Circular dichroism (CD) caused by the response of a chiral object to circularly polarized light has been well established, and the strong CD of plasmonic meta-molecules has also become of interest in recent years; however, their response if the light also has orbital angular momentum is unclear. In this paper, the dichroism of a plasmonic cuboid-protuberance chiral structure under the illumination of a light beam with both orbital and spin angular momentums is numerically investigated. Distinguished spectra are observed under the different momentums. The circular dichroism under the combination of vortex beam and light spin is enhanced. This phenomenon is attributed to the partial spatial excitation of the nanoparticle, and the strong dichroism is simultaneously caused because of the interaction of the induced electric and magnetic modes and other higher-order modes caused by the partial excitation of the vortex beam. This research provides further insight into chiral light-matter interactions and the dichroism of light with orbital angular momentum.

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In plasmonic induced chirality, the circular dichroism of achiral nanoparticles (NPs) caused by Coulombic interactions between metal nanoparticles (NPs) and chiral molecules has been studied. Under resonance conditions, dye molecules and metal NPs produce large Rabi splitting due to strong coupling. If the resonance of chiral molecules is at the resonance of the plasmon, it is unclear what will happen to the strong interactions between the chiral plasmon and chiral molecules. In this paper, we investigate a coupled spherical core–shell model and analyze its spectra under excitation by circularly polarized light (CPL). Based on the Coulombic interactions between NPs and chiral molecules, we demonstrate how various factors affect this coupling. We have determined that three mechanisms are responsible for the interactions between plasmons and chiral molecules: strong coupling (Rabi splitting up to 243 meV), enhanced absorption, and induced transparency. The interactions between CPL and chiral molecules with same chiralities are stronger than those of the opposite chirality. The linewidth values of the splitted peaks are closer than those of the opposite chirality, which shows that for Rabi splitting with chiral molecules, there are more complicated mechanisms responsible for the interactions. This result will be helpful for further investigation of interactions between plasmons and chiral molecules.

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Quantum theory of surface plasmons is very important for studying the interactions between light and different metal nanostructures in nanoplasmonics. In this work, using the canonical quantization method, the SPPs on nanowires and their orbital and spin angular momentums are investigated. The results show that the SPPs on nanowire carry both orbital and spin momentums during propagation. Later, the result is applied to the plasmonic nanowire waveguide to show the agreement of the theory. The study is helpful for the nano wire based plasmonic interactions and the quantum information based optical circuit in the future.