Abstract
In the context of this work, a prototype hybrid photoacoustic (PA) and optical system for the on-line monitoring of laser cleaning procedures is presented. The developed apparatus has enabled the detection of MHz frequency range acoustic waves generated during the laser ablation process. The intrinsically generated PA signals combined with high resolution optical images provide the opportunity to follow the cleaning process accurately and in real time. Technical mock-ups have been used to demonstrate the potential of this novel technique with emphasis given to applications that refer to the restoration of Cultural Heritage (CH) surfaces. Towards this purpose, the real time monitoring of the laser assisted removal of unwanted encrustation from stonework has been achieved using IR and UV wavelengths. This novel approach has allowed for the precise determination of the critical number of laser pulses required for the elimination of the encrustation layer, while highlighting the dominant ablation mechanisms according to the irradiation wavelength. The promising results obtained using the prototype hybrid PA and optical system can open up new perspectives in the monitoring of laser cleaning interventions, promoting an improved restoration outcome.
Highlights
Laser assisted removal of unwanted material from artworks has been established as a highly precise and safe restoration intervention in the last decades, often substituting conventional cleaning methods
We have developed a hybrid photoacoustic and optical system for the in-situ and real-time monitoring of laser cleaning and the investigation of the laser ablation mechanisms that dominate the cleaning with IR and UV laser wavelengths
We have demonstrated the potential of the system for the monitoring of laser cleaning with IR and UV wavelengths, both individually and simultaneously in a variety of fluence values
Summary
Laser assisted removal of unwanted material from artworks has been established as a highly precise and safe restoration intervention in the last decades, often substituting conventional cleaning methods. Laser cleaning relies on the ablation of a material upon its irradiation with an intense and short-pulse laser beam at a wavelength that is strongly absorbed by this material[1,2] It is a delicate and irreversible process which, due to the exceptionally complex nature of the deposition layers and the, often fragile, condition of the original artworks’ surface, requires careful selection of the irradiation parameters (i.e. laser wavelength, fluence values, number of applied pulses, pulse duration, repetition rate etc.)[3,4,5]. Residues and discoloration may be observed, if the employed fluence or the number of pulses is not adequate for the total elimination of the crust Along these lines, significant research efforts have been dedicated to the optimization of the laser parameters and the cleaning process, as well as, the monitoring of the ablation progress through micro or non-destructive analytical and diagnostic techniques
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