laser cavities, etc. Also, it is shown numerically that the anisotropic nature of layered media significantly affects on optical properties of the structures.     

Discrete-mode cancellation mechanism for high-Q integrated optical cavities with small modal volume

A mechanism to reduce radiation loss from integrated optical cavities without a complete photonic bandgap is introduced and demonstrated. It is applicable to any device with a patterned substrate (including both low and high index-contrast systems), when it supports discrete guided or leaky modes through which power escaping the cavity can be channeled into radiation. One then achieves the associated increase in Q by designing the cavity such that the near-field pattern becomes orthogonal to these discrete modes, therefore canceling the coupling of power into them and thus reducing the total radiation loss. The method is independent of any delocalization mechanism and can be used to create high-Q cavities with small modal volume.     

Absorption spectra versus field distribution for metal-dielectric three-dimensional photonic crystals

The absorption spectra of three-dimensional metal-dielectric photonic crystals (PCs) are studied using computer simulation by the finite difference time domain method and the layered Korringa-Kohn-Rostoker method. The band structure of a three-dimensional dielectric PC is obtained by the plane wave expansion method. The explanation of absorption spectra of PC based on its comparison with the band structure and Fabry-Perot resonances inside a PC plate is given. The intensity distribution of an electric field using FDTD inside the metal-dielectric PC for three various structures is analyzed. It is shown that spherical cavities in a dielectric PC “focus” the field inside cavities at certain wavelengths. This leads to an increase of absorption at these wavelengths if metal spheres are located in the centers of those cavities. This effect can be considered as an analogue of the Borrmann effect in X-ray spectroscopy.     

一种金属腔体中微波断层成像的最优分层非均一背景

针对基于金属腔体的微波断层成像系统,提出了一种最优分层非均一背景的设计方法.该方法使用一种新的微波断层成像积分算子评价方法和模拟退火法等最优化方法.首先,介绍了一种基于有限元法的微波断层成像积分算子计算方法.然后,提出一种新的微波断层成像积分算子度量,该度量可以综合评价整个积分算子奇异值谱,并通过一组仿真研究证明该度量与反演结果的误差具有相关性;该度量用一个数值综合评价一个积分算子,可以方便地应用于最优化算法中;利用模拟退火法选择圆形金属腔体中分层非均一背景的每一层介质的相对介电常数,从而获得一个最优分层非均一背景.最后,对尺寸小于半波长的圆柱目标和"凹"字形复杂目标进行仿真研究,仿真结果证明该最优分层非均一背景可以提高微波断层成像算法的收敛速度,提高反演结果的准确性.     

Radiation from a Line Source Placed in Two-dimensional Photonic Crystals

A novel formulation of radiation from a localized line source placed in two-dimensional photonic crystals consisting of layered periodic arrays of parallel circular cylinders is presented. The method employs the spectral domain approach. The spectral response of the photonic crystals to the line source excitation is calculated using the lattice sums, the T-matrix of a circular cylinder, and the generalized reflection and transmission matrices of the layered system. The far-zone radiated field is obtained using the conventional asymptotic method to the spectral response. The radiation patterns of the localized line source sandwiched by two photonic crystals are numerically studied.     

一种开边界条件及其在内潮模拟中的应用

提出一种辐射强迫开边界条件，可以同时作为主动和被动边界条件使用，既可应用于潮汐模拟，也可应用于其他海洋动力过程的模拟.在一个内外模态分离的内潮模型中对各种开边界条件进行对比：在外模态中，Dirichlet条件、辐射强迫条件、Flather条件和松弛条件的对比表明辐射强迫条件与Flather条件表现最好，但辐射强迫条件比Flather条件所需的观测数据更少，具有更广泛的适用性；在内模态中，松弛条件、Sommerfeld辐射条件和基于模态分解的Sommerfeld辐射条件的对比表明松弛条件表现最好.     

Physical processes upon the optical discharge propagation in optical fiber

Recent theoretical works on the physics of the fiber fuse effect in optical fiber are reviewed. A qualitative interpretation of the significant increase in the absorption of quartz glass with increasing temperature is presented. The results of the 2D simulation of the optical discharge propagation in optical fiber are analyzed. The results of the simulation are in agreement with the recent measurements of the spatial distribution of the bright-spot radiation intensity. It is demonstrated that the recently demonstrated fast propagation of the optical discharge can be interpreted as light detonation. A mechanism for the formation of a chain of cavities in the fiber-fuse track is considered. It is demonstrated that this effect cannot be interpreted using the Rayleigh capillary instability due to the relatively high viscosity of glass. The periodicity of the cavities can be related to an instability of a new type. A high-density double layer of charges emerges at the plasma-liquid interface. A tendency towards an increase in the surface owing to the repulsion of like charges provides for a development of the instability that causes the formation of the chain of cavities.     

The Theory of Block Structures in Problems on the Strength of Galleries and Constructions with Multiple Connections

Doklady Physics - It is shown that the boundary-value problem for a layered medium with parallel multiple cavities is reduced to the Riemann vector problem. To solve it, a factorization method is...     

