Contactless testing of the surface of materials

The terahertz (THz) regime is rich in emerging possibilities for sensing and imaging. THz radiation has particular applications in optical metrology like the characterization of the surface topography of technical materials. Interferometry in the visible or near-IR wavelength regime becomes difficult or impossible if the surface roughness exceeds of a tenth of the wavelength. To support these applications, we discuss so-called hybrid techniques for generating, detecting THz "light", and demonstrate two methods for the accurate determination of the surface topography: THz reflectometry and THz heterodyne profilometry.