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- Bariumalumoborosilicate glass (1)
- Bariumalumoborosilicate glass surfaces (1)
- Ceramics (1)
- Femtosecond laser ablation (1)
- Femtosecond techniques (1)
- Laser (1)
- Laser ablation (1)
- Laser cleaning (1)
- Nanosecond techniques (1)
- Optical properties (1)
We present surface micro-modifications of bariumalumoborosilicate glasses with a high transformation temperature near 700 °C. Laser processing of the glass substrate was realized by using ultra-short laser pulses at 800 nm. The morphological conversion of the laser-treated surfaces was characterized by scanning force microscopy and nano-indentation. A hardness increase by at least a factor of six on the laser ablation crater edge relative to illuminated non- ablated areas shows that the material in the crater walls underwent drastic morphological and mechanical changes. In this heat- and shock-affected zone, the material became more elastic as a result of increased stress.
The interaction of nanosecond laser pulses in the ultraviolet wavelength range and femtosecond laser pulses in the near-infrared region with the semiconductor SiC and the composite compound SiCTiCTiB2 was investigated. Surface analytical techniques, such as XPS, depth profile (DP), and micro-Raman spectroscopy (?-RS) were used to identify the chemical changes between untreated and laser-treated areas. Single-pulse irradiation led to material modifications in the condensed state in most instances. Multi-pulse results differed depending on the pulse duration. Crystal structure changes were observed as a consequence of laser-induced melting and resolidification. In air contact all components underwent oxidation reactions according to thermodynamic expectations. Exceptions were observed under exclusion of oxygen, SiC was reduced to elemental Si.
Near-ablation threshold investigations focusing on the generation of periodic nanostructures and their correlation with physico-chemical
properties of the solid phase such as e.g., the material-dependent surface energy, were conducted. Molecular dynamic modelling in the
sub-picosecond time domain was used to consider ultrafast opto-electronic processes triggering surface reorganization reactions.
Fluid containment of solid interfaces showed strong influence on the resulting micro- and nanostructures due to its drastic reduction of the
surface energy. The phenomena are discussed in respect to the minimization of the surface free energy in dependence of material composition
and interfacial structure.
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.
Ultrashort pulse laser microstructuring (pulse duration 130 fs, wavelength 800 nm, repetition rate 2 Hz) of titanium nitride (TiN) films on silicon substrates was performed in air using the direct focusing technique. The lateral and vertical precision of laser ablation was evaluated. The TiN ablation threshold changed with the number of pulses applied to the surface due to an incubation effect. An ablation depth per pulse below the penetration depth of light was observed. Columnar structures were formed in the silicon substrate after drilling through the TiN layer.
Laser ablation with femtosecond pulses (130 fs, wavelength 800 nm, repetition rate 2 Hz) was compared with nanosecond-pulse ablation (10 ns, wavelength 266 nm, repetition rate 2.5 Hz) of bariumalumoborosilicate glass in air using the direct focusing technique. Different ablation thresholds and heat-affected zones were observed. The lateral and vertical machining precision was evaluated. Single nanosecond laser pulses in the far UV resulted in a bubble or a circular hole in the centre of the illuminated spot, depending on the applied fluence. The ablation behaviour in the case of near-IR femtosecond pulses contrasted to this. Bubble formation was not detected. It needed repeated pulses at the same spot to modify the surface until material removal could be observed (incubation). Cavity dimensions of less than the beam diameter were achieved in this case.