Effect of absorption on terahertz surface plasmon polaritons propagating along periodically corrugated metal wires

In this paper, a rigorous method for analyzing surface plasmon polaritons (SPPs) on a periodically corrugated metal wire has been formulated, based on a modal expansion of electromagnetic fields. Compared with the previous method, our method takes into account the finite conductivity of the wire as well as higher-order modes within the wire grooves in the expansion, thus is able to accurately calculate the loss of these spoof SPPs propagating along the wire. In the terahertz frequency range, the properties of the loss of spoof SPPs on corrugated Al wires are analyzed. The loss of the spoof SPPs grows significantly with the increase of field confinement, and it is often considerably large when the frequency is close to the asymptotic frequency. The effect of absorption on the energy concentration and superfocusing of terahertz radiation is also analyzed, and found to be tolerably small, except very close to the asymptotic frequency.