Standoff Raman spectroscopy for architectural interiors from 3-15 m distances.

Portable and mobile Raman spectroscopy systems are increasingly being adopted in in situ non-invasive examination of artworks given their high specificity in material identification. However, these systems typically operate within centimeter range working distances, making the examination of large architectural interiors such as wall paintings in churches challenging. We demonstrate the first standoff Raman spectroscopy system for in situ investigation of historic architectural interior at distances > 3 m. The 780 nm continuous wave laser-induced standoff Raman system was successfully deployed for the in situ examination of wall paintings, at distances of 3-15 m, under ambient light. It is able to identify most common pigments while maintaining a very low laser intensity to avoid light induced degradation. It is shown to complement our current method of standoff remote surveys of wall paintings using spectral imaging.