Multipass-Enhanced Multicomponent Photoacoustic Gas Sensing with a Hierarchically Coupled H-Type Resonator

A multipass hierarchically coupled H-type resonator-based photoacoustic sensing system for multicomponent gas detection is proposed. By hierarchically coupling and serially arranging multiple H-type photoacoustic cells (H-PACs), with the reuse of buffer chambers and resonant cavities, several available resonant frequencies are generated at different locations, enabling the highly sensitive detection of three target gases. Furthermore, the incorporation of a multipass cell (MPC) effectively enhances the light-gas interaction, thereby improving the detection performance of the system. Meanwhile, three excitation beams with different wavelengths share a common optical path, significantly increasing the system's integration level. Distributed feedback (DFB) diode lasers with center wavelengths of 1653.72, 1531.58, and 1572.34 nm were employed to selectively excite CH4, C2H2, and CO2, respectively. The experimentally measured resonant frequencies at the three detection positions were 1320, 3515, and 5430 Hz, respectively, showing good agreement with the finite-element simulation results. The introduction of an MPC achieved a photoacoustic (PA) signal enhancement factor of approximately 12.43. The experimental evaluation confirms the reliable quantitative detection performance of CH4, C2H2, and CO2, while no significant cross-interference is observed among the different sensing positions. According to the Allan deviation analysis, minimum detection limits (MDLs) of 21.05 ppb, 4.68 ppb, and 2.63 ppm were achieved for CH4, C2H2, and CO2, respectively, at an averaging time of 300 s.