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Updated: Aug 6, 2026
10:42
Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing
Published on: March 22, 2019
Gas Detection via Absorption-Induced Phase Shift Retrieved by Phase Demodulation in Intensity-Modulated Absorption
Yushuo Song1,2, Shunda Qiao2, Hanxu Ma1,2
1Zhengzhou Advanced Research Institute, Harbin Institute of Technology, Zhengzhou450008, China.
Analytical Chemistry
|July 16, 2026
Summary
This study introduces a new laser absorption spectroscopy method that encodes gas concentration in optical phase, overcoming laser instability and intensity noise for sensitive detection. The technique significantly improves sensitivity and stability for trace gas analysis.
Area of Science:
- Spectroscopy
- Analytical Chemistry
- Laser Technology
Background:
- Laser absorption spectroscopy sensitivity is limited by intensity noise.
- Conventional methods rely on direct optical power measurements, which are unstable.
- Laser instability hinders accurate trace gas detection.
Purpose of the Study:
- To develop a novel gas sensing strategy overcoming intensity noise limitations.
- To encode gas concentration information in optical phase for intrinsic noise immunity.
- To achieve high-sensitivity trace gas detection.
Main Methods:
- Modulating laser intensity and transmitting through the target gas.
- Demodulating the first-harmonic (1f) component of the transmitted signal.
- Extracting phase shift induced by gas absorption using dispersive response.
Main Results:
- Achieved detection limits of 0.9 ppm (high concentration) and 18.6 ppb (low concentration) for acetylene (C2H2).
- Demonstrated 7.1-fold and 3.6-fold sensitivity improvements over conventional intensity demodulation.
- Validated performance across a wide dynamic range using single-pass cell and CEAS.
Conclusions:
- The proposed phase-encoding strategy offers superior stability and sensitivity.
- This method provides a robust solution for high-sensitivity trace gas detection.
- Phase-based demodulation overcomes inherent limitations of intensity-based measurements.
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