Photoacoustic spectroscopy based on vertical cruciform multi-stepped photoacoustic cell achieving ppb-level acetylene detection

A photoacoustic spectroscopy (PAS) based on vertical cruciform multi-stepped photoacoustic cell (CMS-PAC) was developed to achieve highly sensitive detection of trace acetylene (C2H2) gas. Compared with the T-type PAC, the CMS-PAC has improved sensitivity through optimization of both the structural design and the direction of laser incidence. Through finite element simulation analysis, when the incidence direction of modulated laser was placed horizontally, the acoustic intensity of the CMS-PAC was ∼2.45 times higher than that of the T-type PAC. When the modulated laser was applied vertically, the acoustic intensity achieved by the CMS-PAC was ∼11 times higher than that along the horizontal incidence direction. The sensitivities of the CMS-PAC-based PAS system have reached 15.06 and 1.83 pm/ppm, along the vertical and horizontal directions, respectively. Combined with assessment using Allan deviation, the CMS-PAC-based PAS system achieved a minimum detection limit of 3.04 ppb@100 s in the vertical direction, and 23.06 ppb@100 s in the horizontal direction. The proposed CMS-PAC not only enhances acoustic intensity through optimized resonant cavity structures but also improves detection sensitivity with the optimized direction of laser incidence, providing a novel perspective for designing highly sensitive and compact PACs.