“…The strategy of getting a qualitative increase of SHG from centrosymmetric metals by designing nanostructures of asymmetric geometrical shapes was identified . It was found that in order to make it efficient, the SHG engineering should rely on a certain selection rule, expressed in a semi‐empirical criterion as where E 2 is the SHG field, is the surface nonlinear susceptibility tensor component, considered to be the dominant SHG source, and are the components of the fields perpendicular to the metal‐dielectric boundary for the modes at the fundamental and SH frequencies, respectively, and the integration is performed over the nanostructure surface. Particularly, this approach was used to optimise SHG from multiresonant coupled nanoantennas (Figure c) .…”