Laser Induced Breakdown Spectroscopy (LIBS) is an established tool for the identification of metals in laser plasmas and it is proposed to use the spectral emission as a process monitor tool to detect complete removal of the protective layer material.  Referencing spectral signatures to the overall plasma brightness should enable reliable detection of the disappearance of the tracked spectral signature from the protective layer, thus providing a reliable end point detection, without having to detect the appearance of signature signal from the base.

The laser ablation process requires high efficiency and high ablation rates at the one hand, however close the the end point very high depth resolution is required.  This dual and contradictory requirement might be best addressed by a dual laser process, with initial ablation by ns-pulses to remove a large fraction of the protection layer, followed by ultra-short pulse laser ablation.