The effect of the photoacoustic Field-Photoacoustic cell coupling term on the performance of the gas detection system

The optimization of the photoacoustic cell (PAC) has always been a research hotspot in the photoacoustic spectroscopy (PAS) based gas detection technology. Herein, a new influential factor of the PA signals intensity, photoacoustic field (PAF)-PAC coupling term was proposed. In addition, the simulation of the sound pressure distribution in the PAC and the PAS gas detection experiment were carried out. The results show that: the length LC and radius RC of the resonator both have an impact on the sound pressure distribution, the strongest sound pressure intensity appears when LC = 95 mm. Besides, when LC is in the range of 35 -65 mm, the sound pressure intensity decreases with the increased RC, whereas it increases with RC when LC is in the range of 80 -125 mm. With the shortening of the focal length F-0, the dimension of the light beam and the maximum light intensity reduces and enhances, respectively. In particular, when F-0 = 16 mm, the integral value along the major axis of the light spot has the peak value, which also changes with the distance l(2) from the laser head to the convex lens, and the peak value appears when l(2) = 4 mm. In addition, the optimal response of the gas detection system (GDS) occurs when l(1) = 0 mm, l(2) = 2 mm, l(3) = 2 mm. LC has a significant impact on the representative signal intensity (RSI), and the influence is mainly result from the PAF-PAC coupling term. However, the effect of the RC on the RSI can be approximately negligible.