An Ultrahighly Sensitive CH₄-TDLAS Sensor Based on an 80-m Optical Path Length Multipass Cell with a Dense Circular...

Area of Science:

• Gas sensing technologies
• Laser spectroscopy
• Environmental monitoring

Background:

• Methane (CH4) is a potent greenhouse gas requiring sensitive detection methods.
• Traditional sensors often lack the required sensitivity and stability for real-time monitoring.
• Tunable Diode Laser Absorption Spectroscopy (TDLAS) offers high selectivity and sensitivity for gas analysis.

Purpose of the Study:

• To develop an ultra-highly sensitive methane sensor using TDLAS.
• To optimize a multipass cell (MPC) for enhanced optical path length (OPL) in a compact volume.
• To achieve a low minimum detection limit (MDL) for real-time methane monitoring.

Main Methods:

• Utilized tunable diode laser absorption spectroscopy (TDLAS) for methane detection.
• Employed an 80-m optical path length (OPL) multipass cell (MPC) with 15 independent circles.
• Implemented wavelength modulation spectroscopy (WMS) to reduce noise and improve detection.
• Analyzed sensor performance using Allan deviation for long-term stability assessment.

Main Results:

• Achieved an actual OPL of 81.58 m in a compact 361 cm3 volume, yielding an RLV of 22.6 cm-2.
• Demonstrated excellent linear response to methane concentrations.
• Determined an initial minimum detection limit (MDL) of 13.46 ppb.
• Improved MDL to 1.36 ppb at 400 s averaging time via Allan deviation analysis.
• Successfully detected and tracked simulated laboratory methane leakage in real time.

Conclusions:

• The developed CH4-TDLAS sensor offers ultrahigh sensitivity and excellent long-term stability.
• The sensor's performance is suitable for effective real-time detection and tracking of methane concentration changes.
• The optimized MPC design significantly enhances the sensor's detection capabilities.