Resonant helical dichroism in twisted dielectric metastructures

TL;DR

This paper demonstrates the design and experimental realization of twisted dielectric metastructures that exhibit resonant helical dichroism, enabling enhanced interaction with vortex beams carrying orbital angular momentum for advanced nanophotonic applications.

Contribution

It introduces a novel resonant helical dichroism effect in twisted dielectric metastructures, expanding the capabilities of structured light in nanophotonics.

Findings

Resonant HD observed for OAM up to 3.

High quality factor nonlocal photonic modes achieved.

Enhanced light-matter interaction with vortex beams.

Abstract

Circular dichroism, arising from interactions with light fields of opposite spin angular momentum, has become a fundamental tool for molecular characterization. Meanwhile, helical dichroism (HD) - the dichroic response to vortex beams carrying opposite orbital angular momentum (OAM) - offers an alternative approach for probing chiral molecules and photonic structures. Previous demonstrations of HD have been limited to non-resonant light-matter interactions with chiral micro- and nanostructures, leaving the realization of resonance helical dichroism largely unexplored. Here, we present the design and implementation of twisted dielectric metastructures, composed of an array of rotated silicon trimer nanostructures harnessing nonlocal photonic modes with a high quality factor of several dozen that enable strong resonant HD for OAM values up to $10$. We experimentally demonstrate resonantly enhanced HD for strongly focused OAM beams with the magnitude of topological charges from $1$ to $3$. Our findings pave the way for resonant nanophotonics involving OAM beams, unlocking the full potential of structured light for applications in molecular sensing, optical imaging, nonlinear optics, and optical data storage.