07 Fakultät Konstruktions-, Produktions- und Fahrzeugtechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/8
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Item Open Access General mathematical model for the period chirp in interference lithography(2023) Bienert, Florian; Graf, Thomas; Abdou Ahmed, MarwanItem Open Access Theoretical investigation on the elimination of the period chirp by deliberate substrate deformations(2022) Bienert, Florian; Graf, Thomas; Abdou Ahmed, MarwanWe present a theoretical investigation on the approach of deliberately bending the substrate during the exposure within laser interference lithography to compensate for the period chirp. It is shown that the yet undiscovered function of the surface geometry, necessary to achieve the zero-chirp case (i.e. having a perfectly constant period over the whole substrate) is determined by a first-order differential equation. As the direct analytical solution of this differential equation is difficult, a numerical approach is developed, based on the optimization of pre-defined functions towards the unknown analytical solution of the differential equation by means of a Nelder-Mead simplex algorithm. By applying this method to a concrete example, we show that an off-center placement of the substrate with respect to the point sources is advantageous both in terms of achievable period and substrate curvature and that a fourth-order polynomial can greatly satisfy the differential equation leading to a root-mean-square deviation of only 1.4 pm with respect to the targeted period of 610 nm.Item Open Access Generation of a radially polarized beam in a polycrystalline ceramic Yb:Lu2O3 thin-disk laser(2023) Didychenko, Denys; Esser, Stefan; Beirow, Frieder; Savchenko, Anton; Pruss, Christof; Graf, Thomas; Abdou Ahmed, MarwanAbstractWe report on the generation of a continuous-wave (CW) radially polarized beam with an Yb:Lu2O3 polycrystalline ceramic disk in a thin-disk laser (TDL) oscillator. A circular grating-waveguide mirror (CGWM) with a high polarization discrimination given by a reflectivity difference between the two orthogonal polarization states of 44.6% was used as a polarization-selective cavity end-mirror. An output power of 175 W was achieved with an optical efficiency of 39.6%. A high degree of radial polarization of 96.2% and a beam propagation factor of M2hor. = 2.05 and M2ver. = 2.32 were measured at the maximum output power.Item Open Access Simple spatially resolved period measurement of chirped pulse compression gratings(2023) Bienert, Florian; Röcker, Christoph; Graf, Thomas; Abdou Ahmed, MarwanItem Open Access Detrimental effects of period-chirped gratings in pulse compressors(2023) Bienert, Florian; Röcker, Christoph; Dietrich, Tom; Graf, Thomas; Abdou Ahmed, MarwanItem Open Access Single-crystal and ceramic Yb:Lu2O3 gain media for thin-disk oscillators(2023) Esser, Stefan; Xu, Xiaodong; Wang, Jun; Zhang, Jian; Graf, Thomas; Abdou Ahmed, MarwanWe report on the direct comparison of single-crystal and ceramic Yb3+:Lu203 gain media with respect to emission spectra, fluorescence lifetime, depolarization, and laser performance in a continuous-wave thin-disk laser oscillator. The most efficient laser operation was achieved with a single-crystal disk in multimode operation with a slope efficiency of 72.1% and an average output power of 997 W. At the same temperature level, a ceramic disk delivered 861 W with a slope efficiency of 68.6%. In fundamental-mode operation, the highest average power of 360 W and highest optical efficiency of 41.3% were obtained with a ceramic disk. For the single-crystal disk, the fundamental-mode output power was limited to 113 W at an optical efficiency of 29%, potentially due to stress within the crystal.