Highly Sensitive, Calibration-Free WM-DAS Method for Recovering Absorbance-Part II: Experimental Analysis

Area of Science:

• Spectroscopy
• Physical Chemistry
• Combustion Science

Background:

• Direct absorption spectroscopy (DAS) is limited by noise and spectral resolution.
• Wavelength modulation spectroscopy (WMS) enhances sensitivity but requires careful parameter optimization.
• Accurate characterization of spectral line parameters is crucial for quantitative gas analysis.

Purpose of the Study:

• To experimentally validate the proposed wavelength modulation-direct absorption spectroscopy (WM-DAS) method.
• To investigate the robustness, temporal resolution, and narrow scan performance of WM-DAS.
• To demonstrate real-world applications in high-temperature environments.

Main Methods:

• Experimental validation of WM-DAS in a high-temperature tube furnace.
• Investigation of WM-DAS performance across various modulation frequencies (0.1–100 kHz) and scan indexes (3.3–11.1).
• Extraction of characteristic spectra to eliminate electromagnetic and random-frequency noises.

Main Results:

• Effective elimination of noise, achieving high signal-to-noise ratio (SNR) > 500.
• Accurate line profile generation even for weak absorption signals.
• Measurement of CO spectral line parameters (collisional broadening, Dicke narrowing) and their temperature dependence.

Conclusions:

• The proposed WM-DAS method offers robust and accurate spectral measurements in high-temperature environments.
• High-speed (1 ms) measurements of temperature and CO concentration in a McKenna flat flame were successfully demonstrated.
• WM-DAS is a promising technique for quantitative gas analysis and combustion diagnostics.