Characterization of Thin Film Liquids by Multilayer Structure in THz Time Domain Reflection Spectroscopy

The characterization of thin film liquids is not as straightforward as bulk materials, as it requires accurate control of the thin film thickness and precise measurements of the amplitude and phase of the signals. We propose a multilayer structure for terahertz (THz) time domain reflection spectroscopy (TDRS) characterization of thin film liquids, the equations for this geometry are derived and the water-ethanol mixtures with various concentrations are measured, the refractive indices and absorption coefficients extracted from the proposed geometry and ordinary bulk reflection geometry match well. This work demonstrates that the proposed multilayer structure can be used to extract the optical properties of liquids by using a tiny amount of the sample, it can be potentially applied to characterize valuable biological aqueous solutions in the future.