三环非均匀混合偏振同轴矢量光束的聚焦特性

基于Richards-Wolf矢量衍射积分公式,数值分析了同轴三环非均匀混合偏振矢量光束经过高数值孔径透镜的聚焦特性。该矢量光束由同轴三环局域线偏振矢量光束通过一个相位延迟角为δ的液晶相位延迟器产生,光束偏振变为包含线偏振、圆偏振和椭圆偏振的混合态。同轴三环局域线偏振矢量光束的偏振分布是由径向向内偏振的外环光束、径向向外偏振的内环光束和线偏振方向与径向方向夹角为φ2的中环光束构成。数值模拟结果显示该混合偏振矢量光束的聚焦强度分布与参数φ2和相位延迟角δ密切相关,当选取适当的φ2和δ时,在焦平面附近产生沿光轴方向的三维多点光俘获结构——暗光链,这在光学微操纵领域具有潜在的应用价值。     

离轴矢量光束的紧聚焦特性

基于理查德-沃尔夫矢量衍射积分理论,数值研究了离轴矢量光束经过高数值孔径透镜后的紧聚焦特性.通过对比分析偏振奇点离轴的径向、角向矢量光束紧聚焦后,焦点附近的强度和相位分布规律,提出了一种由广义柱矢量光束设计紧聚焦场的方法.此外,通过分析矢量光束自旋分量的聚焦行为和自旋轨道耦合所诱导的自旋角动量分布变化,讨论了偏振奇点离轴对称破缺对高阶矢量光束紧聚焦场空间结构,特别是其自旋角动量空间分布的影响.该研究结果不仅对矢量光场的紧聚焦特性进行了补充,也为改进和完善焦场分布提供了理论参考.     

LCVR和AOTF的光谱偏振测量新策略

现有利用液晶相位可变延迟器(LCVR)和声光可调谐滤光器(AOTF)的偏振测量方法较为繁琐,故提出了一种光谱偏振测量新策略,去除了机械运动,并且相位延迟量的选取从四组减少为两组。采用两个LCVR和一个AOTF,通过两个相同型号探测器分别测量±1级衍射光,实现光谱偏振测量。电脑控制LCVR和AOTF的驱动系统分别实现所需相位延迟量和波长选择,通过扫描射频驱动整个频段得到被测光的光谱信息。叙述了方法的具体原理,分析了AOTF的偏振模型,通过理论计算LCVR和AOTF的Muller矩阵,推导出了相应的斯托克斯(Stokes)矢量中的I,Q,U的测量公式。分析并仿真了相位延迟量微小偏差对整个系统测量误差的影响,结果显示相位延迟量在±π/100范围内相对误差<3%。实验验证了测量系统的可行性和准确性,测量误差总体<6%。为偏振测量提供了一种简单可行且精度较高的新方法,具有重要的应用价值。     

轴对称矢量光束聚焦特性研究现状及其应用

轴对称矢量光束是一种空间非均匀偏振光束, 中心光强为零, 经物镜聚焦后能在焦点附近产生空间场分量. 在高变迹系数光学系统成像情况下, 与线偏光、圆偏光相比, 径向偏振光与光瞳滤波技术及图像复原技术结合, 能获得较小焦斑, 提高横向分辨力. 介绍了轴对称矢量光束的特性, 基于电偶极子辐射模型和矢量衍射理论研究了轴对称矢量光束经高数值孔径物镜聚焦后的特性, 系统介绍了基于轴对称矢量光束实现光斑紧聚焦的几种方法, 并简述了轴对称矢量光束在差动共焦超分辨成像领域的研究设想. 关键词： 差动共焦显微技术 紧聚焦 光瞳滤波 轴对称矢量光束     

基于Pancharatnam-Berry相位调控产生混合偏振矢量光束

提出了一种基于Pancharatnam-Berry(PB)相位调控产生混合偏振矢量光束的方法.按照光轴随空间坐标变化的规律,用相位延迟为π的PB相位元件对PB相位进行操控,获得局域偏振为线偏振的矢量光束,将此矢量光束入射到四分之一波片,产生混合偏振矢量光束.通过测定斯托克斯参数重构输出光场的偏振分布,实验结果表明:当以θ0=0的线偏振光入射时,输出光场包含庞加莱球上垂直于S3轴经线圆上所有偏振态的混合矢量光场;当以θ0=π/2的线偏振光入射时,输出光场包含庞加莱球上垂直于S1轴经线圆上所有偏振态的混合矢量光场.     

