光折变晶体LiNbO_3:Fe中的特殊散射现象

用柱面透镜把经针孔滤波器扩束的激光束沿某一个方向聚焦成细丝状(或长条状),细丝状光束垂直入射到LiNbO_3:Fe晶体上,在远场位置观察散射光.我们发现光散射的方向与晶体的c轴方向不一致,不仅沿着晶体的c轴方向有散射光出现,沿光束的条形方向也出现很强的散射光.     

基于受激布里渊散射的宽带宽和高精度的微波频率瞬时测量

提出了一种基于受激布里渊散射效应的瞬时频率测量方法.未知信号经过强度调制作为泵浦光,矢量网络分析仪产生的信号经过相位调制作为扫描信号光,当泵浦光和扫描信号光之间满足相位匹配条件时,受激布里渊散射效应发生并实现相位调制到强度调制的转换,未知信号的频率被测量.实验验证可以测量0.5 GHz-27 GHz的微波信号的频率,最大误差小于20 MHz.     

激光陀螺基片散射收集系统的设计与分析

研究了散射测量在激光陀螺用石英基片表面检测中的应用.比较发现,收集物镜比积分球更有利于体散射的消除,更适用于直接检测超光滑石英基片表面的散射测试系统.用ZEMAX设计了散射光收集物镜,使其数值孔径达到了0.4,并完全消除了轴上距离大于1.5 mm的散射点的体散射|为了消除光电倍增管输出本身随时间长漂的问题,设计了特定的散射光收集系统的结构,将散射光和反射光分时打在同一个光电倍增管上.分析发现,这种设置能有效消除光电倍增管输出随时间趋势性漂移的问题,增强了系统长时间的稳定性,有效保障了其工程实用性.     

磁性材料中的光散射

磁性材料,由于多数是可见光不透明的,长期以来与光散射研究似乎无关。然而这些介质中的磁性激发和声子一样是能够与入射光发生作用,造成非弹性散射的。研究这些散射能提供介质中磁性激发的各种信息。近几年散射谱仪技术的发展,尤其是多通Brillouin散射谱仪的出现,为开发磁介质光散射提供了技术基础。这些研究陆续取得了一系列引人注目的成果,Brillouin散射,因此称为磁学研究的新的特殊方法。考虑到磁学工作者的兴趣,本文首先概述光散射的基本概念,分析光与磁性激发的耦合机制,然后介绍基于多通Fabry-Perot干涉仪的Brillouin散射实验。最后讨论对几种典型磁性材料的研究结果,用以说明磁介质光散射的应用性,前景及特点。     

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.     

多站观测空间目标可见光散射特性及相关性分析

鉴于空间目标的光散射特性对目标的探测、跟踪与识别等空间突防技术具有十分重要的应用价值,利用双向反射分布函数（BRDF）将光辐射的入射照度和目标的散射亮度联系起来,结合目标的几何建模与轨道理论,计算出某时刻在东北3站观测风云卫星可见光散射亮度变化情况, 其峰值随时间依次达到或接近于7.510-3 W/cm2sr,而新疆阿勒泰散射亮度在东北3站达到峰值时只有3.7510-3 W/cm2sr,得出东北3站点卫星光散射亮度趋势相似,只是由于纬度差异使变化趋势在时间上有所延迟,而在与之经度有很大差别的新疆地区的阿勒泰站点的亮度变化趋势则有很大不同。该方法已经在获取空间目标更多信息选择多站观测中取得应用。     

Fractal Character of Dynamic Light Scattering of Particles

Dynamic light scattering signals from particles, exhibit fractal characteristics. This feature can be used to determine the particle size. The use of the fractal dimension, as a quantitative method to analyze the properties of dynamic light scattering signals from submicron particles, is presented. The analysis is performed directly on the time‐resolved scattered intensity, and the Box Dimensions of light scattering signals of particles with diameters 100, 200, 500 and 1000 nm. The experimental results show that the fractal dimensions of light scattering signals correlate well with particle size. In the submicron size range, the smaller the particles, the larger their fractal dimensions. Compared with the PCS technique, only several hundreds of samples are required in the fractal method. Therefore, the data processing is easily accomplished. However, this method only provides the mean particle size, but not the particle size distribution.     

