用动态光散射时间相干度法测量纳米颗粒粒径

针对传统动态光散射法测量纳米颗粒粒径算法复杂、速度慢、成本高等问题,提出了一种通过改变动态散射光信号时间相干度来测量纳米颗粒粒径的方法,并对其所采用的算法和测量系统进行研究.首先,介绍了动态光散射测量法的基本原理,并引出系统相干度的概念(包括时间相干因子和空间相干因子).接着,从光电探测器的统计特性出发,通过对光子计数...     

动态散斑对比度颗粒测量法

提出了基于线阵CCD相机的动态散斑对比度颗粒测量方法和系统,用于解决动态光散射研究涉及的动态光散射软件相关算法运算量大、实时性较差,以及不能测量高黏度溶液中颗粒的问题。首先,从传统动态光散射理论出发,基于光学统计理论,建立了动态散斑对比度的模型。然后,根据Siegert公式,推导了动态散斑对比度与动态散射光场自相关函数的关系。最后,得到了低浓度和高浓度下动态散斑对比度与颗粒粒径的关系。分别对粒径分布为(490±20)nm的标准乳胶球颗粒水溶液和纳米二氧化钛粉体(粒径分布:450~500nm)甘油溶液进行了测量。结果表明:动态散斑对比度测量法的运算量小,且能测量高黏度溶液中的纳米颗粒,重复测量误差小于2%,满足了动态光散射的国标要求。     

基于FFT的动态散射光谱密度测量技术研究

为了研究动态光散射纳米颗粒测量技术,提出了基于FFT的动态散射光AR模型功率谱密度测量法。首先采用FFT建立信号的AR功率谱密度模型,然后通过计算信号自相关矩阵的秩得到AR模型的阶数P,由于任何信号的自相关与其频域的功率谱密度是一个傅里叶变换对,因此,信号功率谱密度的衰减宽度等价于其自相关函数的衰减宽度,这样通过计算动态光散射信号的功率谱密度衰减宽度,进而得到待测颗粒的粒径,最后将此方法的实验结果与传统的光子相关光谱法实验所测得的数据进行了比较。结果表明：该技术具有误差小、重复性好的优势,有着很大的实用价值。     

用动态光散射现代谱估计法测量纳米颗粒

为了解决目前动态光散射软件信号分析法采用的自相关和功率谱估计存在分辨率和方差较低,以及能谱泄漏问题,提出了基于现代功率谱估计的动态光散射信号分析法。对该系统所采用的现代功率谱估计算法和测量系统进行了研究。首先,介绍了动态光散射测量法涉及的光子相关光谱理论和散射光谱估计理论。接着,描述了基于现代功率谱估计的动态散射光谱法,特别是其中阶数p的计算方法。然后,介绍了测量系统,包括硬件部分的光学系统和信号采集处理系统,软件部分的系统开发流程。最后,对粒径分别为30、50、100nm的乳胶球标准颗粒溶液(透光率为96%)进行了实验。实验结果表明:现代谱估计分析法的测量均值误差和重复性误差的平均值分别为1.88%和1.62%,满足国标要求的均值误差和重复性误差2%。     

多粒子的侧向散射光偏振性质分析

分别用直径0.22μm和0.494μm的粒子与过滤的蒸馏水制成不同浓度的悬浮液作为散射粒子场,来寻求用散射光分析未知群粒子场粒子性质的新的方法.实验结果表明,多粒子散射的散射光总光强与单粒子相似,但其垂直偏振分量和水平偏振分量却随着观测面内散射角的改变而有着显著的不同变化,此结论可用于探测未知群粒子场粒子和入射光相关性质的新方法.     

纳米颗粒粒度测量方法进展

本文介绍了测量纳米颗粒粒度时应用广泛的几种方法:透射电镜观察法(TEM观察法)、扫描电镜(SEM)观察法、X射线衍射线宽法(谢乐公式)的原理、适用范围及其优缺点。文中介绍了纳米测量技术的发展趋势并简单总结了动态光散射法、超声测量法的发展现状。动态光散射法、超声测量法具有不破坏、不干扰体系原有状态的优点,特别适用于工业化生产中产品粒径的检测。     