角向偏振涡旋光的紧聚焦特性研究以及超长超分辨光针的实现

系统研究了角向矢量涡旋光的紧聚焦焦斑特性,解释了焦平面自旋角动量局域化分布的形成原因.角向矢量涡旋光可分解为左、右旋圆偏振电场叠加,将分解所得的左、右旋分量分别经大数值孔径透镜聚焦,总聚焦电场可视为左、右旋分量聚焦电场的干涉叠加.经分析研究后发现,左、右旋分量各自聚焦电场的纵向分量大小相等、相位相反,完全干涉相消,使得总聚焦电场的纵向分量消失;而各自聚焦电场的横向分量则完全相反,几乎不发生干涉,总聚焦电场表现为非相干叠加.角向偏振光引入涡旋相位后,使得左、右旋电场分量的轨道角动量的拓扑荷数发生变化,拓扑荷数的绝对值不再相等,而是恒定差值为2.因此左、右旋电场的横向分量由于携带不同的拓扑荷数,分别聚在焦平面的不同位置,而横向分量发生非相干叠加,不相互影响,最终形成了总电场偏振态的局域化分布,即自旋角动量局域化分布的现象.随后,本文横向对比了1阶角向矢量涡旋光和径向偏振矢量光的超分辨焦斑特性,分析了各自的优、缺点以及影响焦斑尺寸的因素.最后,兼顾了超分辨光针的性能和实际实现难度,设计了6环带的二元相位板对1阶角向矢量涡旋光进行了波前调制,实现了横向半高全宽为0.391λ,纵向半高全宽为25...     

矢量光束空间偏振编码的研究

矢量光束独特的空间偏振结构使之应用于空间偏振编码成为可能。提出了一种用一阶矢量光束的偏振分布进行极角空间编码的方法。通过矢量光束生成、光束偏振分布再调制实现了空间编码光束的生成,并采用斯托克斯参数法对空间编码光束进行检测。实验结果证实了一阶矢量光束应用于极角空间偏振编码的可行性,为基于空间偏振编码的激光驾束制导提供了新方法。     

4pi聚焦系统中振幅和相位调制的径向偏振涡旋光束聚焦特性的研究

基于Richards-Wolf矢量衍射积分公式, 研究了径向偏振涡旋光束在振幅和相位调制下的4pi聚焦特性.振幅调制是通过振幅滤波实现, 即改变入射光束起始积分值达到调节,相位调制是通过添加相位延迟角δ 的液晶相位延迟器来改变入射光束的偏振态.模拟结果显示,随着振幅的减小, 4pi聚焦系统焦点附近的光轴上呈现出多光球结构; 而相位调制对焦点附近的光强分布产生拉伸作用, 即调节入射光束的拓扑核m和相位延迟器的延迟角δ,可以得到特殊的光强分布. 随着相位δ增大, m=0产生的多光球结构慢慢向光链结构转变,最终变成暗通道;而m=1产生的光链结构慢慢变成光球结构; m=2产生的暗通道变成光球和光链叠加的结构, 这种特殊聚焦光束在光学微操纵领域具有潜在的应用价值. 关键词： 物理光学 偏振 光链 4pi聚焦系统     

径向偏振高阶贝塞尔-高斯涡旋光束的传输及其偏振特性

理论和实验研究了径向偏振高阶贝塞尔-高斯涡旋光束在自由空间传输的光强分布和偏振特性.数值计算表明,在无衍射区域,随着传输距离的增加,光强分布基本保持不变;对于零阶光束,其偏振态一直保持径向偏振不变;对于高阶光束,其偏振态发生变化,由初始的径向偏振逐渐变为椭圆偏振和线偏振的杂化状态.实验上,利用径向偏振转换器、螺旋相位板和轴棱锥元件产生了径向偏振高阶贝塞尔-高斯涡旋光束,探测了其通过不同偏振片后的光强分布.实验结果与理论结果基本相符合.该研究也提供了一种产生杂化偏振矢量光束的方法.     

