Fixed-size double-resonant nanolaminate plasmonic nanoantennas with wide spectral tunability and high optical cross-sections

Abstract

Plasmonic nanoantennas can support localized surface plasmon (LSP) modes to concentrate light at the nanoscale. Although “single-resonant” plasmonic nanoantennas are sufficient for applications based on single-photon processes, “double-resonant” or “multiresonant” plasmonic nanoantennas are more favorable for multiphoton nonlinear processes or wavelength-multiplexing multifunctional operations. Despite significant efforts, current multiresonant plasmonic nanoantennas still face challenges in achieving wide spectral tunability and high excitability for multiple LSP modes under strict geometric size-footprint constraints. Here, we propose and numerically demonstrate that fixed-size nanolaminate plasmonic nanoantennas (NLPNAs) consisting of multiple metal/insulator layers can support two highly excitable LSP modes with electrical dipole (ED) and magnetic dipole (MD) characteristics. Notably, the resonant wavelength of both ED and MD modes are broadly tunable in the near-infrared range between ∼700 nm and ∼1000 nm by controlling the thickness ratio between individual metal and insulator layers without changing the overall size. While the ED mode in NLPNAs can have large scattering cross-sections suitable for applications based on plasmonic emission/scattering processes, the MD mode has large absorption cross-sections desirable for applications based on plasmonic photothermal effects. We further reveal that NLPNAs’ broad double-resonance tunability originates from the out-of-plane geometric dependence of the elementary ED/MD modes in the building blocks and their optical coupling.