Optical Component-Free Dual-Gas Quartz-Enhanced Photoacoustic Spectroscopy Sensor Based on Highly Integrated...

We proposed and demonstrated an optical component-free dual-gas quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor. Two mid-infrared interband cascade lasers (ICLs) emitting at 4.59 μm were employed as the optical sources in the sensor. The two ICLs were integrated with a photoacoustic detection unit without any additional optical components. In addition, we used two quartz tuning forks (QTFs) as the acoustic detectors, with slightly different resonance frequencies (30.72 and 32.768 kHz), in order to achieve simultaneous dual-gas sensing with minimal acoustic interference. The gas sensing properties of the sensor was studied with target analytes of carbon monoxide (CO) and nitrous oxide (N₂O), while water vapor was added to the gas mixture to accelerate the vibration-translation rate of the gas molecules. For detections of CO and N₂O, the sensor achieved sub-ppm detection limits (MDL), e.g., 180 and 710 ppb (ppb) with optimal integration times of 500 and 700 s, respectively, based on an Allan deviation analysis and the evaluated long-term performance of the sensor.