聚焦径向调制Bessel-Gaussian光束实现亚波长尺寸纵向偏振光束

亚波长尺寸纵向偏振光束在粒子加速,单个分子偶极矩测量,二次谐波成像和纵向偏振共焦显微镜等方面有非常广泛的应用.本文提出径向调制的Bessel-Gaussian光束模型,经高数值孔径显微物镜聚焦可以获得高纯度的纵向偏振光束.利用矢量衍射理论数值模拟了焦点附近光强分布、磁场分布和能流密度空间分布.结果表明光斑半高全宽度可以达到0.4λ.该方法无需环形孔径或环形相位滤波器,光能利用率高,分辨率好,达到改进各种应用的效果. 关键词： Bessel-Gaussian光束 纵向偏振光束 聚焦 亚波长     

Focal shift of three-portion concentric piecewise cylindrical vector beam

Focal shift of a concentric piecewise cylindrical vector beam is investigated by means of vector diffractive theory. A section of the beam consists of three concentric portions. The center circle portion and outer annular portion are radial polarized, and the inner annular portion is generalized polarized. The phase of the inner annular portion is tunable. For certain geometric parameters of the beam, the focal shift occurs and can be adjusted by phase shift and polarized direction of the inner annular portion. For some cases, a three-peak focal pattern may occur, and peaks shift in the same direction, and one local minimum also shifts. For some other cases, a two-peak focal pattern may occur with shifting peaks. The tunable quantitative focal shift is investigated in detail.     

相位板偏振偏转角对径向偏振光的梯度力分布的影响

 研究了同心分区偏振偏转相位板对径向偏振光梯度力的调制效应。给出了相位板各部分偏振偏转角不同时,光学梯度力的分布情况。模拟结果表明:随着同心分区相位板各部分的半径和偏振旋转角的改变,光学梯度力方向及大小明显变化,且会产生许多可控的梯度力分布模式,可应用于微粒的收集、分离和合并。结果显示同心分区相位板对径向偏振光的调制可以用来生成可调光镊。     

Focal shift in radially polarized beam with high NA lens axicon by using radial cosine phase wavefront

Focal shift in radially polarized beam with radial cosine phase wavefront are investigated theoretically by vector diffraction theory. The wavefront phase distribution is cosine function of radial coordinate. Simulation results show that when the radially polarized beam with radial cosine wavefront phase is focused, the focal pattern differs considerably with frequency parameter in the cosine function term. On increasing C, focus can shift along optical axis and focal pattern changes remarkably. Focus may move in different direction under different condition. Focal shift distance fluctuates on increasing C, and fluctuation amplitude also increases simultaneously. In addition, focal shift direction can also be adjusted by changing frequency parameter in cosine function.     

Concentric piecewise azimuthally polarized beam by a pure phase plate

Focusing properties of the azimuthally polarized beam induced by a pure phase plate are investigated theoretically. The pure phase plate consists of two concentric portions, one center circle portion and one outer annular portion, through which the azimuthally polarized beam passed evolves into concentric piecewise azimuthally polarized beam. When the phase shift of the center portion is π, one ring focus may evolve into novel focal patterns with increasing radius of the center circle portion, such as cylindrical crust focus, two-ring focus, and three-ring focus. And if the geometrical parameters are unchanged, focal patterns also changes considerably with tunable phase of the center portion. Ring focus shifts along the optical axis on the increasing phase. Some optical gradient force distributions and dependence of focal shift on phase shift are also illustrated. This kind of concentric piecewise azimuthally polarized beam can be used in optical manipulation technology.     

