CO₂ Sensing Using Symmetrical Three-Wavelength Precompensated Current-Modulated Tunable Diode Laser Absorption...

Area of Science:

• Spectroscopy
• Laser Technology
• Gas Analysis

Background:

• Tunable diode laser absorption spectroscopy (TDLAS) is a powerful technique for gas concentration measurement.
• Existing TDLAS systems face challenges with wavelength stability and reproducibility, particularly under varying thermal conditions.

Purpose of the Study:

• To introduce and demonstrate a novel symmetrical three-wavelength toggling archetype for TDLAS.
• To improve the accuracy, reproducibility, and temperature stability of gas concentration measurements.

Main Methods:

• Utilized a TDLAS system operating at 1.5714 µm with a 2 kHz update rate, targeting CO2 absorption lines.
• Implemented precompensated diode-current pulses to counteract thermal time constants and a 10 Hz current loop for absolute wavelength referencing.
• Benchmarked the new three-wavelength method against a two-wavelength TDLAS technique.

Main Results:

• Achieved noteworthy wavelength stability of 0.6 pm for three wavelengths separated by ~70 pm.
• Demonstrated a fourfold improvement in reproducibility over 24 days compared to a two-wavelength TDLAS system.
• Showed a 7.9 times weaker correlation between concentration and temperature, indicating enhanced thermal stability.

Conclusions:

• The novel three-wavelength toggling TDLAS system provides superior reproducibility and temperature stability for gas concentration measurements.
• The adaptable design, avoiding wavelength filters, makes it suitable for various gases and absorption lines.
• This TDLAS system is well-suited for sensitive gas analysis applications requiring high accuracy and reliability.