# Helicity-preserving optical cavity modes for enhanced sensing of chiral molecules

## TL;DR

This paper introduces a novel helicity-preserving optical cavity using silicon disks that significantly amplifies circular dichroism signals, enabling more sensitive detection of chiral molecules compared to traditional Fabry-Perot cavities.

## Contribution

The study presents a new cavity design that enhances chiral molecule sensing by preserving light helicity, surpassing conventional cavities in CD signal amplification.

## Key findings

- Enhancement of CD signals by over two orders of magnitude.
- Helicity-preserving modes with large transverse momentum and long lifetimes.
- Contrast with conventional Fabry-Perot cavities showing reduced CD despite intensity enhancement.

## Abstract

Researchers routinely sense molecules by their infrared vibrational "fingerprint" absorption resonances. In addition, the dominant handedness of chiral molecules can be detected by circular dichroism (CD), the normalized difference between their optical response to incident left- and right- handed circularly polarized light. Here, we introduce a cavity composed of two parallel arrays of helicity-preserving silicon disks that allows to enhance the CD signal by more than two orders of magnitude for a given molecule concentration and given thickness of the cell containing the molecules. The underlying principle is first-order diffraction into helicity-preserving modes with large transverse momentum and long lifetimes. In sharp contrast, in a conventional Fabry-Perot cavity, each reflection flips the handedness of light, leading to large intensity enhancements inside the cavity, yet to smaller CD signals than without the cavity.