In-plane interferometry of terahertz surface plasmon polaritons

The paper is devoted to the development of interferometric schemes for determining the complex refractive index κ = κ′+i•κ″ κ of surface plasmon-polaritons (SPPs) of the terahertz (THz) spectral range. As the value of κ depends on the dielectric constant ϵm of the metal surface guiding the SPPs it can be used for determining m in the far infrared what other optical methods fail to do due to high reflectivity of metals. We discuss two types of THz SPP interferometers in which the interference pattern is formed as a result of the interaction of SPP beams themselves rather than bulk waves produced by these beams. The first type of interferometers are static devices that enable one to investigate fast processes on the metal surface, while the second type are dynamic ones that make it possible to realize Fourier spectroscopy of the metal surface and its transition layer at THz frequencies. Devices of the both types produce interferograms enabling one to determine the real and the imaginary parts of κ. The results of experiments on the interaction of THz SPPs with flat mirrors and beam - splitting plates, the key elements of the THz SPP interferometers, are presented. © Published under licence by IOP Publishing Ltd.