Three-dimensional particle imaging by defocusing method with an annular aperture

We propose an annular-aperture-based defocusing technique for three-dimensional (3D) particle metrology from a single camera view. This simple configuration has high optical efficiency and the ability to deal with overlapped defocused images. Initial results show that an uncertainty in depth of 23 microm can be achieved over a range of 10 mm for macroscopic systems. This method can also be applied in microscopy for the measurement of fluorescently doped microparticles, thus providing a promising solution for 3D flow metrology at both macroscales and microscales.     

A study on particle identification in PTV particle mask correlation method

An algorithm for particle identification in PTV, which is classified in the category?particle mask correlation method, is presented and tested. A typical brightness pattern of a particle image is referred to as a particle mask. The particle mask is centered on a pixel in the image plane and the cross correlation between the particle mask and a region of the image plane centered on the given pixel is calculated. The particle mask is scanned over the entire image plane and the cross correlation coefficient is calculated at each pixel location. Small subareas with high correlation coefficients indicate central areas of particle images.     

Trajectory Ambiguities in Phase Doppler Systems: Study of a near forward and a near-backward geometry

Generalized Lorenz-Mie theory for the scattering of arbitrarily shaped beams by spherical particles has been applied to two standard phase Doppler layouts, employing receiving units at 30° and 150° off-axis locations. It is shown that the particle trajectory effects may lead to inaccurate size measurements for the near-forward receiver and may make the near-backward measurements totally misleading when a large particle size range (1:40) needs to be covered. Only limited improvements can be achieved by using two phase-shift signals from a single receiving unit for discrimination. The errors associated with the trajectories are also detrimental to the concentration measurements based on the existing criteria. However, an extended optical system employing two identical receiving units, located symmetrically about the plane of the laser beams, provides a robust solution to the trajectory ambiguity. It can be used to measure correctly the particle size and the particle location in the measuring volume. The difficulties associated with estimating the effective size of the measuring volume as a function of the particle diameter (in order to determine the true size distribution and the particle number density) may also be resolved by employing an extended system. Hence, despite a higher cost, this arrangement is attractive, at least for obtaining some benchmark simultaneous measurements of sizes and velocities in two-phase particulate flows.     

3D Flame surface density measurements via orthogonal cross-planar mie scattering in a low-turbulence bunsen flame

Quasi-instantaneous Mie scattering measurements were conducted to determine the flame surface location using two orthogonal planes to obtain the 3D orientation and measurement of 3D flame surface density (FSD) on a stabilised piloted Bunsen burner with turbulence levels of 1 to 2.5 times the laminar flame speed. A double-pulsed 527 nm high-frequency laser (part of a high-frequency particle image velocimetry dual-head setup) was split into two separated laser beams through a polarizer to generate laser sheets at 3 kHz on a vertical plane and a horizontal plane. The vertical plane across the centerline of the Bunsen-stabilized flame was kept constant, whilst the height of the horizontal plane was adjusted from the base of the flame for different heights. The flame edge was defined as the location where droplet tracers disappear, and calculated based on the local change in the number density of the flame edge. Projections of the flame normal vector onto two measurement planes were used to calculate directing angles on each plane, and the 3D FSD was estimated based on the measured angles at the intersecting lines of two planes. A comparison of the 2D to 3D FSD magnitudes was made, for cases with and without mean angle corrections. The results show that the 2D FSD approximations are lower than the 3D measurements by a factor of 20–30% if uncorrected, and up to 28% after corrections.     

Fisher-Rényi entropy product and information plane

Connection between Fisher information and Rényi entropy has been established. This link allows us to define the Fisher-Rényi information plane and an entropic product in terms of these quantities. New Rényi uncertainty relations are obtained for single particle densities of many particle systems in position-momentum conjugate spaces.     

Flow characteristics of an offset jet over a surface mounted square rib

A three-dimensional offset jet flow over a surface mounted square rib was investigated using particle image velocimetry at Reynolds number of 7600. The square rib was mounted at three different locations downstream of the nozzle exit. Contour and profile plots in the symmetry plane were used to investigate the effect of the rib on the mean flow distribution and turbulence statistics. Changing the rib location enhanced the mixing and entrainment characteristics of the jet thereby leading to larger wall-normal spread rates. The quadrant analysis revealed a significant contribution of all events towards the Reynolds shear stress. The joint probability density function analysis showed that the structures within the outer shear layer of the jet differed from those of boundary layers. Results from the two-point correlation analysis indicated that the introduction of a surface mounted rib modified the flow structures within the developing region. However, there was no significant structural difference between the flow with mounted rib and the no rib case within the self-similar region. The proper orthogonal decomposition was used to examine how changes in rib location modified the dynamics of the energetic modes towards the turbulent kinetic energy and Reynolds shear stress within the developing and self-similar regions.     

