Attenuated Total Reflection Terahertz Time-Domain Spectroscopy: Uncertainty Analysis and Reduction Scheme

Terahertz time-domain spectroscopy (THz-TDS) in the attenuated total reflection (ATR) configuration is ideally suited to characterize highly absorptive media. In this paper, we analyze the impact of random phase and amplitude errors and prism misalignment on the optical constants extracted from the ATR THz-TDS measurements. Analytical models together with empirical data suggest that, among those factors, small prism misalignment has a relatively strong impact on the optical constants. We propose an alternative configuration for ATR THz-TDS that significantly reduces the impact of prism misalignment between the reference and sample measurements. As a result, this configuration facilitates repetitive reference and sample scans to mitigate the effect from long-term signal drifts. Based on this proposed method, the measured optical constants of distilled water and pure ethanol have a significantly reduced uncertainty. The presented analysis and method can be used to improve the measurement accuracy in standard ATR THz-TDS setups.