title: Polarization-Independent Multiple Fano Resonances in Plasmonic Nonamers for Multimode-Matching Enhanced Multiband Second-Harmonic Generation.
abstract: 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.
authors.forename: Shao-Ding
authors.initials: SD
authors.lastname: Liu
authors.affiliation: Institute of Materials Research and Engineering, A*STAR , 2 Fusionopolis Way, Singapore 138634.
authors.forename: Eunice Sok Ping
authors.initials: ES
authors.lastname: Leong
authors.affiliation: Department of Applied Physics, The Hong Kong Polytechnic University , Hong Kong, China.
authors.forename: Guang-Can
authors.initials: GC
authors.lastname: Li
authors.affiliation: Department of Applied Physics, The Hong Kong Polytechnic University , Hong Kong, China.
authors.forename: Yidong
authors.initials: Y
authors.lastname: Hou
authors.affiliation: Institute of Materials Research and Engineering, A*STAR , 2 Fusionopolis Way, Singapore 138634.
authors.forename: Jie
authors.initials: J
authors.lastname: Deng
authors.affiliation: Institute of Materials Research and Engineering, A*STAR , 2 Fusionopolis Way, Singapore 138634.
authors.forename: Jing Hua
authors.initials: JH
authors.lastname: Teng
authors.affiliation: Department of Physics, The Chinese University of Hong Kong , Hong Kong, China.
authors.forename: Hock Chun
authors.initials: HC
authors.lastname: Ong
authors.affiliation: Department of Applied Physics, The Hong Kong Polytechnic University , Hong Kong, China.
authors.forename: Dang Yuan
authors.initials: DY
authors.lastname: Lei
keywords: Fano resonances; higher-order plasmon modes; metallic nanostructures; plasmonic oligomers; second-harmonic generation