Numerical and experimental depth profile analyses of coated and attached layers by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is applied for depth profile analysis of different thicknesses of copper foils attached on steel and aluminum substrates. In order to account interfacial effects, depth profile analysis of copper coated on steel is also carried out. Experiments are done at ambient air and at two different wavelengths of 266 and 1064 nm of a Nd:YAG laser with pulse durations of 5 ns. A three-dimensional model of multi-pulse laser ablation is introduced on the base of normal evaporation mechanism and the simulation results are compared with the experiments. A normalized concentration (C^N) is introduced for determination of interface position and results are compared with the usually used normalized intensity (I^N). The effect of coating thickness on average ablation rate and resolution of depth profiling are examined. There is a correlation coefficient higher than 0.95 between the model and experimental depth profiles based on the C^N method. Depth profile analysis on the base of C^N method shows a better depth resolution in comparison with I^N method .Increase in the layer thickness, leads to a decrease in the ablation rate.