Fig. 2: A great variability of visual diffuse and specular responses is obtained with a restricted set of manufacturing parameters.

a SEM image of a metasurface. The scale bar represents 500 nm. b Ping-pong ball setup used to visualise the diffuse component of the BRDF upon illumination with a focused supercontinuum laser beam. c Photographs of the ping-pong ball show the diffuse responses for 27 metasurfaces under 45° incident illumination, with nominal square features of side length \({\ell}=95,130\) and \(170\,{{\rm{nm}}}\), densities \(\rho={\mathrm{2,5}}\) and \(10\,{{{\rm{\mu }}}{{\rm{m}}}}^{-2}\), and packing fractions \(p={\mathrm{0.1,0.3}}\) and \(0.5\). The two white dots indicate the incident and specular directions. Specular colours recorded at 10° incidence for the metasurfaces are displayed as uniformly coloured rectangles. SEM images depict the arrangement, size, and density of the metaatoms. Note that the metasurface with \({\ell}=130\,{\mathrm{nm}}\), \(p=0.5\) and \(\rho=2\,{{{\rm{\mu }}}{{\rm{m}}}}^{-2}\) has been damaged during sample handling.