Radiationless electromagnetic interference: evanescent-field lenses and perfect focusing

Diffraction restricts the ability of most electromagnetic devices to image or selectively target objects smaller than the wavelength. We describe planar subwavelength structures capable of focusing well beyond the diffraction limit, operating at arbitrary frequencies. The structure design, related to that of Fresnel plates, forces the input field to converge to a spot on the focal plane. However, unlike the diffraction-limited zone plates, for which focusing results from the interference of traveling waves, the subwavelength plates control the near field and, as such, their superlensing properties originate from a static form of interference. Practical implementations of these plates hold promise for near-field data storage, noncontact sensing, imaging, and nanolithography applications.