Highly stable gas measurement technique: Ultra-accurate wavelength locking

A highly stable gas measurement technique based on ultra-accurate wavelength locking is proposed. This technique utilizes the third harmonic differential signal to suppress non-absorption interference, thereby improving wavelength locking accuracy and enabling high-stability gas measurements. The technique is tested across three optical path configurations, with systematic evaluation of the locking accuracy, measurement stability, detection limits, and universality. The results demonstrate that this technique improves locking accuracy by at least 13 %, and remains effective even when the reference optical path exhibits absorption. Based on this technique, a 75 % improvement in signal stability was achieved in low-pressure CO₂ measurement, and during a continuous 9-hour measurement of varying CO concentrations, the signal fluctuation was only 0.12 %, with a minimum detection limit of 25 ppb. The improvement in locking accuracy of this technique under different temperature and pressure conditions has also been verified. This technique, with lower system cost and higher locking accuracy, provides a feasible solution for enhancing the stability and accuracy of laser absorption spectroscopy gas measurement systems.