TY - JOUR A1 - Krüger, Jörg A1 - Kautek, Wolfgang A1 - Niino, H. T1 - Biomaterial immobilization on polyurethane films by XeCl excimer laser processing JF - Applied physics A N2 - 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. PY - 2001 DO - https://doi.org/10.1007/s003390000617 SN - 0947-8396 VL - 72 IS - 1 SP - 53 EP - 57 PB - Springer CY - Berlin AN - OPUS4-926 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Rudolph, Pascale A1 - Krüger, Jörg A1 - Baudach, Steffen A1 - Kautek, Wolfgang T1 - Femtosecond pulse laser processing of TiN on silicon JF - Applied surface science N2 - 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. KW - Femtosecond laser ablation KW - Titanium nitride KW - Silicon KW - Optical properties PY - 2000 DO - https://doi.org/10.1016/S0169-4332(99)00481-X SN - 0169-4332 SN - 1873-5584 VL - 154-155 SP - 659 EP - 663 PB - North-Holland CY - Amsterdam AN - OPUS4-802 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 JF - Applied surface science 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 - Krüger, Jörg A1 - Kautek, Wolfgang A1 - Lenzner, M. A1 - Sartania, S. A1 - Spielmann, Ch. A1 - Krausz, F. T1 - Laser micromachining of barium aluminium borosilicate glass with pulse durations between 20 fs and 3 ps JF - Applied surface science KW - Laser micromachining KW - Subpicosecond laser ablation KW - Barium aluminium borosilicate glass PY - 1998 SN - 0169-4332 SN - 1873-5584 IS - 127-129 SP - 892 EP - 898 PB - North-Holland CY - Amsterdam AN - OPUS4-887 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krüger, Jörg A1 - Kautek, Wolfgang T1 - The Femtosecond Pulse Laser: a New Tool for Micromachining JF - Laser physics KW - Femtosekundenlaser KW - Mikrobearbeitung PY - 1999 SN - 1054-660X SN - 1531-8494 IS - 9,1 SP - 30 EP - 40 PB - MAIK Nauka/Interperiodica Publ. CY - Moscow AN - OPUS4-712 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krüger, Jörg A1 - Kautek, Wolfgang A1 - Lenzner, M. A1 - Krausz, F. T1 - Precision laser ablation of dielectrics in the 10-fs regime JF - Applied physics A N2 - 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. KW - Laser ablation PY - 1999 DO - https://doi.org/10.1007/s003390050906 SN - 0947-8396 VL - 68 IS - 3 SP - 369 EP - 371 PB - Springer CY - Berlin AN - OPUS4-825 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 JF - Applied physics A 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 - Kautek, Wolfgang A1 - Pentzien, Simone A1 - Conradi, Andrea A1 - Krüger, Jörg A1 - Brzezinka, Klaus-Werner T1 - Pulsed-laser deposition and boron-blending of diamond-like carbon (DLC) thin films JF - Applied surface science KW - Pulslaser KW - Bor KW - Dünnfilmtechnologie KW - Dünnfilm, diamantartig PY - 1996 SN - 0169-4332 SN - 1873-5584 VL - 106 SP - 158 EP - 165 PB - North-Holland CY - Amsterdam AN - OPUS4-630 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kautek, Wolfgang A1 - Rudolph, Pascale A1 - Krüger, Jörg A1 - Rosenfeld, A. A1 - Lorenz, M. A1 - Ashkenasi, D. T1 - Morphological and mechanical investigations of bariumalumoborosilicate glass surfaces processed with 700-fs laser pulses JF - Applied physics A N2 - 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. T2 - 5th International Conference on Laser Ablation ; COLA '99 CY - Göttingen, Germany DA - 1999-07-19 KW - Bariumalumoborosilicate glass surfaces PY - 1999 DO - https://doi.org/10.1007/s003390051523 SN - 0947-8396 VL - 69 IS - 7 SP - S759 EP - S761 PB - Springer CY - Berlin AN - OPUS4-775 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krüger, Jörg A1 - Kautek, Wolfgang A1 - Newesely, H. T1 - Femtosecond-pulse laser ablation of dental hydroxyapatite and single-crystalline fluoroapatite JF - Applied physics A N2 - Laser microdrilling of healthy human enamel and dentine using 300 fs pulses at a wavelength of 615 nm and 3 Hz repetition rate leads to an enhanced structuring quality in comparison with nanosecond-laser results. Microcracking and damage to neighboring tissue can be reduced. Ablation threshold fluences for 100 laser pulses of 0.3 J cm-2 (human dentine), 0.6 J cm-2 (human enamel) and 0.8 J cm-2 (single crystalline fluoroapatite) could be determined. Ablation depths per pulse below 1 7m were observed. T2 - 5th International Conference on Laser Ablation ; COLA '99 CY - Göttingen, Germany DA - 1999-07-19 PY - 1999 DO - https://doi.org/10.1007/s003390051426 SN - 0947-8396 VL - 69 IS - 7 SP - S403 EP - S407 PB - Springer CY - Berlin AN - OPUS4-779 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krüger, Jörg A1 - Kautek, Wolfgang A1 - Lenzner, M. A1 - Krausz, F. T1 - Incubation of laser ablation in fused silica with 5-fs pulses JF - Applied physics A N2 - Zusammenfassung The threshold fluences for laser-induced damage of fused silica with single 5-fs pulses from a Ti:sapphire laser system were determined by extrapolating the ablated volume to zero. These thresholds are about 4 times as high as the values previously obtained from multi-shot experiments. This result is interpreted in terms of an irreversible modification of the original material below the single-shot threshold (incubation). KW - Laser PY - 1999 DO - https://doi.org/10.1007/s003390051034 SN - 0947-8396 VL - 69 IS - 4 SP - 465 EP - 466 PB - Springer CY - Berlin AN - OPUS4-799 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krüger, Jörg A1 - Kautek, Wolfgang A1 - Lenzner, M. A1 - Krausz, F. T1 - Photoablation with sub-10 fs laser pulses JF - Applied surface science N2 - Ablation experiments in several glasses with single and multishot irradiation by laser pulses in the 10-fs pulse duration domain are presented; physical and technological implications are discussed. We demonstrate that these short pulses offer the potential for lateral and vertical machining precision of the order of 100 nm. KW - Ablation KW - Laser pulses KW - Femtosecond pulses PY - 2000 DO - https://doi.org/10.1016/S0169-4332(99)00432-8 SN - 0169-4332 SN - 1873-5584 VL - 154-155 SP - 11 EP - 16 PB - North-Holland CY - Amsterdam AN - OPUS4-800 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rudolph, Pascale A1 - Bonse, Jörn A1 - Krüger, Jörg A1 - Kautek, Wolfgang T1 - Femtosecond- and nanosecond-pulse laser ablation of bariumalumoborosilicate glass JF - Applied physics A N2 - 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. T2 - 5th International Conference on Laser Ablation ; COLA '99 CY - Göttingen, Germany DA - 1998-07-19 KW - Laser ablation KW - Bariumalumoborosilicate glass PY - 1999 DO - https://doi.org/10.1007/s003390051524 SN - 0947-8396 VL - 69 IS - 7 SP - S763 EP - S766 PB - Springer CY - Berlin AN - OPUS4-801 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Baudach, Steffen A1 - Kautek, Wolfgang A1 - Krüger, Jörg A1 - Welsch, E. T1 - Femtosecond laser damage of a high reflecting mirror JF - Thin solid films N2 - Multiple pulse investigations of 130-fs Ti:sapphire laser-induced damage of a high reflecting mirror consisting of alternating ?/4-layers of Ta2O5 and SiO2 and a single 500-nm Ta2O5 film were performed. In both cases, fused silica served as the substrate. For a fixed number of 1000 laser pulses per spot, a decrease in the damage threshold fluence of the mirror by a factor of two was observed by changing the repetition rate from 10 Hz to 1 kHz. A single 500-nm Ta2O5 film shows higher damage resistance compared to the mirror. The mirror and the Ta2O5 film samples were partially coated with a 300-nm-thick aluminium layer. The aluminium coating does not influence the damage threshold of the dielectrics underneath. KW - Aluminium KW - Laser ablation KW - Optical coatings KW - Silicon oxide PY - 2002 DO - https://doi.org/10.1016/S0040-6090(02)00074-3 SN - 0040-6090 IS - 408 SP - 297 EP - 301 PB - Elsevier CY - Amsterdam AN - OPUS4-1382 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krüger, Jörg A1 - Niino, Hiroyuki A1 - Yabe, A. T1 - Investigation of excimer laser ablation threshold of polymers using a microphone JF - Applied surface science N2 - 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. KW - Laser ablation KW - Polymer KW - Treshold KW - Microphone KW - Acoustic measurement KW - Incubation PY - 2002 DO - https://doi.org/10.1016/S0169-4332(02)00418-X SN - 0169-4332 SN - 1873-5584 VL - 197-198 SP - 800 EP - 804 PB - North-Holland CY - Amsterdam AN - OPUS4-1920 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kautek, Wolfgang A1 - Rudolph, Pascale A1 - Daminelli-Widany, Grazia A1 - Krüger, Jörg T1 - Physico-chemical aspects of femtosecond-pulse-laser-induced surface nanostructures JF - Applied physics A N2 - 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. PY - 2005 DO - https://doi.org/10.1007/s00339-005-3211-7 SN - 0947-8396 VL - 81 SP - 65 EP - 70 PB - Springer CY - Berlin AN - OPUS4-7403 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krüger, Jörg A1 - Martin, Sven A1 - Mädebach, Heinrich A1 - Urech, L. A1 - Lippert, T. A1 - Wokaun, A. A1 - Kautek, Wolfgang T1 - Femto- and nanosecond laser treatment of doped polymethylmethacrylate JF - Applied surface science N2 - 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. KW - Laser ablation KW - Laser beam machining KW - Doping thin films KW - Polymers-radiation effects PY - 2005 DO - https://doi.org/10.1016/j.apsusc.2005.01.078 SN - 0169-4332 SN - 1873-5584 VL - 247 SP - 406 EP - 411 PB - North-Holland CY - Amsterdam AN - OPUS4-7470 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Daminelli-Widany, Grazia A1 - Krüger, Jörg A1 - Kautek, Wolfgang T1 - Femtosecond laser interaction with silicon under water confinement JF - Thin solid films N2 - Femtosecond laser interaction with silicon was investigated in water and in air, with 130-fs laser pulses at 800 nm wavelength. Under water confinement, higher modification thresholds, lower ablation depths and similar incubation factors were found in comparison to the dry experiment. Morphological features of the laser-induced cavities also differed. In contrast to air experiments, debris redeposition was negligible, while the ablated material remained suspended in the water layer phase. Underwater cavities obtained at high fluences and high number of pulses per spot showed anomalous profiles, consistent with a strong spatial deformation of the laser beam coupled into the target. Ripples formed at the edges of the modified area showed varying spacings: f100 and f700 nm for water and air experiments, respectively. Differences to the air experiment were related to a complex combination of fluence-dependent non-linear effects occurring in the water layer and to pulse-number-dependent shielding effects induced by cavitation bubbles and suspended ablated material. KW - Laser ablation KW - Silicon KW - Solid electrolyte interface KW - Water PY - 2004 DO - https://doi.org/10.1016/j.tsf.2004.04.043 SN - 0040-6090 VL - 467 IS - 1-2 SP - 334 EP - 341 PB - Elsevier CY - Amsterdam AN - OPUS4-4008 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krüger, Jörg A1 - Sorg, N. A1 - Reif, J. A1 - Kautek, Wolfgang T1 - In situ second harmonic generation measurements during the electrodeposition of Ni on n-Si(111) JF - Applied surface science PY - 1993 SN - 0169-4332 SN - 1873-5584 VL - 69 SP - 388 EP - 392 PB - North-Holland CY - Amsterdam AN - OPUS4-11657 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kautek, Wolfgang A1 - Mitterer, S. A1 - Krüger, Jörg A1 - Husinsky, W. A1 - Grabner, G. T1 - Femtosecond-Pulse Laser Ablation of Human Corneas JF - Applied physics A N2 - A femtosecond pulse laser in the visible spectral region shows promise as a potentially new powerful corneal sculpting tool. It combines the clinical and technical advantages of visible wavelengths with the high ablation quality observed with nanosecond-pulse excimer lasers at 193 nm. A femtosecond and a nanosecond dye laser with pulse durations of 300 fs and 7 ns, and centre wavelengths at 615 nm and 600 nm, respectively, both focused to an area of the order of 10–5 cm2, have been applied to human corneal ablation. Nanosecond laser pulses caused substantial tissue disruption within a 30–100 m range from the excision edge at all fluences above the ablation threshold of F th60 J cm–2 (I th9 GW cm–2). Completely different excisions are produced by the femtosecond-pulse laser: high quality ablations of the Bowman membrane and the stroma tissue characterised by damage zones of less than 0.5 m were observed at all fluences above ablation threshold of F th1 J cm–2 or I th3 TW cm–2 (3×1012 W cm–2). The transparent cornea material can be forced to absorb ultrashort pulses of extremely high intensity. The fs laser generates its own absorption by a multiphoton absorption process. PY - 1994 DO - https://doi.org/10.1007/BF00332446 SN - 0947-8396 VL - 58 IS - 5 SP - 513 EP - 518 PB - Springer CY - Berlin AN - OPUS4-11659 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kautek, Wolfgang A1 - Sorg, N. A1 - Krüger, Jörg T1 - Femtosecond pulse laser second harmonic generation on semiconductor electrodes JF - Electrochimica acta KW - Femtosecond pulse laser KW - Second harmonic generation (SHG) KW - Electrochemistry KW - Semiconductor electrode KW - Silicon KW - Silicon oxide KW - Oxide growth PY - 1994 SN - 0013-4686 SN - 1873-3859 VL - 39 IS - 8/9 SP - 1245 EP - 1249 PB - Elsevier Science CY - Kidlington AN - OPUS4-11660 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kautek, Wolfgang A1 - Pentzien, Simone A1 - Röllig, Mathias A1 - Rudolph, Pascale A1 - Krüger, Jörg A1 - Maywald-Pitellos, C. A1 - Bansa, H. A1 - Grösswang, H. A1 - König, E. T1 - Near-UV laser interaction with contaminants and pigments on parchment: laser cleaning diagnostics by SE-microscopy, VIS-, and IR-spectroscopy JF - Journal of cultural heritage PY - 2000 SN - 1296-2074 SN - 1778-3674 VL - 1 IS - sup.1 PB - Elsevier CY - Paris AN - OPUS4-5981 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hertwig, Andreas A1 - Martin, Sven A1 - Krüger, Jörg A1 - Kautek, Wolfgang T1 - Interaction area dependence of the ablation threshold of ion-doped glass JF - Thin solid films N2 - The laser ablation behaviour of ion-doped glass filter materials under irradiation with femtosecond laser pulses was investigated with respect to spot size and repetition rate. The damage threshold fluence of Schott BG18 depends on the size of the irradiated area. The effect is discussed in terms of a defect-site model. KW - Femtosecond KW - Laser KW - Materials processing KW - Ablation KW - Threshold KW - Glass PY - 2004 DO - https://doi.org/10.1016/j.tsf.2003.11.131 SN - 0040-6090 VL - 453-454 SP - 527 EP - 530 PB - Elsevier CY - Amsterdam AN - OPUS4-11046 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hertwig, Andreas A1 - Martin, Sven A1 - Krüger, Jörg A1 - Kautek, Wolfgang T1 - Surface damage and color centers generated by femtosecond pulses in borosilicate glass and silica JF - Applied physics A N2 - Color center generation by femtosecond laser pulses (30 fs) is observed in a fluence range below the damage threshold in an alkali-free barium borosilicate (BBS) glass, and in a thin layer of SiO2 on a fused silica substrate. The color centers are characterized spectroscopically. The optical density of the color centers in BBS glass is by two orders of magnitude higher than that in silica. A healing process with a time constant of about 30 h can be found. PY - 2004 UR - http://www.sciencedirect.com/science/journal/0926860X DO - https://doi.org/10.1007/s00339-004-2634-x SN - 0947-8396 VL - 79 SP - 1075 EP - 1077 PB - Springer CY - Berlin AN - OPUS4-11047 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pentzien, Simone A1 - Rabin, Ira A1 - Hahn, Oliver A1 - Krüger, Jörg A1 - Kleber, F. A1 - Hollaus, F. A1 - Diem, M. A1 - Sablatnig, R. ED - Park, J.