Giant Enhancement of the Chiro-Optic Response of Chiral Plasmonic Media using Structured Light

I.V.A.K. Reddy, V. Sukhotskiy, A. Baev, E.P. Furlani, P.N. Prasad, J.W. Haus
University at Buffalo SUNY,
United States

Keywords: structured light, chiral metasurfaces, plasmonics, circular dichroism, biosensing

Summary:

We propose an approach to achieve a great enhancement and broad spectral tunability of the chiro-optic response of plasmonic metasurfaces by exploiting their interaction with light of complex polarization, endowed with both spin (SAM) and orbital angular momentum (OAM). As a proof of principle, we employ full-wave computational analysis to investigate the response of a circularly polarized transverse Laguerre-Gaussian beam having a structured wavefront, incident on a chiral metasurface composed of a two-dimensional array of gold nanohelix meta-atoms. For the first time, our analysis reveals unprecedented amplification of circular dichroism, which is a manifestation of the total angular momentum of the incident light being enantio-selectively transferred to the chiral medium. The spectral response of the meta-atoms can be designed to produce a rich manifold of narrow spectral lines with steep E-field gradients. The proposed approach opens up opportunities for new spectroscopic modalities to probe fundamental molecular structure and behavior, as well as unique, multiplexed biochemical sensing technologies. It should stimulate the development of a new class of engineered chiral metamaterials in the form of versatile ultra-thin media that will manifest unmatched optical performance for a range of applications, including a new direction for spin photonics, which can exploit the high reflection contrast between opposite spins. Past work has shown that such media can be fabricated using helical chiral polymers with tethered gold nanoparticles. Using these media in conjunction with OAM light, many optical phenomena can be enhanced by orders of magnitude. We demonstrate a versatile tunability of enhanced coupling between structured light, carrying both SAM (circular polarization) and OAM, and plamonic nanohelix metamaterials. We also discuss relevant applications that can leverage this coupling.