Orbital Angular Momentum Driven Plasmonic Probes for Nanoscale Chirality Imaging  

Optical vortex beams have been used in many applications, such as nanoscale imaging, telecommunications, sensing, and so on, due to their unique azimuthal phase distribution. In this talk, I present the development of plasmonic fiber probes for nanoscale chirality imaging and their applications in probing the interaction of vortex beams with helical metastructures as well as chiral molecules. The vortex beam carrying an orbital angular momentum (OAM) exhibits a phase singularity, which offers a new platform for distinguishing the enantiomers of the chiral molecule. I will detail the design, simulation, fabrication, and characterization of plasmonic OAM probes integrated with a polarization-maintaining ring-core vortex fiber. This configuration facilitates free-space vortex beam generation and stable propagation through the fiber, simplifying the optical setup and enhancing optical stability. Numerical simulations reveal the nano-focusing of the OAM beam when plasmonic nanostructures are incorporated on the vortex fiber facet. Experimental helicity measurements confirm the stable transmission of the circularly polarized-OAM beam through the nanostructures fabricated on the straight-cleaved vortex fiber facet. Furthermore, helical dichroism measurements reveal that engineered helical metastructures exhibit a strong helical response to the incident OAM beam, indicating efficient coupling between the OAM and the structural helicity of the metasurfaces.