TY - JOUR A1 - Kunz, C. A1 - Bonse, Jörn A1 - Spaltmann, Dirk A1 - Neumann, C. A1 - Turchanin, A. A1 - Bartolomé, J. F. A1 - Müller, F. A. A1 - Gräf, S. T1 - Tribological performance of metal-reinforced ceramic composites selectively structured with femtosecond laser-induced periodic surface structures N2 - The impact of femtosecond (fs) laser-induced periodic surface structures (LIPSS) on tribological properties was investigated for metal-reinforced ceramic composites (Al2O3-ZrO2-Nb). For this purpose, the metallic niobium (Nb) phase was selectively structured with LIPSS in an air environment with different values of the fs-laser peak fluence by near-infrared fs-laser radiation (λ = 1025 nm, τ = 300 fs, frep = 1 kHz), taking advantage of the different light absorption behavior of ceramic and metal. The tribological performance was evaluated by reciprocating sliding tests in a ball-on-disc configuration using Ringer's solution as lubricant. The surfaces were characterized before and after laser irradiation by optical microscopy, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy and by measuring the contact angle with Ringer's solution. The LIPSS formation resulted in an increased wetting of the surface with the lubricant. Moreover, the selectively structured composite surfaces revealed a coefficient of friction significantly reduced by a factor of ~3 when compared to the non-irradiated surface. Furthermore, the formation of a laser-induced oxidation layer was detected with NbO as the most prominent oxidation state. Selectively structured composites with outstanding mechanical properties and enhanced tribological performance are of particular interest for biomedical applications. KW - Laser-induced periodic surface structures (LIPSS) KW - Femtosecond laser ablation KW - Ceramic matrix composites KW - Tribology PY - 2020 DO - https://doi.org/10.1016/j.apsusc.2019.143917 SN - 0169-4332 SN - 1873-5584 VL - 499 IS - 1 SP - 143917 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-49255 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Höhm, S. A1 - Koter, Robert A1 - Hartelt, Manfred A1 - Spaltmann, Dirk A1 - Pentzien, Simone A1 - Rosenfeld, A. A1 - Krüger, Jörg T1 - Tribological performance of sub-100-nm femtosecond laser-induced periodic surface structures on titanium N2 - Sub-100-nm laser-induced periodic surface structures (LIPSS) were processed on bulk titanium (Ti) surfaces by femtosecond laser pulse irradiation in air (30 fs pulse duration, 790 nm wavelength). The laser peak fluence, the spatial spot overlap, and the number of overscans were optimized in a sample-scanning geometry in order to obtain large surface areas (5 mm × 5 mm) covered homogeneously by the LIPSS. The laser-processed regions were characterized by optical microscopy (OM), white light interference microscopy (WLIM) and scanning electron microscopy (SEM). The friction coefficient of the nanostructured surfaces was tested during 1000 cycles under reciprocal sliding conditions (1 Hz, 1.0 N normal load) against a 10-mm diameter ball of hardened 100Cr6 steel, both in paraffin oil and in engine oil used as lubricants. Subsequently, the corresponding wear tracks were qualified by OM, SEM, and energy dispersive X-ray analyses (EDX). The results of the tribological tests are discussed and compared to that obtained for near wavelength-sized fs-LIPSS, processed under somewhat different irradiation conditions. Some constraints for a beneficial effect of LIPSS on the tribological performance are provided. KW - Femtosecond laser ablation KW - Laser-induced periodic surface structures, LIPSS KW - Friction KW - Wear KW - Nanostructures KW - Surface functionalization PY - 2016 UR - http://www.sciencedirect.com/science/article/pii/S0169433215026987 DO - https://doi.org/10.1016/j.apsusc.2015.11.019 SN - 0169-4332 SN - 1873-5584 VL - 374 SP - 190 EP - 196 PB - Elsevier B.V. CY - Amsterdam, Netherlands AN - OPUS4-35937 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kirner, Sabrina V. A1 - Slachciak, Nadine A1 - Elert, Anna Maria A1 - Griepentrog, Michael A1 - Fischer, Daniel A1 - Hertwig, Andreas A1 - Sahre, Mario A1 - Dörfel, Ilona A1 - Sturm, Heinz