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Waves and Beams
Published in Rajpal S. Sirohi, Optical Methods of Measurement, 2018
Optical vortices find many applications in interferometry, such as in the study of fractally rough surfaces, beam collimation testing, optical vortex metrology, and microscopy. An optical vortex interferometer employing three-wave interference can be used for tilt and displacement measurement, wavefront reconstruction, 3D scanning, and super-resolution microscopy. Spiral interferometry, where a spiral phase element is used as a spatial filter, removes the ambiguity between elevation and depression in the surface height of a test object. Lateral shear interferometers have been used to study gradients of phase-singular beams. It has been shown that shearograms do not represent true phase gradients when vortices are presents in the optical fields. However, lateral shear interferometry is a potential technique for the detection of both an isolated vortex and randomly distributed vortices in a speckle field. It is a simple, robust, and self-referencing technique, which is insensitive to vibrations. Unlike the existing interferometric techniques of vortex detection, it does not require any high-quality plane or spherical reference wavefront to form an interference pattern.
Jones Matrices and Polarization Properties
Published in Russell A. Chipman, Wai-Sze Tiffany Lam, Garam Young, Polarized Light and Optical Systems, 2018
Russell A. Chipman, Wai-Sze Tiffany Lam, Garam Young
Next, vortex retarders will be explored as an example of the application of Jones matrices. An optical vortex is a phase singularity about a zero of an electromagnetic field.21Figure 5.9 (left) shows a vortex in circularly polarized light. In this example, the phase varies by 2π about a zero at the center of the pupil phase map. The phase is continuous around the zero, but discontinuous crossing the zero. This is a screw dislocation; in this map, the phase has the form arctan(y/x). Other vortices can take the form m arctan(y/x), where m is the order of the vortex. Figure 5.9 (right) shows an ordinary zero of the field for comparison.
Asymmetric Gaussian Vortices
Published in V. V. Kotlyar, A. A. Kovalev, A. P. Porfirev, Vortex Laser Beams, 2019
V. V. Kotlyar, A. A. Kovalev, A. P. Porfirev
In Refs. [22,272], A. Zeilinger et al. proposed that photon pairs with entanglement of the orbital angular momentum (OAM) states could be detected in the course of spontaneous parametric down-conversion by illuminating a “fork” hologram (used for generating optical vortices) by a shifted Gaussian beam. Their idea was that as a result of a small shift between the centers a linear combination of a Gaussian and a Laguerre-Gaussian (LG) beam was generated. It has also been shown experimentally [273] that OAM-entangled Stokes and anti-Stokes photons can be generated via four-wave mixing in a hot atomic ensemble and a shift between the centers of the Gaussian beam and the “fork” hologram. There are also studies of the transformation of optical vortices in the classical theory of light. Here, the optical vortex is meant as a laser beam with an isolated intensity null on the optical axis and with a spiral phase, having an integer topological charge. In Ref. [274] it was studied theoretically in which way an axial shift of the center of the Gaussian beam waist from the plane of a spiral phase plate (SPP), combined with a diffractive lens (spiral lens), affected the optical vortex. The propagation of an optical vortex through an opaque screen perforated with multiple pinholes with their centers lying on a circle was experimentally investigated in Ref. [275]. In this case, an nth order optical vortex was shown to split into n first order optical vortices. In [276], the transformation of an optical vortex by applying different ellipticity ratios was reported. This work [276] was done as a continuation of earlier works on the study of elliptic optical vortices [11,60]. In Ref. [277], a method of optical vortex generation was proposed, based on a set of small pinholes in an opaque screen with their centers located on a spiral. Small deformations of the guiding spiral led to the distortion of the optical vortex shape.
Polarization characteristics of radially polarized partially coherent vortex beam in anisotropic plasma turbulence
Published in Waves in Random and Complex Media, 2021
Jiangting Li, Jiachao Li, Lixin Guo, Mingjian Cheng, Luo Xi
An optical vortex is often described as a special light field with a spiral phase structure or phase singularity. Since Allen et al. proved in 1992 that a vortex beam carries a certain orbital angular momentum in propagation, vortex beams have attracted widespread attention and are widely used in the fields of optical communication, optical trapping, and molecular optics. In 1995, He et al. proved experimentally that vortex beams that carry the orbital angular momentum could be used to manipulate tiny particles [4]. In 2002, Wolf et al. studied how switching affects completely coherent spatially polychromatic light through pupil diffraction [5]. In 2017, Porfirev A P, Kirilenko M S, Khonina S N et al. studied the propagation of vortex laser beams in a random aerosol medium [6]. In 2008, Gbur G et al. proved that the topological charge of such a beam is a robust quantity that could be used as an information carrier in optical communications by simulating and analyzing the propagation of vortex beams through weak-to-strong atmospheric turbulence [7]. At the same time, vortex beams have been studied by many scholars to understand their propagation characteristics in turbulence due to their ability to carry orbital angular momentum [8–15]. Various types of vortex beams, such as flat-topped vortex beams, Laguerre-Gauss vortex beams, Bessel vortex beams, etc., have been studied in order to reduce the influence of turbulence on beam propagation.
Comparison of microparticle manipulating characteristics of canonical vortex beam and power-exponent-phase vortex beam
Published in Journal of Modern Optics, 2021
Zhonghua Pei, Sujuan Huang, Yi Chen, Cheng Yan
Since Ashkin's first observation of the acceleration of freely suspended particles by radiation forces, optical trapping and manipulation have attracted extensive attention from several researchers [1]. This technique has become a powerful tool in modern science and technology [2,3], especially in physics for manipulating particles [4–6], and in biology for manipulating living cells and biological tissues [7–9]. It is well known that the action of light on particles is the result of momentum and energy exchange between photons and particles [10]. However, optical manipulation with Gaussian beams, which are used to capture microparticles with a specific size, shape, and refractive index [11–13], cause considerable thermal damage to biological cells or microparticles. This limits the application of optical tweezers based on Gaussian beams in the fields of biology and microfluidics. Another type of structured light field, commonly known as an optical vortex (OV) has the characteristics of a spiral phase wavefront and photon orbital angular momentum (OAM). The transfer of photon OAM to atoms, molecules, particles, and other materials in an OV field, can help realise the manipulation of particles noninvasively, and without causing damage [14–16]. Therefore, vortex beams have been attracting increasing attention.
Fresnel and Fraunhofer diffraction of (l,n)th-mode Laguerre–Gaussian laser beam by a fork-shaped grating
Published in Journal of Modern Optics, 2019
The optical vortex beams can appear spontaneously in a laser cavity with cylindrical geometry, for instance the Laguerre–Gaussian (LG) laser beams with non-zeroth azimuthal mode number, or, they can be generated by using some diffractive optical elements (DOEs) and gratings, like phase spiral plates (4, 5), helical axicons (6–9), helical lens (10) and spiral zone plates (11).