方形环孔和圆环孔形成的散斑场及相位奇异特性的理论分析和实验验证

通过对方形环孔和圆环孔形成的散斑场及其相位奇异性的研究,发现在某一平面上实部和虚部零值线的位置关系出现了复杂相切相交的情况,复杂相切相交点也形成相位奇异,并且其周围相位分布与传统的实部零值线与虚部零值线相交形成的奇异点周围相位的螺旋变化不同,呈现出对称性和不连续性的特征.方形环孔和圆环孔形成的散斑场的散斑颗粒分布与传统方孔不同,受散射孔径的调制分别排成水平或竖直的条纹状轮廓和类似于圆形的轮廓,在散斑场的局部光强图中出现了很多类似于圆形的黑暗区域,称其为"光强暗核",其中心对应着一个相位分布较均匀的涡旋.     

大散射角散斑场中有关相位奇异新特性的研究

利用散斑场和参考光的干涉提取散斑场复振幅和相位, 研究了不同散射角下散斑场相位的分布规律以及相位奇异处光波复振幅实部零值线和虚部零值线夹角、光强等值线离心率的统计特性. 在大散射角散斑中发现了一种新的相位奇异现象, 即相位奇异线; 研究了相位在跨越奇异线时的突变规律及涡旋状相位的分布特征, 发现在相位奇异线处存在着呈双曲线或抛物线状的光强等值线.     

涡旋光束形成的散斑场光强和相位的分布特性

通过对不同拓扑荷的涡旋光束经随机表面散射后在衍射区形成的横向和纵向光强分布的模拟,发现散斑颗粒的横向和纵向的平均尺寸比用高斯光束照明随机表面产生的散斑颗粒平均尺寸小很多,并且随着涡旋光束拓扑荷和光斑半径的增大而减小,同时散斑场相位涡旋的密度随着涡旋光束拓扑荷和光斑半径的增大而增大。利用这种方法可以方便地选择不同拓扑荷和光斑半径的涡旋光束照射随机表面,得到合适的散斑颗粒来捕获更小的微粒。这种结果还可以用来降低散斑噪声。     

磁流体中微粒运动情况的初步分析

针对磁流体显示器件的结构特征,设计了对称双光束激光散斑剪切实验,着重研究电磁场驱动条件下磁流体中磁微粒的运动状况.解决了激光散斑剪切干涉实验中磁流体液面影响观察磁微粒运动的问题,并分析了磁流体液面在电磁场驱动下的变化规律和影响范围.在此实验基础上,观察到磁流体的聚集、堆起和碰撞现象,在电磁场驱动下,磁微粒表现出周期性运...     

高斯相关随机表面光散射散斑场相位奇异及其特性的理论研究

通过对二维高斯相关随机表面在远场平面上产生的散斑场及其相位的计算模拟, 发现在某一平面上除了实部零值线与虚部零值线有传统相交之外, 还有相切和重合的情况.切点和重合线也可以形成相位奇异, 并且其周围相位分布与传统的实部零值线与虚部零值线相交形成的奇点周围相位的螺旋变化不同, 呈现出对称性和不连续性的特征. 随着光波的传播, 在不同的观察面上散斑场复振幅的实部零值线和虚部零值线的相对位置经历了由相切到重合再到相交的演变过程, 相位奇异现象也随之发生变化. 关键词： 相位奇异 相位跃变 散斑场     

多针孔散射屏形成的散斑场分布特性的研究

利用多针孔孔径随机散射屏详细分析了夫琅禾费衍射区的散斑场中的相位和相位涡旋的统计特性,发现散斑相位涡旋的分布具有区域相似性和团簇现象,其中有2个、4个和6个正负相位涡旋形成的独立单元。这些新现象与普通单一孔径形成的散斑相位涡旋的分布完全不同。改变随机散射屏前孔径上小针孔的数量和间距,散斑颗粒和相位涡旋的密度随着改变。     

散斑场相位涡旋及其传播特性的实验研究

用CCD记录散斑场和参考光的干涉图样, 利用傅里叶变换法实现了散斑场复振幅以及相位分布的实验提取, 在复振幅实部零值线和虚部零值线切点处出现一种新的相位奇点, 与两条零值线交点处的传统相位奇点周围单调螺旋变化的相位分布不同, 绕切点一周的相位具有先增大后减小几乎呈对称性分布的特性, 为了解释这种新的相位奇点,提出了准孪生相位涡旋的概念. 在理论研究散斑场强度的纵向自相关函数的基础上, 实验观察散斑场相位涡旋的传播, 发现在光强纵向相关长度范围内的不同传播距离处的观察面上, 复振幅实部和虚部随机变化而涡旋的 关键词： 相位涡旋 散斑 干涉     

