表面上方微粒及微粗糙度偏振光散射特性

为了区分由表面上方微粒和表面微粗糙度两种散射机理引起的散射光,利用偏振双向反射分布函数,并借助于由,■,■组成的正交右手基组表示了入射电场和散射电场。从理论上给出了两种不同散射机理在不同偏振状态下的双向反射分布函数与入射面外方位角之间的变化关系,并通过对这两种散射机理下的偏振双向反射分布函数的比较发现,利用p偏振入射产生的p偏振散射光(BRDFpp)可以将表面上方微粒和表面微粗糙度两种散射机理区分开来。     

Untersuchung der Lichtstreuung von transparenten Einfachschichten auf Glassubstraten

Investigations of Light Scattering from Transparent Single Layers on Glass Substrates In the present paper the influence of stochastic interface roughness as well as film thickness on light scattering from dielectric single layers is investigated. By calculations carried out on base of Elson's vector scattering theory especially the importance of correlation functions of microroughness is analyzed. Measurements made from sputtered TiO₂-films show dominating interface scattering and an interference phenomenon, depending on film thickness.     

Streuung elektromagnetischer Oberflächen- und Volumenwellen an rauhen Oberflächen. Teil I. Allgemeine Grundlagen

Scattering of Electromagnetic Surface and Bulk Waves from Rough Surfaces. Part I. General Theory A classical theory of scattering of electromagnetic surface and bulk waves on rough surfaces (dielectrics or conductors) is given. The primary wave creates a surface polarization on the rough boundary presenting the source for the radiation of scattering. These roughness-caused polarization must be considered in the wave equations and in the boundary conditions of the fields, too. General expressions for the spectral power density of surface and bulk scattering waves will be given. The excitation of surface polarization can result from primary waves homogenously or inhomogenously.     

气泡/泡沫覆盖粗糙海面电磁散射的修正双尺度法研究

提出了风驱粗糙海面覆盖水气泡层的‘体-面’复合模型.基于修正的双尺度粗糙面散射理论、MIE理论和矢量辐射传输理论,比较了水气泡与实心水粒子的电磁散射特性的差异,分析了海面泡沫覆盖率与风速、气-海温差的关系.在有、无泡沫层情形下,采用高斯和经验海谱,讨论了单站、双站散射系数与入射角、方位角、风速、风向、极化等参量的关系,并将数值计算的结果与相关文献的测量值进行了比较和分析. 关键词： 电磁散射 海面复合模型 修正双尺度法 MIE     

极化合成孔径雷达海面成像模拟及分析

海浪极化SAR成像模拟对海面散射的研究有重要的意义.基于海浪谱理论,在考虑大、小尺度海浪影响的基础上,构建了双尺度的随机粗糙海面.根据该海面模型,利用Bragg散射模型,小扰动模型与速度聚束理论,模拟了不同状况下海浪的极化SAR图像.并针对海浪参数对极化图像的影响进行了分析,结果符合成像统计特性,得出了一些有益于海浪信...     

A new bistatic model for electromagnetic scattering from perfectly conducting random surfaces

In this paper, we extend the Kirchhoff approach, which is widely used for near-nadir backscattering calculations, to include the proper polarization sensitivity for general bistatic scattering from gently sloping, perfectly conducting surfaces. Previously, Holliday has shown how the inclusion of terms from the second iteration of the surface-current integral equation is required to obtain agreement with the small perturbation method for backscattering conditions. Here we employ a similar approach by retaining all terms in this iterative expansion through first order in the surface slope to derive expressions for the standard Kirchhoff field as well as for a supplementary field that contains the polarization sensitivity. A polarization vector notation is introduced to simplify the inclusion of tilting effects from larger-scale features on the scattering surface. In connection with this latter development, we provide a clarification of the earlier work by Valenzuela on this topic together with an extension to the bistatic problem. These extensions to the standard Kirchhoff approach form the basis for our composite bistatic scattering model which should provide a convenient and powerful tool for calculations involving passive as well as active microwave scattering from random surfaces.     

