群体粒子场圆偏入射光侧向散射的角分布实验研究(英文)

对圆偏振光入射到群体粒子场时侧向散射光随角度分布的特性进行了实验研究,散射介质为直径0.065μm和1.24μm的粒子与过滤的蒸馏水所构成的不同浓度的悬浮液。实验结果表明,粒子侧向散射光的各种成分在探测平面内相对散射角度始终呈现对称分布的规律,而随着粒子尺寸、浓度、探测深度的变化,散射光强也相应出现变化,但变化不明显。     

降雨粒子的无线紫外光散射特性

紫外光与降雨粒子相互作用发生散射,散射光特性改变能够反映降雨粒子的相关物理特性（如粒子尺寸参数、浓度、形态）,因此研究粒子的物理参数对散射光特性的影响对有效提高光谱法定量探测降水的精度有很大意义。由于雨滴在非球形降水粒子中具有代表性,以群雨滴粒子为例,采用T矩阵理论,利用紫外光直视和非直视单次散射模型,分析了入射光波长、群雨滴粒子形态、降雨强度、粒径大小与散射光强之间的关系。并用蒙特卡洛方法仿真分析了非球形群雨滴粒子在不同降雨强度和粒径下散射角与散射光强之间的关系,以及降雨环境中的风切变对紫外光散射特性的影响。通过理论及仿真分析,得到了不同群雨滴粒子形态下的路径损耗,不同降雨强度、风切变率和粒径下的散射光强分布。仿真结果表明：在紫外光直视与非直视通信方式下,降雨环境中的通信质量比晴天条件下的通信质量差,即路径损耗增大。当粒径分布已知时,随着降雨强度的增大,衰减系数增大,路径损耗增加,且直视通信方式的路径损耗比非直视降低7 dB左右。随着降雨强度、风切变率和粒子粒径的增大,散射光强曲线整体呈下降趋势,其中,降雨强度的变化对散射光强分布影响程度最大。相同通信距离时,不同降雨强度下的紫外光散射光强分布均随着散射角的增大而减小,当散射角继续增大到90°时,有效散射体体积逐渐减小,接收到的光子能量减小,暴雨中的散射光强衰减程度最大。相同降雨强度下考虑风切变时,相比较无风时的路径损耗增大5 dB左右。除此之外,还研究了椭球形和切比雪夫形粒子对紫外光散射光强的影响,结果表明当粒子粒径分布相同时,椭球形粒子的散射光强衰减较广义切比雪夫形粒子大。根据散射粒子的散射光强分布以及路径损耗能够区分雨滴粒子是否由相同粒径及形态组成,为粒子测量提供理论基础。分析降水中群雨滴粒子的光散射特性,为提高光谱法评估降水衰减的数值模拟方面提供理论依据,为光学技术在探测识别降水现象等气象领域的广泛应用提供了设计参考。     

光学材料中横向SBS的稳态分析

 从非线性光学的耦合波理论出发，建立了种子光入射的窄带泵浦的横向受激布里渊散射的二维理论模型，并对稳态情形进行了数值模拟，得到了散射光强的二维分布。计算表明，散射光场在入射面内呈现出“局部集中”的特点，而且由于“空间压缩”效应，使得获得的最大散射光强远大于初始泵浦光强。还分析了光场及材料参数对获得的散射光强的影响，得出：入射的激光功率密度越大，光学元件的横向尺寸越长，材料的吸收系数越小，受激散射产生的散射光和弹性声波强度就越大，在材料内部引起的应力也越强，从而越有可能造成材料的破坏。     

尘埃粒子计数器中光源对传感器光通量的影响分析

在Mie散射理论基础上，由单分散射的光强表达式导出在偏振光的入射条件下一定立体角内的散射光通量的表达式，并与自然光入射作比较。计算了在相同强度不同光源入射下，尘埃粒子计数器的两种常用散射光收集系统收集的散射光通量。结果表明：采用近前向散射光收集系统得到的光通量相等；而采用直角方向散射光收集系统时两者并不相等，且在平面偏振光入射时，收集的散射光通量还跟探测器中心与入射光偏振方向夹角有关。用MATLAB编程计算，得出了在探测器中心与偏振方向的夹角成90°或270°位置时，收集的散射光通量有极值的结论，为激光尘埃计数器传感器光学设计提供了依据。     

微粒子的线度对Mie散射光强度影响的研究

根据Mie散射理论,研究了粒子线度对Mie散射光强的影响,不同性质的粒子,其影响效果不同,在固定入射波长条件下,散射光强随粒子线度呈周期变化,同时发现H2O微粒子散射光强峰峰间距与粒子的线度和波长的关系可简单的表示为Δa=-0.133 3+0.222λ.     

