Ppb-level mid-infrared ethane detection based on three measurement schemes using a 3.34-μm continuous-wave interband cascade laser
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A ppb-level mid-infrared ethane (C2H6) sensor was developed using a continuous-wave, thermoelectrically cooled, distributed feedback interband cascade laser emitting at 3.34 μm and a miniature dense patterned multipass gas cell with a 54.6-m optical path length. The performance of the sensor was investigated using two different techniques based on the tunable interband cascade laser: direct absorption spectroscopy (DAS) and second-harmonic wavelength modulation spectroscopy (2f-WMS). Three measurement schemes, DAS, WMS and quasi-simultaneous DAS and WMS, were realized based on the same optical sensor core. A detection limit of ~7.92 ppbv with a precision of ±30 ppbv for the separate DAS scheme with an averaging time of 1 s and a detection limit of ~1.19 ppbv with a precision of about ±4 ppbv for the separate WMS scheme with a 4-s averaging time were achieved. An Allan–Werle variance analysis indicated that the precisions can be further improved to 777 pptv @ 166 s for the separate DAS scheme and 269 pptv @ 108 s for the WMS scheme, respectively. For the quasi-simultaneous DAS and WMS scheme, both the 2f signal and the direct absorption signal were simultaneously extracted using a LabVIEW platform, and four C2H6 samples (0, 30, 60 and 90 ppbv with nitrogen as the balance gas) were used as the target gases to assess the sensor performance. A detailed comparison of the three measurement schemes is reported. Atmospheric C2H6 measurements on the Rice University campus and a field test at a compressed natural gas station in Houston, TX, were conducted to evaluate the performance of the sensor system as a robust and reliable field-deployable sensor system.
KeywordsC2H6 Concentration Wavelength Modulation Spectroscopy C2H6 Sample Direct Absorption Spectroscopy Triangular Signal
Chunguang Li acknowledges support by China Scholarship Council (Grant No. 201406170107). Chuantao Zheng acknowledges the support by China Scholarship Council (Grant No. 201506175025), the National Natural Science Foundation of China (Grant No. 61307124) and the Changchun Municipal Science and Technology Bureau (Grant No. 14KG022). Lei Dong acknowledges support by National Natural Science Foundation of China (Grant Nos. 61575113 and 61275213). Weilin Ye acknowledges the support by China Scholarship Council (Grant No. 201508440112). Frank Tittel acknowledges support by the National Science Foundation (NSF) ERC MIRTHE award, a Robert Welch Foundation Grant C-0586 and a NSF Phase II SBIR (Grant No. IIP-1230427DE DE) and DOE ARPA-E awards # DE-0000545 with Aeris Technologies, Inc. and # DE-0000547 with Maxion Technologies, Inc.
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