title: Photoacoustic imaging reveals hidden underdrawings in paintings.
abstract: A novel, non-invasive, imaging methodology, based on the photoacoustic effect, is introduced in the context of artwork diagnostics with emphasis on the uncovering of hidden features such as underdrawings or original sketch lines in paintings. Photoacoustic microscopy, a rapidly growing imaging method widely employed in biomedical research, exploits the ultrasonic acoustic waves, generated by light from a pulsed or intensity modulated source interacting with a medium, to map the spatial distribution of absorbing components. Having over three orders of magnitude higher transmission through strongly scattering media, compared to light in the visible and near infrared, the photoacoustic signal offers substantially improved detection sensitivity and achieves excellent optical absorption contrast at high spatial resolution. Photoacoustic images, collected from miniature oil paintings on canvas, illuminated with a nanosecond pulsed Nd:YAG laser at 1064 nm on their reverse side, reveal clearly the presence of pencil sketch lines coated over by several paint layers, exceeding 0.5 mm in thickness. By adjusting the detection bandwidth of the optically induced ultrasonic waves, photoacoustic imaging can be used for looking into a broad variety of artefacts having diverse optical properties and geometrical profiles, such as manuscripts, glass objects, plastic modern art or even stone sculpture.
authors.affiliation: Institute of Electronic Structure and Laser, Foundation for Research and Technology Hellas, Heraklion, Crete, Greece. tserevel@iesl.forth.gr.
authors.forename: George J
authors.initials: GJ
authors.lastname: Tserevelakis
authors.affiliation: Department of Chemistry, University of Crete, Heraklion, Crete, Greece.
authors.forename: Ilianna
authors.initials: I
authors.lastname: Vrouvaki
authors.affiliation: Institute of Electronic Structure and Laser, Foundation for Research and Technology Hellas, Heraklion, Crete, Greece.
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Siozos
authors.affiliation: Institute of Electronic Structure and Laser, Foundation for Research and Technology Hellas, Heraklion, Crete, Greece.
authors.forename: Krystallia
authors.initials: K
authors.lastname: Melessanaki
authors.affiliation: Institute of Electronic Structure and Laser, Foundation for Research and Technology Hellas, Heraklion, Crete, Greece.
authors.forename: Kostas
authors.initials: K
authors.lastname: Hatzigiannakis
authors.affiliation: Institute of Electronic Structure and Laser, Foundation for Research and Technology Hellas, Heraklion, Crete, Greece.|Department of Physics, University of Crete, Heraklion, Crete, Greece.
authors.forename: Costas
authors.initials: C
authors.lastname: Fotakis
authors.affiliation: Institute of Electronic Structure and Laser, Foundation for Research and Technology Hellas, Heraklion, Crete, Greece.
authors.forename: Giannis
authors.initials: G
authors.lastname: Zacharakis