中红外CH_4检测中非对称椭球气室优化及实验研究

Optimization and experimental study of a novel asymmetric ellipsoid gas-cell in mid-infrared CH_4 detection

为了在中红外（MIR）CH4浓度检测中降低检测下 限和提高探测灵敏度,提出了一种非 对称椭球聚光镜气室。在充分考虑线光源和双窗口探测器外形及尺寸的条件下,建立了 完备的非对称椭球聚光镜气室物理模型,导出了直射功率、反射功率、聚光效率和灵敏 度系数的表达式。通过计算分析,得到了同时获得较高聚光效率和高灵敏度系数的条件,以 及非对称椭球聚光镜的优化参数。利用优化制作的非对称椭球聚 光镜气室,建立了CH4检测系统。检测结果显示,系统的检测下限约为 5×10^－6；低浓度范围（0～100×10^－6）的探测灵敏度约为6~7×10^－6；在高浓度范围内（1～40×10^－3）,探测灵敏度随气体浓度增 加而增加,约为20~160×10^－6。检测结果表明,优化后的 CH4检测系统实现了较低的检测下限和较高的灵敏度。

In order to decrease the minimum detection limit （MDL） and increase the dete ction sensitivity,a novel asymmetric ellipsoid light-collector multi-pass gas-cell is proposed fo r the application in mid-infrared CH4concentration detection.Under the full consideration of foot -prints and sizes of wire light-source and dual-channel detector,thorough modeling on the light co llector gas-cell is established,and formulations and expressions including direct incident power,r eflected incident power,light collection efficiency and sensitivity-related coefficient are deri ved.Through calculation and analysis,parameter conditions are obtained for achieving both h igh light collection efficiency and high sensitivity-related coefficient,the structural parameters of the gas-cell are derived,and the gas-cell is then fabricated.Based on the fabricated gas-ce ll with optimized parameters, the CH4detection system is established,and detection performance is demonstra ted.Experimental results show that the minimum detection limit is about 5×1^-6,the detection sensitivity is determined to be about 6-7×10^-6 under the low concentration range of 0-100×10^-6, within high concentration range of 1-40×10^-3,the detection sensitivity decreases as the concentration increases,which varies from 20×10^-6 to 160×10^-6.Due to car eful design and optimization on asymmetric ellipsoid gas-cell,this detection system exhibits good performance including higher detection sensitivity and lower MDL.