Electro-Optics Program, University of Dayton, Dayton, Ohio 45469, USA.
Opt Lett. 2012 Feb 15;37(4):581-3. doi: 10.1364/OL.37.000581.
Owing to a geometric phase effect, an isosceles triangular aperture etched into thin metal film leads to constructive or destructive interference of surface plasmons excited at the two equal sides under linearly polarized illumination. Through appropriate spatial arrangement of an array of triangles, a highly confined focal spot beyond the diffraction limit can be achieved at the geometric center under azimuthally polarized excitation with field enhancement comparable to a bull's eye plasmonic lens under radially polarized illumination. Through simply rotating the orientation of each triangle aperture by 90°, the plasmonic structure defocuses the same azimuthal polarization illumination due to destructive interference caused by a geometric π-phase difference between the two sides of the triangle and between the adjacent triangles.
由于几何相位效应，在薄金属膜中刻蚀出的等腰三角形光阑会导致在两个相等的边上激发的表面等离激元产生相长或相消干涉，当用线偏振光照明时。通过三角形阵列的适当空间排列，可以在角向偏振激发下在几何中心实现高度限制的焦点，其场增强可与径向偏振激发下的牛眼等离子透镜相当。通过简单地将每个三角形光阑的取向旋转 90°，由于三角形两边之间以及相邻三角形之间的几何π相移差引起的相消干涉，等离子体结构使相同的角向偏振光失焦。
