Crosstalk effects of the surface layers of metallic samples on laser-induced breakdown spectroscopy measurements

Abstract

Material ablation driven by focused laser pulses is an important aspect of laser-induced breakdown spectroscopy (LIBS). It has frequently been used to ablate non-representative layers from the surface or to generate analytic depth profiles of samples. In this paper we discuss the crosstalk effects of the locally ablated surface on the LIBS measurement of the underlying bulk material. As a measuring object, a model artefact is chosen consisting of an iron-free brass bulk sample on which a steel plate with a thickness of 500 μm was brought in close contact. This steel sheet acts as a surrogate for a non-representative surface layer. It is shown by LIBS measurements and cross polish methods that an indirect interaction between the expanding plasma originating from the substrate and the surface layer at the crater walls as well as a recasting of the ablated material from the steel plate have a notable influence on LIBS measurements of the underlying bulk sample. By a two-step ablation sequence crosstalk effects can be reduced to levels equivalent to those persisting for the model artefact without the steel sheet.