Polarization-controlled terahertz super-focusing

Metasurfaces have shown unprecedented capabilities in manipulating the phase, intensity, and polarization of electromagnetic waves. The coupling efficiency of surface plasmon polaritons is overcome by polarization sensitivity metasurfaces, but they face challenges in the application of high-intensity-based SPPs confined to the surface of a metal. Based on spiral arrays combined with a concentric groove, we experimentally demonstrate the application-oriented and polarization-controlled terahertz superfocusing by emitting high-efficiency radially convergent SPPs into free space to form a focal spot beyond the diffraction limit. The full wave at half maximum of the focal spot is 0.38 lambda, and it shows tunable intensity (the overall intensity of the focused spot can be tuned) by controlling the polarization state of the incident waves. This work paves a way towards imaging, data storage, and lithography. Published by AIP Publishing.