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Miniaturized pacemakers with a surface consisting of a Ti alloy may have to be removed after several years from their implantation site in the heart and shall, therefore, not be completely overgrown by cells or tissue. A method to avoid this may be to create at the surface by laser-ablation self-organized sharp conical spikes, which provide too little surface for cells (i.e., fibroblasts) to grow on. For this purpose, Ti-alloy substrates were irradiated in the air by 790 nm Ti:sapphire femtosecond laser pulses at fluences above the ablation threshold. The laser irradiation resulted in pronounced microstructure formation with hierarchical surface morphologies. Murine fibroblasts were seeded onto the laser-patterned surface and the coverage by cells was evaluated after 3–21 days of cultivation by means of scanning electron microscopy. Compared to flat surfaces, the cell density on the microstructures was significantly lower, the coverage was incomplete, and the cells had a clearly different morphology. The best results regarding suppression of cell growth were obtained on spike structures which were additionally electrochemically oxidized under acidic conditions. Cell cultivation with additional shear stress could reduce further the number of adherent cells.
Recent publications indicate that the order of electrochemical anodization (before or after the laser processing step) plays an important role for the response of bone-forming osteoblasts—an effect that can be utilized for improving permanent dental or removable bone implants. For exploring these different surface functionalities, multimethod morphological, structural, and chemical characterizations are performed in combination with electrochemical pre- and postanodization for two different characteristic microspikes covered by nanometric laser-induced periodic surface structures on Ti–6Al–4V upon irradiation with near-infrared ps-laser pulses (1030 nm wavelength, ≈1 ps pulse duration, 67 and 80 kHz pulse repetition frequency) at two distinct sets of laser fluence and beam scanning parameters. This work involves morphological and topographical investigations by scanning electron microscopy and white light interference microscopy, structural material examinations via X-ray diffraction, and micro-Raman spectroscopy, as well as near-surface chemical analyses by X-ray photoelectron spectroscopy and hard X-ray photoelectron spectroscopy. The results allow to qualify the mean laser ablation depth, assess the spike geometry and surface roughness parameters, and provide new detailed insights into the near-surface oxidation that may affect the different cell growth behavior for pre- or postanodized medical implants.
The exciting properties of micro- and nano-patterned surfaces found in natural species hide a virtually endless potential of technological ideas, opening new opportunities for innovation and exploitation in materials science and engineering. Due to the diversity of biomimetic surface functionalities, inspirations from natural surfaces are interesting for a broad range of applications in engineering, including phenomena of adhesion, friction, wear, lubrication, wetting phenomena, self-cleaning, antifouling, antibacterial phenomena, thermoregulation and optics. Lasers are increasingly proving to be promising tools for the precise and controlled structuring of materials at micro- and nano-scales. When ultrashort-pulsed lasers are used, the optimal interplay between laser and material parameters enables structuring down to the nanometer scale. Besides this, a unique aspect of laser processing technology is the possibility for material modifications at multiple (hierarchical) length scales, leading to the complex biomimetic micro- and nano-scale patterns, while adding a new dimension to structure optimization. This article reviews the current state of the art of laser processing methodologies, which are being used for the fabrication of bioinspired artificial surfaces to realize extraordinary wetting, optical, mechanical, and biological-active properties for numerous applications. The innovative aspect of laser functionalized biomimetic surfaces for a wide variety of current and future applications is particularly demonstrated and discussed. The article concludes with illustrating the wealth of arising possibilities and the number of new laser micro/nano fabrication approaches for obtaining complex high-resolution features, which prescribe a future where control of structures and subsequent functionalities are beyond our current imagination.
