Inverse Design of Chiral Structures for Giant Helical Dichroism

TL;DR

This paper presents an inverse design approach to create chiral structures that significantly enhance helical dichroism responses to orbital angular momentum beams, surpassing natural and existing structures in strength.

Contribution

The study introduces a novel inverse design method using adjoint topology optimization to maximize helical dichroism in chiral structures under OAM beam illumination.

Findings

Achieved a giant HD response of approximately 107% at 800 nm wavelength.

Designed chiral structures with optimized geometry for enhanced OAM-based chiroptical interactions.

Demonstrated distinct helicity-dependent interactions between structure and OAM beams.

Abstract

Investigating chiral light-matter interactions is essential for advancing applications in sensing, imaging, and pharmaceutical development. However, the chiroptical response in natural chiral molecules and subwavelength chiral structures is inherently weak, with the characterization tool limited to optical methods that utilize the light with spin angular momentum (SAM). To overcome this, orbital angular momentum (OAM) beams, characterized by helical wavefronts, have emerged as a compelling research focus. Helical dichroism (HD) describes the differential absorbance of OAM beams with opposite signs of topological charges. By using inverse design with adjoint methods for topology optimization, we design the chiral structure optimized to increase HD response under OAM beam incidence, demonstrating a giant HD response of ~107% with topological charges $|\pm\ell|$ = 3 at the wavelength of 800 nm. This study reveals distinct helicity-dependent interactions between the structure and OAM beams, highlighting the potential for custom-tuned chiroptical responses.