Photochemical effects in the UV laser ablation of polymers: Implications for laser restoration of painted artworks

Abstract.

The photochemical modifications induced in the UV ablation of molecular substrates are examined in model systems of polymer films (PMMA) doped with a highly photosensitive organic pigment (1-iodonaphthalene). Ablation by nanosecond laser pulses at 248 nm is shown to result in an increase of photolysis yields and in the efficient formation of new products. In sharp contrast, photoproduct formation in the corresponding ablation with 500 fs pulses is well defined and limited. Thus, besides its well-acknowledged thermal advantage, fs ablation is shown to provide a high degree of control over the induced photochemical modifications. The results of the study are correlated with the specific procedures that have been defined for the efficient restoration of painted surfaces with minimal photochemical modification to the substrate.