Herein, Ti6Al4V alloy is surface modified by femtosecond laser ablation. The microstructure image obtained by secondary electron microscopy reveals a combination of micrometer spikes or cones superimposed by nanoripples (laser‐induced periodic surface structures). To make the surface hydrophilic, anodization is performed resulting in further smoothness of microstructure and a final thickness of 35 ± 4 nm is estimated for oxide produced after anodization at 10 V (scan rate = 0.1 V s−1) versus standard hydrogen electrode. The obtained electrochemically active surface area (ECSA) is approximately 8 times larger compared with flat mirror polished Ti6Al4V surface. Combined chemical analysis by Pourbaix diagram and X‐ray photoelectron spectroscopy (XPS) analyses reveal that titanium and aluminum are passivating into TiO2 and Al2O3, but the dissolution of aluminum in the form of solvated ion is inevitable. Finally, cell seeding experiments on anodized and laser‐treated titanium alloy samples show that the growth of murine fibroblast cells is significantly suppressed due to unique surface texture of the laser‐treated and anodized titanium alloy sample.
Hemocompatible materials are needed for internal and extracorporeal biomedical applications, which should be realizable by reducing protein and thrombocyte adhesion to such materials. Polyethers have been demonstrated to be highly efficient in this respect on smooth surfaces. Here, we investigate the grafting of oligo- and polyglycerols to rough poly(ether imide) membranes as a polymer relevant to biomedical applications and show the reduction of protein and thrombocyte adhesion as well as thrombocyte activation. It could be demonstrated that, by performing surface grafting with oligo- and polyglycerols of relatively high polydispersity (>1.5) and several reactive groups for surface anchoring, full surface shielding can be reached, which leads to reduced protein adsorption of albumin and fibrinogen. In addition, adherent thrombocytes were not activated. This could be clearly shown by immunostaining adherent proteins and analyzing the thrombocyte covered area. The presented work provides an important strategy for the development of application relevant hemocompatible 3D structured materials.
Periodic self-organization of matter beyond the diffraction limit is a puzzling phenomenon, typical both for surface and bulk ultrashort laser processing. Here we compare the mechanisms of periodic nanostructure formation on the surface and in the bulk of fused silica. We show that volume nanogratings and surface nanoripples having subwavelength periodicity and oriented perpendicular to the laser polarization share the same electromagnetic origin. The nanostructure orientation is defined by the near-field local enhancement in the vicinity of the inhomogeneous scattering centers. The periodicity is attributed to the coherent superposition of the waves scattered at inhomogeneities. Numerical calculations also support the multipulse accumulation nature of nanogratings formation on the surface and inside fused silica. Laser surface processing by multiple laser pulses promotes the transition from the high spatial frequency perpendicularly oriented nanoripples to the low spatial frequency ripples, parallel or perpendicular to the laser polarization. The latter structures also share the electromagnetic origin, but are related to the incident field interference with the scattered far-field of rough non-metallic or transiently metallic surfaces. The characteristic ripple appearances are predicted by combined electromagnetic and thermo-mechanical approaches and supported by SEM images of the final surface morphology and by time-resolved pump-probe diffraction measurements.
Irradiation with ultra-short (femtosecond) laser beams enables the generation of sub-wavelength laser-induced periodic surface structures (LIPSS) over large areas with controlled spatial periodicity, orientation, and depths affecting only a material layer on the sub-micrometer scale. This study reports on how fs-laser irradiation of commercially available Nb foil samples affects their superconducting behavior. DC magnetization and AC susceptibility measurements at cryogenic temperatures and with magnetic fields of different amplitude and orientation are thus analyzed and reported. This study pays special attention to the surface superconducting layer that persists above the upper critical magnetic field strength Hc2, and disappears at a higher nucleation field strength Hc3. Characteristic changes were distinguished between the surface properties of the laser-irradiated samples, as compared to the corresponding reference samples (non-irradiated). Clear correlations have been observed between the surface nanostructures and the nucleation field Hc3, which depends on the relative orientation of the magnetic field and the surface patterns developed by the laser irradiation.
