Plasmonics properties of nano-torus: An FEM method

Nano-torus particles are promising in nano-photonics applications. In this paper, we investigate the plasmonics resonant spectrum of torus and the corresponding horizontal and vertical dimers with the finite element method (FEM) based on strict electromagnetic theory. Compared with sphere, single torus and horizontal dimer under perpendicular polarization are characterized with narrower line width and wider tunability throughout visible and infrared frequencies. These properties make single torus and horizontal dimer suitable for high sensitivity sensing. Furthermore, Purcell factor and local field enhancement of horizontal dimer which are important to high efficient single photon devices are one order of magnitude higher than those of single torus respectively. However, vertical dimer under perpendicular polarization has no above advanced characteristics.