Design and Performance Analysis of Novel Mid-Infrared Enhanced Hollow Waveguide for Gas Isotope Ratio Measurements

Gas isotope ratio measurements based on laser spectroscopy are often used for ecosystem and medical analysis. This paper reports for the first time the design of a novel mid-infrared enhanced hollow waveguide (EHWG) gas sensor based on multiple-reflection cavity-enhanced absorption spectroscopy (CEAS). This method avoids the shortcomings of existing hollow waveguide (HWG) single path measurement, while the effective optical path length and measurement limit have also been greatly increased. Based on a 4.32 μm quantum cascade laser, three stable heavy isotope ratios in carbon dioxide were simultaneously measured, and the measurement precision (δ¹³C ∼ 0.36‰, δ¹⁸O ∼ 0.46‰, δ¹⁷O ∼ 0.88‰) was found to be better compared to previous studies. By comparing the ¹³C-urea breath "gold standard" test in hospital physical examinations, the enormous potential of this method in manufacturing miniaturized, broad-spectrum, multifunctional, and lightweight is demonstrated, and it is expected to become the first choice for trace volume gas measurements in the new generation.