Proc. Natl Acad. Sci. USA 111, 1708–1713 (2014)

Credit: © 2014 NAS

Studying the layered structure of a painting is useful for checking its authenticity and learning more about its creation. This generally requires physically removing a cross-sectional sample from the artwork, which is a destructive process. Non-destructive macroscopic methods such as X-radiography can be useful, but the information they provide is limited. Now, Tana Elizabeth Villafana and colleagues from the USA have applied the concept of femtosecond pump–probe microscopy, which is popular for biological imaging, to non-destructive three-dimensional imaging of paintings. The team shows that a combination of multispectral and multi-delay pump–probe spectroscopy can generate virtual cross-sections of paintings with molecular and structural contrast, even for pigments with linear absorption spectra that are broad and relatively featureless. Increased spectral ranges of the pump and probe beams (from the near-infrared to the visible range) and the variable time delay of the pump–probe pulses are keys to addressing the complexity introduced by the large range of possible pigments in the paint layers; they permit the in situ three-dimensional imaging of paintings with molecular specificity. The team says that the method can be applied to a wide range of cultural objects, making it of interest to conservation science.