Nanophotonics and Metrology Laboratory, Swiss Federal Institute of Technology Lausanne (EPFL) , 1015 Lausanne, Switzerland.
Department of Physics, Chalmers University of Technology , 412 96 Göteborg, Sweden.
Nano Lett. 2017 Sep 13;17(9):5258-5263. doi: 10.1021/acs.nanolett.7b01412. Epub 2017 Aug 30.
Electromagnetic metasurfaces with strong nonlinear responses and angular selectivity could offer many new avenues for designing ultrathin optics components. We investigated the optical second harmonic generation from plasmonic metasurfaces composed of aligned gold nanopillars with a pronounced out-of-plane tilt using a flexible nonlinear Fourier microscope. The experimental and computational results demonstrate that these samples function as wavevector-selective nonlinear metasurfaces, that is, the coherent second harmonic signal does not only depend on the polarization and wavelength of the excitation beam, but also of its direction of incidence, in spite of the subwavelength thickness of the active layer. Specifically, we observe that the nonlinear response can vary by almost two orders-of-magnitude when the incidence angle is changed from positive to negative values compared to the surface normal. Further, it is demonstrated that these metasurfaces act as a directional nonlinear mirrors, paving the way for new design of directional meta-mirrors in the nonlinear regime.
具有强非线性响应和角度选择性的电磁超表面可为设计超薄光学元件提供许多新途径。我们使用灵活的非线性傅里叶显微镜研究了由具有明显面外倾斜的取向金纳米柱组成的等离子体超表面的光学二次谐波产生。实验和计算结果表明，这些样品作为波矢选择非线性超表面起作用，也就是说，相干二次谐波信号不仅取决于激发光束的偏振和波长，还取决于其入射角，尽管活性层的厚度小于波长。具体而言，我们观察到，与表面法线相比，当入射角从正值变为负值时，非线性响应可以变化近两个数量级。此外，还证明了这些超表面可以作为定向非线性反射镜，为非线性状态下的定向 meta-mirror 的新设计铺平了道路。
