高效产生任意矢量光场的一种方法

提出一种高效产生任意矢量光场的方法.利用两个光束偏移器分别对两个正交线偏振分量进行分束与合束,将传统激光模式转化为任意矢量光场.所产生矢量光场的偏振态和相位分布通过相位型空间光调制器(SLM)加载相应的相位实时调控.由于光路系统中不涉及任何衍射光学元件和振幅分光元件,光场转换效率高,仅取决于SLM的反射率,并且光路系统结构紧凑、稳定,同轴性易于调节.实验结果显示,采用反射率为79%的相位型SLM产生矢量光场的转换效率可达到58%.     

紧聚焦轴对称矢量光场波前调控及应用

作为光波最重要的本征物理属性之一,光场偏振态在研究光与物质相互作用中占有重要地位。矢量光场的波前调控为其聚焦场提供了更加复杂、更加灵活可控的振幅、相位以及偏振态分布,丰富了光与物质相互作用的手段,为材料表征提供了传统线偏振、圆偏振光场所不可替代的研究方法,具有重要的物理意义和实际应用价值。本文将综述矢量光场最新的研究进展,详细介绍矢量光场的偏振态特性、产生方法,以及紧聚焦轴对称矢量光场波前调控在远场小尺度光斑的产生、磁光记录、单分子/颗粒取向探测、任意三维偏振态的产生、高密度数据存储、信息加密以及矢量光场波前重构等方面的重要应用。     

Mapping phases of singular scalar light fields

We implement experimentally a simple method for accurate measurements of phase distributions of scalar light fields. The method is based on the polarimetric technique for recording the polarization maps of vector fields, where coaxial superposition of orthogonally polarized reference and signal beams allows the signal phase to be reconstructed from the polarization map of the total field. We demonstrate this method by resolving topologically neutral pairs of closely positioned vortices in a speckle field and recovering the positions of vortices within a Laguerre-Gaussian beam with the topological charge three.     

基于光学全息的任意矢量光的生成方法

基于光学全息的角度复用特性, 根据空间光调制器对光场的相位和振幅调制原理, 通过加载产生任意矢量光所需要的相位分布, 设计了一种生成任意矢量光的方法. 该方法首先利用光学全息技术记录空间光调制器加载的相位, 从而制作一个全息光栅; 再现过程中, 两束具有相同入射角度的参考光照射全息光栅, 使得两束再现光相干叠加, 进而获得可调控的任意矢量光. 该方法能够避免复杂偏振态的出现, 并且具有生成光路简单、方便操作、生成矢量光的偏振纯度高等优势. 通过计算机模拟生成了任意矢量光, 获得了很好的效果.     

柱矢量光束的角动量性质

介绍了非近轴光束的表示理论,利用该表示理论很好地解决了非近轴光束的角动量问题,发现非近轴光束的总角动量可以严格地分解成自旋和轨道两部分,但是两者都依赖于由偏振椭圆度表征的光束的偏振状态。主要研究了柱矢量光束的角动量问题。给出了动量空间和位形空间中的柱矢量光束表达式和角动量算符表达式。通过分析两个空间中的角动量算符及柱矢量光束表达式,发现在这两种空间中,具有螺旋型相位的柱矢量光束是角动量算符沿着传播方向的分量的本征态,其本征值与偏振椭圆度无关,这为计算这类特殊光束的角动量提供了一种新方法。     

Tight focusing of axially symmetric polarized vortex beams

Tight focusing of axially symmetric polarized vortex beams is studied numerically based on vector diffraction theory. The mathematical expressions for the focused fields are derived. Simulation results show that the focused fields and phase distributions at focus are largely influenced by both the polarization order and topological charge of the incident beams. Moreover, focal spots with flat-topped or tightly-focused patterns can be flexibly achieved by carefully choosing the polar- ization order and the topological charge, which confirms the potential of such beams in wide applications, such as optical tweezers, laser printing, lithography, and material processing.     

Blazed vector gratings fabricated using photosensitive polymer liquid crystals and control of polarization diffraction

The blazed vector grating possessing antisymmetric distributions of the birefringence were fabricated by exposing the line-focused linearly polarized ultraviolet light on the photosensitive polymer liquid crystals. The polarization states of the diffraction beams can be highly and widely controlled by designing the blazed structures, and the diffraction properties were well-explained by Jones calculus.     

Shaping of focal field with controllable amplitude,phase, and polarization

We propose a method for configuring the distribution of amplitude, phase, and polarization in the focal region of vector beams. The polarization and phase of incident beam is spatially tailored so that it can produce a focal field that has elaborately prescribed shapes. Our work focuses on the design of a special focus structure with two oval rings, wherein a phase gradient and polarization gradient exist in the inner and outer rings, respectively. The incident light yielding the desired focal field is determined based on an iterative scheme involving vectorial diffraction calculations and fast Fourier transforms. Simulations and experiments demonstrate the generation of a focal field with phase and polarization gradients, which may find applications in optical manipulation.     

A method for generating double-ring-shaped vector beams

We propose a method for generating double-ring-shaped vector beams. A step phase introduced by a spatial light modulator(SLM) first makes the incident laser beam have a nodal cycle. This phase is dynamic in nature because it depends on the optical length. Then a Pancharatnam–Berry phase(PBP) optical element is used to manipulate the local polarization of the optical field by modulating the geometric phase. The experimental results show that this scheme can effectively create double-ring-shaped vector beams. It provides much greater flexibility to manipulate the phase and polarization by simultaneously modulating the dynamic and the geometric phases.     

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.     

