Laser Spectroscopy Based On An External Cavity Quantum Cascade Laser

Volatile organic compounds(VOCs),as an important class of organic pollutants,have direct toxic to animals and plants,and also are flammable and explosive.In case of leakage,it may easily lead to fire and explosion accidents,which seriously affect human health,ecological environment and social stability.Therefore,it is of great practical significance to carry out real-time on-line monitoring technology research on VOCs and grasp its distribution,emission and leakage in a timely manner.Compared to the traditional gas detection technology,the absorption spectroscopy has been rapidly developed,especially tunable diode laser absorption spectroscopy(TDLAS)has been widely applied to the measurement research of various types of pollution gases for its advantages of high sensitivity and resolution,fast response and nondestructive detection.In view of the characteristic of the broadband absorption spectrum of the VOCs in the mid-infrared band,a broadband external cavity quantum cascade laser(ECQCL)combining with the classical TDLAS detection technology which constitutes the external cavity quantum cascade laser spectroscopy has become an effective means to realize the precise analysis and remote sensing of VOCs in recent years.In this paper,a measurement system for the analysis of VOCs is built by using a commercial ECQCL as excitation light source and combined with the self-developed quartz tuning fork photodetector.By measuring the absorption spectra of N2O,the linearity of the experimental system and the reliability of the QCTF were examined.The typical VOCs,such as ethanol and acetone,were tested in theory and experiment in-depth.The experimental measured absorption spectra have a good agreement with the reference spectra of PNNL data.In terms of experimental data processing,the component identification and quantitative analysis of multi-component VOC were realized by combining the self-established multiple linear regression algorithm and cubic spline interpolation algorithm.In addition,the experimental study on the remote sensing technology of VOCs was carried out,the absorption spectra of ethanol and acetone were obtained under slow and fast laser scanning mode at a distance of 30 m respectively,which laid a good foundation for the future research on online monitoring of hazardous chemicals leakage.