Digitally Addressable Focusing of Light into a Subwavelength Hot Spot

We show that a plasmonic metamaterial can act as a far-field to near-field transformer that focuses a free-space beam of light into a subwavelength energy hot spot at a prescribed location with a spot size only a small fraction of the wavelength. The hot spot position on the metamaterial can be prescribed and moved at will from one metamolecule of the array to another in a digital fashion simply by modulating the input phase profile, thus providing new opportunities for imaging and optical data processing.