偏振遥感在伪装目标识别上的应用及对抗措施

 为了研究偏振遥感对伪装目标的识别特点,分别对不同颜色的伪装网进行了偏振参数测量和成像实验。通过数据分析发现,伪装网的散射偏振度受观测条件和材料自身特性（如反射率、折射率和表面粗糙度）影响很大;伪装涂层对入射光的散射作用可以分为面散射和体散射,其中面散射具有起偏振作用而体散射具有消偏振作用;与自然背景相比,伪装目标的偏振特征非常显著,利用偏振遥感可以有效地识别出常规侦察手段所不能发现的伪装目标。通过偏振遥感的侦察原理和特点分析,提出了可以利用表面结构设计和烟雾等方法对抗偏振遥感的侦察。     

The region of validity of perturbation theory

We present a study of the region of validity of perturbation theory applied to rough surface scattering. We solve numerically the case of a periodic surface or grating varying in one dimension. For a statistical ensemble of gratings with a sufficiently long period one may obtain a good approximation of rough surface scattering. We use this to test the validity of perturbation theory.

Only the perfect conductor case was considered. We find that as the grazing angle becomes small the perturbation result for the TE (E horizontal) polarization remains valid, while for the TM (E vertical) polarization it breaks down. The results show that the perturbation results should be used carefully when being compared with experimental data at grazing angles.     

基于微面元理论的“猫眼”目标回波散射偏振特性研究

为了研究"猫眼"目标表面回波散射偏振特性,基于微面元理论建立了偏振双向反射分布函数模型,指出线偏振光在"猫眼"目标表面回波散射的偏振度与目标表面粗糙度、复折射率以及入射角、探测角有关。主要研究"猫眼"目标表面粗糙度对其回波散射偏振度的影响,利用Matlab仿真得到"猫眼"目标回波偏振度与目标表面粗糙度参数σ的关系曲线。选择经过不同砂纸打磨的硅片作为"猫眼"目标进行实验,当硅片表面均方根高度分别为0.067μm、0.554μm、0.726μm、1.651μm、1.893μm时,其表面回波散射偏振度的测量值依次为98.83%、98.16%、96.08%、94.91%、94.6%,表明"猫眼"目标回波散射的偏振度随其表面粗糙度的增大而减小。     

Region of validity of perturbation theory for dielectrics and finite conductors

We present a study of region of validity of first-order perturbation theory applied to rough surface scattering. The scattering problem is solved numerically for the case of periodic surface or gratings varying in one dimension. Scattering of electromagnetic waves from an ensemble of gratings of sufficiently long period will give a good approximation to the case of an infinite rough surface. We use this to test the validity of the first-order perturbation theory. Use of an infinite periodic surface allows us to give results for a range of angle of incidence covering those representing a low grazing angle, near 90° from the mean surface normal. We consider the case for perfect dielectrics and finite conductors. The real and imaginary parts of the refractive index used were limited to less than three due to the numerical instability of the numerical calculation method involved. We find that for perfect dielectrics the first-order small perturbation theory remains for TE polarization valid for all incidence angles, while for TM polarization it seems to fail if the incidence angle approaches the Brewster angle.     

The region of validity of perturbation theory

Abstract

We present a study of the region of validity of perturbation theory applied to rough surface scattering. We solve numerically the case of a periodic surface or grating varying in one dimension. For a statistical ensemble of gratings with a sufficiently long period one may obtain a good approximation of rough surface scattering. We use this to test the validity of perturbation theory.

Only the perfect conductor case was considered. We find that as the grazing angle becomes small the perturbation result for the TE (E horizontal) polarization remains valid, while for the TM (E vertical) polarization it breaks down. The results show that the perturbation results should be used carefully when being compared with experimental data at grazing angles.     

