07 Fakultät Konstruktions-, Produktions- und Fahrzeugtechnik

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/8

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Institute: search.filters.UBSInstitut.Graduate School of Excellence for Advanced Manufacturing Engineering (GSaME)Author: search.filters.author.Abdou Ahmed, Marwan

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    Process limits for percussion drilling of stainless steel with ultrashort laser pulses at high average powers
    (2022) Brinkmeier, David; Holder, Daniel; Loescher, André; Röcker, Christoph; Förster, Daniel J.; Onuseit, Volkher; Weber, Rudolf; Abdou Ahmed, Marwan; Graf, Thomas
    The availability of commercial ultrafast lasers reaching into the kW power level offers promising potential for high-volume manufacturing applications. Exploiting the available average power is challenging due to process limits imposed by particle shielding, ambient atmosphere breakdown, and heat accumulation effects. We experimentally confirm the validity of a simple thermal model, which can be used for the estimation of a critical heat accumulation threshold for percussion drilling of AISI 304 steel. The limits are summarized in a processing map, which provides selection criteria for process parameters and suitable lasers. The results emphasize the need for process parallelization.
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    Influence of fabrication deviations on the polarization-maintaining behavior of inhibited-coupling guiding hollow-core fibers
    (2024) Chen, Bowen; Kühlthau, Tim; Röhrer, Christian; Graf, Thomas; Abdou Ahmed, Marwan
    Numerical simulations were conducted to analyze the influence of the design parameters of tubular inhibited-coupling guiding hollow-core photonic crystal fibers (IC-HCPCFs) on the bending-induced phase shift. The possibility to implement polarization-maintaining (PM) tubular IC-HCPCFs using a low-birefringence approach (with a modal birefringence parameter B<7×10-9) is discussed. Two different tubular IC-HCPCF designs with 7 and 8 glass capillaries are proposed for operation at a wavelength of 1030 nm. The numerical simulation predicts low guiding losses and a PM behavior sustaining a degree of linear polarization (DOLP) larger than 90% after 10 m of fiber with a bend radius larger than 0.2 m. This shows great potential for high-power beam delivery in an industrial environment. The influence that fabrication deviations have on the polarization-maintaining behavior was also investigated and indicates tight fabrication tolerances for both proposed fiber designs. Small deviations from the ideal symmetrical structure can lead to an enhancement of undesired modal birefringence. To ensure a DOLP larger than 90% at the exit of a 10 m-long fiber and for a bending radius > 0.2 m precise control of the drawing parameters during the fiber production is required, which is challenging but is considered to be technically feasible.