Proof of Concept: Macro‐Raman Mapping of a Three‐Dimensional Object

ABSTRACT Macro‐Raman mapping has been proposed as a novel technique to visualise the molecular distribution over a surface of typically several tens of cm 2 . By combining large stages with a fibre‐optic probe head of a Raman spectrometer and appropriate data processing, it is possible to obtain large Raman maps. Therefore, a data cube containing thousands of spectra is processed in such a way that the relevant spectral information is represented as different colours in the image. A mapping experiment consists of the alignment, the recording of the spectra and postprocessing. In the current work, it is aimed to deliver a proof of concept of the macro‐Raman mapping of a three‐dimensional (3‐D) object, such as a statue. When Raman mapping experiments are performed using microscope objectives, the surface should be relatively flat, and the distance between the surface and the spectrometer cannot display abrupt changes. Therefore, the macro‐Raman set‐up needs to be equipped with a long working distance lens. By measuring for each point the distance to the surface, and by knowing the positions of the stage, the recorded spectral information is related to the 3‐D position of the measurement point. Thus, a 3‐D point cloud is obtained, and the linked spectral information is colour‐coded to obtain a 3‐D macro‐Raman map. To be able to record information from all areas of the painted statuette, including from points that are on planes parallel to the laser beam, several maps have been recorded, and the point clouds were merged, resulting in a complete reconstruction of the 3‐D artefact.