Sensitive detection of carbon monoxide based on a QEPAS sensor with a 2.3 μm fiber-coupled antimonide diode laser

In this paper, a sensitive quartz-enhanced photoacoustic spectroscopy (QEPAS)-based carbon monoxide (CO) sensor using a 2.3 μm continuous wave (CW) distributed feedback (DFB) fiber-coupled antimonide diode laser is demonstrated for the first time. Wavelength modulation spectroscopy and a second-harmonic detection technique are used to reduce the sensor background noise and simplify the data process. Water vapor is added into a 1000 ppm CO:N₂ gas mixture to improve the vibrational-translational relaxation rate of the analyzed CO for the purpose of enhancement of the QEPAS signal. After the modulation depth is optimized, a minimum detection limit of 43.3 ppm at the 4294.6 cm^-1 absorption line is achieved when the modulation depth is set to 0.32 cm^-1.