Second harmonic generation in periodic metal-insulator-metal nanoparticle arrays

We investigate second harmonic generation from vertically stacked metal-insulator-metal nanobars arranged in a two-dimensional rectangular array. At specific angles of incidence, the nonlinear emission is maximized due to the near-field enhancement associated with the surface lattice resonance from the periodic arrangement, regardless of the number of insulator layers embedded in each nanoantenna. Intuitively, stacking should increase second harmonic generation with the number of metal layers. In fact, the maximum emission was reached at the highest stacking, but experimental results also indicate a far more complex relation between the individual layers. Due to the small vertical distance between the metallic layers, the fields in each nanogap are strongly coupled, leading to the generation of gap-plasmons and magnetic modes.