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

Laser-induced plasma spectrometry (LIPS) is an appealing technique for depth profiling purposes due to its capabilities for performing fast analysis in air at atmospheric pressure without limitations of sample size or nature. At a fixed laser wavelength, pulse width, experiment geometry and sample type, the irradiance is the factor that will affect both the averaged ablation rate and depth resolution. In the present work, a detailed description of the effect of laser irradiance on averaged ablation rate and depth resolution of Ni-Cu-coated brass samples is presented. The results demonstrate that 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 explain the experimental results.