Boosting nonlinear frequency conversions with plasmonic nanostructures at near-ultraviolet (UV) frequencies remains a great challenge in nano-optics. Here we experimentally design and fabricate a plasmon-enhanced second-harmonic generation (PESHG) platform suitable for near-UV frequencies by integrating aluminum materials with grating configurations involved in structural heterogeneity. The SHG emission on the proposed platform can be amplified by up to three orders of magnitude with respect to unpatterned systems. Furthermore, the mechanism governing this amplification is identified as the occurrence of quasi-Bragg plasmon modes near second-harmonic wavelengths, such that a well-defined coherent interplay can be attained within the hot spot region and facilitate the efficient out-coupling of local second-harmonic lights to the far-field. Our work sheds light into the understanding of the role of grating-coupled surface plasmon resonances played in PESHG processes, and should pave an avenue toward UV nanosource and nonlinear metasurface applications.

中文翻译：

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准布拉格等离子体模式，用于在近紫外频率下产生高效等离子体增强二次谐波

在近紫外 (UV) 频率下使用等离子体纳米结构增强非线性频率转换仍然是纳米光学领域的一大挑战。在这里，我们通过将铝材料与涉及结构异质性的光栅配置集成，实验性地设计和制造了适用于近紫外频率的等离子体增强二次谐波产生 (PESHG) 平台。相对于无模式系统，所提议平台上的 SHG 发射最多可以放大三个数量级。此外，控制这种放大的机制被确定为在二次谐波波长附近出现准布拉格等离子体模式，这样可以在热点区域内获得明确定义的相干相互作用，并促进局部秒的有效外耦合-远场的谐波光。