Chiral optical fields: A unified formulation of helicity scattered from particles and dichroism enhancement

TL;DR

This paper presents a unified theoretical framework for understanding and enhancing optical dichroism and helicity scattering in chiral electromagnetic fields, overcoming limitations of traditional circular dichroism techniques.

Contribution

It introduces a general formulation based on the optical theorem of helicity, enabling dichroism analysis in all scattering processes and proposing methods to enhance dichroism signals.

Findings

Dichroism arises in any scattering process of chiral fields, regardless of object chirality.

New beam configurations with elliptic polarization can enhance helicity extinction rates.

The approach overcomes weak signals and material limitations of standard circular dichroism.

Abstract

We establish a general unified formulation which, using the optical theorem of electromagnetic helicity, shows that dichorism is a phenomenon arising in any scattering -or diffraction- process, elastic or not, of chiral electromagnetic fields by objects either chiral or achiral. It is shown how this approach paves the way to overcoming well-known limitations of standard circular dichroism, like its weak signal or the difficulties of using it with magnetodielectric particles. Based on the angular spectrum representation of optical fields with only right circular or left circular plane waves, we introduce beams with transverse elliptic polarization and posessing a longitudinal component. Then our formulation for general optical fields shows how to enhance the extinction rate of incident helicity, (and therefore the dichroism signal), versus that of energy of the light scattered or emitted by a particle, or viceversa.