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Heritage Science
Fig. 3 | Heritage Science

Fig. 3

From: Listening to laser light interactions with objects of art: a novel photoacoustic approach for diagnosis and monitoring of laser cleaning interventions

Fig. 3

PAcSAA method for the assessment of thin layers thickness in paintings. a PAcSAA experimental setup. b–d OCT profiles of three primary red magenta paint layers on glass substrates, with measured thickness (red bars) at 50, 100 and 200 μm respectively. e–g Corresponding normalized PA amplitude spectra for the primary red magenta paint layers presented in (b–d). Dashed curves indicate a 4th order polynomial fitting for the predominant low-frequency bands (10–80 MHz). h Plot of ATF versus OCT measured thickness for the investigated paint layers. Error bars correspond to the standard deviation of 5 sequential ATF measurements performed at different regions of the mock-up. Black line represents the fitting of the experimental points using an exponential decay function. i MAP PA image of a painting mock-up at 1064 nm. j MAP PA image of the same mock-up using the second harmonic wavelength at 532 nm. k PAcSAI image of color-coded paint thickness values estimated according to the exponentially fitted curve shown in (h). Figure adapted from [46] and [47]

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