低压水汽及氢氧同位素波长调制检测OA

Weak absorption and spectral overlap limit trace isotope detection under low-pressure dynamic conditions.To address this issue,a wavelength modulation spectroscopy(WMS)method is proposed for hydrogen and oxygen isotope measurements in water vapor.A distributed feedback(DFB)laser centered at 1.863 μm was employed,and a miniaturized detection system with a 12 m optical path and an 80 cm³ ab-sorption cell was developed.By means of a single scan,simultaneous detection of H216O,H217O,H218O,and HDO was achieved.Calibration experiments were performed using different standard water samples,and relationships were established between the fitted integrated area ratios and isotope reference values.Hydrogen and oxygen isotope ratios,together with the corresponding δ values,were then obtained.The fitted integrated areas exhibited linear relationships with water vapor pressure,with correlation coefficients exceeding 0.99.Under a steady pressure of 340 Pa,the optimal integration times were determined to be 18 s,23 s,and 20 s for δD,δ18O,and δ17O,respectively.The minimum Allan deviations were 2.015‰,3.636‰,and 1.317‰.Simulated lunar-soil experiments further verified dynamic isotope monitoring,and isotope variations during adsorption fractionation were successfully captured.The 10%-90%pressure response time was 71 s.A comparison experiment was also conducted using a direct absorption system at 2.731 μm as a reference,with an optical path length of 25 m.Consistent δD variation trends were ob-served in both systems.The proposed method enables steady-state and dynamic measurements of hydro-gen and oxygen isotopes in water vapor under low-pressure conditions,thereby providing technical support for miniaturized in situ isotope detection in dynamic environments.