TY - CHAP A1 - Girschikofsky, Maiko A1 - Rosenberger, Manuel A1 - Belle, Stefan A1 - Brutschy, Malte A1 - Waldvogel, Siegfried A1 - Hellmann, Ralf T1 - α-Cyclodextrin functionalized planar Bragg grating sensor for the detection of small arene traces in solvamt vapour T2 - 14th international meeting on chemical sensors (IMCS 2012) KW - sensor detection KW - Bragg-Reflektor Y1 - 2012 SN - 978-3-9813484-2-2 U6 - https://doi.org/10.5162/IMCS2012/7.5.1 SP - 646 EP - 648 ER - TY - CHAP A1 - Heilmann, Eva-Maria A1 - Hellmann, Ralf T1 - Water jet guided laser cutting using a green disc laser T2 - Proceeding XXV microCAD, International scientific conference, 2011, Section K: Material science/Material processing technologies KW - Wasserstrahlschneiden KW - Laserbearbeitung Y1 - 2014 ER - TY - CHAP A1 - Bischoff, Kay A1 - Mücke, Dominik A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - UV-Femtosecond-Laser Structuring of Silicon Carbide T2 - International Congress on Applications of Lasers & Electro-Optics (ICALEO) 2023 N2 - 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. KW - Femtosekundenlaser KW - Siliciumcarbid Y1 - 2023 ER - TY - CHAP A1 - Franz, Daniel A1 - Mücke, Dominik A1 - Kunz, Tim A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - UV picosecond laser drilling of ABF film material for printed circuit boards using laser burst mode and beam shaping T2 - International Congress on Applications of Lasers & Electro-Optics (ICALEO) 2023 N2 - 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. KW - Pikosekundenbereich KW - Laserbohren Y1 - 2023 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 - CHAP A1 - Kefer, Stefan A1 - Pape, Natalie A1 - Gries, Nikola A1 - Roth, Gian-Luca A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Towards Pressure Sensors Based on Polymer Planar Bragg Gratings T2 - Organic Photonic Materials and Devices XXV N2 - 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. KW - Bragg grating KW - pressure sensor KW - integrated photonics KW - cyclic olefin copolymers KW - femtosecond laser KW - Bragg-Reflektor KW - Drucksensor Y1 - 2023 SN - 9781510659414 U6 - https://doi.org/10.1117/12.2648723 ER - TY - CHAP A1 - Girschikofsky, Maiko A1 - Rosenberger, Manuel A1 - Belle, Stefan A1 - Hellmann, Ralf T1 - Surface modifications of planar bragg grating refractive index sensors for gas detection T2 - Proceedings of the XXVI International MicroCAD Conference – Sensing Technologies, Miskolc (Hungary) KW - surface modification KW - Bragg-Reflektor Y1 - 2012 ER - 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 -