TY - JOUR A1 - Rung, Stefan A1 - Christiansen, Anne A1 - Hellmann, Ralf T1 - Influence of film thickness on laser ablation threshold of transparent conducting oxide thin-films JF - Applied Surface Science KW - Laserablation KW - Dünnschichttechnik Y1 - 2014 VL - 305 SP - 347 EP - 351 ER - TY - CHAP A1 - Rung, Stefan A1 - Bischoff, Christian A1 - Jäger, Erwin A1 - Umhofer, Udo A1 - Hellmann, Ralf T1 - Laser thin film ablation with multiple beams and tailored beam profiles T2 - Proceedings of SPIE 8967, Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XIX KW - Thin film KW - Ablation KW - Top-Hat KW - Parallel Processing KW - Beam-Splitter KW - Laserablation KW - Dünnschichttechnik Y1 - 2014 VL - 8967 ER - TY - JOUR A1 - Rung, Stefan A1 - Rexhepi, Mal A1 - Bischoff, Christian A1 - Hellmann, Ralf T1 - Laserscribing of thin films using top-hat laser beam profiles JF - Journal of Laser Micro/Nanoengineering KW - Laser scribing KW - laser beam shaping KW - Top-Hat KW - Dünne Schicht KW - Laser Y1 - 2013 VL - 8 IS - 3 SP - 309 EP - 314 ER - TY - CHAP A1 - Rung, Stefan A1 - Rexhepi, Mal A1 - Hellmann, Ralf T1 - Beam shaping for enhanced through-put of laser ablation of transparent conductive films T2 - Proceedings of the XXVII MicroCAD International Scientific Conference KW - Laserablation Y1 - 2013 VL - 2013 ER - TY - JOUR A1 - Bischoff, Christian A1 - Rung, Stefan A1 - Hellmann, Ralf T1 - Efficient micromachining of thin film layers with nanosecond lasers – beam shaping optics improve process quality and enhance throughput JF - Laser Technik Journal KW - Laser KW - Nanosekundenbereich KW - Dünne Schicht Y1 - 2012 VL - 9 IS - 5 SP - 15 EP - 20 ER - TY - CHAP A1 - Bischoff, Christian A1 - Jäger, Erwin A1 - Rung, Stefan A1 - Hellmann, Ralf T1 - Diffractive beam shaping optics for efficient micromachining T2 - Proceedings of the LASYS (Internationale Fachmesse für Laser-Materialbearbeitung) – SLT (Stuttgarter Lasertage) 2012 KW - micromachining KW - Laserbearbeitung Y1 - 2012 ER - TY - CHAP A1 - Rung, Stefan A1 - Hellmann, Ralf T1 - Laser scribing of metallized transparent conductive oxide – A comparative study using top hat and Gaussian beam profiles T2 - Proceedings of the XXVI International MicroCAD Conference – Material Processing Technologies KW - laser scribing KW - Laserbearbeitung KW - Laserritzen Y1 - 2012 ER - TY - JOUR A1 - Preusch, Florian A1 - Rung, Stefan A1 - Hellmann, Ralf T1 - Influence of Polishing Orientation on the Generation of LIPSS on Stainless Steel JF - Journal of Laser Micro/Nanoengineering KW - Laserbearbeitung KW - Nicht rostender Stahl Y1 - 2016 U6 - https://doi.org/10.2961/jlmn.2016.01.0025 VL - 11 SP - 137 EP - 142 ER - TY - JOUR A1 - Rung, Stefan A1 - Barth, Johannes A1 - Hellmann, Ralf T1 - Characterization of Laser Beam Shaping Optics Based on Their Ablation Geometry of Thin Films JF - Micromachines N2 - Thin film ablation with pulsed nanosecond lasers can benefit from the use of beam shaping optics to transform the Gaussian beam profile with a circular footprint into a Top-Hat beam profile with a rectangular footprint. In general, the quality of the transformed beam profile depends strongly on the beam alignment of the entire laser system. In particular, the adjustment of the beam shaping element is of upmost importance. For an appropriate alignment of the beam shaper, it is generally necessary to observe the intensity distribution near the focal position of the applied focusing optics. Systems with a low numerical aperture (NA) can commonly be qualified by means of laser beam profilers, such as a charge-coupled device (CCD) camera. However, laser systems for micromachining typically employ focus lenses with a high NA, which generate focal spot sizes of only several microns in diameter. This turns out to be a challenge for common beam profiling measurement systems and complicates the adjustment of the beam shaper strongly. In this contribution, we evaluate the quality of a Top-Hat beam profiling element and its alignment in the working area based on the ablated geometry of single pulse ablation of thin transparent conductive oxides. To determine the best achievable adjustment, we develop a quality index for rectangular laser ablation spots and investigate the influences of different alignment parameters, which can affect the intensity distribution of a Top-Hat laser beam profile. KW - Dünne Schicht KW - Laserablation Y1 - 2014 VL - 5 IS - 4 SP - 943 EP - 953 ER - TY - CHAP A1 - Jäger, Erwin A1 - Rädel, Ulrich A1 - Bischoff, Christian A1 - Umhofer, Udo A1 - Rung, Stefan A1 - Hellmann, Ralf T1 - Laser micromachining – parallel processing with multiple top hat beams T2 - 8th International Conference on Photonic Technologies LANE 2014 KW - Laserbearbeitung Y1 - 2014 ER - TY - JOUR A1 - Rung, Stefan A1 - Hellmann, Ralf T1 - Laser-Induced Period Surface Structures to Improve Solderability of Electrical Solder Pads JF - Applied Sciences KW - Laserstrahllöten Y1 - 2021 UR - https://www.mdpi.com/2076-3417/12/1/80/htm U6 - https://doi.org/10.3390/app12010080 VL - 2022 IS - 12/1 SP - 80 EP - 88 ER - TY - JOUR A1 - Rung, Stefan A1 - Häcker, Niklas A1 - Hellmann, Ralf T1 - Thermal imaging of high power ultrashort pulse laser ablation of alumina towards temperature optimized micro machining strategies JF - IOP Conference Series: Materials Science and Engineering KW - Ultrakurzzeitlaser KW - Aluminiumoxide Y1 - 2021 UR - https://iopscience.iop.org/article/10.1088/1757-899X/1135/1/012027 U6 - https://doi.org/0.1088/1757-899X/1135/1/012027 VL - 1135 IS - 012027 SP - 1 EP - 9 ER - TY - CHAP A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Current results on laser-based production of complex optics in glass T2 - 10. Wetzlarer Herbsttagung "Moderne Optikfertigung", 29. - 30. September 2020, Wetzlar KW - Laserbearbeitung KW - Fertigungstechnik Y1 - 2020 ER - TY - CHAP A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - UKP-Prozess mit anschließendem CO2-Laserpolieren zur Fertigung komplexer Optiken T2 - 10. Workshop Laserbearbeitung von Glaswerkstoffen KW - Linse KW - Array KW - Laserbearbeitung KW - Ultrakurzzeitlaser KW - Kohlendioxidlaser Y1 - 2020 ER - TY - JOUR A1 - Zettl, Julian A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Tangential Laser Turning of Fused Silica Using Ultra-short Laser Pulses JF - Journal of Laser Micro/Nanoengineering N2 - Laser turning with ultra-short laser pulses provides the possibility of manufacturing rotationally symmetric geometries, even of hard to machine materials as fused silica, down to a micrometer scale. In this laser micro machining approach, the laser beam is oriented perpendicularly to the rotational axis and tangentially to the material, whereas the target geometry is realized by moving the constantly rotating specimen according to the specified geometry under the focused laser spot. Due to the fric-tion-less laser ablation it is possible to realize a turning process in fused silica without the use of a contacting tool and therefore without causing mechanical tensions in the work piece. The processing head focuses the laser to a calculated spot size of 18 μm in diameter and the applied processing gas pressure assists in removing the ablated material. In this study, femto-second laser turning of fused silica with a diameter of 3.7 mm is investigated. The influence of the applied pulse energy is stated and the use of a trepanning optic during the turning process is characterized. Furthermore, compre-hensive parameter studies in order to optimize roughness and to find the maximum achievable abla-tion rate are shown. Limited by the mechanical speed of the rotational axis, the highest feasible abla-tion rate is 19.5 mm³/min. A roughness of Ra 0.65 μm are demonstrated. KW - Ultra-short Laser Pulses KW - Laser Turning KW - Fused Silica KW - Ablation Rate KW - Process Efficiency KW - Laserbearbeitung KW - Mikrobearbeitung KW - Quarzglas KW - Ultrakurzer Lichtimpuls Y1 - 2021 U6 - https://doi.org/10.2961/jlmn.2021.01.2008 VL - 16 IS - 1 SP - 42 EP - 46 ER - TY - JOUR A1 - Zettl, Julian A1 - Klar, Maximilian A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Laser turning with ultrashort laser pulses JF - Journal of Manufacturing Processes N2 - We report on a comprehensive micromachining study of rotationally symmetric parts using femtosecond laser. A laser turning process with tangential impingement of the laser radiation complemented by a trepanning optics is implemented as to accomplish a true laser lathe micromachining approach. With the objective of optimized ablation rate and reduced surface roughness, the influence of pulse energy, feed rate, trepanning diameter and angular beam incidence, respectively, is investigated for processing stellite rods. We find the smallest feasible feature sizes of 8.5 μm in diameter and smoothest surfaces with an arithmetic average of the roughness profile as low as 0.18 μm. The surface