Strong Acousto-Plasmonic Coupling in Film-Coupled Nanoparticles Mediated by Surface Acoustic Waves

Abstract

The interaction between phonons and localized plasmons in film-coupled nanoparticles designs can be exploited both for modulating the scattered electromagnetic field and the understanding of the mechanical vibrations at nanoscale. In this paper, we show by finite element numerical analysis an enhanced optomechanical interaction in a film-coupled gold nanoridges or pillars mediated by surface acoustic waves. The metallic nanoparticles are placed atop a multilayer structure consisting of a thin dielectric spacer covering a gold film layer on a silicon dioxide/or silicon substrate. Optical simulations reveal the existence of surface localized plasmons in the infrared range confined under the nanoparticles in the dielectric spacer and/or in between such particles. Optomechanical coupling between the plasmonic modes and localized phonons is evaluated from the shift in the plasmon eigenfrequency. It is found that the compressional, the in-phase compressional and the out-of-phase flexural modes, yield the highest coupling rates. Such phonons are excited by means of SAW launched from the system inlet in front of the particles. The findings in this paper could help design new generation of acousto-optic modulators monitored by fast coherent surface acoustics.