In order to detect trace methane (CH4) with non contact, the proposed manuscript describes high sensitivity trace methane detector using quantum cascaded laser (QCL) with centre wavelength at 7.5 μm, which is based on combination of Tunable Diode Laser Absorption Spectroscopy (TDLAS) and Wavelength Modulation Spectroscopy (WMS). Under room temperature, the spectrum of QCL can scan CH4 absorption line via adjusting the injection current of QCL. Meanwhile, a compact herriott cell (40 cm long and 800 ml volume) is utilized to achieve a total optical path with 16 meters length. The aforementioned detector is applied to detect CH4 with different concentrations, results show that the relative detection error is less than 7%, the lowest detection is 1×10-6. Meanwhile, the researchers can detect other gases through replace lasers with different wavelength.
Spectroscopy, TDLAS-WMS, Trace Methane, Quantum Cascaded Laser (QCL), Herriott Cell
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