Dutta Chizuko M, Ali Tamer A, Brandl Daniel W, Park Tae-Ho, Nordlander Peter
Department of Physics and Astronomy, Rice University, M.S. 61, Houston, Texas 77005-1892, USA.
J Chem Phys. 2008 Aug 28;129(8):084706. doi: 10.1063/1.2971192.
Using the plasmon hybridization method, we investigate the optical properties of metallic tori of different shapes and for different polarizations. The plasmon energies are found to be strongly dependent on polarization and on the aspect ratio of the torus, which we define as the ratio of the radii of the two circles that define the structure. For incident light polarized in the plane of the torus, the optical spectrum is characterized by two features, a long wavelength highly tunable dipolar plasmon resonance, and a short wavelength mode corresponding to excitation of several higher order torus modes. For aspect ratios smaller than 0.8, we find that the energy of the tunable dipolar torus mode can be described analytically as an infinite cylinder plasmon of a wavelength equal to the length of the tube. For perpendicular polarization, the spectrum exhibits a single feature made up of several closely spaced higher order torus modes which are only weakly dependent on the aspect ratio. The calculated optical properties are found to be in excellent agreement with results from numerical finite difference time domain calculations and with results from other groups.
利用等离子体激元杂交方法，我们研究了不同形状和不同偏振的金属环面的光学性质。发现等离子体激元能量强烈依赖于偏振和环面的纵横比，我们将其定义为定义该结构的两个圆的半径之比。对于在环面平面内偏振的入射光，光谱具有两个特征，一个是长波长的高度可调偶极等离子体激元共振，另一个是对应于几个高阶环面模式激发的短波长模式。对于纵横比小于0.8的情况，我们发现可调偶极环面模式的能量可以解析地描述为波长等于管长的无限圆柱等离子体激元。对于垂直偏振，光谱呈现出由几个紧密间隔的高阶环面模式组成的单一特征，这些模式仅微弱地依赖于纵横比。计算得到的光学性质与数值有限差分时域计算结果以及其他研究小组的结果非常吻合。
