Maximizing the electromagnetic chirality of thin metallic nanowires at optical frequencies

TL;DR

This paper develops a gradient-based optimization method to design thin metallic nanowires with maximal electromagnetic chirality at optical frequencies, surpassing traditional helical structures, for enhanced chiral metamaterials.

Contribution

It introduces a novel optimization approach for designing nanowires with unprecedented electromagnetic chirality measures at optical frequencies.

Findings

Optimized nanowires exceed traditional helices in chirality measures.

Numerical examples demonstrate the effectiveness of the optimized designs.

Optimized nanowires are suitable as building blocks for advanced chiral metamaterials.

Abstract

Electromagnetic waves impinging on three-dimensional helical metallic metamaterials have been shown to exhibit chiral effects of large magnitude both theoretically and in experimental realizations. Chirality here describes different responses of scatterers, materials, or metamaterials to left and right circularly polarized electromagnetic waves. These differences can be quantified in terms of electromagnetic chirality measures. In this work we consider the optimal design of thin metallic free-form nanowires that possess measures of electromagnetic chirality as large as fundamentally possible. We focus on optical frequencies and use a gradient based optimization scheme to determine the optimal shape of highly chiral thin silver and gold nanowires. The electromagnetic chirality measures of our optimized nanowires exceed that of traditional metallic helices. Therefore, these should be well suited as building blocks of novel metamaterials with an increased chiral response. We discuss a series of numerical examples, and we evaluate the performance of different optimized designs.