Quasi-Simultaneous Sensitive Detection of Two Gas Species by Cavity-Ringdown Spectroscopy with Two Lasers

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Environmental Science

Background:

• Cavity Ring-Down Spectroscopy (CRDS) is a sensitive technique for gas analysis.
• Accurate isotopic ratio measurements are crucial for environmental studies and source attribution.
• Existing methods may face limitations in simultaneous multi-species detection.

Purpose of the Study:

• To develop an advanced CRDS system for high-precision, quasi-simultaneous isotopic analysis of methane (CH4).
• To demonstrate the system's capability in detecting 12CH4 and 13CH4 in ambient air.
• To achieve high sensitivity and low uncertainty in isotopic ratio determination.

Main Methods:

• Utilized a step-scanning and dithering method for precise laser wavelength-to-cavity resonance matching.
• Employed a dual-laser system operating at 1654 nm and 1658 nm for simultaneous spectral detection.
• Measured the ringdown time of an optical cavity with a ringdown time of approximately 340 µs.

Main Results:

• Achieved a high detection sensitivity of 2.8 × 10^-11 cm^-1 Hz^-1/2 (noise-equivalent absorption coefficient).
• Demonstrated high precision determination of δ13CH4 in air with an uncertainty of about 1.3‰.
• Successfully performed spectral detections of 12CH4 and 13CH4 in air samples.

Conclusions:

• The developed CRDS system offers a robust platform for precise, simultaneous isotopic analysis of methane.
• The system's high sensitivity and accuracy make it suitable for environmental monitoring.
• This technology holds promise for applications in climate change research and atmospheric studies.