Terahertz surface plasmon polariton propagation and focusing on   periodically corrugated metal wires
  In this letter we show how the dispersion relation of surface plasmon polaritons (SPPs) propagating along a perfectly conducting wire can be tailored by corrugating its surface with a periodic array of radial grooves. In this way, highly localized SPPs can be sustained in the terahertz region of the electromagnetic spectrum. Importantly, the propagation characteristics of these spoof SPPs can be controlled by the surface geometry, opening the way to important applications such as energy concentration on cylindrical wires and superfocusing using conical structures. 
Stefan A. Maier (1), Steve R. Andrews (1), L. Mart\'in-Moreno (2), F.   J. Garc\'ia-Vidal (3) ((1) Centre for Photonics and ...