Two-dimensional spiral plasmonic structures have emerged as a versatile approach to generate near-field vortex fields with tunable topological charges. We demonstrate here a far-field approach to observe the chiral second-harmonic generation (SHG) at designated visible wavelengths from a single plasmonic vortex metalens. This metalens comprises an Archimedean spiral slit fabricated on atomically flat aluminum epitaxial film, which allows for precise tuning of plasmonic resonances and subsequent transfer of two-dimensional materials on top of the spiral slit. The nonlinear optical measurements show a giant SHG circular dichroism. Furthermore, we have achieved an enhanced chiral SHG conversion efficiency (about an order of magnitude greater than the bare aluminum lens) from monolayer tungsten disulfide (WS₂)/aluminum metalens, which is designed at the C-exciton resonance of WS₂. Since the C-exciton is not a valley exciton, the enhanced chiral SHG in this hybrid system originates from the plasmonic vortex field-enhanced SHG under the optical spin–orbit interaction.

中文翻译：

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单层WS ₂ /铝等离子涡旋金属手性产生第二手性谐波

二维螺旋等离激元结构已经成为一种通用的方法，可以生成具有可调拓扑电荷的近场涡旋场。我们在这里展示了一种远场方法，用于从单个等离激元涡旋金属原子中在指定的可见波长处观察手性二次谐波生成（SHG）。这种金属元素包括在原子平坦的铝外延膜上制造的阿基米德螺旋形狭缝，可以精确调整等离子体共振，并随后在螺旋形狭缝的顶部转移二维材料。非线性光学测量显示出巨大的SHG圆二色性。此外，我们通过单层二硫化钨（WS ₂）获得了提高的手性SHG转换效率（比裸铝透镜大一个数量级）。）/铝金属，这是根据WS ₂的C激子共振而设计的。由于C激子不是谷类激子，因此在这种混合系统中，手性SHG的增强来自于在自旋轨道相互作用下的等离激元涡旋场增强的SHG。