Experimental investigation on plasma temperature of Ca by laser—induced breakdown spectroscopy

The )lasma temperature is an important factor in quantitative analysis by laser induced breakdown spectroscopy(LIBS)．The plasmas were generated by a Nd：YAG laser 0n the surface of sample and detected by an Echelle spectrograph and an Intensified Charge—Couplea Device(ICCD)．The spectrum of 300 nm to 450 nm recorded several spectral lines of Ca component such as Ca II 31 5．9 nm．Ca II 317．9 nrn．Ca 1I 393．4 nm，Ca Ⅱ 396．9 nm，Ca I 422．7 nm and so on．It is known that the change of plasma temperature has influence on the line intensity from the equation for quantitative LIBS analysis．It was assumed that the plasm as produced in the experiment were in local thermodynamic equilibrium(LTE)．The temperature variations were deduced bv tine four 0ne—ionized Ca spectral lines and the Boltzmann plot，and the relationship between the plasma temperature and the concentration was obtained too．The plasma temperature increased when the concentration increased．When the mass fraction of Ca was lower than 0.50, the increase velocity of the plasma temperature was small. When the mass fraction of Ca was higher than 0.50, the increase was large．The hypothesis of local thermal equilibrium conditions of the plasma was confirmed in this experiment.