@inproceedings{GirschikofskyRosenbergerBelleetal.2012, author = {Girschikofsky, Maiko and Rosenberger, Manuel and Belle, Stefan and Brutschy, Malte and Waldvogel, Siegfried and Hellmann, Ralf}, title = {α-Cyclodextrin functionalized planar Bragg grating sensor for the detection of small arene traces in solvamt vapour}, series = {14th international meeting on chemical sensors (IMCS 2012)}, booktitle = {14th international meeting on chemical sensors (IMCS 2012)}, isbn = {978-3-9813484-2-2}, doi = {10.5162/IMCS2012/7.5.1}, pages = {646 -- 648}, year = {2012}, subject = {Bragg-Reflektor}, language = {en} } @inproceedings{HeilmannHellmann2011, author = {Heilmann, Eva-Maria and Hellmann, Ralf}, title = {Water jet guided laser cutting using a green disc 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}, year = {2011}, subject = {Wasserstrahlschneiden}, language = {en} } @inproceedings{BischoffMueckeEsenetal.2023, author = {Bischoff, Kay and M{\"u}cke, Dominik and Esen, Cemal and Hellmann, Ralf}, title = {UV-Femtosecond-Laser Structuring of Silicon Carbide}, 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 ultraviolet ultrashort pulsed laser processing of silicon carbide. Laser ablated cavities are evaluated with respect to their ablation rates, surface roughness and overall quality by varying the laser pulse fluence. Using this type of laser, high edge quality and surface roughness down to 107 nm can be achieved with an ablation efficiency of up to 0.228 mm 3 W -1 min -1. Functional surfaces are produced by generating laser induced periodic surface structures. The comparison with infrared wavelength underlines the advantages of the ultraviolet wavelength for laser micro machining this material. Significant differences with respect to the measured ablation depths and roughness as well as generated micro-and nanostructures appear. While infrared ablation is dominated by a chipping mechanism above a critical fluence of 9.93 Jcm -2 , higher ablation rates are observed with strong quality losses at the same time. In comparison to the infrared emission wavelength, in general , a significantly higher processing quality is achieved with the ultraviolet emission wavelength. In addition, the influence of spot size and repetition rate in UV processing is investigated. By increasing these parameters, a process acceleration without quality losses is enabled. The generation of a sophisticated microstructure exemplifies the advantages of processing silicon carbide with the UV laser reported here.}, subject = {Femtosekundenlaser}, language = {en} } @inproceedings{FranzMueckeKunzetal.2023, author = {Franz, Daniel and M{\"u}cke, Dominik and Kunz, Tim and Rung, Stefan and Esen, Cemal and Hellmann, Ralf}, title = {UV picosecond laser drilling of ABF film material for printed circuit boards using laser burst mode and beam shaping}, 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 an experimental study of laser microvia percussion drilling of Ajinomoto build-up film (ABF) material using an ultrashort pulsed laser in the ultraviolet region. In order to optimize the drilling quality in terms of the fabricated taper and microvia diameter, the MHz burst mode is used in combination with both a Gaussian and a top-hat laser intensity distribution. To evaluate the influence of the top-hat beam shape on defocusing, microvias were drilled at different z-positions in the range of 200 μm evenly distributed around the focal plane. The drilling quality was evaluated by laser scanning microscopy and metallography. When using a top-hat beam shape, a reduced taper of down to 26.8 \% on average is achieved compared to a Gaussian beam. For the application of 3 intra-burst pulses, we find an improvement of the taper by 11.6\% compared to the single pulse mode due to the increasing heat accumulation. Using a top-hat beam shape in combination with the MHz burst mode, an 18.2 \% reduction in laser drilling time for a microvia with a similar taper is remarkable, demonstrating the high potential for scaling throughput in electronics manufacturing.