Fixed Dual-Thickness Terahertz Liquid Spectroscopy Using a Spinning Sample Technique

The conventional double-modulated terahertz differential time-domain spectroscopy (double-modulated THz-DTDS) of liquids requires linear dithering of the sample to rapidly vary the sample thickness in order to produce the required sample and reference signals. Linear dithering, however, imposes a fundamental limitation as it introduces mechanical noise into the system, thereby contributing to measurement uncertainty. In this paper, we address this limitation for the terahertz spectroscopy of liquids by using a fixed dual-thickness sample mounted on a spinning wheel. The concept of spinning the sample allows rapid switching between two fixed sample thicknesses in order to produce sample and reference signals without the introduction of added mechanical noise. We validate this new technique by measuring the dielectric properties of a number of liquids and confirm the results against the Debye relaxation model.