Light Scattering by Large Particles

In the framework of the eikonal picture, the Glauber expression for the scattering amplitude is extended to the whole angular domain and to intermediate and even low energies (under some restrictions on the scattering potential) in the context of light scattering by large particles. Differential cross sections illustrate clearly the difference between Glauber's results and those given here.     

Light Scattering by Commercial Sugar Solutions

Using a direct measure of scattered light, it was found that commercial sugar solutions scatter light predominantly in a forward direction. The scattering at angles less than 30° was as much as one hundred times that at right angles to the incident beam.It was found that the light scattering by commercial sugar solutions is inversely dependent on wavelength to a power of between 2 and 3, and that severe multiple scattering occurs when the turbidity of the solution is larger than 2×10⁻¹cm⁻¹ at 436 mµ. The scattering of commercial sugar solutions is compared with that of highly purified sucrose.A method is discussed that will enable a good approximation of the turbidity of commercial sugar solutions to be made from a single forward scattering measurement at an angle of about 20° with respect to the incident light beam. A correction for scattered light in transmission measurements of these solutions is also introduced.     

Light Scattering by Composite Rough Surfaces

Abstract

Light scattering from a dielectric surface with composite roughness is considered, where the surface irregularities are modelled as a superposition of two roughness types of different length scales. Geometrical optics and the Rayleigh-Rice expansion, respectively, are employed in describing the scattering from the two roughness structures. Contrary to previous work, we concentrate on bistatic cross-sections, which are calculated analytically for scattering in the plane of incidence, and resulting plots for various parameter values are shown, especially for small-scale correlation lengths of the order of the wavelength of the incident light. The main effects of the small-scale roughness are an overall decrease of the coherent reflectance and a depolarization of the scattered light, which in the plane of incidence is not present for scattering from a surface with a single scale of roughness. It is, however, concluded that scattering at the surface and volume scattering have to be taken into account in order to explain the experimentally found degrees of depolarization.     

Drop Tower Setup for Dynamic Light Scattering in Dense Gas-Fluidized Granular Media

Investigation of dynamics in dense granular media is challenging. Here we present a setup that facilitates gas fluidization of dense granular media in microgravity. The dynamics is characterized using diffusing wave spectroscopy. We demonstrate that agitated granular media reach a steady state within fractions of a second in drop tower flights. The intensity autocorrelation functions obtained in microgravity show a remarkable dependence on sample volume fraction and driving strength. A plateau in correlation emerges at low volume fractions and strong driving, while correlation decays only very slowly but continuously at high packing fractions. The setup allows to independently set sample volume fraction and driving strength, and thus extends the possibilities for investigations on dynamics in dense granular on ground.     

双层球形颗粒的光散射计算

在光散射颗粒测量技术中,Mie散射理论的计算非常重要。本文中讨论了双层球形颗粒光散射的计算方法,对计算过程中不同函数参量选用了合适的递推计算方法,改进的计算方法克服了以前算法在实际运算中遇到的误差。计算了若干物理量,如消光系数、散射系数、吸收系数以及CPU运算速度。计算结果表明,选用的方法简单、迅速、稳定且误差小。     

Diffraction Properties of Absorbing Cylinders Suspended in Outside Absorbing Media

The forms of the diffracted E and H fields, for absorbing cylinders with radii small compared to the wavelength and suspended in outside absorbing media, have been determined from Maxwell's equations and boundary conditions, when these cylinders are illuminated by plane periodic electromagnetic waves in a direction perpendicular to their axes, and the electric vector is parallel or perpendicular to the axes. From these E and H fields the time averages of the radiant flux and the electric field energy densities consist of exponentially increasing or decreasing background terms, characteristic of the incident and diffracted waves, and interaction terms, which generate exponentially decreasing maxima and minima or interference fringes, whose radial spacings increase with the angle from the direction of incidence. The radiant fluxes have properties characteristic of creeping waves. Particular attention has been devoted to determining the boundary conditions for each of the vector fields and retaining the proper coefficients, so that direct comparisons can be made between the two polarizations. In all cases the magnitudes and forms of these vector fields are functions of the material constants of both media, the wavelength, the modes being excited, the cylinder radius and the polarization used.     

