Bortchagovsky E, Colas des Francs G, Naber A, Fischer U C
Institute of Semiconductor Physics of NASU, pr.Nauki 45, Kiev 03028 Ukraine.
J Microsc. 2008 Feb;229(Pt 2):223-7. doi: 10.1111/j.1365-2818.2008.01890.x.
A triangular nanoaperture in an aluminium film was used previously as a probe in a scanning near-field optical microscope to image single fluorescent molecules with an optical resolution down to 30 nm. The high-resolution capability of the triangular aperture probe is because of a highly confined spot of the electric near field which emerges at an edge of the aperture, when the incident light is polarized perpendicular to this edge. Previous numerical calculations of the near-field distribution of a triangular aperture in a planar metal film using the field susceptibility technique yielded a nearly quantitative agreement with the experimental results. Using the same numerical technique we now explored the possibility for a further confinement of the electric near field and an increase in its intensity by modifications of the form of a triangular aperture. By introducing a kink on an edge pointing into the aperture, an arrow-shaped aperture is formed with one convex and three concave metal corners. It turns out that this form leads to a substantial further confinement of the near-field intensity at the convex corner. By extending the wings of this arrow-shaped aperture a further 5-fold increase of the intensity can be obtained without a deterioration of the confined spot.
先前，铝膜中的三角形纳米孔径被用作扫描近场光学显微镜中的探针，以对单个荧光分子进行成像，光学分辨率低至30纳米。三角形孔径探针的高分辨率能力归因于当入射光垂直于孔径边缘偏振时，在孔径边缘出现的高度受限的电近场光斑。先前使用场磁化率技术对平面金属膜中三角形孔径的近场分布进行的数值计算与实验结果几乎达成了定量一致。现在，我们使用相同的数值技术，探索通过修改三角形孔径的形状来进一步限制电近场并提高其强度的可能性。通过在指向孔径的边缘上引入一个扭结，形成了一个箭头形孔径，有一个凸金属角和三个凹金属角。结果表明，这种形状导致凸角处的近场强度进一步大幅受限。通过将这个箭头形孔径的翼展进一步延伸，可以在不使受限光斑变差的情况下使强度再提高5倍。
