Growth of terahertz surface plasmon propagation length due to thin-layer dielectric coating

Here we consider a longstanding problem: why terahertz (THz) surface plasmons (SPs) do not run so far as the Drude theory predicts. We experimentally demonstrated that the main cause for this paradox was a drastic rise in the SP radiative losses at THz frequencies, not violation of the theory. Analysis of SPs induced with the radiation of the Novosibirsk free electron laser (λ=130 μm) showed that a thin dielectric layer (≈λ/250) on a metal surface can reduce the losses substantially and hence enlarge the SP propagation length several times. Furthermore, it was found that there was an optimal layer thickness corresponding to the minimum total SP energy losses; the cause of this phenomenon is discussed.