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.     

Parabolic nondiffracting optical wave fields

We demonstrate the existence of parabolic beams that constitute the last member of the family of fundamental nondiffracting wave fields and determine their associated angular spectrum. Their transverse structure is described by parabolic cylinder functions, and contrary to Bessel or Mathieu beams their eigenvalue spectrum is continuous. Any nondiffracting beam can be constructed as a superposition of parabolic beams, since they form a complete orthogonal set of solutions of the Helmholtz equation. A novel class of traveling parabolic waves is also introduced for the first time.     

Reconfigurable directional couplers and junctions optically induced by nondiffracting Bessel beams

We put forward the concept of reconfigurable structures optically induced by mutually incoherent nondiffracting Bessel beams in Kerr-type nonlinear media. We address collinear couplers and X junctions and show how one can tune the switching properties of such structures by varying the intensity of the Bessel beams.     

Solid immersion axicon: maximizing nondiffracting or Bessel beam resolution

A new type of optical configuration--a solid immersion axicon (SIAX)--is proposed. Similar to a solid immersion lens for Gaussian beams, a SIAX increases the diffraction-limited resolution for propagating Bessel beams by a factor of the refractive index of the media. For incident radial polarization, the scheme generates the smallest focal spot available for nondiffracting beams. The configuration can be implemented with either refractive or diffractive axicons. The scheme may find use in microscopy, imaging, lithography and data storage, and other applications requiring nondiffracting beam characteristic features such as very large focal depth.     

被动方式产生近似无衍射贝塞尔光技术

无衍射光束具有中心光斑小且不随传播距离变化、自再现、产生局域空心光等特点,由于这些特殊的光束特性而在许多领域,如计量学,经典光学,非线性光学和生命科学等领域中得到广泛的应用。无衍射光束的产生与变换是目前的一个研究热点。通过衍射理论、干涉理论和几何光学方法可对无衍射光进行描述。实现无衍射贝塞尔光束的方法可分为主动式和被动式。本文主要综述地介绍了几种被动式产生近似无衍射贝塞尔光束的最新技术,通过分析其优缺点,给出了这些技术的适用范围。     

Asymmetric Mathieu beams

We report the generation of asymmetric Mathieu beams: invariant intensity optical profiles that can be described by three parameters. The first one describes the amount of ellipticity, the second one takes into account the degree of asymmetry of the profile, and the third parameter denotes the angular position, where it is localized with the respective asymmetry. We propose a simple angular spectrum to generate these nondiffracting beams,and we report how it changes their distribution of power and orbital angular momentum in function with their ellipticity and degree of asymmetry. We confirm the existence of these invariant beams by propagation in an experimental setup.     

Controlling the evolution of nondiffracting speckle by complex amplitude modulation on a phase-only spatial light modulator

In this work we investigate the structure of nondiffracting speckle fields, both experimentally and theoretically. We are able to produce very good agreement between the experimentally recorded and theoretically calculated fields by using complex amplitude modulation on a phase-only spatial light modulator to implement controlled ring-slit experiments for the generation of nondiffracting speckle fields. The structure of the nondiffracting speckle due to binary and continuous phase modulations for both a uniform and a normal distribution is investigated. We find that we are able to engineer whether the nondiffracting field will appear as speckle or a structured zero-order Bessel beam by adjusting the standard deviation in the distribution. Having the ability to control where in the spectrum, from fully-developed nondiffracting speckle to a symmetric zero-order Bessel beam, the nondiffracting field will exist can prove to be a useful resource in the non-destructive testing of materials.     

Interference of traveling nondiffracting beams

We study numerically the interference resulting from the superposition of two Bessel beams propagating in free space. We discuss how to obtain such beams and show the existence of the self-imaging effect during propagation. The evolution of the superimposed Bessel beams is analyzed on the basis of the evolution of the individual beams. Our exact numerical predictions contradict previous approximated analytical treatments, showing that they can lead to quantitatively wrong results and misleading conclusions.     

Generation of nondiffracting Bessel beams by use of a spatial light modulator

A laser beam with phase singularities is an interesting object to study in optics and may have important applications in guiding atoms and molecules. We explore the characteristics of a singularity in a nondiffracting Bessel beam experimentally by use of a programmable spatial light modulator with 64-level phase holograms. The diffraction efficiency with 64-level phase holograms is greatly improved in comparison with that obtained with a binary grating. The experiments show that the size and deflection angle of the beam can be controlled in real time. The observations are in agreement with scalar diffraction theory.     

Controlled spatial shaping of nondiffracting patterns and arrays

It is verified that the condition of nondiffracting propagation of an optical beam provides the degrees of freedom that are applicable to the controlled shaping of the beam's transverse intensity profile. The proposed method of beam shaping permits experimental realization of nondiffracting patterns and arrays with a predetermined spatial shape.     

