Interaction of Structured Light with a Chiral Plasmonic Metasurface: Giant Enhancement of Chiro-Optic Response

We propose an approach to achieve giant enhancement and broad spectral tunability of the chiro-optic response of plasmonic metasurfaces by exploiting interaction with complex light, endowed with both spin and orbital angular momentum. As a proof of principle, we employ full-wave computational analysis to investigate the response of a structured, circularly polarized transverse Laguerre-Gaussian beam incident on a chiral metasurface composed of a two-dimensional array of gold nanohelix meta-atoms. Our analysis reveals for the first time unprecedented amplification of circular dichroism that is a manifestation of the total angular momentum of the incident light being enantioselectively transferred to the medium. We also demonstrate that the spectral response of the meta-atoms can be designed to produce a rich manifold of narrow spectral lines with steep gradients. The approach proposed here opens up opportunities for new spectroscopic modalities to probe fundamental molecular structure and behavior, as well as unique, multiplexed biochemical sensing technologies, and a new class of engineered chiral metamaterials in the form of versatile ultrathin media with unmatched optical performance for a gamut of applications, including a new direction for spin photonics, exploiting high reflection contrast between opposite spins.