基于金属狭缝阵列的各向异性偏振分束器

在金属-电介质结构的基础上提出了一种基于金属狭缝阵列的各向异性偏振分束器,并采用有限元法研究了横磁(TM)和横电(TE)偏振光入射后结构所表现出的负反射和镜面反射等特性.计算结果表明,当偏振光的入射角设定在20?—70?时,入射的TM光发生强烈的负反射,而TE光的负反射很弱,并随着波长的增加而急剧下降.分析可得偏振分束光栅的理想负反射点和反射面的完美对称响应效果.通过仿真得到了理想负反射点的取值范围.结合严格耦合波法软件,计算不同偏振光入射时负反射和镜面反射条件下的反射率,其消光比高达10~6.     

Method of Coupled Waves in the Theory of Diffraction of Light by Elastic Waves in Crystals

Diffraction of light by elastic waves in crystals is described by the method of coupled waves in a form different from that used by other researchers. The difference is determined by the treatment of two pairs of orthogonal coordinate systems whose principal axes are oriented along the directions of phase and energy transfer of two optical waves interacting on a sound wave. Due to this, the equations of coupled waves assume the most compact form, which was previously unknown for crystals. These equations are easily solved by the conventional methods in terms of quasi-plane waves and also admit of a wider class of solutions for bounded interaction regions. Two different diffraction regimes are compared in the present work, namely, the transmission and reflection diffraction. It is indicated that the suggested approach allows one to refine the parameters that define the efficiency of diffraction of light by elastic waves in crystals.     

Surface wave effect on light scattering from one-dimensional photonic crystals

Light scattering and reflection measurements using attenuated total reflection technique for s polarization of the incident light on a finite one-dimensional photonic crystal are reported. Angular specular reflection was measured experimentally to determine, the optimum thickness, the angular position of the surface mode, and the number of bi-layers of the system. It was demonstrated that the position of the surface mode inside the last film is close to the asymptotic value when the number of periods is increased. Spectral reflection measurements were made to determine experimentally the band gap width and measure the dispersion relation of the surface mode inside this band. The corresponding field amplitude was calculated (∣E∣²) showing that in resonant conditions it has a maximum near the surface. The angular dependence of the scattered light measured displays a peak caused by singles cattering and located approximately at the excitation angle of the surface electromagnetic mode. When the incident light is in resonance with the surface electromagnetic wave, it is found experimentally that the scattering of light is enhanced overall by approximately one order of magnitude in comparison with the off-resonance case.     

Thermal expansion measurements of the quasi-one-dimensional conductor K0.30MoO3

The charge density wave (CDW) dynamics of the quasi-one-dimensional conductor K_0.30MoO₃ shows two different regimes depending on the temperature: a strongly damped CDW motion above ∼50 K and CDW motion with almost no damping below ∼50 K. In a search for a characterization of this CDW behaviour, we performed thermal expansion measurements on K_0.30MoO₃ single crystals in the temperature range 4-250 K. In addition to the anomaly observed at the Peierls transition at 180 K along the [102] direction, an anomaly is observed at ∼50 K along the [−201] and [102] directions. The results are discussed in relation with the change in the CDW rigidity at ∼50 K.     

Intense directional lasing from a deformed square-shaped organic-inorganic hybrid glass microring cavity

Intense directional light emission from a deformed square-shaped organic light-emitting microring cavity was observed. The ring cavity was a dye-doped organic-inorganic hybrid glass film coated upon a square-shaped fiber. From the near-field and far-field emission patterns and their emission spectra we found, for the first time to our knowledge, the simultaneous existence of chaotic whispering-gallery modes and four-bounce reflection modes. The two types of mode have different emission directions, different lasing thresholds, and different spectral linewidths. High-contrast angle-modulated light emission was also observed. We could control modulation and angular spread of emission by controlling the deformation of the cavity.     

