Abstract
A trace gas sensor based on pulsed cavity ring-down spectroscopy (CRDS) was developed for measurement of the ν4 fundamental vibrational band of ammonia (NH3) centered at 1468.898 cm−1. A pulsed distributed feedback quantum cascade laser (DFB-QCL) operating at 6.8 µm (1470.58 cm−1) quite well covered the absorption band of the ammonia and strong fundamental vibrational absorption bands of different molecular gases in this unexplored region. The cavity was partially evacuated down to 0.4 Atm by a turbo-molecular pump to reduce the partial interference between the NH3 spectra and water near the absorption peak of ammonia. A sensitivity of nine parts per billion was reached for a measurement time of 120 s as well as an optical path length of 226 m. The device demonstrated high spectral performance and versatility due to its wide tuning range, narrow linewidth, and comparatively high-energy mid-IR radiation in the relatively unexplored 6.8 µm region, which is very important for high-resolution spectroscopy of a variety of gases.
Highlights
Mid-IR (MIR) absorption spectroscopy is an extremely effective tool for detection of molecular trace gases [1,2,3]
We have developed a cavity ring-down spectroscopic sensor for trace gas detection using a pulsed
distributed feedback (DFB) QC laser emitting in the region around 6.8 μm
Summary
Mid-IR (MIR) absorption spectroscopy is an extremely effective tool for detection of molecular trace gases [1,2,3]. It is well appreciated that the MIR spectral wavelength range stretching from 3 μm to 10 μm contains a wealth of strong fundamental vibrational absorption bands of different molecular gases, and is suitable for trace gas sensing applications, such as environmental monitoring, biomedical diagnostics, and control of toxic industrial chemicals [4]. The detection of gases, such as CH4 , CO2 , NO2 , SO2 , and NH3 , at the level of parts per billion (ppb) plays an essential role in environmental and agricultural monitoring. Ammonia is the third most abundant nitrogen-containing compound in the atmosphere, playing an essential role in the nitrogen cycle [5] It is mostly used in agricultural activities to manufacture. The highly sensitive detection of part per billion of the ν2 fundamental vibrational band of NH3 around
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