Evaluation of LIBS LIF Raman spectroscopies to analyze materials from cultural heritage

The aim of this research project is the development of a hybrid system in laboratory coupling together three analytical techniques (LIBS, LIF and Raman spectroscopy) in a single instrument. The relevance for combining these three spectroscopies is to identify a material (molecular and elemental analysis) without any preliminary preparation, regardless of its organic or inorganic nature, on the surface and in depth, without any surrounding light interference thanks to time resolution. Such instrumentation would allow characterizing different materials from cultural heritage such as copper corrosion products and wall paintings organized in stratigraphic layers. A complete study on LIBS-LIF-Raman hybrid was carried out from conception to instrumental achievement, as well as automatic control to data fusion processing in order to elaborate a strategy of analysis according to the material and to be able to address conservation issues. From instrumental's point of view, we succeeded in condensing the three spectroscopies by using single laser for excitation and two spectrometers (time-resolved and not time-resolved) for light collection. Regarding the optical mount, the use of a parabolic mirror allowed exciting the surface of the sample with three different excitation wavelengths joined on a single optical path with similar probe area. The parametric study revealed the influence and the optimization of each parameter to enhance signal collection. An important work on data fusion was carried out in order to take advantage of discriminating power of each spectroscopy into final condense information. Finally, from engineering's point of view, computer programming was implemented for data processing as well as for automatic control of the instrumentation. Thanks to this holistic approach, we succeeded to address science in conservation issues often found in analyzing materials from cultural heritage such as the presence of an organic coating as well as its identification, and the different inorganic layers through the sample. Some challenges remain to be taken up especially in optimizing Raman scattering collection for in depth analyses. (author)