Influence of ns-laser wavelength in laser-induced breakdown spectroscopy for discrimination of painting techniques

TL;DR

This study investigates how different ns-laser wavelengths affect the ability of laser-induced breakdown spectroscopy to discriminate ancient painting techniques, focusing on plasma characteristics and spectral emissions.

Contribution

It introduces a method to compare laser wavelengths for improved identification of painting binders using plasma control and chemometric analysis.

Findings

Wavelength influences the separation of painting techniques.

Plasma electron temperature correlates with spectral differences.

Optimal wavelength range enhances binder identification.

Abstract

The influence of ns-laser wavelength to discriminate ancient painting techniques such as are fresco, casein, animal glue, egg yolk and oil was investigated in this work. This study was carried out with a single shot laser on samples covered by a layer made of a mixture of the cinnabar pigment and different binders. Three wavelengths based on Nd: YAG laser were investigated (1064, 532 and 266 nm). The plasma is controlled at the same electron temperature after an adjustment of pulse energy for these three wavelengths on a fresco sample without organic binder. This approach allows to eliminate the effects of laser pulse energy and the material laser absorption. Afterwards, the emission spectra were compared to separate different techniques. The organic binding media has been separated based on the relative emission intensity of the present CN or C 2 rovibrational emissions. In order to test the capability of separating or identifying, the chemometric approach (PCA) was applied to the different matrix. The different solutions in term of wavelength range to optimise the identification was investigated. We focused on the evaluation for the laser wavelength to insure a better separation. The different capacity was interpreted by differentiating 1 Corresponding author. E-mail address: vincent.detalle@culture.gouv.fr 2 the binders by the altered interaction mechanisms between the laser photon and the binders. Also, the electron temperature in the plasma was estimated, which provided the evidences to our findings.