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The applicability of excimer laser at 308 nm and Nd:YAG laser at 532 nm with fluences below 0.86 J/cm2 for cleaning of cellulose and paper materials was evaluated. The extent of degradation of purified cotton cellulose and Fabriano paper after laser treatment as well as after a period of accelerated humid oven ageing was determined by following the changes in the degree of polymerization. While irradiation of paper with the excimer laser at 308 nm results in depolymerization of cellulose accompanied by a decrease in ISO brightness, no detrimental effects of Nd:YAG laser treatments were observed.
Template Electrodeposition of Nanowire Arrays on Gold Foils Fabricated by Pulsed-Laser Deposition
(1995)
A detailed diagnostic study of the interaction of nanosecond laser pulses from the near-ultraviolet into the near-infrared
wavelength range with various types of contemporary and ancient parchments is presented. The advantages of laser
cleaning due to the absence of chemical agents, spectroscopic selectivity, micro-precision, computer-aided handling can
only be verified when physico-chemical diagnostics guarantee destructionless processing. Scanning Electron Microscopy
(SEM) data are correlated with morphological changes in dependence on the laser fluence and wavelength. The
question, to what extent the chemical degradation of collagen is affected by various laser treatment parameters, could be
resolved by Transmission Electron Microscopy (TEM) of collagen fibres collected from the outermost laser-exposed
surface layer. It is also shown how Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT), and
Pyrolysis Capillary Gaschromatography (PY-CGC) can be employed in the chemical diagnostics of laser cleaning of
parchment. This study suggests that the ageing status of parchment artefacts plays a major role in assessing the laser
cleaning limits.
Laser cleaning of delicate biological composite materials such as ancient parchment manuscripts from the 15th and 16th century and printed paper from the 19th century is demonstrated with an ultraviolet excimer pulsed laser at 308 nm. Laser fluence levels must stay below the ablation and destruction threshold of the parchment or paper substrate, and have to surpass the threshold of the contaminant matter. Foreign layers to be removed must exhibit a higher optical density than the artifact substrates. Synthetic carbonaceous dirt modelled by water-soluble black crayons showed a characteristically weak featureless laser-induced plasma spectroscopy spectrum near the noise limit. It turned out that laser-induced plasma spectroscopy is of limited use in monitoring halting points (or etch-stops) because it relies on the destruction not only of the laterally inhomogenously distributed contaminant but also of pigment phases on a microscopically rough parchment substrate. Laser-induced fluorescence spectroscopy, however, promises to be a valuable non-destructive testing technique for etch-stop monitoring.
A detailed diagnostic study of the interaction of nanosecond laser pulses from the near-ultraviolet to the near-infrared wavelength range with various types of contemporary and ancient parchments is presented. The advantages of laser cleaning due to the absence of chemical agents, spectroscopic selectivity, micro-precision and computer-aided handling can only be verified when physico-chemical diagnostics guarantee destructionless processing. Scanning electron microscopy data are correlated with chemical degradation and morphological changes dependent on the laser fluence and wavelength. It is also shown how transmission electron microscopy, diffuse reflectance infrared Fourier transform spectroscopy, and pyrolysis capillary gas chromatography can be employed in the chemical diagnostics of laser cleaning of parchment. This study suggests that the ageing status of parchment artefacts plays a major role in assessing the laser cleaning limits.