Two-Tier Nanolaminate Plasmonic Crystals for Broadband Multiresonant Light Concentration with Spatial Mode Overlap

Effective trapping and nanolocalization of different colored photons simultaneously at the same position remain a challenge in nanophotonics research but can boost applications based on nonlinear multiphoton processes. For achieving broadband nanoscale light concentration, a promising strategy is to employ multiresonant plasmonic devices that support multiple hybridized surface plasmon modes with spatial overlap at several different resonance wavelengths. However, high-order plasmonic modes from hybridization tend to have a dark multipolar nature and are less useful due to weak interactions with free-space light. Here, it is reported that nanolaminate plasmonic crystals in a two-tier configuration can support many (approximate to 10) spatially overlapped and highly-excitable hybridized plasmonic modes under free-space light illumination between 400 and 1400 nm. Combination of nanoimprinting lithography and multilayered physical vapor deposition techniques enables wafer-scale fabrication of nanolaminate plasmonic crystals consisting of nanolaminate nanodome and nanohole arrays as the two closely-separated subsystems, and measurements demonstrate their multiresonant plasmonic responses in good agreement with numerical calculations. Coupled-mode theory analysis reveals that the unique broadband multiresonant responses of the two-tier nanolaminate plasmonic crystals are due to the synergistic effects of the strong near-field interactions between the modes in the nanodome and nanohole subsystems and the ground-plane-like loading effect from the nanohole subsystem.