Simultaneous measurement of ammonia and ethylene using hollow waveguide‐based wavelength modulation spectroscopy with a 9.56 μm quantum cascade laser.

Simultaneous measurement of ammonia and ethylene is of great significance for atmospheric environmental monitoring, industrial process controlling and medical respiratory diagnosing. A wavelength modulation spectroscopy based on a 9.56 μm quantum cascade laser (QCL) and a hollow waveguide with a length of 5 m is reported for simultaneous gas sensing of ammonia (NH3) and ethylene (C2H4). The strong absorption lines of NH3 and C2H4 located at 1046.4 and 1045.97 cm−1, respectively, are selected, which can be covered by current tuning of the QCL. Based on the measured frequency modulation characteristics of the QCL, the modulation amplitude is optimized. The sensor performance evaluation shows that it has a sensitivity of 63.2 ppb and 0.775 ppm for NH3 and C2H4 respectively, with time resolution of 1 s. Furthermore, Allan variance analysis shows that the detection limit of NH3 and C2H4 can reach 7 ppb and 45 ppb, respectively, for about 100 s averaging time. The system is stable and robust, thus could be used in real‐time monitoring of atmospheric environment and extended to the field of exhaled breath analysis in the future. [ABSTRACT FROM AUTHOR]