Local versus bulk circular dichroism enhancement by achiral all-dielectric nanoresonators

TL;DR

This paper investigates how achiral dielectric nanodisks can enhance optical chirality for circular dichroism, emphasizing the importance of spatial distribution, nanostructure geometry, and substrate effects for designing nanophotonic chiroptical devices.

Contribution

It provides a theoretical analysis of spatial chirality enhancement around dielectric nanodisks, highlighting the influence of aspect ratio, averaging procedures, and substrates on optimal nanostructure design.

Findings

Chirality enhancement varies with disk aspect ratio and direction.

Optimal nanostructure properties depend on whether maximum or average chirality is desired.

Substrate presence significantly affects the spatial distribution of optical chirality.

Abstract

Large optical chirality in the vicinity of achiral high index dielectric nanostructures has been recently demonstrated as useful means of enhancing molecular circular dichroism. We theoretically study the spatial dependence of optical chirality enhancement in the vicinity of high index dielectric nanodisks and highlight its importance for the design of nanophotonic platforms for circular dichroism enhancement. Using a T-matrix framework, we demonstrate that depending on disk aspect ratio chirality is enhanced preferentially along different directions. We employ various statistical procedures (including surface, volume and orientation averaging) that are necessary to predict the enhancement of chiroptical effects and show that optimal properties of a nanostructure depend substantially on whether spatial maximum or average chirality enhancement is sought after. Similarly, the optimal choice of the nanostructure is influenced by the presence of substrate, which limits the space available to be occupied by analyte molecules and impacts the optical chirality in the vicinity of the nanostructure.