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Abstract：
Chirality, the lack of mirror symmetry, can be mimicked in nanophotonics and plasmonics by breaking the symmetry in light-nanostructure interaction. Here we report on versatile use of nanosphere lithography for the fabrication of low-cost metasurfaces, which exhibit broadband handedness- and angle-dependent extinction in the near-infrared range, thus offering extrinsic chiro-optical behavior. We measure wavelength and angle dependence of the extinction for four samples. Two samples are made of polystyrene nanospheres asymmetrically covered by silver and gold in one case and silver only in the other case, with a nanohole array at the bottom. The other two samples are nanohole arrays, obtained after the nanosphere removal from the first two samples. Rich extrinsic chiral features are governed by different chiro-optical mechanisms in the three-dimensional plasmonic semi-shells and planar nanohole arrays. We also measure Stokes parameters in the same wavelength and incidence angle range and show that the transmitted fields follow the extrinsic chirality features of the extinction dissymmetry. We further study the influences of the nanostructured shapes and in-plane orientations on the intrinsic vs extrinsic chirality. The nanoholes are modelled as oval shapes in metal, showing good agreement with the experiments. We thus confirm that nanosphere lithography can provide different geometries for chiral light manipulation at the nanoscale, with the possibility to extend functionalities with optimized oval shapes and combination of constituent metals.
摘要：
Chirality,缺乏镜像对称性，可以通过打破光-纳米结构相互作用中的对称性来模拟纳米光子学和等离子体激元。在这里，我们报告了纳米球光刻技术在低成本超表面制造中的广泛使用，在近红外范围内表现出宽带手和角度相关的消光，从而提供外在的手性光学行为。我们测量了四个样品的消光的波长和角度依赖性。两种样品由聚苯乙烯纳米球制成，一种情况下仅由银和金不对称覆盖，另一种情况下仅由银覆盖，底部有纳米孔阵列。另外两个样品是纳米孔阵列，在从前两个样品中去除纳米球后获得。丰富的外在手性特征受三维等离子体半壳和平面纳米孔阵列中不同的手性光学机制控制。我们还在相同的波长和入射角范围内测量斯托克斯参数，并表明透射场遵循消光不对称性的外在手性特征。我们进一步研究了纳米结构形状和面内取向对内在和外在手性的影响。纳米孔在金属中被建模为椭圆形，与实验表现出良好的一致性。因此，我们确认纳米球光刻可以为纳米级的手性光操纵提供不同的几何形状，与扩展功能与优化的椭圆形和组成金属的组合的可能性。
