THz-TDS Reflection Measurement of Coating Thicknesses at Non-Perpendicular Incidence: Experiment and Simulation

Time-domain spectroscopy (TDS) in the terahertz (THz) frequency range is gaining importance nondestructive testing of dielectric materials. One application layer thickness measurement a coating layer. To determine from data, refractive index must be known surveyed range. For perpendicular incidence radiation, methods exist to extract data themselves without prior knowledge. This paper extends these for non-perpendicular incidence, where polarization radiation becomes important. Furthermore, modifications considering effects surface roughness are introduced. The new verified using sample Inconel steel coated with yttria-stabilized zirconia (YSZ) and COMSOL simulations setup. validate measurements, scanning electron microscopy (SEM) images structure used. results show good agreement an average error 1% simulation under 4% experimental compared reference measurements.