Ma Zixian, Zhang Xin, Hu Yanwen, Yin Hao, Li Zhen, Chen Zhenqiang, Fu Shenhe
Opt Lett. 2022 Jul 1;47(13):3219-3222. doi: 10.1364/OL.464571.
We demonstrate a technique for diffraction-limit focusing, on the basis of a spatial truncation of incident light using spirally structured slit motifs. The spiral pattern leads to a global phase domain where the diffractive wave vectors are distributed in phase. We fabricate such a spiral pattern on a 60-nm-thick metallic film, capable of converting an orbital-angular-momentum beam to a non-helical high-resolution diffractive focusing beam, resulting in a high numerical aperture of 0.89 in air, and of up to 1.07 in an oil-immersion scenario. The topological complementarity between the incident beam and the slit motifs generates broadband subwavelength focusing. The idea can be extended to large-scale scenarios with larger constituents. The presented technique is more accessible to low-cost fabrications as compared with metasurface-based focusing elements.
我们展示了一种基于使用螺旋结构狭缝图案对入射光进行空间截断的衍射极限聚焦技术。螺旋图案导致一个全局相位域，其中衍射波矢量以相位分布。我们在60纳米厚的金属膜上制作了这样的螺旋图案，它能够将轨道角动量光束转换为非螺旋高分辨率衍射聚焦光束，在空气中产生高达0.89的高数值孔径，在油浸情况下高达1.07。入射光束和狭缝图案之间的拓扑互补性产生宽带亚波长聚焦。该想法可以扩展到具有更大组件的大规模场景。与基于超表面的聚焦元件相比，所提出的技术更易于低成本制造。
