The change of stable isotope ratio of carbon dioxide (δ¹³CO₂) in respiratory gases of patients before and after taking medicine can be used to judge whether Helicobacter pylori exists in patients’ intestines and stomach. The 4.3 μm band of blackbody radiation source and infrared dual path structure are selected for measurement, the incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS) technology was used to change the structure of the light path on one side of ¹³CO₂ to make sure that the absorption intensity of ¹³CO₂ and ¹²CO₂ was in the same order of magnitude. The influence of different types of optical cavity, coating method of lens and reflectivity of mirror on effective optical path were compared in this article and the effective optical path length was the largest when the semi-stable cavity with 90% reflectivity and Ge coating material was used. The standard deviation of the measurement results was 0.191%, which met the requirements of the precision and accuracy of the measurement index in medical detection. The system had the advantages of high precision, small volume, and accurate measurement results, which is of great significance for medical auxiliary detection.

通过患者服药前后呼吸气体中二氧化碳稳定同位素比值(δ ¹³ CO ₂ )的变化，可以判断患者的胃肠道中是否存在幽门螺杆菌。选择4.3 μm波段的黑体辐射源和红外双路结构进行测量，采用非相干宽带腔增强吸收光谱（IBBCEAS）技术改变¹³ CO ₂一侧的光路结构，确保¹³ CO ₂和¹² CO ₂的吸收强度处于同一数量级。比较了不同类型的光腔、透镜镀膜方式和反射镜反射率对有效光路的影响，当采用90%反射率的半稳态腔体和Ge镀膜材料时，有效光路长度最大。用过的。测量结果的标准偏差为0.191%，满足医学检测中测量指标的精密度和准确度要求。该系统具有精度高、体积小、测量结果准确等优点，对医疗辅助检测具有重要意义。