Simulation and analysis of a laser photoacoustic system for trace gas monitoring

This paper presents a simulation-based optimization of a CO 2 laser photoacoustic spectroscopy (CO 2 LPAS) system for high-precision pollutant monitoring. Using a cylindrical stainless steel resonant cell, the absorption characteristics of ethylene, benzene, toluene, ammonia, and ozone over the 9.2–10.8 µm spectral window were modeled. The results presented in this paper demonstrate exceptional sensitivity, with simulated limits of quantification (LoQ, S/N=3) of 0.49 ppbV for ethylene and 0.75 ppbV for ammonia (corresponding to LoD values, S/N=1, of 0.163 ppbV and 0.25 ppbV, respectively), supported by a cross-sensitivity matrix for efficient species discrimination. A critical focus of this study is the investigation of vibro-translational ( V - T ) relaxation processes catalyzed by water vapor. It has been shown that relative humidity significantly amplifies the photoacoustic signal, and we propose a second-order polynomial compensation algorithm to maintain measurement accuracy under different environmental conditions. In addition, a finite element model has been developed to analyze the acoustic modes and sound pressure distribution within the resonator. The cell, characterized by a resonant frequency of 564 Hz and a quality factor of 16.1, was found to be primarily limited by background noise rather than intrinsic electronic or thermal noise. These findings provide a robust framework for the development of highly sensitive, real-time gas sensors for environmental and industrial applications.