Cavity ring-down spectroscopy using an EC-QCL operating at 7.5 <i>µ</i>m for direct monitoring of methane isotopes in air

Maity, Abhijit; Pal, Mithun; Banik, Gourab Dutta; Maithani, Sanchi; Pradhan, Manik

doi:10.1088/1612-202x/aa8584

Cited by 51 publications

(34 citation statements)

References 20 publications

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“…As both high sensitivity and real-time detection are of great significance to environmental monitoring, CRDS is a suitable method for atmospheric trace-gas monitoring. Moreover, CRDS also has the potential for use in exhaled breath tests (Mashir and Dweik, 2009), since the exhaled air contains many biomarker trace gases (for example CH 4 , NO, N 2 O, and NH 3 ; De Lacy Costello et al, 2013, Brubaker, 2016, Bleakley and Tiedje, 1982, and Kearney et al, 2002 that reflect some physiological processes and/or diseases in human body. However, mid-infrared (mid-IR) CRDSs for trace-gas detections were rarely reported in the early days because of the unavailability of mid-IR laser sources.…”

Section: Introductionmentioning

confidence: 99%

High-precision measurements of nitrous oxide and methane in air with cavity ring-down spectroscopy at 7.6 µm

Tang

Wang

2019

Atmos. Meas. Tech.

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Abstract. A high-sensitivity methane (CH4) and nitrous oxide (N2O) sensor based on mid-infrared continuous-wave (CW) cavity ring-down spectroscopy (CRDS) techniques was developed for environmental and biomedical trace-gas measurements. A tunable external-cavity mode-hop-free (EC-MHF) quantum cascade laser (QCL) operating at 7.4 to 7.8 µm was used as the light source. The effect of temperature fluctuation on the measurement sensitivity of the CRDS experimental setup was analyzed and corrected, and a sensitivity limit of absorption coefficient measurement of 7.2×10-10 cm−1 was achieved at 1330.50 cm−1 with an average of 139 measurements or 21 s averaging time and further improved to 2.3×10-10 cm−1 with an average of 3460 measurements, or 519 s averaging time. For the targeted CH4 and N2O, absorption lines located at 1298.60 and 1327.07 cm−1 with temperature effect correction detection limits of 13 and 11 pptv were experimentally achieved with 10.4 and 10.2 s averaging times and could be further improved to 5 and 9 pptv with 482.5 and 311 s averaging times, respectively. Four spectral bands (1298.4 to 1298.9 cm−1, 1310.1 to 1312.3 cm−1, 1326.5 to 1328 cm−1, and 1331.5 to 1333 cm−1) in the spectral range from 1295 to 1335 cm−1 were selected for the separate and simultaneous measurements of CH4 and N2O under normal atmospheric pressure, and all were in good agreements. The concentrations of CH4 and N2O of atmospheric air collected at different locations and of exhaled breath were measured and analyzed. Continuous measurements of CH4 and N2O concentrations of indoor laboratory air over 45 h were also taken. It was found that anaerobic bacteria in the water and soil of wetlands might significantly increase the CH4 concentration in the air. The measured N2O concentration in the central city area was somewhat lower than the reported normal level in open air. Our results demonstrated the temporal and spatial variations of CH4 and N2O in the air.

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Section: Introductionmentioning

confidence: 99%

High-precision measurements of nitrous oxide and methane in air with cavity ring-down spectroscopy at 7.6 µm

Tang

Wang

2019

Atmos. Meas. Tech.

