A portable low-power QEPAS-based CO2 isotope sensor using a fiber-coupled interband cascade laser

• Published in: Sensors and actuators. B, Chemical Vol. 246; pp. 710 - 715
• Main Authors: Wang, Zhen, Wang, Qiang, Ching, Jessica Yuet-Ling, Wu, Justin Che-Yuen, Zhang, Guanfeng, Ren, Wei
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.2017
• Subjects: CO2 isotope; Interband cascade laser; Mid-infrared fiber; Quartz-enhanced photoacoustic spectroscopy; Mid-infrared fiber; CO2 isotope; Quartz-enhanced photoacoustic spectroscopy; Interband cascade laser
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2017.02.133

•A CO2 isotope sensor was developed using off-beam QEPAS with a low-power interband cascade laser (ICL) at 4.35μm.•The ICL was coupled into a solid-core fiber with a single-mode output to eliminate the ambient CO2 interference.•The sensor achieved an average precision of <1‰ for the isotopic ratio determination by exploiting three CO2 isotope lines.•A software-based signal processing method was used to reduce the system size, weight and complexity. Current field and medical applications demand better quantification of CO2 isotopic ratios with high sensitivity, fast time-response, portable instrument size, and low power consumption. We report such a CO2 isotope sensor using quartz-enhanced photoacoustic spectroscopy (QEPAS) with a continuous-wave interband cascade laser (ICL). The ICL emitting at 4.35μm with a low drive current (35–60mA) and optical power (<2.6mW) covered the P(43) and P(44) lines of 12CO2 and the R(18) line of 13CO2 with a single current scan. The ICL radiation was coupled into a solid-core (100-μm core diameter) indium fluoride optical fiber with a coupling efficiency of 88%. We successfully delivered the single-mode laser beam from the fiber output into the off-beam QEPAS spectrophone enclosed in a compact gas cell. The generated photoacoustic signal was acquired and analyzed by a digital lock-in amplifier to obtain its second harmonic (2f) component. Our sensor is capable of analyzing the CO2 isotopic ratio with an average precision of <1‰, which fulfills the precision requirements of most medical and field applications.