Temperature-Insensitive Fibre-Optic Acceleration Sensor Based on Intensity-Referenced Fibre Bragg Gratings

A temperature-insensitive acceleration sensor using two fibre Bragg gratings （FBGs）, based on reflection spectrum intensity modulation and optical power detection, is proposed and demonstrated. A cantilever beam is used to generate acceleration-induced axial strain along two sensing gratings, which are glued on the two opposite surfaces of the beam. Because the two gratings operate within the linear spectral range of a light source, formed by a thermally-tunable extrinsic Fabry-Perot optical filter, the intensity difference of the two reflections from the gratings is proportional to the acceleration applied. This eliminates the need for sophisticated wavelength interrogation of the gratings, and it also endows the sensor with immunity to temperature variation. Compared with a commercial micromachined accelerometer, the sensor is proven to be capable of accurately detecting acceleration.     

Total internal reflection of a Gaussian light beam

An approximate theoretical model for calculating the reflected and refracted fields of a Gaussian light beam at a plane interface between two isotropic media is formulated on the basis of a Fourier integral. In the vicinity of the critical angle of incidence (for total internal reflection) the model predicts the presence of two refracted beams, one displaced along the interface by an amount equal to the Goos-Hänchen shift; curvature of the phase fronts and nonalignment of the effective directions of energy and phase propagation occur for each beam, as in an anisotropic medium.     

频谱编码深度成像实验研究

频谱编码显微镜是用衍射光栅和光谱分析装置来获得显微图像.样品上不同的位置被不同的波长照明,通过对反射光光谱进行解码来得到空间信息.搭建了一个基于超连续光源和自制光谱仪的频谱编码显微成像系统,其横向分辨率为1.72±0.13μm(编码线方向)和1.26±0.08μm(垂直于编码线方向),测得不同横向位置处的轴向分辨率有差异.对离体猪肝组织不同部位进行了成像(可见血管、肝窦内皮细胞和肝细胞);对鸡心组织以10μm深度间隔进行成像,测得不同深度处结构信息不一样.结果表明,采用该频谱编码成像的方法能够进行高分辨的深度成像.     

表层厚度渐变一维耦合腔光子晶体的反射相位特性及其应用

利用传输矩阵法研究了表层厚度渐变的一维非对称耦合腔光子晶体的反射相位特性. 研究表明, 光子禁带内(包括缺陷模附近)的反射率在98%以上, 且基本不受表层厚度影响, 特别是, 在非正入射情况下, 简并的缺陷模随着表层厚度的变化会发生分裂; 进一步研究发现, 在缺陷模分裂处附近, TE, TM偏振的反射相位以及它们之间的相位差均敏感地依赖于表层厚度的变化, 从而使得反射光的偏振态也随表层厚度的变化而敏感变化, 其物理机理在于缺陷模分裂所造成的剧烈相位变化. 基于上述特性, 设计了一种表层厚度呈二维周期变化的一维光子晶体结构, 从该结构反射的激光经透镜聚焦后, 在聚焦区域同时存在各种偏振态(包括沿不同方向的线偏振、左旋或右旋圆偏振、椭圆偏振等)的子光束, 它们叠加后在聚焦区域将产生具有无规相位和无规偏振态的光场. 以上结果能有效降低激光的相干性, 在激光核聚变等领域有潜在的应用价值.     

Image analysis for the destabilization process of the petal pattern in a liquid crystal light valve with rotational optical feedback

The destabilization process from the static petal pattern to the fluctuating petal pattern in a liquid crystal light valve with optical rotational feedback is investigated experimentally. When a spatial rotation of π/6 is imposed on the feedback, the six-fold static petal pattern appears. At a threshold voltage of the bifurcation, rotationally propagating patches arise on the petals. With the increase of applied voltage, the motion of the patches becomes irregular and fluctuations of the pattern develop. By measuring the time correlation function for the spatial wave numbers along the azimuthal direction in polar coordinates, it is found that a half of the fundamental spatial mode relevant to the six-fold petal pattern plays an important role in the bifurcation process. The development of fluctuations is also analyzed by the Karhunen-Loéve decomposition in detail.     

