Meta-Optical Chirality and Emergent Eigen-polarization Modes via Plasmon Interactions

Matthew Moocarme,Nicholas V Proscia,Luat T Vuong

doi:10.1038/srep40718

Matthew Moocarme, Nicholas V Proscia + Show 1 more

Open Access

https://doi.org/10.1038/srep40718

Copy DOI

Abstract

The response of an individual meta-atom is often generalized to explain the collective response of a metasurface in a manner that neglects the interactions between meta-atoms. Here, we study a metasurface composed of tilted achiral meta-atoms with no spatial variation of the unit cell that derives appreciable optical chirality solely from the asymmetric interactions between meta-atoms. The interactions between meta-atoms are considered to stem from the Lorentz force arising from the Larmor radiation of adjacent plasmonic resonators because their inclusion in a simple model accurately predicts the bonding/anti- bonding modes that are measured experimentally. We also experimentally observe the emergence of multiple polarization eigenmodes, among other polarization-dependent responses, which cannot be modeled with the conventional formalism of transmission matrices. Our results are vital to the precise characterization and design of metasurfaces.

Highlights

The response of an individual meta-atom is often generalized to explain the collective response of a metasurface in a manner that neglects the interactions between meta-atoms
Chiral metasurfaces can be defined as those that exhibit a response dependent on the incident circular-polarization handedness, though the specific mechanism behind the phenomena has been debated; it has been argued that planar structures such as metasurfaces cannot exhibit true optical activity (OA) or circular dichroism (CD) without the excitation of magnetic resonances since certain 3D symmetry properties are not satisfied[7,8]
We study rectangular plasmonic resonators whose arrangement leads to chiral phenomena at normal incidence, or identical tilted achiral nanostructures in a lattice that lead to a chiral response

Summary

M qm κκ13xy

The perpendicular Lorentz force couples to the orthogonal modes of the different resonators, which leads to optical chirality in the metasurface. The strength of the parallel force F|| scales approximately with the experimentally-measured spectral splitting of transmission resonances. The interaction force leads to other experimentally-measured polarization-dependent metasurface responses. We illuminate the metasurface with linearly-polarized light (ellipticity χ < 1°) at a wavelength λ = 660 nm and observe that the transmitted changes in the azimuthal and elliptical components of the fields, Δψand Δχ, depend on the angle of linear polarization [Fig. 3(a)]. The discrepancies between theoretical and experimental OR indicate the limit of the transmission matrix formalism that assumes that all resonators oscillate in-phase, which may not be true when an interaction force is present between meta-atoms. The corresponding system of equations in our model predicts multiple polarization eigenmodes that are observed at visible wavelengths and at low illumination power, independent of illumination intensity

Discussion and Conclusion

Methods