Applications Of Laser Spectroscopy In Environmental Monitoring

All natural materials have their special atomic or molecular structures, which can be observed as different kinds of absorption/emission spectra, fluorescence spectra, etc. By analyzing their spectra, one could obtain the components, corresponding contents, and other inherent characteristics of the measured materials. Since the invention of the laser, laser spectroscopy has been widely used in many fields;such as biomedicine, biology, agriculture and environmental monitoring, etc. The main aim of the present thesis work is to utilize laser spectroscopy to develop exploratory and applicable research technique in environmental monitoring, including atmospheric gas monitoring, agricultural pest monitoring and food safety monitoring.With the rapid development of Chinese economy and society, the worsening atmospheric environment becomes more and more problematic, which highly demands advanced technologies to monitor and control the atmospheric environment. The differential absorption LIDAR technique is an advanced optical remote sensing method, utilizing gas absorption spectroscopy to detect many kinds of atmospheric pollutants. By detecting the atmospheric backscattering signal of the laser pulses which would be switched alternatively between wavelengths on and slightly off the gas absorption peak, the range-resolved concentration for the gas of interest can be retrieved. This technique can realize large-range, in situ and dynamic3D monitoring of the atompsheric pollutants. In the present work, a dye laser and an optical parametric oscillator are utilized as light sources to develop differential absorption LIDAR systems and explore relevant applications. A first Chinese differential absorption lidar system, which was able to monitor the atmospheric mercury concentration, was developed using a dye laser, and the system performance was well calibrated by the oxygen absorption lines in the ultraviolet region. At the same time, atmospheric atomic mercury and nitric oxide molecules were efficiently monitered, and the exploratory research on an atmospheric photolysis gas indicator-glyoxal-is also performed with a three wavelengths differential absorption LIDAR method.The advanced laser-induced fluorescence LIDAR technique, for the first time, is utilized to study agricultural pest. With the help of this technique, one could track the moving or migration behavior of the agricultural pest, and even classify certain types of pests. The new research presented greatly encourages future research and applications of this technique in this field. It is especially useful for tracking the moving behavior of pest/insect around different types of pheromones.The laser-induced fluorescence technique, apart from its remote sensing application, can also be used in food safety studies. In the present work, the laser-induced fluorescence technique, combined with principal component analysis, for the first time, was successfully utilized for classification and quality assessment of Chinese jasmine and oolong tea samples. A compact multiple light-emitting diodes based fluorescence system was also developed. By analyzing the fluorescence spectra induced by different wavelengths, one could evaluate the classification and quality of tea samples more accurately, e.g, Longjing tea. The proposed technique could be further developed and applied in many other food safety fields.