Portable Raman spectrometer Rigaku Xantus-2™



The portable Raman spectrometer available in MOLAB provides non-invasive in situ analyses of the molecular composition of the material surface substances. In Heritage field, Raman spectroscopy is a technique of choice for the characterization of inorganic and organic pigments used in panel, canvas and mural paintings and decorated objects. The great advantage of this technique stems from the unequivocal molecular identification, which corresponds to a specific pigment. Therefore, the outcomes supply information about the artist technique through the identification of the employed pigments, colorants etc., as well as on the conservation state, due to the characterization of decay and conservation products.

To derive non-invasive information about the internal part of the materials, a new Raman technique, micro-Spatially Offset Raman Spectroscopy (micro-SORS), has been developed. Micro-SORS permits to acquire data from compounds located below the surface (in the micrometric range) in a non-invasive way.

The method has been recently optimized for portable instruments, using Xantus 2TM Rigaku spectrometer and a motorized stage enabling micrometric movements of the instrument from the artwork surface. At each increasing distance, which corresponds to increasing defocusing of the laser illumination and collection areas, a Raman spectrum is collected. This defocusing mechanism allows detecting deep Raman photons emerging on the surface laterally from the laser illumination area.. Micro-SORS has strong potentials on Cultural Heritage field since it opens the way to the reconstruction of the painted layer sequence and/or to the identification of decay products hidden by the surface.



Rigaku Xantus-2™ portable Raman spectrometer is equipped with a thermoelectrically cooled CCD 2000 × 256 Pixel and enabled two excitation wavelengths (785 nm e 1064 nm) to be deployed. Spectral resolution is 7-10 cm-1 and spectral range from 200 to 2200 cm-1. The laser has an adjustable intensity in the range from 30mW to 490 mW and acquisition time in the range between ms to few min. The laser beam can be focused both with a low magnification lens and a 20X microscope objective which is applied to the instrument through a metallic adapter developed in our laboratory. The instrument is compact (138x274x98 cm) and put on a motorized micro stage enabling movements along the surface perpendicular axis with high accuracy and reproducibility; this allows achieving the correct laser focus on the surface and performing micro-SORS measurements. The instrument and the micro stage are put on a tripod.

Micro-SORS modality is carried out displacing away the instrument from the imaged position through sequential micrometric movements controlled by software. Spectral elaboration is performed using Origin-Pro and OPUS software.



Claudia Conti


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