Trace gas detection system based on multi-reflection differential Helmholtz cell and VMD-airPLS algorithm

In this paper, a photoacoustic spectroscopy sensor based on multi-reflection differential Helmholtz cell and Variational Mode Decomposition-adaptive iteratively reweighted penalized least squares (VMD-airPLS) algorithm is proposed to improve the signal-to-noise ratio (SNR) and reduce the response time of the system. The Helmholtz photoacoustic cell, fabricated from brass, allows multiple reflections of the laser light within its resonant cavity, effectively increasing the gas absorption path by a factor of ∼ 6. The VMD-airPLS algorithm suppresses incoherent noise and slowly varying baseline noise over time. To validate the performance of the system, methane is measured using a laser with a wavelength of 1653.7 nm. Experimental results demonstrate a significant enhancement in the sensitivity of system, up to approximately 2.2 times, and an improvement in the SNR by up to approximately 4.2 times compared to single-pass system. The minimum detection limit for methane is ∼ 96.79 ppb.