Improving Measurement Accuracy of Multi-Component Gas Sensing System Using Passive Locking Achromatic Multipass Absorption Cell

High-accuracy multi-component gas sensing systems are required to monitor the geochemical gas in the atmosphere for early warning of earthquakes. On the basis of an achromatic model, an achromatic structure is developed using ridged-shaped windows to eliminate the optical system dispersion. A passive locking structure is designed based on a multi-layer rotationally symmetrical model to lock the cavity state. A passive locking achromatic multipass absorption cell (PLAMAC) is developed based on the achromatic and passive locking structures to improve the optical transmission performance and the environment adaptability. A temperature control subsystem is developed to lock the PLAMAC state and control the gas temperature. A gas sensing system is developed using the PLAMAC to realize the high-accuracy measurement of multi-component gas. The PLAMAC enables chromatic aberration-free transmission in the wavelength range of 1.55 μm to 2.35 μm and achieves perfect locking at environment temperatures of -10 °C to 40 °C. The systematic errors are 0.93‰@1653.7 and 0.91‰@2329.05 nm for 500 parts per million by volume (ppmv) CH 4 and 0.92‰@1572.3 and 0.91‰@2004.5 nm for 1000 ppmv CO 2 within the confidence interval of 98%. The PLAMAC system has higher accuracy over a wide spectral range and greater environment adaptability than the sensing system based on MAC-41. Experiments verify that the PLAMAC system has significant advantages in multi-gas exploration with wide temperature variations.