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 - 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 - 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 - 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 - 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 - CHAP A1 - Risch, Anna A1 - Hellmann, Ralf T1 - Laser induced modification of GZO thin film T2 - Proceeding XXV microCAD, International scientific conference, 2011, Section K: Material science/Material processing technologies KW - Laser KW - Dünne Schicht Y1 - 2014 SP - 69 EP - 74 ER - TY - CHAP A1 - Hasenstab, Stefan A1 - Adelmann, Benedikt A1 - Hellmann, Ralf T1 - Laser Cutting of Alumina and Aluminum Nitride with a 500 W Single Mode Fiber Laser T2 - XXVII. microCAD International Scientific Conference KW - Laserschneiden KW - Aluminiumoxide Y1 - 2013 ER - TY - CHAP A1 - Risch, Anna A1 - Hellmann, Ralf T1 - ITO thin film laser patterning by picosecond laser T2 - Proceeding XXV microCAD, International scientific conference, 2011, Section K: Material science/Material processing technologies KW - Laserbearbeitung Y1 - 2014 SP - 63 EP - 68 ER - TY - CHAP A1 - Belle, Stefan A1 - Scheurich, Steffen A1 - Hellmann, Ralf T1 - Interrogation water content in organic solvents by planar bragg grating sensors T2 - Proceedings SENSOR KW - Bragg-Reflektor KW - Sensor Y1 - 2014 SN - 978-3-9810993-6-2 IS - Vol. II, P3.2 SP - 324 EP - 329 ER - TY - CHAP A1 - Roth, Gian-Luca A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Internal micro structuring of transparent optical polymers by fs laser T2 - Laser-based Micro-and Nanoprocessing XIV 2020 N2 - Lab-on-chip systems are based on components to transport, mix, separate and analyse small volumes of different fluids. The consecutive integration of more complex functions into a single and compact chip demands on multilayer systems. As the classical production using a stacking and joining of single processed layers is elaborate and limited in terms of multilayer structures, an uprising trend to fabricate those devices is the internal, three dimensional processing of transparent substrates by using ultrashort laser pulses. In this study, we report on the generation of internal hollow architectures created by focused 514nm femtosecond laser pulses inside optical polymer bulk materials of different polymers. The three-dimensional channel layout is implemented by moving the sample using three-dimensional motorized stages, allowing arbitrary complex shaped internal channel architectures. Size and cross sectional shape of a single internal generated microchannel are determined by the intensity distribution of the focal voxel. In particular, we show a comprehensive parameter study to improve this laser process with respect to a higher processing speed and stability. KW - Femtosekundenlaser Y1 - 2020 U6 - https://doi.org/10.1117/12.2543487 VL - 11268 SP - 112681L PB - International Society for Optics and Photonics ER - TY - CHAP A1 - Sauer, Theresia A1 - Kefer, Stefan A1 - Ruppert, Wolfgang A1 - Hellmann, Ralf A1 - Kaloudis, Michael T1 - Integration of Bragg grating sensors in components made of carbon fiber reinforced polymers T2 - Tagungsband der 20. GMA/ITG-Fachtagung Sensoren und Messsysteme 2019, 25.06.2019 - 26.06.2019, Nürnberg, Deutschland N2 - This contribution discusses the integration of polymer planar Bragg grating sensors (PPBG) into carbon fiber reinforced polymer (CFRP) components. For the first time, it is shown that PPBGs based on cyclic olefin copolymers can be integrated into commercial-grade composites, thereby withstanding the demanding production processes. Pre-impregnated fibers are stacked and partially modified to form a sensor pocket. Afterwards, the CFRP specimen containing the optical sensor is cured in a heated mechanical press for 2 hours at a pressure of 7 bar and a temperature of 120 °C. A subsequent evalutaion of the sensor signal shows a Bragg wavelength shift of 1236 pm and a decline in signal amplitude of -2 dB. Three-point flexural tests of the cured sample reveal a linear behavior of the sensor signal towards external loads. The determined sensitivity in dependence of the CFRP specimen's maximum central deflection is -112 pm/mm, while correlation to the applied force results in a sensitivity of -5 pm/N. KW - Bragg grating sensors KW - carbon fiber reinforced polymers KW - cyclic olefin copolymers KW - structural health monitoring KW - Bragg-Reflektor Y1 - 2019 SN - 978-3-9819376-0-2 U6 - https://doi.org/10.5162/sensoren2019/P3.12 SP - 806 EP - 810 ER - TY - CHAP A1 - Schwarz, Simon A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Homogeneous low spatial frequency LIPSS on dielectrics generated by beam-shaped femtosecond pulsed laser irradiation T2 - LPM2018 The 19th International Symposium on Laser Precision Microfabrication KW - Femtosekundenlaser Y1 - 2018 ER - TY - CHAP A1 - Marx, Jan A1 - Esen, Cemal A1 - Lutz, Christian A1 - Hellmann, Ralf A1 - Ostendorf, Andreas T1 - Holographic tuning of physical axicons N2 - Axicon generated Bessel beams are a popular tool for high aspect ratio precision laser drilling. Spot diameter and working distance are given by the geometric parameters of the axicon and the wavelength used. Thus, it is difficult to manipulate the beam shape of a Bessel beam for a given setup. Spatial light modulators (SLMs) overcome limitations in flexibility. However, due to the limited phase shift of SLMs, only Bessel beams with flat cone angles and large focal length can be generated. In this contribution, an approach for generating Bessel beams with a shorter, but tunable focal length is presented. A physical axicon was combined with an SLM. A holographic image of a negative axicon is put on the SLM to generate a ring beam, which is focused by a subsequent physical axicon to get a small focal diameter. Thus, different sized high aspect ratio micro holes can be drilled without using any moving components. KW - Bessel beam KW - Micro drilling KW - Axicon KW - Spatial light modulator KW - Beam shaping KW - Bessel-Bündel KW - Axicon KW - Strahlformung, Laser Y1 - 2023 VL - 2023 IS - 154 SP - 1 EP - 9 PB - LiM 2023 Proceedings ER - TY - CHAP A1 - Kefer, Stefan A1 - Zettl, Julian A1 - Schmauss, Bernhard A1 - Esen, Cemal A1 - Hellmann, Ralf ED - Kling, Rainer ED - Pfleging, Wilhelm ED - Watanabe, Akira T1 - High-Precision Micromachining of Sapphire Towards Optical Waveguiding Structures using Femtosecond Lasers T2 - Laser-based Micro- and Nanoprocessing XVII N2 - While sapphire is one of the most durable materials, its properties entail that high-precision machining, especially in the sub-millimeter regime, is still challenging. This contribution demonstrates and discusses novel femtosecond laser-based micromachining approaches for the fabrication of rotational-symmetric sapphire workpieces, specifically the generation of optical fibers by means of laser lathe of sapphire rods and the practical realization of windmill fibers. In addition, volume refractive index modification in planar sapphire substrates is presented to induce photonic crystal waveguides. The micromachined structures are comprehensively examined with respect to geometric fidelity, surface roughness, refractive index modification, and potential optical waveguiding properties. All micromachining approaches are done by means of frequency-doubled or frequency-tripled femtosecond laser radiation. Different laser optical setups including laser scanning head, spatial beam profilers including a spatial light modulator and axial rotatory movement of the specimen are employed for micro structuring and in-depth refractive index modifications. In particular for laser lathe, a sophisticated scanning pattern, in combination