基于多模激光吸收光谱的CO浓度高灵敏度测量

Sensitive detection of CO based on tunable multi-mode diode laser absorption spectroscopy

为提高多模激光吸收光谱技术的探测灵敏度,采用1 570nm多模二极管激光器为光源,以程长为100m的离散镜片型多通池作为气体吸收池,将多模二极管激光关联光谱技术、波长调制技术和长程吸收技术相结合,建立了一套具有高检测灵敏度和高稳定性的气体分子光谱测量系统。实验中将多模激光分成两束,一束作为参考光通过已知目标气体浓度的参考池,另一束通过混有待测气体的测量池,测量光信号和参考光信号被同时探测和解调。通过计算待测气体和参考池气体之间二次谐波信号峰值高度之间的关系,反演出CO的浓度。利用该装置测量了CO气体在1 570nm附近的近红外吸收光谱。实验表明,CO浓度测量值与真实浓度值之间具有良好的线性关系,线性度为0.9995,平均偏差为1.19%,对CO的探测极限为37.3×10-6,对同一样品在30min内的30次连续测量的标准偏差为0.839%,表明了系统良好的稳定性。

A multi-mode laser absorption spectroscopy system with high detection sensitivity and high stability is built using an F-P multi-mode diode laser near 1570 nm as the light source. In order to improve the detection limit of the system,a discrete lens-type multi-pass cell with path length of 100 m is employed as the measurement absorption cell. The multi-mode diode laser correlation spectroscopy, wavelength modulation technology and long path absorption spectroscopy are combined to improve the performance of the system. In the experiment, the laser beam is spitted into two parts, which pass through the reference cell and measurement cell, respectively. The measuring light and the reference light signals are detected simultaneously. The performance of the system is validated by measuring the concentration of carbon monoxide （CO）. The CO concentrations are derived from the relationship between the normalized WMS-2f signal peak heights of the measurement and reference signals which are selected based on high signal to noise ratio and correlation coefficient. The calculation results show that there is a highly linear relationship between the measured and actual CO concentrations,and the linearity is 0. 999 5 over the whole tested range. A detection limit of 37.3 ppm is achieved. The standard deviation of 0. 839 % is obtained using 30 successive measurements with each measurement time of -10 s during 30 min,which demonstrates the good stability of the system.