Thermal grating velocimetry

A method is reported for time- and space-resolved nonintrusive velocimetry of high-speed gas flows by measurement of the Doppler shift of light scattered from a laser-induced thermal grating. The principle is demonstrated by use of a pulsed frequency-doubled Nd:YAG laser to induce a thermal grating in NO(2) seeded into an argon flow. Signals are generated by Bragg scattering of probe beams at the fundamental frequency of the same Nd:YAG laser. Flow velocities in the range 30-180 ms(-1) are measured, in agreement with values obtained with a Pitot tube. The measurement uncertainties obtained indicate that a precision of 1% is feasible for flows at Mach 1.     

聚合物中多重光散射传导的Monte Carlo数值模拟

基于米氏散射(Mie scattering)理论,建立填充分散粒子群的聚合物对光散射传导的Monte Carlo数学模型.在此基础上,编写了一套仿真模拟程序.通过模拟单个光子在聚合物中的多重散射运动过程,把问题扩展到以激光束或线状光为入射源,得到在聚合物板块内的光传导情况,并且在计算机上图像化地重现整个物理过程,对输出光强的分布情况进行模拟统计分析.模拟结果表明,利用体散射机制,可以将点光源和线光源转换为平面光输出,输出光的状态可以通过对比计算结果实施有效控制.     

A Theoretical and Experimental Study to Measure the Concentration and Particle Size Distribution in Two‐Phase Flows

Based on light scattering theory, an optical method is presented for measuring the concentration and particle size distribution of the dispersed phase in two‐phase flows. A prototype was also constructed. Comprehensive computer simulation and numerical calculations were carried out to calibrate the correctness of this method. An experimental study was also performed in gas–solid and gas–liquid two‐phase flows. The results of the measurements are given and discussed in detail.     

Selective stop-band switching in two-dimensional multicomponent photonic crystals

A comprehensive theoretical investigation of the stop-band switching in two-dimensional multicomponent photonic crystals is carried out. The calculations are performed within the analytical model based on analysis of the scattering form-factor. Earlier, this approach was used to describe experimental data obtained in a study of synthetic opals representing three-dimensional photonic crystals. We report here on the development of a new version of this model applicable to the class of two-dimensional photonic crystals. The existence of resonant (non-switchable) stop-bands and the possibility of selectively controlling light flows propagating at different wavelengths is predicted. These effects draw up new guidelines for the design of two-dimensional photonic crystals possessing desired optical qualities.     

红外区磷化稼散射强度的计算与分析

根据Mie散射理论,对磷化稼粒子光散射特性进行了数值计算与理论分析,得到了散射强度与散射角、入射波长以及偏振度与散射角的关系。研究表明,红外波段光散射很小,前向散射占有优势,粒子半径越大,前向散射越强,并且在散射角900方向上能观测到线偏振光,对研究GaP红外光学特性提供了理论参考。     

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。     

微纳粒子光学散射分析

为实现利用光学方式对微纳尺度粒子性质的研究,探讨了亚微米线及亚微米球对光电磁波的散射效应.微纳米尺度粒子的光学散射,散射粒子尺寸与入射光波长尺寸可满足米氏(Mie)散射条件.利用Matlab数值模拟的方式,将分析结果以模拟图的形式清晰地展现出来.满足尺寸条件的层状粒子以及任意多个散射粒子存在时对电磁波的散射都可采用Mie散射分析方法,并且针对多粒子散射,分析了散射体位于不同位置时对散射造成的影响.通过分析光学散射光场相关的微分散射截面及近场散射电磁场分布,可得出散射光场随散射角度的变化趋势,以及散射光场受各类因素的影响,包括入射光偏振态、散射粒子尺寸、散射粒子结构及粒子构成层数、散射粒子数量等的影响,也包括一些隐含因素对散射光场的影响,如散射粒子与周围介质的相对折射率.本文的科学意义体现在:与入射光波长尺寸可比的亚微米尺度的粒子,可用作传感器,对于其位移的探测可通过光学方式来实现,而由于粒子本身特性对散射光的影响具有一定的参考价值,从而使通过光学方式对机械位移的读出具有更高准确度.研究结果对于光学方式探测亚微米线机械振动具有指导意义.     

