Optically-isotropic responses induced by discrete rotational symmetry of nanoparticle clusters

TL;DR

This paper shows that nanoparticle clusters with discrete rotational symmetry exhibit optical responses that are invariant to the polarization of incident light across all wavelengths, due to their symmetry properties.

Contribution

It introduces a general method to achieve polarization-independent optical responses in scattering systems based on their rotational symmetry.

Findings

Polarization-invariant extinction, scattering, and absorption responses demonstrated

Optical responses are robust and purely due to rotational symmetry

Applicable to various light scattering applications such as sensing and photovoltaics

Abstract

Fostered by the recent progress of the fields of plasmonics and metamaterials, the seminal topic of light scattering by clusters of nanoparticles is attracting enormous renewed interest gaining more attention than ever before. Related studies have not only found various new applications in different branches of physics and chemistry, but also spread rapidly into other fields such as biology and medicine. Despite the significant achievements, there still exists unsolved but vitally important challenges of how to obtain robust polarisation-invariant responses of different types of scattering systems. In this paper, we demonstrate polarisation-independent responses of any scattering system with a rotational symmetry with respect to an axis parallel to the propagation direction of the incident wave. We demonstrate that the optical responses such as extinction, scattering, and absorption, can be made independent of the polarisation of the incident wave for all wavelengths. Such polarisation-independent responses are proven to be a robust and generic feature that is purely due to the rotational symmetry of the whole structure. We anticipate our finding will play a significant role in various applications involving light scattering such as sensing, nanoantennas, optical switches, and photovoltaic devices.