Spectroscopic Absorption System for Multigas Detecting in a Wide Wavelength Region From 3.1 to 10.5 <i>μ</i>m Based on Flexible Low-Loss Waveguide Cells

This study presents a multi-gas detection system based on low-loss hollow waveguide, demonstrating significant improvements in both detection sensitivity and accuracy. The system utilizes 4 hollow waveguides optimized for different mid-infrared bands, coupled with a broadband thermal infrared light source and tunable Fabry-Pérot detectors. The hollow waveguides, which are inner-coated with silver iodide and silver films, exhibit low transmission loss and high flexibility, enabling efficient gas sensing. Experiments were conducted to detect greenhouse gases (CH<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub>, CO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>), toxic gases (CO, NO, SO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>), and atmospheric pollutants (CCl<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>F<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>) at various concentrations. The system achieved detection limits of 58.7 ppm for CH<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub>, 5.18 ppm for CO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>, 85.1 ppm for CO, 70.1 ppm for NO, 5.79 ppm for SO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>, and 30.9 ppm for CCl<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>F<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>. The system demonstrates high sensitivity and selectivity, with potential for further improvement through noise reduction and data fusion techniques. This cost-effective and compact system offers a robust solution for real-time multi-gas detection in environmental monitoring, industrial safety, and medical diagnostics.