Focus evolution of linearly polarized Lorentz beam with sine-azimuthal variation wavefront induced by one on-axis optical vortex

Focus evolution of linearly polarized Lorentz beam with sine-azimuthal variation wavefront induced by one on-axis optical vortex was investigated theoretically in this article. Calculation results show that the focal pattern can be altered considerably by the charge number of on-axis optical vortex under condition of certain beam parameters and phase parameter that indicates the sine phase change frequency on increasing azimuthal angle. And the focal evolution principle differs remarkably for different beam parameters and the phase parameter. In focus evolution process, some novel focal patterns appear, including annular focal pattern, two-peak focal pattern, intensity lines, hexagon containing two peaks, swallowtail shape, multipede shape, and complex focal pattern. Introduction of optical vortex adds one controllable parameter to alter focal pattern, which may extend application of Lorentz beam in some focusing systems.     

Propagation of Gaussian background vortex beams diffracted at a half-plane screen

Taking the Gaussian background vortex beam with topological charge +2 as a typical example, a closed-form expression for vortex Gaussian beams passing through a half-plane screen is derived and used to study the propagation dynamics of on-axis and off-axis vortex diffracted beams, and to compare with the case of the free-space propagation. It is shown that there may exist many phase singularities or no phase singularity of vortex diffracted Gaussian beams in the diffraction field. Number and position of phase singularities are dependent on the vortex position at the source plane and propagation distance. The creation, motion and annihilation of phase singularities in the diffraction field may appear by varying the vortex position and propagation distance.     

椭圆涡旋光束在海洋湍流中的传输特性

本文采用分步相位屏方法来仿真椭圆涡旋光束在海洋中的实际传输情况,并对椭圆涡旋光束在海洋湍流中的传输光强和闪烁因子进行了仿真。研究发现,椭圆涡旋光束在海洋传输过程中,光斑会发生明显的旋转,同时光斑会产生暗核且暗核个数与光束的拓扑荷数相等。一个拓扑荷数为m的相位奇点会分裂成m个拓扑荷数为1的相位奇点,并且海洋湍流越强,光斑受到的干扰越严重。研究还发现,在较弱的海洋湍流中,随着传输距离的增加,椭圆涡旋光束的闪烁因子会低于高斯光束和涡旋光束的闪烁因子,而且在远距离处拓扑荷数越大闪烁因子降低越明显,同时也发现,传播一段距离后涡旋光束的闪烁因子会低于高斯光束的闪烁因子。在较强湍流中,椭圆涡旋光束的闪烁因子会交叠在一起。对于不同强度的海洋湍流,随着均方温度耗散率的增大,椭圆涡旋光束的轴上点闪烁因子也增大。在同一传输距离处,束腰宽度越小的椭圆涡旋光束闪烁因子越小。     

Observed scattering into a dark optical vortex core

The dark core of an optical vortex was used to detect on-axis, forward-scattered light from a colloidal solution in the single and multiple scattering regimes. Using no adjustable parameters we obtain good agreement with a concentration-dependent scattering model.     

Radially polarized hollow Gaussian beam with on-axis spiral optical vortex

The focusing properties of radially polarized hollow Gaussian beam (HGB) with on-axis spiral optical vortex are investigated theoretically by vector diffraction theory. The phase wavefront of HGB is the function of radial coordinate. Calculation results show that the focusing properties can be altered considerably by beam order of HGB, topological charge of the on-axis optical vortex, and phase parameter that characterizes the radial phase wavefront distribution. Higher topological charge induces focal evolution from one focal spot to annular focal pattern in transverse direction, while phase parameter can lead to focal shift along optical axis remarkably. In addition, focal shift direction can also be adjusted by changing varying direction of phase parameter.     

Dynamic Optical Vortex Trajectory Guided by the Symmetric Pearcey Gaussian Vortex Beam in the Uniformly Moving Parabolic Potential

This paper analytically and numerically proposes the propagation dynamics of the symmetric Pearcey Gaussian vortex beam (SPGVB) in the uniformly moving parabolic potential. The optical vortex located in the initial plane produces a vortex channel in the presence of the uniformly moving parabolic potential, called the vortex trajectory. The vortex trajectory can be manipulated dynamically by configuring different combinations of the parameters, and the optical intensity and the focal position can also be affected. Moreover, the spatial dynamic vortex trajectory is derived analytically, and the 2D on-axis and off-axis vortex scenarios are also presented. Our work expands the methods of the vortex trajectory manipulation and may broaden more practical potential applications in the particle manipulation.     

Tight focusing properties of radially polarized Lorentz–Gaussian beam

Focusing properties of radially polarized Lorentz–Gauss beam with one on-axis optical vortex was investigated by vector diffraction theory. Results show that intensity distribution in the focal region can be altered considerably by charge number of the optical vortex and the beam parameters. Many novel focal patterns may occur, Such as Peak-centered, donut focal shapes which is potentially useful in optical tweezers, material processing and laser printing.     

