Optical Chirality of Gold Chiral Helicoid Nanoparticles in the Strong Coupling Region

Abstract

The far- and near-field chirality properties are usually characterized by circular dichroism (CD) and optical chirality (OC), respectively. As a light–matter interaction for the hybrid states consisting of plasmons and excitons, the strong coupling interactions can affect the original chiral electromagnetic modes. However, there are few works on this influence process, which prevents an in-depth understanding of chirality. Here, we theoretically investigate both the far-field and near-field characteristics of the chiral plasmonic gold helicoid nanoparticle (GHNP) to explore the chirality mechanism further. We found that the electromagnetic field distribution of GHNP consists of one dark mode and two bright modes. The dark mode is observed more clearly in CD than in extinction spectra. Two bright modes can strongly couple with excitons respectively, which is confirmed by the anticrossing behavior and mode splitting exhibited in the extinction and CD spectra. We also analyzed the near-field OC distribution of the GHNP hybrid system and obtained the chiral responses as well as the spectral correspondence between OC and CD. Furthermore, although the strong coupling interaction changes the energy levels, resulting in mode splitting, the chiral hotspot distributions of both the upper polariton branch and lower polariton branch are consistent with the original bright mode in OC maps. Our findings provide guidance for the design of structures with strong chiral responses and enhance the comprehension of chiral strong coupling systems.

Chiro-plasmon responses of x-shaped titanium nitride (TiN) nanoarrays by numerical simulations

“…Chiral plasmon metamaterials have found broad applications in various fields such as chiral sensing [2][3][4], optical devices [5,6], analytical chemistry [7][8][9], and so on [10][11][12][13][14]. As one of the crucial parameters of chiral optical response, CD is defined as the difference in the absorption of chiral structures illuminated by left-handed and right-handed circularly polarized lights [15], and it is also reported to be estimated by the spectra difference in the scattering, extinction and/or transmittance spectra [16][17][18]. Typically, large CD signals in the UV range can come from the helical geometry of molecular systems, however, strong optical CD effect in the visible to near infrared range is usually weak which limit its potential application for biosensors and optoelectronic devices.…”

Tuning the Plexcitonic Optical Chirality Using Discrete Structurally Chiral Plasmonic Nanoparticles

“…Moreover, recent advances also demonstrated that CD measurements may be more advantageous in probing chiral plasmon−exciton coupling in the plexcitonic complexes. 42,44,69 Thus, we employed CD spectroscopy to further investigate the plexcitonic optical chirality, with special attention given to the Rabi splitting that was observed in CD spectra. Chiral plexcitonic complexes exhibit coherent coupling between the chiral plasmons of AuAg NRs and excitons of the J aggregates, resulting in the formation of two new plexcitonic modes: an upper plexciton branch (UPB) and a lower plexciton branch (LPB).…”

“…Plasmonic NPs with an intrinsic chiral structure provide a promising approach for constructing hybrid plexcitonic systems with tunable optical chirality. Like chiral structures prevalent in nature such as nucleic acids and proteins, inorganic NPs can also possess structural chirality. − Recent advances have witnessed great success in the geometric control and optical tuning of chiral plasmonic NPs. − Chiral plasmonic NPs with tunable optical chirality can be controlled by changing chiral molecules, the seeds, and other synthetic parameters during the growth processes. − Moreover, theoretical and experimental observations have demonstrated interesting far-field and near-field interplay between chiral plasmonic nanostructure and excitons, particularly in the strong coupling regime. − Despite these pioneering efforts, tuning the plexcitonic optical chirality through the coupling between the chiral plasmonic nanostructure and excitons remains a significant challenge.…”

“…The simulation results effectively illustrate that, in our case, the CD spectrum proves to be more sensitive to plasmon–exciton coupling than the extinction spectrum. Moreover, recent advances also demonstrated that CD measurements may be more advantageous in probing chiral plasmon–exciton coupling in the plexcitonic complexes. ,, Thus, we employed CD spectroscopy to further investigate the plexcitonic optical chirality, with special attention given to the Rabi splitting that was observed in CD spectra.…”