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现有的近红外石英增强型光声光谱技术(QEPAS)痕量二氧化碳气体检测存在信噪比低,灵敏度较低,检测下限较高,有效测量范围窄的问题,难以满足在环境监测,工业生产等方面的检测需求。搭建了近红外QEPAS痕量CO_2气体检测系统,选择了中心波长为1.58μm(1580.0395nm)的窄线宽分布反馈式半导体激光器(DFB)为激励光源,并对系统进行优化设计。采用波长调制方法,选用四组不同浓度CO_2气体作为检测对象,研究了波长调制深度对二次谐波信号幅值的影响,确定最佳调制电流为10mA,提高了检测信号幅值;并对光声探测模块进行了优化设计,降低了噪声信号幅值,优化后系统的信噪比提高为优化前的2.2倍。对优化后的系统进行了检测极限灵敏度测量实验,系统的检测极限灵敏度从优化前的240ppm降低为83ppm,信噪比为12。证明了这些优化方法有效地降低了系统的检测下限,提高了检测灵敏度和信噪比,增强了对复杂环境的适应性。
The existing near-infrared Quartz Enhanced Photoacoustic Spectroscopy (QEPAS) trace carbon dioxide gas detection has the problems of low signal-to-noise ratio, low sensitivity, high detection limit and narrow effective measurement range, which makes it difficult to meet the requirements of environmental monitoring, industrial production And other aspects of testing needs. A near-infrared QEPAS trace CO 2 gas detection system was set up. A narrow linewidth distributed feedback semiconductor laser (DFB) with a center wavelength of 1.58μm (1580.0395nm) was selected as the excitation light source, and the system was optimized. The wavelength modulation method was used to select four different concentrations of CO 2 gas as the detection object. The effect of wavelength modulation depth on the amplitude of the second harmonic signal was studied. The optimal modulation current was 10mA and the detection signal amplitude was increased. The acoustic detection module is optimized to reduce the amplitude of the noise signal, and the signal-noise ratio of the optimized system is improved to 2.2 times before the optimization. The sensitivity of the system was tested. The detection limit sensitivity of the system was reduced from 240ppm before optimization to 83ppm with a signal to noise ratio of 12. It is proved that these optimization methods effectively reduce the detection limit of the system, improve the detection sensitivity and signal-noise ratio, and enhance the adaptability to complex environments.