Electromagnetic exploration of far-field super-focusing nanostructured metasurfaces.

Planar multi-annular nanostructured metasurfaces have provided a new way to realize far-field optical super-resolution focusing and nanoscopic imaging, due to the delicate interference of propagating waves diffracted from the metasurface mask. However, so far there are no proper methods that can be used to essentially interpret the super-focusing and nano-imaging mechanisms. This research proposes an electromagnetic methodology for the super-resolution investigation of nanostructured metasurfaces. We have physically modeled the polarization-dependent transmission effect of the subwavelength nanostructure and the vectorial imaging process of a high-numerical-aperture microscopic system. We have found theoretically and experimentally that the current design theories may produce imprecise results; the microscopic imaging experimental method can only detect transversely polarized electric field component and cannot map out three-dimensional total electric energy density distribution behind metasurfaces. This method will potentially be used in far-field nanoscopy, nanolithography, high-density optical storage, etc.