Ultra-sensitive Experimental Detection of Chiral Meso-structures by Orbital Angular Momentum of Light

TL;DR

This paper demonstrates a novel method for directly detecting chiral microstructures using orbital angular momentum of light, achieving a giant helical dichroism of about 120%, which enhances chiral spectroscopy capabilities.

Contribution

The study introduces the first experimental observation of giant helical dichroism induced by OAM beams interacting with chiral microstructures, surpassing previous small dichroism levels.

Findings

Achieved ~120% helical dichroism with OAM beams and chiral structures.

Demonstrated sign-opposite HD values to distinguish chirality.

Showed robust HD performance across various structural parameters.

Abstract

Circular dichroism (CD) induced by spin angular momentum of light is vital to investigate the chirality of microscopic objects such as molecules, proteins and metamaterials. However, orbital angular momentum (OAM) of light failed to directly implement an interaction with chiral molecules, which remains poorly understood. Even with the enhancement of unique plasmonic nanoparticle aggregates, the helical dichroism (HD) is still at a small level of ~0.6%. Here, we experimentally report the direct observation of a giant HD at the level of ~120% by matching the scales of chiral microstructures and OAM beams. Our results reveal a strong interaction between OAM beams and chiral microstructures in terms of their distinct reflectance, resulting in sign-opposite HD values to distinguish their chirality. Such unique HD phenomenon is investigated experimentally under various diameters and helical pitches of chiral structures, showing the robust performance. This HD technique can widely extend the responding areas of chiral spectroscopy in biology, material science and nanotechnology.