roughness, however, appears to be limited by the occurrence of laser induced periodic surface structures provoked by the femtosecond laser radiation. Furthermore, the variation of the fluence in accordance to the incidence on a curved surface is discussed and the heat input into the material is examined through a longitudinal cross section. KW - Ultrashort laser pulses KW - Turning KW - Ablation rate KW - Tangential processing KW - Trepanning optic KW - Ultrakurzer Lichtimpuls KW - Laserbearbeitung KW - Mikrobearbeitung KW - Femtosekundenlaser Y1 - 2021 U6 - https://doi.org/10.1016/j.jmapro.2021.06.025 VL - 2021 IS - 68 SP - 1562 EP - 1568 ER - TY - JOUR A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Enhanced ablation efficiency using GHz bursts in micromachining fused silica JF - Optics Letters KW - Fräsen KW - Mikrobearbeitung KW - Quarzglas KW - Femtosekundenlaser Y1 - 2021 VL - 46 IS - 2 SP - 282 EP - 285 ER - TY - JOUR A1 - Schwarz, Simon A1 - Götzendorfer, Babette A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Compact Beam Homogenizer Module with Laser-Fabricated Lens-Arrays JF - applied sciences KW - Femtosekundenlaser KW - Linse KW - Array Y1 - 2021 VL - 2021 IS - 11 SP - 1018 EP - 1018 ER - TY - JOUR A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Ultrashort pulsed laser backside ablation of fused silica JF - Optics Express KW - Femtosekundenlaser KW - Quarzglas KW - Mikrobearbeitung Y1 - 2021 VL - 29 IS - 15 SP - 23477 EP - 23486 ER - TY - JOUR A1 - Rung, Stefan A1 - Bokan, Kevin A1 - Kleinwort, Frederick A1 - Schwarz, Simon A1 - Simon, Peter A1 - Klein-Wiele, Jan-Hendrik A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Possibilities of Dry and Lubricated Friction Modification Enabled by Different Ultrashort Laser-Based Surface Structuring Methods JF - Lubricants N2 - In this contribution we report on the possibilities of dry and lubricated friction modification introduced by different laser surface texturing methods. We compare the potential of Laser-Induced Periodic Surface Structures and Laser Beam Interference Ablation on 100Cr6 steel in a linear reciprocating ball-on-disc configuration using 100Cr6 steel and tungsten carbide balls with load forces between 50mN and 1000 mN. For dry friction, we find a possibility to reduce the coefficient of friction and we observe a pronounced direction dependency for surfaces fabricated by Laser Beam Interference Ablation. Furthermore, Laser-Induced Periodic Surface Structures result in a load-dependent friction reduction for lubricated linear reciprocating movements. This work helps to identify the modification behaviour of laser generated micro structures with feature sizes of approximately 1μm and reveals new possibilities for surface engineering KW - laser-induced periodic surface structures KW - laser beam interference ablation KW - dry friction KW - lubricated friction KW - laser surface texturing KW - Laser KW - Oberflächenstruktur Y1 - 2019 U6 - https://doi.org/10.3390/lubricants7050043 VL - 7 IS - 43 SP - 1 EP - 13 ER - TY - JOUR A1 - Rung, Stefan A1 - Bokan, Kevin A1 - Rutsch, Kevin A1 - Schwarz, Simon A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Laser Induced Periodic Surface Structures on 100Cr6 Steel for Modification of Friction Demonstrated with Stribeck Test JF - Journal of Laser Micro/Nanoengineering N2 - In this contribution, we report on surface functionalization by introducing laser induced periodic surface structures on 100Cr6 bearing steel to modify complex tribological properties. The advanced approach of this study is the measurement of the coefficient of friction by performing a ball-on-disk Stribeck test on laser structured surfaces with polytetrafluoroethylene balls in a lubricant environment. The Stribeck test reveals the modified friction behavior using translation speeds up to 106 mm/min and load forces between 100 mN and 5000 mN. Our results show increased stiction and coefficient of friction for laser structured surfaces in the regime of boundary lubrication which is attributed to the laser induced surface asperities. Decreased coefficient of friction is observed in the regime of mixed and hydrodynamic lubrication, i.e. for velocities higher than 1000 mm/min, for surfaces covered by laser induced periodic surface structures with low spatial frequency. KW - Laser KW - Oberflächenstruktur Y1 - 2018 U6 - https://doi.org/10.2961/jlmn.2018.03.0004 VL - 13 IS - 3 SP - 160 EP - 165 ER -