Department of Physics and Astronomy, Rice University, Houston, TX 77005, USA.
Proc Natl Acad Sci U S A. 2013 Jun 4;110(23):9215-9. doi: 10.1073/pnas.1220304110. Epub 2013 May 20.
Plasmonic nanoclusters, an ordered assembly of coupled metallic nanoparticles, support unique spectral features known as Fano resonances due to the coupling between their subradiant and superradiant plasmon modes. Within the Fano resonance, absorption is significantly enhanced, giving rise to highly localized, intense near fields with the potential to enhance nonlinear optical processes. Here, we report a structure supporting the coherent oscillation of two distinct Fano resonances within an individual plasmonic nanocluster. We show how this coherence enhances the optical four-wave mixing process in comparison with other double-resonant plasmonic clusters that lack this property. A model that explains the observed four-wave mixing features is proposed, which is generally applicable to any third-order process in plasmonic nanostructures. With a larger effective susceptibility χ(3) relative to existing nonlinear optical materials, this coherent double-resonant nanocluster offers a strategy for designing high-performance third-order nonlinear optical media.
等离子体纳米团簇是耦合金属纳米粒子的有序组装，由于亚辐射和超辐射等离子体模式之间的耦合，支持独特的光谱特征，称为 Fano 共振。在 Fano 共振内，吸收显著增强，产生具有增强非线性光学过程潜力的高度局域、强烈的近场。在这里，我们报告了一种在单个等离子体纳米团簇中支持两个不同 Fano 共振相干振荡的结构。我们展示了这种相干性如何与其他缺乏这种特性的双共振等离子体团簇相比增强了光学四波混频过程。提出了一个解释观察到的四波混频特征的模型，该模型通常适用于等离子体纳米结构中的任何三阶过程。与现有的非线性光学材料相比，这种相干的双共振纳米团簇具有更大的有效磁化率 χ(3)，为设计高性能三阶非线性光学介质提供了一种策略。
