Elusive pure anapole excitation in homogenous spherical nanoparticles with radial anisotropy

TL;DR

This paper demonstrates that radial anisotropy in homogeneous dielectric nanospheres enables the realization of a pure anapole excitation by suppressing other multipole contributions, advancing scattering control in nanophotonics.

Contribution

It introduces the use of radial anisotropy to achieve pure anapole excitation in dielectric nanospheres, overcoming previous limitations due to multipole mixing.

Findings

Radial anisotropy suppresses magnetic and other multipole excitations.

Pure anapole excitation is achievable without compromising scattering cancellation.

Potential applications in scattering control and nanophotonics are enabled.

Abstract

For homogenous isotropic dielectric nanospheres with incident plane waves, Cartesian electric and toroidal dipoles can be tunned to cancel each other in terms of far-field scattering, leading to the effective anopole excitation. At the same time however, other multipoles such as magnetic dipoles with comparable scattered power are simultanesouly excited, mixing with the anopole and leading to a non-negligible total scattering cross section. Here we show that for homogenous dielectric nanospheres, radial anisotropy can be employed to significantly suppress the other multipole excitation, which at the same time does not compromise the property of complete scattering cancallation between Cartesian electric and toroidal dipoles. This enables an elusive pure anopole excitation within radially anisotropic dielectric nanospheres, which may shed new light to many scattering related fundamental researches and applications.