Effects of laser-induced periodic surface structures on the superconducting properties of Niobium
(2020)
It is well known that the use of ultrashort (fs) pulsed lasers can induce the generation of (quasi-) periodic nanostructures (LIPSS, ripples) on the surface of many materials. Such nanostructures have also been observed in sample’s surfaces irradiated with UV lasers with a pulse duration of 300 ps. In this work, we compare the characteristics of these nanostructures on 1-mm and on 25-μm thick niobium sheets induced by 30 fs n-IR and 300 ps UV pulsed lasers. In addition to conventional continuous or burst mode processing configurations, two-dimensional laser beam and line scanning modes have been investigated in this work. The latter allows the processing of large areas with a more uniform distribution of nanostructures at the surface. The influence of the generated nanostructures on the superconducting properties of niobium has also been explored. For this aim, magnetic hysteresis loops have been measured at different cryogenic temperatures to analyse how these laser treatments affect the flux pinning behaviour and, in consequence, the superconductor’s critical current values. It was observed that laser treatments are able to modify the superconducting properties of niobium samples.
This Conference Proceedings volume contains a selection of the contributions presented in Symposium C “Laser-material interactions for tailoring future applications” organized during the annual Spring Meeting of the European Materials Research Society (E-MRS) held from May 2nd to 6th 2016 in the Lille Grand Palais, France.
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.
Copolyesters with an alternating sequence of terephthalic acid and aliphatic dicarboxylic acids were prepared with three different methods. First, dicarboxylic acid dichlorides were reacted with bis(2-hydroxyethyl)terephthalate (BHET) in refluxing 1,2-dichlorobenzene. Second, the same monomers were polycondensed at 0-20 °C in the presence of pyridine. Third, dicarboxylic acid dichlorides and silylated BHET were polycondensed in bulk. Only this third method gave satisfactory molecular weights. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry revealed that the copolyesters prepared by the pyridine and silyl methods might have contained considerable fractions of cyclic oligoesters and polyesters despite the absence of transesterification and backbiting processes. The alternating sequences and thermal properties were characterized with 1H NMR spectroscopy and differential scanning calorimetry measurements, respectively. In agreement with the alternating sequence, all copolyesters proved to be crystalline, but the crystallization was extremely slow [slower than that of poly(ethylene terephthalate)]. A second series of alternating copolyesters was prepared by the polycondensation of silylated bis(4-hydroxybut- yl)terephthalate with various aliphatic dicarboxylic acid dichlorides. The resulting copolyesters showed significantly higher rates of crystallization, and the melting temperatures were higher than those of the BHET-based copolyesters. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3371-3382, 2001
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.
Damage experiments of absorbing filters (Schott BG18 and BG36) were performed with Ti:sapphire laser pulses with durations from 30 fs to 340 fs (800 nm, 1 kHz) in air. The direct focusing technique was employed under single- and multi-pulse irradiation conditions. Ablation threshold fluences were determined from a semi-logarithmic plot of the ablation crater diameter vs. laser fluence. The damage threshold fluence decreases for shorter pulse durations. In the investigated pulse duration range, the measured multi-pulse ablation threshold fluences are practically similar to those of undoped glass material (~1 Jcm-2). That means that the multi-pulse ablation threshold is independent on the doping level of the filters. For more than 100 pulses per spot and all pulse durations applied, the threshold fluence saturates. This leads to technically relevant damage threshold values in the femtosecond laser pulse duration domain.
Commercially available absorption filters (Schott BG18 and BG36) were investigated with respect to their single- and
multi-pulse ablation threshold using laser pulses from a Ti:Sapphire laser in the range between 30 and 340 fs. It could be
observed, that the threshold fluence decreases for shorter pulse durations. The similarity of the measured multi-pulse
threshold fluences with those of undoped glass material (around 1 J/cm^2 for a pulse duration of 30 fs) suggests that, for
very short pulses, the threshold is independent on the doping level and therefore, linear absorption does not significantly
contribute to laser-induced damage. For >100 pulses per spot and all pulse durations applied, the threshold fluences
saturate. This independence on the number of applied pulses leads to technically relevant damage threshold values.
KrF excimer laser ablation of polyethylene terephthalate (PET), polyimide (PI) and polycarbonate (PC) in air was studied by an in situ monitoring technique using a microphone. The microphone signal generated by a short acoustic pulse represented the etch rate of laser ablation depending on the laser fluence, i.e., the ablation strength. From a linear relationship between the microphone output voltage and the laser fluence, the single-pulse ablation thresholds were found to be 30 mJ cm-2 for PET, 37 mJ cm-2 for PI and 51 mJ cm-2 for PC (20-pulses threshold). The ablation thresholds of PET and PI were not influenced by the number of pulses per spot, while PC showed an incubation phenomenon. A microphone technique provides a simple method to determine the excimer laser ablation threshold of polymer films.
Femto- and nanosecond laser ablation of polymethylmethacrylate (PMMA) and PMMA doped with a linear absorber was
investigated in the infrared spectral region. Ablation thresholds were determined and incubation phenomena were identified. The
degree of incubation was calculated employing a phenomenological model. The influence of the pulse duration on the
machining quality of the polymers was examined. The presence of an absorbing chromophore is not a prerequisite for a
controllable fs-laser structuring in contrast to the ns-treatment. Surface swelling always accompanied ablation.
AES Depth profiling of semiconducting multilayer structures using an ion beam bevelling technique
(1997)
Ultra-short pulse laser seeding techniques for silicon crystallite growth on amorphous substrates
(1999)
Mixtures of hexamethyldisiloxane (HMDSO) and oxygen have been used for deposition of SiO2-like layers by plasma polymerization under low-pressure conditions onto polyethylene and polystyrene used as basecoat. Water glass was cast onto these 0.5 µm plasma thick siloxane-like layers with a thickness of 5 to 40 µm. The adhesion of these bilayer systems and their flame resistance were tested.
The effect of different plasma parameters such as monomer/gas ratio, pressure and power input into the discharge on the deposition rate and the composition of the formed layers was studied. Characterization and chemical composition of the formed films were performed using infrared, X-ray photoelectron and solid state nuclear magnetic resonance spectroscopy.
Peel strengths of composites were measured and the locus of peel front propagation was detected. Thermal properties of composites were analyzed by thermo-gravimetric analysis. Finally, the fire-retardant properties of thick coated polymers were determined by exposure to flames and the behavior of coatings on the polymers during flaming was observed visually.
The formation of laser-induced periodic surface structures (LIPSS) in different materials (metals, semiconductors, and dielectrics) upon irradiation with linearly polarized fs-laser pulses (τ~30–150 fs, λ~800 nm) in air environment is studied experimentally and theoretically. In metals, predominantly low-spatial-frequency-LIPSS with periods close to the laser wavelength λ are observed perpendicular to the polarization. Under specific irradiation conditions, high-spatial-frequency-LIPSS with sub-100-nm spatial periods (~λ/10) can be generated. For semiconductors, the impact of transient changes of the optical properties to the LIPSS periods is analyzed theoretically and experimentally. In dielectrics, the importance of transient excitation stages in the LIPSS formation is demonstrated experimentally using (multiple) double-fs-laser-pulse irradiation sequences. A characteristic decrease of the LIPSS periods is observed for double-pulse delays of less than 2 ps.
The formation of laser-induced periodic surface structures (LIPSS) on two different silica polymorphs (single-crystalline synthetic quartz and commercial fused silica glass) upon irradiation in air with multiple linearly polarized single- and double-fs-laser pulse sequences (τ = 150 fs pulse duration, λ = 800nm center wavelength, temporal pulse separation Δt < 40 ps) is studied experimentally and theoretically. Two distinct types of fs-LIPSS [so-called low-spatial-frequency LIPSS (LSFL) and high-spatial-frequency LIPSS (HSFL)] with different spatial periods and orientations were identified. Their appearance was characterized with respect to the experimental parameters peak laser fluence and number of laser pulses per spot. Additionally, the 'dynamics' of the LIPSS formation was addressed in complementary double-fs-pulse experiments with varying delays, revealing a characteristic change of the LSFL periods. The experimental results are interpreted on the basis of a Sipe-Drude model considering the carrier dependence of the optical properties of fs-laser excited silica. This new approach provides an explanation of the LSFL orientation parallel to the laser beam polarisation in silica—as opposed to the behaviour of most other materials.
