Measurement of δ18O in water vapor using a tunable diode laser based spectrometer

A system based on the tunable diode laser absorption spectroscopy (TDLAS) was described, ensuring the real-time, continuity, high-precision, and rapid time response measurement of the isotope ratio of 18 O/ 16 O in water vapor from 3729.8 cm − 1 to 3730.8 cm − 1 . A detailed description of the system's implementation was provided and the precision and accuracy of the measurement system were analyzed after verification in the laboratory environment. The absorbance achieved a high signal-to-noise ratio (SNR) with a 20.4 cm optical path and was compared to HITRAN simulations. Allan variance was used to evaluate the reliability of the system and the results showed that the precision of the 18 O/ 16 O ratio was 5.274‰ at 1 s and improved to 0.088‰ at 191 s. The system provides the potential for applications in environmental, geological, ecological, and energy fields, and additional information for comparison and standard development in determining oxygen isotope composition in water vapor via laser spectrometry.