基于CW-QCL的长光程温度气体高灵敏检测方法研究

发布时间：2017-12-28 01:03

本文关键词：基于CW-QCL的长光程温度气体高灵敏检测方法研究　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：复杂生态环境温室气体不同空间、时间尺度的浓度监测是了解温室气体源与汇的基础。目前适应生态环境温室气体长期连续监测的技术手段仍有待研究。可调谐半导体激光吸收光谱(Tunable Diode Laser Absorption Spectroscopy,TDLAS)是一种非侵入式光谱测量技术,具有高选择、高灵敏度、高分辨等特点,与目前新兴的中红外量子级联激光器(Quantum Cascade Laser,QCL)相结合,可实现分子"基频"吸收光谱测量,进一步提高检测灵敏度,达到温室气体区域环境监测需求。本文深入研究了长光程开放光路的中红外波长调制TDLAS技术,设计并集成了一套长光程CH4和N20连续监测系统,研究了多组分气体交叉干扰下的光谱反演算法,实现多种温室气体高精度快速连续监测。本文选择了大气中两大主要温室气体CH4和N20作为目标气体,利用HITRAN数据库对实际大气环境进行了吸收谱线的模拟与分析,选取了1275cm-1附近CH4和N2O的相邻吸收谱线,实现了单激光器双组分测量。研究了 1275cm-1波段的CW-QCL激光器的调制特性,并结合实际测量环境对调制参数进行了优化。在系统光机设计过程中,使用二向色镜解决了红外长光程(公里量级)多光束同轴耦合的问题,设计了反射式离轴激光准直结构及基于离轴抛物面镜的开放光路收发一体光机结构,能够实现公里量级的长光程开放光路监测。本文深入研究了基于标定与免标定的多组分光谱-浓度反演算法。基于标定方法,首先提出了基于标定的多元线性拟合的WMS(Wavelength Modulation Spectroscopy)多组分反演方法,利用该方法实现了 CH4和N2O浓度准确测量,测量误差均小于5%,验证了该消除交叉干扰方法的可行性。在WMS免标定拟合算法中,通过模拟的方法并结合实际测量的激光器频率和强度响应,细致的研究了激光器的非线性频率响应与强度非线性响应对谐波信号的影响。将测量的无吸收光强信号与准确的激光器频率响应模型相结合,优化了基于吸收线型的免标定浓度反演模型,采用无吸收的光强信号即避免了原有算法模型中非常规强度响应情况下(尤其非线性响应显著)准确的强度解析模型的建立问题,包含了所有的光强信息(非线性响应特性、寄生的无法消除的干涉噪声、背景吸收特征等);采用包含一阶和二阶频率响应项及其时间依赖系数的激光器频率响应模型,实现了 v(t)的准确测量,解决了原有常规激光器频率响应模型的应用局限问题,使该算法模型适于非线性显著或非常规强度响应情况,更具普适性。以CH4为例,对该免标定方法进行了很好的验证,在浓度为60～1200ppm*m(A～0.029～0.57cm-1)范围内,WMS免标定拟合残差均小于2%,反演浓度线性度达到0.99996。在测量系统设计与浓度反演算法的研究基础上,测试与分析了该测量系统的精度、稳定性、线性度及检测限等性能指标,测试结果表明该系统完全满足环境大气CH4和N20同时在线测量的需求。利用该测量系统,在合肥科学岛进行了外场实验,实现了环境大气CH4和N2O的连续高灵敏监测(光程690m),为不同生态环境尺度不同时间分辨下的温室气体高灵敏测量奠定了基础。
[Abstract]:The concentration monitoring of different space and time scale in the complex ecological environment is the basis of understanding the greenhouse gas source and sink. At present, the technical means to adapt to the long-term continuous monitoring of the greenhouse gases in the ecological environment are still to be studied. Tunable diode laser absorption spectroscopy (Tunable Diode Laser Absorption Spectroscopy, TDLAS) is a non intrusive spectral measurement technology, has the characteristics of high selectivity, high sensitivity, high resolution, and mid infrared quantum cascade lasers currently emerging (Quantum Cascade Laser, QCL) combination, can realize the "fundamental" molecular absorption spectrum the measurement, further improve the detection sensitivity, to achieve regional environmental monitoring of greenhouse gas demand. In the infrared wavelength modulation TDLAS technology this paper deeply studies the long open path design, and integrates a set of long path CH4 and N20 continuous monitoring system, studied the spectral inversion algorithm of multi-component gas interference, to achieve a variety of greenhouse gases, high precision and fast continuous monitoring. This paper chooses two major greenhouse gases in the atmosphere of CH4 and N20 as the target gas, the atmospheric environment has been simulated and analyzed the absorption spectrum by using HITRAN database, 1275cm-1 CH4 and N2O near the adjacent absorption lines are selected to achieve a single laser double component measurement. The modulation characteristics of the 1275cm-1 band CW-QCL laser are studied, and the modulation parameters are optimized with the actual measurement environment. In the mechanical design process, the use of two to solve the long path infrared dichroic mirror (kilometers) multi beam coaxial coupling problem, design a reflective off-axis laser collimating structure and off-axis parabolic mirror open optical transceiver structure based on optical monitoring of the long path to achieve the open kilometers. In this paper, a multi component spectral density inversion algorithm based on calibration and demarcation is studied in this paper. Based on the calibration method, first proposed the multiple linear fitting calibration based on WMS (Wavelength Modulation Spectroscopy) multi component inversion method, realizes the accurate measurement of CH4 and N2O concentration by using this method, the measurement error is less than 5%, verified the feasibility of the method to eliminate interference. In the WMS calibration free algorithm, the influence of nonlinear frequency response and intensity nonlinear response of laser on harmonic signal is studied in detail by simulating method and combining with the measured frequency and intensity response of laser. The absorption intensity signal and the laser frequency response model combined with accurate measurement, optimize the calibration free concentration inversion model based on linear absorption, the absorption intensity signal of avoiding the conventional strength response under the situation of the original algorithm in the model (especially the nonlinear response significantly) establish strength accurate analytical models, including all the light intensity (nonlinear response characteristics, can eliminate the parasitic interference noise, background absorption characteristics); the laser frequency contains one order and two order frequency response and time dependent coefficient of response model, implementation of V (T) of the accurate measurement, to solve the problem of the original application limitations of conventional lasers the frequency response model, the algorithm model is suitable for nonlinear or non conventional strength significantly in response to the situation, has more universality. Taking CH4 as an example, the calibration method is verified well. Within the range of 60 ~ 1200ppm*m (A ~ 0.029 ~ 0.57cm-1), the WMS calibration free residuals are less than 2%, and the inversion concentration linearity reaches 0.99996. Based on the research of measurement system design and concentration inversion algorithm, the accuracy, stability, linearity and detection limit of the measurement system are tested and analyzed. The test results show that the system fully meets the online measurement needs of CH4 and N20 in the ambient air. Based on the measurement system, outfield experiments were carried out in Hefei Science Island to achieve continuous high-sensitivity monitoring of CH4 and N2O in ambient air (690m), which laid the foundation for high-sensitivity measurement of greenhouse gases under different environmental scales and time scales.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O433;TN248

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