Dual heterostructures integrating noble-metal and copper chalcogenide nanoparticles have attracted a great deal of attention in nonlinear optics, because coupling of their localized surface plasmon resonances (LSPRs) substantially enhances light–matter interactions through local-field effects. Previously, enhanced cascaded third-harmonic generation was demonstrated in Au/CuS heterostructures mediated by harmonically coupled surface plasmon resonances. This suggests a promising approach for extending nonlinear enhancement to higher harmonics by adding an additional nanoparticulate material with higher-frequency harmonic resonances to the hybrid films. Here we report the first observation of enhanced cascaded fourth- and fifth-harmonic generation in Al/Au/CuS driven by coupled LSPRs at the fundamental (1050 nm), second harmonic (525 nm), and third harmonic (350 nm) of the pump frequency. An analytical model based on incoherent dipole–dipole interactions among plasmonic nanoparticles accounts for the observed enhancements. The results suggest a novel design for efficiently generating higher harmonics in resonant plasmonic structures by means of multiple sum-frequency cascades.

中文翻译：

---

Al/Au/CuS 纳米粒子薄膜产生高达五阶的谐波

集成贵金属和铜硫族化物纳米颗粒的双异质结构在非线性光学领域引起了广泛关注，因为它们的局域表面等离子体共振（LSPR）的耦合通过局域场效应显着增强了光与物质的相互作用。此前，在谐波耦合表面等离子体共振介导的 Au/CuS 异质结构中，增强了级联三次谐波的产生。这表明通过向混合薄膜中添加具有更高频率谐波共振的附加纳米颗粒材料，将非线性增强扩展到更高的谐波是一种有前途的方法。在这里，我们报告了在基波（1050 nm）、二次谐波（525 nm）和三次谐波（350 nm）处耦合局域表面等离子体共振（LSPR）驱动的 Al/Au/CuS 中增强级联四次和五次谐波生成的首次观察结果。泵频率。基于等离子体纳米颗粒之间不相干偶极-偶极相互作用的分析模型解释了观察到的增强。结果提出了一种新颖的设计，可以通过多个和频级联在共振等离子体结构中有效地产生高次谐波。