with an incremental axial rotatory movement of the specimen, allows for the precise diameter reduction of sapphire rods with 250 µm diameter to fibers with outer diameters of 25 µm. By supporting the workpiece with a V-groove fixture, multi-mode fibers with lengths up to 20 cm can be processed with an average surface roughness of 250 nm. Additionally, an adapted ablation scanning sequence enables the first practical demonstration of sapphire windmill fibers. Furthermore, using a spatial light modulator allows for the adaption of the laser propagation properties as to enable volume refractive index modifications with free-form arrangement. Hexagonal patterns of refractive index modifications surrounding a pristine waveguide core are fabricated and single-mode waveguiding at 1550 nm is verified. Finally, the possibility of integrating Bragg gratings into this photonic waveguide type is demonstrated KW - sapphire KW - femtosecond laser KW - micromachining KW - laser lathe KW - rod-to-fiber KW - Femtosekundenlaser KW - Saphir Y1 - 2023 SN - 9781510659230 U6 - https://doi.org/10.1117/12.2648758 SP - 3 EP - 11 ER - TY - CHAP A1 - Heilmann, Eva-Maria A1 - Hellmann, Ralf T1 - High Speed Fibre Laser Material processing of Stainless Steel Tapes Under Tension T2 - XXV International MicroCAD Conference - Material Processing Technologies, Miskolc (Hungary), 21-25 KW - Lasertechnologie Y1 - 2011 ER - TY - CHAP A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Hellmann, Ralf T1 - High quality one-dimensional low spatial frequency LIPSS on sapphire generated by Top-Hat beam shaped ultrashort-pulsed laser T2 - MultiScience - XXXI. microCAD International Multidisciplinary Scientific Conference KW - Ultrakurzzeitlaser Y1 - 2017 ER - TY - CHAP A1 - Dudutis, Juozas A1 - Pipiras, Jokūbas A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Hellmann, Ralf A1 - Račiukaitis, Gediminas A1 - Gečys, Paulius T1 - Glass cutting by oblate-tip axicon-generated Bessel-Gaussian beams T2 - Open Readings, 63rd International Conference for Students of Physics and Natural Sciences KW - Laserschneiden KW - Glas Y1 - 2019 ER - TY - CHAP A1 - Glaab, Johannes A1 - Hellmann, Ralf T1 - Germicidal potential of ultraviolet-LED emitting different wavelength for the inactivation of indigenous coliform bacteria T2 - Water research conference, Lissabon, Portugal KW - Lumineszenzdiode KW - Kolibakterium Y1 - 2014 ER - TY - CHAP A1 - Roth, Gian-Luca A1 - Wolf, Bastian A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Generation of internal 3D microfluidic architectures in polymers by fs laser processing T2 - Lasers in Manufacturing 2019 N2 - Microfluidic lab on chip systems require components to transport, mix, separate and analyse small volumes of different fluids. In this study, we report on the laser generation of internal hollow architectures created by focused 514 nm femtosecond laser pulses inside PMMA bulk material. Size and cross-sectional shape of a single internal generated microchannel are determined by the intensity distribution inside the focal voxel and can be controlled either by the numerical aperture of the focusing objective or by laser beam shaping. As both approaches are practically limited with respect to the realizable cross-sectional shapes, we present a process based on an internal hatching to expand the achievable channel cross-sections and thereby enable the possibility to create complex 3D shaped internal structures. This process is applied to create fully internal functional microfluidic elements such as mixers which are part of most polymer lab-on-chip systems. KW - Femtosekundenlaser Y1 - 2019 ER - TY - CHAP A1 - Kefer, Stefan A1 - Pape, Natalie A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Fabrication of Lattice-Like Waveguides in Planar Cyclic Olefin Copolymers T2 - 28th International Conference on Optical Fiber