The High-sensitivity Detection Technology For Trace Gases Based On Cavity Ring-down Spetroscopy

Recently,with develops in industries of environment monitoring,process monitoring,medical examination,etc.,ultra-sensitivity trace gas detection technologies with features of real-time,ultra-high sensitivity,versatility and environmental adaptability are required much more.However,the traditional detection methods based on techniques such as chemical analysis,mass spectrometry,and semiconductor gas sensors are difficult to meet such requirements.Thus,laser spectroscopy technologies,represented by cavity enhanced absorption spectroscopy?CEAS?,cavity ring-down absorption spectroscopy?CRDS?and tunable diode laser absorption spectroscopy?TDLAS?has become a hot spot in the field of trace gas detection,due to many unparalleled advantages,such as ulti-sensitivity,low cross responce and high stability,over conventional technologies.A CRDS trace gas detection system using 7.6?m mid-infrared quantum cascade laser as a light source was developed in this thesis.methane?CH4?and nitrous oxide?N2O?in atmosphere were detected and analyzed with high-precision.The interference of water vapor on the system was discussed.The detection of sulfur hexafluoride?SF6?and its derivatives was explored.The main research contents are:?1?The first CRDS detection system using 7.6?m mid-infrared quantum cascade laser as the light source in China was developed.The error source of the system was discussed in detail.the influence of temperature fluctuation on the measurement results was analyzed quantitatively.The absorption coefficient detection sensitivity of the system is as low as 2.32×10^-10 cm^-11 correcting the influence of temperature,which is nearly an order of magnitude better than the reported similar systemby.?2?The trace components in the atmosphere is studied in this system.Four optimal detecting band for CH₄ and N₂O between 1290cm^-1 and 1380cm^-1 were reported.The influence of trace water vapor in the air on the measurement results was analyzed quantitively.The slow release of water vapor in the gas pool was discussed.The detection relative accuracy of 2ppbv for CH₄ and N₂O was reported.?3?A deep drying method for laser spectrum trace gas detection system were invented.Through the combination of two sets of drying systems inside and outside the cavity,the water vapor concentration in the testing gas is able to be maintained for a long time without affecting the detection.