Fig. 2
From: Dielectric metasurface zone plate for the generation of focusing vortex beams
Design and fabrication of the dielectric metasurface zone plates. a–d The calculated phase profiles of the metasurface zone plates with topological charges of (a) l = 2, (b) l = 3, (c) l = +/− 2, (d) l = +/− 3. e–h The top-view SEM images of the fabricated metasurfaces corresponding to (a–d). Scale bar: 20 μm. i–l The side-view SEM images corresponding to (e–h). Scale bar: 1 μm