Sensors N2 - This work demonstrates the femtosecond laser-based fabrication of lattice-like waveguides in planar cyclic olefin copolymers. An overview of the fabrication process is provided and waveguiding in the C-band is proven via optical near-field analysis. KW - Wellenleiter KW - Femtosekundenlaser Y1 - 2023 SN - 978-1-957171-30-2 U6 - https://doi.org/10.1364/OFS.2023.Th6.69 ER - TY - CHAP A1 - Kefer, Stefan A1 - Rosenberger, Manuel A1 - Hessler, Steffen A1 - Girschikofsky, Maiko A1 - Belle, Stefan A1 - Roth, Gian-Luca A1 - Schmauß, Bernhard A1 - Hellmann, Ralf T1 - Fabrication and Applications of Polymer Planar Bragg Grating Sensors based on Cyclic Olefin Copolymers T2 - 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) N2 - This contribution reviews recent advancements, current research and possible applications of polymer planar Bragg grating (PPBG) sensors with a focus on the utilization of cyclic olefin copolymer (COC) substrates. COC-PPBGs can be handled and fabricated efficiently by employing a single writing step procedure which features simultaneous generation of waveguide and Bragg grating structure within an injection molded substrate. The resulting photonic structures exhibit an attenuation as low as 1.2 dB cm-1 and a reflectivity up to 99 %. The potential of COC-PPBGs for high-temperature applications is proven by demonstrating temperature measurements up to 160 °C. Moreover, it is possible to employ single PPBGs for multidimensional stress and strain sensing or even three-dimensional shape reconstruction. Due to their excellent properties, it is feasible to integrate COC-PPBGs into commercial-grade carbon fiber reinforced polymer workpieces for structural health monitoring. Furthermore, utilization of appropriate coatings enables functionalization of PPBGs for refractive index sensing and thus biochemical applications. Beside the fabrication and characterization of COC-based PPBGs, this contribution exemplifies and reviews such applications. KW - Bragg gratings , Gratings , Optical waveguides , Temperature sensors , Substrates KW - Optischer Sensor KW - Bragg-Reflektor Y1 - 2020 UR - https://ieeexplore.ieee.org/document/9021801 SN - 978-1-7281-5304-9 U6 - https://doi.org/10.1109/PIERS-Fall48861.2019.9021801 SP - 647 EP - 655 PB - Institute of Electrical and Electronics Engineers ER - TY - CHAP A1 - Adelmann, Benedikt A1 - Hellmann, Ralf T1 - DOE based optimization of fibre laser cutting of metals T2 - Proceeding XXV microCAD, International scientific conference, 2011, Section K: Material science/Material processing technologies KW - Laserschneiden KW - Faserlaser Y1 - 2014 SP - 7 EP - 12 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 - Adelmann, Benedikt A1 - Hellmann, Ralf T1 - Different modulation schemes in fibre laser cutting T2 - Proceeding XXV microCAD, International scientific conference, 2011, Section K: Material science/Material processing technologies KW - Laserschneiden KW - Faserlaser Y1 - 2014 SP - 1 EP - 6 ER - TY - CHAP A1 - Kaloumenos, Mareiki A1 - Amrhein, Frank A1 - Glaab, Johannes A1 - Sauer, Michael A1 - Hellmann, Ralf A1 - Kaloudis, Michael T1 - Development of a UV-Light Source with Highest Power Density Based on Light Emitting Diode Technology for Applications in Production Engineering, in Production Engineering and manufacturing Systems T2 - Proceedings of the XXIV International Scientific Conference Miskolc, Ungarn KW - Lumineszenzdiode Y1 - 2010 ER - TY - CHAP A1 - Rosenberger, Manuel A1 - Belle, Stefan A1 - Hellmann, Ralf T1 - Detection of unlabeled DNA hybridization with a planar bragg grating sensor T2 - Proceeding XXV microCAD, International scientific conference, 2011, Section R KW - Bragg-Reflektor KW - Sensor Y1 - 2014 SP - 67 EP - 72 ER - TY - CHAP A1 - Rosenberger, Markus A1 - Belle, Stefan A1 - Hellmann, Ralf T1 - Detection of unlabeled DNA