-I. ED - Kim, J. T1 - Can Modern Technologies Defeat Nazi Censorship? T2 - ACCV 2012 Workshops, 11th Asian conference on computer vision N2 - Censorship of parts of written text was and is a common practice in totalitarian regimes. It is used to destroy information not approved by the political power. Recovering the censored text is of interest for historical studies of the text. This paper raises the question, whether a censored postcard from 1942 can be made legible by applying multispectral imaging in combination with laser cleaning. In the fields of art conservation (e.g. color measurements), investigation (e.g. Analysis of underdrawings in paintings), and historical document analysis, multispectral imaging techniques have been applied successfully to give visibility to information hidden to the human eye. The basic principle of laser cleaning is to transfer laser pulse energy to a contamination layer by an absorption process that leads to heating and evaporation of the layer. Partial laser cleaning of postcards is possible; dirt on the surface can be removed and the obscured pictures and writings made visible again. We applied both techniques to the postcard. The text could not be restored since the original ink seems to have suffered severe chemical damage. T2 - ACCV 2012 Workshops, 11th Asian conference on computer vision CY - Daejeon, Korea DA - 05.11.2012 KW - Laser cleaning KW - Multispectral imaging KW - Image restoration KW - Image enhancement PY - 2013 SN - 978-3-642-37483-8 SN - 0302-9743 VL - II IS - LNCS 7729 SP - 13 EP - 24 PB - Springer CY - Berlin Heidelberg AN - OPUS4-28160 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mann, Guido A1 - Pentzien, Simone A1 - Krüger, Jörg T1 - Beam diameter dependence of surface damage threshold of fused silica fibers and preforms for nanosecond laser treatment at 1064 nm wavelength JF - Applied surface science N2 - 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. KW - Laser-induced damage threshold KW - Nanosecond laser KW - Optical fiber KW - Fused silica KW - Spot size KW - Defect model PY - 2013 DO - https://doi.org/10.1016/j.apsusc.2013.03.088 SN - 0169-4332 SN - 1873-5584 VL - 276 SP - 312 EP - 316 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-28310 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Krüger, Jörg A1 - Höhm, S. A1 - Rosenfeld, A. T1 - Femtosecond laser-induced periodic surface structures JF - Journal of laser applications N2 - 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. KW - Laser-induced periodic surface structures (LIPSS) KW - Femtosecond laser ablation KW - Ultrafast optical techniques KW - Silicon KW - Titanium KW - Silica PY - 2012 DO - https://doi.org/10.2351/1.4712658 SN - 1042-346X SN - 1938-1387 VL - 24 IS - 4 SP - 042006-1 EP - 042006-7 PB - Laser Institute of America CY - Orlando, Fla., USA AN - OPUS4-26198 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Symietz, Christian A1 - Lehmann, Erhard A1 - Gildenhaar, Renate A1 - Hackbarth, Andreas A1 - Berger, Georg A1 - Krüger, Jörg T1 - Mechanical stability of Ti6Al4V implant material after femtosecond laser irradiation JF - Journal of applied physics N2 - The surface of a titanium alloy (Ti6Al4V) implant material was covered with a bioactive calcium alkali phosphate ceramic with the aim to accelerate the healing and to form a stronger bond to living bone tissue. To fix the ceramic powder we used a femtosecond laser, which causes a thin surface melting of the metal. It is a requirement to prove that the laser irradiation would not reduce the lifetime of implants. Here we present the results of mechanical stability tests, determined by the rotating bending fatigue strength of sample rods. After describing the sample surfaces and their modifications caused by the laser treatment we give evidence for an unchanged mechanical stability. This applies not only to the ceramic fixation but also to a comparatively strong laser ablation. KW - Aluminium alloys KW - Bending strength KW - Bioceramics KW - Bone KW - Calcium compounds KW - Fatigue KW - Fatigue testing KW - High-speed optical techniques KW - Laser ablation KW - Melting KW - Orthopaedics KW - Prosthetics KW - Rods (structures) KW - Surface treatment KW - Titanium alloys KW - Vanadium alloys PY - 2012 DO - https://doi.org/10.1063/1.4737576 SN - 0021-8979 SN - 1089-7550 VL - 112 IS - 2 SP - 023103-1 - 023103-5 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-26200 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Höhm, S. A1 - Rosenfeld, A. A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Femtosecond laser-induced periodic surface structures on silica JF - Journal of applied physics N2 - 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. KW - High-speed optical techniques KW - Laser beam effects KW - Refractive index KW - Silicon compounds KW - Surface structure PY - 2012 DO - https://doi.org/10.1063/1.4730902 SN - 0021-8979 SN - 1089-7550 VL - 112 IS - 1 SP - 014901-1 - 014901-9 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-26201 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Höhm, S. A1 - Rosenfeld, A. A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Area dependence of femtosecond laser-induced periodic surface structures for varying band gap materials after double pulse excitation JF - Applied surface science N2 - 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. KW - Laser-induced periodic surface structures (LIPSS) KW - Femtosecond laser ablation KW - Double-pulse experiments KW - Ultrafast optical techniques KW - Mach-Zehnder interferometer PY - 2013 DO - https://doi.org/10.1016/j.apsusc.2012.10.188 SN - 0169-4332 SN - 1873-5584 VL - 278 SP - 7 EP - 12 PB - North-Holland CY - Amsterdam AN - OPUS4-28601 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Hertwig, Andreas A1 - Koter, Robert A1 - Weise, Matthias A1 - Beck, Uwe A1 - Reinstädt, Philipp A1 - Griepentrog, Michael A1 - Krüger, Jörg A1 - Picquart, M. A1 - Haro-Poniatowski, E. T1 - Femtosecond laser pulse irradiation effects on thin hydrogenated amorphous carbon layers JF - Applied physics A N2 - The irradiation of ~0.9-µm-thick hydrogenated amorphous carbon (a-C:H) layers deposited on silicon substrates with single femtosecond (fs) laser pulses (35 fs pulse duration, 790 nm centre wavelength) in air is studied experimentally. Irradiation spots have been generated with different peak fluences and subsequently investigated by optical topometry, micro Raman spectroscopy and microscale mechanical indentation in order to evaluate their microscopic, topographical, structural and mechanical properties (e.g. elastic modulus). By this multi-method approach, a clear separation of different effects (delamination and graphitisation) becomes possible. The joint application of mechanical and spectroscopic techniques provides unique insights into the effects of the fs-laser radiation on the carbon layer. PY - 2013 DO - https://doi.org/10.1007/s00339-012-7170-5 SN - 0947-8396 VL - 112 IS - 1 SP - 9 EP - 14 PB - Springer CY - Berlin AN - OPUS4-28629 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Höhm, S. A1 - Rosenfeld, A. A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Femtosecond diffraction dynamics of laser-induced periodic surface structures on fused silica JF - Applied physics letters N2 - 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. KW - High-speed optical techniques KW - Laser beam effects KW - Silicon compounds KW - Surface structure PY - 2013 DO - https://doi.org/10.1063/1.4790284 SN - 0003-6951 SN - 1077-3118 VL - 102 IS - 5 SP - 054102-1 EP - 054102-4 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-27646 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mann, Guido A1 - Jurke, Mathias A1 - Zoheidi, M. A1 - Krüger, Jörg T1 - Influence of mechanical stress on nanosecond laser-induced damage threshold of fused silica JF - Applied surface science N2 - Optical multimode fibers made of fused silica are widely used for transmission of high power laser pulses. Bending of fibers creates mechanical stress inside the material. The bend stress of a fiber can be calculated from bend radius, geometrical fiber parameters and Young's Modulus of the fiber core material and reaches typically values of 220 MPa. A thermo-elastic model of Kusov et al. predicts a quadratic dependence of laser-induced damage threshold fluence with applied stress. In the present study, fiber preform material F300 (Heraeus) was loaded mechanically with pressures up to 220 MPa representing 20% of the pressure resistance of fused silica. Bulk laser-induced damage thresholds (LIDT) were evaluated using a longitudinal multimode Q-switched Nd:YAG laser (1064 nm) at a pulse duration of 12 ns with polarization states parallel and perpendicular to the stress direction. LIDT of fused silica samples of about 700 J/cm2 were found. LIDT did not show a dependence on mechanical pressure and polarization state which is a consequence of the small ratio of maximum applied stress (220 MPa) to Young's Modulus of fused silica (72.5 GPa). KW - Laser-induced damage threshold KW - LIDT KW - Nanosecond laser KW - Fused silica KW - Mechanical stress KW - Optical fiber PY - 2012 DO - https://doi.org/10.1016/j.apsusc.2012.01.049 SN - 0169-4332 SN - 1873-5584 VL - 258 IS - 23 SP - 9153 EP - 9156 PB - North-Holland CY - Amsterdam AN - OPUS4-26225 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rosenfeld, A. A1 - Rohloff, M. A1 - Höhm, S. A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Formation of laser-induced periodic surface structures on fused silica upon multiple parallel polarized double-femtosecond-laser-pulse irradiation sequences JF - Applied surface science N2 - 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. KW - Laser-induced periodic surface structures (LIPSS) KW - Femtosecond laser ablation KW - Double-pulse experiments KW - Fused silica KW - Michelson interferometer PY - 2012 DO - https://doi.org/10.1016/j.apsusc.2011.09.076 SN - 0169-4332 SN - 1873-5584 VL - 258 IS - 23 SP - 9233 EP - 9236 PB - North-Holland CY - Amsterdam AN - OPUS4-26226 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Höhm, S. A1 - Rohloff, M. A1 - Rosenfeld, A. A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Dynamics of the formation of laser-induced periodic surface structures on dielectrics and semiconductors upon femtosecond laser pulse irradiation sequences JF - Applied physics A N2 - 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. PY - 2013 DO - https://doi.org/10.1007/s00339-012-7184-z SN - 0947-8396 VL - 110 IS - 3 SP - 553 EP - 557 PB - Springer CY - Berlin AN - OPUS4-27787 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Höhm, S. A1 - Rosenfeld, A. A1 - Krüger, Jörg T1 - Sub-100-nm laser-induced periodic surface structures upon irradiation of titanium by Ti:sapphire femtosecond laser pulses in air JF - Applied physics A N2 - 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. PY - 2013 DO - https://doi.org/10.1007/s00339-012-7140-y SN - 0947-8396 VL - 110 IS - 3 SP - 547 EP - 551 PB - Springer CY - Berlin AN - OPUS4-27788 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krüger, Jörg A1 - Meja, P. A1 - Autric, M. A1 - Kautek, Wolfgang T1 - Femtosecond pulse laser ablation of anodic oxide coatings on aluminium alloys with on-line acoustic observation JF - Applied surface science N2 - The 125-fs laser ablation behaviour (800 nm) of aluminium and anodic oxide coatings on an AlMgSi1 alloy was investigated. The multi-pulse ablation threshold of aluminium at 1.2 J cm-2 was less than that of the oxides of 2–3 J cm-2. Aluminium exhibited a single pulse modification (melting) threshold of 0.3 J cm-2. These values derived from an evaluation of the crater geometry coincided with on-line acoustic measurements. The detected microphone voltage amplitude increased linearly with the laser fluence. The morphology of the ablation craters on aluminium indicated melt formation and displacement of a homogeneous melt phase due to the recoil action of the expanding metal vapour. The laser-processed ceramic oxide phases, on the other hand, showed a spongy resolidified melt layer, which denotes a collocated in-depth formation both of a melt and a gas phase. These phenomena are discussed in terms of the relative dominance of penetration depth of laser light and heat affected zones in the investigated materials with strongly varying optical and thermodynamical properties. KW - Laser ablation KW - Acoustic measurement KW - Microphone KW - Aluminium KW - Aluminium oxide PY - 2002 SN - 0169-4332 SN - 1873-5584 VL - 186 IS - 1-4 SP - 374 EP - 380 PB - North-Holland CY - Amsterdam AN - OPUS4-6324 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Baudach, Steffen A1 - Krüger, Jörg A1 - Kautek, Wolfgang A1 - Lenzner, Matthias T1 - Femtosecond laser ablation of silicon-modification thresholds and morphology JF - Applied physics A N2 - We investigated the initial modification and ablation of crystalline silicon with single and multiple Ti:sapphire laser pulses of 5 to 400 fs duration. In accordance with earlier established models, we found the phenomena amorphization, melting, re-crystallization, nucleated vaporization, and ablation to occur with increasing laser fluence down to the shortest pulse durations. We noticed new morphological features (bubbles) as well as familiar ones (ripples, columns). A nearly constant ablation threshold fluence on the order of 0.2 J/cm2 for all pulse durations and multiple-pulse irradiation was observed. For a duration of ,100 fs, significant incubation can be observed, whereas for 5 fs pulses, the ablation threshold does not depend on the pulse number within the experimental error. For micromachining of silicon, a pulse duration of less than 500 fs is not advantageous. PY - 2002 DO - https://doi.org/10.1007/s003390100893 SN - 0947-8396 VL - 74 IS - 1 SP - 19 EP - 25 PB - Springer CY - Berlin AN - OPUS4-6328 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Jeschke, H.O. A1 - Garcia, M.E. A1 - Lenzner, Matthias A1 - Bonse, Jörn A1 - Krüger, Jörg A1 - Kautek, Wolfgang T1 - Laser ablation thresholds of silicon for different pulse durations: theory and experiment JF - Applied surface science N2 - The ultrafast laser ablation of silicon has been investigated experimentally and theoretically. The theoretical description is based on molecular dynamics (MD) simulations combined with a microscopic electronic model. We determine the thresholds of melting and ablation for two different pulse durations =20 and 500 fs. Experiments have been performed using 100 Ti:Sap-phire laser pulses per spot in air environment. The ablation thresholds were determined for pulses with a duration of 25 and 400 fs, respectively. Good agreement is obtained between theory and experiment. KW - Laser ablation KW - Pulse duration KW - Threshold of silicon PY - 2002 DO - https://doi.org/10.1016/S0169-4332(02)00458-0 SN - 0169-4332 SN - 1873-5584 VL - 197-198 SP - 839 EP - 844 PB - North-Holland CY - Amsterdam AN - OPUS4-6314 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Martin, Sven A1 - Hertwig, Andreas A1 - Lenzner, Matthias A1 - Krüger, Jörg A1 - Kautek, Wolfgang T1 - Spot-size dependence of the ablation threshold in dielectrics for femtosecond laser pulses JF - Applied physics A N2 - The multi-pulse ablation threshold of barium borosilicate glass was measured using 30-fs pulses of a high repetition rate (1 kHz) laser system. The threshold fluence was found to decrease with increasing beam radius ranging from 20 to 400 m. Two existing models are applied by considering thermal accumulation and point defects, respectively . PY - 2003 DO - https://doi.org/10.1007/s00339-003-2213-6 SN - 0947-8396 VL - 77 IS - 7 SP - 883 EP - 884 PB - Springer CY - Berlin AN - OPUS4-6317 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - v. Woedtke, T. A1 - Abel, P. A1 - Krüger, Jörg A1 - Kautek, Wolfgang T1 - Subpicosecond-pulse laser microstructuring for enhanced reproducibility of biosensors JF - Sensors and actuators B: Chemical N2 - Curved substrates can be micro-structured by laser ablation, which is not possible with standard lithographic methods. The novel femtosecond-pulse laser technique allows the production of defined and reproducible micro-perforations of originally analyte-impermeable membranes. The trans-membrane analyte flux can be controlled both by the variation of the laser focus diameter resulting in different areas of single perforations, and the number of perforations in arrays on small membrane areas. This leads to a higher degree of variability as well as reproducibility of the diffusion qualities of sensor membranes, and marks the main innovation with this technique compared to the hand-made mechanical perforation by specially grinded needles used up to now. Touchless micro-perforation of small membrane areas with negligible heat damage of the structures adjacent to the perforation allows the application of ‘analyte door’ membranes directly onto curved surfaces of miniaturized needle-sensors assigned for in vivo glucose monitoring, for the first time. KW - Biosensor KW - Glucose KW - Membrane perforation KW - Subpicosecond laser ablation KW - Reproducibility PY - 1997 DO - https://doi.org/10.1016/S0925-4005(97)80330-9 SN - 0925-4005 SN - 1873-3077 VL - 42 IS - 3 SP - 151 EP - 156 PB - Elsevier CY - Amsterdam [u.a.] AN - OPUS4-11513 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kautek, Wolfgang A1 - Pentzien, Simone A1 - Rudolph, Pascale A1 - Krüger, Jörg A1 - König, E. T1 - Laser interaction with coated collagen und cellulose fibre composites: fundamentals of laser cleaning of ancient parchment manuscripts and paper JF - Applied surface science N2 - 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. KW - Laser KW - Parchment KW - Papery KW - Spectroscopy KW - Laser cleaning PY - 1998 SN - 0169-4332 SN - 1873-5584 VL - 127-129 SP - 746 EP - 754 PB - North-Holland CY - Amsterdam AN - OPUS4-11516 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lenzner, Matthias A1 - Krüger, Jörg A1 - Sartania, S. A1 - Cheng, Z. A1 - Spielmann, Ch. A1 - Mourou, G. A1 - Kautek, Wolfgang A1 - Krausz, F. T1 - Femtosecond Optical Breakdown in Dielectrics JF - Physical review letters N2 - We report measurements of the optical breakdown threshold and ablation depth in dielectrics with different band gaps for laser pulse durations ranging from 5 ps to 5 fs at a carrier wavelength of 780 nm. For tau <100 fs, the dominant channel for free electron generation is found to be either impact or multiphoton ionization (MPI) depending on the size of the band gap. The observed MPI rates are substantially lower than those predicted by the Keldysh theory. We demonstrate that sub-10-fs laser pulses open up the way to reversible nonperturbative nonlinear optics (at intensities greater than 1014 W/cm2 slightly below damage threshold) and to nanometer-precision laser ablation (slightly above threshold) in dielectric materials. PY - 1998 SN - 0031-9007 SN - 1079-7114 VL - 80 IS - 18 SP - 4076 EP - 4079 PB - American Physical Society CY - Ridge, NY AN - OPUS4-11518 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krüger, Jörg A1 - Lenzner, Matthias A1 - Martin, Sven A1 - Lenner, M. A1 - Spielmann, Ch. A1 - Fiedler, A. A1 - Kautek, Wolfgang T1 - Single- and multi-pulse femtosecond laser ablation of optical filter materials JF - Applied surface science N2 - 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. KW - Damage KW - Femtosecond laser ablation KW - Filter KW - Incubation KW - Laser safety KW - Threshold PY - 2003 DO - https://doi.org/10.1016/S0169-4332(02)01389-2 SN - 0169-4332 SN - 1873-5584 VL - 208-209 SP - 233 EP - 237 PB - North-Holland CY - Amsterdam AN - OPUS4-11545 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Martin, Sven A1 - Krüger, Jörg A1 - Hertwig, Andreas A1 - Fiedler, A. A1 - Kautek, Wolfgang T1 - Femtosecond laser interaction with protection materials JF - Applied surface science N2 - 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. KW - Damage KW - Femtosecond laser ablation KW - Laser safety KW - Threshold KW - Aluminium KW - Textile PY - 2003 DO - https://doi.org/10.1016/S0169-4332(02)01392-2 SN - 0169-4332 SN - 1873-5584 VL - 208-209 SP - 333 EP - 339 PB - North-Holland CY - Amsterdam AN - OPUS4-11546 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krüger, Jörg A1 - Kautek, Wolfgang T1 - Femtosecond pulse visible laser processing of fibre composite materials JF - Applied surface science N2 - A first investigation on the ablation of composite materials like carbon and silicon-carbide reinforced alumo- and borosilicate glasses by 300 fs laser pulses (620 nm) in comparison to experiments with 17 ns pulse excimer laser (308 nm) treatment is presented. In all composites, femtosecond laser scans with a fluence of less than 2 J cm-2 produce well defined cuts with smooth side walls in contrast to the nanosecond laser result where extremely incongruent ablation is observed. Visible lasers should not be applicable because SiC and the glasses are practically transparent. Visible subpicosecond pulses of high intensity in the TW cm-2 range allow multi-photon absorption accompanied by incubation phenomena. The morphology of the groove edges reveal the contrasting ablation thresholds and rates of the fibre and glass materials. The ablation thresholds of the transparent components, i.e. the glass matrices and SiC, are about one order of magnitude greater than that of carbon which is ~ 0.15 J cm-2. Incubation effects are important for the absorption mechanisms in the transparent materials. When a critical number of pulses has not been reached at the SiC-glass composites, only the glass is preferentially ablated, and the fibres remain intact. This is in contrast to the C-glass composites where the ablation behaviour is opposite. PY - 1996 SN - 0169-4332 SN - 1873-5584 VL - 106 SP - 383 EP - 389 PB - North-Holland CY - Amsterdam AN - OPUS4-11506 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krüger, Jörg A1 - Kautek, Wolfgang T1 - Femtosecond-pulse visible laser processing of transparent materials JF - Applied surface science N2 - High-power lasers in industrial and R & D applications raise the general problem of reliability and degradation of optical components. A systematic study of nonlinear interaction of various transparent dielectric materials as e.g. glasses, fused silica, and polymers, with laser-pulses in the intensity range of up to 1013 W cm-2 is presented. On the other hand, femtosecond-pulse laser processing in the visible spectral range (300 fs; 620 nm, ~ 2 eV) allows precise microstructuring of transparent dielectrics without disruption of the remnant material. Damage and ablation threshold fluences occur above 1.2 J cm-2 at both silicate glasses and fused silica. Two different photon absorption mechanisms have been observed. The first occurs during the initial laser pulses in the incubation range. There, multiphoton absorption results in moderate energy volume densities. These are sufficient to generate morphological changes and optically active defect sites (colour centres) which provide a much higher absorptivity relevant for the second mechanism. It results in gasification without participation of melt. PY - 1996 SN - 0169-4332 SN - 1873-5584 VL - 96-98 SP - 430 EP - 438 PB - North-Holland CY - Amsterdam AN - OPUS4-11509 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kautek, Wolfgang A1 - Krüger, Jörg A1 - Lenzner, M. A1 - Sartania, S. A1 - Spielmann, Ch. A1 - Krausz, F. T1 - Laser ablation of dielectrics with pulse durations between 20 fs and 3 ps JF - Applied physics letters PY - 1996 SN - 0003-6951 SN - 1077-3118 VL - 69 IS - 21 SP - 3146 EP - 3148 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-11496 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hertwig, Andreas A1 - Krüger, Jörg A1 - Weise, Matthias A1 - Beck, Uwe T1 - Hydrogen-Containing Amorphous Carbon Layers as Optical Materials in the Near-IR Spectral Range JF - Plasma processes and polymers N2 - Hydrogenated amorphous carbon layers were deposited on various substrates by means of a plasma CVD process with a RF substrate bias as well as an ECR plasma source. The optical properties of the a-C:H layers were obtained via spectroscopic ellipsometry and correlated with their mechanical and chemical properties. The layers from pure RF plasma exhibit a higher absorption constant in the visible spectral range and a higher refractive index. All layers are nearly transparent in the NIR spectral range making them candidates for optical thin layer systems. The laser damage behaviour of the a-C:H layers was investigated with ultrashort pulses. The damage thresholds were consistent with the absorption constants of the layers. Interesting damage morphologies were observed indicating a sensitivity of this experiment to sub-structures in the layer. KW - Kohlenstoffschichten KW - Optische Konstanten KW - Ellipsometrie KW - Laser-Material-Bearbeitung KW - Amorphous KW - Diamond-like carbon KW - Hydrocarbons KW - Laser ablation KW - Optical proper PY - 2007 SN - 1612-8850 SN - 1612-8869 VL - 4 IS - S1 SP - S76 EP - S82 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-14862 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mann, Guido A1 - Vogel, Jens A1 - Preuß, Rüdiger A1 - Vaziri, Pouya A1 - Zoheidi, M. A1 - Eberstein, Markus A1 - Krüger, Jörg T1 - Nanosecond laser-induced surface damage of optical multimode fibers and their preforms JF - Applied physics A N2 - High-power optical multimode fibers are essential components for materials processing and surgery and can limit the performance of expensive systems due to breakdown at the end faces. The aim of this paper is the determination of laser-induced damage thresholds (LIDT) of fibers (FiberTech) and preforms (Heraeus Suprasil F300). Preforms served as models. They were heated up to maximum temperatures of 1100, 1300 and 1500°C and cooled down to room temperature at rates of 10 K min-1 (oven) and ~105 K min-1 (quenched in air) to freeze in various structural states simulating different conditions similar to a drawing process during the production of fibers. Single- and multi-pulse LIDT measurements were done in accordance with the relevant ISO standards. Nd:YAG laser pulses with durations of 15 ns (1064 nm wavelength) and 8.5 ns (532 nm) at a repetition rate of 10 Hz were used. For the preforms, LIDT values (1-on-1) ranged from 220 to 350 J/cm² (1064 nm) and from 80 to 110 J/cm² (532 nm), respectively. A multi-pulse impact changed the thresholds to lower values. The LIDT (1064 nm wavelength) of the preforms can be regarded as a lower limit for those of the fibers. PY - 2008 DO - https://doi.org/10.1007/s00339-008-4576-1 SN - 0947-8396 VL - 92 IS - 4 SP - 853 EP - 857 PB - Springer CY - Berlin AN - OPUS4-17779 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krüger, Jörg A1 - Dufft, Daniela A1 - Koter, Robert A1 - Hertwig, Andreas T1 - Femtosecond laser-induced damage of gold films JF - Applied surface science N2 - Single- and multi-shot ablation thresholds of gold films in the thickness range of 31–1400 nm were determined employing a Ti:sapphire laser delivering pulses of 28 fs duration, 793 nm center wavelength at 1 kHz repetition rate. The gold layers were deposited on BK7 glass by an electron beam evaporation process and characterized by atomic force microscopy and ellipsometry. A linear dependence of the ablation threshold fluence Fth on the layer thickness d was found for d ≤ 180 nm. If a film thickness of about 180 nm was reached, the damage threshold remained constant at its bulk value. For different numbers of pulses per spot (N-on-1), bulk damage thresholds of ~0.7 J cm-2 (1-on-1), 0.5 J cm-2 (10-on-1), 0.4 J cm-2 (100-on-1), 0.25 J cm-2 (1000-on-1), and 0.2 J cm-2 (10000-on-1) were obtained experimentally indicating an incubation