Three-dimensional photonic-crystal emission through thermal excitation

A three-dimensional tungsten photonic crystal is thermally excited and shown to emit light at a narrow band, lambda = 3.3-4.25 microm. The emission is experimentally observed to exceed that of the free-space Planck radiation over a wide temperature range, T = 475-850 K. It is proposed that an enhanced density of state associated with the propagating electromagnetic Bloch waves in the photonic crystal is responsible for this experimental finding.     

The optical method of caustics

An overview of the basic principles of the optical method of caustics for the determination of stress intensity factors in crack problems is presented. The method is based on the assumption that the state of stress in the neighborhood of the crack tip is plane stress. However, the state of stress changes from plane strain very close to the tip to plane stress at a critical distance from the tip through an intermediate region where the stress field is three-dimensional. The caustic is the image of the so-called initial curve on the specimen and, therefore, depends on the state of stress along the initial curve. For the determination of stress intensity factors the values of the stress-optical constants are needed. These values depend strongly on the state of stress being plane stress, plane strain or three-dimensional. This complicated the experimental determination of stress intensity factors. For the characterization of the state of affairs near the crack tip a phenomenological triaxiality factor is introduced. A methodology based on the use of optically birefringent materials is developed for the determination of stress intensity factors without paying attention to the location of the initial curve in the plane stress, plane strain or three-dimensional region. Finally, a comparison of the methods of photoelasticity and caustics takes place, and the potentialities and limitations of both methods for the solution of crack problems are explored.     

Single-particle trajectories in a cusped magnetic field

The trajectories of a single charged particle in relation to the cusp axis and cusp plane in a cusped magnetic field are numerically studied. The results show that the particle reflected by the cusp field forms a double helix; i.e., the helix itself makes a helical motion. The location of the reflection point extends well into the injection side of the cusp plane, suggesting that a diverging magnetic field of appropriate geometry may be able to reflect a charged particle. However, the location of the reflection point does not alter the nature of the trajectory     

Experimental observation of a superfluid gyroscope in a dilute Bose-Einstein condensate

We have observed a three-dimensional gyroscopic effect associated with a vortex in a dilute Bose-Einstein condensed gas. A condensate with a vortex possesses a single quantum of circulation, and this causes the plane of oscillation of the scissors mode to precess around the vortex line. We have measured the precession rate of the scissors oscillation. From this we deduced the angular momentum associated with the vortex line and found a value close to Planck's over 2pi per particle, as predicted for a superfluid.     

A novel method for determining the single particle potential directly from the measured single particle density: Application to the charge density difference between the isotones <Superscript>206</Superscript>Pb–<Superscript>205</Superscript>Tl

We present a novel method, based on the single particle Schroedinger equation, to determine the central potential (mean-field) directly from the single particle matter density and its first and second derivatives. As an example, we consider the experimental data for the charge density difference between the isotones ²⁰⁶Pb–²⁰⁵Tl, deduced by phase shift analysis of elastic electron scattering cross-section measurements and corresponds to the shell model 3s_1/2 proton orbit, and determine the corresponding single particle potential. We also present results of least-square fits to parametrized single particle potentials. The 3s_1/2 wave functions of the determined potentials reproduce fairly well the experimental data within the quoted errors. More accurate experimental data, with uncertainty smaller by a factor of two or more, may answer the question how well can the data be reproduced by a calculated 3s_1/2 wave function.     

Use of continuous-wave illumination for two-photon three-dimensional optical bit data storage in a photobleaching polymer

We show that a continuous-wave laser beam at an infrared wavelength of 800 nm can be used for two-photon three-dimensional bit data storage in a photobleaching polymer. We successfully demonstrate recording and reading of six layers of data bits with a transverse bit separation of 4.3microm and an axial layer separation of 20microm . This result leads to a three-dimensional bit density of approximately 3Gbits/cm(3) .     