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“…As mentioned above, high-resolution measurements of l-doublet splittings of OCS were made using the cw-CRDS method coupled with an EC-QCL operating at λ∼5.2 μm (1923 cm −1 ). The experimental arrangement of the cw-CRDS system has been described in detail previously [16][17][18][19] and therefore only salient features of the spectrometer are given here. In a classical cw-CRDS system, the decay rate of a laser light trapped in a highfinesse optical cavity is measured and the direct absorption of molecular spectral lines is recorded.…”

Section: Experimental Techniquementioning

confidence: 99%

Cavity ring-down spectroscopy measurements ofl-type doubling of hot bands in Δ vibrational states of OCS near 5.2μm

et al. 2018

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We investigated the l-type doubling in the (14 2 0)←(02 2 0) weak hot band transition of carbonyl sulphide (OCS) for l=2 (i.e. Δ state) vibrational state. High-resolution spectroscopic measurements of l-doublet splittings of OCS were carried out using cavity ring-down spectroscopy (CRDS) technique employing a continuous-wave (cw) external-cavity quantum cascade laser (EC-QCL) operating at ∼5.2 μm. The rotationally resolved spectra of l-doublet splittings between the parity doublet e and f sub-states of OCS were recorded by probing the rotational lines from J=22 to J=29 in the R branch belonging to the weak hot band transition. Subsequently, we determined the l-type doubling constant, transition dipole moment, rotational constant and centrifugal distortion constant for both e and f components of the (14 2 0) vibrational state with relatively high rotational states of OCS. As the measurement of l-doublet splitting in l=2 or higher states of OCS remains challenging due to extremely small splitting, therefore our findings suggest that the observation of the l-type doubling in Δ vibrational state (l=2) with new values of the several spectroscopic parameters as mentioned above will be useful for better understanding of linear polyatomic molecular properties in general from high-resolution spectroscopic data.

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“…Among commonly used detection techniques for trace C 2 H 2 , resonant cavity-based infrared laser absorption spectroscopy techniques have attracted a lot of interest with the advantages of high detection sensitivity, fast response, and small sample volume. Techniques such as cavity ringdown spectroscopy (CRDS) [6,7,8] and cavity-enhanced absorption spectroscopy (CEAS) [9,10] make use of high-finesse optical cavities that greatly increase the effective optical path length, thereby improving the detection sensitivity.…”

Section: Introductionmentioning

confidence: 99%

Long-Term Stable Online Acetylene Detection by a CEAS System with Suppression of Cavity Length Drift

Feng

2019

Sensors

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A trace acetylene (C2H2) detection system was demonstrated using the cavity-enhanced absorption spectroscopy (CEAS) technique and a near-infrared distributed feedback (NIR-DFB) laser. A Fabry–Perot (F–P) cavity with an effective optical path length of 49.7 m was sealed and employed as a gas absorption cell. Co-axis cavity alignment geometry was adopted to acquire a larger transmitted light intensity and a higher sensitivity compared with off-axis geometry. The laser frequency was locked to the cavity fundamental mode (TEM00 mode) by using the Pound–Drever–Hall (PDH) technique continuously. By introducing a cavity length-locking loop, the drift of the cavity length was suppressed, and the stability of the system was enhanced. To demonstrate the efficacy of the system, a C2H2 absorption spectrum near 6534.36 cm−1 was acquired by tuning the laser operation temperature. Measurements of C2H2 samples with different concentrations were carried out, and a good linear relationship between C2H2 concentration and the cavity-transmitted signal voltage was observed. The measurement results showed the system could work stably for more than 2 h without major fluctuations. The Allan variance analysis results demonstrated a detection limit of 9 parts-per-billion (ppb) with an averaging time of 11 s corresponding to a minimum detectable absorption coefficient of 1.1 × 10−8 cm−1.

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Cavity ring-down spectroscopy using an EC-QCL operating at 7.5 µm for direct monitoring of methane isotopes in air

Cited by 51 publications

References 20 publications

High-precision measurements of nitrous oxide and methane in air with cavity ring-down spectroscopy at 7.6 µm

High-precision measurements of nitrous oxide and methane in air with cavity ring-down spectroscopy at 7.6 µm

Cavity ring-down spectroscopy measurements ofl-type doubling of hot bands in Δ vibrational states of OCS near 5.2μm

Long-Term Stable Online Acetylene Detection by a CEAS System with Suppression of Cavity Length Drift

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