随机电磁涡旋光束的深聚焦特性

基于德拜矢量积分理论,研究了随机电磁涡旋光束经过大数值孔径透镜之后的聚焦特性及透镜的数值孔径、入射光束的偏振度、拓扑荷以及横向相干长度对焦平面附近聚焦光束的光强分布和相干度的影响.结果表明:适当地选择相关参量,可在焦平面上得到椭圆形光斑的光强分布以及平顶光强分布.随机电磁涡旋光束在焦平面上同一点处两个相互垂直分量之间的相干度,不同两点处两个相同分量之间的相干度以及不同两点处两个相互垂直分量之间的相干度研究表明,入射光束的拓扑荷和横向相干长度对聚焦光束的相干性有着十分明显的影响.     

Bessel beams: Effects of polarization

An approximation to a Bessel beam produced by tightly focusing linearly polarized light is known to produce a smaller central lobe than focusing plane polarized light. This is because the plane polarized wave gives a broad central lobe caused mainly by a parasitic longitudinal field component. It is known that this problem can be overcome by focusing radially polarized light. Here we demonstrate that other polarization distributions based on a linear combination of transverse electric (TE1) and transverse magnetic (TM1) fields can give a beam even narrower than for the radially polarized case. Special cases of this combination are identified, corresponding to the smallest width (TE1), and the maximum peak intensity compared with the side lobes (electric dipole polarization). Axially-symmetric forms can be generated by illumination with elliptically polarized light. A particular case is azimuthal polarization with a phase singularity, which is equivalent to TE1. For a semi-angular aperture of 60°, the TE1 case gives a central lobe width 9% narrower than for radially polarized illumination, while for plane polarized illumination it is 12% wider than the radially polarized case.     

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     

The focus of light – theoretical calculation and experimental tomographic reconstruction

We present numerical calculations on the field distribution in the focus of an optical system with high numerical aperture. The diffraction integrals which are based on the Debye approximation are derived and evaluated for a radially polarized input field with a doughnut-shaped intensity distribution. It is shown that this mode focusses down to a spot size significantly smaller as compared to the case of linear polarization. An experimental setup to measure the three-dimensional intensity distribution in the focal region is presented, which is based on the knife-edge method and on tomographic reconstruction. Received: 14 July 2000 / Published online: 30 November 2000     

Sharper focus for a radially polarized light beam

We experimentally demonstrate for the first time that a radially polarized field can be focused to a spot size significantly smaller [0.16(1)lambda(2)] than for linear polarization (0.26lambda(2)). The effect of the vector properties of light is shown by a comparison of the focal intensity distribution for radially and azimuthally polarized input fields. For strong focusing, a radially polarized field leads to a longitudinal electric field component at the focus which is sharp and centered at the optical axis. The relative contribution of this component is enhanced by using an annular aperture.     

平面波照射下无限大导体板上周期孔阵屏蔽效能的解析研究

本文针对平面电磁波对无限大导体平板上周期孔阵的透射问题,首先用Bethe小孔理论将孔阵表示成偶极子阵列,然后用平均化处理得到均匀的等效磁化/极化强度,进而引入等效面源导出透射电磁波表达式,最终给出了孔阵对平面电磁波屏蔽效能的解析公式.该公式分别针对横电和横磁两种极化方式,将屏蔽效能表示成孔阵周期面积、孔的极化系数、波长和入射角的简单函数,其计算结果与全波仿真结果一致性好.结果表明,透射场强的幅值与孔极化系数和波频率成正比,与周期面积成反比;在横电极化方式,波频率和周期面积不变的情况下,透射场强的幅值与入射角的余弦值成正比,入射角越大屏蔽效能越高;在横磁极化方式下,透射场强幅值与入射角的关系相对复杂,但在入射角较小时与入射角的余弦值近似成反比,总体上入射角越大屏蔽效果越低.     

The focusing property of vector Bessel-Gauss beams by a high numerical aperture objective

The rich available transverse intensity structure of vector Bessel-Gauss beams make it important to probe into the focusing property by high numerical aperture objective. In this paper, we obtain the analytical expressions of azimuthally, radially and longitudinally polarized components in the focal area of the objective after tight focusing. Theoretical analysis and the numerical simulation show that, the transverse intensity distributions of the focused beams still have doughnut-like structure, two separate peak structure and circularly aligned array structure. The focused beam spots obtained by an objective with annular aperture usually have smaller spots than with circular aperture. The focused beam of the vector Bessel-Gauss beam with lowest mode number m = 0 is a radially and azimuthally polarized doughnut-like beam with no longitudinal component. These properties and results are useful in optical trapping and particle alignment.     

