Laser-induced breakdown spectroscopy; molecular LIBS; femtosecond LIBS; chloride contamination; pitting corrosion;

Laser-induced breakdown spectroscopy (LIBS) with pulsed laser excitation is a well-established method for analyzing the atomic components of an unknown sample based on their characteristic emission spectra. However, standard LIBS analysis provides insufficient results if the atoms to be measured exhibit weak elemental emission lines or if characteristic elemental spectra are disturbed by overlapping stronger lines of other elements in the sample. The analysis of the molecular emission bands arising in the plasma cooling phase seems to be a promising solution. The analysis is carried out by the observation of newly formed radicals and diatomic molecules whose strong molecular emission bands can often be found in the visible spectral region and offer a higher detection sensitivity. This generally requires a time resolved measurement of the LIBS spectra, but we show that in some cases this is not necessarily needed. As an application we present the measurement of chloride contamination in concrete that could help to estimate the repair demand of infrastructure buildings in future.