Coherent light scattering spectroscopy for supersonic flow measurements

A unified discussion on coherent light scattering spectroscopy and its spectral dependence on molecular gas velocity, temperature and density is presented. The feasibility of using coherent Raman spectroscopy techniques for nonintrusive measurements of supersonic flow parameters is demonstrated and recent laboratory as well as wind tunnel experiments are reviewed. In addition, the advantages of using coherent Rayleigh-Brillouin spectroscopy for measuring high pressure flows are discussed.     

共振光散射技术测定核酸的研究进展

核酸分析是生命科学研究中最重要的技术之一。目前主要是应用核酸内源紫外吸收光谱的紫外分光光度法和基于荧光探针分子与核酸相互作用的荧光分光光度法。紫外分光光度法灵敏度低 ,荧光分光光度法试剂昂贵 ,有毒性。近年来 ,共振光散射技术在核酸分析中的应用得到了迅速的发展。核酸的共振光散射分析方法可以用普通的荧光分光光度计进行测定 ,应用安全、便宜的试剂获得很高的灵敏度。简要介绍了共振光散射分析的基本原理 ,并对近年来利用共振光散射技术分析核酸的研究进行了评述。内容主要包括利用有机染料分子作为核酸的共振光散射探针的分析方法 ;基于阳离子表面活性剂、金属离子及其络合物以及药物与核酸相互作用的分析方法 ;核酸形成大粒子的散射分析方法。     

Simultaneous determination of velocity,turbulence and particle concentration of a turbulent flow using laser cross-beam photon-correlation spectroscopy

A turbulent velocity model is proposed to describe certain types of turbulent flows. An expression of the photon correlation function for laser cross-beam light scattering based on this model is presented, and it is found to give excellent agreement with experimental data. With least-square fitting, the measured spectrum allows the simultaneous determination of the mean flow velocity, turbulent velocity, and the number of scatterers.     

Monte Carlo simulation of light scattering from size distributed sub-micron spherical CdS particles in a volume element

Simulation of polarized light scattering by spherical particles having modal radius of 180 nm is presented in this paper. A Monte Carlo method which is based on the Stokes-Mueller formalism developed in ANSI Standard C-language is used for simulation. Single scattering is considered in our program with monodispersed sub-micron sized spherical CdS particles. We have considered only θ dependent scattering as described by Mie theory for spherical CdS particles. The experiments for studying light scattering properties of these particles were conducted in a designed and developed laser based light scattering studies setup. The simulation results were compared with experimental results and theoretical results obtained purely from Mie theory. The closeness of agreement or disagreement between these results is discussed in this paper.     

Determination of g and mu using multiply scattered light in turbid media

We propose an inversion scheme to reconstruct the scattering coefficient mu and the anisotropy factor g that characterize the optical properties of a turbid medium. It is based on a theory for the scattering of light inside the medium from an angularly collimated light source. We demonstrate the feasibility of this method using light scattering data obtained from a Monte Carlo simulation.     

The effect of multiple scattering in disperse media on polarization characteristics of scattered light

The effect of scattering of different multiplicity on polarization characteristics of scattered light is studied by the Monte Carlo computer simulation technique. The scattering multiplicity distribution versus the direction of scattering and dimensions of the scattering system is obtained for monodisperse systems of spherical particles of different size. The angular dependences of the elements of the light-scattering matrix (LSM) are calculated. It is shown that in a system of spherical particles, specific features of the LSM structure associated with multiple scattering have much in common with similar features of the LSM in systems of nonspherical particles under conditions of single scattering. The angular dependences of the degree of depolarization of the scattered light are studied.     

圆柱坐标系下生物组织中激光传输的七流模拟

提出了圆柱坐标系下生物组织中激光传输的七流模型,根据此模型进行的计算结果与直角坐标系下七流模型的计算结果比较,二者吻合较好.在此基础上,研究了组织光学性质对激光在组织内传输过程的影响,结果表明:散射效应使入射激光分布到更大的组织范围内,并使激光的穿透率降低,但其影响是有限的,即当散射系数增大到一定程度后,组织内的激光能量分布就不再有明显的变化.相对而言,吸收系数对组织内激光能量分布的影响比散射系数要大,各向异性系数增大使组织内的散射趋于前向散射,激光能量分布也更深入组织内部.     

