Compact and full-range carbon dioxide sensor using photoacoustic and resonance dependent modes

Area of Science:

• Optical sensing technologies
• Spectroscopic analysis
• Environmental monitoring instrumentation

Background:

• Accurate carbon dioxide (CO2) detection is crucial for various applications, including environmental monitoring and industrial process control.
• Existing CO2 sensors often face limitations in sensitivity, dynamic range, or linearity, necessitating improved detection methodologies.

Purpose of the Study:

• To develop a compact and robust optical excitation photoacoustic sensor for high-sensitivity and full linear range detection of CO2.
• To integrate dual detection modes, wavelength modulated photoacoustic spectroscopy (WMPAS) and resonant frequency tracking (RFT), for comprehensive CO2 measurement.

Main Methods:

• Development of a self-integrated laser module with a quantum cascade laser (QCL), distributed feedback (DFB) laser, and He-Ne laser for time-division multiplexing.
• Utilized WMPAS for CO2 detection below 20% with a noise equivalent concentration (NEC) of 240 ppt.
• Employed RFT mode with a He-Ne laser for CO2 detection in the 20%-100% range.

Main Results:

• Achieved a noise equivalent concentration (NEC) as low as 240 ppt and a normalized noise equivalent absorption coefficient (NNEA) of 4.755 × 10⁻¹⁰ W cm⁻¹/√Hz with WMPAS.
• Demonstrated a dynamic range of 11 orders of magnitude for CO2 detection.
• The dual-mode sensor achieved full-range CO2 detection (0-100%) with R² ≥ 0.9993 and a response time of 5 seconds.

Conclusions:

• The developed compact photoacoustic sensor effectively combines WMPAS and RFT for sensitive, linear, and full-range CO2 detection.
• This integrated sensor provides a versatile solution for accurate CO2 monitoring across a wide spectrum of concentrations.
• The sensor's performance highlights its potential for advanced environmental and industrial applications requiring precise gas analysis.