Excitation of nonradiating magnetic anapole states with azimuthally polarized vector beams.

Aristeidis G Lamprianidis,Andrey E Miroshnichenko

doi:10.3762/bjnano.9.139

Aristeidis G Lamprianidis, Andrey E Miroshnichenko

Open Access

https://doi.org/10.3762/bjnano.9.139

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Abstract

Nonradiating current configurations have been drawing the attention of the physics community for many years. It has been demonstrated recently that dielectric nanoparticles provide a unique platform to host such nonradiating modes, called “anapoles”. Here we study theoretically the excitation of such exotic anapole modes in silicon nanoparticles using structured light. Alternative illumination configurations, properly designed, are able to unlock hidden behavior of scatterers. Particularly, azimuthally polarized focused beams enable us to excite ideal anapole modes of magnetic type in dielectric nanoparticles. Firstly, we perform the decomposition of this type of excitation into its multipolar content and then we employ the T-matrix method to calculate the far-field scattering properties of nanoparticles illuminated by such beams. We propose several configuration schemes where magnetic anapole modes of simple or hybrid nature can be detected in silicon nanospheres, nanodisks and nanopillars.

Highlights

The triumph of Maxwell’s equations is associated with the unification of electric and magnetic phenomena on the same footing, which has led to the prediction of existence of an electromagnetic radiation, which can carry energy and momentum
We will properly design its geometry and, its excitation field, in order to achieve the desired scattering response. In the former sections, we proved that an azimuthally polarized focused beam that is rotationally symmetric, i.e., that has a zero orbital angular momentum: m = 0, bears only multipoles of magnetic type for particles that are located over the optical axis
It is connected with the coincidence of the weak coupling of the excitation with the second right singular vector, which has a multipolar content of magnetic type and corresponds to a significantly large singular value that could potentially spoil the excitation of the anapole state

Summary

Introduction

The triumph of Maxwell’s equations is associated with the unification of electric and magnetic phenomena on the same footing, which has led to the prediction of existence of an electromagnetic radiation, which can carry energy and momentum. (5) A particle with spherical symmetry has a T-matrix that is diagonal over all its indices α, μ, ν: where bα,ν are the well-known Mie scattering coefficients, which in the case of homogeneous spheres are given by the formula: the right-singular vectors that correspond to singular values equal to zero:

Results

Conclusion