空间散斑场捕获大量吸光性颗粒及其红外显微观测

光镊技术被广泛应用于捕获和操纵微纳米尺寸颗粒,主要包括捕获水中透明性颗粒和空气中吸光性颗粒两种类型.本文用激光束照射毛玻璃散射片,透射光经透镜会聚后在透镜的像平面附近产生了主观散斑场.该散斑场为空间分布,包含大量的亮斑和暗斑.大量由亮斑包围的暗斑如同一个个空间能量陷阱,被用来捕获大量的吸光性墨粉颗粒,被捕获颗粒的尺寸约2—8μm,密度约1—2 g/cm3.采用红外显微镜拍摄到空间散斑场捕获颗粒的红外像,红外图像显示被捕获颗粒吸光后温度升高,证实了空间散斑场捕获吸光性颗粒的机理为光泳力原理.     

白蛋白酸致变性的动态激光散斑研究

利用动态激光散斑的方法研究了白蛋白的酸致变性过程。首先,利用动态散斑理论模拟生成了动态散斑序列图;然后,利用模拟和实验散斑图的时间序列散斑图及其灰度共生矩阵对白蛋白的酸致变性过程进行了分析;接着,又利用灰度共生矩阵的惯性矩和不同阶段的四幅散斑图的平均对比度图对该过程进行了更深入的研究。理论模拟和实验研究结果表明,在白蛋白酸致变性过程中,胶体溶液中的蛋白质微粒的运动由剧烈逐渐变得缓慢;同时,微粒数量减少而微粒尺寸增加。研究表明,动态激光散斑方法是一种实时、快速、有效的研究白蛋白变性过程的新手段。     

时间序列散斑干涉场中相位函数的计算

散斑干涉或电子散斑干涉计量应用于连续运动或变形物体时,就会产生一个时变的散斑干涉场,通过摄像系统连续地采集这一时变散斑场,可获得一系列时间序列散斑干涉图,通过对序列散斑图上各点在时间轴上光强值的变化进行分析,提出了一种基于时间序列的分析方法,用以提取干涉场的相位值,进而获得物体全场变形信息。     

菲涅耳衍射区和夫琅和费衍射区的动态部分相干光散斑场特性

研究了菲涅耳衍射区和夫琅和费衍射区动态部分相干光散斑的特性.利用部分相干光互强度传播的理论，得出了在部分相干光照明时，由运动散射体产生的动态散斑光强时空交叉的自相关函数的一般形式，并由此得出了散斑沸腾和平移的一般规律.通过适当选择光源和调整光路参数，在实验上得到了菲涅耳和夫琅和费衍射区的部分相干光散斑，对夫琅和费面上的动态部分相干光散斑的平移和沸腾现象进行了定性研究；采用光子计数及数据自动采集的方法，对部分相干光散斑随时间的演化及动态部分相干光散斑的沸腾进行了定量测量.这些实验结果与理论结果相符合. 关键词： 部分相干光动态散斑 时空交叉相关函数 沸腾     

Dynamic laser speckles and their application to velocity measurements of the diffuse object

In connection with the parameters of the optical configuration used to produce speckles and under illumination of a Gaussian beam over a moving diffuse object, this paper discusses the statistical properties of dynamic speckles produced in the diffraction and image fields by the diffuse object moving in a plane with constant velocity. Especially, the space-time correlation function of the dynamic speckle intensity is examined in detail. Two typical speckle motions of translation and boiling are interpreted for various optical configurations in the diffraction and image fields. As one of the interesting applications of dynamic speckles to metrology, various methods for velocity measurements of the diffuse object are introduced.     

水下高斯界面背向散射超声散斑场的相位奇异

为了精确描述超声散斑场的特性,提出了采用计算机模拟产生超声散斑场的方法.利用模拟产生的高斯相关随机表面,获得了这类表面远场超声散斑场,同时得到了声强分布和相位分布.与实验产生的散斑场进行对比,建立了超声散斑场接收的实验系统,取与计算模拟相同的参数,获得了实验散斑场.通过对比发现:计算机模拟产生的超声散斑场相位存在奇异点,奇异点周围相位分布类似漩涡,计算机模拟产生的散斑场与实验得到的散斑场强度分布相似,强度值比实验产生的散斑场强度大,携带有用信息的高亮散斑较多,暗点较少,更利于研究和分析.     