behavior. A characteristic layer thickness of Lc ˜ 180 nm can be defined which is a measure for the heat penetration depth within the electron gas before electron–phonon relaxation occurs. Lc is by more than an order of magnitude larger than the optical absorption length of α-1 ˜ 12 nm at 793 nm wavelength. KW - Single- and multi-shot ablation KW - Ti:sapphire laser KW - Gold films PY - 2007 SN - 0169-4332 SN - 1873-5584 VL - 253 IS - 19 SP - 7815 EP - 7819 PB - North-Holland CY - Amsterdam AN - OPUS4-15686 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mann, Guido A1 - Vogel, Jens A1 - Preuß, Rüdiger A1 - Vaziri, Pouya A1 - Zoheidi, M. A1 - Eberstein, Markus A1 - Krüger, Jörg T1 - Nanosecond laser damage resistance of differently prepared semi-finished parts of optical multimode fibers JF - Applied surface science N2 - Optical multimode fibers are applied in materials processing (e.g. automotive industry), defense, aviation technology, medicine and biotechnology. One challenging task concerning the production of multimode fibers is the enhancement of laser-induced damage thresholds. A higher damage threshold enables a higher transmitted average power at a given fiber diameter or the same power inside a thinner fiber to obtain smaller focus spots. In principle, different material parameters affect the damage threshold. Besides the quality of the preform bulk material itself, the drawing process during the production of the fiber and the preparation of the fiber end surfaces influence the resistance. Therefore, the change of the laser-induced damage threshold of preform materials was investigated in dependence on a varying thermal treatment and preparation procedure. Single and multi-pulse laser-induced damage thresholds of preforms (F300, Heraeus) were measured using a Q-switched Nd:YAG laser at 1064 nm wavelength emitting pulses with a duration of 15 ns, a pulse energy of 12 mJ and a repetition rate of 10 Hz. The temporal and spatial shape of the laser pulses were controlled accurately. Laser-induced damage thresholds in a range from 150 J cm-2 to 350 J cm-2 were determined depending on the number of pulses applied to the same spot, the thermal history and the polishing quality of the samples, respectively. KW - Laser ablation KW - Optical fibers KW - Physical radiation damage KW - Radiation treatment KW - Glass transitions KW - Glasses PY - 2007 DO - https://doi.org/10.1016/j.apsusc.2007.09.032 SN - 0169-4332 SN - 1873-5584 VL - 254 IS - 4 SP - 1096 EP - 1100 PB - North-Holland CY - Amsterdam AN - OPUS4-16207 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Eberstein, Markus A1 - Mann, Guido A1 - Vogel, Jens A1 - Zoheidi, M. A1 - Krüger, Jörg T1 - Influence of Technological Parameters on Nanosecond Laser-induced Surface Damage of Optical Multimode Fibers JF - Advanced materials research N2 - High-power optical multimode fibers are essential components for materials processing and surgery and can limit the reliability of expensive systems due to breakdown at the end faces. The breakdown threshold of fibers is determined by intrinsic materials properties and parameters of the technology applied. The aim of this paper is the identification of technological parameters that are crucial for the fiber quality. Fibers were drawn from preforms of Heraeus SWU with core material F300 and a low amount of OH-. Both, the cladding (fluorine doped SiO2) to core diameter ratio (CCDR) and the drawing speed were varied. CCDR values between 1.05 and 1.4 were used. Afterwards, the laser-induced damage thresholds (LIDT) of the fibers were determined. For comparison, also samples from preforms, which underwent different thermal treatments above the transition temperature, were tested with respect to their damage resistivity. Single and multi pulse LIDT measurements were done in accordance with the relevant ISO standards. Nd:YAG laser pulses with durations of 15 ns (1064 nm wavelength) and 8.5 ns (532 nm) at a repetition rate of 10 Hz were utilized. For the fibers, LIDT values (1-on-1, 1064 nm and 532 nm) increased with growing CCDR and with decreasing drawing velocities. KW - Silica glass KW - Multimode fiber KW - Nanosecond laser KW - Damage threshold PY - 2005 SN - 1022-6680 SN - 1662-8985 VL - 39-40 SP - 225 EP - 230 PB - Trans Tech Publ. CY - Zurich AN - OPUS4-17339 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krüger, Jörg A1 - Pentzien, Simone A1 - Conradi, Andrea T1 - Cleaning of artificially soiled paper with 532-nm nanosecond laser radiation JF - Applied physics A N2 - 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. KW - Laser cleaning KW - Paper KW - Colorimetry PY - 2008 DO - https://doi.org/10.1007/s00339-008-4476-4 SN - 0947-8396 VL - 92 IS - 1 SP - 179 EP - 183 PB - Springer CY - Berlin AN - OPUS4-17331 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Urech, L. A1 - Lippert, T. A1 - Wokaun, A. A1 - Martin, Sven A1 - Mädebach, Heinrich A1 - Krüger, Jörg T1 - Removal of doped poly(methylmetacrylate) from tungsten and titanium substrates by femto- and nanosecond laser cleaning JF - Applied surface science N2 - 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. KW - Poly(methylmetacrylate) KW - Laser treatment KW - Tungsten KW - Titanium KW - Femtosecond PY - 2006 DO - https://doi.org/10.1016/j.apsusc.2005.07.109 SN - 0169-4332 SN - 1873-5584 VL - 252 IS - 13 SP - 4754 EP - 4758 PB - North-Holland CY - Amsterdam AN - OPUS4-12368 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Derrien, Thibault A1 - Krüger, Jörg A1 - Itina, T.E. A1 - Höhm, S. A1 - Rosenfeld, A. A1 - Bonse, Jörn T1 - Rippled area formed by surface plasmon polaritons upon femtosecond laser double-pulse irradiation of silicon JF - Optics express N2 - The formation of near-wavelength laser-induced periodic surface structures (LIPSS) on silicon upon irradiation with sequences of Ti:sapphire femtosecond laser pulse pairs (pulse duration 150 fs, central wavelength 800 nm) is studied theoretically. For this purpose, the nonlinear generation of conduction band electrons in silicon and their relaxation is numerically calculated using a two-temperature model approach including intrapulse changes of optical properties, transport, diffusion and recombination effects. Following the idea that surface plasmon polaritons (SPP) can be excited when the material turns from semiconducting to metallic state, the 'SPP active area' is calculated as function of fluence and double-pulse delay up to several picoseconds and compared to the experimentally observed rippled surface areas. Evidence is presented that multi-photon absorption explains the large increase of the rippled area for temporally overlapping pulses. For longer double-pulse delays, relevant relaxation processes are identified. The results demonstrate that femtosecond LIPSS on silicon are caused by the excitation of SPP and can be controlled by temporal pulse shaping. PY - 2013 DO - https://doi.org/10.1364/OE.21.029643 SN - 1094-4087 VL - 21 IS - 24 SP - 29643 EP - 29655 PB - Optical Society of America CY - Washington, DC AN - OPUS4-29650 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Rosenfeld, A. A1 - Krüger, Jörg T1 - On the role of surface plasmon polaritons in the formation of laser-induced periodic surface structures upon irradiation of silicon by femtosecond-laser pulses JF - Journal of applied physics N2 - The formation of nearly wavelength-sized laser-induced periodic surface structures (LIPSSs) on single-crystalline silicon upon irradiation with single or multiple femtosecond-laser pulses (pulse duration τ=130 fs and central wavelength λ=800 nm) in air is studied experimentally and theoretically. In our theoretical approach, we model the LIPSS formation by combining the generally accepted first-principles theory of Sipe and co-workers with a Drude model in order to account for transient intrapulse changes in the optical properties of the material due to the excitation of a dense electron-hole plasma. Our results are capable to explain quantitatively the spatial periods of the LIPSSs being somewhat smaller than the laser wavelength, their orientation perpendicular to the laser beam polarization, and their characteristic fluence dependence. Moreover, evidence is presented that surface plasmon polaritons play a dominant role during the initial stage of near-wavelength-sized periodic surface structures in femtosecond-laser irradiated silicon, and it is demonstrated that these LIPSSs can be formed in silicon upon irradiation by single femtosecond-laser pulses. KW - Ab initio calculations KW - Elemental semiconductors KW - High-speed optical techniques KW - Laser beam effects KW - Polaritons KW - Silicon KW - Solid-state plasma KW - Surface plasmons KW - Surface structure PY - 2009 DO - https://doi.org/10.1063/1.3261734 SN - 0021-8979 SN - 1089-7550 VL - 106 IS - 10 SP - 104910-1 - 104910-5 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-20453 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Krüger, Jörg T1 - Pulse number dependence of laser-induced periodic surface structures for femtosecond laser irradiation of silicon JF - Journal of applied physics N2 - The formation of nearly wavelength-sized laser-induced periodic surface structures (LIPSS) on single-crystalline silicon upon irradiation with single (N = 1) and multiple (N ≤ 1000) linearly polarized femtosecond (fs) laser pulses (pulse duration τ = 130 fs, central wavelength λ = 800 nm) in air is studied experimentally. Scanning electron microscopy (SEM) and optical microscopy are used for imaging of the ablated surface morphologies, both revealing LIPSS with periodicities close to the laser wavelength and an orientation always perpendicular to the polarization of the fs-laser beam. It is experimentally demonstrated that these LIPSS can be formed in silicon upon irradiation by single fs-laser pulses—a result that is additionally supported by a recent theoretical model. Two-dimensional Fourier transforms of the SEM images allow the detailed analysis of the distribution of the spatial frequencies of the LIPSS and indicate, at a fixed peak fluence, a monotonous decrease in their mean spatial period between ~770 nm (N = 1) and 560 nm (N = 1000). The characteristic decrease in the LIPSS period is caused by a feedback-mechanism acting upon excitation of surface plasmon polaritons at the rough silicon surface which is developing under the action of multiple pulses into a periodically corrugated surface. KW - Elemental semiconductors KW - Fourier transforms KW - Laser beam effects KW - Optical microscopy KW - Polarisation KW - Polaritons KW - Scanning electron microscopy KW - Silicon KW - Surface morphology KW - Surface plasmons PY - 2010 UR - http://jap.aip.org/resource/1/japiau/v108/i3/p034903_s1 DO - https://doi.org/10.1063/1.3456501 SN - 0021-8979 SN - 1089-7550 VL - 108 IS - 3 SP - 034903-1 - 034903-5 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-21804 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Krüger, Jörg T1 - Probing the heat affected zone by chemical modifications in femtosecond pulse laser ablation of titanium nitride films in air JF - Journal of applied physics N2 - A new approach is presented to quantify the so-called "heat affected zone" (HAZ) during femtosecond laser pulse processing. Ablation of titanium nitride (TiN) thin films (~3 μm thickness) by multiple femtosecond laser pulses (τ=130 fs, λ=800 nm) in air environment was studied by means of two different surface analytical methods both being sensitive to chemical alterations at the surface. Scanning Auger electron microscopy was applied for a visualization of the spatial distribution of specific elements (Ti, O) within the laser-modified areas. The chemical state of the irradiated surface was revealed by complementary x-ray photoelectron spectroscopy. Both methods were used for a depth-profiling chemical analysis (tracking the elements Ti, N, O, and C) using an Ar-ion beam for surface sputtering. In a narrow laser fluence range slightly below the ablation threshold of TiN significant superficial oxidation can be observed leading to the formation of substoichiometric TiO2-x. At fluences above the ablation threshold, an increased titanium concentration is observed within the entire ablation craters. Following upon sputter removal the elemental distribution into the depth of the nonablated material, the results allow an estimation of the heat-affected zone for femtosecond laser ablation in air environment. According to our analyses, the HAZ extends up to a few hundreds of nanometers into the nonablated material. KW - Femtosecond laser ablation KW - Heat affected zone KW - Titanium nitride KW - Scanning Auger electron microscopy KW - X-ray KW - Photoelektron spectroscopy PY - 2010 UR - http://link.aip.org/link/?JAP/107/054902 DO - https://doi.org/10.1063/1.3311552 SN - 0021-8979 SN - 1089-7550 VL - 107 IS - 5 SP - 054902-1 - 054902-5 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-20949 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Höhm, S. A1 - Herzlieb, M. A1 - Rosenfeld, A. A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Formation of laser-induced periodic surface structures on fused silica upon two-color double-pulse irradiation JF - Applied physics letters N2 - The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of fused silica with multiple irradiation sequences consisting of laser pulse pairs (50 fs single-pulse duration) of two different wavelengths (400 and 800 nm) is studied experimentally. Parallel polarized double-pulse sequences with a variable delay Δt between -10 and +10 ps and between the individual fs-laser pulses were used to investigate the LIPSS periods versus Δt. These two-color experiments reveal the importance of the ultrafast energy deposition to the silica surface by the first laser pulse for LIPSS formation. The second laser pulse subsequently reinforces the previously seeded spatial LIPSS frequencies. PY - 2013 DO - https://doi.org/10.1063/1.4850528 SN - 0003-6951 SN - 1077-3118 VL - 103 IS - 25 SP - 254101-1 EP - 254101-4 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-29812 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Mann, Guido A1 - Krüger, Jörg A1 - Marcinkowski, M. A1 - Eberstein, M. T1 - Femtosecond laser-induced removal of silicon nitride layers from doped and textured silicon wafers used in photovoltaics JF - Thin solid films N2 - The removal of a 75- to 90-nm-thick passivating silicon nitride antireflection coating from standard textured multicrystalline silicon photovoltaic wafers with