A1 - Pentzien, Simone A1 - Koter, Robert A1 - Spaltmann, Dirk A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Tribological performance of titanium samples oxidized by fs-laser radiation, thermal heating, or electrochemical anodization N2 - Commercial grade-1 titanium samples (Ti, 99.6%) were treated using three alternative methods, (i) femtosecond laser processing, (ii) thermal heat treatment, and (iii) electrochemical anodization, respectively, resulting in the formation of differently conditioned superficial titanium oxide layers. The laser processing (i) was carried out by a Ti:sapphire laser (pulse duration 30 fs, central wavelength 790 nm, pulse repetition rate 1 kHz) in a regime of generating laser-induced periodic surface structures (LIPSS). The experimental conditions (laser fluence, spatial spot overlap) were optimized in a sample-scanning setup for the processing of several square-millimeters large surface areas covered homogeneously by these nanostructures. The differently oxidized titanium surfaces were characterized by optical microscopy, micro Raman spectroscopy, variable angle spectroscopic ellipsometry, and instrumented indentation testing. The tribological performance was characterized in the regime of mixed friction by reciprocating sliding tests against a sphere of hardened steel in fully formulated engine oil as lubricant. The specific tribological performance of the differently treated surfaces is discussed with respect to possible physical and chemical mechanisms. KW - Femtosecond laser KW - Titanium KW - Oxidation KW - Friction PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-445609 DO - https://doi.org/10.1007/s00339-018-1745-8 SN - 0947-8396 SN - 1432-0630 VL - 124 IS - 4 SP - 326, 1 EP - 10 PB - Springer-Verlag AN - OPUS4-44560 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Abere, M. J. A1 - Zhong, M. A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Ultrafast laser-induced morphological transformations N2 - Ultrafast laser processing can be used to realize various morphological surface transformations, ranging from direct contour shaping to large-area-surface functionalization via the generation of “self-ordered” micro- and nanostructures as well as their hierarchical hybrids. Irradiation with high-intensity laser pulses excites materials into extreme conditions, which then return to equilibrium through these unique surface transformations. In combination with suitable top-down or bottom-up manufacturing strategies, such laser-tailored surface morphologies open up new avenues toward the control of optical, chemical, and mechanical surface properties, featuring various technical applications especially in the fields of photovoltaics, tribology, and medicine. This article reviews recent efforts in the fundamental understanding of the formation of laser-induced surface micro- and nanostructures and discusses some of their emerging capabilities. KW - Laser ablation KW - Laser-induced periodic surface structures (LIPSS) KW - Surface morphology KW - Oxidation KW - Tribology PY - 2016 DO - https://doi.org/10.1557/mrs.2016.271 SN - 0883-7694 SN - 1938-1425 VL - 41 IS - 12 SP - 969 EP - 974 PB - Cambride University Press AN - OPUS4-38637 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Baudach, Steffen A1 - Bonse, Jörn A1 - Krüger, Jörg A1 - Kautek, Wolfgang T1 - Ultrashort pulse laser ablation of polycarbonate and polymethylmethacrylate N2 - Ablation experiments with ultrashort laser pulses (pulse duration 150 fs, wavelength 800 nm) on polymers (PC, PMMA) relevant for biomedical technology have been performed in air. The lateral and vertical machining precision was evaluated by optical, atomic force and scanning electron microscopy. The ablation threshold reaches values in the range of 0.5–2.5 J/cm2 and depends significantly on the number of laser pulses applied to the same spot. The hole diameters are influenced by the laser fluence and the number of laser pulses. The relation between the ablation threshold and the number of laser pulses applied to the same spot is described in accordance with an incubation model. KW - Femtosecond laser ablation KW - Polymer KW - Polycarbonate KW - Polymethylmethacrylate PY - 2000 DO - https://doi.org/10.1016/S0169-4332(99)00474-2 SN - 0169-4332 SN - 1873-5584 VL - 154-155 SP - 555 EP - 560 PB - North-Holland CY - Amsterdam AN - OPUS4-803 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Wrobel, Jerzy A1 - Krüger, Jörg A1 - Kautek, Wolfgang T1 - Ultrashort-pulse laser ablation of indium phosphide in air N2 - Ablation of indium phosphide wafers in air was performed with low repetition rate ultrashort laser pulses (130 fs, 10 Hz) of 800 nm wavelength. The relationships between the dimensions of the craters and the ablation parameters were analyzed. The ablation threshold fluence depends on the number of pulses applied to the same spot. The single-pulse ablation threshold value was estimated to be fth(1)=0.16 J/cm2. The dependence of the threshold fluence on the number of laser pulses indicates an incubation effect. Morphological and chemical changes of the ablated regions were characterized by means of scanning electron microscopy and Auger electron spectroscopy. PY - 2001 DO - https://doi.org/10.1007/s003390000596 SN - 0947-8396 VL - 72 IS - 1 SP - 89 EP - 94 PB - Springer CY - Berlin AN - OPUS4-1068 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Böttcher, Katrin A1 - Schmitt Rahner, M. A1 - Stolzenberg, U. A1 - Kraft, Sebastian A1 - Bonse, Jörn A1 - Feist, C. A1 - Albrecht, D. A1 - Pullner, B. A1 - Krüger, Jörg T1 - Worst-case X-ray photon energies in ultrashort pulse laser processing N2 - Ultrashort pulse laser processing can result in the secondary generation of unwanted X-rays if a critical laser irradiance of about 10^13 W/cm^2 is exceeded. Spectral X-ray emissions were investigated during the processing of tungsten and steel using three complementary spectrometers (based on CdTe and silicon drift detectors) simultaneously for the identification of a worst-case spectral scenario. Therefore, maximum X-ray photon energies were determined, and corresponding dose equivalent rates were calculated. An ultrashort pulse laser workstation with a pulse duration of 274 fs, a center wavelength of 1030 nm, pulse repetition rates between 50 kHz and 200 kHz, and a Gaussian laser beam focused to a spot diameter of 33 µm was employed in a single pulse and burst laser operation mode. Different combinations of laser pulse energy and repetition rate were utilized, keeping the average laser power constant close to the maximum power of 20 W. Peak irradiances ranging from 7.3 × 10^13 W/cm^2 up to 3.0 × 10^14 W/cm^2 were used. The X-ray dose equivalent rate increases for lower repetition rates and higher pulse energy if a constant average power is used. Laser processing with burst mode significantly increases the dose rates and the X-ray photon energies. A maximum X-ray photon energy of about 40 keV was observed for burst mode processing of tungsten with a repetition rate of 50 kHz and a peak irradiance of 3 × 10^14 W/cm^2. KW - Ultrashort pulsed laser KW - X-ray emission KW - X-ray spectrum KW - X-ray energies KW - Radiation protection PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-566176 DO - https://doi.org/10.3390/ma15248996 VL - 15 IS - 24 SP - 1 EP - 17 PB - MDPI AN - OPUS4-56617 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Legall, Herbert A1 - Schwanke, Christoph A1 - Pentzien, Simone A1 - Dittmar, G. A1 - Bonse, Jörn A1 - Krüger, Jörg T1 - X-ray emission as a potential hazard during ultrashort pulse laser material processing N2 - In laser machining with ultrashort laser pulses unwanted X-ray radiation in the keV range can be generated when a critical laser intensity is exceeded. Even if the emitted X-ray dose per pulse is low, high laser repetition rates can lead to an accumulation of X-ray doses beyond exposure safety limits. For 925 fs pulse duration at a center wavelength of 1030 nm, the X-ray emission was investigated up to an intensity of 2.6 × 10^14 W/cm2. The experiments were performed in air with a thin disk laser at a repetition rate of 400 kHz. X-ray spectra and doses were measured for various planar target materials covering a wide range of the periodic table from aluminum to tungsten. Without radiation shielding, the