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- Zeitschriftenartikel (19) (entfernen)
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- Laser cleaning (5)
- Femtosecond laser (4)
- Friction (3)
- Femtosecond laser ablation (2)
- Laser-induced periodic surface structures (LIPSS) (2)
- Paper (2)
- Wear (2)
- Ablation (1)
- Ancient manuscripts (1)
- Bor (1)
- Central Asia (1)
- Colorimetry (1)
- DDT (1)
- Decontamination (1)
- Defect model (1)
- Dünnfilm, diamantartig (1)
- Dünnfilmtechnologie (1)
- Femtosecond laser processing (1)
- Fused silica (1)
- Image enhancement (1)
- Image restoration (1)
- Laser (1)
- Laser impact on surfaces (1)
- Laser-induced X-ray emission (1)
- Laser-induced damage threshold (1)
- Laser-induced periodic surface structures, LIPSS (1)
- Metals (1)
- Microscopy (1)
- Multispectral imaging (1)
- Nanosecond laser (1)
- Nanostructures (1)
- Optical fiber (1)
- Oxidation (1)
- Papery (1)
- Parchment (1)
- Pigments (1)
- Pulslaser (1)
- Radiation protection (1)
- Silk Road (1)
- Spectroscopy (1)
- Spot size (1)
- Surface functionalization (1)
- Titanium (1)
- Titanium nitride films (1)
- Tribology (1)
- Ultrashort laser material interaction (1)
- Wall paintings (1)
- Wood (1)
Organisationseinheit der BAM
Single-pulse damage thresholds of hydrogenated amorphous carbon (a-C:H) films were measured for 8-ns laser pulses at 532-nm wavelength. Layer thicknesses from below the optical penetration depth to above the thermal diffusion length (60 nm13 µm) were examined. After correction of the damage-threshold values for the fraction of energy effectively absorbed by the material, the damage threshold was found to increase linearly with the layer thickness, also for film thicknesses below the optical penetration depth of a-C:H. The threshold fluence reached the bulk value for a layer thickness equal to the thermal diffusion length. The thermal diffusion coefficient was obtained from fitting the experimental data. Several phenomena like graphitization, blistering, exfoliation, and ablation were observed for different fluence regimes and film thicknesses.
Optical fibers made of fused silica are a common method of transmitting high laser pulse energies. Failure of those fibers is a significant risk. The determination of laser-induced damage thresholds (LIDT) on fiber end facets according to ISO 21254 standard is needed. In the past, single pulse nanosecond laser experiments showed an improvement of LIDT with increasing fiber core diameter for 1064 nm wavelength and a constant beam diameter of 50 µm.
This paper pays particular attention to the influence of the laser beam diameter on damage resistance. All-silica fiber types (LEONI) with different core diameters (100–600 µm) were investigated using beam diameters in a range from 30 µm to 100 µm. For comparison experiments on fused silica preform material (Heraeus F300) were performed. On one hand, surface LIDT of fused silica preform material decreases significantly with increasing beam size. A model considering a random distribution of point defects explains the experimental data qualitatively. On the other hand, LIDT of fiber end facets stays constant. White light microscopy results suggest that the point defect density on fiber end facets is lower compared to the preform surface due to an excellent surface polish quality.
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.
Analyse häufig verwendeter europäischer Papiere. Im Fokus: Fasermaterial, Füllstoffe und Leimung
(2007)
Restauratoren können verschiedene Papierarten mit dem bloßen Auge aufgrund von Merkmalen in der Textur und der Oberflächenbeschaffenheit, seinem Aussehen im Durchlicht sowie an Griff und Klang grob unterscheiden. Dabei ist sich der Restaurator stets der Tatsache bewusst, dass es sich lediglich um eine erste grobe Einschätzung handeln kann. Erst bei mikroskopischen Analysen und physikalischen Experimenten treten Charakteristika zu Tage, die eine weitere Annäherung an die Zusammensetzung des Papiers und damit seiner Provenienz erlauben. Gegenstand dieser Arbeit war es, ein europäisches Hadernpapier, ein holzhaltiges Zeichenpapier und ein Whatman®-Filterpapier mit zwei mikroskopischen Methoden und einer Verbrennungstechnik zu untersuchen. Das Fasermaterial, die Füllstoffe, die Leimung und eventuelle Verunreinigungen wurden detailliert evaluiert. Neben konventioneller Lichtmikroskopie kam die weniger bekannte Umweltrasterelektronenmikroskopie (ESEM = Environmental Scanning Electron Microscopy) zum Einsatz, die neben der bildlichen Darstellung der Probenoberflächen zusätzlich eine Elementanalyse derselben gestattet. Letzteres erfordert allerdings das Vorhandensein eines zusätzlichen Röntgenspektrometers. Darüber hinaus wurden die verschiedenen Papiere trocken verascht. Es wurde eine oxidative Zerstörung der organischen Stoffe gewährleistet bis nur noch nichtbrennbare mineralische Asche zu verzeichnen war. Die Komplementarität der eingesetzten Methoden wird demonstriert und ein Einblick in die Zusammensetzung und Struktur der Papiere ermöglicht. Die Analysemethoden sind durch ihren partiell zerstörenden Charakter bzw. Limitierungen hinsichtlich der Objektgröße nur bedingt für die Untersuchung am Original geeignet, sehr wohl aber dafür, das Probenmaterial für Versuchsreihen genau zu definieren und zu standardisieren.
Characterization of laser-generated microparticles by means of a dust monitor and SEM imaging
(2006)
Nanosecond laser (1064 nm wavelength) cleaning of artificially soiled paper as a model sample simulating a real-world artwork was performed. During the cleaning process, the ejection of particles was monitored in situ by means of a dust monitor (8 size classes, ranging from 0.3 µm to >2 µm) and ex situ using a mini-cascade impactor (MKI, 5 stages). The cleaning result was analyzed by scanning electron microscopy (SEM) considering possible laser-induced damages to the substrate. Size distributions of emitted particles were measured depending on the processing parameters: laser fluence, F, and pulse number per spot, N. High numbers of large (>2 µm) particles were collected by the mini-cascade impactor indicating a gas dynamical liftoff process. Obviously, these particles were not affected by the laser-matter interaction. The different methods (SEM, MKI, and dust monitor) are compared with respect to their usefulness for a proper interpretation of the cleaning results.
Cleaning of paper is a challenging task due to the fact that a contamination should be removed and a fragile organic original material has to be preserved. Pulsed laser cleaning of artificially soiled Whatman© filter paper samples serving as models for historical paper was performed. Different cleaning strategies employing 8-ns laser pulses at 532 nm wavelength were applied to clean paper avoiding undesired effects like discoloration (yellowing) and mechanical deterioration of the substrate. Multi shot experiments with low-energy pulses were compared with single pulse investigations utilizing high pulse energies achieving a constant energy load incident on the samples in both cases. The cleaning efficiency and possible yellowing effects were evaluated by means of a multi spectral imaging system. An extensive microscopic analysis of the cleaned parts of the samples provided insight into the remaining soiling on the surface and in the bulk of the paper material after laser treatment. As a reference, a hard and a soft eraser were used to clean the samples.