基于异质材料的有效介电常数理论, 仿真了二维亚波长银粒子/孔的等效复介电常数, 证实了亚波长金属银粒子/孔的光谐振特性。对于在介质内放置银粒子的模型, 当光频率高于银的等离子体频率时, 异质材料的等效介电常数的实部为负; 在等离子体频率附近, 等效介电常数的虚部存在谐振峰, 粒子增大, 谐振峰红移; 在谐振频率点, 银粒子周围局域场最大。在金属银上开孔, 并填充不同介电常数的材料时, 也存在类似的效应。并且孔内填充材料的介电常数增大, 谐振峰红移, 在相同介电常数的条件下, 孔增大, 谐振峰蓝移。光谐振现象与金属粒子/孔的形状有关, 因此, 光与亚波长金属粒子/孔相互作用的机理为等离子体模和谐振模, 异质材料的有效介电常数理论是研究亚波长金属粒子/孔异常光增强现象的有力工具。

Based on effective permittivity theory of heterogeneous material, the effective complex permittivity of two-dimensional subwavelength Ag particle/hole has been simulated. The optical resonance properties of Ag particle/hole are verified. For the Ag particle-dielectric composite structure, the effective permittivity has a negative real part when the optical frequency is larger than the plasmon frequency of Ag. The imaginary part of the effective permittivity shows a resonance near the plasmon frequency of Ag, and the resonance peak displays a red shift with the increase of radius of Ag particle. By calculating the electric field distribution, it is found that optical resonance results in very strong local field enhancements around the Ag particle at the resonant frequency. Similar phenomena are observed for the structure of Ag block with a single hole filled with different materials, and resonant peak shows red shift with the increase of permittivity in the hole, while the resonant peak is blue-shifted with the increase of radius of the hole filled with the same material. In addition, the optical resonance can be controlled by adjusting the size and geometry of the particle/hole. Therefore, the mechanisms for the interaction of light with particle/hole are surface plasmon mode and resonant mode, and the effective-medium theory is a powerful tool for exploring the intriguing enhanced optical transmission phenomena.