Study On Optical Properties Of Multi - Cut Gold Nanometer Ring Array

Surface plasmon (SP), which is the coupled mode of incident electromagnetic wave and free charges on a metal surface. According to manifestation of SP, it can be divided into the following two types:propagating surface plasmon polaritons (SPPs) and localized surface Plasmon (LSP). Near and far field characteristics of noble metal nanoparticles mainly derived from their LSP. Many studies have found that localized surface plasmon resonance (LSPR) characteristics on the metal surface is very sensitive to the shape, size, dielectric properties, the surrounding medium of the metal nanoparticles. In addition, LSP can make surface electric field enhance in a particular area of nanoparticles, which improves the efficiency of optical response significantly. These features make LSP used widely in surface enhanced raman scattering, nonlinear optics, biology medicine, etc. Chiral metal micro-nano structure is emerging in recent years, which is widely used in many fields, the surface plasmon resonance characteristics of chiral metal micro-nano structure can cause the specific optical properties. This thesis uses the finite element method (FEM) to study the optical properties of multicut split-ring (MSR) arrays, bilayered multicut split-ring (BMSR) arrays and twisted BMSR arrays. The main research works of this thesis are listed as follows:(1) We study the LSPR of MSR arrays and the effects of incident light polarization angle, structure parameters on LSPR by finite element method. The simulative results show that the transmission spectra are not dependent on the incident light polarization angle, but the local surface electric field is very dependent on incident light polarization angle. When the structure parameters of MSR arrays change, the transmission spectra redshift or blueshift and we explain the shift using the aspect ratio of nanoparticles.(2) We designed a bilayered structure-BMSR arrays to study the physical mechanism of transmission valley and the effects of incident light polarization angle, structure parameters on transmission spectra. The results show there is another resonance mode -magnetic resonance mode with respect to MSR arrays, the structure in this mode can be equivalent to LC circuits. The transmission spectra are not dependent on incident light polarization angle. The change in structure parameters makes the transmittance spectra redshift or blueshift.(3) Mutually twisted BMSR is chiral structure and we study its circular dichroism (CD). With the increase in the twisted angle, strong CD effect appears within three wavelength ranges. By investigating the current distributions on the inner metallic surfaces (facing each other) for the RCP and LCP incidence at a CD peak, we obtain the physical mechanism of CD effect. Finally, we calculate the CD spectra of twisted BMSR arrays under different structure parameters.