# Differential photoacoustic-stimulated Raman spectroscopy (DPA-SRS) for high-sensitivity hydrogen detection

## TL;DR

A new method called DPA-SRS is developed to detect hydrogen with high sensitivity by combining photoacoustic and Raman spectroscopy techniques.

## Contribution

The paper introduces a novel DPA-SRS method that simplifies hydrogen detection using a single laser and advanced signal processing.

## Key findings

- DPA-SRS achieves a hydrogen detection limit of 0.65 ppm under atmospheric conditions.
- The method uses a dual-color light field to enhance the nonlinear thermoacoustic effect for hydrogen identification.
- A differential H-type resonant cell improves anti-interference capability and signal extraction.

## Abstract

To detect non-polar, infrared-inactive hydrogen, a Differential Photoacoustic-Stimulated Raman Spectroscopy (DPA-SRS) method is proposed. Utilizing the SRS process, a portion of the pump light is converted into intense Stokes light corresponding to the hydrogen Raman shift, eliminating complex dual-laser configurations. The nonlinear thermoacoustic effect is excited by this dual-color light field, endowing Photoacoustic Spectroscopy with the capability for hydrogen fingerprint identification. Raman cell pressure was optimized to achieve a synergistic enhancement of the Stokes conversion efficiency and the Four-Wave Mixing effect. Furthermore, an acoustic mode-optimized differential H-type resonant photoacoustic cell was designed, which effectively enhances anti-interference capability through the differential detection mechanism. Distinct from traditional lock-in amplification methods, a time-frequency transformation algorithm was employed to precisely extract the frequency-domain photoacoustic signal from the broadband time-domain acoustic signal. Experimental results demonstrate that the DPA-SRS system exhibits excellent linearity and achieves a Limit of Detection of 0.65 ppm under atmospheric conditions.