基于光声光谱技术的CO气体探测

A photoacoustic spectroscopy measurement system for CO gas based on a 2.3 μm mid-infrared tunable diode laser was built, and the CO absorption line at 4300.699 cm⁻¹ was selected as the sensing target. In order to eliminate the influence of the long relaxation time of CO molecules on the measurement, the method of mixing water vapor in the experimental gas was adopted to enhance the photoacoustic signal. By optimizing the modulation parameters, the optimal modulation amplitude and modulation frequency of the system were determined to be 4.29 cm⁻¹ and 785 Hz respectively. Under the optimal experimental conditions, there is a good linear relationship between the second harmonic signal of the selected spectral line and the CO concentration, with a linearity of 0.994. Using this relationship, the volume fraction of CO in the air was retrieved to be approximately 2.13×10⁻⁶. Finally, the Allan variance was used to analyze the long-term stability of the system under dry and wet conditions, and the detection limits of the system under dry and wet conditions were obtained to be 1.18×10⁻⁷ and 0.58×10⁻⁷ respectively, verifying that the addition of water vapor can effectively improve the detection sensitivity of the system for CO.

搭建了基于2.3μm中红外可调谐二极管激光器的CO气体的光声光谱测量系统,并选取4300.699cm-1处的CO吸收谱线作为传感目标。为了消除较长的CO分子弛豫时间对测量的影响,采用在实验气体中混入水汽的方式来增强光声信号。通过优化调制参数确定出系统的最佳调制振幅和调制频率分别为4.29cm~(-1)和785Hz。在最优的实验条件下,所选谱线的二次谐波信号与CO浓度间具有良好的线性关系,其线性度为0.994,利用该关系反演出空气中CO的体积分数约为2.13×10~(-6)。最后利用Allan方差对干湿条件系统的长期稳定性进行了分析,得到系统在干湿条件下的探测极限分别为1.18×10~(-7)和0.58×10~(-7),验证了水汽的加入可以有效提高系统对CO的探测灵敏度。