CW EC-QCL-based sensor for simultaneous detection of H₂O, HDO, N₂O and CH₄ using multi-pass absorption spectroscopy

Area of Science:

• Environmental Science
• Analytical Chemistry
• Spectroscopy

Background:

• Accurate monitoring of atmospheric gases like H₂O, HDO, N₂O, and CH₄ is crucial for climate and environmental studies.
• Existing sensing technologies may face limitations in simultaneous detection, sensitivity, or portability.

Purpose of the Study:

• To demonstrate a novel sensor system for the simultaneous detection of atmospheric H₂O, HDO, N₂O, and CH₄.
• To achieve high sensitivity and accuracy in gas concentration measurements using a compact laser-based system.

Main Methods:

• Employed a continuous wave, external-cavity quantum-cascade laser (CW EC-QCL) operating at ~7.8 µm.
• Utilized a compact, dense pattern multi-pass gas cell with a 57.6 m effective path-length.
• Applied first-harmonic-normalized wavelength modulation spectroscopy with second-harmonic detection (WMS-2f/1f) for data processing.

Main Results:

• Achieved simultaneous detection of H₂O, HDO, N₂O, and CH₄.
• Demonstrated minimum detection limits: 1.77 ppmv for H₂O, 3.92 ppbv for HDO, 1.43 ppbv for N₂O, and 2.2 ppbv for CH₄.
• Reported experimental measurements of ambient air composition.

Conclusions:

• The developed CW EC-QCL sensor system offers a sensitive and simultaneous method for atmospheric gas analysis.
• The system's performance, including low detection limits, makes it suitable for environmental monitoring applications.