hybridization with a planar Bragg Grating Sensor T2 - XXV International MicroCAD Conference – Sensing Technologies, Miskolc (Hungary) KW - Bragg-Reflektor Y1 - 2014 IS - Section R SP - 67 EP - 72 ER - TY - CHAP A1 - Rosenberger, Manuel A1 - Belle, Stefan A1 - Hellmann, Ralf T1 - Detection of biochemical reaction and DNA hybridization using a planar bragg grating sensor T2 - Proceeding SPIE, Vol. 8073, article id: 80730C KW - Bragg-Reflektor KW - Sensor Y1 - 2014 U6 - https://doi.org/10.1117/12.886785 IS - 8073 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 - Adelmann, Benedikt A1 - Hellmann, Ralf T1 - Comparative study of experimentally determined and simulated mechanical strength of fiber laser cut alumina substrates T2 - Proceedings of the 7th International Congress on Laser Advanced Materials Processing KW - Laserschneiden KW - Faserlaser KW - Aluminiumoxide Y1 - 2015 VL - 2015 IS - 15 SP - 1 EP - 9 ER - TY - CHAP A1 - Schwarz, Simon A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - CO2 laser polishing of femtosecond shaped micro-optical components T2 - 3rd Conference on Laser Polishing LaP 2018 KW - Kohlendioxidlaser Y1 - 2018 ER - TY - CHAP A1 - Dudutis, Juozas A1 - Pipiras, Jokūbas A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Hellmann, Ralf A1 - Gečys, Paulius T1 - Bessel beam formation with all laser fabricated axicon - case of glass dicing applications T2 - COLA 2019, 15th International Conference on Laser Ablation KW - Laserbestrahlung Y1 - 2019 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 - CHAP A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Axicon fabrication with ultrashort and CO2 laser T2 - LPM2018 The 19th International Symposium on Laser Precision Microfabrication KW - Ultrakurzzeitlaser KW - Kohlendioxidlaser Y1 - 2018 ER - TY - CHAP A1 - Scheurich, Steffen A1 - Belle, Stefan A1 - Hellmann, Ralf A1 - So, Sik A1 - Sparrow, Ian A1 - Emmerson, Greg T1 - Application of a silica-on-silicon planar optical waveguide. Bragg grating sensor for organic liquid compound detection T2 - SPIE Optics an optoelectronics conference, Proceedings of SPIE, Vol. 7356, Prag, CR KW - Bragg-Reflektor KW - Sensor Y1 - 2014 SN - 978-0819476302 IS - 7356 ER - TY - CHAP A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - All laser-based fabrication of optical elements T2 - Proceedings of SPIE 11270, Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XX KW - Ultrakurzzeitlaser KW - Kohlendioxidlaser KW - Femtosekundenlaser Y1 - 2020 ER - TY - CHAP A1 - Bischoff, Kay A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Acceleration of Femtosecond Reductive Laser Sintering of Copper(II) Oxide for Conductive Copper Patterns on Cyclic Olefin Copolymers T2 - International Congress on Applications of Lasers & Electro-Optics (ICALEO) 2023 N2 - We report on the acceleration of femtosecond reductive laser sintering of copper (II) oxide on the surface of transparent cyclic olefin copolymers (COC) by varying the focus size to generate metallic copper (Cu) layers. By using different focusing conditions, different process speeds are achieved, and the structural accuracies are controlled. The formation of Cu lines is observed for different focus sizes at various scan speeds, which is attributed to laser exposure duration and chemical reaction time. The formed lines are categorized and measured by optical microscopy and provide the basis for two-dimensional Cu surfaces. By hatching, high quality conductive films are produced with an increased focus diameter of up to 400 µm at a scan speed of 400 mm/s and a hatch distance of 250 µm resulting in a multiple increased process speed by a factor of thirteen compared to previous research. Using 4-tip measurement , a low sheet resistance of 0.165 Ω/sq was validated on these Cu films, which have an atomic Cu content of 89.5%. KW - Femtosekundenlaser Y1 - 2023 ER -