One of the most important materials presenting and witnessing human culture is paper. The cleaning of paper is often necessary because contamination must be removed so that the fragile organic substrate can be preserved. The conventional cleaning methods are mechanical or involve the application of chemicals. These methods can damage drawings or print layers to some extent or make the original paper substrate brittle. More specifically, the use of a scalpel blade can cause damage to fibers. Chemical cleaning is difficult to perform locally, can dissolve foreign matter that then migrates into the paper substrate, or involves volatile organic compounds that can be harmful to the conservator. There is, therefore, a need for new conservation technologies aimed at the safe cleaning of paper. Lasers have proved to be an appropriate tool for cleaning as the energy dose and penetration depth at the specific point of contamination can be controlled. Additionally, if used properly, laser cleaning is not destructive to the paper.
Aufgrund des hohen Wirkungsgrades und der vielfältigen Einsatzmöglichkeiten können Brennstoffzellen einen wichtigen Beitrag zur zukünftigen Energieversorgung leisten. Für die Optimierung der Brennstoffzellentechnik ist es erforderlich, die während des Zellbetriebs ablaufenden Prozesse zu verstehen und exakt zu charakterisieren. Ein ausbalanciertes Wassermanagement ist die Grundlage für die optimale Leistungsfähigkeit einer wasserstoffbetriebenen Zelle. Das während des Betriebs entstehende Wasser muss die Membran ausreichend befeuchten, um deren Protonenleitfähigkeit aufrechtzuerhalten. Andererseits behindern zu große Wasseransammlungen in der Zelle die Gaszufuhr durch die porösen Materialien sowie in den Kanälen der Gasverteilerstrukturen. Alterungsphänomene einzelner Zellkomponenten können die Verteilung der Wasseransammlungen und somit das Wassermanagement empfindlich stören und so die Leistungsfähigkeit der Brennstoffzelle herabsetzen. Zur Analyse der Wasserverteilung werden zerstörungsfreie, bildgebende Methoden, wie die Ex-situ-Neutronentomografie und die In-situ-Synchrotronradiografie, eingesetzt. Diese Methoden können während des Brennstoffzellenbetriebs mit weiteren Messverfahren, beispielsweise der ortsaufgelösten Stromdichtemessung, kombiniert werden. Auf diese Weise werden einzelne Komponenten, wie zum Beispiel die Gasdiffusionsschichten, charakterisiert.
The formation of laser-induced periodic surface structures upon irradiation of titanium, silicon, and fused silica with multiple irradiation sequences consisting of parallel polarized Ti:sapphire femtosecond laser pulse pairs (pulse duration 50–150 fs, central wavelength ~800 nm) is studied experimentally. The temporal delay between the individual near-equal energy fs-laser pulses was varied between 0 and 5 ps with a temporal resolution of better than 0.2 ps. The surface morphology of the irradiated surface areas is characterized by means of scanning electron microscopy (SEM). In all materials a decrease of the rippled surface area is observed for increasing delays. The characteristic delay decay scale is quantified and related to material dependent excitation and energy relaxation processes.
Auf Grund des hohen Wirkungsgrades und der vielfältigen Einsatzmöglichkeiten stellen Brennstoffzellen sowie Brennstoffzellenverbünde eine vielversprechende Energiequelle dar. Daher ist es wichtig, die Prozesse während des Betriebs einer Brennstoffzelle exakt charakterisieren zu können, um diese im nächsten Schritt zu optimieren.
So ist ein ausbalanciertes Wassermanagement in einer mit Wasserstoff betriebenen Zelle ausschlaggebend für ihre Leistungsfähigkeit. Für eine dauerhafte Leistungsfähigkeit muss das entstehende Wasser die Membran feucht halten, um so die Protonenleitfähigkeit aufrecht zu erhalten. Zu viel Wasser kann jedoch die Gaszufuhr durch die porösen Materialien in Richtung Membran verhindern.