Comparison of three kinds of polarized Bessel vortex beams propagating through uniaxial anisotropic media

A comparison of differently polarized Bessel vortex beams propagating through a uniaxial anisotropic slab is discussed in terms of the vector wave function expansions.The magnitude profiles of electric field components, the transformation of polarization modes, and the distributions of orbital angular momentum(OAM) states of the reflected and transmitted beams for different incident angles are numerically simulated.The results indicate that the magnitude profiles of electric field components for different polarization modes are distinct from each other and have a great dependence on the incident angle,thus the transformation of polarization modes which reflects the change of energy can be affected largely.As compared to the x and circular polarization incidences, the reflected and transmitted beams for the radial polarization incidence suffer the fewest transformation of polarization modes, showing a better energy invariance.The distributions of OAM states of the reflected and transmitted beams for different polarization modes are diverse as well, and the derived OAM states of the transmitted beam for radial polarization present a focusing effect, concentrating on the state between two predominant OAM states.     

Polarization-independent photochromic diffraction in a dye-doped liquid crystal

We report the observation of polarization-independent photochromic diffraction in an azo-dye-doped liquid crystal. The generation of the phase grating is more than 90% independent of the polarization of the writing beams, and the diffraction by the phase grating is more than 90% independent of the polarization of the probe beam. Unpolarized lamp light was also used to generate real-time phase gratings and self-diffraction. For the first time to our knowledge, photochromic phase modulation and light diffraction that exhibit more than 90% polarization independence for both writing and probe beams were produced in an anisotropic liquid-crystalline material.     

Coherent and incoherent polarization encoding of electromagnetic fields

We study a method generating certain distributions of the degree and state of polarization of a light field across a transverse beam cross-section. We use the introduced polarization encoding scheme to study the distribution of polarization ellipses in a cross-section of a beam generated by superposing two encoded beams, the effects of coherence relation between the input beams on this distribution were theoretically analyzed and illustrated by contour plots of the parameters representing polarization ellipses.     

Switchable vector vortex beam generation using an optical fiber

We present our experimental results on directly transforming a circular-polarized Gaussian beam into linear-polarized vector vortex beams using a two-mode fiber and demonstrate switching between the different 0th-order vector vortex modes excited and guided in the fiber. Depending on the handiness of circular-polarization of the input Gaussian light beam, its launch angle with respect to the fiber axis and by changing them appropriately it is possible to excite and switch between the different vector vortex modes and its coherent linear superposition supported by the two-mode fiber. The output optical beams due to the selectively excited vector modes in the fiber are characterized by using a rotating analyzer and a two-beam interferometer setup to study the polarization and the phase behavior of the vector vortex beam.     

Topological defects, geometric phases, and the angular momentum of light

Recent reports on the intriguing features of vector vortex bearing beams are analyzed using geometric phases in optics. It is argued that the spin redirection phase induced circular birefringence is the origin of topological phase singularities arising in the inhomogeneous polarization patterns. A unified picture of recent results is presented based on this proposition. Orbital angular momentum (OAM) shift within the light beam has exact equivalence with the angular momentum holonomy associated with the geometric phase consistent with our conjecture.     

紧聚焦条件下相干反斯托克斯拉曼散射信号场的矢量分析

在相干反斯托克斯拉曼散射(coherent anti-Stokes Raman scattering,CARS)显微镜中,共线传输的紧聚焦高斯光束激发具有不同形状和尺寸的待测样品所产生的CARS信号场的空间分布决定了整体系统的结构特点.建立了紧聚焦条件下球形样品产生CARS信号场的理论模型.利用矢量波动方程分析了紧聚焦条件下线偏振的高斯光束的光场强度和相位分布.利用格林函数求解该模型中CARS信号场的矢量波动方程,模拟计算得到了不同直径球形样品的远场CARS信号场的空间分布.理论分析和模拟计算结果表明,对于小体积的球形样品,前向和背向传输的CARS信号场强度接近,因此采用大数值孔径物镜背向探测方式即可获得高对比度图像.对于大体积球形样品,CARS信号场的强度大幅增强,且发射方向主要集中在前向的一定立体角内.因此,采用小数值孔径物镜即可有效收集前向传输的CARS信号.     

Higher-order Poincaré sphere, stokes parameters, and the angular momentum of light

A higher-order Poincaré sphere and Stokes parameter representation of the higher-order states of polarization of vector vortex beams that includes radial and azimuthal polarized cylindrical vector beams is presented. The higher-order Poincaré sphere is constructed by naturally extending the Jones vector basis of plane wave polarization in terms of optical spin angular momentum to the total optical angular momentum that includes higher dimensional orbital angular momentum. The salient properties of this representation are illustrated by its ability to describe the higher-order modes of optical fiber waveguides, more exotic vector beams, and a higher-order Pancharatnam-Berry geometric phase.     

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。     

基于扭曲向列液晶空间光调制器的矢量光生成

基于扭曲向列型液晶空间光调制器的旋光特性, 根据空间光调制器所加电压和加载相位与旋光角度的对应关系, 设计了可以生成多种涡旋矢量光的通用光路. 利用该原理和光路系统, 在实验上生成了多种携带轴对称相位的矢量光以及图案般复杂的矢量光, 观察和检测了它们的偏振特性, 获得了较好的实验结果. 并且模拟了具有涡旋相位的矢量光的紧聚焦场, 分析了它们的紧聚焦特性. 由于这种生成矢量光的方法光路装置简单、操作容易, 产生矢量光的过程中几乎不损失能量, 并且不存在聚焦过程, 因此在如强激光矢量光束与物质相互作用、激光加速等方面具有重要的应用潜力.