Nonlinear optical effects of sub-5 nm plasmonic nanogap metasurfaces

Plasmonic metasurfaces with sub-5nm dielectric nano-gaps arranged in a large two-dimensional array pave the way to a huge boosting of nonlinear optical effects due to the joint action of a strong field enhancement inside the gap, together with the presence of collective radiative resonances. We studied the nonlinear emission of these metasurfaces in dependence of different gap parameters and illumination conditions. This is a step towards the experimental investigation of nonlinear effects in structures, where light-matter interaction is strongly affected by quantum effects.