Influence of light coupling configuration and alignment on the stability of HWG-based gas sensor system for real-time detection of exhaled carbon dioxide

Zhou, Tao, Wu, Tao, Zhang, Huailin, Wu, Qiang, Chen, Weidong, Ye, Chenwen and He, Xingdao (2019) Influence of light coupling configuration and alignment on the stability of HWG-based gas sensor system for real-time detection of exhaled carbon dioxide. IEEE Sensors Journal, 19 (24). pp. 11972-11979. ISSN 1530-437X

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Abstract

A mid-infrared tunable diode laser absorption spectroscopy (TDLAS) gas sensor based on hollow waveguide (HWG) gas cell for real-time exhaled carbon dioxide (eCO2) detection is reported. A 2.73 μm distributed feedback (DFB) laser was used to target a strong CO2 absorption line, and wavelength modulation spectroscopy (WMS) with the second harmonic (WMS-2.) was used to retrieve the CO2 concentration with high sensitivity. The influence of different parameters, including coupling configuration of HWG, laser-to-HWG and HWG-to-detector coupling alignment on the stability of the HWG sensor is systematically studied. The HWG eCO2 sensor showed a fast response time of 2.7s, detection limit of 17 ppmv, and measurement precision of 20.9 ppmv with a 0.54 s temporal resolution. The eCO2 concentrations changed in breath cycles were measured in real time. The Allan variance indicated that the detection limit can reach 1.7 ppmv, corresponding to a detection sensitivity of 1.3(215)10-8 cm-1Hz-1/2, as the integration time increases to 26 s. This work demonstrates the performance characteristics and merits of HWG eCO2 sensor for exhaled breath analysis and potential detection for other exhaled gases.

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