近红外QEPAS痕量CO_2检测系统优化研究

Optimization research on detection system for tracing CO_2 based on near-infrared QEPAS

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 CO2 detection based on near-infrared quartz-enhanced photoacoustic spectroscopy （QEPAS） has some defects including low signal-to-noise ratio （SNR）,low sensitivity,high lower-limited detection and narrow effective measurement range.These defects make the detection difficult to meet the needs of environmental monitoring and industrial production.A near-infrared QEPAS CO2 detection system was built.It chose the narrow linear width distributed feedback semiconductor laser （DFB） as excitation light source with center wavelength of 1.58μm and optimal designed the system.Chose 4 groups of CO2 with different concentrations as the tested objects based on wavelength modulation method.Studied the influence of the wavelength modulation depth on amplitudes of second-harmonic signal to ensure the optimum modulation current was 10 mA and improved detection signal amplitudes.And the acoustic detection module （ADM） design was optimized to reduce noise signal amplitudes.After optimization,the SNR of the system was 2.2 times improved than that of previous.The detection limit sensitivity of the system was reduced to 83 ppm.The above results proved that these optimization effectively lower detection limit and improve detection sensitivity,SNR and the adaptability to complex environment.