Nanophotonic chiral sensing: How does it actually work?

TL;DR

This paper develops a comprehensive theoretical framework for nanophotonic chiral sensing, elucidating the underlying light-matter interactions and enabling more efficient spectral predictions, which advances the understanding and design of chiral sensors.

Contribution

It introduces a general perturbation-based theory for chiral light-matter interactions in arbitrary resonators, bridging the gap between simple models and numerical simulations.

Findings

Identifies resonance shift and mode excitation changes as key interaction mechanisms.

Provides a more efficient method for spectral prediction in chiral sensing.

Offers insights for optimizing nanophotonic structures for enhanced chiral detection.

Abstract

Nanophotonic chiral sensing has recently attracted a lot of attention. The idea is to exploit the strong light-matter interaction in nanophotonic resonators to determine the concentration of chiral molecules at ultra-low thresholds, which is highly attractive for numerous applications in life science and chemistry. However, a thorough understanding of the underlying interactions is still missing. The theoretical description relies on either simple approximations or on purely numerical approaches. We close this gap and present a general theory of chiral light-matter interactions in arbitrary resonators. Our theory describes the chiral interaction as a perturbation of the resonator modes, also known as resonant states or quasi-normal modes. We observe two dominant contributions: A chirality-induced resonance shift and changes in the modes excitation and emission efficiencies. Our theory brings new and deep insights for tailoring and enhancing chiral light-matter interactions. Furthermore, it allows to predict spectra much more efficiently in comparison to conventional approaches. This is particularly true as chiral interactions are inherently weak and therefore perturbation theory fits extremely well for this problem.