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.     

Focal shifting of transversely polarized beam using cosine phase plate

Focal shift of transversely polarized beams induced by cosine phase masks are investigated theoretically by vector diffraction theory. Results show that when the transversely polarized beam with radial cosine wavefront phase is focused, the focal pattern differs considerably with frequency parameter in the cosine function term. Increasing the value of frequency parameter in the cosine part of the phase mask, focal shift may occur, simultaneously, the focal shift direction may change. Moreover, by altering frequency parameter or phase variation parameter of the phase mask will change the energy distributions of maximum intensity peak and other small intensity peaks. And novel focal patterns also evolve considerably, such as from only one peak to five of multiple peaks. The tunable focal shift can be used to construct controllable optical tweezers.     

Focal shift in radially polarized hollow Gaussian beam

Focal shift in radially polarized hollow Gaussian beam (HGB) with radial wavefront distribution is investigated theoretically. The wavefront phase distribution is cosine function of radial coordinate. Simulation results show that the intensity distribution in focal region of the radially polarized HGB can be adjusted considerably by the beam order of HGB n and cosine parameter C that indicates the phase change degree. On increasing C, focus can shift along optical axis and focal pattern changes remarkably. Focus may move in different direction under different condition. Focal shift distance fluctuates on increasing C, and fluctuation amplitude also increases simultaneously. In addition, threshold value of C for focal shift from one side to the other side of the paraxial focal plane differs for different n.     

Focusing of radially polarized beam with radial cosine phase wavefront

Radially polarized beam has gained much interest recently due to its properties and applications. In this article, the focusing properties of radially polarized beam with radial cosine phase wavefront are investigated theoretically. Results show that when the radially polarized beam with radial cosine wavefront phase is focused, the focal pattern differs considerably with frequency parameter in the cosine function term. In the high numerical aperture focusing system, focal shift occurs, and novel focal patterns evolve considerably, for instance, from only one peak to two or multiple overlapping peaks. In addition, peak intensity ratio of radially polarized component to longitudinal polarized component in the focal region fluctuates smoothly for low-frequency parameter, then drops sharply, and comes back remarkably with increasing frequency parameter. Simultaneously focal shift increases slowly, and then decreases, suddenly, focal shift sign changes that results from focal switch phenomenon, and then fluctuates.     

Tight Focusing Properties of Radially Polarized Gaussian Beams with Pair of Vortices

The tight focusing properties of a radially polarized Gaussian beam with a nested pair of vortices having a radial wave front distribution are investigated theoretically by the vector diffraction theory.The results show that the optical intensity in the focal region can be altered considerably by changing the location of the vortices nested in a radially polarized Gaussian beam.It is noted that focal evolution from one annular focal pattern to a highly confined focal spot in the transverse direction is observed corresponding to the change in the location of the optical vortices in the input plane.It is also observed that the generated focal hole or spot lead to a focal shift along the optical axis remarkably under proper radial phase modulation.Hence the proposed system may be applied to construct tunable optical traps for both high and low refractive index particles.     

Focusing properties of spirally polarized hollow Gaussian beam

Focusing properties of spirally polarized hollow Gaussian beam (HGB) are investigated theoretically by vector diffraction theory in this article. Results show that the optical intensity in focal region of spirally polarized HGB can be altered considerably by the beam order, numerical aperture of the focusing system, and spiral parameter that indicates the polarization spiral degree of the spirally polarized HGB. Spiral parameter can induce focal pattern change in axial direction remarkably, while beam order and numerical aperture affect radial foal pattern more obviously. The tunable principle of the focal pattern by spiral parameter differs very considerably under condition of different numerical aperture and beam order. Many novel focal patterns may occur in focal pattern evolution. It was also found that focal shift and focal depth can be altered significantly by spiral parameter and beam order.