Terahertz Coherence Tomography for In-Container Liquid Characterization

For on-site measurements, large, expensive, conventional terahertz pulse time domain systems for non-destructive evaluation will potentially superseded by compact electronic-based terahertz systems. However, common electronic detectors are not capable of detecting the phase of received signals, complicating the characterization of multilayer samples. We propose a practical method for the characterization of in-container liquid samples using swept-source terahertz coherence tomography in reflection configuration. We demonstrate this technique in the 220–330 GHz frequency band to quantify the principle components of common alcoholic beverages, namely, water, sugar, and ethanol, with sensitivity to ethanol concentration below 0.4%v/v, whilst simultaneously recovering information about the container. Additionally, the method allows real-time observation of dilution in the mixtures. The proposed method facilitates measurement with significantly reduced experimental overhead and critically, is compatible with incoherent terahertz cameras for quantitative imaging.