线性偏振光激发的错位表面等离子体激元纳米结构聚焦

利用扫描近场光学显微镜观测并分析了两种表面等离子体激元纳米结构对表面等离子体激元(SPP)的激发和聚焦现象.用线偏振光照射有半个周期相位差的环状沟槽结构与有半个周期位相差的环状狭缝结构,得到了单点的SPP聚焦.有限时域差分法的模拟结果验证了实验中观测的现象.这两种相位错位的表面等离子体激元纳米结构,突破了由于干涉导致的线偏振光不能得到单个聚焦点的限制.与采用径向偏振光激发而得到单个聚焦点的方法相比,线偏振光不需要聚焦,也不需要将光束中心对准纳米结构的几何中心即可得到单点聚焦。

Nanofocusing by phase delayed plasmonic nanostructures illuminated with a linearly polarized light

We report the near-field nanofocusing through two types of plasmonic nanostructures consisting of annular grooves and annular slit, respectively. The radius of one half of each circle is designed to be bigger than the other half by half wavelength of the surface plasmon polaritons. By illuminating the structures with linearly polarized light, one single tight focal spot was detected by the scanning near-field optical microscope. Compared with the method of using radially polarized light, this method does not need to keep the center of the illuminating light right on the center of the structure, hence is much easier to use. Furthermore, theoretical simulations based on the finite-difference time-domain method testified the experimental results.