Hybrid 3D spiral WSe2 plasmonic structure for highly efficient SHG. (a) Schematic illustration of a hybrid spiral WSe2 plasmonic structure where a single WSe2 sits on top of the MgF2 layer near the Ag film. (b) Spatial resolved spectra collected from the hybrid spiral WSe2 structure shown in the inset. Inset: SH image of a single hybrid spiral WSe2 structure excited with a CW laser (1064 nm). (c) Measured SHG intensity as a function of FW laser power, which fits to a square dependence. (d) Spectra of SHG and FW from hybrid spiral WSe2 plasmonic structure excited with 1064 nm CW laser.