光在水中吸附膜层气泡上的散射特性

光在水中大尺度气泡上散射特性的研究多是基于Davis模型.该模型没有考虑到吸附膜层对光在气泡上散射的影响,而海水中的大多数气泡都有膜层附着,这些膜层会影响到气泡的光散射特性.本文从几何光学的角度出发,建立了吸附膜层气泡的体积散射函数简化公式.在此理论基础上,模拟计算了尺度远大于入射光波长的大气泡散射光强分布曲线,得出光照射下气泡上散射光强的远场特性,讨论了影响气泡散射光强分布的主要因素.并与无膜气泡光散射分布曲线比较,讨论了油膜膜厚、折射率等参量对气泡的光散射特性影响.得出结论:吸附膜层气泡的光强分布曲线与无膜气泡相似,但吸附膜层会削弱前向散射光,增强后向散射光.     

雾霾粒子的紫外光散射特性研究

紫外光与雾霾粒子发生散射后,其散射信道特性能够反映雾霾粒子的相关物理信息,利用无线紫外光单次和多次散射信道模型,采用Mie散射和T矩阵理论分析了霾粒子在不同形态和浓度下的紫外光散射信道特性,以及散射角对散射光强的影响,并完成了紫外光在雾霾环境下的实测。通过理论及仿真分析,得到了不同霾粒子形态下的紫外光通信路径损耗以及光强分布。结果表明：紫外光直视通信方式下,路径损耗随着霾粒子浓度的增大而增大,且通信质量差于晴朗天。非直视通信方式中,在短距离通信时,高霾浓度下的路径损耗小于中低霾浓度,然而随着通信距离的继续增大,高雾霾浓度下的通信质量急剧下降,低霾浓度下通信质量最终达到最优,且距离为200 m时通信质量能优于晴朗环境。当通信距离相同时,三种雾霾浓度下的紫外光散射光强分布均随着散射角的增大而减小,当散射角继续增大并超过90°时,低霾浓度下的散射光强最大。主要原因是虽然散射角继续增大,但是有效散射体体积逐渐减小,因此低霾浓度下的散射光强较大。且当粒子粒径相同时,球形粒子的衰减较非球形粒子大。雾霾环境下实测结果与仿真结果相类似,证明了仿真结果的正确性,并在一定程度上证明了实际大气中雾霾非球形粒子多于球形粒子。     

超强激光在均匀等离子体中的背向拉曼散射放大机制

使用等离子体背向受激拉曼散射对激光进行放大时,等离子体的密度、温度和长度都会对激光的放大效果产生影响.为了探究等离子体密度对结果的影响,本文使用一维粒子模拟程序模拟了波长为800 nm的泵浦激光入射到均匀等离子体中,等离子体密度和泵浦光光强对散射光光谱的影响.模拟结果表明,等离子体密度降低会导致散射光的波长变短,而泵浦光的光强在一定范围内降低会增加散射光中背向散射光的比例.通过分析散射光的光强和等离子体的密度,发现前向拉曼散射是等离子体密度变化的原因.模拟结果对等离子体背向受激拉曼散射放大的实验研究具有重要的指导意义.     

利用T矩阵模型计算水体中非球形悬浮颗粒物光散射特性

水体中悬浮颗粒物的光散射特性是影响基于直接光谱法水质检测结果准确性的一个重要参数。依据T矩阵模型,研究了紫外-可见光照射下水体中非球形悬浮颗粒物的光散射强度特性。以藻类和泥沙类颗粒物为例,构造了椭球、圆柱和广义Chebyshev三种非球形粒子光散射模型,分析了入射光波长、悬浮颗粒物形状、复折射率与相对散射光强之间的关系,计算了不同悬浮颗粒物相对散射光强随波长、颗粒物尺寸以及旋转角变化的情况。数值仿真结果表明,不同种类非球形悬浮颗粒物的散射光强度均呈现出显著的变化。在200~800nm波长范围内,随入射波长的增大,粒子几何尺寸所带来影响逐渐减小,散射特性主要由复折射率决定。当粒子尺寸小于0.2μm或接近1μm时,在入射光波长位于紫外或红外的条件下,散射光强度较大且呈现强烈振荡;而当粒子尺寸r=0.3~0.9μm,散射强度较稳定,接近于0且受到入射光波长的干扰较小。这可为提高紫外-可见吸收光谱法的检测精度、抑制散射干扰提供一定依据。     

气溶胶激光散射信号的特征分析

本文应用Mie散射理论对微球体粒子光散射的性质进行了理论分析与数值计算,得出了散射光分布与微球体尺度参数、复折射率之间的关系。结果表明:不同尺度参数的粒子的散射光强的分布相差极大,随着尺度参数的增加散射光强越来越集中于前向;复折射率的变化对散射光强影响不大。并且在边界层大陆乡村型霾的气溶胶模型下对大气气溶胶的体角散射系数进行了分析与数值计算,得出:气溶胶粒子的散射光强主要分布在前向,并且随着散射角的增加有规律的减小。由此提出了利用气溶胶粒子体散射系数的性质,通过测量散射点前向散射光强和延迟时间来实现激光束的近轴定位的方法。     

Thick GEM with a resistive coating

The results of testing a detector based on a thick gas electron multiplier (GEM) are presented. Impact of the TGEM dielectric charging on detector physical parameters is assessed based on simulation and experimental results. The further development of the detector—TGEM with resistive coating was constructed and tested. The test results are presented and compared to a standard thick GEM.     

