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large, expensive, conventional terahertz pulse time domain systems for non-destructive evaluation will potentially superseded by compact electronic-based terahertz systems.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.