(a) SH intensity dependence versus fundamental intensity for both the bull’s-eye structure and the bare aperture.^[69] (b) Factor of SHG emission enhancement as a function of the shell thickness for different resonance frequencies.^[70] (c) SHG from a flat centrosymmetric triangular nanocavity on Ag film.^[73] (d) SERS spectrum and SE-FSRS spectrum of trans-1, 2-bis (4-pyridyl) ethylene (BPE)-functionalized nanoantennas.^[74]