光散射粒度测量中Mie理论两种改进的数值计算方法

本提出了两种Ｍｉｅ散射程序算法：改进连分式方法和修正倒推法。改进连分式方法对Ｌｅｎｔｚ提出的连分式数值计算方法进行了改进,ｉｅ程序的计算范围大大拓宽;颗粒当量直径达到１０＾５,折射率虚部绝对值达到１０＾５。解决了以往一些算法不稳定的现象。     

Mie理论在静态光散射粒度测量的应用下限研究

测量下限是光散射颗粒测试技术的关键问题。本文通过理论分析、比较归一化散射光强的分布图和构造方差函数F(d)对颗粒散射光的光强分布进行了定性和定量的讨论,对Mie散射向Rayleigh散射趋近的情况进行了分析,讨论了散射光光强大小的分布,分析了测量不同粒径的颗粒的可行性,最终得到在入射光源是波长为0.6328μm的He-Ne激光器的情况下,当粒径d取200nm以上时,不同粒径颗粒的M ie散射光强分布有较大差别,适合用静态光散射的方法来判断颗粒粒径。     

激光粒度测量的应用与前景

激光粒度仪是一种应用广泛而又比较有发展前途的粒度测量设备.介绍了激光粒度仪的测量原理,介绍和对比了Fraunhofer衍射和Mie散射理论在激光粒度仪中的应用,探讨了如何评价激光粒度仪以及在线测量的一些技术难题,并展望了激光粒度仪的应用前景和发展方向.     

非晶硅液晶光阀

本文介绍反射式非晶硅液晶光阀的研制方法，并对其光电性能进行了研究，提出非晶硅液晶光阀的参数设计模型。     

Two-colour Dynamic Light Scattering

Abstract

The design, alignment and operation of improved two-colour dynamic light scattering equipment which effectively suppresses multiple scattering and allows the study of the Brownian dynamics of optically turbid samples is described. The technique operates by cross-correlating scattered light of two different colours. With the appropriate scattering geometry, only singly scattered light contributes to the time-dependent part of the measured intensity cross-correlation function thus allowing straightforward interpretation of the data. To demonstrate the performance of the instrument we have studied various colloidal suspensions. Although dilute enough that free diffusion of the particles can be assumed, the samples ranged from quite transparent to distinctly turbid. We have confirmed that the measured cross-correlation functions accurately reflect only single scattering even in the presence of strong multiple scattering.     

A Characterization of Light Scattering by Small Dielectric Spheres

Abstract

While using the standard Mie formulae to calculate the intensity distribution of light scattered by a small dielectric sphere, we have noticed some new qualitative results which suggest a boundary between a scattering regime qualitatively similar to the well known Rayleigh scattering distribution and that observed for rather larger particles. This may be of practical use when considering the position of photodetectors in light scattering experiments, for example particle velocimetry. The reason for such a transition has been discovered, using an unusual approximation in which the diameter of a sphere is made very small and its refractive index very large, with their product and the wavelength held constant.     

以中空多孔碳纤维为主体的轻质吸波材料吸波性能研究

根据阻抗匹配原理和电磁波传播规律,以中空多孔聚丙烯腈(PAN)碳纤维为主要吸收剂,分别添加以炭黑、碳纤维和羰基铁粉为吸收剂的匹配层,制备了双层轻质雷达吸波材料,并考察了其吸波性能.结果表明,双层结构设计和不同吸收剂的复合对提高材料的吸波性能起着重要的作用.以羰基铁粉作吸收剂的匹配层比以炭黑和碳纤维作吸收剂的匹配层对提高以中空多孔碳纤维吸波材料的吸波性能更为显著.所制备的材料在厚度为2.90mm,密度为1.28g/cm³时,在4~18GHz频率范围内反射率≤-8dB的带宽为11.42GHz,反射率≤-10dB的带宽为10.90GHz.