Constructing Spin Density Vector Twists With Spin Density Singularity

Abstract

In this article, we propose a non-orbital angular momentum (OAM) method for constructing the spiral twists of spin density (SD) vectors in three-dimensional (3D) optical fields. This is realized by generating strings of SD singularities in a longitudinal plane of a strongly focused HG10 mode beam with circular polarization. We demonstrate that in this plane, the SD singularities manifest themselves as the Gouy phase difference. Through observing the Gouy phase difference, the strings of the SD singularities and their topological reactions are examined. It is found that the spiral twists of SD vectors are constructed in the two-dimensional (2D) space between two strings and their twisting behaviors can be adjusted by the topological reactions of the strings. This finding shows that the spiral twists can be formed in a 2D space rather than the 1D space in previous studies, which provides a more flexible way to utilize this rotational degree of freedom. Our result also clarifies that although the spiral twists of SD vectors can be a result of spin-orbital angular momentum interaction, the OAM is not a necessary condition for the generation of these twists. Our theoretical proposal for structuring SD vectors may have applications in 3D optical manipulation.

Topological Approach of Characterizing Optical Skyrmions and Multi‐Skyrmions

“…Of particular interest to the experimentalist are 2D skyrmions, sometimes called 'baby skyrmions', which can be realized in paraxial beams, offering an easily accessible and re-configurable platform for the investigation of topological features and their propagation dynamics. [14][15][16][17][18][19] Unlike magnetic skyrmions, freely propagating paraxial optical skyrmions are only constrained by Maxwell's equations, and therefore offer a versatile platform for the investigation of exotic topological structures. [20] The generation of topological states of light opens up new avenues for the controlled interaction of DOI: 10.1002/lpor.202300155 photons with material quasi-particles such as plasmons, phonons, and excitons.…”

Photonic Wheels and Polarization Möbius Strips in Highly-Confined Trigonometric Beams

“…effects in nanoscale [13], [14], such as in controlling the light-matter interactions [15]. Also, the structures of the spin density vectors in 3D space are of special interest to help understand the physical nature of 3D optical fields, for instance the spiral twisting structures of spin density vectors [16]- [21], which has been found to be a result of SOIs [16], [17], [20], and more specially, the purely transverse structures of spin density vectors which lead to an interesting optical phenomenon-'photonic wheels' [22]- [30], implying that light can spin in the plane with the propagation direction like a wheel [23], [26], [31]. It has been proved that the photonic wheels not only are fundamentally meaningful, such as their strong connection with the geometrical spin Hall effect of light [32]- [35] but also have various applications, for instance in observing the SOIs [36], in on-chip and interchip optical circuitry and quantum computing [22], [23], [26].…”

Effect of Degree of Polarization on Localized Spin Density in Tightly Focusing of Vortex Beams

“…The orbit-to-spin degree of freedom, i.e., the orbitally induced spin AM in the tightly focused field, on the other hand, has received much less attention. The effects of the initial polarization state distribution and the topological charge of vortex phase on the orbitally induced spin AM in the tightly focused field have been studied numerically [26]- [32]. More recently, Zhang and coauthors proposed a principle experimental method for identifying the induced spin AM in the tightly focused beam by measuring the orientation of the major axis of the captured ellipsoidal particles in optical tweezers [33].…”