Simultaneous estimation of thickness and refractive index by combining transmission and reflection measurements

摘要

Investigating layer thicknesses with terahertz time-domain spectroscopy usually requires the refractive index of the layer of interest. The refractive index is either investigated beforehand by independent measurements or it is measured simultaneously. The challenge of a simultaneous determination is that measuring two unknown values requires the use of two linearly independent equations. To address this challenge, our approach is to combine transmission and reflection time-of-fiight measurements. By combining these measurements, we obtain a system of two linearly independent equations for the two unknown values: thickness and average refractive index. We experimentally validate our simultaneous estimation approach by measuring calibration foils of different thicknesses.