Li Guang-Can, Lei Dangyuan, Qiu Meng, Jin Wei, Lan Sheng, Zayats Anatoly V
Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices, School of Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou, China.
Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong, China.
Nat Commun. 2021 Jul 15;12(1):4326. doi: 10.1038/s41467-021-24408-x.
Efficient frequency up-conversion of coherent light at the nanoscale is highly demanded for a variety of modern photonic applications, but it remains challenging in nanophotonics. Surface second-order nonlinearity of noble metals can be significantly boosted up by plasmon-induced field enhancement, however the related far-field second-harmonic generation (SHG) may also be quenched in highly symmetric plasmonic nanostructures despite huge near-field amplification. Here, we demonstrate that the SHG from a single gold nanosphere is significantly enhanced when tightly coupled to a metal film, even in the absence of a plasmon resonance at the SH frequency. The light-induced electromagnetic asymmetry in the nanogap junction efficiently suppresses the cancelling of locally generated SHG fields and the SH emission is further amplified through preferential coupling to the bright, bonding dipolar resonance mode of the nanocavity. The far-field SHG conversion efficiency of up to [Formula: see text] W is demonstrated from a single gold nanosphere of 100 nm diameter, two orders of magnitude higher than for complex double-resonant plasmonic nanostructures. Such highly efficient SHG from a metal nanocavity also constitutes an ultrasensitive nonlinear nanoprobe to map the distribution of longitudinal vectorial light fields in nanophotonic systems.
在各种现代光子应用中，对纳米尺度下相干光的高效频率上转换有很高的需求，但在纳米光子学中这仍然具有挑战性。贵金属的表面二阶非线性可以通过等离子体诱导的场增强而显著增强，然而，尽管近场有巨大的放大，但在高度对称的等离子体纳米结构中，相关的远场二次谐波产生（SHG）也可能被淬灭。在这里，我们证明，即使在SH频率不存在等离子体共振的情况下，单个金纳米球与金属膜紧密耦合时，其SHG也会显著增强。纳米间隙结中的光诱导电磁不对称有效地抑制了局部产生的SHG场的抵消，并且通过优先耦合到纳米腔的明亮的键合偶极共振模式，SH发射进一步放大。从直径为100 nm的单个金纳米球中展示了高达[公式：见原文]W的远场SHG转换效率，比复杂的双共振等离子体纳米结构高两个数量级。这种来自金属纳米腔的高效SHG也构成了一种超灵敏的非线性纳米探针，用于绘制纳米光子系统中纵向矢量光场的分布。
