Experimental Study On The Nanosecond And Femtosecond Laser-induced Breakdown Spectroscopy Of Aluminum

Laser induced breakdown spectroscopy technology is an emission spectra technology that uses a high-intensity laser pulse to bombard a sample to generate plasma and then collects the emission spectra of excited ions or atoms in plasma for the detection and analysis of elements.The technology has the characteristics of no complicated sample preparation,few sampling,fast detection and in-situ analysis and remote detection.It has been widely used in component analysis,environmental testing,biological research and food safety and other fields.In this dissertation,the current research status at home and abroad,advantages and disadvantages,application fields of laser induced breakdown spectroscopy have been introduced.The process of laser induced plasma emission spectra,the mechanism of laser induced plasma and the time resolved characteristics of laser induced plasma emission spectra have been analyzed.The spectral line broadening mechanism and the calculation methods of laser induced plasma characteristic parameters have been described,and the nanosecond and femtosecond LIBS experimental devices have been constructed.Based on the above theory and devices,the following experimental study has been carried out.In the experiment of the aluminum's nanosecond laser induced breakdown spectroscopy,the time-resolved spectroscopy of the aluminum plasma was obtained.And the occurrence time and evolution mechanism of the continuous background spectra,the ionic spectral line and the atomic spectral line in this time-resolved spectroscopy were analyzed and explained.The characteristic lines in the wavelength range of 250-400 nm were calibrated when the delay time was 2 us in the time-resolved spectroscopy.The electron temperature and electron density of nanosecond laser induced aluminum plasma were calculated and analyzed.Among them,the method used to calculate the electron temperature of the aluminum plasma was boltzmann plot method,and the changing rules of the aluminum plasma's electron temperature with the laser energy and delay time were obtained.The method for calculating the electron density of the aluminum plasma was the stark broadening method,and the changing rules of the aluminum plasma's electron density with the laser energy and delay time were also obtained.The local thermodynamic equilibrium(LTE)was verified by McWhirter criterion,and the result showed that the aluminum plasma was consistent with the hypothesis of local thermodynamic equilibrium in this experiment.In the experiment of the aluminum's femtosecond laser induced breakdown spectroscopy,the time-resolved spectroscopy of the aluminum plasma was obtained,too.This dissertation analyzed and explained the occurrence time and evolution mechanism of the continuous background spectra,the ionic spectral line and the atomic spectral line in this time-resolved spectroscopy which was compared with the time-resolved spectroscopy of the nanosecond laser induced aluminum plasma.Meanwhile,the characteristic lines in the wavelength range of 250-400 nm were calibrated when the delay time was 100 ns in the time-resolved spectroscopy of the femtosecond laser induced aluminum plasma.The self absorption phenomena of emission spectral line of femtosecond laser induced aluminum plasma were analyzed,and the changing rules of the self absorption degree with the laser energy and delay time were obtained.At last,the single femtosecond laser pulse experiment was carried out,and the changing rules of the emission spectral line intensity of aluminum plasma induced by single femtosecond laser pulse with the number of excitation at the same point and laser energy were obtained.In the LIBS detection experiment of the aluminum surface adsorption element,when high purity aluminum sheet was bombarded by the single nanosecond laser pulse,non-aluminum element emission lines appeared.Contrasted with the excitation lines of sodium carbonate and sodium sulfate tablets,the emission lines of the non-aluminum element was proved to be generated by the sodium atom.And the experimental results showed that the Na element was only adsorbed on the surface of aluminum.Then the origin of the Na element was explored,the results showed that the Na element on the aluminum surface came from the air environment.