Photoacoustic Ringdown Spectroscopy for Rapid Hydrogen Detection.

Rapid detection of hydrogen (H) is essential for industrial production and environmental monitoring. Beat frequency photoacoustic spectroscopy offers an inherent measurement speed of milliseconds but at the cost of sensitivity. To overcome this limitation, we propose a novel photoacoustic ringdown spectroscopy (PARS) technique that enables both fast and highly sensitive H detection. By utilizing acetylene (CH) as a pump gas, we exploit its strong near-infrared absorption properties to indirectly measure H concentration, compensating for the low sensitivity of direct detection methods due to the weak absorption of H. To achieve the optimal signal-to-noise ratio (SNR) and enhance detection sensitivity, we perform theoretical analysis and experimental verification of a trade-off factor to optimize the photoacoustic cell (PAC) and key excitation parameters, including ringing frequency and residual modulation frequency (RMF). The sensor achieves an Allan deviation of 526 ppm at 50 ms and a minimum detection limit of 8.68 ppm with an integration time of 183.5 s, covering a broad H concentration range from 0 to 30%. The gas response time of this system is experimentally determined to be ∼3.9 s based on the temporal response measurements. This PARS H detection technology demonstrates significant potential for applications in H leak detection and real-time monitoring in safety-critical environments.