}, subject = {Pikosekundenbereich}, language = {en} } @inproceedings{SchwarzRungEsenetal.2020, author = {Schwarz, Simon and Rung, Stefan and Esen, Cemal and Hellmann, Ralf}, title = {UKP-Prozess mit anschließendem CO2-Laserpolieren zur Fertigung komplexer Optiken}, series = {10. Workshop Laserbearbeitung von Glaswerkstoffen}, booktitle = {10. Workshop Laserbearbeitung von Glaswerkstoffen}, year = {2020}, subject = {Linse}, language = {en} } @inproceedings{KeferPapeGriesetal.2023, author = {Kefer, Stefan and Pape, Natalie and Gries, Nikola and Roth, Gian-Luca and Schmauss, Bernhard and Hellmann, Ralf}, title = {Towards Pressure Sensors Based on Polymer Planar Bragg Gratings}, series = {Organic Photonic Materials and Devices XXV}, booktitle = {Organic Photonic Materials and Devices XXV}, isbn = {9781510659414}, doi = {10.1117/12.2648723}, year = {2023}, abstract = {While Bragg grating-based optical devices have shown promising performances for pressure sensing applications, their sensitivity, especially in the low-pressure regime, is unsatisfying and needs to be optimized by elaborate designs, such as cantilevers or other extrinsic mechanical transducers. This contribution demonstrates and discusses a novel concept for optical pressure sensors based on polymer planar Bragg gratings. Waveguide and Bragg grating are fabricated underneath the surface of a temperature-stable and humidity-insensitive cyclic olefin copolymer substrate by means of a femtosecond laser. Based on the employed direct-writing procedure, in combination with adaptive, in-situ beam shaping with a spatial light modulator, writing depth, i.e., location of the photonic structures within the substrate, as well as Bragg grating periodicity and positioning can be deliberately chosen. Afterwards, the polymer substrate is post-processed with a high-precision micro mill, so a diaphragm comprising the integrated photonic structures is generated. The resulting diaphragm exhibits a thickness of 300 µm and a diameter of 10 mm. Finally, the optical sensor is packaged and sealed to form an air-filled gas pocket underneath the diaphragm. Deformations of the diaphragm by external pressure changes translate to strain variations along the waveguide axis and thus perturb the Bragg grating period. This leads to changes in the grating's wavelength of main reflection, which can be evaluated in order to quantify the relative external pressure. With this straightforward optical sensor concept, pressure sensitivities up to 39 pm kPa-1, within relative pressures ranges from 78 kPa to 372 kPa, are achieved.}, subject = {Bragg-Reflektor}, language = {en} } @inproceedings{GirschikofskyRosenbergerBelleetal.2012, author = {Girschikofsky, Maiko and Rosenberger, Manuel and Belle, Stefan and Hellmann, Ralf}, title = {Surface modifications of planar bragg grating refractive index sensors for gas detection}, series = {Proceedings of the XXVI International MicroCAD Conference - Sensing Technologies, Miskolc (Hungary)}, booktitle = {Proceedings of the XXVI International MicroCAD Conference - Sensing Technologies, Miskolc (Hungary)}, year = {2012}, subject = {Bragg-Reflektor}, language = {en} } @inproceedings{FranzRothRungetal.2021, author = {Franz, Daniel and Roth, Gian-Luca and Rung, Stefan and Esen, Cemal and Hellmann, Ralf}, title = {Superimposed beam deflection using acousto-optical deflectors in combination with a galvanometer scanner}, series = {Lasers in Manufacturing - LiM 2021}, booktitle = {Lasers in Manufacturing - LiM 2021}, year = {2021}, subject = {Galvanometer}, language = {en} } @inproceedings{GlaabHellmann2010, author = {Glaab, Johannes and Hellmann, Ralf}, title = {Small-scale low-through UV-C LED disinfection device, in waste processing and recycling}, 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{SchwarzRungHellmann2016, author = {Schwarz, Simon and Rung, Stefan and Hellmann, Ralf}, title = {Simulation of process parameters towards the generation of low spatial frequency LIPSS on dielectric materials}, series = {MultiScience - XXX. microCAD International Multidisciplinary Scientific Conference}, booktitle = {MultiScience - XXX. microCAD International Multidisciplinary Scientific Conference}, year = {2016}, subject = {Laserbestrahlung}, language = {en} } @inproceedings{KeferSchmaussHellmann2023, author = {Kefer, Stefan and Schmauss, Bernhard and Hellmann, Ralf}, title = {Sapphire-Based Planar Bragg Grating Devices}, 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.W2.4}, year = {2023}, abstract = {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.