High-accuracy topography measurement of optically rough surfaces with THz radiation

Characterization of the surface figure of technical materials by interferometry in the visible or near-IR wavelength regime becomes difficult or impossible if the surface is rough on the length scale of a tenth of the wavelength used. In this case, THz radiation can provide an interesting alternative. We demonstrate two methods for the accurate determination of the surface topography: THz heterodyne profilometry and THz ESAD (extended shear angle difference) deflectometry.