Kinetics of water flow through a polymer gel

The water flow through the poly(acrylamide) gel under a constant water pressure is measured by newly designed apparatus. The Young modulus and Poisson’s ratio of the rod shape gels are measured by the uni-axial elongation experiments, which determine the longitudinal modulus independently from the water flow experiments. The time evolution of the water flow in the dilute gel is calculated based on the collective diffusion model of the polymer network coupled with the friction between the polymer network and the water. The calculated results are compared with the time evolution of the flow experiments, and the values of the longitudinal modulus and the friction coefficient are estimated. The estimated values are consistent with the results of our mechanical-response experiments and the light scattering experiments reported previously. We find that the time evolution of the water flow is well described by a single characteristic relaxation time predicted by our model for dilute gels.     

基于经典小波变换的布里渊光时域反射计光信号处理

布里渊光时域反射计结构的布里渊散射分布式光纤传感器检测的是自发散射光,信号非常微弱,而且频带在几十兆赫兹以上,难以应用普通相干解调方法。针对传感散射光信号特点,提出基于经典(Morlet)小波变换的光相干检测方法。首先采用微波电光调制产生频移参考光和自发布里渊散射光进行相干检测,再应用经典小波变换进行散射光信号的幅度解调,得到信噪比改善的布里渊散射传感光信号。给出了数值模拟和实验数据处理结果,表明经典小波变换能较好地处理布里渊光时域反射计检测信号。并和基于希尔伯特(Hilbert)变换的传感信号处理方法进行了对比,发现此方法优于基于希尔伯特变换的信号处理。     

冷原子介质中基于相干诱导高反射带和高透射带的全光路由控制

以相干诱导光子带隙结构为工作基础,提出了一种可对两个弱光信号的传播路径同时进行动态调控的新型全光路由控制方案。利用描述光波在空间周期介质中相干散射的传输矩阵理论,结合描述单频激光与多能级原子共振相互作用的密度矩阵方程,计算了作为控制媒介的相干驱动超冷原子系综的稳态反射光谱和稳态透射光谱。结果表明,通过改变两个较强相干激光的空间模式、强度和频率等参数,可在探测跃迁共振频率附近建立反射率约为95%或者透射率约为95%的两个特殊频带。对这样的相干诱导高反射带和高透射带进行了实时动态调控,可根据需要引导两个不同频率的弱光信号进入指定的网络通道。该方案很好地满足了在量子信息处理领域对弱光信号进行全光路由控制时的低损耗和低形变要求。     

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。     

空间目标可见光散射特性与可视条件研究

采用椭偏法和总体积分散射法分别测量和计算了空间目标包层材料和太阳能板的材料参数,以及相应的双向反射分布函数。并根据此参数对空间简单体目标可见光谱散射特性进行了理论计算和实验校模。结合目标的几何建模和轨道理论,利用Modtran大气传输模型计算了不同时刻的背景辐射,以及在不同地面观测站观测时空间目标的亮度变化以及背景辐射的影响,并分析了目标的可视条件。计算表明,清晨或傍晚,背景辐射小于空间目标的散射,是观测的最佳时段。     

Lysosome-damage-induced scattering changes coincide with release of cytochrome c

Light scattering measurements made at visible wavelengths have the ability to quantify subcellular morphology. Apoptosis, or programmed cell death, is associated with distinct morphological signatures such as mitochondrial swelling and nuclear condensation as well as characteristic biochemical signaling pathways, many of which are initiated by the release of cytochrome c from the mitochondria into the cytosol. In this Letter, we examine the time course of mitochondrial morphology changes as reported by light scattering and the subcellular location of cytochrome c measured by immunofluorescence microscopy in response to intracellular cell death signaling induced by photodynamic damage to lysosomes. We report that within this system, release of cytochrome c from the mitochondria into the cytosol occurs approximately simultaneously with mitochondrial-morphology-induced light scattering changes, providing further evidence that light scattering has the potential to play an important role in future studies of cell death biology.     