Nondiffracting wave beams in non-Hermitian Glauber–Fock lattice

We theoretically study non-Hermitian Glauber–Fock lattice with nonuniform hopping. We show how to engineer this lattice to get nondiffracting wave beams and find an exact analytical solution to nondiffracting localized waves. The exceptional points in the energy spectrum are also analyzed.     

Nondiffracting beams in periodic media

We identify nondiffracting beams in two-dimensional periodic systems, exhibiting symmetry properties and phase structure characteristic of the band(s) they are associated with.     

Holographic generation of a class of nondiffracting fields with optimum efficiency

We discuss the accurate generation of complex optical fields using phase holograms that provide the optimum diffraction efficiency. In each considered case, the phase modulation of the employed hologram is identical to the phase of the desired optical field. We show that periodic and quasiperiodic nondiffracting optical fields, mathematically obtained through the superposition of multiple plane waves, can be generated with high fidelity using this approach.     

Trapping and guiding microparticles with morphing autofocusing Airy beams

We observe optical trapping and manipulation of dielectric microparticles using autofocusing radially symmetric Airy beams. This is accomplished by exploiting either the inward or outward transverse acceleration associated with their chirped wavefronts. We experimentally demonstrate, for the first time to our knowledge, that such Airy beams morph into nondiffracting Bessel beams in their far-field. Furthermore, the ability of guiding and transporting microparticles along the primary rings of this class of beams is explored.     

Free-space laser beams with pulsing on-axis intensities

Summary We present a family of laser beams with spatially pulsing on-axis intensity. They are obtained by summation of nondiffracting Bessel beams. They are shown to be able to realize, with good approximation, any spatial periodic on-axis intensity in the period limits set by the frequency of the monochromatic source of light used. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Vector Helmholtz-Gauss and vector Laplace-Gauss beams

We demonstrate the existence of vector Helmholtz-Gauss (vHzG) and vector Laplace-Gauss beams that constitute two general families of localized vector beam solutions of the Maxwell equations in the paraxial approximation. The electromagnetic components are determined starting from the scalar solutions of the two-dimensional Helmholtz and Laplace equations, respectively. Special cases of the vHzG beams are TE and TM Gaussian vector beams, nondiffracting vector Bessel beams, polarized Bessel-Gauss beams, modes in cylindrical waveguides and cavities, and scalar Helmholtz-Gauss beams. The general expression of the vHzG beams can be used straightforwardly to obtain vector Mathieu-Gauss and vector parabolic-Gauss beams, which to our knowledge have not yet been reported.     

On the concept of "tractor beams"

We demonstrate the existence of a class of optical beams where the nonconservative forces can be locally oriented in a direction opposite to the propagation wave vector. Objects placed in the vicinity of these locations will move toward the source of light. The behavior of these negative forces is discussed for the particular case of nondiffracting rotating scale-invariant vector electromagnetic waves.     

Efficient Generation of Customized Caustics: Nondiffracting Deltoid and Pentagram Beams

This study puts forward a powerful new strategy that allows highly efficient generation of the shaping transverse nondiffracting caustics that concentrate around the expected curve. First, under the condition of stationary phase approximation, as the typical example of caustic beams, the analytical formula of nondiffracting deltoid and pentagram caustics is theoretically derived. Based on the obtained analytical formula, the desired caustics of deltoid and pentagram are numerically simulated. Hence, their optical shape and the propagation characteristics of nondiffracting caustics can be investigated. Then, based on the given generating mechanism, the corresponding experimental system to experimentally explore the nondiffracting deltoid and pentagram caustics with good self-healing properties is constructed. Compared with the previous generating methods, the proposed method has a high light energy utilization.     

自加速类贝塞尔-厄米-高斯光束的理论和实验研究

空间相位调制一直是设计新型自加速光束的重要方法.参照类贝塞尔光束产生的思路,从理论上提出了一种新型的自加速无衍射类贝塞尔-厄米-高斯光束,并从数值模拟和实验两个方面研究此光束沿不同轨道的演化.理论上通过对厄米-高斯光束进行相位调制,产生了不同模式的自加速类贝塞尔-厄米-高斯光束.采用分步傅里叶算法模拟了(0,1),(1,0),(1,1)和(1,2)阶类贝塞尔-厄米-高斯光束沿预设轨道的传输过程.采用计算全息和空间光调制技术在实验中观察了类贝塞尔-厄米-高斯光束沿预设轨道的传输,例如抛物、双曲、双曲正割和三维轨道.实验观察与理论结果符合得很好.实验验证了不同阶类贝塞尔-厄米-高斯光束的奇特光斑结构,验证了光束的非衍射特性及传输轨道的可控性,且理论模拟验证了光束的自修复特性.作为此前研究的类贝塞尔光束的一般形式,本文所得到的光束可用于构造出更加新型实用的光束.