TY - CHAP A1 - Franz, Daniel A1 - Roth, Gian-Luca A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Superimposed beam deflection using acousto-optical deflectors in combination with a galvanometer scanner T2 - Lasers in Manufacturing - LiM 2021 KW - Galvanometer Y1 - 2021 ER - TY - CHAP A1 - Glaab, Johannes A1 - Hellmann, Ralf T1 - Small-scale low-through UV-C LED disinfection device, in waste processing and recycling T2 - Proceedings of the XXIV international Scientific conference Miskolc, Ungarn KW - Lumineszenzdiode KW - Desinfektionsapparat Y1 - 2014 ER - TY - CHAP A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Hellmann, Ralf T1 - Simulation of process parameters towards the generation of low spatial frequency LIPSS on dielectric materials T2 - MultiScience - XXX. microCAD International Multidisciplinary Scientific Conference KW - Laserbestrahlung KW - Quarzglas Y1 - 2016 ER - TY - CHAP A1 - Kefer, Stefan A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Sapphire-Based Planar Bragg Grating Devices T2 - 28th International Conference on Optical Fiber Sensors N2 - This study reports on the long-term stability and the high-temperature capability of sapphire-based photonic crystal waveguides with integrated Bragg gratings. Furthermore, their Bragg grating reflectivity as well as their temperature sensitivity is quantified. KW - Bragg-Reflektor KW - Wellenleiter Y1 - 2023 SN - 978-1-957171-30-2 U6 - https://doi.org/10.1364/OFS.2023.W2.4 ER - TY - CHAP A1 - Kefer, Stefan A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - POLYMER PLANAR BRAGG GRATINGS BASED ON BULK CYCLIC OLEFIN COPOLYMERS: FABRICATION AND FUNCTIONALIZATION T2 - Proceedings of Student Conference on Sensors, Systems and Measurement 2021 KW - Bragg-Reflektor Y1 - 2021 UR - https://scssm.fel.cvut.cz/wp-content/uploads/2021/07/Proceedings-SCSSM-2021.pdf SN - 978-80-01-06822-9 ER - TY - CHAP A1 - Scheurich, Steffen A1 - Belle, Stefan A1 - Hellmann, Ralf A1 - So, Sik A1 - Sparrow, Ian A1 - Emmerson, Greg T1 - Planar optical waveguide bragg grating chemical sensor for online process control T2 - 3rd integrated optics - sensors, sensing structures and methodes Korbielow, PL KW - Bragg-Reflektor KW - Sensor Y1 - 2014 ER - TY - CHAP A1 - Sommer, David A1 - Hornung, Simon A1 - Esen, Cemal A1 - Hellmann, Ralf ED - Gu, Bo ED - Chen, Hongqiang T1 - Optimization of mechanical properties of additive manufactured IN 718 parts combining LPBF and in-situ high-speed milling T2 - Laser 3D Manufacturing XI KW - Hybrid additive manufacturing KW - High-speed Milling KW - Hot isostatic pressing KW - Fatigue behaviour KW - Hochgeschwindigkeitsfräsen Y1 - 2024 U6 - https://doi.org/http://dx.doi.org/10.1117/12.3000952 PB - SPIE ER - TY - CHAP A1 - Hühnlein, Kristof A1 - Tschirpke, Katrin A1 - Hellmann, Ralf T1 - Optimisation of laser cutting using design of experiment - A comparative study of cutting thin ceramic layers using a fibre laser and a CO2 laser T2 - Physics procedia T2 - 6th international conference on laser assisted net shape engineering KW - Laserschneiden Y1 - 2014 SN - 1875-3892 VL - 5 IS - Part B SP - 243 EP - 252 ER - TY - CHAP A1 - Lutz, Christian A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Marx, Jan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Optical system for multi Bessel beam high power ultrashort pulsed laser processing using a spatial light modulator T2 - Lasers in Manufacturing - LiM 2021 N2 - We report on an optical setup for multi Bessel beam processing combining a refractive axicon and a spatial light modulator. Based on their particular beam profile, Bessel beams exhibit various advantages over conventional Gaussian beams for ultrashort pulsed laser processing. Especially for micromachining of transparent materials, applications such as micro-hole drilling or the generation of voids benefit from the increased focal length of the applied Bessel beam. In addition, on account of the significantly increased average output power of industrial ultrashort pulsed lasers over the last years, there is a high demand on multi spot applications for using the available laser power in efficient production processes. Our optical concept combines the dynamic possibilities of beam splitting using spatial light modulator with the benefits of Bessel beams facilitating multi Bessel beam processing. KW - Ultrakurzzeitlaser KW - Lichtmodulator Y1 - 2021 ER - TY - CHAP A1 - Rosenberger, Manuel A1 - Belle, Stefan A1 - Hellmann, Ralf T1 - Optical interrogation of chemical and temperature bragg grating sensors using tunable fiber coupled bandpass filter T2 - Proceeding XXV microCAD, International scientific conference, 2011, Section H KW - Bragg-Reflektor Y1 - 2014 SP - 25 EP - 30 ER - TY - CHAP A1 - Rosenberger, Manuel A1 - Belle, Stefan A1 - Hellmann, Ralf T1 - Optical interrogation of bragg grating sensors using tunable fibre based bandpass filter T2 - Proceedings of the 20st international science conference, Mittweida KW - Bragg-Reflektor KW - Sensor Y1 - 2014 ER - TY - CHAP A1 - Belle, Stefan A1 - Rosenberger, Manuel A1 - Hellmann, Ralf T1 - Optical fibre sensing in the production process and storage of biofuels T2 - Proceeding XXV microCAD, International scientific conference, 2011, Section A KW - Biokraftstoff Y1 - 2014 SP - 21 EP - 26 ER - TY - CHAP A1 - Adelmann, Benedikt A1 - Neumeier, Benedikt A1 - Schleier, Max A1 - Wilmann, Eugen A1 - Hellmann, Ralf T1 - Optical cutting tear detection system for industrial fiber laser based cutting machines T2 - Lasers in Manufacturing Conference 2015 KW - Laserschneiden KW - Faserlaser Y1 - 2015 ER - TY - CHAP A1 - Kalmár, László A1 - Hellmann, Ralf A1 - Régert, Tamás A1 - Varga, Zoltan T1 - Numerical simulation of heat transfer procedure in high power LED modules T2 - Proceedings of the 12th technical and scientific meeting KW - Lumineszenzdiode KW - Wärmeübertragung KW - Simulation Y1 - 2011 SP - 18 EP - 20 ER - TY - CHAP A1 - Kalmár, László A1 - Hellmann, Ralf A1 - Régert, Tamás A1 - Varga, Zoltan T1 - Numerical investigation of unsteady heat transport procedure in high power LED module T2 - GEP KW - LED module KW - Lumineszenzdiode Y1 - 2012 VL - 2012 IS - 1 SP - 43 EP - 46 ER - TY - CHAP A1 - Kalmár, László A1 - Hellmann, Ralf A1 - Régert, Tamás A1 - Varga, Zoltan T1 - Numerical investigation of heat transport procedure in high power LED modules T2 - Proceedings of the XXVI International MicroCAD Conference, Miskolc (Hungary) KW - heat transport procedure KW - Lumineszenzdiode KW - Wärmeübertragung Y1 - 2012 SP - 43 EP - 46 ER - TY - CHAP A1 - Sommer, David A1 - Truetsch, Ben A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Microstructural Fracture Behaviour of PBF-LB/M Inconel 718 Components within different HIP Processes T2 - Lasers in Manufacturing, München, Juni 2025 N2 - We report on a study of different hot isostatic pressing (HIP) cycles, improving the mechanical properties of additively manufactured Inconel 718 components. For this, PBF-LB/M built components are post-processed by different HIP sequences, as gas pressure and processing time are varied, leading to differences in microstructure and material characteristics. Static and dynamic mechanical testing are performed, evaluating the changes in mechanical properties with particular focus on the ultimate tensile strength and endurance limit. Furthermore, metallographic analysis is employed to investigate the achieved density and microhardness. Microstructural analysis, showing the grain boundaries, is used to identify generated phases and precipitations of the material matrix. Moreover, the fracture behaviour is classified by grain deformation during mechanical testing. As the HIP leads to microstructural changes of Inconel 718 components, mechanical properties can be improved significantly, enhancing the ultimate tensile strength and simultaneously the endurance limit. KW - Isostatisches Heißpressen Y1 - 2025 ER - TY - CHAP A1 - Koller, Georg A1 - Hessler, Steffen A1 - Rosenberger, Manuel A1 - Belle, Stefan A1 - Hellmann, Ralf T1 - Micro-structured optical waveguide fabrication in PMMA using low frequency reactive ion etching T2 - Proceedings of the XXVI International MicroCAD Conference – Sensing Technologies, Miskolc (Hungary) KW - waveguide fabrication KW - Wellenleiter Y1 - 2012 ER - TY - CHAP A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Manufacturing of optical elements by non-contact laser processing T2 - Seventh European Seminar on Precision Optics Manufacturing, Proceedings KW - Laserbearbeitung KW - Optisches Bauelement Y1 - 2020 IS - 11478 ER - TY - CHAP A1 - Risch, Anna A1 - Hühnlein, Kristof A1 - Knöll, Jürgen A1 - Hellmann, Ralf T1 - Laserscribing of transparent conductive oxides - a comparative study using nanosecond and picosecond pulsed solid state lasers T2 - Proceedings of the 20st International Scientific Conference, Mittweida, 2009 KW - Festkörperlaser Y1 - 2014 ER -