Research Of Optical Properties Of Au Nanoring With Discrete Dipole Approximation Method

Annular nano-structure is a desired field of research in recent years.This research mainly calculates the optical properties of non-concentric annulus where an internal annular ring deviates from center.We find that the extinction curve peak wavelength red shifts when electric vibration path effective width decreases.In Chapter 1,we introduce the basic concept of surface plasmon and the recent studies of the different structures of metal nanoparticles,especially the study of annular structure.In Chapter 2,we introduce discrete dipole approximation(DDA).It can calculate the absorption,scattering,extinction properties of the target.We use Green function method to solve wave equation to obtain these properties.In Chapter 3,we introduce the DDSCAT 7.2,a kind of software on the basis of discrete dipole approximation method.It can calculate the optical properties of arbitrary structure in principle.We explain the type and setting of parameters in the package.In Chapter 4,we calculate the optical properties of Au annuluses with different structural parameters using the DDSCAT 7.2.First we calculate the resonance characteristics of an annulus.The peak wavelength(i.e.the local surface plasmon resonance wavelength)red shifts when the internal circle moves along the z axis.The peak wavelength also red shifts when the internal circle moves along the y axis,but the redshift is not obvious because the inner circle moves along polarization direction of incident light.We rotate the inner circle around the center.The resonance wavelength blue shifts as the rotation angle increasing.Finally we calculate the resonance characteristics of the double annuluses.We add a concentric annulus to the right of the non-concentric annulus along the polarization direction.We change the rotation angle of the inner ring on the left side and compute the resonance properties of the ring structure.When the left ring is non-concentric,the extinction properties strongly depend on the polarization direction of incident light.