无衍射贝塞尔光束相干的理论与实验

分别使用两种不同底角的轴棱锥产生无衍射贝塞尔光束。理论分析了单束贝塞尔光及两束贝塞尔光相干叠加后光场的光强分布,分析了产生的局域空心光束在一个完整周期内的特性。数值模拟了光沿纵向传播时光场的横向光强分布,并给出了相关的实验。对单束贝塞尔光及两束贝塞尔光干涉后的中心光斑的大小进行了测量,测量结果与理论计算结果吻合。     

无衍射光束的产生及其应用

近年来,随着激光技术的快速发展,相继产生了多种在远距离传输后中心光斑保持不变的无衍射光束,包括贝塞尔光束、高阶贝塞尔光束、马丢光束、高阶马丢光束、余弦光束、抛物线光束以及艾里光束.无衍射光束在激光打孔、激光精密准直、光学精密控制、光学微操控、光通信、等离子体导向、光子弹产生、光通信、自聚焦光束的合成以及非线性光学等领域中有着广泛的应用.本文介绍了各类无衍射光束的数学表达式、产生方法及对应的实验结果;就无衍射光束的特性和应用进行了归纳和讨论;并对其在未来的研究与应用前景中发挥的重要作用进行了简要总结与展望.     

基于调制光束的空间相干性获得局域空心光束

通过调制部分相干光的空间相干性,实现了局域空心光束的产生。理论上根据范西泰特-策尼克定理及标量衍射积分,构造出具有一定空间相干性的部分相干光,并研究其聚焦特性。实验上采用理论上要求的光学系统来构造具有特定空间相干性的部分相干光,并采用薄透镜聚焦部分相干光。研究表明,当构造出的部分相干光经透镜聚焦,可得到局域空心光束。研究了光学系统的参数及透镜焦距对产生局域空心光束的影响,结果显示：光阑的拦截比及透镜的焦距越大,获得的空心光束的尺寸就越大。     

无衍射特殊光束的产生与三维表征

无衍射光束(如贝塞尔光束、艾里光束)因具有无衍射、自愈合的特性, 在很多领域都有广泛的应用. 本文提出使用纯相位型空间光调制器对光场的复振幅进行调控, 从而可以产生多种复杂模式的无衍射光束, 如强度可独立调控的多个零阶贝塞尔光束, 两个高阶贝塞尔光束干涉生成的花瓣状无衍射光束, 具有多个主瓣的加速光束等特殊的无衍射光束. 通过在待测焦场附近放置一个平面反射镜, 使其沿光轴快速扫描光场, 并由数字相机同步拍摄反射回来的一系列二维光场强度分布信息, 可实现对无衍射光束三维光场强度分布的快速测量和表征. 本实验方法和技术可以快速产生各种复杂的特殊光场并获得其精确的三维可视化重建效果, 在光学显微、光学俘获、光学微加工等领域有潜在的应用价值.     

余弦-高斯光束的焦平面及其位置

在余弦_高斯光束通过薄透镜聚焦系统的光场分布函数的基础上,利用二阶矩定义导出了聚焦余弦_高斯光束的光斑函数的解析表达式,由此求得束腰宽度及位置,进而给出了余弦_高斯光束的相对焦移的解析表达式。分析了光学系统参数以及光束参数对实际焦平面位置的影响并作了数值计算。     

聚焦高阶Bessel-Gauss光束重建的理论和实验研究

提出利用薄透镜元件对聚焦后的高阶Bessel-Gauss光束进行重建. 基于衍射理论, 分析了高阶Bessel-Gauss光束聚焦后的重建行为, 数值模拟高阶Bessel-Gauss光束经薄透镜聚焦再通过另一薄透镜重建的三维光场分布和截面光强分布图. 结果表明, 高阶Bessel-Gauss光束经单个薄透镜后产生中空的局域空心光束, 在焦点位置处为圆环, 尔后迅速发散; 在焦点后合适位置处放入另一薄透镜可矫正焦点后发散的光束, 使得其后光场不变, 仍满足Bessel分布; 实验结果与理论分析相符合. 研究结果对光镊、粒子捕获与操控具有一定的指导意义. 关键词： 衍射理论 传输矩阵 高阶Bessel-Gauss光束 重建     

Annular-focus zone lens for increasing the intensities of created Bessel beams

In this paper we proposes a new concept of annular-focus zone lens and its design procedure based on binary optics. An investigation of the diffraction efficiencies and the transverse intensity distributions on the focal plane of the designed annular-focus zone lenses is presented. This special kind of zone lens may be used to increase the intensities of Durnin's diffraction-free beams.     

