Study On The Circular Dichroism Of Double-layer Metal Slits And Bimetallic Rod Structures

Surface plasmon (SP), which is electromagnetic oscillation wave formed by the interaction between free charges in metal micro-nano structure and the incident electromagnetic wave. It has attracted a lot of attention due to their special optical properties. Surface plasmon is closely related to the morphology of the nanostructure, the environmental material, the polarization state of incident light and so on. Therefore, we can change these factors to control the surface plasmon of the nanostructures, in order to satisfy their applications in physics, chemistry and biomedical areas.Metal micro-nano chiral structure has gradually become the research hotspot of artificial chiral structure in recent years. Under the strong interaction between nanostructure and right-hand and left-hand circularly polarized light, the different surface plasmon resonance make it produce the strong circular dichroism (circular dichroism, CD). Due to the circular dichroism strongly depends on the structure parameters, we can change the structure parameters to control the circular dichroism.This paper uses the finite element method to simulate the CD effect of two kinds of chiral metal micro-nano structure, and their dependence on structural parameters are also studied. The specific contents and results of this paper are listed as follows:(1) Gold bilayered slit arrays with rectangular holes embedded into the metal surface are designed to enhance the CD effect of gold bilayered slit arrays. For the structure, the rectangular holes in these arrays block electric currents and generate localized surface plasmons around these holes, thereby strengthening the CD effect. The CD enhancement factor depends strongly on the rotational angle and the structural parameters of the rectangular holes. This factor can be enhanced further by drilling two additional rectangular holes into the metal surfaces of the arrays. These results help to design plamon chiral nanostructures with the strong CD effect and large electric fields.(2) We put forward a way that use dielectric layer to enhance the circular dichroism of double metal nanorods arrays planar chiral structure, and study the circular dichroism of double metal nanorods arrays structure covered with dielectric. Results show that compared with double metal nanorods arrays planar chiral structure, double metal nanorods arrays structure covered with dielectric not only can produce a stronger CD effect, but also form a new mode caused by the dielectric layer. Under the circularly polarized light irradiation, two metal nanorods formed the equivalent electric dipole, the introduction of the dielectric layer make two electric dipole a larger phase difference. Two dipole formed bonding or antibonding pattern are coincide with the CD mechanism in Born-Kuhn model, thus this structure can produce a stronger CD effect. The CD effect is strongly depends on the refractive index of the dielectric and the thickness of the dielectric layer. These results not only contribute to a better understanding of the CD physical mechanism, but also have a certain guiding significance on the experimental preparation of chiral structure with CD effect.