Ppb-Level Photoacoustic Gas Detection Using Spatiotemporal Resonance Coupling.

Photoacoustic spectroscopy (PAS) is a sensitive technique for trace gas detection, where the photoacoustic cell (PAC) critically influences overall system sensitivity. However, conventional optimization strategies rely primarily on single-domain resonance enhancement, limiting further acoustic amplification. This study proposes a spatiotemporal resonant gain coupling (ST-RGC) mechanism to amplify photoacoustic signals by integrating spatial standing waves with time-domain energy accumulation. A composite-type PAC realizes this mechanism through a coupled-resonance topology, with critical dimensions optimized via finite element analysis (FEA). Using CHCl3 (0-10 ppm) as the target analyte, the device enhances the signal by a factor of 2.9 compared to an identically dimensioned H-type PAC, achieving a sensitivity of 0.55 V/ppm versus 0.19 V/ppm and linearity of R2 = 0.999. Furthermore, the composite-type PAC improves the SNR and reduces the background fluctuations in the demodulated output, lowering the minimum detection limit (MDL) from 200.53 to 20.73 ppb. Therefore, the ST-RGC mechanism advances the PAC design paradigm from single-domain optimization to spatiotemporal coupling, establishing a transferable framework for high-sensitivity trace gas detection.