a typical diffused 90-Ω/sq-emitter upon irradiation with near-infrared femtosecond laser pulses (790 nm central wavelength, 30 fs pulse duration) is studied experimentally. The laser irradiation areas are subsequently characterized by complementary optical microscopy, scanning electron microscopy and depth profiling chemical analyses using secondary ion mass spectrometry. The results clarify the thin-film femtosecond laser ablation scenario and outline the process windows for selective antireflection coating removal. KW - Photovoltaics KW - Solar cell KW - Laser processing KW - FS-laser ablation KW - Silicon nitride PY - 2013 DO - https://doi.org/10.1016/j.tsf.2013.07.005 SN - 0040-6090 VL - 542 SP - 420 EP - 425 PB - Elsevier CY - Amsterdam AN - OPUS4-28874 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Krüger, Jörg T1 - Structuring of thin films by ultrashort laser pulses JF - Applied physics A N2 - Modern life and global communication would not be possible without technologically tailored thin films; they are omnipresent in daily life applications. In most cases, the films are deposited entirely at the carrying substrates in a specific processing step of the device or sample. In some cases, however, removal or modification must be performed locally, i.e., site-controlled and material selective through an additional laser processing step. For that ultrashort laser pulses with durations in the femtosecond and picosecond range can provide unique advantages and capabilities in industrially scalable schemes. This article reviews the current state of the research and corresponding industrial transfer related to the structuring of thin films by ultrashort pulsed lasers. It focuses on the pertinent historic developments, reveals the relevant physical and chemical effects, explores the ultimate limits, and discusses selected industrial and scientific applications. KW - Thin films KW - Laser processing KW - Ultrashort lasers KW - Laser damage KW - Femtosecond laser ablation PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-565732 DO - https://doi.org/10.1007/s00339-022-06229-x SN - 0947-8396 SN - 1432-0630 VL - 129 IS - 1 SP - 1 EP - 38 PB - Springer CY - Berlin AN - OPUS4-56573 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 JF - Materials 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 - Stolzenberg, U. A1 - Schmitt Rahner, M. A1 - Pullner, B. A1 - Legall, Herbert A1 - Bonse, Jörn A1 - Kluge, M. A1 - Ortner, A. A1 - Hoppe, B. A1 - Krüger, Jörg T1 - X-ray emission hazards from ultrashort pulsed laser material processing in an industrial setting JF - Materials N2 - Interactions between ultrashort laser pulses with intensities larger than 10^13 W/cm^2 and solids during material processing can lead to the emission of X-rays with photon energies above 5 keV, causing radiation hazards to operators. A framework for inspecting X-ray emission hazards during laser material processing has yet to be developed. One requirement for conducting radiation protection inspections is using a reference scenario, i.e., laser settings and process parameters that will lead to an almost constant and high level of X-ray emissions. To study the feasibility of setting up a reference scenario in practice, ambient dose rates and photon energies were measured using traceable measurement equipment in an industrial setting at SCHOTT AG. Ultrashort pulsed (USP) lasers with a maximum average power of 220 W provided the opportunity to measure X-ray emissions at laser peak intensities of up to 3.3 × 10^15 W/cm^2 at pulse durations of ~1 ps. The results indicate that increasing the laser peak intensity is insufficient to generate high dose rates. The investigations were affected by various constraints which prevented measuring high ambient dose rates. In this work, a list of issues which may be encountered when performing measurements at USP-laser machines in industrial settings is identified. KW - X-ray emission hazards KW - Ultrashort pulsed laser KW - Radiation protection KW - Industrial applications KW - Protection housing PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-538632 DO - https://doi.org/10.3390/ma14237163 SN - 1996-1944 VL - 14 SP - 1 EP - 17 PB - MDPI CY - Basel AN - OPUS4-53863 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Legall, Herbert A1 - Bonse, Jörn A1 - Krüger, Jörg T1 - Review of x-ray exposure and safety issues arising from ultra-short pulse laser material processing JF - Journal of Radiological Protection N2 - Laser processing with ultra-short laser pulses enables machining of materials with high accuracy and throughput. The development of novel laser Technologies with laser pulse repetition rates up to the MHz range opened the way for industrial manufacturing processes. From a radiological point of view this evolution is important, because x-ray radiation can be generated as an unwanted side effect in laser material processing. Even if the emitted x-ray dose per pulse is comparably low, the x-ray dose can become hazardous to health at high laser repetition rates. Therefore, radiation protection must be considered. This article provides an overview on the generation and detection of x-rays in laser material processing, as well as on the handling of this radiation risk in the framework of radiological protection. KW - Ultra-short pulse laser processing KW - Laser-induced x-ray emission KW - Radiation protection PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-522376 DO - https://doi.org/10.1088/1361-6498/abcb16 VL - 41 IS - 1 SP - R28 EP - R42 AN - OPUS4-52237 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Mann, Guido A1 - Krüger, Jörg ED - Jitsuno, T. ED - Shao, J. ED - Rudolph, W. T1 - Nanosecond laser damage of optical multimode fibers T2 - Proceedings of SPIE N2 - For pulse laser materials processing often optical step index and gradient index multimode fibers with core diameters ranging from 100 to 600 μm are used. The design of a high power fiber transmission system must take into account limitations resulting from both surface and volume damage effects. Especially, breakdown at the fiber end faces and self-focusing in the fiber volume critically influence the fiber performance. At least operation charts are desirable to select the appropriate fiber type for given laser parameters. In industry-relevant studies the influence of fiber core diameter and end face preparation on laser-induced (surface) damage thresholds (LIDT) was investigated for frequently used all-silica fiber types (manufacturer LEONI). Experiments on preform material (initial fiber material) and compact specimens (models of the cladding and coating material) accompanied the tests performed in accordance with the relevant LIDT standards ISO 21254-1 and ISO 21254 2 for 1-on-1 and S-on-1 irradiation conditions, respectively. The relation beam diameter vs. LIDT was investigated for fused silica fibers. Additionally, laser-induced (bulk) damage thresholds of fused silica preform material F300 (manufacturer Heraeus) in dependence on external mechanical stress simulating fiber bending were measured. All experiments were performed with 10-ns laser pulses at 1064 and 532 nm wavelength with a Gaussian beam profile. T2 - Pacific Rim Laser Damage 2016 CY - Yokohama, Japan DA - 18.05.2016 KW - laser damage KW - optical fiber KW - nanosecond laser KW - fused silica PY - 2016 DO - https://doi.org/10.1117/12.2238515 VL - 9983 SP - 99830T AN - OPUS4-37140 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CHAP A1 - Symietz, Christian A1 - Krüger, Jörg ED - Vilar, Rui T1 - Stability of laser surface modified implants T2 - Laser Surface Modification of Biomaterials: Techniques and applications N2 - A new technique to fix bioceramic powder on a titanium alloy by using femtosecond laser pulses is presented. It is shown that gentle fixation of a bioactive dielectric material on a metallic model implant is successful. This is potentially a new tool for the improvement of bone prostheses. An advantage of the ultrashort pulses is the very low heat influx into the whole sample. There is only a very thin interaction zone during the fixing, which is the metal surface in contact with the ceramic layer. Neither the fixed ceramic particles nor the major part of the metal suffer any modification. The stability of the model implant (ceramic on metal) is investigated by rotating bending fatigue tests. No indication of a reduction of the mechanical stability compared to untreated metallic reference samples was found. KW - Bone implant KW - Calcium phosphate coating KW - Femtosecond laser KW - Laser-induced fixation KW - Titanium alloy PY - 2016 SN - 978-0-08-100883-6 SN - 978-0-08-100942-0 DO - https://doi.org/10.1016/B978-0-08-100883-6.00004-6 SN - 2049-9485 IS - 111 SP - Chapter 4, 127 EP - 143 PB - Elsevier ET - 1st edition AN - OPUS4-36790 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Derrien, Thibault A1 - Koter, Robert A1 - Krüger, Jörg A1 - Höhm, S. A1 - Rosenfeld, A. A1 - Bonse, Jörn T1 - Plasmonic formation mechanism of periodic 100-nm-structures upon femtosecond laser irradiation of silicon in water JF - Journal of applied physics N2 - The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of silicon by multiple (N = 100) linearly polarized Ti:sapphire femtosecond laser pulses (duration τ = 30 fs, center wavelength λ0 ~ 790 nm) is studied experimentally in air and water environment. The LIPSS surface morphologies are characterized by scanning electron microscopy and their spatial periods are quantified by two-dimensional Fourier analyses. It is demonstrated that the irradiation environment significantly influences the periodicity of the LIPSS. In air, so-called low-spatial frequency LIPSS (LSFL) were found with periods somewhat smaller than the laser wavelength (ΛLSFL ~ 0.7 × λ0) and an orientation perpendicular to the laser polarization. In contrast, for laser processing in water a reduced ablation threshold and LIPSS with approximately five times smaller periods ΛLIPSS ~ 0.15 × λ0 were observed in the same direction as in air. The results are discussed within the frame of recent LIPSS theories and complemented by a thin film based surface plasmon polariton model, which successfully describes the tremendously reduced LIPSS periods in water. PY - 2014 DO - https://doi.org/10.1063/1.4887808 SN - 0021-8979 SN - 1089-7550 VL - 116 IS - 7 SP - 074902-1 EP - 074902-8 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-31209 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Koter, Robert A1 - Hartelt, Manfred A1 - Spaltmann, Dirk A1 - Pentzien, Simone A1 - Höhm, S. A1 - Rosenfeld, A. A1 - Krüger, Jörg T1 - Femtosecond laser-induced periodic surface structures on steel and titanium alloy for tribological applications JF - Applied physics A N2 - Laser-induced periodic surface structures (LIPSS, ripples) were generated on stainless steel (100Cr6) and titanium alloy (Ti6Al4V) surfaces upon irradiation with multiple femtosecond laser pulses (pulse duration 30 fs, central wavelength 790 nm). The experimental conditions (laser fluence, spatial spot overlap) were optimized in a sample-scanning geometry for the processing of large surface areas (5 × 5 mm²) covered homogeneously by the nanostructures. The irradiated surface regions were subjected to white light interference microscopy and scanning electron microscopy revealing spatial periods around 600 nm. The tribological performance of the nanostructured surface was characterized by reciprocal sliding against a ball of hardened steel in paraffin oil and in commercial engine oil as lubricants, followed by subsequent inspection of the wear tracks. For specific conditions, on the titanium alloy a significant reduction of the friction coefficient by a factor of more than two was observed on the laser-irradiated (LIPSS-covered) surface when compared to the non-irradiated one, indicating the potential benefit of laser surface structuring for tribological applications. PY - 2014 DO - https://doi.org/10.1007/s00339-014-8229-2 SN - 0947-8396 VL - 117 IS - 1 SP - 103 EP - 110 PB - Springer CY - Berlin AN - OPUS4-31450 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Derrien, Thibault A1 - Krüger, Jörg A1 - Itina, T.E. A1 - Höhm, S. A1 - Rosenfeld, A. A1 - Bonse, Jörn T1 - Rippled area formed by surface plasmon polaritons upon femtosecond laser double-pulse irradiation of silicon: the role of carrier generation and relaxation processes JF - Applied physics A N2 - The formation of laser-induced periodic surface structures (LIPSS, ripples) upon irradiation of silicon with multiple irradiation sequences consisting of femtosecond laser pulse pairs (pulse duration 150 fs, central wavelength 800 nm) is studied numerically using a rate equation system along with a two-temperature model accounting for one- and two-photon absorption and subsequent carrier diffusion and Auger recombination processes. The temporal delay between the individual equal-energy fs-laser pulses was varied between 0 and ~4 ps for quantification of the transient carrier densities in the conduction band of the laser-excited silicon. The results of the numerical analysis reveal the importance of carrier generation and relaxation processes in fs-LIPSS formation on silicon and quantitatively explain the two time constants of the delay-dependent decrease of the low spatial frequency LIPSS (LSFL) area observed experimentally. The role of carrier generation, diffusion and recombination is quantified individually. PY - 2014 DO - https://doi.org/10.1007/s00339-013-8205-2 SN - 0947-8396 VL - 117 IS - 1 SP - 77 EP - 81 PB - Springer CY - Berlin AN - OPUS4-31451 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mann, Guido A1 - Vogel, Jens A1 - Zoheidi, M. A1 - Eberstein, Markus A1 - Krüger, Jörg T1 - Breakdown limits of optical multimode fibers for the application of nanosecond laser pulses at 532 nm and 1064 nm wavelength JF - Applied surface science N2 - For many applications, optical multimode fibers are used for the transmission of powerful laser radiation. High light throughput and damage resistance are desirable. Laser-induced breakdown at the end faces of fibers can limit their performance. Therefore, the determination of laser-induced damage thresholds (LIDT) at the surface of fibers is essential. Nanosecond (1064 nm and 532 nm wavelength) single-shot LIDT were measured according to the relevant standard on SiO2 glass preforms (Suprasil F300) as basic materials of the corresponding fibers. For 10 kinds of fused silica fibers (FiberTech) with core diameters between 180 µm and 600 µm, an illumination approach utilizing a stepwise increase of the laser fluence on a single spot was used. For both wavelengths, the LIDT values (0% damage probability) obtained by means of the two methods were compared. The influence of surface preparation (polishing) on damage resistance was investigated. For equal surface finishing, a correlation between drawing speed of the fibers and their surface LIDT values was found. In addition to the surface measurements, bulk LIDT were determined for the preform material. KW - Fiber waveguides KW - Physical radiation damage KW - Laser-beam impact phenomena KW - Glasses KW - Radiation treatment PY - 2009 DO - https://doi.org/10.1016/j.apsusc.2008.07.157 SN - 0169-4332 SN - 1873-5584 VL - 255 IS - 10 SP - 5519 EP - 5522 PB - North-Holland CY - Amsterdam AN - OPUS4-19036 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mann, Guido A1 - Jurke, Mathias A1 - Zoheidi, M. A1 - Eberstein, Markus A1 - Krüger, Jörg T1 - Influence of core diameter and coating material on nanosecond laser-induced damage threshold of optical multimode fibers JF - Journal of optoelectronics and advanced materials N2 - Single and multi pulse laser-induced damage thresholds (LIDT) of core, cladding, and coating materials of high-power optical multimode fibers were determined in accordance with ISO 11254 for 532 nm and 1064 nm wavelength in the 10-ns pulse duration regime with spatial Gaussian beam shape. For all-silica fibers, LIDT increases with rising core diameter in a range between 100-600 µm for a constant cladding-core ratio of 1.2. The damage resistance of the low refracting cladding (0.3 % fluorine doped fused silica) is comparable to the undoped SiO2 core. Coating materials show significantly lower LIDT than light-guiding parts of the fibers. KW - Fiber waveguides (42.81.Qb) KW - Physical radiation damage (61.80.