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Paper des Monats
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Zusammenfassung
The surface chemical modification of polyurethane (PU) films was performed by an UV laser-induced chemical reaction in a polysaccharide solution. This process may be applicable as hydrophilic packaging of implantable medical devices and in vivo sensors. When a PU film in contact with an aqueous alginic acid (AAC) solution was irradiated with a XeCl laser, the PU film turned hydrophilic. Contact angles of water on the film were reduced from 110° to 60°. Since light absorption of the AAC solution at 308 nm was negligibly small, reactive sites were generated solely on the PU surface. There, AAC could be immobilized by chemical bonds thus allowing for a nanometer-scaled grafting of this biomolecule. The mechanism was investigated by surface analyses with Fourier-transform infrared spectroscopy (FT-IR), dye staining, ultraviolet-visible (UV-VIS) spectroscopy, and scanning electron microscopy (SEM) techniques. A one-photon photochemical process could beidentified.
Optical filters and fabrics are important parts of laser safety equipment such as goggles and curtains. A choice of these materials with varying absorption spectra is investigated with respect to their resistance to Ti:sapphire femtosecond laser radiation (800 nm wavelength, 1 kHz repetition rate). Pulse durations down to 30 fs and multiple-pulse irradiation conditions are employed to evaluate technically relevant damage thresholds. The ablation threshold fluences of the absorbing filters are comparable to those observed for transparent materials with 30-fs-pulses. These investigations together with scanning electron microscopy of the surface morphology after laser treatment provide insight into the interaction mechanism of the short pulses with the materials.
The removal and accelerated corrosion monitoring of metal coating systems is of general interest in materials science
and engineering technology. The femtosecond and nanosecond laser ablation and delamination at 800 nm and 532 nm,
respectively, of anodic oxide layers on aluminium alloys in electrolyte contact were investigated. Laser-induced
modifications of the oxide layer resulted in an ionic contact between electrolyte and metal, which produced a current
transient and thus allowed the in-situ electrochemical monitoring of the modification. Oxide coatings with different
optical properties, almost transparent and opaque, were examined. The transparent anodic oxides showed contrasting
ablation mechanisms in the nanosecond and femtosecond pulse duration regime: nanosecond pulses caused spallation,
whereas femtosecond treatment led to ablation. Current signals measured in the transparent film were consistent with
light absorption below the metal-oxide interface and with film spallation. Irradiation of the opaque coating yielded ionic
current transients within the so-called shock-affected-zone of the oxide layer. This investigation provided insight into the
role of the penetration depth of light and the heat-affected zone, the extent of the shock-affected zone, and the defect
formation in the coating and at the solid-solid interface between metal and oxide.
Zusammenfassung
Laser pulses in the 10-fs domain provide a quality of micromachining of fused silica and borosilicate glass that is unobtainable with longer pulses in the range of several 100 femtoseconds up to picoseconds. The shortening of the pulses reduces the statistical behavior of the material removal and the ablation process thus attains a more deterministic and reproducible character. The improved reproducibility of ablation is accompanied by significantly smoother morphology. This offers the potential for lateral and vertical machining precision of the order of 100 nm and 10 nm, respectively.
Abstract Femtosecond laser micromachining has excited vivid attention in various industri-
al fields and in medicine owing to the advantages of ultrashort laser pulses compared to
long-pulse treatment.These are mainly the reduction of the laser fluence needed to induce
ablation and the improvement of the contour sharpness of the laser-generated structures.
Recently,special attention was paid to femtosecond laser experiments on nonabsorbing in-
organic dielectrics.This is due to the fact that optical damage in dielectric optical elements
limits the performance of high-power laser systems.Despite the fact that a large variety of
organic polymers can be machined with excimer lasers successfully,the involvement of
thermal processes can lead to an unsatisfactory quality of the structures.Ultrashort,fs-laser
pulses might be an alternative for the treatment of polymers.Therefore,femtosecond laser
machining investigations of dielectrics and polymers are reviewed in this paper.Similarities
and differences of the ablation behavior of both material classes are discussed.The influ-
ence of the bandgap on the ablation threshold in dependence on the pulse duration,the en-
hancement of the machining precision with a shortening of the pulse duration,incubation
phenomena,and morphological features appearing on the surface after femtosecond laser
treatment are mentioned.Possible applications,e.g.,in medicine and biosensors,are de-
scribed.