A comparison of spectroscopy standards and optical constant retrieval techniques in FTS and TDS measurements

In both Fourier Transform Spectroscopy and Time-Domain Spectroscopy in the THz frequency region, many of the measurements are performed on samples of a single material and given known thickness to either characterize a material sample, characterize a reference substrate of material for a subsequent measurement, or where superior data on that sample exists, calibrate the system accurately. In this short letter, we present some standard formulas for the retrieval of material optical constants and compare the techniques across different systems while pointing out advantages and disadvantages of each depending on the measurement's purpose both in Transmission and Reflection spectroscopy. In doing so, we show a comparison of a standard sample (sapphire) applying standard retrieval techniques to Fourier Transform spectroscopy and Time Domain Spectroscopy.