Triply-Resonant Plasmonic Metasurfaces for Multimodal Enhancement

Multimodal plasmonic structures offer promise for applications such as fluorescence enhancement, wavelength multiplexing, and enhanced nonlinear generation. However, these structures may be leveraged by exploiting the high field enhancements present in film-coupled systems. Here, we present designs for triply-resonant film-coupled plasmonic metasurfaces. By exploiting asymmetry in several plasmonic unit cell geometries, we show that these geometries are capable of supporting three plasmonic modes that are independently tunable and polarization-dependent. Furthermore, we observe high field enhancements due to field confinement in the subwavelength gap between the nanostructure and film. By coupling absorption and spontaneous emission to the different plasmonic modes, and taking advantage of high field enhancement in the gap, one can potentially increase the efficiency of field-dependent processes, such as fluorescence, sum frequency generation (SFG) and difference frequency generation (DFG).