采用离散偶极子近似(DDA)方法研究渐变锥形金属纳米结构的超聚焦效应

Analysis of super focusing effect in tapered metal nano-structure with discrete dipole approximation method

利用离散偶极子近似(discrete dipole approximation,DDA)方法对渐变锥形金属纳米结构中的超聚焦效应进行了分析和讨论.数值计算证明该结构能够较好地实现对入射光场能量的纳米尺度汇聚.基于解析和数值模型进一步分析了超聚焦效应与入射光波长、结构角度、结构厚度以及材料损耗之间的关系.计算结果表明,通过合理设计参数,结构尖端的场强可增至入射场强的几十到上百倍,从而实现明显的光场超聚焦效果.另外证明采用DDA方法建模金属纳米结构具有相当好的计算精度和速度.

The super focusing effect in tapered metal nano-structure is analyzed and discussed with discrete dipole approximation （DDA） method. Numerical result proves that the light field can be focused to nano-scale spot within this structure, and the relation between its super focusing ability and incident wavelength, structure＇s vertex angle, thickness and metal＇s dissipation is discussed, based on both analytic and numerical model. The results suggest that the electric field can be enhanced decades even hundreds times with properly designed parameters, which leads to a significant super focusing effect of light field. It also proves that the metal nano-structure can be modeled by DDA method with good simulation precision and speed.