Measurement of Trace Hydrogen in Atmosphere Using Polarized Raman Spectroscopy

As a clean energy source, the demand for hydrogen gas (H2) in industrial and commercial sectors is growing. To effectively monitor H2 leaks during production, storage, transportation and use, it is necessary to perform real-time detection of trace amounts of H2 in atmospheric conditions. However, the optical detection of trace hydrogen faces significant challenges due to the extremely weak electric quadrupole transitions of hydrogen molecules, making absorption spectroscopy measurements difficult. Raman spectroscopy has great potential for measuring trace gases, but its application is limited by sensitivity. In this work, a cavity-enhanced Raman spectroscopy technique incorporating Pound-Drever-Hall (PDH) frequency locking was presented. By measuring polarized Raman spectra, cavity enhancement significantly amplified the gas scattering signal intensity, and it leveraged the discriminability in polarization characteristics among Raman peaks of different vibrational modes to simplify complex Raman spectra and eliminate interference from water vapor during hydrogen gas measurement. This method achieved a low detection limit of 0.06 μmol/mol (at 1 atm) for hydrogen, enabling direct sampling and continuous measurement of hydrogen in ambient air with a relative measurement precision of 5%, which demonstrated its capability for quantitative measurement of trace H2 in complex gas environments.