利用矩形金属周期阵列实现局域电场的增强和共振波长的可控

摘要

The authors have designed a novel type of periodic rectangular pit nanostructure substrate based on the surface plas-mon principle.Finite element method was employed to simulate the optical near-field distribution.Strongly enhanced field whose electric intensity Emax/E0 can be as high as 20 at resonance frequency appears around pithead of the periodic structure.As the pe-riod of structure,pit length l,widthωand environment change,the authors observe the regular shifting of plasmon resonant wavelength which can cover the range from 500 to 1 000 nm.The red shifts of SPR resonance peaks are increased with the incre-ment of period Px when incident light is polarized along x axis.An abrupt decrease in localized electric field in the pit is observed as incident wavelength approaches Px .This is due to the satisfaction of wave vector matching condition and the excitation of propagating SPP.SPR resonance peaks also red shifts with the increment on pit length l and environment dielectric refractive in-dex,presenting a linear dependence with pit length l.While the resonance peaks are blue shifted with the increment of pit widthω.The results presented in this paper will provide a way to tune the plasmon resonant wavelength.Inspired by Jain’s report, SPR resonance peaks’shifting with the changing of structure parameters can be explained by viewing the rectangular pit nano-structure as combination of two pairs of dipole-dipole coupling models along x and y axis respectively.%基于表面等离激元共振（SPR）的原理，设计了一种具有矩形凹槽周期阵列微结构的金属增强基底。利用有限元方法对基底表面附近电场的分布进行了理论模拟分析，结果表明在SPR共振情况下，其凹槽微结构坑口处可得到强局域场，局域电场强度Emax／E0可达20。通过改变结构的周期、凹槽长度l、宽度ω以及环境介质，SPR共振峰发生规律性的移动，波长覆盖范围为500～1000 nm。入射光沿x方向偏振的情况下，随着结构x方向周期Px 的增加，SPR共振峰明显红移。当入射光波长与Px 相当时，观察到凹槽内局域电场突然减小的现象。这是由于满足了波矢匹配条件，传播型SPP被激发导致的。改变凹槽长度l，发现共振波长随l的增加红移，近似呈线性关系。环境介质折射率的增加也会引起共振峰的红移。而凹槽宽度ω的增加将导致其蓝移。这种规律性的移动为实现共振波长的调控提供了途径。受Jain研究报道的启发，矩形凹槽结构可以等效为两对偶极耦合模型的组合，从而解释SPR共振峰随结构参数变化而发生的移动。