Alterungsphänomene der einzelnen Komponenten können dieses sensible Wassermanagement stören und so die Leistungsfähigkeit einer Brennstoffzelle
herabsetzen. Zum tieferen Verständnis der Wasserverteilung werden zerstörungsfreie Methoden, wie zum Beispiel die ex situ Neutronentomografie oder die in situ Synchrotronradiografie eingesetzt. Letztere Methode kann während des Brennstoffzellenbetriebs in Kombination mit weiteren Messmethoden, wie der ortsaufgelösten Stromdichtemessung, eingesetzt werden. So können einzelne Brennstoffzellenkomponenten, wie die Gasdiffusionsschichten, charakterisiert werden.
Femtosecond diffraction dynamics of laser-induced periodic surface structures on fused silica
(2013)
The formation of laser-induced periodic surface structures (LIPSS) on fused silica upon irradiation with linearly polarized fs-laser pulses (50 fs pulse duration, 800?nm center wavelength) is studied experimentally using a transillumination femtosecond time-resolved (0.1 ps-1 ns) pump-probe diffraction approach. This allows to reveal the generation dynamics of near-wavelength-sized LIPSS showing a transient diffraction at specific spatial frequencies even before a corresponding permanent surface relief was observed. The results confirm that the ultrafast energy deposition to the materials surface plays a key role and triggers subsequent physical mechanisms such as carrier scattering into self-trapped excitons.
The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of fused silica with multiple irradiation sequences of parallel polarized Ti:sapphire femtosecond laser pulse pairs (160 fs pulse duration, 800 nm central wavelength) was studied experimentally. For that purpose, a Michelson interferometer was used to generate near-equal-energy double-pulse sequences allowing the temporal pulse delay between the parallel-polarized individual fs-laser pulses to be varied between 0 and 40 ps with ~0.2 ps temporal resolution. The surface morphologies of the irradiated surface areas were characterized by means of scanning electron and scanning force microscopy. In the sub-ps delay range a strong decrease of the LIPSS periods and the ablation crater depths with the double-pulse delay was observed indicating the importance of the laser-induced free-electron plasma in the conduction band of the solids for the formation of LIPSS.
The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of fused silica and silicon with multiple (NDPS) irradiation sequences consisting of linearly polarized femtosecond laser pulse pairs (pulse duration ~150 fs, central wavelength ~800 nm) is studied experimentally. Nearly equal-energy double-pulse sequences are generated allowing the temporal pulse delay Δt between the cross-polarized individual fs-laser pulses to be varied from -40 ps to +40 ps with a resolution of ~0.2 ps. The surface morphologies of the irradiated surface areas are characterized by means of scanning electron and scanning force microscopy. Particularly for dielectrics in the sub-ps delay range striking differences in the orientation and spatial characteristics of the LIPSS can be observed. For fused silica, a significant decrease of the LIPSS spatial periods from ~790 nm towards ~550 nm is demonstrated for delay changes of less than ~2 ps. In contrast, for silicon under similar irradiation conditions, the LIPSS periods remain constant (~760 nm) for delays up to 40 ps. The results prove the impact of laser-induced electrons in the conduction band of the solid and associated transient changes of the optical properties on fs-LIPSS formation.
The formation of laser-induced periodic surface structures (LIPSS) on titanium upon irradiation with linearly polarized femtosecond (fs) laser pulses (τ = 30 fs, λ = 790 nm) in an air environment is studied experimentally and theoretically. In the experiments, the dependence on the laser fluence and the number of laser pulses per irradiation spot has been analyzed. For a moderate number of laser pulses (N < 1000) and at fluences between ~0.09 and ~0.35 J/cm², predominantly low-spatial-frequency-LIPSS with periods between 400 nm and 800 nm are observed perpendicular to the polarization. In a narrow fluence range between 0.05 and 0.09 J/cm², high-spatial-frequency-LIPSS with sub-100-nm spatial periods (~λ/10) can be generated with an orientation parallel to the polarization (N = 50). These experimental results are complemented by calculations based on a theoretical LIPSS model and compared to the present literature.
