Evanescent Field Polarization for Giant Chiroptical Modulation from Achiral Gold Half-Rings: Theoretical Insight from Simulations

Metal nanoantennas have been under intense investigation due to their strong light−matter interactions and significant polarization sensitivities determined by their structure. For applications seeking to realize on-chip polarization-discriminating nanoantennas, efficient energy conversion from surface waves to far-field radiation is desirable. However, the response of individual nanoantennas to the particular polarization states achievable in surface waves, such as evanescent fields, has not yet been thoroughly studied.
Here, we report the giant modulation of the visible light scattering predicted from gold half-ring, pinwheel, rods, and other nanoantennas excited through total internal reflection of left- and right-handed circularly polarized light, by exploiting the distinct polarization properties of surface evanescent waves [ACS Nano, 12, 11657 (2018); PNAS, 117, 16143, (2020)]. This result provides a fundamentally different mechanism for chiroptical responses requiring a phase delay between transverse and longitudinal electric field oscillations, not found in free-space light. Specifically, we focus on the insight provided by the electromagnetic simulations, performed with COMSOL Multiphysics software, of the systems of interest and aspects of their chiroptical response.