measured radiation doses at this high repetition rate clearly exceed the regulatory limits. Estimations for an adequate radiation shielding are provided. KW - Laser-induced X-ray emission KW - Ultrashort laser material interaction KW - Femtosecond laser KW - Radiation protection PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-448431 DO - https://doi.org/10.1007/s00339-018-1828-6 SN - 0947-8396 SN - 1432-0630 VL - 124 IS - 6 SP - Article 407, 1 EP - 8 PB - Springer AN - OPUS4-44843 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Böttcher, Katrin A1 - Kraft, Sebastian A1 - Weise, Matthias A1 - Bonse, Jörn A1 - Krüger, Jörg T1 - X-ray emission during ultrafast laser grooving N2 - Ultrashort pulse lasers offer the possibility to process materials with minimal heat input and high precision. However, the X-ray emission at high laser peak intensities represents an undesirable side effect. A laser system (1030 nm wavelength, 40 W maximum average laser power, 925 fs pulse duration, 100 μJ maximum pulse energy, 400 kHz pulse repetition frequency) was used to analyze the X-ray skin dose rates for applied peak intensities between 9.2 × 10^12 W/cm^2 and 1.3 × 10^14 W/cm^2 for mild steel, stainless steel and tungsten during groove processing. The lowest laser peak intensity at which X-ray emission could be measured was 9.2 × 10^12 W/cm^2 for processing of stainless steel. The X-ray emission showed a characteristic evolution in dependence on the number of overscans at the same line positions. For low peak intensities, a measurable X-ray emission only begins after a few passes. The number of scans to reach the maximum dose rate increases with lower laser peak intensity. Analysis of the evolving surface topography by white light interference microscopy in connection with ray-tracing simulations led to the interpretation that the increase in X-ray emission is due to the local intensity redistribution by multiple reflection within the laser-generated grooves which is promoted by a particular choice of the linear laser polarization. KW - Ultrashort pulsed laser KW - Laser-induced X-rays KW - X-ray hazard KW - X-ray emission PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-639483 DO - https://doi.org/10.1007/s00339-025-08728-z SN - 1432-0630 VL - 131 IS - 8 SP - 1 EP - 12 PB - Springer CY - Berlin AN - OPUS4-63948 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Legall, Herbert A1 - Schwanke, Christoph A1 - Bonse, Jörn A1 - Krüger, Jörg T1 - X-ray emission during ultrashort pulse laser processing N2 - The industrial use of ultrashort laser pulses has made considerable progress in recent years. The reasons for this lie in the availability of high average powers at pulse repetition rates in the several 100 kHz range. The advantages of using ultrashort laser pulses in terms of processing precision can thus be fully exploited. However, high laser intensities on the workpiece can also lead to the generation of unwanted X-rays. Even if the emitted X-ray dose per pulse is low, the accumulated X-ray dose can become significant for high-repetition-rate laser systems so that X-ray exposure safety limits must be considered. The X-ray emission during ultrashort pulse laser processing was investigated for a pulse duration of 925 fs at 1030 nm wavelength and 400 kHz repetition rate. Industrially relevant materials such as steel,aluminum and glass were treated. Tungsten served as reference. X-ray spectra were recorded, and X-ray dose measurements were performed for laser treatment in air. For laser intensities > 2 × 10^13 W/cm2, X-ray doses exceeding the regulatory exposure limits for members of the public were found. Suitable X-ray protection strategies are proposed. T2 - SPIE Photonics West CY - San Francisco, USA DA - 02.02.2019 KW - Laser-induced X-ray emission KW - Ultrashort laser material interaction KW - Radiation protection PY - 2019 SN - 978-1-5106-2459-7 DO - https://doi.org/10.1117/12.2516165 SN - 0277-786X SN - 1996-756X VL - 10908 SP - 1090802-1 EP - 1090802-7 PB - SPIE - The international society for optics and photonics CY - Bellingham, WA, USA AN - OPUS4-47510 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -