Subwavelength far-field imaging at visible and ultraviolet wavelengths using broadband surface plasmon waves

Abstract

The optical diffraction limit has stood for a long time in the way of achieving higher optical resolution in far-field imaging, photolithography, and optical data storage. We present here a simple and original concept for broadband far-field imaging in the visible and ultraviolet range that beats this limit. A finite-sized ultrathin metallic slab is used to encode subwavelength details of the broadband field radiated by an object. This field excites a set of surface plasmon modes on the finite-sized slab that radiates in the far field. A numerical time reversal imaging process is applied to reconstruct the image of the object with a resolution smaller than \ensuremath{\lambda}/6 for a gold slab and \ensuremath{\lambda}/8 for a silver slab. With these structures, the highest spatial frequencies are no longer limited by the pitch of the array of the subwavelength resonators as in classical metalenses. We show that the resolution depends mainly on the intrinsic properties of the metal but can be slightly controlled by the geometry design of the slab. Thanks to advances in the control of light in space and time, this concept would provide a promising alternative for high-resolution imaging techniques in the visible and ultraviolet range.