[A trace methane gas sensor using mid-infrared quantum cascaded laser at 7.5 microm]

Area of Science:

• Environmental Science
• Analytical Chemistry
• Spectroscopy

Context:

• Accurate, real-time monitoring of atmospheric trace gases is crucial for environmental research and policy.
• Existing methods for continuous gas measurement can be complex, require calibration, or lack sensitivity.
• Development of compact, stable, and sensitive instruments is needed for in situ environmental monitoring.

Purpose:

• To present a novel, compact instrument for in situ, continuous, and sensitive measurement of trace gases in air.
• To demonstrate the instrument's capability for accurate, real-time measurement of ambient methane (CH4) concentrations.
• To showcase the instrument's potential for field deployment and adaptation for other gases.

Summary:

• A compact instrument employing a thermoelectrically cooled (TEC) pulsed Fabry-Perot (FP) quantum cascaded laser (QCL) operating at 7.5 micrometers and a liquid nitrogen (LN) cooled Mercury Cadmium Telluride (HgCdTe) mid-infrared (MIR) detector was developed.
• The instrument features a 20 cm open-path cell with a gold ellipsoid mirror for high optical absorption and achieves a stability of 5.2 x 10(-3) for ambient CH4 measurements (200 micromol x mol(-1)).
• Integrated software and time-discriminating electronics enable continuous, quantitative trace gas measurements without calibration, leveraging CH4's fundamental spectral absorption band.

Impact:

• The developed instrument provides a stable and sensitive platform for real-time, in situ field measurements of environmental gases like methane.
• Its adaptability, by substituting QCLs at different wavelengths, allows for the detection of various other gases of environmental concern.
• This technology can significantly enhance environmental monitoring capabilities, supporting climate change research and pollution control efforts.