Galanty Matan, Shavit Omer, Weissman Adam, Aharon Hannah, Gachet David, Segal Elad, Salomon Adi
1Department of Chemistry, BINA Nano Center for Advanced Materials, Bar-Ilan University, Ramat-Gan, Israel.
Attolight AG, EPFL Innovation Park, Building D, 1015 Lausanne, Switzerland.
Light Sci Appl. 2018 Aug 15;7:49. doi: 10.1038/s41377-018-0053-6. eCollection 2018.
Second harmonic generation (SHG) is forbidden for materials with inversion symmetry, such as bulk metals. Symmetry can be broken by morphological or dielectric discontinuities, yet SHG from a smooth continuous metallic surface is negligible. Using non-linear microscopy, we experimentally demonstrate enhanced SHG within an area of smooth silver film surrounded by nanocavities. Nanocavity-assisted SHG is locally enhanced by more than one order of magnitude compared to a neighboring silver surface area. Linear optical measurements and cathodoluminescence (CL) imaging substantiate these observations. We suggest that plasmonic modes launched from the edges of the nanocavities propagate onto the smooth silver film and annihilate, locally generating SHG. In addition, we show that these hotspots can be dynamically controlled in intensity and location by altering the polarization of the incoming field. Our results show that switchable nonlinear hotspots can be generated on smooth metallic films, with important applications in photocatalysis, single-molecule spectroscopy and non-linear surface imaging.
二次谐波产生（SHG）对于具有反演对称性的材料是被禁止的，比如块状金属。对称性可以通过形态学或介电不连续性被打破，然而来自光滑连续金属表面的SHG可以忽略不计。利用非线性显微镜，我们通过实验证明了在被纳米腔包围的光滑银膜区域内SHG得到增强。与相邻的银表面区域相比，纳米腔辅助的SHG在局部增强了一个多数量级。线性光学测量和阴极发光（CL）成像证实了这些观察结果。我们认为从纳米腔边缘发射的等离子体模式传播到光滑银膜上并湮灭，局部产生SHG。此外，我们表明通过改变入射场的偏振，可以动态控制这些热点的强度和位置。我们的结果表明，可切换的非线性热点可以在光滑金属膜上产生，在光催化、单分子光谱和非线性表面成像方面具有重要应用。