-x) KW - Laser-beam impact phenomena (79.20.Ds) KW - Glasses (81.05.Kf) PY - 2010 SN - 1454-4164 VL - 12 IS - 3 SP - 711 EP - 714 PB - INOE & INFM CY - Bucharest AN - OPUS4-21083 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Koter, Robert A1 - Weise, Matthias A1 - Hertwig, Andreas A1 - Beck, Uwe A1 - Krüger, Jörg T1 - Influence of film thickness and optical constants on femtosecond laser-induced ablation of hydrogenated amorphous carbon films JF - Journal of optoelectronics and advanced materials N2 - Hydrogenated amorphous carbon layers were deposited on BK7 glass in a plasma-assisted chemical vapor deposition process. Low and high refracting films with thicknesses d ranging from 11 nm to 5.8 µm were produced having refractive indices n between 1.68 and 2.41 and linear absorption coefficients of α~100 cm-1 and α~20000 cm-1 at 800 nm wavelength as a result of different plasma modes. Laser ablation thresholds Fth in dependence on d were determined using 30-fs laser pulses. Low absorbing layers show a constant Fth while Fth increases with rising d up to the optical penetration depth of light α-1 for high absorbing films. KW - Physical radiation damage (61.80.-x) KW - Laser-beam impact phenomena (79.20.Ds) KW - Radiation treatment (81.40.Wx) KW - Carbon (81.05.Uw) KW - Optical constants (78.20.Ci) PY - 2010 SN - 1454-4164 VL - 12 IS - 3 SP - 663 EP - 667 PB - INOE & INFM CY - Bucharest AN - OPUS4-21084 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Symietz, Christian A1 - Lehmann, Erhard A1 - Gildenhaar, Renate A1 - Krüger, Jörg A1 - Berger, Georg T1 - Femtosecond laser induced fixation of calcium alkali phosphate ceramics on titanium alloy bone implant material JF - Acta biomaterialia N2 - Femtosecond lasers provide a novel method of attaching bioceramic material to a titanium alloy, thereby improving the quality of bone implants. The ultrashort 30 fs laser pulses (790 nm wavelength) penetrate a thin dip-coated layer of fine ceramic powder, while simultaneously melting a surface layer of the underlying metal. The specific adjustment of the laser parameters (pulse energy and number of pulses per spot) avoids unnecessary melting of the bioactive calcium phosphate, and permits a defined thin surface melting of the metal, which in turn is not heated throughout, and therefore maintains its mechanical stability. It is essential to choose laser energy densities that correspond to the interval between the ablation fluences of both materials involved: about 0.1-0.4 J cm-2. In this work, we present the first results of this unusual technique, including laser ablation studies, scanning electron microscopy and optical microscope images, combined with EDX data. KW - Bone implant KW - Bioceramic coating KW - Titanium KW - Calcium phosphate KW - Femtosecond laser PY - 2010 DO - https://doi.org/10.1016/j.actbio.2010.02.016 SN - 1742-7061 VL - 6 IS - 8 SP - 3318 EP - 3324 PB - Elsevier CY - Amsterdam AN - OPUS4-21446 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Rosenfeld, A. A1 - Krüger, Jörg T1 - Implications of transient changes of optical and surface properties of solids during femtosecond laser pulse irradiation to the formation of laser-induced periodic surface structures JF - Applied surface science N2 - The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of silicon wafer surfaces by linearly polarized Ti:sapphire femtosecond laser pulses (pulse duration 130 fs, central wavelength 800 nm) is studied experimentally and theoretically. In the experiments, so-called low-spatial frequency LIPSS (LSFL) were found with periods smaller than the laser wavelength and an orientation perpendicular to the polarization. The experimental results are analyzed by means of a new theoretical approach, which combines the widely accepted LIPSS theory of Sipe et al. with a Drude model, in order to account for transient (intra-pulse) changes of the optical properties of the irradiated materials. It is found that the LSFL formation is caused by the excitation of surface plasmon polaritons, SPPs, once the initially semiconducting material turns to a metallic state upon formation of a dense free-electron-plasma in the material and the subsequent interference between its electrical field with that of the incident laser beam resulting in a spatially modulated energy deposition at the surface. Moreover, the influence of the laser-excited carrier density and the role of the feedback upon the multi-pulse irradiation and its relation to the excitation of SPP in a grating-like surface structure is discussed. KW - Femtosecond laser ablation KW - Laser-induced periodic surface structures KW - (LIPSS) KW - Optical properties KW - Surface plasmon polaritons KW - Semiconductors KW - Silicon PY - 2011 DO - https://doi.org/10.1016/j.apsusc.2010.11.059 SN - 0169-4332 SN - 1873-5584 VL - 257 IS - 12 SP - 5420 EP - 5423 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-23309 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Symietz, Christian A1 - Lehmann, Erhard A1 - Gildenhaar, Renate A1 - Koter, Robert A1 - Berger, Georg A1 - Krüger, Jörg T1 - Fixation of bioactive calcium alkali phosphate on Ti6Al4V implant material with femtosecond laser pulses JF - Applied surface science N2 - Bone implants made of metal, often titanium or the titanium alloy Ti6Al4V, need to be surface treated to become bioactive. This enables the formation of a firm and durable connection of the prosthesis with the living bone. We present a new method to uniformly cover Ti6Al4V with a thin layer of ceramics that imitates bone material. These calcium alkali phosphates, called GB14 and Ca10, are applied to the metal by dip coating of metal plates into an aqueous slurry containing the fine ceramic powder. The dried samples are illuminated with the 790 nm radiation of a pulsed femtosecond laser. If the laser fluence is set to a value just below the ablation threshold of the ceramic (ca. 0.4 J/cm²) the 30 fs laser pulses penetrate the partly transparent ceramic layer of 20–40 µm thickness. The remaining laser fluence at the ceramic–metal interface is still high enough to generate a thin metal melt layer leading to the ceramic fixation on the metal. The laser processing step is only possible because Ti6Al4V has a lower ablation threshold (between 0.1 and 0.15 J/cm²) than the ceramic material. After laser treatment in a fluence range between 0.1 and 0.4 J/cm², only the particles in contact with the metal withstand a post-laser treatment (ultrasonic cleaning). The non-irradiated rest of the layer is washed off. In this work, we present results of a successful ceramic fixation extending over larger areas. This is fundamental for future applications of arbitrarily shaped implants. KW - Bone implant KW - Bioceramic coating KW - Titanium KW - Calcium phosphate KW - Femtosecond laser PY - 2011 DO - https://doi.org/10.1016/j.apsusc.2010.10.046 SN - 0169-4332 SN - 1873-5584 VL - 257 IS - 12 SP - 5208 EP - 5212 PB - North-Holland CY - Amsterdam AN - OPUS4-23310 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rohloff, M. A1 - Das, S.K. A1 - Höhm, S. A1 - Grunwald, R. A1 - Rosenfeld, A. A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Formation of laser-induced periodic surface structures on fused silica upon multiple cross-polarized double-femtosecond-laser-pulse irradiation sequences JF - Journal of applied physics N2 - The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of fused silica with multiple irradiation sequences consisting of five Ti:sapphire femtosecond (fs) laser pulse pairs (150 fs, 800 nm) is studied experimentally. A Michelson interferometer is used to generate near-equal-energy double-pulse sequences with a temporal pulse delay from -20 to +20 ps between the cross-polarized individual fs-laser pulses (~0.2 ps resolution). The results of multiple double-pulse irradiation sequences are characterized by means of Scanning Electron and Scanning Force Microscopy. Specifically in the sub-ps delay domain striking differences in the surface morphologies can be observed, indicating the importance of the laser-induced free-electron plasma in the conduction band of the solids for the formation of LIPSS. KW - Atomic force microscopy KW - Conduction bands KW - High-speed optical techniques KW - Laser beam effects KW - Scanning electron microscopy KW - Silicon compounds KW - Surface morphology PY - 2011 DO - https://doi.org/10.1063/1.3605513 SN - 0021-8979 SN - 1089-7550 VL - 110 IS - 1 SP - 014910-1 - 014910-4 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-24049 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bonse, Jörn A1 - Solis, J. A1 - Spielmann, C. A1 - Lippert, T. A1 - Krüger, Jörg T1 - Damage mechanisms in polymers upon NIR femtosecond pulse laser irradiation: sub-threshold processes and their implications for laser safety applications T2 - AIP Conference Proceedings 1278 N2 - This contribution investigates laser-induced damage of thin film and bulk polymer samples, with the focus on physical processes occurring close to the damage threshold. In-situ real-time reflectivity (RTR) measurements with picosecond (ps) and nanosecond (ns) temporal resolution were performed on thin polymer films on a timescale up to a few microseconds (µs). A model for polymer thin film damage is presented, indicating that irreversible chemical modification processes take place already below the fluence threshold for macroscopic damage. On dye-doped bulk polymer filters (as used for laser goggles), transmission studies using fs-and ps-laser pulses reveal the optical saturation behavior of the material and its relation to the threshold of permanent damage. Implications of the sub-threshold processes for laser safety applications will be discussed for thin film and bulk polymer damage. T2 - International high-power laser ablation conference CY - Santa Fe, USA DA - 2010-04-18 KW - Polymer KW - Laser damage KW - Ultrashort laser pulses KW - Time-resolved reflectivity measurements KW - Laser safety PY - 2010 UR - http://link.aip.org/link/?APCPCS/1278/56/1 SN - 978-0-7354-0828-9 DO - https://doi.org/10.1063/1.3507148 N1 - Serientitel: AIP conference proceedings – Series title: AIP conference proceedings IS - 1278 SP - 56 EP - 64 PB - American Institute of Physics CY - Melville, NY, USA AN - OPUS4-22156 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pentzien, Simone A1 - Conradi, Andrea A1 - Koter, Robert A1 - Krüger, Jörg T1 - Cleaning of artificially soiled paper using nanosecond, picosecond and femtosecond laser pulses JF - Applied physics A N2 - Cleaning of cultural assets, especially fragile organic materials like paper, is a part of the conservation process. Laser radiation as a non-contact tool offers prospects for that purpose. For the studies presented here, paper model samples were prepared using three different paper types (pure cellulose, rag paper, and wood-pulp paper). Pure cellulose serves as reference material. Rag and woodpulp paper represent essential characteristics of the basic materials of real-world artworks. The papers were mechanically soiled employing pulverized charcoal. Pure and artificially soiled paper samples were treated with laser pulses of 28 fs (800 nm wavelength) and 8–12 ns (532 nm) duration in a multi pulse approach. Additionally, the cellulose reference material was processed with 30 ps (532 nm) laser pulses. Damage and cleaning thresholds of pure and soiled paper were determined for the different laser regimes. Laser working ranges allowing for removal of contamination and avoiding permanent modification to the substrate were found. The specimens prior and after laser illumination were characterized by light-optical microscopy (OM) and scanning electron microscopy (SEM) as well as multi spectral imaging analysis. The work extends previous nanosecond laser cleaning investigations on paper into the ultra-short pulse duration domain. KW - Laser cleaning KW - Ablation KW - Laser impact on surfaces KW - Paper KW - Femtosecond laser PY - 2010 DO - https://doi.org/10.1007/s00339-010-5809-7 SN - 0947-8396 VL - 101 IS - 2 SP - 441 EP - 446 PB - Springer CY - Berlin AN - OPUS4-22155 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Derrien, T. J.