Focused THz wave from a spintronic terahertz Fresnel Zone Plate emitter

Spintronic terahertz emitters (STEs) with the feature of low cost and high performance are considered as one of the most potential terahertz (THz) sources for the future applications of THz waves. At present, the demand for a STE with some additional functions apart from the generation of a THz wave only has become more and more urgent. THz lenses, as a wavefront control device, which is one of the indispensable elements in a THz system, are widely used in THz focus and image systems. However, the common THz lenses are bulky and costly and not applicable for some miniaturization and integration THz systems. Based on two nonferromagnetic film with comparable magnitude of spin Hall angle, but with opposite sign, a binary-phase spintronic terahertz Fresnel Zone Plate emitter (ST-FZPE) is proposed in this paper. Compared with reported THz emitters with a FZP structure, the ST-FZPE is low cost, easy to be fabricated and has a higher efficiency of directing emission focused THz wave. As a planar optical element, the ST-FZPE has tremendous significance to realize integration and miniaturization of THz devices and systems, and it has potential applications in the field of THz bio-sensing, THz imaging and THz communication in the future.