Ablation experiments employing Ti:sapphire laser pulses with durations from 30 to 340 fs (centre wavelength 800 nm, repetition rate 1 kHz) were performed in air. Absorbing filters (Schott BG18 and BG36) served as targets. The direct focusing technique was used under single- and multi-pulse irradiation conditions. Ablation threshold fluences were determined from a semi-logarithmic plot of the ablation crater diameter versus laser fluence. The threshold fluence decreases for a shorter pulse duration and an increasing number of pulses. The multi-pulse ablation threshold fluences are similar to those of undoped glass material (~1 J cm-2). That means that the multi-pulse ablation threshold is independent on the doping level of the filters. For more than 100 pulses per spot and all pulse durations applied, the threshold fluence is practically constant. This leads to technically relevant ablation threshold values.
Textile, aluminium and polyethylene used as components in laser protection curtains were investigated with respect to their ablation behaviour. Employing 33-fs pulses (800 nm wavelength, 1 kHz repetition rate), ex situ geometrical measurements of the ablation cavities and in situ acoustic investigations with a microphone were performed to determine the ablation thresholds in the single- and multi-pulse cases. The acoustical method proved advantageous for complex surface morphologies and/or single laser pulse interactions. Incubation phenomena can be observed for all the materials studied. Technically relevant multi-pulse ablation thresholds are presented and are compared with the single-pulse (1-on-1) irradiation.
Die Mikro- und Nanotechnologie gehört zu den Schlüsseltechnologien des 21. Jahrhunderts mit hohen Wachstumsprognosen, wie auch die im Auftrag des BMBF durchgeführte Studie “Nanotechnologie als wirtschaftlicher Wachstumsmarkt” von 2004 ausführlich darstellt. Aus diesem Trend resultiert ein steigender Bedarf an Messsystemen, die Nanostrukturen prozessnah bzw. im Fertigungsprozess charakterisieren können. Virtuelle Messgeräte liefern Erkenntnisse zur Entwicklung neuartiger Messsysteme, Analyse und Optimierung bestehender Verfahren sowie die Bestimmung der Messunsicherheit und modellbasierten Korrektur systematischer Fehler. Der virtuelle Messprozess umfasst neben dem Messmittel auch die Probe und die Wechselwirkungen zwischen beiden. In diesem Beitrag werden virtuelle Messgeräte vorgestellt sowie deren Anwendung diskutiert.
Results of a round-robin experiment in multiple-pulse LIDT measurement with ultrashort pulses
(2004)
Subpicosecond Emission from Mercury and Silver into Electrolyte Solution: An Experimental Study
(1997)
The influence of different laser pulse lengths on the removal of a polymer layer from metal substrates was investigated. As model systems, doped poly(methylmetacrylate) (PMMA) on titanium and tungsten substrates were selected.
The ablation threshold and irradiation spot morphology of titanium and tungsten were compared for femtosecond (fs) and nanosecond (ns) laser irradiation and different pulse numbers. Nanosecond laser treatment resulted in a non-homogeneous surface morphology for both titanium and tungsten substrates. Femtosecond irradiation of tungsten revealed a homogeneous ablation spot with little changes in the surface morphology. For titanium, the formation of columnar structures within the irradiation spot was observed.
Two different dopant concentrations were used for PMMA to achieve an equal linear absorption coefficient for the femto- and nanosecond laser wavelengths of 790 and 1064 nm. The best results were achieved for the removal of doped PMMA by femtosecond laser irradiation, where only a minimal modification of the metal surface was detected. In the case of nanosecond laser exposure, a pronounced change of the structure was observed, suggesting that damage-free cleaning of the selected metal may only be possible using femtosecond laser pulses. Different experimental parameters, such as laser fluence, pulse repetition rate and sample speed were also investigated to optimize the cleaning quality of doped PMMA from tungsten substrates with femtosecond laser pulses.