Vortex-edge dislocation interaction in the presence of an astigmatic lens

The vortex-edge dislocation interaction in the presence of an astigmatic lens is studied both analytically and numerically, where the effect of astigmatism is stressed. It is shown that for the aberration-free case the edge dislocation bending and break up into a pair of oppositely charged vortices and the shift of the initial vortex appear. The astigmatism leads to some richer vortex evolution behavior. By suitably varying the astigmatic coefficient of the lens, the motion, creation, annihilation and shift to infinity of vortices take place. The off-axis distance additionally affects the vortex evolution behavior for the case of the on-axis vortex and off-axis edge dislocation interaction. In the vortex evolution process the total topological charge is not conserved in general.     

The system design and assemble for the high resolution telescope system with segmented aperture

A design method along with its results, for a space optical system with high resolution and wide field of view, is described. Such optical systems can be used in the infrared as well as visible configurations. The proposed design is based on an on-axis Ritchey-Chrétien system with corrected lens element while the primary mirror is a segmented aperture. Here the on-axis concept allows wide-field enabling a variety of observations designed for the multi-object spectrometer instruments, optimized for low scattering and low emission of light. The use of segmented mirrors in the optical system allows adopting any method for its fabrication purposes. Segment results are discussed and the image quality of the design based on these results is evaluated in this paper.     

一种新的纯位相型计算全息图及其应用

本文提出了一种新的制作纯位相型计算全息图的两孔编码方法并用实验加以证实.用本编码法制作的纯位相型计算全息图的特点是:(1)可记录、复现任意的复函数光场;(2)光场在全息图的光轴上再现,空间带宽积大,衍射效率高.     

Interaction of the vortex and edge dislocation embedded in a cosh-Gaussian beam

The interaction of the vortex and edge dislocation embedded in a cosh-Gaussion (ChG) beam is studied, where the both dislocations are on-axis, off-axis, or one is on-(off-) axis. It is shown that by varying a beam parameter of the ChG background beam or in the free-space propagation, the break-up of the edge dislocation and the motion, creation and annihilation of vortices may take place. In the vortex evolution process the topological charge is not conserved in general. The results are illustrated numerically and compared with the previous work.     

Breaking of rotational symmetry in cylindrically bounded 2D electron plasmas and 2D fluids

Off-axis final states of cylindrically bounded 2D fluids can develop from initially unstable, but cylindrically symmetric, 2D vorticity distributions. Experiments with electrons in a Malmberg-Penning trap, as well as 2D fluid simulations, demonstrated that such states result when the initial vorticity distribution is close to the boundary, while less extended distributions lead to on-axis states. A simple thermodynamic model, maximizing the entropy of a state consisting of a diffuse background surrounding a strong coherent vortex, is shown to quantitatively predict this bifurcation, while conserving circulation, angular momentum, and energy.     

使用离焦望远镜系统合成轴上平顶光束的一种新方法

提出了用平顶多高斯光束作为理想光束和使用离焦望远镜系统合成轴上平顶光束的一种新方法.在近轴近似下,基于柯林斯衍射积分公式推导出轴上光场和入射光场的解析表达式,并做了物理分析.光束阶数N,平顶长度参数L,平顶中心位置z_c和纵向中心空间频率S_c对轴上光强分布的影响用数值计算例做了说明.比较表明,该方法优于文献中使用矩形函数模拟理想光束合成轴上平顶光束的方法. 关键词： 轴上平顶光束 平顶多高斯光束 离焦望远镜系统 傅里叶变换     

多色部分相干偏心光束在non-Kolmogorov湍流中的传输

推导了多色部分相干偏心光束在non-Kolmogorov 湍流中传输的总光强、轴上光谱、相干度的解析表达式, 研究了光束偏心参数β 、湍流广义指数α和源光谱带宽Ω对激光传输特性的影响. 研究表明: β越大, 则光束重心偏离传输轴越远, 相干度的不对称性越明显, 但是, β对轴上光谱几乎没有影响; 湍流广义指数α对总光强、 轴上光谱和相干长度的影响是非单调的, 当α=3.1时, 湍流对光束传输特性的影响最大. 值得指出的是: 在某些传输距离处, 不同α对应的轴上光谱位移量相同; 在某些传输距离处, 轴上光谱位移量为零, 且该传输距离与Ω无关, 但湍流使得该传输距离缩短. 所得结论对多色部分相干偏心光束在 湍流大气中传输的相关应用具有重要意义. 关键词： non-Kolmogorov湍流 多色部分相干偏心光束 光谱强度 相干度     

Effect of spherical aberration on scintillations of Gaussian beams in atmospheric turbulence

The effect of spherical aberration on scintillations of Gaussian beams in weak, moderate and strong turbulence is studied using numerical simulation method. It is found that the effect of the negative spherical aberration on the on-axis scintillation index is quite different from that of the positive spherical aberration. In weak turbulence, the positive spherical aberration results in a decrease of the on-axis scintillation index on propagation, but the negative spherical aberration results in an increase of the on-axis scintillation index when the propagation distance is not large. In particular, in weak turbulence the negative spherical aberration may cause peaks of the on-axis scintillation index, and the peaks disappear in moderate and strong turbulence, which is explained in physics. The strong turbulence leads to less discrepancy among scintillations of Gaussian beams with and without spherical aberration.     

部分相干平顶光束在梯度折射率介质中的传输特性

利用广义惠更斯-菲涅尔衍射积分方法,推导出部分相干平顶光束在梯度折射率介质中传输的交叉谱密度函数解析表达式,对部分相干平顶光束在梯度折射率介质中的传输特性进行了分析,并进一步讨论了介质梯度折射率系数、光束阶数以及光束相干性对传输特性的影响.结果表明,部分相干平顶光束在梯度折射率介质中传输时的轴上光强分布呈现周期性变化了,且周期由梯度折射率系数决定,而与光束相干性无关.光束阶数越高、相干性越好、介质梯度折射率系数越大,则在介质中的轴上峰值光强越大.并且,在光强峰值位置附近的光强分布随传输距离的变化非常剧烈.     

高斯涡旋光束的光束传输因子和峭度参数

基于强度二阶矩定义, 导出了高斯涡旋光束光束传输因子即M² 因子的解析表达式, 高斯涡旋光束的M² 因子唯一取决于拓扑电荷数n. 数值计算表明, 高斯涡旋光束的M² 因子随着拓扑电荷数n的增大而增大. 基于强度高阶矩, 还导出了高斯涡旋光束经傍轴ABCD光学系统传输时峭度参数的解析表达式, 高斯涡旋光束的峭度参数取决于拓扑电荷数n、参数δ、矩阵元A和矩阵元D. 在自由空间传输时, 高斯涡旋光束的峭度参数仅取决于拓扑电荷数n和参数δ. 自由空间传输时, 高斯涡旋光束峭度参数的变化规律为: 峭度参数随参数δ的增大先减小而后趋向于一最小值, 随拓扑电荷数n的增大而减小. 这一研究有助于高斯涡旋光束的实际应用.     

Desorption/ionization of acrylamide in aqueous solutions in atmospheric pressure air using a microdischarge with vortex focusing of ions

A method of desorption/ionization in a microdischarge with ion vortex focusing (vortex focusing microdischarge, VFM) is suggested. A glow microdischarge is initiated in an air flow, and resulting ions act on the surface of interest. As a model compound, an aqueous solution of acrylamide is taken. Desorption/ionization taking place under atmospheric pressure is followed by the mass-spectrometric identification of the ions. The operating parameters of the VFM system are studied and optimized. Upon optimization of the system, the detection limit of acrylamide trace amounts in aqueous solutions is determined using the suggested method of desorption/ionization and analyte ion focusing with a vortex (swirling) jet. The acrylamide detection limit is found to be 2 × 10^?3 g/L.     

A clustering-based approach to vortex extraction

Since vortex is an important flow structure and has significant influence on numerous industrial applications, vortex extraction is always a research hotspot in flow visualization. This paper presents a novel vortex extraction method by employing a machine learning clustering algorithm to identify and locate vortical structures in complex flow fields. Specifically, the proposed approach firstly chooses an objective, physically based metric that describes the vortex-like behavior of intricate flow and then normalizes the metric for applying on different flow fields. After that, it performs the clustering on normalized metric to automatically determine vortex regions. Our method requires relatively few flow variables as inputs, making it suitable for vortex extraction in large-scale datasets. Moreover, this approach detects all vortices in the flow simultaneously, thereby showing great potential for automated vortex tracking. Extensive experimental results demonstrate the efficiency and accuracy of our proposed method in comparison with existing approaches.     

Intensity distribution around the focal regions of real axicons

We present a theoretical and experimental study of the intensity distribution of a laser beam, after its propagation through a real axicon. We show that, while an ideal axicon generates Bessel-like radial intensity profile and smooth on-axis intensity around the focal region, in practice, the bluntness of the tip of the axicon causes significant deviations from these profiles. In particular, strong oscillations occur on the on-axis intensity. The input beam size also plays a strong role; for small beams the axicon acts more like a conventional lens, while for the large ones, it exhibits two focal regions. We also propose scheme for apodization. In all cases, the experiments match closely with the calculations. Our results show that axicons cannot be assumed to always generate smooth on-axis intensities and the structures coming from the real profiles should be taken into account for most applications.