Use of THz Reflectometry for Roughness Estimations of Archeological Metal Surfaces

In this work, using a time domain spectrometer, we have investigated the reflection of terahertz (THz) pulses from surfaces that exhibit a variable degree of roughness. The study was mainly aimed at assessing the influence of the surface texture on the amplitude and the shape of the pulses reflected by stratified materials and at exploring the potential of this technique for achieving quantitative information on the roughness of the material interfaces hit by the THz beam. The behavior of the reflected THz pulses was investigated by considering angular measurements on a set of suitable mock-ups. Measurements were carried out on an authentic archeological Roman coin that exhibited different corrosion situations. An electromagnetic model was used for estimating the roughness of outer and inner surfaces. The comparison of the results with those provided by other techniques made it possible to parameterize the surface texture such as the traditional contact micro-profilometry and the more recently used 3D digital microscopy.