基于中红外差频光源的水汽高分辨率变温吸收光谱研究

The accurate and comprehensive experimental data of water vapor, especially its collision broadening and temperature-dependent coefficients, are important to atmospheric science applications. The study of high-resolution mid-infrared absorption spectroscopy of water vapor in the atmospheric temperature range is still an open question, mainly caused by the lack of appropriate light source and effective experimental measurement approach. The proposal proposed here is to use a new manufactured BaGa4Se7 as frequency converter crystal to produce 3~11 μm radiation via difference frequency generation (DFG), and combined with the temperature-controlled absorption cell with three-optical path and the multispectrum nonlinear least squares technique, to study the water vapor absorption spectroscopy in the actual atmospheric environment (from room temperature to about 220K). Several strategies which are very helpful to improve the system performance will be implemented into the setup: measure the water vapor in the flowing state and previously set the required moisture concentration in the absorption cell to resolve the problem due to molecule viscosity; a high precision F-P etalon is used together with an electro-optical modulator to enhance the frequency accuracy of the DFG in order to obtain the water vapor absorption spectrum with high resolution and frequency accuracy. This protocol will be able to offer a new method for the measurement of water vapor absorption spectrum at low temperature, as well as provide more comprehensive and accurate experimental data for the study of atmospheric detection and laser atmospheric transmission research. At the meantime, the line model of water molecule as well as the theoretical calculation model will be benefit from the research.

红外波段水分子的谱线参数，特别是碰撞展宽及其温度依赖系数等光谱参数，在大气科学领域有着广泛的应用。由于缺乏合适的光源以及有效的实验测量方法，中红外大气温度范围内水汽高分辨率变温吸收光谱研究仍然是一个有待深入研究的课题。本申请拟采用新型BaGa4Se7晶体作为频率转换器件产生3~11μm中红外差频光，与三光路可控温吸收池联用，结合多光谱拟合程序，开展水汽变温吸收光谱特性研究。通过预先设置吸收池内所需的水汽浓度以及测量流动状态下的水汽，解决由水分子粘滞性导致的光谱测量难题；把高精细度标准具和电光调制器联用以提高差频光源的频率精度，进而获得高分辨、高频标的水汽吸收光谱。本研究能提供一种测量变温条件下水汽吸收光谱的新方法，可为大气探测、激光大气传输研究提供系统、准确的基础实验数据，还可以为水分子光谱参数理论计算模型CRB的改进提供有效判据，并且能够完善实际大气条件下水分子吸收线形模型。

水分子红外波段的吸收光谱在大气探测、激光大气传输等领域有着广泛的应用。本项目主要开展了红外波段水分子吸收光谱和水汽浓度测量方面的研究。取得的主要进展包括：基于BaGa4Se7晶体发展了一套在3.15~7.92μm之间连续可调的中红外差频光源；编写了一款可同时处理多张实验光谱的多光谱拟合程序；研制了一款FSR 为749.52MHz、稳定性约为5.39MHz•h-1的标准具，自制了双光程气体多通吸收池，在此基础上发展了一种单吸收池双光程同步测量水分子吸收光谱的测量装置，利用该装置测量了1μm处水分子的吸收光谱，采用多光谱拟合程序获得了该波段水分子的光谱参数；此外，我们还基于3.38μm分布反馈式连续可调谐激光器和新型小体积、长光程多通吸收池研制了一款可同时探测水汽和甲烷浓度的紧凑型气体传感器。