Second-harmonic generation (SHG) has rapidly advanced with the miniaturization of on-chip devices and has found many applications, including optical frequency conversion, nonlinear imaging, and quantum technology. However, owing to the obvious phase-matching constraints involved in nonlinear optical interactions in bulk crystals and the decrease in the length and strength of nonlinear interactions in nanophotonic and surface/interface systems, improving the SHG efficiency and manipulating its optical properties at the nanoscale are challenging tasks. Herein, a monocrystalline silver microplate and nanocube-coupled nanocavity with double-resonance plasmonic modes and an ultrasmall gap were constructed, resulting in efficiently enhanced SHG. In particular, the SHG from the silver microplate (111) is polarization-dependent, and the anisotropy of the SHG in the plasmonic nanocavity can be further controlled via the superposition of symmetries at the interface and plasmonic waveguide-cavity modes. The interfacial SHG provides technology for developing lattice surface atomic arrangement and nanostructure rapid characterization, nonlinear light sources, and on-chip nonlinear nanophotonic devices.

中文翻译：

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双共振增强等离子体纳米腔中对称性叠加产生界面二次谐波

二次谐波产生（SHG）随着片上器件的小型化而迅速发展，并已找到许多应用，包括光学频率转换、非线性成像和量子技术。然而，由于块体晶体中非线性光学相互作用存在明显的相位匹配约束，以及纳米光子和表面/界面系统中非线性相互作用的长度和强度的降低，提高SHG效率并在纳米尺度上操纵其光学性质是有待解决的问题。具有挑战性的任务。在此，构建了具有双共振等离子体模式和超小间隙的单晶银微板和纳米立方耦合纳米腔，从而有效增强了倍频。特别地，来自银微板（111）的SHG是偏振相关的，并且等离子体纳米腔中的SHG的各向异性可以通过界面处的对称性和等离子体波导腔模式的叠加来进一步控制。界面SHG提供了开发晶格表面原子排列和纳米结构快速表征、非线性光源和片上非线性纳米光子器件的技术。