Characterization of Photopolymerized Microscopic Chiral Structures Using Photonic Orbital Angular Momentum

TL;DR

This paper presents a low-cost, accessible method for fabricating and characterizing microscale chiral structures using digital micromirror devices and liquid-crystal spatial light modulators, demonstrating their chiroptical properties via helical dichroism.

Contribution

The authors develop a practical platform combining maskless photolithography and vortex beam characterization to produce and analyze microscale chiral structures without specialized high-end equipment.

Findings

HD signals of ~30% observed for 15-micrometer structures

Finite-difference time-domain simulations match experimental spectra

OAM response distinguishes enantiomers and achiral controls

Abstract

The controlled fabrication and chiroptical characterization of microscale chiral structures remain central challenges in photonics, sensing, and metamaterial engineering. Here we demonstrate an accessible, low-cost platform that combines digital micromirror device-enabled maskless photolithography with capillarity-induced self-assembly to produce polymer chiral microstructures of deterministic handedness, and a liquid-crystal spatial light modulator to generate vortex beams for their characterization via helical dichroism (HD). Using a standard 532 nm laser, we observe HD signals of approximately 30% for microstructures with a characteristic diameter of about 15 micrometers. Rigorous finite-difference time-domain simulations performed on three-dimensional geometries reconstructed from high-resolution Scanning Electron Microscopy data reproduce the experimental HD spectra and confirm the role of structural handedness in driving the differential orbital angular momentum (OAM) response. Near-mirror-symmetric HD spectra for opposite-handed enantiomers, combined with a vanishing response for achiral controls, establish OAM as a robust and spatially selective chiral probe at the microscale. Crucially, both fabrication and characterization rely on equipment standard in an optics laboratory, without recourse to femtosecond sources, plasmonic substrates, or costly photoresists. These results open practical pathways toward OAM-driven chiral sensing, enantioselective detection, and photonic logic devices.