Institute of Materials Research and Engineering, A*STAR , 2 Fusionopolis Way, Singapore 138634.
Department of Applied Physics, The Hong Kong Polytechnic University , Hong Kong, China.
ACS Nano. 2016 Jan 26;10(1):1442-53. doi: 10.1021/acsnano.5b06956. Epub 2016 Jan 6.
Plasmonic oligomers composed of metallic nanoparticles are one class of the most promising platforms for generating Fano resonances with unprecedented optical properties for enhancing various linear and nonlinear optical processes. For efficient generation of second-harmonic emissions at multiple wavelength bands, it is critical to design a plasmonic oligomer concurrently having multiple Fano resonances spectrally matching the fundamental excitation wavelengths and multiple plasmon resonance modes coinciding with the harmonic wavelengths. Thus far, the realization of such a plasmonic oligomer remains a challenge. This study demonstrates both theoretically and experimentally that a plasmonic nonamer consisting of a gold nanocross surrounded by eight nanorods simultaneously sustains multiple polarization-independent Fano resonances in the near-infrared region and several higher-order plasmon resonances in the visible spectrum. Due to coherent amplification of the nonlinear excitation sources by the Fano resonances and efficient scattering-enhanced outcoupling by the higher-order modes, the second-harmonic emission of the nonamer is significantly increased at multiple spectral bands, and their spectral positions and radiation patterns can be flexibly manipulated by easily tuning the length of the surrounding nanorods in the nonamer. These results provide us with important implications for realizing ultrafast multichannel nonlinear optoelectronic devices.
由金属纳米粒子组成的等离子体低聚物是一类最有前途的平台，可产生具有前所未有的光学特性的 Fano 共振，从而增强各种线性和非线性光学过程。为了在多个波长带中高效地产生二次谐波发射，关键是设计一种等离子体低聚物，使其具有多个光谱上与基本激发波长匹配的 Fano 共振，以及多个与谐波波长一致的等离子体共振模式。到目前为止，这种等离子体低聚物的实现仍然是一个挑战。本研究从理论和实验上证明，由金纳米十字周围的八个纳米棒组成的等离子体九聚体同时在近红外区域维持多个偏振无关的 Fano 共振和几个可见光光谱中的高阶等离子体共振。由于 Fano 共振对非线性激发源的相干放大以及高阶模式的高效散射增强外耦合，九聚体的二次谐波发射在多个光谱带中显著增强，并且它们的光谱位置和辐射模式可以通过灵活地调整九聚体周围纳米棒的长度来轻松地操纵。这些结果为实现超快多通道非线性光电设备提供了重要启示。