聚焦高斯涡旋光束焦区电场和磁场的偏振奇点

以高斯涡旋光束为例,研究了聚焦场中电场和磁场的偏振奇点变化规律.结果表明,高斯涡旋光束经透镜聚焦后,在焦区存在二维和三维电场和磁场的偏振奇点,其位置一般不重合.适当改变与焦面的距离以及光阑截断参数等出现圆偏振奇点的移动、产生和湮没.不同二维和三维电场和磁场圆偏振奇点湮没所对应的各参数临界值不同.在二维电场中,几何焦面上会有V点的产生.     

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     

Effect of polarization on focal depth in high numerical apertures optical systems

The generalized cylindrical vector beam is just a linear combination of radial and azimuthal polarization. For radially polarized light in the focal plane, there are two electric field components, the radial component and z-component whose magnitude increase with the increase of numerical aperture. By contrast, for azimuthally polarized light in the focal plane, there is only one electrical field component in the azimuthal polarization, it is easy to understand the difference between the two polarization effects. In this paper, we demonstrate how this phenomenon can be harnessed to make a properly selected polarization component to achieve high focal depth in high numerical aperture systems. Numerical simulations show that the evolution of the focal shape is very considerable by changing polarization rotation angle of the generalized cylindrical vector beam. And some interesting focal spots and focal split may occur. And if the ratio of radial and azimuthal polarization is set properly by changing the polarization rotation angle, a largest focal depth is achieved. The tunable range of the focal depth is very considerable. The ratio of radial and azimuthal polarization is different in different NA optical system for obtaining the largest focal depth. We will denote a technique of polarization-assisted high focal depth in high numerical aperture systems.     

慧差对线偏振贝塞耳-高斯光束聚焦场的影响

利用Richards-Wolf矢量衍射积分公式,获得线偏振贝塞耳-高斯光束经具有初级慧差的高数值孔径系统聚焦后的三维光场复振幅函数,根据复振幅函数模拟了不同慧差系数下线偏振贝塞耳-高斯光束各分量及总光场在焦平面上的光强分布模式。研究结果表明,初级慧差使线偏振贝塞耳-高斯光束聚焦光场在焦平面的分布由双轴对称变成单轴对称,光强模式发生改变;各分量及总光场的光强模式中的光斑位置随初级慧差系数的增大偏离光轴;大的初级慧差使焦平面出现干涉条纹。     

三环位相型光瞳滤波器的横向超分辨与轴向焦深扩展

用矢量衍射方法分析了线偏振光入射到带有三环位相型光瞳滤波器的高数值孔径物镜时,焦点的轴向和横向光强分布.数值模拟结果表明,高数值孔径物镜聚焦时需同时考虑光强的轴向和横向分布.通过加入三环位相光瞳滤波器,在实现横向超分辨的同时实现了光学系统轴向焦深扩展和轴向光强分布平坦化,并且位相调制深度变化时,会出现轴向焦移现象.对三环位相光瞳滤波器结构进行了优化,得出了优化结果. 关键词： 光学超分辨 扩展焦深 位相型光瞳滤波器 矢量衍射方法     

Focusing of linearly-, and circularly polarized Gaussian background vortex beams by a high numerical aperture system afflicted with third-order astigmatism

Effects of third-order astigmatism on the focused structure of linearly and circularly polarized Laguerre-Gaussian beams have been investigated by using vectorial Debye-Wolf integral. The results have been presented for total intensity distribution and squares of the polarization components at the focal plane of a high numerical aperture system, for two values of the topological charge. Astigmatism results in the stretching of the intensity pattern as well as of the squares of the polarization components. A split is observed in the intensity pattern of a focused beam having double topological charge, and also in the pattern of the longitudinal polarization component of circularly polarized beam even with unit topological charge.     

Tight focusing of J0-correlated Gaussian Schell-model beam through high numerical aperture

Based on the vectorial Debye diffraction theory, the tight focusing of a linearly polarized J₀-correlated Gaussian Schell-model (JGSM) beam through high numerical aperture (NA) is investigated. The components of intensity distributions as well as the 3D degree of polarization of light at the focal plane are depicted by numerical integrations, respectively. It is shown that intensity distributions as well as the degree of polarization of focused field not only strongly depend on the global correlation length of the JGSM beam but also relate to the focusing parameter of NA. It is also indicated that the weight of the longitudinal intensity component would enhance in the focal plane, as long as either the correlation length of the JGSM beam or the focusing parameter of NA increases.     

