Enhanced Transmission Characteristics Of Multilayer Metal Wedge Slits And Circular Dichroism Of Silver Nanorod Dimers

Surface plasmon (SP), which is the coupled mode of incident electromagnetic wave and free charges on a metal surface. It is a kind of unusual optical properties. According to Electronic oscillation, it can be divided into the following two types: propagating surface plasmon polaritons (SPPs) along the metal and medium interface, and localized surface plasmon (LSP) can not spread due to the nano structure size limit. Due to the SP in photocatalysis, nano integrated photonics, optical sensing, biomarkers, solar cells, as well as surface enhanced Raman spectroscopy, and other fields have broad application prospects, the SP have received a lot of attention lately. Plasmonics is now becoming a rapidly developing field.In this paper, the optical properties of tapered multilayer slits and Silver Nanocuboid Heterodimers have been studied by using the finite element method (FEM). The main research works of this thesis are listed as follows:(1) This paper proposes the metal/medium/metal tapered multilayer slits——a tapered multilayer slit is composed of upper and lower monolayer slits that are separated by a dielectric layer structure. Transmission properties are strongly dependent on structural parameters. This study indicates that, the effective refractive index of the tapered multilayer slits changed with the parameters of medium varied. In accordance with that, the optical transmission of broadband of tapered multilayer slits can be manipulated. Furthermore, the asymmetry and the smaller deviation of the two separated monolayers do not alter the performance of broadband, and the enhanced transmission of the tapered multilayer slits obviously in the infrared region. The transmission properties are robust against the asymmetry, and deviation of the two separated monolayer slits. This finding can thus guide the fabrication of such slits and their future applications in nearfield optics.(2) This paper proposes a chiral structure——Silver Nanocuboid Heterodimers arrays. The physical mechanisms of the resonance valleys under the left-hand circularly polarized light and right-handed circularly polarized light have been studied. Transmission spectra, normalized electric-field distribution, and surface current density were investigated. The circular dichroism (CD) effect is strongly dependent on structural parameters. This study indicates that, the nanocuboid heterodimers can generate a CD effect. The chiral system of the nanocuboid heterodimer can be viewed as a right-handed enantiomer, in which bonding modes are easier to be excited under RCP illumination than under LCP illumination. Conversely, antibonding modes are easier to be excited under LCP illumination than under RCP illumination. These characteristics bring different resonance peak transmittances with heterodimers under different circularly polarized light incident, and thus produce circular dichroism. This investigation can help not only in the design of chiral plasmonic structures to generate CD effects but also in understanding the physical mechanisms of CD effects.