Irradiance-dependent depth profiling of layered materials using laser-induced plasma spectrometry

Laser-induced plasma spectrometry (LIPS) is an appealing technique for dept h profiling purposes due to its capabilities for performing fast analysis i n air at atmospheric pressure without limitations of sample size or nature. At a fixed laser wavelength, pulse width, experiment geometry and sample t ype, the irradiance is the factor that will affect both the averaged ablati on rate and depth resolution. In the present work, a detailed description o f the effect of laser irradiance on averaged ablation rate and depth resolu tion of Ni-Cu-coated brass samples is presented. The results demonstrate th at the best depth resolution does not correspond with the minimum ablation rate. Several facts concerning the redeposition of material around the rim of the craters and energy gradients in the laser beam are proposed to expla in the experimental results.