Peculiar effective optical anisotropy of planar isotropic lattices of sub-wavelength disks

Here, we demonstrate that the peculiar effective optical properties of planar lattices of nanoparticles clearly distinguish them from those typical for bulk crystals. Particularly, on the basis of theoretical considerations and experimental results, we prove that the effective planar optical anisotropy of nominally isotropic planar lattices is defined not by their “crystallography” but by the orientation of the plane of incidence of the exciting light relative to the lattice orientation, as a result of spatial dispersion. We demonstrate that such properties of isotropic lattices of interacting nanoparticles that seem peculiar from the point of view of standard crystal optics are fundamental ones, which are clearly exhibited in the case of planar layers.