Nonlinear imaging techniques as non-destructive, high-resolution diagnostic tools for cultural heritage studies

Here, we present a review of the implementation of nonlinear imaging microscopy techniques such as second and third harmonic generation (SHG-THG) and multi-photon excitation fluorescence (MPEF), as high-resolution, non-invasive diagnostic tools for cultural heritage studies. Specifically, the above nonlinear modalities are employed for the precise three-dimensional (3D) delineation of the protective layers bulk in model multilayer painting artworks. The high axial resolution thickness determination of protective layers through the use of THG imaging and the identification of the chemical composition of the artefacts via MPEF measurements are depicted. Furthermore, we reveal the potential of MPEF imaging measurements for the identification of the corrosion layers in silver-based artefacts. Finally, nonlinear modalities are employed for the assessment of the affected region and the obtainment of depth information during laser cleaning of polymeric coatings.