Figure 1.

(a) 3D scheme of the PVL. The geometrical parameters of the spiral slits include a slit width of 200 nm, pitch of 763 nm, gold thickness of 150 nm, and Si₃N₄ thickness of 100 nm. R₀, namely the initial radius of the spirals, is fixed to 4 μm to reduce the effect of direct scattering of light from the grooves. (b) Scanning electron microscope image of an example of fabricated structure. (c–e) |E| maps (vertical cross-section) and E_z maps (metal surface plots) of the central region of the PVLs in the case of a PV impinging with topological charge of l = 1 propagating through a flat PVL center (c), scattered by a conical tip with a zero-basis curvature radius (r_c) (d), and by a conical tip with large r_c (e). (f) |E| maps in the case of a smoothed conical tip (same parameters as in (e)) illuminated by a PV with the indicated l values.