一种新空心光束的理论及实验研究

提出了一种用来描述空心光束的新理论模型——空心高斯光束模型，通过控制光束参数可以方便地调制空心光束黑斑的大小.导出了空心高斯光束经傍轴光学系统的解析传输变换公式.利用导出的公式计算分析了空心高斯光束在自由空间的传输特性.在实验上利用矩阵本征值方法设计了能输出空心高斯光束的光学谐振腔，对实验上得到的空心高斯光束进行了传输特性的研究.结果表明，理论和实验相吻合.该空心高斯光束产生的光势阱为控制冷原子提供了一条新途径. 关键词： 空心高斯光束 光学谐振腔 传输特性     

Diffractionless beams and their use for harmonic generation

Use of diffraction-free beams to generate low-order harmonics in xenon jets has been investigated. Nearly diffractionless beams have been generated from a Ti : sapphire, 100 fs, laser system by focussing ring-type radiation, which has been produced in two different ways: either, by inserting an annular slit into the incident Gaussian beam, or by placing a doublet of axicons in a vertex-to-vertex configuration before the focussing lens. The results obtained with the first scheme are discussed and interpreted in terms of a simple perturbative model of the harmonic generation (HG) process. The first measurements performed with the doublet of axicons are also reported and discussed.     

Generation of diffraction-free vectorial elliptic hollow beams with space-varying inhomogeneous polarizations

Diffraction-free vectorial elliptic hollow beams (vEHBs) are generated by an optical system composed of a short elliptic hollow fiber (EHF) and an axicon. Each beam has a closed elliptic annular intensity profile and space-varying polarization states in its diffraction-free distance of more than 1 m. The generated beams have a counter-clockwise or clockwise periodically-rotated inhomogeneous polarization. And the spin angular momentum (SAM) of the vEHBs is 1ħ or -1ħ which is consistent with the type of dual-mode in the EHF and the periodic polarization rotations of the vEHBs. The vEHBs have potential applications in optically trapping and micromanipulating the micro- or nano-particles, quantum information transmission, and Bose-Einstein condensates, etc.     

Off-axis flat-topped multi-Gaussian beam and its propagation through paraxial optical system

Off-axis flat-topped multi-Gaussian beam is proposed as an extension of flat-topped multi-Gaussian beam. The electric field of off-axis flat-topped multi-Gaussian beam is expressed as a superposition of a series of off-axis Gaussian beams. Propagation formulae for off-axis flat-topped multi-Gaussian beam through aligned and misaligned optical system are derived. As a numerical example, propagation properties of off-axis flat-topped multi-Gaussian beam in free space and through a misaligned thin lens are discussed.     

Propagation properties of partially polarized Gaussian Schell-model beams through an axis-unsymmetric paraxial ABCD system

By using the beam coherence-polarization (BCP) matrix approach, analytical propagation equations of partially polarized Gaussian Schell-model (PGSM) beams through an axis-unsymmetric paraxial optical ABCD system are derived, which enable us to study the propagation-induced polarization changes and irradiance distributions at any propagation distance of PGSM beams through axis-unsymmetric systems within the framework of the paraxial approximation. Detailed numerical results for a PGSM beam passing through a bifocal lens are presented to illustrate the propagation properties of PGSM beams. A comparison with the previous work is also made.     

一类新平顶光束的束传播因子

 基于迭加原理，引入了利用双曲余弦-高斯光束的相干迭加而得的新光束，结果表明这类迭加光场的场强分布在适当参数条件下可具有平顶结构，并且分析了这类迭加所得的平顶光束的束传播因子与束参数的关系。     

Generation of thin and hollow beams by the axicon with a large open angle

We propose a method to produce diffraction-free thin and hollow beams. The method is based on Laguerre-Gaussian (LG) beams incident on a large open-angle axicon. We use the vector diffraction integrals and stationary phase method to deduce a simple and analytical formula of the propagating field of the linearly polarized LG beams through an axicon. The numerical results show that the hollow beams of whose diameter is in the order of the wavelength can be obtained by using the axicon with the refractive index n = 2 and the open angle α = 25°. These diffraction-free thin and hollow beams may be very useful to accurately trap and manipulate atoms. However, when the open angle is over large, the conversion efficiency from the LG beam to the diffraction-free hollow beam will decrease obviously.     

