As a promising clean energy source, hydrogen requires reliable safety monitoring. Due to lack of a permanent dipole moment, it is "infrared-inactive" and cannot be effectively measured by absorption-based techniques. Raman spectroscopy can provide molecular fingerprinting, but its extremely weak signal limits the sensitivity. These factors together hinder the real-time hydrogen monitoring in complex industrial environments.

In a study published in Photoacoustics, a research team led by FANG Yonghua from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences developed a novel method called Differential Photoacoustic Stimulated Raman Spectroscopy (DPA-SRS) which enables high-sensitivity hydrogen detection at concentrations as low as 1 ppm under atmospheric pressure.

The DPA-SRS technique integrated stimulated Raman scattering with photoacoustic detection to significantly enhance signal strength. A 532 nm pump beam generated a high-intensity 683 nm Stokes beam, forming a dual-color excitation field that matched the vibrational energy levels of hydrogen. This process induced stimulated Raman transitions, followed by vibration-to-translation relaxation, which converted molecular excitation into detectable acoustic signals.

By combining a custom-designed differential H-type resonant photoacoustic cell with advanced weak-signal processing algorithms, the proposed DPA-SRS system achieved a minimum detection limit of 0.65 ppm (3σ) for hydrogen.

This work provides a new strategy for the high-sensitivity detection of trace non-polar gases in complex environments, paving the way for improved hydrogen safety monitoring in future energy systems.