32 Hofmann, Jörg Holly, Carlo Kaierle, Stefan 418910 RWTH Aachen University Aachen German 1 Online-Ressource : Illustrationen In laser material processing, optical systems are used e.g. for beam guidance and shaping. Particularly with laser powers in the multi-kilowatt range, the absorbed laser light leads to heating of the optical elements. One consequence is the so-called thermal lens effect. The thermal lens effect leads to a change in the focal length of the optical system and thus to a shift in the focal position relative to the workpiece. This can lead to reduced machining quality or even to an abortion of the machining process. This thesis therefore investigates various concepts for active and passive compensation of thermal effects. A passive approach for the compensating of thermal effects is investigated using the example of plastic optics for a laser power of 15 W. Compared to glass optics, plastic optics exhibit thermal effects that are about 100 times greater at the same laser power, which is why their range of application has so far been limited to optical systems with laser powers <<1 W. On the other side, they offer considerable cost-saving potential due to their injection molding production. Passive compensation of thermal effects through a different combination of thermoplastics is not possible due to their similar material parameters. This work therefore pursues a passive approach in which the geometry of an existing plastic lens is adapted for a specific operating condition. This approach extends the power range that has been effectively usable to date. To this end, the laser and material parameters relevant to the thermo-optical design are first identified using a sensitivity analysis and measured using various measurement methods. The lens geometry is then optimized for the operating condition based on the laser and material parameters. The adapted lens geometry is produced by injection moulding and then characterized with regard to its optical properties. The compensated lens geometry has a Gaussian intensity distribution in the focal plane but deviates from the target value by 27% in terms of its focal length. The thermal effects during the laser machining process can also be intensified by process-related contamination of the optics, in particular the protective glass. In practice, the protective glass is therefore replaced at regular intervals. By compensating for the thermal effects over time, it would be possible to extend the necessary service intervals or increase the process accuracy. Due to the temporal change of the thermal effects that occur, passive compensation is not possible here. As an alternative, active compensation of thermal effects is therefore demonstrated using a new type of measurement and control system. The measurement of the focus position is based on the evaluation of the characteristic diffraction pattern of an amplitude mask integrated into the beam path, the so-called Bahtinov mask. The diffraction pattern is evaluated using different evaluation algorithms. Following experimental validation, the measurement concept is being further developed for coaxial integration in almost any laser material processing system. Measurements show a determination of the focus position over a range of ±2.5 mm with an average deviation of 42.52 μm. Veröffentlicht auf dem Publikationsserver der RWTH Aachen University ; Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2025 ; 2, ; PUB:(DE-HGF)11, ; Dissertation / PhD Thesis Dissertation Rheinisch-Westfälische Technische Hochschule Aachen 2025 2025 RWTH-2025-04723 2025 https://publications.rwth-aachen.de/record/1011781