Influence Of Defocusing Distance On The Laser-Induced Cu Plasma Spectra In Air

In view of laser technique rapidly developing, the plasma of laser has been widely used in various research domains. The interaction mechanism of laser-pulsed with solid targets and the plasma evolution are complex. They depend on the laser pulse characteristics, targets, buffer gas and others. The characteristics include wavelength, pulse duration, energy, targets, the pressure of buffer gas and so on. Many scholars have had plentiful and available researches, but the relevant mechanism of radiation need to be revealed. Varying defocusing distance laser-induced breakdown spectroscopy (LIBS) technique is used to analysis the emission mechanism of element from plasma generated by focusing a powerful laser beam on material surface.The plasma spectra have been measured with a pulsed Nd: YAG laser which induces plasma from a metal copper target. Varying defocusing distance the influence of the relative intensity and spectral structure in various laser focusing distances from the target is studied. At the same time we study space characteristics of emission spectra measured with different laser deviation distances to the sample. The influence of the air plasma is studied by discussing the relative intensity and the full width half maximum of N II 500.52nm spectra in various laser power intensities. Space distribution characters of electron temperature are measured with defocusing distances at 1mm before the sample , 0mm on the sample surface, and 2mm back the sample. At the same time we analyze the plasma characteristics and mechanism. The results show that the spectral structure, spectral intensity and electron temperature prominently depend on the defocusing distances. The phenomenon that the relative intensity and spectral species prominently depend on the deviation distance can be explained by the laser power density. The focusing position 2mm back the sample surface can be found that produces the maximum of copper atom spectra intensity and the electron temperature maximum. The phenomenon that the spectral intensities fall off at the focusing position 0.5mm and 1.0mm below the sample surface can be interpreted by the shielding effect.