微米球粒的宽角度光散射的数值模拟研究

采用米氏散射理论，提出一种在传统前向散射布局基础上，增加大角度探测器的实验装置，并对散射光作偏振探测，从而实现对微米直径范围的球粒进行直径分布测量的方法。数值模拟发现散射光强的垂直偏振分量与假设的目标散射光强的垂直偏振分量之间的根均方差为最小。采用Phillips-Twomey算法，设定罗辛-罗姆勒（RR）分布，通过拟合散射光强的垂直偏振分量的角分布曲线获得罗辛-罗姆勒分布中的直径参数和直径分布宽度参数。该方法在理论上快速准确。所提方案在实验上也切实可行。     

SrWO_4晶体受激拉曼散射的各向异性

以四方晶系SrWO4晶体为例,研究其非主轴偏振配置的受激拉曼散射特性。用532nm皮秒脉冲激光作为泵浦源,以单次通过的方式研究了a切SrWO4晶体的受激拉曼散射增益随泵浦光偏振方向的变化,由此确定出拉曼增益的各向异性。针对由[WO4]2-四面体对称伸缩引起的924cm-1的最强频移的实验显示:当入射光沿a轴和c轴偏振时,拉曼增益系数出现两个极大值,增益分别为10.1cm/GW和14.2cm/GW;当入射光沿a,c轴中分线方向偏振时,拉曼增益系数出现两个极小值,为7.1cm/GW。结合拉曼张量及非极性晶格振动模拉曼散射强度解释了上述物理现象,证明了实验结果与理论相符。     

基于后向光散射的颗粒测量技术研究

颗粒粒径和颗粒折射率是光散射颗粒测量技术中的重要参数。为了实现颗粒粒径的测量及其分档,在广义Mie理论基础上,分析了颗粒粒径及折射率对后向散射光能分布的影响,并得到了后向散射光能分布随颗粒粒径及折射率呈周期变化规律。实验验证结果表明,后向散射光能与颗粒粒径及颗粒浓度有关。研究结果可为后续的颗粒测量研究提供参考。     

纳米二氧化硅粒径分析

本文对2个系列的纳米二氧化硅样品进行粒径分析。对单分散的纳米二氧化硅颗粒分别采用透射电镜和图像分析法、X射线小角散射法和动态光散射法测定其粒径,得到一致的结果。采用2种图像分析软件对另一纳米二氧化硅颗粒的透射电镜照片统计其粒径,得到一致的结果。     

表面散射浊度测量研究

本文在理论上计算了球形粒子对光的单次散射及多重散射解 ,证明了通过检测 90°方向散射光强度来获得样品浊度方案的优越性。随着样品浊度的增加 ,当考虑样品的多重光散射后 ,90°方向散射光强与浊度的线性度下降。设计了表面散射浊度在线测量系统 ,当 Formazin标准液在 0～ 1 0 0 0 NTU范围内时 ,获得了散射光强与浊度的线性度优于± 3% ,测量结果表明用表面散射法来测量浊度具有测量范围宽、线性好的优点。     

Accurate hyper-Rayleigh scattering polarization measurements

Apparatus and methods are described for measurement of the polarization dependence of hyper-Rayleigh scattering near 90° scattering angle with 0.1% accuracy for all four configurations where the incident and scattered light is linear polarized either parallel or perpendicular to the scattering plane. Measurements are made with large collection aperture and extrapolated to zero collection numerical aperture (NA = 0). Fiber coupling allows the system to be easily reconfigured for either polarization or spectral measurements.     

Development of a graphite polarization analyzer for resonant inelastic x-ray scattering

Resonant inelastic x-ray scattering (RIXS) is a powerful technique for studying electronic excitations in correlated electron systems. Current RIXS spectrometers measure the changes in energy and momentum of the photons scattered by the sample. A powerful extension of the RIXS technique is the measurement of the polarization state of the scattered photons which contains information about the symmetry of the excitations. This long-desired addition has been elusive because of significant technical challenges. This paper reports the development of a new diffraction-based polarization analyzer which discriminates between linear polarization components of the scattered photons. The double concave surface of the polarization analyzer was designed as a good compromise between energy resolution and throughput. Such a device was fabricated using highly oriented pyrolytic graphite for measurements at the Cu K-edge incident energy. Preliminary measurements on a CuGeO(3) sample are presented.     

