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Birth of optical vortices in propagating fields with an original fractional topological charge
V.V. Kotlyar 1,2, A.A. Kovalev 1,2, A.P. Porfirev 1,2

1 IPSI RAS – Branch of the FSRC "Crystallography and Photonics" RAS,
443001, Samara, Russia, Molodogvardeyskaya 151,
2 Samara National Research University, 443086, Samara, Russia, Moskovskoye Shosse 34

 PDF, 1440 kB

DOI: 10.18287/2412-6179-CO-715

Pages: 493-500.

Full text of article: Russian language.

Abstract:
In contrast to the orbital angular momentum (OAM), which is conserved on free space propagation, the topological charge (TC) of a paraxial optical vortex (OV) is not conserved in the general case. Here, we investigate a Gaussian beam with a fractional TC in the original plane and demonstrate both theoretically and numerically how the TC changes in the course of propagation. Depending on the proximity of the topological charge to an even or odd integer number, an optical vortex with the original fractional TC is shown to behave in a number of different ways. For simple OVs (Laguerre-Gaussian or Bessel-Gaussian modes), TC is conserved both in propagation and after weak phase distortions. An experiment shows that when scattered by a random phase screen, the integer TC of an OV is conserved right up to a random phase variation of π. Therefore, in the case of weak turbulences, it is expedient to measure a discretely varying TC instead of a continuously varying OAM.

Keywords:
optical vortex, fractional topological charge, near-field diffraction, Fresnel diffraction, far-field diffraction.

Citation:
Kotlyar VV, Kovalev AA, Porfirev AP. Birth of optical vortices in propagating fields with an original fractional topological charge. Computer Optics 2020; 44(4): 493-500. DOI: 10.18287/2412-6179-CO-715.

Acknowledgements:
This work was partly funded by the RF Ministry of Science and Higher Education within a government project of FSRC «Crystallography and Photonics» RAS (Introduction and Conclusion), Russian Science Foundation (Project No. 18-19-00595, experiment), and Russian Foundation for Basic Research (Project No. 18-29-20003, theoretical results, and Project No. 18-07-01129, simulation results).

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