Impact of Surface Structures on THz Reflection

THz reflection measurements are a promising tool for material identification. Even visually identical objects might be differentiated due to their individual frequency response in the THz frequency range. However, surface roughness and buried structures with dimensions in the range of the wavelength might prevent identification due to scattering and diffraction effects. In this paper, we investigate whether 3D-printed and CNC-milled samples with nearly identical surface profiles can be distinguished in THz-TDS measurements. Although the samples show nearly identical measurement results, we find a discrepancy between the measurements and a simulation based on Fresnel equations as well as the Rayleigh roughness coefficient.