As a promising clean energy source, hydrogen (H2) requires reliable safety monitoring. However, lacking a permanent dipole moment, it is "infrared-inactive" and cannot be effectively measured by conventional absorption-based techniques. Although Raman spectroscopy can provide molecular fingerprinting, it' s extremely weak signal limits sensitivity. Together, these factors hinder real-time hydrogen monitoring in complex industrial environments.
Recently, 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 study was published in Photoacoustics.
The DPA-SRS technique integrated stimulated Raman scattering (SRS) 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 (V–T) 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, according to the team.
Schematic diagram of the DPA-SRS hydrogen detection system (Image by LI Zhengang)
Software algorithm processing results of photoacoustic signals. (a) Digital filtering; (b) FFT spectrum conversion (Image by LI Zhengang)