Electromagnetic waves in uniaxial crystals with metallized boundaries: Mode conversion,pure reflections,and bulk polaritons

A theory is constructed for the reflection of plane electromagnetic waves in uniaxial crystals with a positive definite permittivity tensor and an arbitrarily oriented metallized boundary. The problem is solved both for general-position orientations corresponding to three-partial reflection and for special conditions allowing two-partial reflections: mode conversions when the incident and reflected waves belong to different sheets of the refraction surface and “pure” reflections when both waves belong to the same sheet. The space of pure reflections is shown to be formed by two types of optical-axis orientations: arbitrary directions in the plane of the crystal surface and in the plane of incidence. The configurations of the conversion surface for optically positive and negative crystals are investigated. A subspace of pure reflections that transform into one-partial bulk polaritons with the energy flux parallel to the surface at grazing incidence has been found. The domain of existence of such bulk eigenmodes is bounded by two “lines” of solutions. These are any directions along the boundary containing the optical axis for ordinary polaritons and the direction along the projection of the optical axis onto the surface at an arbitrary orientation of the axis with respect to the boundary for extraordinary polaritons.     

Quantum mechanics in space-time: The Feynman path amplitude description of physical optics, de Broglie matter waves and quark and neutrino flavour oscillations

Feynman’s laws of quantum dynamics are concisely stated, discussed in comparison with other formulations of quantum mechanics and applied to selected problems in the physical optics of photons and massive particles as well as flavour oscillations. The classical wave theory of light is derived from these laws for the case in which temporal variation of path amplitudes may be neglected, whereas specific experiments, sensitive to the temporal properties of path amplitudes, are suggested. The reflection coefficient of light from the surface of a transparent medium is found to be markedly different to that predicted by the classical Fresnel formula. Except for neutrino oscillations, good agreement is otherwise found with previous calculations of spatially dependent quantum interference effects.     

一种便携式漫反射LED均匀光源的设计与实现

为了满足光电探测仪器校准修正过程中对标准光源的要求,设计了一种采用积分球技术,通过纽扣电池供电的便携式漫反射LED均匀光源。给出了光源的装配图、主要零件3D图及电路图,并对其进行了详细说明。通过Matlab分析光源出光口CCD照片各像素的灰度值,得到出光口?14 mm范围内光强均匀度为95.1%;采用Ocean Optics USB 2000+型光谱仪分析光源出光口光强均匀性及漫反射性,得到沿出光口径方向2个位置光强与中心光强相比,分别下降了2.93%和6.30%的结果。光源出光口平面旋转10°,中心位置光强下降6.30%。测试分析表明:设计的光源具有较好的均匀度和漫反射性,在光电探测仪器校准方面具有一定的应用价值。     

Surface channeling of swift light ions

A fast computer code is developed to provide information about the trajectories of swift light particles incident on crystalline targets under surface channeling conditions. The approximations used in the model are tested by comparison of trajectory calculations with the MARLOWE simulation program. The simulation of experimental energy distributions allows discussing various inelastic energy loss models for the interaction of 150 keV protons with a nickel surface. The results suggest that plasmon excitations are not sufficient to account for the measured energy losses. It is found that the Oen-Robinson formula, including inelastic energy losses by single electron excitations in dense materials reasonably well applies to the reflection of light ions from metallic surfaces in channeling conditions. The measured light intensity emitted from 200 keV He⁺ reflected ions in various directions close to compact atomic surface rows is compared with the calculated reflection coefficient. The results suggest that most of the particles reflected in ionic state do not penetrate the target surface. Detailed comparison between light emission measurements and calculated reflection intensities, however, requires accurate modelling of the surface topography as well as of the deexcitation mechanisms involved in the surface reflection of light ions.     

