Terahertz super-focusing device and its application in bio-detection

We investigate the terahertz super-focusing by designing a novel plasmonic lens consisted of Archimedes spiral air array and a concentric groove. A focal spot with FWHM of almost 0.38λ under right circular polarized light (CPL) illumination is achieved. More important, the intensity of focal spot is about 2 times than that of the conventional in-plane plasmonic lens. In addition, we also propose an innovative device possessed the ability of THz super-focusing and higher transmission. This kind of device consists of three sub-wavelength slits engraved into a metal film and surrounded by the finite periodic grooves on both sides of the metal slab. A hot-spot with FWHM of almost ~1/4 λ and the transmission efficiency ~450% is demonstrated. In this paper, by using such kind of device, 0.9 THz super-focusing device was realized and clear imaging of bio tissue can be obtained.