Response of a plate to a transient pressure wave load

The dynamical behaviour of a Kirchhoff plate under a moving pressure wave is investigated. The results are presented as dynamic amplification factors (DAF). The influence of the load parameters (propagation speed, pressure wave duration) and the plate parameters (slenderness, aspect ratio, damping, etc.) is discussed. Finally results for two examples are presented.     

Beam propagation method in rectangular structures with a high step index

In this paper a simple and effective method to analyze rectangular media with a high step of the refractive index is shown. Comparison of the method with a classical Beam Propagation Method and with analytical solutions for the planar waveguides in the (1+1)dimensional case are presented. There is also shown an influence of a high step of refractive index in (2+1)dimensional structures on the field distribution of guided beams as well as on the far field diffraction. The presented results show that the proposed method is very exact and relatively fast in comparison with other methods.     

Efficient formation of a high-quality beam from a pure high-order Hermite-Gaussian mode

We present a relatively simple method for efficiently transforming a single high-order mode into a nearly Gaussian beam of much higher quality. The method is based on dividing the mode into equal parts that are then combined coherently. We illustrate the method by transforming a Hermite-Gaussian (1, 0) mode with M(x)(2)=3 into a nearly Gaussian beam with M(x)(2)=1. 045 . Experimental results are presented and compared with theoretical results.     

Image of a straight edge in confocal self-interference microscopy

An image of a straight edge in confocal self-interference microscopy (CSIM) is analyzed. Simulations of edge images based on a two-dimensional imaging equation are presented that show a 103% increase in edge gradient and a 43.1% decrease in the 10-90% width. The first experimental results, to our knowledge, for CSIM are presented and show good agreement with the simulation results and a 23% decrease in the 10-90% width.     

Study of the Leakage Loss in a Silica-on-Silicon Slab Waveguide

A simple and efficient method for studying the leakage loss in a conventional silica-on-silicon planar waveguide is presented. The magnitude of the leakage loss is obtained by calculating the complex propagation constant of the leaky waveguide structure. The dependence of the leakage loss on the thickness of the silica buffer layer (as well as the thickness of the silica upper-cladding layer) is investigated. Numerical results are presented and compared to those calculated with the beam propagation method.     

YBCO线圈在低温下的温度仿真分析

近几年,高温超导线材的制造技术已日趋成熟。作为第二代高温超导带材的代表,YBCO在低温下具有的优点使其在超导磁体领域的应用越来越突出。但是在高温超导磁体的运行中会因为受到扰动而失超。为了探讨这个问题,模拟了一个磁体在低温下(20K左右)有加热点扰动时的稳定性情况,即对YBCO线圈在低温下的工作情况进行了模拟仿真。文中根据实验设计的YBCO单饼线圈参数,利用热传导方程和基本电路方程,采用有限元计算方法,模拟出线圈内部的温度分布。分析仿真结果可以为后续实验设计提供参考。     

Study on actuating voltage and switching time of a MOEMS optical switch

The micro-opto-electro-mechanical systems (MOEMS) optical switch with slant lower electrode and with torsion beam on silicon is designed and analyzed theoretically. Based on the torsion dynamics theory, the technique and relative formula are presented for the first time for analyzing the actuating voltage and the switch time. The optimized results of the structural parameters are compared between this technique and the finite element modeling (FEM). Finally, the difference between the experimental results and theoretical data is discussed.     

Towards a scalable fully-implicit fully-coupled resistive MHD formulation with stabilized FE methods

This paper explores the development of a scalable, nonlinear, fully-implicit stabilized unstructured finite element (FE) capability for 2D incompressible (reduced) resistive MHD. The discussion considers the implementation of a stabilized FE formulation in context of a fully-implicit time integration and direct-to-steady-state solution capability. The nonlinear solver strategy employs Newton–Krylov methods, which are preconditioned using fully-coupled algebraic multilevel preconditioners. These preconditioners are shown to enable a robust, scalable and efficient solution approach for the large-scale sparse linear systems generated by the Newton linearization. Verification results demonstrate the expected order-of-accuracy for the stabilized FE discretization. The approach is tested on a variety of prototype problems, including both low-Lundquist number (e.g., an MHD Faraday conduction pump and a hydromagnetic Rayleigh–Bernard linear stability calculation) and moderately-high Lundquist number (magnetic island coalescence problem) examples. Initial results that explore the scaling of the solution methods are presented on up to 4096 processors for problems with up to 64M unknowns on a CrayXT3/4. Additionally, a large-scale proof-of-capability calculation for 1 billion unknowns for the MHD Faraday pump problem on 24,000 cores is presented.     

Comparison between the Results of Simulating the Synchrotron Radiation from a Bending Magnet and Experimental Data

The results of using two (SPECTRA and SRW) programs for simulating synchrotron radiation (SR) are presented. Calculations are performed for coherent SR from a beam of electrons with moderately relativistic energies in a short bending magnet. Simulation is carried out for real beam parameters. A comparison between simulation and experimental data indicates their good agreement. Both general information for the given codes grouped by a number of criteria and specific data on simulating radiation from bending magnets are presented.