Self-referenced interferometric methods to determine topological charge of vortex beams

2020 ◽  
Author(s):  
Praveen Kumar ◽  
Naveen K Nishchal
Keyword(s):  
Topological Charge ◽  
Vortex Beams

scholarly journals High-Efficiency Spin-Related Vortex Metalenses

Nanomaterials ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 1485
Author(s):  
Wei Wang ◽  
Ruikang Zhao ◽  
Shilong Chang ◽  
Jing Li ◽  
Yan Shi ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Topological Charge ◽  
High Efficiency ◽  
Infrared Band ◽  
Mid Infrared ◽  
Integrated Devices ◽  
Vortex Beams ◽  
Topological Charges

In this paper, one spin-selected vortex metalens composed of silicon nanobricks is designed and numerically investigated at the mid-infrared band, which can produce vortex beams with different topological charges and achieve different spin lights simultaneously. Another type of spin-independent vortex metalens is also designed, which can focus the vortex beams with the same topological charge at the same position for different spin lights, respectively. Both of the two vortex metalenses can achieve high-efficiency focusing for different spin lights. In addition, the spin-to-orbital angular momentum conversion through the vortex metalens is also discussed in detail. Our work facilitates the establishment of high-efficiency spin-related integrated devices, which is significant for the development of vortex optics and spin optics.

scholarly journals Sectorial perturbation of vortex beams: Shannon entropy, orbital angular momentum and topological charge

2019 ◽  
Vol 43 (5) ◽  
pp. 723-734 ◽  
Author(s):  
A.V. Volyar ◽  
M.V. Bretsko ◽  
Ya.E. Akimova ◽  
Yu.A. Egorov ◽  
V.V. Milyukov
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Shannon Entropy ◽  
Topological Charge ◽  
External Perturbation ◽  
Informational Entropy ◽  
Large Perturbation ◽  
Wide Range ◽  
Vortex Beams ◽  
Computing Measuring

Transformations of the vortex beams structure subjected to sectorial perturbation were theoretically and experimentally studied. The analysis was based on computing (measuring) the vortex spectrum that enables us to find the orbital angular momentum (OAM) and Shannon entropy (informational entropy). We have revealed that, in the general case, the number of vortices caused by an external perturbation is not related to the topological charge. For arbitrary perturbation, the topological charge remains equal to the initial topological charge of the unperturbed vortex beam. Growth of the vortex number induced by perturbations is associated with the optical uncertainty principle between the sectorial angle and the OAM. The computer simulation has shown that OAM does not depend on the number of vortices induced by perturbations. Moreover, two maxima are formed both in the positive and negative regions of the vortex spectrum. As a result, the OAM does not practically change in a wide range of perturbation angles from 0 to 90 °. However, at large perturbation angles, when the energy is almost equally redistributed between the vortex modes with opposite signs of the topological charge, the OAM rapidly decreases. At the same time, the Shannon entropy monotonically increases with growing perturbation angle. This is due to the fact that the entropy depends only on the number of vortex states caused by external perturbations.

Multi-channeled vortex beam switch with moiré metasurfaces

2021 ◽  
Author(s):  
Cheng Cui ◽  
Zheng Liu ◽  
Bin Hu ◽  
Yurong Jiang ◽  
Juan Liu
Keyword(s):  
Functional Diversity ◽  
Optical Communications ◽  
Topological Charge ◽  
Signal Transmission ◽  
Polarized Light ◽  
Vortex Beam ◽  
Practical Applications ◽  
Linearly Polarized ◽  
Vortex Beams ◽  
Topological Charges

Abstract Tunable metasurface devices are considered to be an important link for metasurfaces to practical applications due to their functional diversity and high adaptability to the application scenarios. Metasurfaces have unique value in the generation of vortex beams because they can realize light wavefronts of any shape. In recent years, several vortex beam generators using metasurfaces have been proposed. However, the topological charge generally lacks tunability, which reduces the scope of their applications. Here, we propose an active tunable multi-channeled vortex beam switch based on a moiré structure composed of two cascaded dielectric metasurfaces. The simulation results show that when linearly polarized light with a wavelength of 810 nm is incident, the topological charge from -6 to +6 can be continuously generated by relatively rotating the two metasurfaces. Meanwhile, different topological charges are deflected to different spatial channels, realizing the function of multi-channeled signal transmission. We also study the efficiency and broadband performance of the structure. The proposed multi-channeled separation method of vortex beams that can actively tune topological charges paves the way for the compactness and functional diversity of devices in the fields of optical communications, biomedicine, and optoelectronics.