Nanoscale microcavity sensor for single particle detection

Recently we demonstrated a biosensor based on a two-dimensional photonic crystal microcavity for detection of proteins. We present a theoretical and experimental study of a modified structure for single particle detection. With an active sensing volume of approximately 0.15 microm(3), the device is capable of detecting approximately 1 fg of matter. Its performance is tested with latex spheres with sizes that fall in the size range of a variety of viruses.     

单相机离焦法测量粒子三维运动轨迹

本文提出一种测量空间粒子三维运动轨迹的新方法。该方法是当利用双孔透镜成像时,单点粒子在离焦光学成像系统中会形成包含粒子空间信息的两点像,根据粒子像在像平面上的位置和间距可以获取空间粒子的三维空间位置。本文用单点发光体模拟单点粒子,用ＣＣＤ摄像机连续摄取粒子的瞬时空间运动图像,用计算机对获得的图像进行处理,可以得到粒子三维运动轨迹。这种方法可以应用于三维流场的流动显示研究     

数字显微全息重建图像的景深扩展研究

显微物镜的景深问题限制数字显微全息在大纵深视场中的应用. 本文充分利用数值重建的特点, 采取低频和高频系数子图上的最大亮度梯度的局部方差作为聚焦判据, 在小波分解域内对显微全息重建图像的景深扩展问题进行了研究. 对倾斜的连续物体碳纤维进行三维重建, 分析了重建距离与直径测量误差的关系. 以超声波雾化器生成的微液滴颗粒场为例, 对离散颗粒场的重建图像进行了景深扩展. 利用基于广义洛伦兹-米散射理论的模型分别模拟1-15 μm 的非透明与透明离散颗粒的显微全息图, 分析了该方法重建的颗粒场的纵深定位误差与夫琅禾费系数的关系, 对比了非透明与透明颗粒纵深定位误差的异同点. 实验和模拟结果显示出该方法对于连续物体和离散颗粒场的显微全息重建图像的景深扩展能力, 且能由此准确重建物体信息.     

强光一号POS等离子体源性能参数测量

以强光一号等离子体源（电缆枪）为研究对象,采用电荷收集器（法拉第杯）对强光一号等离子体源性能参数进行测量。实验结果表明:等离子体发射密度与电缆等离子体枪枪芯到枪口的距离正相关,而发射速度与电缆等离子体枪枪芯到枪口的距离负相关;增大电缆枪驱动电压时,等离子体发射密度增速远小于驱动电流增速。重复性研究表明,对由数十支电缆枪组成的等离子体源而言,单支电缆枪放电分散性对其输出等离子体整体分布均匀性影响不大。不确定度分析表明,通过多次重复实验求平均值,可以有效减小实验结果的不确定度,发射密度测量结果的合成标准不确定度在10%以内。     

窄带高功率微波效应测试中功率密度测量不确定度评估

针对窄带高功率微波（HPM）效应试验的辐射场准确测试需求,分析补充了功率密度参数的测量不确定度主要分量,提出了一个参数更为全面的乘式测量不确定度评估模型。采用B类评估方法,根据相关标准和信息对各分量进行了一组赋值,计算得到了相对形式的分量标准不确定度。给出了评估测试环境影响、位置偏差等分量不确定度半宽度的实验方法,为HPM效应功率密度参数测量不确定度的合理评定提供了参考,为实现其全部分量基于实测数据客观评估测量不确定度提供了操作方法。     

Extended focused imaging of a microparticle field with digital holographic microscopy

We present a numerical technique for extended focused imaging and three-dimensional analysis of a microparticle field observed in a digital holographic microscope working in transmission. The three-dimensional localization of objects is performed using the local focus plane determination method based on the integrated amplitude modulus. We apply the refocusing criterion locally for each pixel, using small overlapping windows, to obtain the depth map and a synthetic image in which all objects are refocused independent from their refocusing distance. A successful application of this technique in the analysis of the microgravity particle flow experiment is presented.     

Trapping and manipulating neutral atoms with electrostatic fields

We report on experiments with cold thermal (7)Li atoms confined in combined magnetic and electric potentials. A novel type of three-dimensional trap was formed by modulating a magnetic guide using electrostatic fields. We observed atoms trapped in a string of up to six individual such traps, a controlled transport of an atomic cloud over a distance of 400 microm, and a dynamic splitting of a single trap into a double well potential. Applications for quantum information processing are discussed.