Great progress in developing 500 MHz single cell superconducting cavity in China

Superconducting cavities have been adopted in many kinds of accelerator facilities such as synchrotron radiation light source, hard X-ray free electron laser linac, colliders and energy recovery linacs (ERL). The 500 MHz superconducting cavities will be a candidate to be installed in the high current accelerators and high current ERLs for their large beam aperture, low higher order modes impedance and high current threshold value. This paper presents great progress in the whole sequence of developing 500 MHz superconducting cavity in China. It describes the first in-house successful development of 500 MHz single cell superconducting cavity including the deep-drawing of niobium half cells, electron beam wielding of cavity, surface preparations and vertical testing. The highest accelerating gradient of the fabricated cavity #SCD-02 higher than 10 MV/m was obtained while the quality factor was better than 4×10⁸ at 4.2 K, which has reached the world level of the same kind of cavities.     

Modification of radiation damage microstructure by helium

Current experimental findings on the effects of helium on the evolution of radiation damage microstructure in metals at temperatures where vacancies are mobile are reviewed. It is shown that helium concentrations as low as a few parts per million promote the formation of cavities and dislocations, may increase or decrease swelling, and can alter the development of precipitate phases. Mechanisms underlying these processes are discussed in terms of the theory of radiation effects. Helium-vacancy trapping and the stabilization of cavities is seen as the unifying, underlying feature. Promotion of cavities is explained by reduction of critical cavity size by helium. This promotion, and the attendant increase in dislocations, changes the point-defect sink strengths and thereby modifies swelling. Correspondingly, solute segregation at sinks is changed, resulting in alteration of precipitate phases.     

Radiation from Bodies with Extreme Acceleration II: Kinematics

When applied to a dipole source subjected to acceleration which is violent and long lasting (extreme acceleration), Maxwell's equations predict radiative power which augments Larmor's classical radiation formula by a nontrivial amount. The physical assumptions behind this result are made possible by the kinematics of a system of geometrical clocks whose tickings are controlled by cavities which are expanding inertially. For the purpose of measuring the radiation from such a source we take advantage of the physical validity of a spacetime coordinate framework (inertially expanding frame) based on such clocks. They are compatible and commensurable with the accelerated clocks of the accelerated source. By contrast, a common Lorentz frame with its mutually static clocks won't do: It lacks that commensurability. Inertially expanding clocks give a physicist a window into the frame of a source with extreme acceleration, and thus can locate that source and measure radiation from it without being subjected to such acceleration himself. The conclusion is that inertially expanding reference frames reveal qualitatively distinct aspects of nature which would not be accessible if inertial frames were the only admissible frames.     

Entanglement Generation Between Two Mechanical Resonators in Two Optomechanical Cavities

A standard model is suggested to explore correlation features of two spatially separated optomechanical cavities. The cavities are coupled through the photon-hopping process. In particular, we investigate the generation of entanglement between mechanical resonators in the strong coupling regime and the two cavities are assumed to be driven by a coherent laser field. In order to quantify entanglement we use the logarithmic negativity. The analytical solutions are presented for the system in a parameter regime very close to the current experimental results. We show that in the presence of the photon hopping process between the cavities, the two mechanical resonators and the field modes can be entangled. This shows clearly that the entanglement can be transfer via radiation pressure of a photon hopping coupling from the intracavity photon-phonon entanglements to an inter-cavity photon-photon or phonon-phonon entanglement.     

Study of He-induced nano-cavities as sinks of oxygen for forming silicon-on-insulator

In the present work, a Cz-Silicon wafer is implanted with helium ions to produce a buried porous layer, and then thermally annealed in a dry oxygen atmosphere to make oxygen transport into the cavities. The formation of the buried oxide layer in the case of internal oxidation （ITOX） of the buried porous layer of cavities in the silicon sample is studied by positron beam annihilation （PBA）. The cavities are formed by 15 keV He implantation at a fluence of 2×10^16 cm^-2 and followed by thermal annealing at 673 K for 30 min in vacuum. The internal oxidation is carried out at temperatures ranging from 1073 to 1473 K for 2 h in a dry oxygen atmosphere. The layered structures evolved in the silicon are detected by using the PBA and the thicknesses of their layers and nature are also investigated. It is found that rather high temperatures must be chosen to establish a sufficient flux of oxygen into the cavity layer. On the other hand high temperatures lead to coarsening the cavities and removing the cavity layer finally.     

