Quantitative analysis of tritiated water using cavity ring-down spectroscopy

Cavity ring-down spectroscopy (CRDS) offers exceptional sensitivity for trace-gas detection, yet its application to quantitative tritium analysis has remained largely unexplored. In this study, we demonstrate mid-infrared CRDS targeting the fundamental ν ₁ vibrational band of tritiated water (HTO) near 4.3\,m. By exploiting this strong fundamental absorption, the system achieves substantially improved detection sensitivity of HTO compared with previous optical approaches. For the first time, a proportional response to tritium activity was experimentally verified with high linearity (R² > 0.99) and excellent repeatability was demonstrated. Practical detection limits were rigorously assessed by accounting for sample introduction and utilization efficiency, enabling a realistic performance evaluation under operational conditions. The system enables quantitative measurements of microliter-scale samples and offers potential for rapid tritium assessment in fusion and accelerator facilities. These results establish a scalable spectroscopic framework for tritium analysis and provide a pathway toward future ultra-high-sensitivity implementations based on advanced CRDS architectures.