He-Ne and cw CO2 laser long-path systems for gas detection

Area of Science:

• Environmental Science
• Optical Engineering
• Spectroscopy

Background:

• Methane leaks from underground pipelines and landfills pose environmental risks.
• Remote sensing techniques are crucial for monitoring diffuse gas emissions.
• Differential absorption spectroscopy offers a method for gas detection.

Purpose of the Study:

• To design and test a laboratory prototype dual He-Ne laser system for methane leak detection.
• To evaluate a dual continuous-wave (cw) carbon dioxide laser system for gas sensing.
• To assess the feasibility of using topographic backscatter for differential absorption measurements.

Main Methods:

• Utilized a dual He-Ne laser system and a dual cw carbon dioxide laser system.
• Employed differential absorption of radiation backscattered from topographic targets.
• Analyzed time-varying differential absorption signals to indicate gas presence.
• Investigated the impact of speckle and atmospheric turbulence on measurement sensitivity.

Main Results:

• Both laser systems demonstrated the utility of differential absorption signals for detecting nearby gas sources.
• Methanol measurements were successfully obtained using the carbon dioxide laser system.
• Limitations in measurement sensitivity were identified, particularly due to speckle and atmospheric turbulence.

Conclusions:

• The developed dual laser systems show potential for effective methane leak detection.
• Topographic targets can be used as a basis for differential absorption measurements.
• Further research is needed to overcome sensitivity limitations caused by speckle and atmospheric effects.