Research on the effect of the laser beam location on the performance of mid-infrared photoacoustic spectroscopy based gas detection system

Photoacoustic (PA) spectroscopy based gas detection has aroused extensive attention for its high sensitivity and portability. Experiments were performed to measure the effect of the radial distance from the geometric center line of the laser beam to the microphone and the axial distance between the laser head and the PA cell window on the PA signals. Three indicators were introduced to characterize the sensitivity and stability exhibited by the gas detection system. The sensitivity decreased with the increase in the axial distance from the geometric center line of the laser beam to the microphone, and the relationship between the normalized sensitivity and the distance was approximately linear. The gas detection system exhibited the optimal sensitivity when the axial and radial distance were 1.5 cm and 2 mm, respectively. To achieve high stability and sensitivity simultaneously, the radial distance 3 mm and axial distance 6.5 to 7.5 mm might be selected.