Plasmonic nanocavities offer prospects for the amplification of inherently weak nonlinear responses at subwavelength scales. However, constructing these nanocavities with tunable modal volumes and reduced optical losses remains an open challenge in the development of nonlinear nanophotonics. Herein, we design and fabricate three-dimensional (3D) metal-dielectric-metal (MDM) plasmonic nanocavities that are capable of amplifying second-harmonic lights by up to three orders of magnitude with respect to dielectric-metal counterparts. In combination with experimental estimations of quantitative contributions of constituent parts in proposed 3D MDM designs, we further theoretically disclose the mechanism governing this signal amplification. We discover that this phenomenon can be attributed to the plasmon hybridization of both dipolar plasmon resonances and gap cavity resonances, such that an energy exchange channel can be attained and helps expand modal volumes while maintaining strong field localizations. Our results may advance the understanding of efficient nonlinear harmonic generations in 3D plasmonic nanostructures.

中文翻译：

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通过 3D 等离子体纳米腔进行非线性光放大

等离子体纳米腔为放大亚波长尺度固有的弱非线性响应提供了前景。然而，构建这些具有可调模态体积和减少光学损耗的纳米腔仍然是非线性纳米光子学发展中的一个公开挑战。在这里，我们设计并制造了三维 (3D) 金属-电介质-金属 (MDM) 等离子体纳米腔，其能够将二次谐波光比电介质-金属对应物放大多达三个数量级。结合对提议的 3D MDM 设计中组成部分的定量贡献的实验估计，我们进一步从理论上揭示了控制这种信号放大的机制。我们发现这种现象可归因于偶极等离子体共振和间隙腔共振的等离子体杂交，因此可以获得能量交换通道并有助于扩大模态体积，同时保持强场定位。我们的结果可能会促进对 3D 等离子体纳米结构中有效非线性谐波产生的理解。