Development of an open-air type laser absorption atmospheric gas monitor with ability of reducing the fluctuation of incident optical power

We develop a real-time atmospheric gas monitoring system with the laser absorption spectrometry (LAS). The advantage of taking the long optical path length is that the system measures the column density and can suppress inhomogeneous because of local distribution of target gas density. In the system, however, deteriorating the measurement accuracy because of the optical fluctuation becomes problem. So an analog processing unit was constructed and contained into the system to reduce the optical fluctuation. Some experiments were carried out and their results showed us the system not only had performance of optical fluctuation reducing but also higher measurement accuracy than the digital operation. We also found that the system had meaningful reliability and accuracy because of good agreement of monitoring results with the absolute humidity and had possibility of detecting the density fluctuation resulting from the gas divergence and diffusing.