-Y. A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Properties of surface plasmon polaritons on lossy materials: lifetimes, periods and excitation conditions JF - Journal of Optics N2 - The possibility to excite surface plasmon polaritons (SPPs) at the interface between two media depends on the optical properties of both media and geometrical aspects. Specific conditions allowing the coupling of light with a plasmon-active interface must be satisfied. Plasmonic effects are well described in noble metals where the imaginary part of the dielectric permittivity is often neglected ('perfect medium approximation (PMA)'). However, some systems exist for which such approximation cannot be applied, hence requiring a refinement of the common SPP theory. In this context, several properties of SPPs such as excitation conditions, period of the electromagnetic field modulation and SPP lifetime then may strongly deviate from that of the PMA. In this paper, calculations taking into account the imaginary part of the dielectric permittivities are presented. The model identifies analytical terms which should not be neglected in the mathematical description of SPPs on lossy materials. These calculations are applied to numerous material combinations resulting in a prediction of the corresponding SPP features. A list of plasmon-active interfaces is provided along with a quantification of the above mentioned SPP properties in the regime where the PMA is not applicable. KW - plasmon lifetime KW - surface plasmon polaritons KW - lossy materials PY - 2016 DO - https://doi.org/10.1088/2040-8978/18/11/115007 SN - 2040-8986 (online) / 2040-8978 (print) VL - 18 IS - 11 SP - 115007 PB - IOP Publishing Ltd AN - OPUS4-37905 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Höhm, S. A1 - Herzlieb, M. A1 - Rosenfeld, A. A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Laser-induced periodic surface structures on fused silica upon cross-polarized two-color double-fs-pulse irradiation JF - Applied surface science N2 - The dynamics of the formation of laser-induced periodic surface structures (LIPSS) on fused silica upon irradiation with linearly polarized fs-laser pulses (50 fs pulse duration) is studied by cross-polarized two-color double-fs-pulse experiments. In order to analyze the relevance of temporally distributed energy deposition in the early stage of LIPSS formation, a Mach-Zehnder interferometer was used for generating multiple double-pulse sequences at two different wavelengths (400 and 800 nm). The inter-pulse delay between the individual cross-polarized pulses of each sequence was systematically varied in the sub-ps range and the resulting LIPSS morphologies were characterized by scanning electron microscopy. It is found that the polarization of the first laser pulse arriving to the surface determines the orientation and the periodicity of the LIPSS. These two-color experiments further confirm the importance of the ultrafast energy deposition to the silica surface for LIPSS formation, particularly by the first laser pulse of each sequence. The second laser pulse subsequently reinforces the previously seeded spatial LIPSS characteristics (period, orientation). KW - Laser-induced periodic surface structures (LIPSS) KW - Femtosecond laser ablation KW - Double-pulse experiments KW - Ultrafast optical techniques KW - Mach-Zehnder interferometer PY - 2015 DO - https://doi.org/10.1016/j.apsusc.2014.09.101 SN - 0169-4332 SN - 1873-5584 VL - 336 SP - 39 EP - 42 PB - North-Holland CY - Amsterdam AN - OPUS4-32860 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Koter, Robert A1 - Hartelt, Manfred A1 - Spaltmann, Dirk A1 - Pentzien, Simone A1 - Höhm, S. A1 - Rosenfeld, A. A1 - Krüger, Jörg T1 - Tribological performance of femtosecond laser-induced periodic surface structures on titanium and a high toughness bearing steel JF - Applied surface science N2 - Laser-induced periodic surface structures (LIPSS, ripples) were processed on steel (X30CrMoN15-1) and titanium (Ti) surfaces by irradiation in air with linear polarized femtosecond laser pulses with a pulse duration of 30 fs at 790 nm wavelength. For the processing of large LIPSS covered surface areas (5 mm × 5 mm), the laser fluence and the spatial spot overlap were optimized in a sample-scanning geometry. The laser-processed surfaces were characterized by optical microscopy (OM), white light interference microscopy (WLIM) and scanning electron microscopy (SEM). Spatial LIPSS periods between 450 and 600 nm were determined. The nanostructured surface regions were tribologically tested under reciprocal sliding conditions against a 10-mm diameter ball of hardened 100Cr6 steel. Paraffin oil and engine oil were used as lubricants for 1000 sliding cycles at 1 Hz with a normal load of 1.0 N. The corresponding wear tracks were analyzed by OM and SEM. In particular cases, the laser-generated nanostructures endured the tribological treatment. Simultaneously, a significant reduction of the friction coefficient and the wear was observed in the laser-irradiated (LIPSS-covered) areas when compared to the non-irradiated surface. The experiments reveal the potential benefit of laser surface structuring for tribological applications. KW - Laser-induced periodic surface structures (LIPSS) KW - Femtosecond laser processing KW - Tribology KW - Metals PY - 2015 DO - https://doi.org/10.1016/j.apsusc.2014.08.111 SN - 0169-4332 SN - 1873-5584 VL - 336 SP - 21 EP - 27 PB - North-Holland CY - Amsterdam AN - OPUS4-32861 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Höhm, S. A1 - Rosenfeld, A. A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Laser-induced periodic surface structures on titanium upon single- and two-color femtosecond double-pulse irradiation JF - Optics express N2 - Single- and two-color double-fs-pulse experiments were performed on titanium to study the dynamics of the formation of laser-induced periodic surface structures (LIPSS). A Mach-Zehnder inter-ferometer generated polarization controlled (parallel or cross-polarized) double-pulse sequences in two configurations – either at 800 nm only, or at 400 and 800 nm wavelengths. The inter-pulse delays of the individual 50-fs pulses ranged up to some tens of picoseconds. Multiple of these single- or two-color double-fs-pulse sequences were collinearly focused by a spherical mirror to the sample surface. In both experimental configurations, the peak fluence of each individual pulse was kept below its respective ablation threshold and only the joint action of both pulses lead to the formation of LIPSS. Their resulting characteristics were analyzed by scanning electron microscopy and the periods were quantified by Fourier analyses. The LIPSS periods along with the orientation allow a clear identification of the pulse which dominates the energy coupling to the material. A plasmonic model successfully explains the delay-dependence of the LIPSS on titanium and confirms the importance of the ultrafast energy deposition stage for LIPSS formation. PY - 2015 DO - https://doi.org/10.1364/OE.23.025959 SN - 1094-4087 VL - 23 IS - 20 SP - 25959 EP - 25971 PB - Optical Society of America CY - Washington, DC AN - OPUS4-34354 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Höhm, S. A1 - Herzlieb, M. A1 - Rosenfeld, A. A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Femtosecond laser-induced periodic surface structures on silicon upon polarization controlled two-color double-pulse irradiation JF - Optics express N2 - Two-color double-fs-pulse experiments were performed on silicon wafers to study the temporally distributed energy deposition in the formation of laser-induced periodic surface structures (LIPSS). A Mach-Zehnder interferometer generated parallel or cross-polarized double-pulse sequences at 400 and 800 nm wavelength, with inter-pulse delays up to a few picoseconds between the sub-ablation 50-fs-pulses. Multiple two-color double-pulse sequences were collinearly focused by a spherical mirror to the sample. The resulting LIPSS characteristics (periods, areas) were analyzed by scanning electron microscopy. A wavelength-dependent plasmonic mechanism is proposed to explain the delay-dependence of the LIPSS. These two-color experiments extend previous single-color studies and prove the importance of the ultrafast energy deposition for LIPSS formation. PY - 2015 DO - https://doi.org/10.1364/OE.23.000061 SN - 1094-4087 VL - 23 IS - 1 SP - 61 EP - 71 PB - Optical Society of America CY - Washington, DC AN - OPUS4-32405 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Höhm, S. A1 - Kirner, Sabrina V. A1 - Rosenfeld, A. A1 - Krüger, Jörg T1 - Laser-induced periodic surface structures — a scientific evergreen JF - IEEE Journal of Selected Topics in Quantum Electronics N2 - Laser-induced periodic surface structures (LIPSS, ripples) are a universal phenomenon and can be generated on almost any material upon irradiation with linearly polarized radiation. With the availability of ultrashort laser pulses, LIPSS have gained an increasing attraction during the past decade, since these structures can be generated in a simple single-step process, which allows a surface nanostructuring for tailoring optical, mechanical, and chemical surface properties. In this study, the current state in the field of LIPSS is reviewed. Their formation mechanisms are analyzed in ultrafast time-resolved scattering, diffraction, and polarization constrained double-pulse experiments. These experiments allow us to address the question whether the LIPSS are seeded via ultrafast energy deposition mechanisms acting during the absorption of optical radiation or via self-organization after the irradiation process. Relevant control parameters of LIPSS are identified, and technological applications featuring surface functionalization in the fields of optics, fluidics, medicine, and tribology are discussed. KW - Laser ablation KW - Nanostructures KW - Surface functionalization KW - Surface texture KW - Laser-induced periodic surface structures (LIPSS) PY - 2017 DO - https://doi.org/10.1109/JSTQE.2016.2614183 SN - 1077-260X SN - 1558-4542 VL - 23 IS - 3 SP - 9000615 PB - IEEE AN - OPUS4-38633 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 JF - MRS Bulletin 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 - Höhm, S. A1 - Rosenfeld, A. A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Laser-induced periodic surface structures on zinc oxide crystals upon two-colour femtosecond double-pulse irradiation JF - Physica Scripta N2 - In order to study the temporally distributed energy deposition in the formation of laser-induced periodic surface structures (LIPSS) on single-crystalline zinc oxide (ZnO), two-colour double-fs-pulse experiments were performed. Parallel or cross-polarised double-pulse sequences at 400 and 800 nm wavelength were generated by a Mach–Zehnder interferometer, exhibiting inter-pulse delays up to a few picoseconds between the sub-ablation 50-fs-pulses. Twenty two-colour double-pulse sequences were collinearly focused by a spherical mirror to the sample surface. The resulting LIPSS periods and areas were analysed by scanning electron microscopy. The delay-dependence of these LIPSS characteristics shows a dissimilar behaviour when compared to the semiconductor silicon, the dielectric fused silica, or the metal titanium. A wavelength-dependent plasmonic mechanism is proposed to explain the delay-dependence of the LIPSS on ZnO when considering multi-photon excitation processes. Our results support the involvement of nonlinear processes for temporally overlapping pulses. These experiments extend previous two-colour studies on the indirect semiconductor silicon towards the direct wide band-gap semiconductor ZnO and further manifest the relevance of the ultrafast energy deposition for LIPSS formation. KW - Laser-induced periodic surface structures, LIPSS KW - Laser ablation KW - Surface plasmon polariton PY - 2017 DO - https://doi.org/10.1088/1402-4896/aa5578 SN - 1402-4896 SN - 0031-8949 VL - 92 IS - 3 SP - Article 034003, 1 EP - 7 PB - IOP CY - Bristol, UK AN - OPUS4-39082 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schmid, M. A1 - Heidmann, B. A1 - Ringleb, F. A1 - Eylers, K. A1 - Ernst, O. A1 - Andree, Stefan A1 - Bonse, Jörn A1 - Boeck, T. A1 - Krüger, Jörg T1 - Locally grown Cu(In,Ga)Se2 micro islands for concentrator solar cells T2 - Proceedings of SPIE 10527, Physics, Simulation, and Photonic Engineering of Photovoltaic Devices VII N2 - Light concentration opens up the path to enhanced material efficiency of solar cells via increased conversion efficiency and decreased material requirement. For true material saving, a fabrication method allowing local growth of high quality absorber material is essential. We present two scalable fs-laser based approaches for bottom-up growth of Cu(In,Ga)Se2 micro islands utilizing either site-controlled assembly of In(,Ga) droplets on laser-patterned substrates during physical vapor deposition, or laser-induced forward transfer of (Cu,In,Ga) layers for local precursor arrangement. The Cu(In,Ga)Se2 absorbers formed after selenization can deliver working solar devices showing efficiency enhancement under light concentration. T2 - SPIE OPTO, 2018 CY - San Francisco, USA DA - 29.01.2018 KW - Chalcopyrite KW - Cu(In,Ga)Se2 KW - Fs-laser patterning KW - Laser-induced forward transfer KW - Micro solar cell PY - 2018 SN - 978-1-5106-1540-3 SN - 0277-786X SN - 1996-756X VL - 10527 SP - 1052707-1 EP - 1052707-9 PB - SPIE CY - Bellingham, WA, USA AN - OPUS4-44450 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bonse, Jörn A1 - Kirner, Sabrina V. A1 - Griepentrog, Michael A1 - Spaltmann, Dirk A1 - Krüger, Jörg T1 - Femtosecond laser texturing of surfaces for tribological applications JF - Materials N2 - Laser texturing is an emerging technology for generating surface functionalities on basis of optical, mechanical, or chemical properties. Taking benefit of laser sources with ultrashort (fs) pulse durations features outstanding precision of machining and negligible rims or burrs surrounding the laser-irradiation zone. Consequently, additional mechanical or chemical post-processing steps are usually not required for fs-laser surface texturing (fs-LST). This work aimed to provide a bridge between research in the field of tribology and laser materials processing. The paper reviews the current state-of-the-art in fs-LST, with a focus on the tribological performance (friction and wear) of specific self-organized surface structures (so-called ripples, grooves, and spikes) on steel and titanium alloys. On the titanium alloy, specific sickle-shaped hybrid micro-nanostructures were also observed and tribologically tested. Care is taken to identify accompanying effects affecting the materials hardness, superficial oxidation, nano- and microscale topographies, and the role of additives contained in lubricants, such as commercial engine oil. KW - Femtosecond laser processing KW - Surface texture KW - Laser-induced periodic surface structures (LIPSS) KW - Friction KW - Wear PY - 2018 UR - http://www.mdpi.com/1996-1944/11/5/801 DO - https://doi.org/10.3390/ma11050801 SN - 1996-1944 VL - 11 IS - 5 SP - 801, 1 EP - 19 PB - MDPI AG CY - Basel, Switzerland AN - OPUS4-44905 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 JF - Applied physics A 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 - Stratakis, E. A1 - Bonse, Jörn A1 - Heitz, J. A1 - Siegel, J. A1 - Tsibidis, G.D. A1 - Skoulas, E. A1 - Papadopoulos, A. A1 - Mimidis, A. A1 - Joel, A.