J0相干角向偏振涡旋光束的深聚焦

通过矢量德拜理论,研究了J0相干角向偏振涡旋光束深聚焦的性质。推导了在焦点区域的光强分布、光谱相干度和偏振度的表达式。数值模拟结果表明,光强分布、相干度和偏振度不仅依赖于相干长度和数值孔径最大角,而且依赖于拓扑电荷数。这种光束在焦平面还可获得非常小的焦点和焦洞。     

Generation of tightly focused twin Bessel beams using circular Dammann gratings under radial polarization incidence

Generation of longitudinally polarized focusing twin Bessel beams in focal region of a high numerical aperture (NA) objective is described based on circular Dammann gratings for radially polarized Bessel–Gauss input fields. Numerical simulations show that, under focusing of an objective of NA=0.95, the depth of focus (DOF) of the focused twin Bessel beams can reach as long as tens or even ～10² of wavelengths while its average transverse spot over the whole range of the DOF is kept subdiffration-limited. At the same time, the longitudinal polarization purity in focus volume is higher than 90% for the central lobe. Therefore, this tightly focused non-diffracting field should be of great interest for applications in numerous areas, such as particle acceleration and manipulation, micromachining, second-harmonic generation, Raman spectroscopy, etc.     

二维光子晶体中与电磁波偏振态无关的自准直

利用有限时域差分法(FDTD)进行数值模拟，在二维光子晶体中实现了电磁波两种偏振态的自准直——全光自准直(full-light-self-collimation).研究表明，通过对光子晶体的结构做适当的调整，可以在较宽频率范围内实现横电波(TE波)和横磁波(TM波)沿着相同方向传播，同时保持较强的能流强度.全光自准直可以显著提高光源利用率和光波导的传播效率，在高密度集成光路中有非常重要的用途. 关键词： 光子晶体 偏振 自准直     

局域椭圆偏振光束强聚焦性质的研究

数值计算了局域椭圆偏振光束强聚焦时在焦平面上的横向场强分布、纵向场强分布、横向能流以及纵向角动量分布.结果显示在焦平面上光束总的纵向角动量为零,但在不同象限光束具有不同方向的纵向角动量.当相位延迟角度在0到π之间变化时横向场强分布基本不变,但纵向场强分布有很明显的变化.液晶相位延迟器由外部电压控制,使其相位延迟角度能在0到π之间可以连续取值.因而液晶相位延迟器的外接电压可以实现对焦平面上的纵向场强以及纵向角动量的实时调控.     

开孔矩形腔体电磁泄漏特性的解析研究

本文提出了一种用于计算开孔矩形腔体电磁泄漏场的解析理论模型.该理论模型先基于模式展开法求解封闭腔场,进而依据Bethe小孔耦合理论将泄漏场与封闭腔场用等效偶极子关联.该模型可以考虑波频率、场源位置、开孔位置及场强观测点位置等因素的影响,计算结果与全波仿真结果一致.本文计算分析了相关因素对电磁屏蔽效能的影响规律,并给出了物理解释.结果表明近场屏蔽效能小于远场屏蔽效能,且近场区电场屏蔽效能与磁场屏蔽效能并不相同.     

电大开孔箱体屏蔽效能分析解析模型

电磁脉冲武器能够通过"前、后门"耦合效应对箱体内部电子元器件及电路板造成损伤,从而对电气电子设备的安全性构成严重威胁,因此,开展箱体电磁屏蔽效能的分析研究具有重要意义.推导了任意入射波条件下电大开孔箱体屏蔽系数的解析解,并在此基础上对箱体屏蔽效能进行了分析研究.首先通过矢量分解,得出任意入射平面波的坐标分量;再基于Cohn模型,获得了电大开孔的等效电偶、磁偶极子;然后通过镜像原理,计算出总的赫兹电矢量位、磁矢量位;最终求得电大开孔箱体内部任意观测点的电场解析解,用于箱体屏蔽系数计算.设计了5组验证性实验,仿真结果表明:该解析算法相对CST的均方误差为11.565 d B,绝对误差为8.015 d B,相关系数为0.921,从而验证了该算法的准确性;解析算法仿真的平均耗时为0.183 s,仅占CST耗时的1/7530,从而验证了该算法的高效性.