A comparison of nanosecond and femtosecond laser-induced plasma spectroscopy of brass samples

The ablation of brass samples in argon shield gas by 170 fs and 6 ns laser pulses has been studied by optical emission spectroscopy of the evolving pl asmas. Differences observed in the temporal behavior of the spectral line i ntensities are explained by the shielding effect of the Ar plasma for ns-pu lses and the free expansion of the plasma of the ablated material in case o f fs-pulses. Brass with different Zn/Cu ratios were used as samples. Differ ent types of crater formation mechanisms in the case of ns- and fs-pulses w ere observed. At 40 mbar argon pressure the thresholds of ablation were fou nd to be similar to 0.1 and similar to 1.5 J cm(-2) for fs- and ns-pulses, respectively. With an internal standardization of zinc to copper it is poss ible to correct for differences in the ablation rates and to obtain linear calibration curves. For optimum experimental conditions, narrower confidenc e intervals for the determination of unknown concentrations were found in c ase of fs-pulses. Within the range of the laser intensities used, no depend ence of the Zn/Cu line intensity ratio on the number of laser pulses applie d to the same ablation spot was observed, neither for fs- nor for ns-pulses , which is interpreted as the absence of fractional vaporization. (C) 2000 Elsevier Science B.V. All rights reserved.