The nature and properties of a plasma

We have good reason to believe that much if not most of the matter in the universe is in the plasma state. This state can be described by comparing it with that of an ordinary gas, which is familiar to all of us, where large numbers of molecules move in all directions with different velocities along criss-cross paths, each sudden change of direction of movement being caused by a collision between two or more particles. But whereas in a gas all particles are electrically neutral, in a plasma charged fragments of formerly neutral molecules, positive and sometimes negative ions and electrons, take part in the random motion together with their neutral companions as well as with light quanta (von Engel 1955). In the gas of many stars, the sun, and certain apparatus in our terrestrial laboratories, charged particles predominate over neutral particles; these conditions approach a state called the fully ionized plasma (Spitzer 1956).     

Thermal convection in a rotating layer of a magnetic fluid

We consider Brownian particles with the ability to take up energy from the environment, to store it in an internal depot, and to convert internal energy into kinetic energy of motion. Provided a supercritical supply of energy, these particles are able to move in a “high velocity” or active mode, which allows them to move also against the gradient of an external potential. We investigate the critical energetic conditions of this self-driven motion for the case of a linear potential and a ratchet potential. In the latter case, we are able to find two different critical conversion rates for the internal energy, which describe the onset of a directed net current into the two different directions. The results of computer simulations are confirmed by analytical expressions for the critical parameters and the average velocity of the net current. Further, we investigate the influence of the asymmetry of the ratchet potential on the net current and estimate a critical value for the asymmetry in order to obtain a positive or negative net current. Received 20 September 1999     

晶体的连续双折射双反射及其集成应用:1×N电光开关

根据惠更斯定理 ,给出了单轴晶体内双折射与全内双反射的光线方向和光波法线方向的普遍公式。并讨论了在晶体内沿多个面的连续双折射双反射 ,分析了前一界面输出量和后一界面输入量之间的联系 ,得到多次双折射双反射后的光线方向和光波法线方向。在此基础上 ,提出一种单块晶体集成的 1×N电光开关 ,即把多个电光调制器安置在全反射面之间。由于双折射效应 ,寻常光和非常光有不同的全内反射 ;给不同的电极对上加上半波电压改变输入光的偏振状态 ,再使光通过不同数目的反射面反射 ,最后输出光就有不同的角度。具有结构简单、插入损耗小、抗干扰性强等优点。给出了 1× 4光开关的实例。     

用于相位突变界面的广义的反射定律和折射定律

考虑到位于两物质界面上的Metasurface对光线传播行为的影响, 从费马原理和边界条件连续两种角度出发, 推导了可用于相位突变界面的广义反射与折射定律. 该定律在界面对光波的相位改变量为零的情况下, 回归为通常的反射定律和折射定律. 利用广义的折射定律和反射定律讨论了介质折射率、界面上的相位梯度等因素对光传播行为的影响, 发现利用广义的折射定律和反射定律很容易实现反常反射和反常折射行为, 并给出了出现反常反射和反常折射的条件, 以此为基础可以实现对光波的随意控制. 依据广义的折射定律和反射定律分析了一维相位掩模板对光场传播行为的影响. 关键词： 超材料 相位突变界面 反射定律 折射定律     

Evaluation of interface wave velocity, reflection coefficients and interfacial stiffnesses of contacting surfaces

The phase velocity of the antisymmetric-mode interface wave as well as the longitudinal and shear wave reflection coefficients have been measured for contacting poly(methyl methacrylate) (PMMA) surfaces subjected to different contact pressures. It has been found that while the reflection coefficients decrease as the contact pressure is increased, the phase velocity of the interface wave increases from that of the Rayleigh wave toward that of the bulk shear wave. From these measurements, the normal and tangential interfacial stiffnesses of the contacting PMMA surfaces have been evaluated as functions of the contact pressure. As a result, the two independent procedures to evaluate the tangential stiffness, namely, from the interface wave velocity and from the shear wave reflection measurements, have yielded mutually consistent results. Furthermore, it has been found that the tangential/normal stiffness ratio and the shear/longitudinal reflection ratio of the contact interface are consistent with the predictions of an existing theoretical model for kissing bond interfaces.