用偏振和有规位相分布抑制线聚焦系统的小尺度不均匀性

研究了一种用以抑制光楔列线聚焦系统在靶面产生的干涉尖端的方法。由这种尖峰引起的小尺度不均匀性对Ｘ射线激光的产生是不利的。利用特殊分布的偏振态和位相，可把尖峰引向更密度伯程度，而且其对比度下降，这将有利于它通过靶物质自身的横向热传导而平滑化。对于四单元的列阵系统，甚至可将尖峰完全消除。     

A new technique for fluid velocimetry based on near field scattering

We show that the time evolution of near-field scattering speckles, originated by a fluid suspension of particles, provides information about the velocity field in the fluid. This information can be extracted from a statistical analysis of speckle fields taken at different times, either by measuring their cross-correlation function or by recovering the power spectrum corresponding to the difference between the two speckle fields. Experimental data are in accordance to the expected behaviors. The results are independent of the scatterer's size, allowing one to exploit the technique also with sub-wavelength tracking particles.     

Dynamic properties of speckled speckles with relation to velocity measurements of a diffuse object

This paper investigates, experimentally, the dynamic properties of triply-scattered speckled speckles and their application to the velocity measurement of a moving diffuse object, which is behind a transparent diffuse screen. The comparison between triply-scattered speckled speckles and singly-scattered normal speckles shows that the triply-scattered speckle pattern has a high degree of randomness in the spatial domain and that its time-varying intensity fluctuations have a rate 72 times that of the normal speckle case in the temporal domain. Consequently, a velocimeter using the triply-scattered speckles can measure the object velocity with a greatly reduced measuring time than when using normal speckles.     

Measurement of vortex motion in a type-II superconductor: A novel use of the neutron spin-echo technique

We have used the neutron spin-echo technique to measure the small energy change of neutrons which are diffracted by a moving vortex lattice in a low-pinning Nb-Ta superconducting sample. A transport current was passed in the mixed state to cause flux line movement. In the case of uniform motion, the flux velocity v(L) was given as expected by the values of electric and magnetic fields, via E = -v(L)wedgeB. We show that with a nonuniformly moving vortex lattice, one can measure the dispersion of the velocities, opening up new possibilities for investigating moving vortex lines.     

A clustered speckle approach to optical trapping

An in situ study of the clustered speckle 3D structure using an optical tweezer setup is presented. Clustered speckles appear when a coherently illuminated diffuser is imaged through a pupil mask with several apertures, properly distributed over a closed path, which is placed before the objective lens of a standard optical trapping system. Thus, light volumes are reduced several times when compared with standard speckles, being even smaller than the focus volume of a Gaussian beam commonly used to trap. Moreover, clustered speckles have odd statistical properties which differentiated it from standard speckles. Then, geometrically ordered multiple trapping arrays, with statistical random distribution of intensities, can be created with this technique. This fact could enable different studies concerning optical binding or new developments in coherent matter wave transport where Optical Trapping has been proven with standard speckles. In this work, a qualitative analysis of clustered speckles in an optical tweezer setup relative to the number of apertures in the mask and their size is carried on. Besides, in the Rayleigh regime, a general quantitative method to characterize the trapping capability of an optical field is proposed. Then, it is applied to clustered speckles. As a result, a relation between aperture size and the maximum size of the particles that could be trapped is found. This fact opens the possibility of engineering the statistic of the trapped particles by properly selecting the pupil mask.     

Extremal Properties for Weakly Correlated Random Variables Arising in Speckle Patterns

Extremal properties of the statistics of speckle pattern are studied in the context of so-called “optically smoothed” light beams of laser-matter interaction. It is shown that the asymptotic statistics of the highest intensity in a speckle pattern, which can be associated with the most intense speckles, follows a Gumbel law, which is in agreement with numerical simulations. It is found that the probability density function of the most intense speckle peaks around the value corresponding to the logarithm of the number of speckles in the considered volume times the average intensity value of the speckle pattern. This result is of great interest for nonlinear processes, like instabilities, where extreme speckles play an important role.