@inproceedings{RischHellmann2011, author = {Risch, Anna and Hellmann, Ralf}, title = {ITO thin film laser patterning by picosecond laser}, series = {Proceeding XXV microCAD, International scientific conference, 2011, Section K: Material science/Material processing technologies}, booktitle = {Proceeding XXV microCAD, International scientific conference, 2011, Section K: Material science/Material processing technologies}, pages = {63 -- 68}, year = {2011}, subject = {Laserbearbeitung}, language = {en} } @inproceedings{BelleScheurichHellmann2009, author = {Belle, Stefan and Scheurich, Steffen and Hellmann, Ralf}, title = {Interrogation water content in organic solvents by planar bragg grating sensors}, series = {Proceedings SENSOR}, booktitle = {Proceedings SENSOR}, number = {Vol. II, P3.2}, isbn = {978-3-9810993-6-2}, pages = {324 -- 329}, year = {2009}, subject = {Bragg-Reflektor}, language = {en} } @inproceedings{RothEsenHellmann2020, author = {Roth, Gian-Luca and Esen, Cemal and Hellmann, Ralf}, title = {Internal micro structuring of transparent optical polymers by fs laser}, series = {Laser-based Micro-and Nanoprocessing XIV 2020}, volume = {11268}, booktitle = {Laser-based Micro-and Nanoprocessing XIV 2020}, publisher = {International Society for Optics and Photonics}, doi = {10.1117/12.2543487}, pages = {112681L}, year = {2020}, abstract = {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.}, subject = {Femtosekundenlaser}, language = {en} } @inproceedings{SauerKeferRuppertetal.2019, author = {Sauer, Theresia and Kefer, Stefan and Ruppert, Wolfgang and Hellmann, Ralf and Kaloudis, Michael}, title = {Integration of Bragg grating sensors in components made of carbon fiber reinforced polymers}, series = {Tagungsband der 20. GMA/ITG-Fachtagung Sensoren und Messsysteme 2019, 25.06.2019 - 26.06.2019, N{\"u}rnberg, Deutschland}, booktitle = {Tagungsband der 20. GMA/ITG-Fachtagung Sensoren und Messsysteme 2019, 25.06.2019 - 26.06.2019, N{\"u}rnberg, Deutschland}, isbn = {978-3-9819376-0-2}, doi = {10.5162/sensoren2019/P3.12}, pages = {806 -- 810}, year = {2019}, abstract = {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.}, subject = {Bragg-Reflektor}, language = {en} } @inproceedings{SchwarzEsenHellmann2018, author = {Schwarz, Simon and Esen, Cemal and Hellmann, Ralf}, title = {Homogeneous low spatial frequency LIPSS on dielectrics generated by beam-shaped femtosecond pulsed laser irradiation}, series = {LPM2018 The 19th International Symposium on Laser Precision Microfabrication}, booktitle = {LPM2018 The 19th International Symposium on Laser Precision Microfabrication}, year = {2018}, subject = {Femtosekundenlaser}, language = {en} } @inproceedings{MarxEsenLutzetal.2023, author = {Marx, Jan and Esen, Cemal and Lutz, Christian and Hellmann, Ralf and Ostendorf, Andreas}, title = {Holographic tuning of physical axicons}, volume = {2023}, number = {154}, publisher = {LiM 2023 Proceedings}, pages = {1 -- 9}, year = {2023}, abstract = {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.}, subject = {Bessel-B{\"u}ndel}, language = {en} } @inproceedings{KeferZettlSchmaussetal.2023, author = {Kefer, Stefan and Zettl, Julian and Schmauss, Bernhard and Esen, Cemal and Hellmann, Ralf}, title = {High-Precision Micromachining of Sapphire Towards Optical Waveguiding Structures using Femtosecond Lasers}, series = {Laser-based Micro- and Nanoprocessing XVII}, booktitle = {Laser-based Micro- and Nanoprocessing XVII}, editor = {Kling, Rainer and Pfleging, Wilhelm and Watanabe, Akira}, isbn = {9781510659230}, doi = {10.1117/12.2648758}, pages = {3 -- 11}, year = {2023}, abstract = {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}, subject = {Femtosekundenlaser}, language = {en} } @inproceedings{HeilmannHellmann2011, author = {Heilmann, Eva-Maria and Hellmann, Ralf}, title = {High Speed Fibre Laser Material processing of Stainless Steel Tapes Under Tension}, series = {XXV International MicroCAD Conference - Material Processing Technologies, Miskolc (Hungary), 21-25}, booktitle = {XXV International MicroCAD Conference - Material Processing Technologies, Miskolc (Hungary), 21-25}, year = {2011}, subject = {Lasertechnologie}, language = {en} } @inproceedings{SchwarzRungHellmann2017, author = {Schwarz, Simon and Rung, Stefan and Hellmann, Ralf}, title = {High quality one-dimensional low spatial frequency LIPSS on sapphire generated by Top-Hat beam shaped ultrashort-pulsed laser}, series = {MultiScience - XXXI. microCAD International Multidisciplinary Scientific Conference}, booktitle = {MultiScience - XXXI. microCAD International Multidisciplinary Scientific Conference}, year = {2017}, subject = {Ultrakurzzeitlaser}, language = {en} } @inproceedings{DudutisPipirasSchwarzetal.2019, author = {Dudutis, Juozas and Pipiras, Jokūbas and Schwarz, Simon and Rung, Stefan and Hellmann, Ralf and Račiukaitis, Gediminas and Gečys, Paulius}, title = {Glass cutting by oblate-tip axicon-generated Bessel-Gaussian beams}, series = {Open Readings, 63rd International Conference for Students of Physics and Natural Sciences}, booktitle = {Open Readings, 63rd International Conference for Students of Physics and Natural Sciences}, year = {2019}, subject = {Laserschneiden}, language = {en} } @inproceedings{GlaabHellmann2010, author = {Glaab, Johannes and Hellmann, Ralf}, title = {Germicidal potential of ultraviolet-LED emitting different wavelength for the inactivation of indigenous coliform bacteria}, series = {Water research conference, Lissabon, Portugal}, booktitle = {Water research conference, Lissabon, Portugal}, year = {2010}, subject = {Lumineszenzdiode}, language = {en} } @inproceedings{RothWolfEsenetal.2019, author = {Roth, Gian-Luca and Wolf, Bastian and Esen, Cemal and Hellmann, Ralf}, title = {Generation of internal 3D microfluidic architectures in polymers by fs laser processing}, series = {Lasers in Manufacturing 2019}, booktitle = {Lasers in Manufacturing 2019}, year = {2019}, abstract = {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.}, subject = {Femtosekundenlaser}, language = {en} } @inproceedings{KeferPapeSchmaussetal.2023, author = {Kefer, Stefan and Pape, Natalie and Schmauss, Bernhard and Hellmann, Ralf}, title = {Fabrication of Lattice-Like Waveguides in Planar Cyclic Olefin Copolymers}, series = {28th International Conference on Optical Fiber Sensors}, booktitle = {28th International Conference on Optical Fiber Sensors}, isbn = {978-1-957171-30-2}, doi = {10.1364/OFS.2023.Th6.69}, year = {2023}, abstract = {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.}, subject = {Wellenleiter}, language = {en} } @inproceedings{KeferRosenbergerHessleretal.2020, author = {Kefer, Stefan and Rosenberger, Manuel and Hessler, Steffen and Girschikofsky, Maiko and Belle, Stefan and Roth, Gian-Luca and Schmauß, Bernhard and Hellmann, Ralf}, title = {Fabrication and Applications of Polymer Planar Bragg Grating Sensors based on Cyclic Olefin Copolymers}, series = {2019 Photonics \& Electromagnetics Research Symposium - Fall (PIERS - Fall)}, booktitle = {2019 Photonics \& Electromagnetics Research Symposium - Fall (PIERS - Fall)}, publisher = {Institute of Electrical and Electronics Engineers}, isbn = {978-1-7281-5304-9}, doi = {10.1109/PIERS-Fall48861.2019.9021801}, pages = {647 -- 655}, year = {2020}, abstract = {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.