Hydrogen Gas Leakage Detection Using Laser Spectroscopy with Emphasis on Absorption Methods

Reliable hydrogen leakage detection requires both adequate concentration resolution and a response compatible with the evolution of a leak. Hydrogen presents a particular challenge for absorption spectroscopy because its homonuclear structure makes electric-dipole rovibrational transitions forbidden, leaving weak quadrupole absorption features. This review examines hydrogen sensing by cavity-enhanced Raman spectroscopy, cavity-enhanced absorption and ring-down spectroscopy, photoacoustic and acoustic methods, light-induced thermoelastic spectroscopy, and tunable diode laser absorption spectroscopy. Conventional electrochemical, semiconductor, catalytic, and coated-fiber sensors provide application context. Representative studies are assessed in terms of the measured quantity, detection limit, acquisition time, optical configuration, environmental dependence, and practical deployment. Indirect measurements based on gas-dependent resonator properties are also considered. The comparison distinguishes hydrogen-specific demonstrations from techniques demonstrated for other gases, and separates gas-cell sensitivity from open-path and standoff performance. Recent advances show that lower reported detection limits can require longer averaging, optical enhancement, or more complex excitation and detection schemes. No single method is preferable for all leakage scenarios. Priorities include comparable performance reporting, interference and drift control, and validation with transient hydrogen plumes under realistic field conditions.