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- Femtosecond laser (4)
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The influence of paper type and state of degradation on laser cleaning of artificially soiled paper
(2011)
Lasers can be a supplemental tool for restorers to overcome some of the limitations of traditional dry cleaning techniques for works of art on paper. The laser working range has to be optimized allowing for safe removal of contamination and limitation of damage to the substrate. This paper addresses the influence of paper type and state of degradation on laser working range. Three types of new paper (pure cellulose, bleached pulp paper, rag paper) were degraded and characterized with respect their degree of polymerization. Laser-induced damage thresholds of new and degraded paper were determined using SEM and viscometry. Additionally, artificially soiled model samples were made using two kinds of soiling, namely pulverized charcoal and soot-blackened standard test dust. Cleaning thresholds of soiled paper samples were evaluated. A working range for all combinations of paper and soiling between 0.05 J/cm2 and 0.5 J/cm2 was found for the application of 8-ns laser pulses at 532 nm wavelength.
Laser cleaning of soiled paper is a challenging task due to the fact that a contamination has to be removed and a fragile organic material has to be preserved. The ejection of particles forms a significant channel for the removal of unwanted surface contaminations and can be exploited for an in-situ monitoring of the cleaning procedure. 532-nm-nanosecond single and multi pulse laser cleaning of artificially soiled Whatman© paper was performed. Particles were registered with a dust monitor. These in-situ experiments were combined with ex-situ investigations of cleaning and substrate damage thresholds by means of light and scanning electron microscopic techniques. The cleaning efficiency measured by a multi-spectral imaging system was compared to the in-situ particle monitoring. Additionally, possible color changes of the paper substrate were evaluated.
Laser cleaning for works of art on paper might be a supplemental, noncontact method to overcome some of the limitations of traditional dry cleaning techniques. Three different types of paper (pure-cellulose filter paper, rag paper, and wood-pulp paper) were mechanically soiled with pulverized charcoal in a standardized procedure to make model samples. These samples were characterized microscopically and by means of lightness measurements using a multi-spectral imaging system. A prototype laser workstation with Laser Class I conditions for the operator was used for the cleaning experiments. For 10-ns laser pulses at a wavelength of 532 nm, a set of laser parameters was established for a successful cleaning of the samples avoiding damage to the paper substrate. Single- and multi-pulse illumination conditions were tested. An extensive microscopic analysis after laser treatment of the cleaned parts of the samples provided insight into the remaining soiling on the surface and in the bulk of the paper material.
In situ FTIR spectroscopy of the Zn-Br battery bromine storage complex at glassy carbon electrodes
(2000)
Noble metal-free nanoparticles (NPs) based on multi-principal element alloys (MPEAs) were synthesized using a one-step pulsed laser ablation in liquids (PLALs) method for the electrochemical reduction of CO2. Laser ablation was performed in pure water or poly-(diallyldimethylammonium chloride) (PDADMAC)-containing an aqueous solution of Al8Cr17Co17Cu8Fe17Ni33 MPEA targets. Transmission electron microscopy (TEM) measurements combined with energy dispersive X-ray (EDX) mapping were used to characterize the structure and composition of the laser-generated MPEA nanoparticles (MPEA-NPs). These results confirmed the presence of a characteristic elemental distribution of a core-shell phase structure as the predominant NP species. The electrocatalytic performance of the laser-generated MPEA-NPs was characterized by linear sweep voltammetry (LSV) demonstrating an enhanced electrocatalytic CO2 activity for PDADMAC-stabilized NPs. The findings of these investigations indicate that MPEAs have great potential to replace conventional, expensive noble metal electrocatalysts.
Noble metal-free nanoparticles (NPs) based on multi-principal element alloys (MPEAs) were synthesized using a one-step pulsed laser ablation in liquids (PLALs) method for the electrochemical reduction of CO2. Laser ablation was performed in pure water or poly-(diallyldimethylammonium chloride) (PDADMAC)-containing an aqueous solution of Al8Cr17Co17Cu8Fe17Ni33 MPEA targets. Transmission electron microscopy (TEM) measurements combined with energy dispersive X-ray (EDX) mapping were used to characterize the structure and composition of the laser-generated MPEA nanoparticles (MPEA-NPs). These results confirmed the presence of a characteristic elemental distribution of a core-shell phase structure as the predominant NP species. The electrocatalytic performance of the laser-generated MPEA-NPs was characterized by linear sweep voltammetry (LSV) demonstrating an enhanced electrocatalytic CO2 activity for PDADMAC-stabilized NPs. The findings of these investigations indicate that MPEAs have great potential to replace conventional, expensive noble metal electrocatalysts.
Until the end of the 1980s many wooden artworks underwent surface treatment by liquid preservatives, e.g. Hylotox-59. DDT (dichlorodiphenyltrichloroethane) crystal structures are formed on the wooden surfaces by the "blooming" of chlorine compounds by time. In addition to an aesthetic disturbance, it is assumed that DDT represents a health risk. Therefore, the removal of DDT crystals from the surfaces is requested. Contaminated wood with natural biocide ageing, gilded and wood carved elements and wooden samples with paint layers were provided by the Schlossmuseum Sondershausen, Germany. Laser cleaning on selected surface areas on the objects was done by means of femtosecond and nanosecond laser pulses. For the same object, cleaning results using 30-fs laser pulses at 800 nm wavelength are compared to findings utilizing 10-ns laser pulses at 1064 nm wavelength. Before and after laser treatment, chlorine measurements at the same surface position were done by X-ray fluorescence analysis (XRF) as an indicator for the presence of DDT. In this way, pointwise chlorine depletion rates can be obtained for the different pulse duration regimes and wavelengths. Additionally, the object surfaces were examined using optical microscopy and multi spectral imaging analysis.