}, subject = {Optischer Sensor}, language = {en} } @inproceedings{AdelmannHellmann2011, author = {Adelmann, Benedikt and Hellmann, Ralf}, title = {DOE based optimization of fibre laser cutting of metals}, series = {Proceeding XXV microCAD, International scientific conference, 2011, Section K: Material science/Material processing technologies}, booktitle = {Proceeding XXV microCAD, International scientific conference, 2011, Section K: Material science/Material processing technologies}, pages = {7 -- 12}, year = {2011}, subject = {Laserschneiden}, language = {en} } @inproceedings{BischoffJaegerRungetal.2012, author = {Bischoff, Christian and J{\"a}ger, Erwin and Rung, Stefan and Hellmann, Ralf}, title = {Diffractive beam shaping optics for efficient micromachining}, series = {Proceedings of the LASYS (Internationale Fachmesse f{\"u}r Laser-Materialbearbeitung) - SLT (Stuttgarter Lasertage) 2012}, booktitle = {Proceedings of the LASYS (Internationale Fachmesse f{\"u}r Laser-Materialbearbeitung) - SLT (Stuttgarter Lasertage) 2012}, year = {2012}, subject = {Laserbearbeitung}, language = {en} } @inproceedings{AdelmannHellmann2011, author = {Adelmann, Benedikt and Hellmann, Ralf}, title = {Different modulation schemes in fibre laser cutting}, series = {Proceeding XXV microCAD, International scientific conference, 2011, Section K: Material science/Material processing technologies}, booktitle = {Proceeding XXV microCAD, International scientific conference, 2011, Section K: Material science/Material processing technologies}, pages = {1 -- 6}, year = {2011}, subject = {Laserschneiden}, language = {en} } @inproceedings{KaloumenosAmrheinGlaabetal.2010, author = {Kaloumenos, Mareiki and Amrhein, Frank and Glaab, Johannes and Sauer, Michael and Hellmann, Ralf and Kaloudis, Michael}, title = {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}, series = {Proceedings of the XXIV International Scientific Conference Miskolc, Ungarn}, booktitle = {Proceedings of the XXIV International Scientific Conference Miskolc, Ungarn}, year = {2010}, subject = {Lumineszenzdiode}, language = {en} } @inproceedings{RosenbergerBelleHellmann2011, author = {Rosenberger, Manuel and Belle, Stefan and Hellmann, Ralf}, title = {Detection of unlabeled DNA hybridization with a planar bragg grating sensor}, series = {Proceeding XXV microCAD, International scientific conference, 2011, Section R}, booktitle = {Proceeding XXV microCAD, International scientific conference, 2011, Section R}, pages = {67 -- 72}, year = {2011}, subject = {Bragg-Reflektor}, language = {en} } @inproceedings{RosenbergerBelleHellmann2011, author = {Rosenberger, Markus and Belle, Stefan and Hellmann, Ralf}, title = {Detection of unlabeled DNA hybridization with a planar Bragg Grating Sensor}, series = {XXV International MicroCAD Conference - Sensing Technologies, Miskolc (Hungary)}, booktitle = {XXV International MicroCAD Conference - Sensing Technologies, Miskolc (Hungary)}, number = {Section R}, pages = {67 -- 72}, year = {2011}, subject = {Bragg-Reflektor}, language = {en} } @inproceedings{RosenbergerBelleHellmann2011, author = {Rosenberger, Manuel and Belle, Stefan and Hellmann, Ralf}, title = {Detection of biochemical reaction and DNA hybridization using a planar bragg grating sensor}, series = {Proceeding SPIE, Vol. 8073, article id: 80730C}, booktitle = {Proceeding SPIE, Vol. 8073, article id: 80730C}, number = {8073}, doi = {10.1117/12.886785}, year = {2011}, subject = {Bragg-Reflektor}, language = {en} } @inproceedings{SchwarzRungEsenetal.2020, author = {Schwarz, Simon and Rung, Stefan and Esen, Cemal and Hellmann, Ralf}, title = {Current results on laser-based production of complex optics in glass}, series = {10. Wetzlarer Herbsttagung "Moderne Optikfertigung", 29. - 30. September 2020, Wetzlar}, booktitle = {10. Wetzlarer Herbsttagung "Moderne Optikfertigung", 29. - 30. September 2020, Wetzlar}, year = {2020}, subject = {Laserbearbeitung}, language = {en} } @inproceedings{AdelmannHellmann2015, author = {Adelmann, Benedikt and Hellmann, Ralf}, title = {Comparative study of experimentally determined and simulated mechanical strength of fiber laser cut alumina substrates}, series = {Proceedings of the 7th International Congress on Laser Advanced Materials Processing}, volume = {2015}, booktitle = {Proceedings of the 7th International Congress on Laser Advanced Materials Processing}, number = {15}, pages = {1 -- 9}, year = {2015}, subject = {Laserschneiden}, language = {en} } @inproceedings{SchwarzEsenHellmann2018, author = {Schwarz, Simon and Esen, Cemal and Hellmann, Ralf}, title = {CO2 laser polishing of femtosecond shaped micro-optical components}, series = {3rd Conference on Laser Polishing LaP 2018}, booktitle = {3rd Conference on Laser Polishing LaP 2018}, year = {2018}, subject = {Kohlendioxidlaser}, language = {en} } @inproceedings{DudutisPipirasSchwarzetal.2019, author = {Dudutis, Juozas and Pipiras, Jokūbas and Schwarz, Simon and Rung, Stefan and Hellmann, Ralf and Gečys, Paulius}, title = {Bessel beam formation with all laser fabricated axicon - case of glass dicing applications}, series = {COLA 2019, 15th International Conference on Laser Ablation}, booktitle = {COLA 2019, 15th International Conference on Laser Ablation}, year = {2019}, subject = {Laserbestrahlung}, language = {en} } @inproceedings{RungRexhepiHellmann2013, author = {Rung, Stefan and Rexhepi, Mal and Hellmann, Ralf}, title = {Beam shaping for enhanced through-put of laser ablation of transparent conductive films}, series = {Proceedings of the XXVII MicroCAD International Scientific Conference}, volume = {2013}, booktitle = {Proceedings of the XXVII MicroCAD International Scientific Conference}, year = {2013}, subject = {Laserablation}, language = {en} } @inproceedings{SchwarzRungEsenetal.2018, author = {Schwarz, Simon and Rung, Stefan and Esen, Cemal and Hellmann, Ralf}, title = {Axicon fabrication with ultrashort and CO2 laser}, series = {LPM2018 The 19th International Symposium on Laser Precision Microfabrication}, booktitle = {LPM2018 The 19th International Symposium on Laser Precision Microfabrication}, year = {2018}, subject = {Ultrakurzzeitlaser}, language = {de} } @inproceedings{ScheurichBelleHellmannetal.2009, author = {Scheurich, Steffen and Belle, Stefan and Hellmann, Ralf and So, Sik and Sparrow, Ian and Emmerson, Greg}, title = {Application of a silica-on-silicon planar optical waveguide. Bragg grating sensor for organic liquid compound detection}, series = {SPIE Optics an optoelectronics conference, Proceedings of SPIE, Vol. 7356, Prag, CR}, booktitle = {SPIE Optics an optoelectronics conference, Proceedings of SPIE, Vol. 7356, Prag, CR}, number = {7356}, isbn = {978-0819476302}, year = {2009}, subject = {Bragg-Reflektor}, language = {en} } @inproceedings{SchwarzRungEsenetal.2020, author = {Schwarz, Simon and Rung, Stefan and Esen, Cemal and Hellmann, Ralf}, title = {All laser-based fabrication of optical elements}, series = {Proceedings of SPIE 11270, Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XX}, booktitle = {Proceedings of SPIE 11270, Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XX}, year = {2020}, subject = {Ultrakurzzeitlaser}, language = {de} } @inproceedings{BischoffEsenHellmann2023, author = {Bischoff, Kay and Esen, Cemal and Hellmann, Ralf}, title = {Acceleration of Femtosecond Reductive Laser Sintering of Copper(II) Oxide for Conductive Copper Patterns on Cyclic Olefin Copolymers}, series = {International Congress on Applications of Lasers \& Electro-Optics (ICALEO) 2023}, booktitle = {International Congress on Applications of Lasers \& Electro-Optics (ICALEO) 2023}, year = {2023}, abstract = {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\%.}, subject = {Femtosekundenlaser}, language = {en} }