Optical chirality density and flux measured in the local density of states of spiral plasmonic structures

Abstract

Efforts to improve enantioselective detection of chiral molecules have initiated great interest in the fields of chiral light and chiral plasmonics. While superchiral light had been reported as highly sensitive enantiomer probes, optical response of chiral molecules can also be boosted at the vicinity of chiral plasmonic structures due to enhanced light-molecule coupling. Here, we apply the fundamental description of chiral light, known as the chirality density and flux, to the local density of states (LDOS) which rules the processes of light-matter interactions. In spiral plasmonic structures, we experimentally demonstrate the mapping of far-field chiral LDOS properties by means of polarimetry analysis. We establish the link between the degree of circular polarization of freely propagating cavity modes and the chirality density and flux. Using the reciprocity theorem, we show that this measure can be used to probe to the near-field chirality associated with surface plasmon field. By mapping the chiral features of the LDOS, we report a helpful method for guiding the design of superchiral light and for the investigation of chiral light-matter interactions, opening doors to improved chiral molecular sensing.