High-definition 3D suspended Archimedean spiral with broadband, spatially extended, and single-handed optical chirality enhancement in Vis-NIR range

Abstract: 3D plasmonic structures can provide giant optical chirality (C) in the near field, enabling strong interactions with enantiomers for chiral sensing applications. However, these structures face several limitations, including narrow operational bandwidth constrained by resonance, flipping handedness of C around the resonant frequency, spatially confined distribution of C, and difficulty in trapping enantiomers. Our numerical predictions reveal that a 3D plasmonic Archimedean spiral (AS) exhibits spectrally broadband, spatially extended and single-handed near-field C in visible-to-near-infrared range. However, realizing highly deterministic 3D AS remains challenging. We develop an effective fabrication strategy that combines focused ion beam milling and template-stripping method to realize high-definition 3D AS. Furthermore, we experimentally characterize the fabricated structure's far-field chiroptical behavior to confirm the predicted optical response. Owing to its conical hole-like geometry, 3D AS can potentially function as a sieve for trapping enantiomer-functionalized nanoparticles in the hot zone with enhanced C for sensitive broadband chirotical detection.