动态光散射研究纳米级PBA/PMMA核壳颗粒的散射特性

运用动态光散射仪研究PBA(聚丙烯酸丁脂)为核,PMMA(聚甲基丙烯酸甲脂)为壳的核壳双层结构颗粒的角度散射光,并通过测量得到的粒径分布进行理论计算,结果表明:测量结果与理论计算结果总体趋势一致,但在前向散射和后向散射两者相差较大,主要由于动态光散射仪测量粒径分布时反演算法剔除占比例很小的大颗粒造成的.     

Laser light scattering in micellar solutions

Summary The laser light scattering apparatus used for both total intensity and quasi-elastic light scattering experiments on micellar solutions is described in detail. The absolute calibration of the scattered intensity is obtained by exploiting the existence of a lower critical consolution point in a low-concentration aqueous solution of a nonionic amphiphile (C₁₂E₈). The obtained results suggest that micellar solutions may represent a very convenient light scattering standard for both static and dynamic experiments. Paper presented at the “Meeting on Lyotropics and Related Fields”, held in Rende, Cosenza, September 13—18, 1982.     

Spatial, Spectral, and Temporal Characteristics of Stimulated Light Scattering in Water

Spatial, temporal, and spectral characteristics of stimulated light scattering (SS) in water were investigated in both nano- and picosecond ranges under different experimental conditions and compared with the analogous characteristics of stimulated light scattering in other liquids. Stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) of light were studied. The results obtained provide useful information on the structure of water, its purity, and additions, which can result in its pollution. The excitation conditions of stimulated light scattering (SS) in one spatial mode and with maximum pulse energy conversion were determined. It is shown that stimulated light scattering can be successfully applied to control water quality (and it can be done very fast) as well as for information processing, i.e., the amplitude–phase structure of complex light fields can be registered in water as a dynamic hologram and reconstructed in real time.     

Optimal design of gold nanoshells for optical imaging and photothermal therapy

Gold nanoshells are of great interest in optical imaging based on their light scattering properties and photothermal therapy due to their light absorption properties. Strong light scattering is essential for optical imaging, while effective photothermal therapy requires high light absorption. In this article, the optimal core radii and shell thicknesses of silica–gold and hollow gold nanoshells, possessing maximal light scattering and absorption at wavelengths between 700 and 1100 nm, are obtained using the Mie theory of a coated sphere. The results show that large-sized gold nanoshells of high aspect ratios (the aspect ratio is defined as the ratio of core radius to shell thickness) are the efficient contrast agents for optical imaging, while smaller gold nanoshells of high aspect ratios are the ideal therapeutic agents for photothermal therapy. From the comparison of the numerical results for silica–gold and hollow gold nanoshells, the latter are seen to offer a little superior light scattering and absorption at smaller particle size. Fitting expressions for the optimal core radii and shell thicknesses are also obtained, which can provide design guidelines for experimentalists to optimize the synthetic process of gold nanoshells.     

Cross photoelastic and thermorefractive light scattering in continuous media

Two additional types of light scattering in continuous media are considered. One is the cross photoelastic scattering from density fluctuations caused by thermodynamic temperature fluctuations and the other is the cross thermorefractive scattering from temperature fluctuations caused by density fluctuations, which manifest themselves in propagation of elastic sound waves. Expressions for the light scattering coefficients for these two types of scattering are obtained. The integral intensities of scattered light are shown to be comparable with the well-known integral intensities of light scattering by fluctuations of density (pressure) and temperature (entropy) for some substances.     

基于Mie散射理论的铌酸锂晶粒散射特性

基于Mie散射理论,对铌酸锂晶粒光散射特性进行了理论分析与数值计算,得到了散射强度分布、偏振度与散射角、散射强度与粒子尺寸参数,以及光学截面与粒子半径的关系。研究表明:前向散射占优势,并随粒子半径的增大而增强;当粒子半径为0.1 μm 左右,散射截面和吸收截面达到最大值。