光在二维无序介质中的动态传播过程

用有限时域差分 FDTD 法研究了光在二维无序介质中的动态传播过程.数值模拟了某一高斯脉冲光束入射到无序介质中光场的空间分布随时间的演化,结果表明：在光束入射的初期,能量从光源区向外传播并出现了清晰的波前传播的特点;经过一定的时间后,有部分能量从光源区向外扩散,而大部分能量逐渐聚集在介质中的一些小区域内,这与整体散射模型关于无序介质中光子局域化的研究相吻合,而且更清晰地呈现了形成光子局域化过程中的物理现象及整体散射干涉效应的重要机理作用.     

共振光散射的时间量子理论

本文发展了Ｓｃｈｏｍｍｅｒｓ的时间观点，定义了时间，尤其是表征量子系统光散射的散射时间和共振散射时间。通过散射时间本征态的假定实现了散射时间的量子化，得到了量子化的共振散射时间。对原子的弹性光散射和Ｒａｍａｎ散射的成功应用推出了原子和原子的价电子逐级电离所形成的离子的所有原子能级的普适近似公式。     

The influence of phase-modulation on femtosecond time-resolved coherent Raman spectroscopy

The influence of phase-modulation on femtosecond time-resolved coherent Raman scattering is investigated theoretically and experimentally. The coherent Raman signal taken as a function of the spectral position shows unexpected temporal oscillations close to time zero. A theoretical analysis of the coherent Raman scattering process indicates that the femtosecond light pulses are amplitude and phase modulated. The pulses are asymmetric in time with more slowly decaying trailing wings. The phase of the pulse amplitude contains quadratic and higher-order contributions.     

Depolarized light scattering from interacting brownian spheres

The initial decay time of the spectrum and the integrated intensity of depolarized light scattered from a system of interacting spherical and optically isotropic colloidal particles as a function of scattering angle is calculated in the double scattering approximation. These quantities can be reduced in the short-time regime to the static structure factor of single scattering, as observed in polarized scattering for systems of intermediate concentrations of colloidal particles. The results are applied to charged polysterene spheres in solutions and it is shown by numerical calculations that the presence of interactions can modify the angular dependence of initial decay time and integrated intensity considerably.     

Monte Carlo simulation of the interaction between an ultra-short pulse and a strongly scattering medium: The case of large particles

Simulations of the transmission of a short light pulse (50 fs) through a strongly scattering medium constituted by water droplets (50-150 μm diameter) are presented. Temporal emerging signals are computed using a Monte Carlo technique. In case of large particles with respect to the pulse duration, the time delay related to the interaction between light and individual particles has to be taken into account, in addition to the time delay related to the travel of light between particles. After careful comparisons with temporal Lorenz-Mie theory, it has been chosen to pre-calculate scattering characteristics of individual droplets using Debye series. Transmitted signals in forward direction and in a small temporal window (0-400 fs) are presented, showing that temporal information on particle size are still observable facing strongly scattering media.     

Fluid-fluid phase separation in colloid-polymer mixtures studied with small angle light scattering and light microscopy

Mixtures of colloidal silica spheres and polydimethylsiloxane in cyclohexane with a colloid-polymer size ratio of about one were found to phase separate into two fluid phases, one which is colloid-rich and one which is colloid-poor. In this work the phase separation kinetics of this fluid-fluid phase separation is studied for different compositions of the colloid-polymer mixtures, and at several degrees of supersaturation, with small angle light scattering and with light microscopy. The small angle light scattering curve exhibits a peak that grows in intensity and that shifts to smaller wave vector with time. The characteristic length scale that is obtained from the scattering peak is of the order of a few μm, in agreement with observations by light microscopy. The domain size increases with time as , which might be an indication of coarsening by diffusion and coalescence, like in the case of binary liquid mixtures and polymer blends. For sufficiently low degrees of supersaturation the angular scattering intensity curves satisfy dynamical scaling behavior.     

一种用多色光作为激发源产生拉曼光谱的新算法

探讨用多色光代替激光作为拉曼光源的新型拉曼光谱仪的可能性。根据拉曼光谱原理, 并通过数学分析, 发现当用多色光照射在样品上时, 所得到的散射光经散射频率校正后在不同频率上的强度分布可以写成样品的Raman-Rayleigh联合散射谱和激发光光源的功率谱的卷积。利用傅里叶变换算法,有可能从多色光照射样品所得到的散射光谱中导出样品的拉曼光谱。基于上述原理,可能发展出不用激光的新一代拉曼光谱仪。