A near-infrared laser dispersion spectrometer with phase modulation for open-path methane sensing

Area of Science:

• Atmospheric science and spectroscopy
• Environmental monitoring technologies
• Laser-based analytical instrumentation

Background:

• Accurate measurement of atmospheric methane (CH4) is crucial for climate change studies.
• Existing methane detection methods can be complex or sensitive to environmental variations.
• Development of robust and cost-effective methane sensors is an ongoing need.

Purpose of the Study:

• To develop a simple, compact, and cost-effective laser-based dispersion spectrometer for atmospheric methane measurement.
• To achieve methane concentration measurements that are immune to variations in optical power.
• To validate the performance of the developed instrument under laboratory and field conditions.

Main Methods:

• Utilized mature near-infrared photonics components for a compact design.
• Implemented phase modulation for optical measurements, enabling power variation immunity.
• Developed a supporting physical model to interpret dispersion measurements.
• Validated the instrument's precision and long-term stability through controlled and continuous atmospheric monitoring.

Main Results:

• Achieved a precision of 2.6 parts per billion (ppb) over a 100 m path length with a 2 s measurement time under laboratory conditions.
• Demonstrated continuous atmospheric methane measurements over a six-day period using an 86 m open path.
• Confirmed the instrument's robustness and immunity to optical power fluctuations.

Conclusions:

• The developed laser-based open-path dispersion spectrometer offers a simple, cost-effective, and reliable solution for atmospheric methane monitoring.
• The instrument's ability to perform measurements immune to optical power variations enhances its practical applicability in diverse environmental settings.
• The successful validation demonstrates the potential of this technology for continuous, high-precision atmospheric gas sensing.