Radiationless Electromagnetic Interference: Perfect Focusing with Evanescent-Field Plates

Planar subwavelength structures are described, which rely on a hitherto unrecognized property of Maxwell's equations to provide superlensing, i.~e., electromagnetic focusing well beyond the diffraction limit, at arbitrary frequencies [1]. The resulting fields bear a striking resemblance to those of negative-index slabs. The structures' design is related to that of the Fresnel plates in that diffraction forces the input field to converge to a spot on the focal plane. Unlike the diffraction-limited zone plates, for which focusing results from standard interference of traveling waves, the subwavelength plates control the near field and, as such, their superlensing properties originate from a new, static form of interference. ~~~~~~~ ~~~~~~~~~~[1] R. Merlin, \textit{Science }\textbf{317}, 927 (2007).