Over-the-Horizon Terahertz Surface Plasmon Locator

The article demonstrates the possibility of creating an over-the-horizon locator with an information carrier of surface plasmon polaritons (SPPs), a kind of surface electromagnetic waves, of the terahertz (THz) spectral range. This possibility is based on the macroscopic propagation length (decimeters) of THz SPPs, as well as on their ability to propagate along convex surfaces of metals. Two schemes of location measurements on gold convex samples using THz SPPs were developed and tested for SPPs generated by free-electron laser radiation with a wavelength of 130 μm. It was found that the intensity of SPPs reflected by an object placed on a conducting surface about 4 cm beyond the horizon line depended on the height of the object above the surface, in accordance with the distribution of the SPP field in the air (a few millimeters or fractions of a millimeter). The distance, orientation, coordinates, and height of an object placed beyond the horizon line can be determined using the SPP locator, which can be applied for localization of hard-to-reach objects on a convex surface.