-C. A1 - Comanns, P. A1 - Krüger, Jörg A1 - Florian, C. A1 - Fuentes-Edfuf, Y. A1 - Solis, J. A1 - Baumgartner, W. T1 - Laser engineering of biomimetic surfaces JF - Materials Science and Engineering: R: Reports N2 - 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. KW - Biomimetic surfaces KW - Laser processing KW - Surface functionalization KW - Bioinspiration KW - Bionic materials PY - 2020 DO - https://doi.org/10.1016/j.mser.2020.100562 SN - 0927-796X VL - 141 SP - 100562-1 EP - 100562-47 PB - Elsevier B.V. AN - OPUS4-50927 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lone, S. A. A1 - Muck, M. A1 - Fosodeder, P. A1 - Mardare, C.C. A1 - Florian, Camilo A1 - Weth, A. A1 - Krüger, Jörg A1 - Steinwender, C. A1 - Baumgartner, W. A1 - Bonse, Jörn A1 - Heitz, J. A1 - Hassel, A.W. T1 - Impact of Femtosecond Laser Treatment Accompanied with Anodization of Titanium Alloy on Fibroblast Cell Growth JF - Physica Status Solidi A N2 - 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. KW - Anodization KW - Femtosecond laser ablation KW - Laser-induced periodic surface structures, LIPSS KW - Ti6Al4V alloys KW - X-ray photoelectron spectroscopy PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-510263 DO - https://doi.org/https://doi.org/10.1002/pssa.201900838 SN - 1862-6300 SN - 1862-6319 VL - 217 IS - 13 SP - 1900838-1 EP - 1900838-9 PB - WILEY-VCH Verlag CY - Weinheim, Germany AN - OPUS4-51026 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Florian, Camilo A1 - Kirner, Sabrina V. A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Surface functionalization by laser-induced periodic surface structures JF - Journal of Laser Applications N2 - In recent years, the improved understanding of the formation of laser-induced periodic surface structures (LIPSS) has led to an emerging variety of applications that modify the optical, mechanical, and chemical properties of many materials. Such structures strongly depend on the laser beam polarization and are formed usually after irradiation with ultrashort linearly polarized laser pulses. The most accepted explanation for the origin of the structures is based on the interference of the incident laser radiation with electromagnetic surface waves that propagate or scatter at the surface of the irradiated materials. This leads to an intensity modulation that is finally responsible for the selective ablation in the form of parallel structures with periods ranging from hundreds of nanometers up to some micrometers. The versatility when forming such structures is based on the high reproducibility with different wavelengths, pulse durations and repetition rate laser sources, customized micro- and nanometric spatial resolutions, and compatibility with industrially relevant processing speeds when combined with fast scanning devices. In this contribution, we review the latest applications in the rapidly emerging field of surface functionalization through LIPSS, including biomimetic functionalities on fluid transport, control of the wetting properties, specific optical responses in technical materials, improvement of tribological performance on metallic surfaces, and bacterial and cell growth for medical devices, among many others. KW - Laser-induced periodic surface structures (LIPSS) KW - Laser processing KW - Surface functionalization KW - Applications PY - 2020 DO - https://doi.org/10.2351/7.0000103 SN - 1938-1387 VL - 32 IS - 2 SP - 022063 PB - Laser Institute of America AN - OPUS4-50780 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmidt, Birgit Angelika A1 - Ziemann, M. A A1 - Pentzien, Simone A1 - Gabsch, T. A1 - Koch, W. A1 - Krüger, Jörg T1 - Technical analysis of a Central Asian wall painting detached from a Buddhist cave temple on the northern Silk Road JF - Studies in Conservation N2 - A great number of Central Asian wall paintings, archeological materials, architectural fragments, and textiles, as well as painting fragments on silk and paper, make up the so called Turfan Collection at the Asian Art Museum in Berlin. The largest part of the collection comes from the Kucha region, a very important cultural center in the third to ninth centuries. Between 1902 and 1914, four German expeditions traveled along the northern Silk Road. During these expeditions, wall paintings were detached from their original settings in Buddhist cave complexes. This paper reports a technical study of a wall painting, existing in eight fragments, from the Buddhist cave no. 40 (Ritterhöhle). Its original painted surface is soot blackened and largely illegible. Grünwedel, leader of the first and third expeditions, described the almost complete destruction of the rediscovered temple complex and evidence of fire damage. The aim of this case study is to identify the materials used for the wall paintings. Furthermore, soot deposits as well as materials from conservation interventions were of interest. Non-invasive analyses were preferred but a limited number of samples were taken to provide more precise information on the painting technique. By employing optical and scanning electron microscopy, energy dispersive X-ray spectroscopy, micro X-ray fluorescence spectroscopy, X-ray diffraction analysis, and Raman spectroscopy, a layer sequence of earthen render, a ground layer made of gypsum, and a paint layer containing a variety of inorganic pigments were identified. KW - Wall paintings KW - Central Asia KW - Silk Road KW - Pigments KW - Microscopy PY - 2016 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-357297 DO - https://doi.org/10.1179/2047058414Y.0000000152 VL - 61 IS - 2 SP - 113 EP - 122 PB - Routledge Taylor & Francis Group CY - London AN - OPUS4-35729 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ringleb, F. A1 - Eylers, K. A1 - Teubner, T. A1 - Boeck, T. A1 - Symietz, Christian A1 - Bonse, Jörn A1 - Andree, Stefan A1 - Krüger, Jörg A1 - Heidmann, B. A1 - Schmid, M. A1 - Lux-Steiner, M. T1 - Regularly arranged indium islands on glass/molybdenum substrates upon femtosecond laser and physical vapor deposition processing JF - Applied Physics Letters N2 - A bottom-up approach is presented for the production of arrays of indium islands on a molybdenum layer on glass, which can serve as micro-sized precursors for indium compounds such as copper-indium-gallium-diselenide used in photovoltaics. Femtosecond laser ablation of glass and a subsequent deposition of a molybdenum film or direct laser processing of the molybdenum film both allow the preferential nucleation and growth of indium islands at the predefined locations in a following indium-based physical vapor deposition (PVD) process. A proper choice of laser and deposition parameters ensures the controlled growth of indium islands exclusively at the laser ablated spots. Based on a statistical analysis, these results are compared to the non-structured molybdenum surface, leading to randomly grown indium islands after PVD. KW - Femtosecond laser KW - Physical vapor deposition KW - Indium KW - Molybdenum substrate KW - Microconcentrator solar cell PY - 2016 DO - https://doi.org/10.1063/1.4943794 SN - 0003-6951 VL - 108 IS - 11 SP - 111904-1 EP - 111904-4 AN - OPUS4-35602 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 JF - Applied Surface Science 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 - Höhm, S. A1 - Herzlieb, M. A1 - Rosenfeld, A. A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Dynamics of the formation of laser-induced periodic surface structures (LIPSS) upon femtosecond two-color double-pulse irradiation of metals, semiconductors, and dielectrics JF - Applied Surface Science N2 - In order to address the dynamics and physical mechanisms of LIPSS formation for three different classes of materials (metals, semiconductors, and dielectrics), two-color double-fs-pulse experiments were performed on Titanium, Silicon and Fused Silica. For that purpose a Mach–Zehnder interferometer generated polarization controlled (parallel or cross-polarized) double-pulse sequences at 400 nm and 800 nm wavelength, with inter-pulse delays up to a few picoseconds. Multiple of these two-color double-pulse sequences were collinearly focused by a spherical mirror to the sample surfaces. The fluence of each individual pulse (400 nm and 800 nm) was always kept below its respective ablation threshold and only the joint action of both pulses lead to the formation of LIPSS. Their resulting characteristics (periods, areas) were analyzed by scanning electron microscopy. The periods along with the LIPSS orientation allow a clear identification of the pulse which dominates the energy coupling to the material. For strong absorbing materials (Silicon, Titanium), a wavelength-dependent plasmonic mechanism can explain the delay-dependence of the LIPSS. In contrast, for dielectrics (Fused Silica) the first pulse always dominates the energy deposition and LIPSS orientation, supporting a non-plasmonic formation scenario. For all materials, these two-color experiments confirm the importance of the ultrafast energy deposition stage for LIPSS formation. KW - Femtosecond laser ablation KW - Double-pulse experiments KW - Laser-induced periodic surface structures (LIPSS) KW - Mach-Zehnder interferometer KW - Ultrafast optical techniques PY - 2016 UR - http://www.sciencedirect.com/science/article/pii/S0169433215031347 DO - https://doi.org/10.1016/j.apsusc.2015.12.129 SN - 0169-4332 SN - 1873-5584 VL - 374 SP - 331 EP - 338 PB - Elsevier CY - Amsterdam, Netherlands AN - OPUS4-35938 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Florian, Camilo A1 - Wonneberger, R. A1 - Undisz, A. A1 - Kirner, Sabrina V. A1 - Wasmuth, Karsten A1 - Spaltmann, Dirk A1 - Krüger, Jörg A1 - Bonse, Jörn T1 - Chemical effects during the formation of various types of femtosecond laser-generated surface structures on titanium alloy JF - Applied Physics A N2 - In this contribution, chemical, structural, and mechanical alterations in various types of femtosecond laser-generated surface structures, i.e., laser-induced periodic surface structures (LIPSS, ripples), Grooves, and Spikes on titanium alloy, are characterized by various surface analytical techniques, including X-ray diffraction and glow-discharge optical emission spectroscopy. The formation of oxide layers of the different laser-based structures inherently influences the friction and wear performance as demonstrated in oil-lubricated reciprocating sliding tribological tests (RSTTs) along with subsequent elemental mapping by energy-dispersive X-ray analysis. It is revealed that the fs-laser scan processing (790 nm, 30 fs, 1 kHz) of near-wavelength-sized LIPSS leads to the formation of a graded oxide layer extending a few hundreds of nanometers into depth, consisting mainly of amorphous oxides. Other superficial fs-laser-generated structures such as periodic Grooves and irregular Spikes produced at higher fluences and effective number of pulses per unit area present even thicker graded oxide layers that are also suitable for friction reduction and wear resistance. Ultimately, these femtosecond laser-induced nanostructured surface layers efficiently prevent a direct metal-to-metal contact in the RSTT and may act as an anchor layer for specific wear-reducing additives contained in the used engine oil. KW - Laser-induced oxide layer KW - Laser-induced periodic surface strctures (LIPSS) KW - Femtosecond laser processing KW - Tribology KW - Surface processing PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-505660 DO - https://doi.org/10.1007/s00339-020-3434-7 SN - 0947-8396 SN - 1432-0630 VL - 126 IS - 4 SP - 266 PB - Springer Nature Switzerland AG AN - OPUS4-50566 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Legall, Herbert A1 - Schwanke, Christoph A1 - Bonse, Jörn A1 - Krüger, Jörg T1 - X-ray radiation protection aspects during ultrashort laser processing JF - Journal of Laser Applications N2 - Ultrashort pulse laser processing of materials allows for precise machining with high accuracy. By increasing the repetition rate to several 100 kHz, laser machining becomes quick and cost-effective. Ultrafast laser processing at high repetition rates and peak intensities above 10^13 W/cm^2 can cause a potential hazard by generation of unwanted x-ray radiation. Therefore, radiation protection must be considered. For 925 fs pulse duration at a center wavelength of 1030 nm, the x-ray emission in air at a repetition rate of 400 kHz was investigated up to a peak intensity of 2.6 × 10^14 W/cm^2. Based on the presented measurements, the properties of potential shielding materials will be discussed. By extending our previous works, a scaling of the x-ray radiation emission to higher peak intensities up to 10^15 W/cm^2 is described, and emitted x-ray doses are predicted. KW - Laser ablation KW - Ultrashort pulse laser processing KW - Laser-induced x-ray emission KW - Radiation protection PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-505677 DO - https://doi.org/10.2351/1.5134778 VL - 32 IS - 2 SP - 022004 AN - OPUS4-50567 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schwibbert, Karin A1 - Menzel, F. A1 - Epperlein, N. A1 - Bonse, Jörn A1 - Krüger, Jörg T1 - Bacterial adhesion on femtosecond laser-modified polyethylene JF - Materials N2 - In this study, femtosecond laser-induced sub-micrometer structures are generated to modify polyethylene (PE) surface topographies. These surfaces were subjected to bacterial colonization studies with Escherichia coli and Staphylococcus aureus as test strains. The results reveal that the nanostructures do not influence S. aureus coverage, while the adhesion of E. coli is reduced. KW - Bacterial adhesion KW - Laser-modified surface KW - Polyethylene KW - Laser-induced nanostructures KW - Biofilm PY - 2019 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-492280 DO - https://doi.org/10.3390/ma12193107 VL - 12 IS - 19 SP - 3107 PB - MDPI CY - Basel, Schweiz AN - OPUS4-49228 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -