Laser-induced Breakdown Spectra Of Organic Compounds In Different Atmospheres

Laser induced breakdown spectroscopy（LIBS）has the advantages of real-time,rapid and in-situ analysis,and has been widely used in industrial testing,environmental monitoring,soil analysis,water heavy metal pollution detection and other aspects.However,there are few researches on LIBS in organic matter.The main reason is that LIBS experiments are generally conducted in air,where the content of N and O elements is very high,and the basic components of organic matter are C,H,N and O.Therefore,the air causes great interference to the spectrum of organic matter,and the LIBS measurement of organic matter in air has great limitations.In order to eliminate this limitation,the spectral properties and plasma properties of nitroglycerin in air,vacuum and argon are analyzed and compared by eliminating the interference of air.In addition,the spectral characteristics of TNT and RDX organic explosives in air and argon were investigated,and the identification of organic explosives was studied by using support vector machine.The main research achievements of this paper are as follows:（1）The plasma properties of nitroglycerin were analyzed in air,vacuum and argon.Compared with that in air,the optimal acquisition delay of characteristic elements of nitroglycerin in vacuum is 1.5μs.The laser-induced plasma lifetime is shorter,and the change of laser energy has less effect on SBR.The optimal acquisition delay of characteristic elements of nitroglycerin in in argon is 2μs.The lifetime of the laser-induced plasma is longer.The change of laser energy has great effect on SBR.（2）The spectral properties of nitroglycerin were analyzed in air,vacuum and argon.The spectral line strength,background strength and spectral line half-width of nitroglycerin in argon are higher than those in air.The spectral line strength,background strength and spectral line half-width of nitroglycerin in vacuum environment are lower than those in air environment.（3）The characteristic spectral lines of TNT and RDX in air and argon were studied.It is found that organic compounds could not be distinguished only by C,H,N and O,C₂and CN molecules are more important in the identification of organic compounds.The formation of C₂ molecule is mainly affected by the molecular structure of the sample,and the formation of CN molecule is mainly affected by the environmental background.（4）TNT and RDX in air and argon environment were distinguished based on SVM.Five kinds of organic interference samples were set up in the experiment,and 100 sets of spectral data were collected for each sample,60 sets of data were used as training samples,and 40 sets of data were used as test samples.The test results show that the SVM has an average recognition rate of 92.86%for 7 samples in air and 99.64%for 7 samples in argon.