Theory of hadron-deuteron elastic scattering in the GeV region

A multiple scattering formalism for the medium energy hadron-deuteron elastic scattering is developed. This approach provides an extension of the Glauber theory incorporating the complete spin structure and the corrections to the eikonal and fixed scatterer approximations. The systematics of the spin observables and their relation to the hadron-deuteron as well as to hadron-nucleon amplitudes are discussed. An approximate cancellation between few corrections to the double scattering term is found which leaves the non-eikonal correction as the dominant one, and often, very important numerically, e.g., in the deuteron tensor polarization. Comparison of the parameter-free predictions of the theory based on the recent NN phase shift amplitudes with the data on polarization observables in pd elastic scattering is made.     

Classical theory of atom–surface scattering: The rainbow effect

The scattering of heavy atoms and molecules from surfaces is oftentimes dominated by classical mechanics. A large body of experiments have gathered data on the angular distributions of the scattered species, their energy loss distribution, sticking probability, dependence on surface temperature and more. For many years these phenomena have been considered theoretically in the framework of the “washboard model” in which the interaction of the incident particle with the surface is described in terms of hard wall potentials. Although this class of models has helped in elucidating some of the features it left open many questions such as: true potentials are clearly not hard wall potentials, it does not provide a realistic framework for phonon scattering, and it cannot explain the incident angle and incident energy dependence of rainbow scattering, nor can it provide a consistent theory for sticking. In recent years we have been developing a classical perturbation theory approach which has provided new insight into the dynamics of atom–surface scattering. The theory includes both surface corrugation as well as interaction with surface phonons in terms of harmonic baths which are linearly coupled to the system coordinates. This model has been successful in elucidating many new features of rainbow scattering in terms of frictions and bath fluctuations or noise. It has also given new insight into the origins of asymmetry in atomic scattering from surfaces. New phenomena deduced from the theory include friction induced rainbows, energy loss rainbows, a theory of super-rainbows, and more. In this review we present the classical theory of atom–surface scattering as well as extensions and implications for semiclassical scattering and the further development of a quantum theory of surface scattering. Special emphasis is given to the inversion of scattering data into information on the particle–surface interactions.     

Spin-polarized low-energy electron diffraction: Theory,experiment and analysis of results from W(001)(1 × 1)

The theory of spin-polarized low-energy electron diffraction (SPLEED) is outlined with an emphasis on symmetry-induced properties and models for the effective single-sphere potential. Details are given of the experimental set-up involving a new type of spin polarization detector based on SPLEED. Numerical calculations for the W(001)(1× 1) surface proceeded in close coordination with measurements of spin polarization (normal to the scattering plane) and intensity. A variety of calculated spin polarization and intensity profiles exhibits features, which are very sensitive to changes in the top interlayer spacing, as well as features sensitive to various ingredients of the potential model. The overall agreement between theory and experiment is very good not only for intensities, but also for spin polarization. It implies a contraction of the topmost interlayer spacing of W(001) with respect to the bulk spacing by 7% ± 1.5%, and supports the use of an energy-dependent exchange part and a nonuniform absorption part in the effective ion-core potential.     

Droplet deformation and alignment for high-efficiency polarization-dependent holographic polymer-dispersed liquid-crystal reflection gratings

Droplet deformation and alignment are achieved in holographic polymer-dispersed liquid-crystal reflection gratings by applying an in situ shear during recording. High diffraction efficiency (99%) is obtained for light polarized parallel to the shear, with nearly zero efficiency for perpendicular polarization, and no increase of incoherent scattering. Permanent polarization dependence is related to stress-induced morphology changes of liquid-crystal droplets that are frozen by polymerization. The system is studied by electron microscopy and modeled by anisotropic coupled-wave and scattering theory. The morphology is consistent with the theory of small deformations of liquid droplets in fluid flow. Diffraction efficiency measurements are in agreement with theory incorporating this morphology as well as concomitant orientation and alignment of liquid-crystal molecules.     

