Terahertz metalenses for evanescent wave focusing and super-resolution imaging

Super-resolution focusing in the metamaterials for both the propagating and evanescent wave emerging from free space is demonstrated based on the gradient-index (GRIN) metalenses. The theoretical investigation reveals that the evanescent wave in free space can be transformed into propagating wave in the metamaterial due to the specific dispersion of the metamaterial. So spatial Fourier transform (FT) with broad input angular spectrum are achieved when the metamaterials are designed with GRIN. Furthermore, the application of super-resolution imaging based on the spatial FT is also presented.