Orientation Averaging of Optical Chirality Near Nanoparticles and Aggregates

TL;DR

This paper develops a superposition T-matrix method to efficiently compute the orientation-averaged optical chirality near nanoparticles and aggregates, aiding the design of nanostructures for enhanced chiroptical spectroscopy.

Contribution

It introduces new formulas for orientation-averaged optical chirality using the superposition T-matrix framework, addressing a key challenge in nano-optics for randomly oriented scatterers.

Findings

Derived efficient orientation-averaging formulas for optical chirality.

Applied formulas to model examples revealing non-intuitive chirality distributions.

Facilitated comprehensive exploration of nanostructure designs for chiroptical enhancement.

Abstract

Artificial nanostructures enable fine control of electromagnetic fields at the nanoscale, a possibility that has recently been extended to the interaction between polarised light and chiral matter. The theoretical description of such interactions, and its application to the design of optimised structures for chiroptical spectroscopies, brings new challenges to the common set of tools used in nano-optics. In particular, chiroptical effects often depend crucially on the relative orientation of the scatterer and the incident light, but many experiments are performed with randomly-oriented scatterers, dispersed in a solution. We derive new expressions for the orientation-averaged local degree of optical chirality of the electromagnetic field in the presence of a nanoparticle aggregate. This is achieved using the superposition T -matrix framework, ideally suited for the derivation of efficient orientation-averaging formulas in light scattering problems. Our results are applied to a few model examples, and illustrate several non-intuitive aspects in the distribution of orientation-averaged degree of chirality around nanostructures. The results will be of significant interest for the study of nanoparticle assemblies designed to enhance chiroptical spectroscopies, and where the numerically-efficient computation of the averaged degree of optical chirality enables a more comprehensive exploration of the many possible nanostructures.