Plasmonic laser nanoablation of silicon by the scattering of femtosecond pulses near gold nanospheres

We present the fabrication of nanostructures ablated on silicon(100) by the plasmonic scattering of 780 nm, 220 fs laser pulses in the near-field of gold nanospheres. We take advantage of the enhanced plasmonic scattering of ultrashort laser light in the particle near-field to ablate well-defined nanocraters. Gold nanospheres of 150 nm diameter are deposited onto a silicon surface and irradiated with a single laser pulse. We studied the effect of laser polarization on the morphology of ablated nanostructures and estimated the minimum fluence for plasmonic nanoablation. When the polarization of the incident radiation is directed at a 45° angle into the substrate surface, a near-field enhancement of 23.1±7.6 is measured, reducing the required silicon ablation fluence from 191±14 mJ/cm² to 8.2±2.9 mJ/cm². Enhancements are also measured for laser polarizations parallel to the substrate surface when the substrate is angled 0° and 45° to the incident irradiation, giving enhancements of 6.9±0.6 and 4.1±1.3, respectively. Generated nanocrater morphologies show a direct imprint of the particle dipolar scattering region, as predicted in our theoretical calculations. The measured near-field enhancement values agree well with the maximum field enhancements obtained in our calculations. The agreement between theory and measurements supports that the nanocraters are indeed formed by the enhanced plasmonic scattering in the near-field of the nanoparticles. PACS 42.62.-b; 52.38.Mf; 81.65.Cf; 81.16.-c; 78.67.Bf     

TEM study of the origin of the surface microroughness in DSL photoetched Si-implanted GaAs wafers

TEM has been used to study the origin of the surface microroughness that formed in both ²⁹Si as-implanted and rapid thermal annealed LEC undoped GaAs wafers after DSL photoetching. The degree of microroughness increased as the implant dose increased from 3 × 10¹² to 3 × 10¹⁴ atoms/cm². It has been found that such a microroughness is due to the fine-scale damage induced by the implantation in the as-implanted wafers and to interstitial dislocation loops in the implanted and then annealed wafers. Microroughness appears during DSL etching because such defects are effective recombination centres for the holes involved in the dissolution of the GaAs surface so that the wafers etch slower at the point-defect clusters and dislocation loops.     

大气中球形粒子的散射特性研究

从Mie理论出发，得到了不同尺度的球形粒子对激光的散射图像及粒子的消光效率曲线。从得到的散射图像可以看出，随着粒子尺度的逐渐增大，散射光强越来越集中到前向散射方向，并且散射光强集中的角度越来越窄。从消光效率曲线可以看出，随着粒子尺度的增加，消光效率因子变化趋于平缓，并逐渐趋向于常数2。最后分析了散射光的偏振度对粒子尺度和散射角的变化关系。从散射光的偏振度随粒子尺度变化图可以看出，粒子散射光的偏振度随粒子尺度的增大而增加，且变化比较明显，而散射光偏振度大小的峰值逐渐趋向于前向方向，随着粒子尺度的增大，散射光偏振度趋于减小。     

A polarized deuteron target in the d(e,e′)np reaction

Asymmetries for scattering of longitudinally polarized electrons from deuterons with a vector polarization as well as asymmetries for scattering of unpolarized electrons from deuterons with a tensor polarization have been considered for inclusive elastic ed scattering. The sensitivity of all asymmetries considered to the electric form factor of the neutron and to the spin structure of the deuteron wave function has been investigated.     

阻抗劈绕射对破碎波后向散射特性的影响

海浪的破碎区会导致海面电磁散射特性发生很大改变,导致海尖峰现象的产生.本文结合阻抗劈结构模型分析了劈绕射对破碎波后向散射特性的影响.首先利用基尔霍夫近似求解破碎波的物理光学场;基于Maliuzhinets方法,从波动方程及精确阻抗边界条件出发,由谱函数的积分形式得到阻抗劈的一致性绕射系数,结合物理光学绕射系数导出阻抗劈等效边缘电磁流;利用边缘绕射场修正物理光学场,得到考虑劈绕射效应的破碎波散射总场.数值结果表明,阻抗劈的绕射场在Keller锥内出现HH极化大于VV极化的现象,因此计入绕射场的影响会使得破碎波生长到临近坍塌阶段时,小擦地角逆风观测出现总场的后向散射截面HH极化大于VV极化的现象,说明劈绕射是造成海尖峰现象产生的原因之一.