Different effect of evanescent modes on acoustic phonon transport in different types of a three-dimensional quantum wire

By the use of the scattering matrix method, we investigate the effect of evanescent modes on acoustic phonon transport and thermal conductance in both convex and concave type three-dimensional quantum wire. Our results show that the evanescent modes can enhance the transmission coefficient and the thermal conductance in the concave type three-dimensional quantum wire. However, for the convex type three-dimensional quantum wire, the evanescent modes can play adverse effect on the phonon transport. When the length of scattering region is large enough, for all types of three-dimensional quantum wire, the influence of evanescent modes on phonon transport becomes very weak.     

Evanescent waves of an annular left-handed material lens

The imaging system formed by an annular left-handed material （LHM） lens as well as the evanescent waves in the lens are simulated numerically with a finite-difference time-domain （FDTD） method. For b - a 〉 λ （a and b are respectively the inner and outer radii of the annular lens, and λ is the wavelength）, when a point source is placed at an internal grid point, we demonstrate that the evanescent waves are produced around the internal interface, and cannot propagate outwards. As for b - a 〈λ ）,, the evanescent waves appear around both the internal and the external interfaces, which remarkably implies the coupling between the two interfaces. Hence it can be inferred that the evanescent waves around the external interface participating in the super-resolution imaging result from the coupling of the evanescent waves around the interface. Moreover, the partly uncomprehended properties of the evanescent waves in the LHM slab are also disclosed. It is conducive to understanding the evanescent waves in the LHMs further.     

Propagation characteristics of the silica and silicon subwavelength-diameter hollow wire waveguides

The basic propagation properties of the silica and silicon subwavelength-diameter hollow wire waveguides have been investigated by comparison. It shows that the silica and silicon subwavelength-diameter hollow wire waveguides have some interesting properties, such as enhanced evanescent field in the cladding, enhanced intensity in the hollow core, and large waveguide dispersion. For the different confinement ability, the enhanced field in the hollow core and cladding of the silica subwavelength-diameter hollow wire is much stronger than that of the silicon one for the same size.     

Optical manipulation of microspheres along a subwavelength optical wire

The propulsion of 3 microm polystyrene spheres along a subwavelength optical wire is demonstrated. Velocities in the range of 7-15 microm/s are observed. Simulations are carried out to evaluate the evanescent field at the waveguide-water suspension interface.     

Spiral-path high-sensitivity silicon photonic wire molecular sensor with temperature-independent response

We demonstrate a new silicon photonic wire waveguide evanescent field (PWEF) sensor that exploits the strong evanescent field of the transverse magnetic mode of this high-index-contrast, submicrometer-dimension waveguide. High sensitivity is achieved by using a 2 mm long double-spiral waveguide structure that fits within a compact circular area of 150 microm diameter, facilitating compatibility with commercial spotting apparatus and the fabrication of densely spaced sensor arrays. By incorporating the PWEF sensor element into a balanced waveguide Mach-Zehnder interferometer circuit, a minimum detectable mass of approximately 10 fg of streptavidin protein is demonstrated with near temperature-independent response.     

Electric field distribution and simulation of avalanche formation due to the passage of heavy ions in a parallel grid avalanche counter

Electric field distributions and their role in the formation of avalanche due to the passage of heavy ions in parallel grid avalanche type wire chamber detectors are evaluated using a Monte Carlo simulation. The relative merits and demerits of parallel and crossed wire grid configurations are studied. It is found that the crossed grid geometry has marginally higher gain at larger electric fields close to the avalanche region. The spatial uniformity of response in the two wire grid configurations is also compared.      

Transmission Characteristics of a Gaussian Electromagnetic Beam by a Cylindrcal Wire Grid

In this paper, the scattering formulae of a Gaussian electromagnetic beam by a cylindrical wire grid are derived. For the summation of Hankel functions, we adopt an integral form of lattice sums, which is developed by Yasumoto and Yoshitomi, to speed up convergence. The reflected and transmitted characteristics of a Gaussian beam by an actual wire grid are thoroughly investigated. Detailed simulation results are presented.     

Fabrication of wire-grid polarizers and dependence of submillimeter-wave optical performance on pitch uniformity

We describe a device for fabricating high-precision free-standing grids of fine wire, suitable for use as polarizing elements for radiation at millimeter and submillimeter wavelengths. Computer control of the winding process makes changing grid parameters particularly convenient and flexible. We present measurements of the mechanical uniformity and of the optical performance of wire grid polarizers made with 25 m and 10 m diameter wire. The flexibility of computer control is exploited to introduce a known degree of randomness in the grid pitch (center-to-center wire spacing), allowing the dependence of polarizer quality on uniformity to be quantified. This information allows prediction of the fabrication tolerances required for polarizers to be used at very high frequencies.     

Simulations of ferrite-dielectric-wire composite negative index materials

We perform extensive finite difference time domain simulations of ferrite based negative index of refraction composites. A wire grid is employed to provide negative permittivity. The ferrite and wire grid interact to provide both negative and positive index of refraction transmission peaks in the vicinity of the ferrite resonance. Notwithstanding the extreme anisotropy in the index of refraction of the composite, negative refraction is seen at the composite air interface allowing the construction of a focusing concave lens with a magnetically tunable focal length.     

Non λ−4 wavelength dependence of rayleigh-scattering loss in waveguides

We show that, in small-core waveguides, where a considerable fraction of radiation power is guided in the evanescent field outside the fiber core, the wavelength dependence of losses induced by Rayleigh scattering can substantially deviate from the λ^?4 scaling law. In the limiting case of an ultrathin waveguiding wire surrounded by air, the ultimate lower bound level of losses, controlled by Rayleigh scattering, asymptotically scales as exp(?κλ²) with radiation wavelength λ, with κ being a wavelength-independent constant.     