Detecting the topological charge of a vortex beam by an arc slit diffraction

2017 ◽  
Vol 31 (23) ◽  
pp. 1750172 ◽  
Author(s):  
Dongzhi Fu ◽  
Hailong Zhou ◽  
Kaiwei Wang ◽  
Pei Zhang ◽  
Jianji Dong ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Diffraction Pattern ◽  
Orbital Angular Momentum ◽  
Topological Charge ◽  
Light Spot ◽  
Far Field ◽  
Vortex Beam ◽  
Efficient Measurement ◽  
Vortex Beams

The simple and efficient measurement of the light orbital angular momentum (OAM) is essential to both the classical and quantum applications with vortex beams. Here, we study the diffraction pattern in the far field when a vortex beam passes through an arc slit and demonstrate experimentally that a light spot of the diffraction pattern has a displacement which is linear to the topological charge (TC) of the incident vortex beam. Based on this property, this method is capable of measuring both modulus and sign of TC of the vortex beam. Furthermore, this scheme allows identifying multiple OAM states simultaneously.

scholarly journals On-Column 2p Bound State with Topological Charge ±1 Excited by an Atomic-Size Vortex Beam in an Aberration-Corrected Scanning Transmission Electron Microscope

2012 ◽  
Vol 18 (4) ◽  
pp. 711-719 ◽  
Author(s):  
Huolin L. Xin ◽  
Haimei Zheng
Keyword(s):  
Topological Charge ◽  
Bound States ◽  
Numerical Solutions ◽  
Incident Beam ◽  
Vortex Beam ◽  
Phase Front ◽  
Atomic Size ◽  
Convergence Angle ◽  
Vortex Beams ◽  
Energy Convergence

AbstractAtomic-size vortex beams have great potential in probing the magnetic moment of materials at atomic scales. However, the limited depth of field of vortex beams constrains the probing depth in which the helical phase front is preserved. On the other hand, electron channeling in crystals can counteract beam divergence and extend the vortex beam without disrupting its topological charge. Specifically, in this article, we report that atomic vortex beams with topological charge ±1 can be coupled to the 2p columnar bound states and propagate for more than 50 nm without being dispersed and losing its helical phase front. We give numerical solutions to the 2p columnar orbitals and tabulate the characteristic size of the 2p states of two typical elements, Co and Dy, for various incident beam energies and various atomic densities. The tabulated numbers allow estimates of the optimal convergence angle for maximal coupling to 2p columnar orbital. We have also developed analytic formulae for beam energy, convergence angle, and hologram-dependent scaling for various characteristic sizes. These length scales are useful for the design of pitch-fork apertures and operations of microscopes in the vortex-beam imaging mode.

Analysis of the topological charge by focusing vortex beams with a cylinder lens

2019 ◽  
Author(s):  
Liang Liu ◽  
Kaiming Wang ◽  
Xiujun Huang ◽  
Hongyan Xu ◽  
Zhenjiang Song ◽  
...  
Keyword(s):  
Topological Charge ◽  
Vortex Beams

Vortex beams with zero orbital angular momentum and non-zero topological charge

2018 ◽  
Vol 104 ◽  
pp. 159-163 ◽  
Author(s):  
V.P. Aksenov ◽  
V.V. Dudorov ◽  
G.A. Filimonov ◽  
V.V. Kolosov ◽  
V.Yu. Venediktov
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Topological Charge ◽  
Vortex Beams
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