一类新平顶光束的束传播因子

基于迭加原理,引入了利用双曲余弦-高斯光束的相干迭加而得的新光束,结果表明这类迭加光场的场强分布在适当参数条件下可具有平顶结构,并且分析了这类迭加所得的平顶光束的束传播因子与束参数的关系。     

Multiple bottle beams based on metasurface optical field modulation and their capture of multiple atoms

Compared to conventional devices, metasurfaces offer the advantages of being lightweight, with planarization and tuning flexibility. This provides a new way to integrate and miniaturize optical systems. In this paper, a metasurface capable of generating multiple bottle beams was designed. Based on the Pancharatnam-Berry (P-B) phase principle, the metasurface lens can accurately control the wavefront by adjusting the aspect ratio of the titanium dioxide nanopillars and the rotation angle. When irradiated by left-handed circularly polarized light with a wavelength of 632.8 nm, the optical system can produce multiple micron bottle beams. Taking two bottle beams as examples, the longitudinal full widths at half-maximum of the optical tweezers can reach 0.85 μ and 1.12 μ, respectively, and the transverse full widths at half-maximum can reach 0.46 μ and 0.6 μ. Also, the number of generated bottle beams can be varied by controlling the size of the annular obstacle. By changing the x-component of the unit rotation angle, the metasurface can also change the shape of the bottle beam — the beam cross-section can be changed from circular to elliptical. This paper also analyzes the trapping of ytterbium atoms by the multi bottle beam acting as optical tweezers. It is found that the multi bottle beam can cool and trap multiple ytterbium atoms.     

Kurtosis parameters of super Lorentzben Gauss beams through a paraxial and real ABCD optical system

Based on the propagation equation of higher-order intensity moments, analytical propagation expressions for the kurtosis parameters of a super Lorentz-Gauss (SLG) SLG₀₁ beam through a paraxial and real ABCD optical system are derived. By replacing the parameters in the expressions of the kurtosis parameters of the SLG₀₁ beam, the kurtosis parameters of the SLG₁₀ and SLG₁₁ beams through a paraxial and real ABCD optical system can be easily obtained. The kurtosis parameters of an SLG₀₁ beam through a paraxial and real ABCD optical system depend on two ratios. One is the ratio of the transfer matrix element B to the product of the transfer matrix element A and the diffraction-free range of the super-Lorentzian part. The other is the ratio of the width parameter of the super-Lorentzian part to the waist of the Gaussian part. As a numerical example, the properties of the kurtosis parameters of an SLG₀₁ beam propagating in free space are illustrated. The influences of different parameters on the kurtosis parameters of an SLG₀₁ beam are analysed in detail.     

Generation of dark hollow beam by use of phase-only filtering

A simple but effective scheme to generate dark hollow beams is proposed by use of phase-only filtering and optical Fourier transform. A Gaussian beam of fundamental mode is modulated by a pre-designed phase mask, which is a piecewise modification of an axicon lens, and followed by a Fourier transform to generate an ideal dark hollow beam at the focal plane. This method has an advantage that the total energy of the beam is conserved under paraxial approximation. Numerical calculations are provided to show the validity of the proposed scheme.     

热光源产生贝塞尔光束的理论与实验

利用热光源获得了近似贝塞尔光束。对多波长光波同时入射轴棱锥的情形进行分析和数值模拟,结果显示轴棱锥后会形成近似贝塞尔光束,但受光场非相干叠加的影响截面光强对比度降低。实验采用卤素灯杯作为产生贝塞尔光束的热光源,针对热光源相干性差的特点设计出一套光学系统,提高光波的空间相干性,再使光波平行透过轴棱锥得到了近似贝塞尔光束。将实验结果与数值计算对比,发现实验所得贝塞尔光束的特性与理论基本吻合,但最大无衍射距离较理论计算所得的短,并对此进行了分析。     

基于调制光束的空间相干性获得局域空心光束

 通过调制部分相干光的空间相干性,实现了局域空心光束的产生。理论上根据范西泰特-策尼克定理及标量衍射积分,构造出具有一定空间相干性的部分相干光,并研究其聚焦特性。实验上采用理论上要求的光学系统来构造具有特定空间相干性的部分相干光,并采用薄透镜聚焦部分相干光。研究表明,当构造出的部分相干光经透镜聚焦,可得到局域空心光束。研究了光学系统的参数及透镜焦距对产生局域空心光束的影响,结果显示：光阑的拦截比及透镜的焦距越大,获得的空心光束的尺寸就越大。