Chiroptical response of an array of isotropic plasmonic particles having a chiral arrangement under coherent interaction.

The chirality and chiroptical response of materials have attracted significant attention for their potential to introduce the new science of light-matter interactions. We demonstrate that collective mode formation under modal coupling between localized surface plasmon resonances (LSPRs) with a chiral arrangement and Fabry-Pérot (FP) nanocavity modes can induce chiroptical responses. We fabricated a cluster of isotropic gold nanodisks with a chiral arrangement (gold nano-windmills, Au-NWs) on the FP nanocavities of TiO₂ and Au film. The differential absorption of the Au-NWs coupled with the FP nanocavities under left- and right-handed circularly polarized light irradiations in the far field was significantly enhanced compared with the differential absorption without the FP nanocavities. Far- and near-field analyses by numerical simulation revealed that the Au-NWs coupled with the FP nanocavities formed a collective mode in the near field, and the collective mode represented the chiroptical response in the far field. The light field with the large helicity, can be used in chiral light-matter interactions. The concept of collective mode formation using isotropic metal nanodisks coupled with FP nanocavities provides a platform for controlling complex light fields.