Nonlinear harmonic generation in sub-5 nm plasmonic nanogap metasurfaces

Plasmonic nano-antennas featuring dielectric nano-gaps confines the electromagnetic field to sub-wavelength volumes, enabling strong field enhancements and thus boosting nonlinear optical effects. Quantum effects, manifesting as a nonlocal macroscopic response, also play an important role in gaps of few nm [1]. The nonlinear signal can be strongly enhanced by arranging identical nano-antennas in an array, leading to the appearance of collective resonances (in our case guided lattice resonances due to their placement on a membrane) where surface waves lock the phase of all the antennas via radiative coupling [2].