A dual-path excitation multiquartz-enhanced photoacoustic spectroscopy (DE-M-QEPAS) sensor was reported for trace gas detection. The system employs a custom multipass cell (MPC) with a pentagonal star-shaped spot pattern, creating dual acoustic sources on both the inner and outer sides of each quartz tuning fork (QTF) prong. This dual-path excitation yielded a 1.31-fold signal enhancement. By further superimposing the outputs from the five QTFs, a combined signal enhancement factor of 3.8 was achieved. A minimum detection limit of 1.33 ppm was obtained for H2O detection at normal atmospheric pressure with a calculated normalized noise equivalent absorption coefficient of 1.23 × 10-8 cm-1W/√Hz.
Shang et al. (Thu,) studied this question.