Similar mechanisms of the laser-induced photomechanical spallation are observed for molecular and metal targets. A coupled atomistic-continuum model that combines a molecular dynamics method with a continuum description of the laser excitation and subsequent relaxation of the conduction band electrons is used for metal targets. A mesoscopic breathing sphere model is used in simulations of laser interaction with molecular targets.
#Lacona viii series
Microscopic mechanisms of photomechanical spallation are investigated in a series of large-scale molecular dynamics simulations performed for molecular and metal targets. Possible mechanisms for polymer decomposition/ablation, as well as the implications for the laser-restoration performances are discussed.
Furthermore, we find a strong dependence of these effects on polymer MW. We find that the etching efficiencies and the morphological modifications upon UV fs irradiation differ drastically from the ones observed in the corresponding ns irradiation. We investigate the etching resolution, the morphology of the etched areas and the chemical modifications induced in the remaining substrate following laser-cleaning protocols. Mw is important also in applications, since it can vary from layer to layer, or from one painting to another.
A very important parameter for our study is polymer Molecular weight (Mw), which relates to the number of bonds that must be broken for material ejection to occur. For a simplified approach, we study polymers (Poly-(methyl methacrylate) PMMA) doped with aromatic compounds, systems that are chemically similar to the painting materials. To this end, we investigate laser ablation of polymers with UV (248 nm) ultrashort (500 fs) laser pulses.
However, for a safe utilization on actual artworks, the effects induced in the substrates by fs laser pulses must be carefully examined. Moreover, from the data collected from the technologies applied in the past, origin, provenance and routing of the artifacts can be concluded.Due to its well known advantages, the use of femtosecond ( fs) laser technology promises the means for overcoming the limitations of nanosecond (ns) laser-based restoration of painted works of art. It is shown that the complementary spectroscopic analysis allows for the in-depth study of the environmental impact on historical objects and delivers indications for the appropriate strategy of the planned conservation activities. From coincidence of the XRF, Raman and LIP data the presence of surface contaminant CaCO 3, the corrosion product FeO(OH) and patina Cu 2 (OH) 3Cl are concluded. The quasi-nondestructive LIP technique applied for stratigraphic sampling performed with an accuracy of ca 2 µm across the multilayer surface coverage reveals such elements as C, Ba and Na in the uppermost layer. The elemental composition is confirmed by the LIP (Laser Induced Plasma) spectroscopic measurements. The composition of the surface layers of the forged iron box lid covered with polychrome (XVI c.), and of the bronze female nude sculpture (antiquity) is obtained from the XRF and µ-Raman spectra. The surface layers resulting from prolonged exposure to the indoor environment and the bulk material of metal artifacts from the collection of National Museum in Gdansk are studied by means of spectroscopic techniques.
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