Metallic transmission screen for sub-wavelength focusing

Introduction: Strong recent interest has centred on near-field imaging systems which produce sub-wavelength resolution. These imaging systems promise increased capabilities in microscopy, lithography, and near-field sensing as well as other applications [1–3]. This Letter describes a simple yet novel metallic transmission screen which focuses an incident electromagnetic wave to a sub-wavelength spot in the near field. The transmission screen was inspired by concepts from holography, where a record of the interference between two waves is used to convert a reference waveform into the desired object waveform [4]. In the remaining sections of this Letter, we explain our two-stage design process, in which we first design an appropriate (in general complex) transmission function, and then implement it with a binary metallic screen. We also display corresponding results from a scalar diffraction calculation and a full-wave simulation demonstrating subwavelength resolution.