Analytical Capability of Defocused µ-SORS in the Chemical Interrogation of Thin Turbid Painted Layers

Claudia Conti; Marco Realini; Alessandra Botteon; Chiara Colombo; Sarah Noll; Stephen R Elliott; Pavel Matousek

doi:10.1177/0003702815615345

Analytical Capability of Defocused µ-SORS in the Chemical Interrogation of Thin Turbid Painted Layers

Appl Spectrosc. 2016 Jan;70(1):156-61. doi: 10.1177/0003702815615345.

Authors

Claudia Conti¹, Marco Realini², Alessandra Botteon², Chiara Colombo², Sarah Noll³, Stephen R Elliott³, Pavel Matousek⁴

Affiliations

¹ Institute for the Conservation and Valorization of Cultural Heritage (ICVBC), National Research Council, Milan, Italy conti@icvbc.cnr.it.
² Institute for the Conservation and Valorization of Cultural Heritage (ICVBC), National Research Council, Milan, Italy.
³ Department of Chemistry, University of Cambridge, Cambridge, UK.
⁴ Central Laser Facility, Research Complex at Harwell, STFC Rutherford Appleton Laboratory, Harwell, Oxford, UK.

Abstract

A recently developed micrometer-scale spatially offset Raman spectroscopy (μ-SORS) method provides a new analytical capability for investigating non-destructively the chemical composition of sub-surface, micrometer-scale thickness, diffusely scattering layers at depths beyond the reach of conventional confocal Raman microscopy. Here, we demonstrate experimentally, for the first time, the capability of μ-SORS to determine whether two detected chemical components originate from two separate layers or whether the two components are mixed together in a single layer. Such information is important in a number of areas, including conservation of cultural heritage objects, and is not available, for highly turbid media, from conventional Raman microscopy, where axial (confocal) scanning is not possible due to an inability to facilitate direct imaging within the highly scattering sample. This application constitutes an additional capability for μ-SORS in addition to its basic capacity to determine the overall chemical make-up of layers in a turbid system.

Keywords: Diffusel scattering; Non-destructive; Paintings; SORS; Spatially offset Raman spectroscopy; Subsurface; Turbid.