Mid-infrared quasi-distributed carbon monoxide gas sensing based on QEPAS and hollow waveguide

In this paper, a mid-infrared quasi-distributed carbon monoxide (CO) gas sensing based on quartz-enhanced photoacoustic spectroscopy (QEPAS) and hollow waveguide (HWG) was proposed for the first time. Three micropores with a diameter of 200 μm were developed at three different locations of a HWG with a length of 30 cm. Three customized low-frequency quartz tuning forks (QTFs) with a resonant frequency of 8.7 kHz were used to detect the photoacoustic signals generated at the micropores to achieve quasi-distributed measurements of CO, which provides a new idea for monitoring the leakage of gas pipelines and so on. In order to improve the performance of the gas detection system, the strongest absorption line with CO located at 2179.77 cm⁻¹ (4.58 µm) was selected as the target absorption line, and a quantum cascade laser (QCL) was used as the excitation source to achieve the detection of CO in the mid infrared spectral region. The experimental results show that all three QTFs have excellent concentration linear response to CO, and the minimum detection limit (MDL) of the three QTFs to CO were 2.40 ppm, 2.59 ppm, and 2.34 ppm, respectively. Finally, the experiment tested the response ability of three QTFs to different concentrations of CO at the same time. The results showed that for micropores with different concentrations, all three QTFs can detect their corresponding concentrations, which proves that the sensor can achieve quasi-distributed measurement.