波长调制离轴积分腔输出光谱技术探测大气碳同位素丰度研究

Carbon isotope analysis is well established diagnostic tool, predominantly for greenhouse gases source and carbon ecological cycle. Currently the main method to measure isotopic abundance is mass spectrometry, but it is too complex to be online monitoring. Wavelength modulation off-axis integrated cavity output spectroscopy (WM-OA-ICOS) is a novel spectral method for highly sensitive gas detection, which has advantages of selectivity, sensitivity and online monitoring. In this project, the accurate WM-OA-ICOS mathematical model will be established based on the multi-beam interference and wavelength modulation principle. Particularly, the cavity loss and the optimal modulation parameters affect the output signals noise ratio. At the same time, the optical transmission path in off-axis integrated cavity with the collimated and couple devices will be analyzed. Furthermore, the constant temperature and low voltage apparatus will be used to avoid the absorption lines interference, and to ensure the stability and the sharpness of the wavelength spectrum. At last, the DFB laser with the center wavelength 2.743um will be used to detected atmospheric carbon isotope abundance in principles of the heavy isotope molecules absorption are stronger than light ones. Moreover, the inversion algorithm will be researched, and then Allan variance will be used to analysis the whole system stability. Finally, the dynamic and efficient monitoring will be realized for atmospheric carbon isotopic, which will support identification of pollution sources and the research about ecological status and trends as advanced tools.

碳同位素分析在判断温室气体排放源汇，研究碳生态循环等领域有重要应用。目前质谱技术是测量同位素丰度的主要方法，但其使用过程复杂难以实现原位在线监测。波长调制离轴积分腔输出光谱（WM-OA-ICOS）技术是实现高灵敏气体同位素探测的新型激光光谱方法,具有高选择性、高灵敏性及实时在线监测等优点。项目拟采用多光束干涉和波长调制原理，建立WM-OA-ICOS输出信号的数学模型，分析腔内损耗、调制参数与输出谐波信号信噪比的关系。研究离轴积分腔及准直、耦合光路的传输路径，采用恒温低压装置，避免谱线对交叉带来的干扰，保证吸收波长稳定性和谱线锐度。选择重同位素分子吸收线强较大的二氧化碳谱线对，用中心波长2.743um的DFB激光器探测大气碳同位素丰度，研究反演算法，由Allan方差分析系统稳定性，初步实现大气碳同位素动态高效监测，为我国开展污染源识别，研究生态环境现状和趋势提供先进手段和技术支撑。

碳同位素分析在判断温室气体排放源汇，研究碳生态循环等领域有重要应用。目前质谱技术是测量同位素丰度的主要方法，但其使用过程复杂难以实现原位在线监测。波长调制离轴积分腔输出光谱（WM-OA-ICOS）技术是实现高灵敏气体同位素探测的新型激光光谱方法,具有高选择性、高灵敏性及实时在线监测等优点。项目主要研究了多光束干涉和波长调制原理，建立了WM-OA-ICOS输出信号的数学模型，分析了腔内损耗、调制参数与输出谐波信号信噪比的关系。仿真模拟了离轴积分腔及准直、耦合光路的传输路径，设计了小体积高稳定性离轴积分光路，同时将腔体改进为恒温低压装置，控制精度分别为0.1℃和1mbar，避免谱线对交叉带来的干扰，保证了吸收波长稳定性和谱线锐度。选择重同位素分子吸收线强较大的二氧化碳谱线对，用中心波长4.328um的量子级联激光器（QCL）激光器探测大气碳同位素丰度，研究测试了QCL激光器性能，针对外界温度变化引起的波长漂移现象，设计了中心波长自锁频电路和控制算法，控制精度为±0.009nm。通过HITRAN数据库，选取了用于测量大气中16O12C16O 、16O13C16O 、16O12C18O 分子的碳和氧同位素丰度的谱线。研究反演算法，由Allan方差分析系统稳定性，浓度探测极限为79ppb，同位素丰度探测精度为0.3‰，初步实现大气碳同位素动态高效监测。通过本项目的实施，有助于实现痕量气体高灵敏探测和稳定同位素分析，为环境保护和污染源确定提供依据和保障，同时深刻理解WM-OA-ICOS这种新型光谱技术的探测机制，建立高灵敏气体探测和稳定同位素分析实时在线精确测量方法，为我国开展污染源识别，研究生态环境现状和趋势提供先进手段和技术支撑。该技术在安全生产、过程控制、医疗诊断、环境生态学等领域具有很广阔的应用前景。