}, subject = {Bragg-Reflektor}, language = {en} } @inproceedings{KeferSchmaussHellmann2021, author = {Kefer, Stefan and Schmauss, Bernhard and Hellmann, Ralf}, title = {POLYMER PLANAR BRAGG GRATINGS BASED ON BULK CYCLIC OLEFIN COPOLYMERS: FABRICATION AND FUNCTIONALIZATION}, series = {Proceedings of Student Conference on Sensors, Systems and Measurement 2021}, booktitle = {Proceedings of Student Conference on Sensors, Systems and Measurement 2021}, isbn = {978-80-01-06822-9}, year = {2021}, subject = {Bragg-Reflektor}, language = {en} } @inproceedings{ScheurichBelleHellmannetal.2009, author = {Scheurich, Steffen and Belle, Stefan and Hellmann, Ralf and So, Sik and Sparrow, Ian and Emmerson, Greg}, title = {Planar optical waveguide bragg grating chemical sensor for online process control}, series = {3rd integrated optics - sensors, sensing structures and methodes Korbielow, PL}, booktitle = {3rd integrated optics - sensors, sensing structures and methodes Korbielow, PL}, year = {2009}, subject = {Bragg-Reflektor}, language = {en} } @inproceedings{HuehnleinTschirpkeHellmann2010, author = {H{\"u}hnlein, Kristof and Tschirpke, Katrin and Hellmann, Ralf}, title = {Optimisation of laser cutting using design of experiment - A comparative study of cutting thin ceramic layers using a fibre laser and a CO2 laser}, series = {Physics procedia}, volume = {5}, booktitle = {Physics procedia}, number = {Part B}, issn = {1875-3892}, pages = {243 -- 252}, year = {2010}, subject = {Laserschneiden}, language = {en} } @inproceedings{LutzSchwarzRungetal.2021, author = {Lutz, Christian and Schwarz, Simon and Rung, Stefan and Marx, Jan and Esen, Cemal and Hellmann, Ralf}, title = {Optical system for multi Bessel beam high power ultrashort pulsed laser processing using a spatial light modulator}, series = {Lasers in Manufacturing - LiM 2021}, booktitle = {Lasers in Manufacturing - LiM 2021}, year = {2021}, abstract = {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.}, subject = {Ultrakurzzeitlaser}, language = {en} } @inproceedings{RosenbergerBelleHellmann2011, author = {Rosenberger, Manuel and Belle, Stefan and Hellmann, Ralf}, title = {Optical interrogation of chemical and temperature bragg grating sensors using tunable fiber coupled bandpass filter}, series = {Proceeding XXV microCAD, International scientific conference, 2011, Section H}, booktitle = {Proceeding XXV microCAD, International scientific conference, 2011, Section H}, pages = {25 -- 30}, year = {2011}, subject = {Bragg-Reflektor}, language = {en} } @inproceedings{RosenbergerBelleHellmann2009, author = {Rosenberger, Manuel and Belle, Stefan and Hellmann, Ralf}, title = {Optical interrogation of bragg grating sensors using tunable fibre based bandpass filter}, series = {Proceedings of the 20st international science conference, Mittweida}, booktitle = {Proceedings of the 20st international science conference, Mittweida}, year = {2009}, subject = {Bragg-Reflektor}, language = {en} } @inproceedings{BelleRosenbergerHellmann2011, author = {Belle, Stefan and Rosenberger, Manuel and Hellmann, Ralf}, title = {Optical fibre sensing in the production process and storage of biofuels}, series = {Proceeding XXV microCAD, International scientific conference, 2011, Section A}, booktitle = {Proceeding XXV microCAD, International scientific conference, 2011, Section A}, pages = {21 -- 26}, year = {2011}, subject = {Biokraftstoff}, language = {en} } @inproceedings{AdelmannNeumeierSchleieretal.2015, author = {Adelmann, Benedikt and Neumeier, Benedikt and Schleier, Max and Wilmann, Eugen and Hellmann, Ralf}, title = {Optical cutting tear detection system for industrial fiber laser based cutting machines}, series = {Lasers in Manufacturing Conference 2015}, booktitle = {Lasers in Manufacturing Conference 2015}, year = {2015}, subject = {Laserschneiden}, language = {en} } @inproceedings{KalmarHellmannRegertetal.2011, author = {Kalm{\´a}r, L{\´a}szl{\´o} and Hellmann, Ralf and R{\´e}gert, Tam{\´a}s and Varga, Zoltan}, title = {Numerical simulation of heat transfer procedure in high power LED modules}, series = {Proceedings of the 12th technical and scientific meeting}, booktitle = {Proceedings of the 12th technical and scientific meeting}, pages = {18 -- 20}, year = {2011}, subject = {Lumineszenzdiode}, language = {en} }