为了研究腔增强吸收光谱技术是否能用于NH3气体浓度的检测, 采用扫描腔长的方法, 以分布反馈式可调谐半导体激光器作光源, 用两块高反射率平凹透镜(反射率约为99.9%, 曲率半径约为1m)组成的光学谐振腔作吸收池, 搭建腔增强吸收光谱装置。在34cm长的吸收池内测量NH3气体分子在1.5μm附近的弱吸收谱线;通过不断增加NH3气体浓度来改变腔内压强, 每充入一次NH3都测量并保存一次吸收光谱。通过数据处理, 分析谱线宽度随气体浓度变化的关系以及吸收度随腔内压强增加的变化情况, 发现都能呈现出良好的线性关系, 并对残差噪声进行统计分析, 得到了3.3×10-8cm-1的最小探测灵敏度。结果表明,高探测灵敏度的腔增强吸收光谱技术, 可以实现NH3气体浓度的测量, 并能得到较好的探测精度。

In order to study whether the cavity-enhanced absorption spectroscopy can be used for the detection of NH3 gas concentration, a cavity-enhanced absorption spectroscopy system was built up. In the system, a tunable distributed feedback diode laser was used as the light source, and a plano-concave optical cavity, consisting of two mirrors with high reflectivity (reflectivity about 99.9% and radius of curvature about 1m), was used as the absorption cavity. Weak absorption spectra of NH3 gas molecules near 1.5μm were measured in the 34cm absorption cell by using cavity length scanning method. The pressure in the cavity was changed by increasing the concentration of NH3 gas. The absorption spectra were measured and stored after charging NH3 each time. By data processing, the relationship between spectral line width and gas concentration was analyzed. And the change of absorbance with the increase of cavity pressure was studied. The results show a good linear relationship. The minimum detection sensitivity of 3.3×10-8cm-1 is obtained by the statistical analysis of the residual noise. The experimental results show that NH3 concentration detection with good detection precision can be realized by using high sensitivity absorption spectroscopy technology.