Sensitive hydrogen detection using off-axis integrated cavity output spectroscopy at 2.1 μm

Reliable hydrogen (H2) detection is essential for advancing hydrogen energy applications. In this study, we report a sensitive H2 detection method using off-axis integrated cavity output spectroscopy. A distributed-feedback laser with fiber output was used to target the H2 absorption transition near 2122 nm. The optical cavity was constructed using two spherical mirrors, each with a reflectivity of 99.985%, providing an effective absorption path length of 2500 m. The Galatry line shape function was selected to accurately fit the narrow absorption feature of H2. Furthermore, we achieved a 1.74-fold improvement in the signal-to-noise ratio by applying radio frequency white noise perturbations. The system's performance was demonstrated by measuring H2 mixtures across a broad concentration range from 1040 ppm to 20.24%. Finally, the Allan–Werle deviation analysis revealed a detection limit of 53 ppm H2 at an average time of 400 s.