Method of adaptive wide dynamic range gas concentration detection based on optimized direct absorption spectroscopy.

Area of Science:

• Spectroscopy
• Analytical Chemistry
• Laser Technology

Background:

• Traditional tunable diode laser absorption spectroscopy (TDLAS) often combines direct absorption spectroscopy (DAS) and wavelength modulation spectroscopy (WMS) for wide dynamic range gas detection.
• Existing methods face limitations in applications requiring wide-range, fast response, and calibration-free measurements, such as high-speed flow fields or industrial monitoring.
• The need for cost-effective and applicable TDLAS-based sensors for diverse scenarios is critical.

Purpose of the Study:

• To develop an Optimized Direct Absorption Spectroscopy (ODAS) method for wide dynamic range gas concentration detection.
• To enhance the applicability and reduce the cost of TDLAS-based sensors.
• To achieve adaptive selection of optimal benchmark spectra for spectral reconstruction in TDLAS.

Main Methods:

• Development of an Optimized Direct Absorption Spectroscopy (ODAS) technique.
• Utilizing signal correlation and spectral reconstruction for enhanced measurement accuracy.
• Experimental verification using methane (CH4) gas concentration detection.

Main Results:

• The ODAS method demonstrated wide dynamic range detection exceeding 4 orders of magnitude (100 ppm to 75 x 10^4 ppm).
• Significantly reduced residual errors from 3.43 to 0.07 when measuring high absorbance (75 x 10^4 ppm) compared to standard DAS.
• Achieved high linear consistency with a correlation coefficient of 0.997 between standard and inverted concentrations across the entire measurement range.

Conclusions:

• The ODAS method provides accurate and reliable gas concentration measurements over a wide dynamic range.
• This technique significantly improves upon traditional DAS and WMS methods in terms of accuracy and residual error reduction.
• The ODAS method expands the application prospects of TDLAS for various industrial and environmental monitoring tasks.