Spin angular momentum at the tight focus of a cylindrical vector beam with an imbedded optical vortex

被引：2
作者：
Kotlyar V.V. [1 ,2 ]
Stafeev S.S. [1 ,2 ]
Telegin A.M. [1 ,2 ]
机构：
[1] Image Processing Systems Institute of the RAS – Branch of FSRC “Crystallography & Photonics” of the RAS, Molodogvardeyskaya 151, Samara
[2] Samara National Research University, Moskovskoye Shosse 34, Samara
来源：
Optik | 2023年 / 287卷
基金：
俄罗斯科学基金会;
关键词：
Optical vortex; Spin angular momentum; Tight focusing; Vector beam;
D O I：
10.1016/j.ijleo.2023.171103
中图分类号：
学科分类号：
摘要：
We discuss sharp focusing of a light field that possess a double (phase + polarization) singularity. An exact analytical expression for the longitudinal projection of the spin angular momentum (SAM) vector at the focus is deduced based on a Richards-Wolf approach. The expression deduced suggests that at the focus, 4(n-1) subwavelength regions are generated (n denotes the cylindrical beam order), which are arranged on a circle centered on the optical axis. In the adjacent regions, the SAM is revealed to change sign, meaning that the light has alternating left- and right-handed elliptic polarization (an optical spin Hall effect) in these regions. At the near-axis focus center, the light is shown to have right-handed elliptical polarization at m> 0 or left-handed elliptic polarization at m< 0, where m denotes the topological charge of the optical vortex. The total longitudinal spin, i.e. the cross-section-averaged longitudinal SAM component, is shown to be zero and conserve upon focusing. Thanks to the presence of an optical vortex with topological charge m, the near-focus transverse energy flow is found to rotate on a spiral path, rotating on a circle at the focus. In the optical axis vicinity, the rotation occurs anticlockwise at m> 0 or clockwise at m< 0. © 2023 Elsevier GmbH
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