Research On The Characteristics And Application Of Laser-induced Plasma

Laser-induced breakdown spectroscopy (LIBS) is a new kind of atomic emis sionspectroscopy analytical technique. Since LIBS has the advantages of rapid detection, littleor non-destruction detection, multi-element analysis, simple sample preparation and thecapacity of remote and online detection, it shows great potential in the field of materialcomponent detection. Nowadays, it is under through a critical time of the LIBS’sdevelopment, the research of LIBS focuses on the fundamentals and extending itsapplications. Besides, the characteristics and applications of the laser-induced plasma stillneed further study. The primary research coverage of this thesis include the followingseveral parts:1. The sequential test and orthogonal test design were proposed to optimize andinvestigate the parameters of LIBS including the delay time of the ICCD, the gate width ofthe ICCD and laser pulse energy, respectively. The results obtained from the sequential testindicate that all these three parameters have much effect on spectral intensity and the SBRof the laser-induced aluminum plasma, strong spectral intensity and optimum SBR areobtained under the optimum combination of these parameters. The impact order of theparameters is laser pulse energy> delay time of the ICCD> gate width of the ICCD by theorthogonal test design. The above researches provide available schemes for theexperimental condition optimization of LIBS in different occasions, and it’s helpful forqualitative and quantitative analysis under the optimum experimental conditions.2. The temporal behaviors, spatial distribution and expansion process of the laser-induced aluminum alloy were investigated. The plasma images at different experimenta lconditions were acquired with a width and time delay controllable ICCD camera, then thespatial and temporal evolution behaviors of the aluminum plasma were analyzed accordingto the images. Besides, the characteristics of the aluminum plasma excitation and emissionwere analyzed by the measurement of the electron temperature and electron number density.The results show that the plasma presents an obvious hierarchical structure, and the areasas well as the temperatures of different regions present different characteristics during thetime evolution process. The electron excitation temperature of the plasma ranges fromabout6500to9200K, and it decreases rapidly in the first3μs. Besides, the electron numberdensity of aluminum plasma is in the order of1017cm-3. The excitation threshold of theplasma is approximate3mJ, there is no significant hierarchical structure when the laser pulse energy is below3mJ. The electron temperature and electron number density of theplasma increase when the laser pulse energy increases from10mJ to100mJ.3. Six kinds of tea leaves were detected and identified by LIBS combined withDiscriminant Analysis Method. Eight analysis indexes were found out according to thedifferences of their LIBS spectra, and then the Discriminant Analysis Method wasemployed to identify the tea leaves. For each kind of tea leaf,100spectra were recorded byspectrometer system and half of each was used as training set to establish discrimina ntfunctions, while the remaining part was used as test set to verify the accuracy of the results,and discriminant the test set as well. The results show that the average correct identificatio nrate of the training samples is98%. In addition, the average correct identification rate ofthe test samples is95.33%, and the reasons of misidentification has been analyzed. Theresults indicate that LIBS is an available scheme for the detection and discrimination ofagricultural products.