Inverse design of chiral structures for giant helical dichroism.

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 conventional characterization tools limited to optical methods that utilize circularly polarized light. To overcome this, optical vortex beams, characterized by helical wavefronts, have emerged as a compelling research focus. Helical dichroism (HD) represents the differential absorbance of vortex beams with opposite signs of topological charges. By using inverse design for topology optimization, we design the chiral structure for enhanced HD response under OAM beam incidence, demonstrating a giant HD response of ∼107% with topological charges |±| = 3 at the wavelength of 800 nm. This study reveals distinct helicity-dependent interactions between the chiral structure and OAM beams, highlighting the potential for highly sensitive chiral devices.