Modulated 3D cross-correlation light scattering: improving turbid sample characterization

Accurate characterization using static light scattering (SLS) and dynamic light scattering (DLS) methods mandates the measurement and analysis of singly scattered light. In turbid samples, the suppression of multiple scattering is therefore required to obtain meaningful results. One powerful technique for achieving this, known as 3D cross-correlation, uses two simultaneous light scattering experiments performed at the same scattering vector on the same sample volume in order to extract only the single scattering information common to both. Here we present a significant improvement to this method in which the two scattering experiments are temporally separated by modulating the incident laser beams and gating the detector outputs at frequencies exceeding the timescale of the system dynamics. This robust modulation scheme eliminates cross-talk between the two beam-detector pairs and leads to a fourfold improvement in the cross-correlation intercept. We measure the dynamic and angular-dependent scattering intensity of turbid colloidal suspensions and exploit the improved signal quality of the modulated 3D cross-correlation DLS and SLS techniques.     

Modeling Clutter from Bosnian and Puerto Rican Rough Ground Surfaces for GPR Subsurface Sensing Applications Using the SDFMM

The Steepest Descent Fast Multipole Method (SDFMM) is used to analyze the distorting effect of random rough ground surfaces on scattered and transmitted electromagnetic waves. Two well-measured loamy soils: Bosnian and Puerto Rican clay loam are investigated, each with a variety of surface roughness. This study is important in understanding the effects of different soil properties and is meant to be an a priori phase of investigating scattering from buried targets under the rough ground. In this work, we investigated the scattering from rough soil ground without buried objects. The SDFMM is an integral equation-based fast algorithm that is well suited for two-dimensional penetrable rough surfaces (3-D scattering) in the frequency domain. The scattered and transmitted near electric field of an incident Gaussian beam are calculated at different locations above and below the mean plane of the dielectric rough interface. The receiver locations above are chosen to simulate GPR measurement protocols. The obtained numerical results show that the scattered field undergoes more distortion than the transmitted field from both soil types. Moreover, the transmitted fields into the higher dielectric constant Puerto Rican soil experience more distortion than those transmitted into Bosnian soil.     

Enabling the measurement of particle sizes in stirred colloidal suspensions by embedding dynamic light scattering into an automated probe head

A novel probe head design is introduced, which enables in-line monitoring of particle sizes in undiluted stirred fluids using dynamic light scattering. The novel probe head separates a small sample volume of 0.65 ml from the bulk liquid by means of an impeller. In this sample volume, particle sizing is performed using a commercially available fiber-optical backscatter probe. While conventional light scattering measurements in stirred media fail due to the superposition of Brownian’ motion and forced convection, undistorted measurements are possible with the proposed probe head. One measurement takes approximately 30 s used for liquid exchange by rotation of the impeller and for collection of scattered light. The probe head is applied for in-line monitoring of the particle growth during microgel synthesis by precipitation polymerization in a one liter laboratory reactor. The in-line measurements are compared to off-line measurements and show a good agreement.     

气溶胶颗粒折射率在光学粒径测量中的影响

针对单颗粒光散射测量方法中被测颗粒折射率会影响测量结果的问题,根据Mie理论和光辐射能通量计算公式,对13种常见气溶胶颗粒,在不同采光中心角θ和采光接收半角β下的散射光辐射能通量F与粒径D关系曲线进行了计算,提出一种基于相对测量误差平均值的评价标准,依据该评价标准定量分析了13种折射率对测量的影响。通过对模拟结果的分析,得出采光结构接收到的光辐射能通量包含前向散射光的条件下,13种颗粒的F-D曲线较为接近,折射率对测量结果的影响相对较小。     

Correlation method for processing speckle patterns of dynamic light scattering by small particles based on spatial averaging of data

A correlation method for processing dynamic light scattering patterns resulting from laser radiation propagation through solutions and suspensions is proposed which is based on spatial averaging of measurement data on the correlation functions of the intensity of light scattered by small particles.     

基于动态光散射信号分形的颗粒测量技术研究

颗粒的动态光散射信号具有分形特征，通过对其特征值的分析，可以得到颗粒粒径信息。采用100nm、200nm、500nm和1000nm4种亚微米粒径范围的标准聚苯乙烯乳胶颗粒样品，分别求取了它们的动态光散射信号的分形维数。实验结果表明，颗粒粒径越小，对应的动态散射光分形维数越大；粒径越大，分形维数越小。从而证明了用分形维数表征颗粒粒径的可行性。与相关方法相比，分形方法具有所需的采样数据少、计算简便、适于实时测量等特点。