金属线栅笼代替空心导体圆柱对辐射波模拟器电磁特性的影响

主要关注空心导体圆柱的等效替代品-圆柱线栅笼的电磁特性,分别基于保角变换和等效电磁场理论进行了等效半径的推导,在此基础上运用电磁仿真软件CST仿真分析了金属线栅的疏密和粗细程度对测试区电场波形的上升沿、脉宽和峰值的影响,并且对比了圆柱线栅笼和空心导体圆柱两种结构的电场分布。分析结果显示,双锥笼型结构完全能够等效代替空心导体圆柱,且进一步验证了等效半径理论的正确性。     

Optical properties of F.I.R. metallic grids: Reflection phase shift measurements

Utilization of metallic grids stacks for F.I.R filters needs a good knowledge of optical properties of each grid. We study here an experimental method in order to determine the wave's change of phase by reflection on a wire grid. We use a Perot-Fabry interferometer constituted by these grids.     

Mid-infrared wire-grid polarizer with silicides

An infrared (IR) polarizer with tungsten silicide (WSi) wire grid was fabricated by two-beam interference exposure and reactive ion etching. To enhance TM transmittance, silicon monoxide was deposited between the WSi wire grid (400 nm period) and a Si substrate. The transmittance was over 80% in the 4-5 microm wavelength range. The ratio of TM and TE transmittances was over 100 (20 dB) in the 2.5-6 microm wavelength range. The fabricated polarizer has higher durability and better compatibility with microfabrication processes compared with conventional IR polarizers.     

A lattice of magneto-optical and magnetic traps for cold atoms

We describe basic periodic trapping configurations for ultracold atoms above surfaces. The approach is based on a simple wire grid and can be scaled to provide large arrays of periodically arranged magnetic or magneto-optical traps. The unit cells of the trap lattices are based on crossed wire segments. By alternating the current directions in the wires of the grid it can be distinguished between 3 basic lattice configurations. As a first demonstration, we used macroscopic wires in a 2 layer configuration to realize the unit cells of the lattices. With this experimental setup, we observe two of the basic unit cells and an array of 2×2 magneto optical traps. Received 29 August 2002 / Received in final form 12 December 2002 Published online 18 February 2003     

Electric field patterns in finite two-dimensional wire photonic lattices

Electric field patterns in finite two-dimensional wire photonics lattices are investigated by means of electromagnetic simulations. These studies reveal a strong analogy with the envelope wavefunction approach extensively used for semiconductor superlattices. Several propagating eigenmodes in the pass-band of the periodic structure as well as evanescent modes in the stop-bands are clearly identified. They are interpreted on the basis of the matching of the wavelength of electromagnetic field to the lattice dimensions with an envelope wavefunction resulting of a Fabry–Pérot effect in the cavity formed by the periodic structure. In terms of transmission coefficient, the calculated frequency dependence are in agreement with those measured in finite metallic rod arrays between 50 and 110 GHz.     

Study of Polarizer Characteristics with a High-Power Terahertz Free Electron Laser

Though wire grid and strip polarizers are widely used for control of submillimeter radiation, both calculated and experimentally measured values of their transmission are often contradict one another. We have measured the transmission of wire and thin-film photolithographic polarizers at a wavelength of 0.13-mm using 100 W free electron laser radiation and compared the results with previous experiments and calculations. Using a thin-film photolithographic polarizer we showed that radiation of the Novosibirsk FEL after traveling through a 14-m beamline is plane-polarized with the degree of polarization better than 99.6%.     

负折射率材料对隐失波的幅度增益

分析了隐失波透过负折射率材料制成的透镜时,可以实现相位的调整,从而实现波的聚焦的原理;另外利用叠加原理(干涉法)及场量匹配法分析了负折射率材料如何实现对隐失波的振幅的放大,得到负折射率材料对隐失波有幅度增益,行波和隐失波都能聚焦成像的结论;并利用传输线理论提出隐失波透过负折射率材料平板时可等效地形成一个LC振荡电路,从而实现对隐失波的幅度增益.     

Manipulation of Particles with Counter-Propagating Evanescent Waves

Two counter-propagating evanescent beams are used to align and manipulate polystyrene particles on a prism surface. Since the radiation pressure transferred laterally from the evanescent wave is negated on both sides, particles can be stably aligned. By projecting a circular and a linear beam spot onto the interface, both multiple and single arrays of particles are achieved. Arrays of particles trapped on the interface can be easily moved adjusting the intensity of incident beams on either side. We also simulate electromagnetic distribution of scattering light that is converted from the evanescent wave using the FDTD method. The results show that scattering light converts from an evanescent wave propagating through a particle array and has a distance longer than that propagating from a normal evanescent wave.     

网格湍流对剪切层中预混火焰结构的影响

本文研究网格湍流对射流剪切层以及建立在其中的预混火焰的影响。利用热线风速仪测量射流的速度场,发现网格湍流使剪切层内湍流强度明显降低,抑制了低频速度脉动,同时增加了湍动能在小尺度脉动上的分配,使湍流更趋于各向同性,这表明网格湍流抑制了剪切层内的大涡和拟序结构。用细丝热电偶测量了火焰温度,结果显示网格湍流使火焰前峰的低频大幅摆动减少,小尺度皱褶增加,火焰区平均温度更高,说明网格湍流有利于剪切层中预混火焰的强化和稳定。