2μm波段高灵敏度离轴积分腔装置实际大气CO2测量

利用分布反馈式(DFB)二极管激光器为光源, 搭建了一套2 μm波段的离轴积分腔输出光谱装置. 利用高纯甲烷气体, 测量了腔镜反射率随腔内气体压力 变化的规律. 当腔内压力为3.59 kPa 时, 标定的镜面反射率为0.99865, 在此条件下, 基长55 cm 的离轴积分腔实现了407.4 m的吸收光程. 选取CO₂ 在4993.7431 cm^-1处的吸收谱线对实际大气中的CO₂浓度进行了测量, 探测限为0.53 ppmv (1σ), 利用小波去噪对光谱信号进行了去噪处理, 信噪比提高了80%, 探测限提高到0.29 ppmv(1σ). 利用搭建的装置在实验室内测量了从上午9时到中午12时实际大气中CO₂的浓度, 并与H₂O/CO₂分析仪进行了同时观测与对比分析, 初步验证了测量装置的可靠性.

High-sensitive off-axis integrated cavity output spectroscopy and its measurement of ambient CO2 at 2 μm

An off-axis integrated cavity output spectroscopy (OA-ICOS) is established by using a fiber-coupled distributed feedback diode laser operating near 2 μm. Its performances are evaluated and optimized through experimental investigation via detecting the pure CH₄ absorptions at different pressures. The reflectivity of the cavity mirror is measured to be 0.99865, which results in the effective total optical pathlength of up to 407.4 m based on a 55 cm cavity. It is shown that the OA-ICOS configuration can be used to obtain very long optical pathlength, leading to pretty high sensitive monitoring of atmospheric trace gases. Based on the developed OA-ICOS, the atmospheric CO₂ measurements are made and its performance is improved by using the wavelet denoising approach. The CO₂ absorption line at 4993.7431 cm^-1 is used for measuring the concentration. The measured results are compared with the results obtaind by a commercial H₂O/CO₂ analyzer. Agreement and disagreement are briefly discussed, and the results show that the OA-ICOS is reliable for detecting the atmospheric trace gases. The limitation of the developed OA-ICOS and the further steps towards the improvement in precision and accuracy are also presented.