Determination of thickness of thin turbid painted over-layers using micro-scale spatially offset Raman spectroscopy

Year: 2016

Authors: Conti C., Realini M., Colombo C., Botteon A., Bertasa M., Striova J., Barucci M., Matousek P.

Autors Affiliation: CNR, ICVBC, Via Cozzi 53, I-20125 Milan, Italy; Univ Florence, CNR, Ist Nazl Ott, Via Nello Carrara 1, I-50019 Sesto Fiorentino, Italy; Univ Florence, LENS, Via Nello Carrara 1, I-50019 Sesto Fiorentino, Italy; STFC Rutherford Appleton Lab, Cent Laser Facil, Res Complex & Harwell, Didcot OX11 0QX, Oxon, England.

Abstract: We present a method for estimating the thickness of thin turbid layers using defocusing micro-spatially offset Raman spectroscopy (micro-SORS). The approach, applicable to highly turbid systems, enables one to predict depths in excess of those accessible with conventional Raman microscopy. The technique can be used, for example, to establish the paint layer thickness on cultural heritage objects, such as panel canvases, mural paintings, painted statues and decorated objects. Other applications include analysis in polymer, biological and biomedical disciplines, catalytic and forensics sciences where highly turbid overlayers are often present and where invasive probing may not be possible or is undesirable. The method comprises two stages: (i) a calibration step for training the method on a well characterized sample set with a known thickness, and (ii) a prediction step where the prediction of layer thickness is carried out non-invasively on samples of unknown thickness of the same chemical and physical make up as the calibration set. An illustrative example of a practical deployment of this method is the analysis of larger areas of paintings. In this case, first, a calibration would be performed on a fragment of painting of a known thickness (e.g. derived from cross-sectional analysis) and subsequently the analysis of thickness across larger areas of painting could then be carried out non-invasively. The performance of the method is compared with that of the more established optical coherence tomography (OCT) technique on identical sample set.

Journal/Review: PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY SERIES A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES

Volume: 374 (2082)      Pages from: 20160049-1  to: 20160049-8

More Information: J.S. is supported by IPERION CH project GA 654028, funded by EU community´s H2020-research infrastructure programme.
KeyWords: Calibration; Chemical analysis; Forecasting; Functional polymers; Optical tomography; Raman spectroscopy; Tomography, Cross sectional analysis; Cultural heritage objects; Cultural heritages; Non-invasive; Paint layer thickness; Raman microscopy; Spatially offset raman spectroscopies; Thickness, Spectrum analysis
DOI: 10.1098/rsta.2016.0049

Citations: 15
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