钢板-空气背衬上含空腔粘弹性材料层的声反射特性

本文研究声波从水中入射到粘弹性材料层-钢板-空气上的反射特性，运用分层介质中的波动理论研究粘弹性层均匀情况的声特性，运用有限元方法研究粘弹性层含空气腔结构情况的声特性。结果表明，改变粘弹性材料消声特性需要综合调整材料的弹性参数；粘弹性层内的空腔结构对声特性产生很大影响，改变其谐振特性和反射系数的收敛特性。文中以含圆锥腔、圆台等复合腔的结构粘弹性层为例，计算了其反射系数的频响特性、谐振模态，并分析了结构的影响。     

Cooperative optical effects in volumes embedded in layered media

A cluster of point sources can generate optical radiation in a manner substantially different from what characterizes the emission of a single point source. Such differences are mainly caused by the cooperation of the sources and are even more remarkable under particular electromagnetic boundary conditions. Furthermore, the geometry of the problem cannot be ignored as it makes an important contribution to the contrast between single source and collective behaviour. This paper tries to explore the subject in view of its applications to coherent scattering that is typical of non‐linear Raman processes. To this end, the classical theories of electromagnetic radiation from a point source (treated as a randomly oriented Hertzian dipole) and of partial coherence are joined into a unified formalism to evaluate light emission from a volume seen as a collection of point sources embedded in a layered medium. In certain reasonable circumstances and beyond the undeniable complexity of the problem, the formalism leads to the relevant advantage of analytical results for the power radiated outside the medium. In other more general cases, fast Fourier transforms can be used in principle. The possibility and convenience of using the theory to model micro‐CARS imaging are illustrated and discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

I. Synchrotron radiation from the large electron-positron storage ring LEP

The properties of synchrotron radiation from LEP are investigated. This radiation from LEP are investigated. This radiation is assumed to be in a parasitic mode without changing any of the operating parameters. At 86 GeV the radiation from the normal bending magnet has a critical energy of 0.4 MeV and a power of ～500 W/m, and is probably of limited interest. High photon energies (10–20 MeV) of high intensity can be obtained from normal and superconducting wiggler magnets. Undulators can give quasi-monochromatic radiation of high brightness with photon energies of up to 5 MeV. New magnet developments might increase this energy range. Quasi-monochromatic γ-rays of ～100 MeV can be created with soft Compton back scattering without disturbing the electron bean. This relies on future free electron lasers in the submillimetre range. The natural collimation, the polarization and the time structure make all these photon beams unique tools for research in nuclear physics. The synchrotron rediation can be used to produced photoneutrons with intensities of up to 10¹⁴ neutrons/s. It is foreseen that LEP will be equipped with superconducting cavities in later stage and that is energy will be increased to ～130 GeV. This will approximately double the photon energies obtained from wigglers and undulators.     

Electromagnetic radiation from filamentary sources in the presence of axially magnetized cylindrical plasma scatterers

Electromagnetic radiation from filamentary electric-dipole and magnetic-current sources of infinite length in the presence of gyrotropic cylindrical scatterers in the surrounding free space is studied. The scatterers are assumed to be infinitely long, axially magnetized circular plasma columns parallel to the axis of the filamentary source. The field and the radiation pattern of each source are calculated in the case where the source frequency is equal to one of the surface plasmon resonance frequencies of the cylindrical scatterers. It is shown that the presence of even a single resonant magnetized plasma scatterer of small electrical radius or a few such scatterers significantly affects the total fields of the filamentary sources, so that their radiation patterns become essentially different from those in the absence of scatterers or the presence of isotropic scatterers of the same shape and size. It is concluded that the radiation characteristics of the considered sources can efficiently be controlled using their resonance interaction with the neighboring gyrotropic scatterers.     

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.     

Coherent diffraction radiation as a source of radiation in far-infrared and terahertz range

The results of measurements of the coherent diffraction radiation yield generated by femtosecond electron beam are presented. It is shown that the simulated and experimental data agreed quite well. The coherent diffraction radiation can be considered as a real candidate to develop a source of radiation in far-infrared and terahertz range.     

Mathematical modeling of random coupling between polarization modes in single-mode optical fibers: VIII. Zero drift in a fiber ring interferometer with a white light source

Different schemes of fiber ring interferometers (FRIs) with a broadband nonmonochromatic radiation source manufactured on the basis of air-silica microstructured single-mode optical fibers (SMOFs) are considered. This source is close in spectral characteristics to a white light source, because the width of its emission spectrum is comparable to the mean wavelength. It is shown that an increase in the width of the spectrum of the radiation source can lead to either a substantial decrease or an increase in the zero drift, depending on the radiation polarization at the FRI entrance. The latter fact has defied explanation within simple phenomenological models of random coupling between polarization modes in SMOFs of an FRI circuit. The observed increase in the zero drift of the FRI can be explained in terms of the dependence of the parameter of polarization conservation (the parameter h) on the light wavelength for highly anisotropic SMOFs. This dependence is weak for nonmonochromatic radiation sources with a relatively small spectral width, for example, superluminescent diodes, which are traditionally used in FRIs. In contrast, for substantially more broadband radiation sources (including air-silica SMOFs), the above dependence is well pronounced and can lead to a number of undesirable effects in FRIs. Different variants of the FRI design are analyzed. It is demonstrated that the zero drift can be noticeably decreased with an increase in the width of the spectrum of the radiation source for an arbitrary radiation polarization at the entrance of an FRI with a depolarizer of nonmonochromatic radiation and a circuit fabricated from a weakly anisotropic SMOF, for which the parameter h does not depend on the light wavelength. The numerical estimates are obtained.