Analyse des Verformungsverhaltens optischer Systeme während der Lasermaterialbearbeitung

The application of high energy lasers for material processing requires a high beam quality. This is e.g. determined by the image quality of the optical elements used for beam guidance and shaping. Until now, in the design of the optical elements several influencing parameters that occur during laser processing have been largely neglected. Reasons for this are the limited knowledge on the operational performance of optical elements for high power lasers (up to 25 kW) and the difficult measurement of the occurring deformations and displacements. Responsible for the deterioration of the desired image properties of the optical elements are, on the one hand, manufacturing inaccuracies, and, on the other hand, statical, dynamical, and thermal forces. Statical forces result from the mounting of the optical components and the applied coolant pressure. Dynamical forces can occur due to vibrations of the mechanical components of the beam guidance and fluctuations of the coolant pressure. The abs orption of a small part of the incident laser radiation leads to a heat-up of the optical element, resulting in a time and space-dependent deformation of the optics. The statical, dynamical, and thermal deformations and displacements occur simultaneously. A systematic analysis of the operational behavior requires a separated consideration of these parameters. Only such a proceeding can lead to a valuation of the influencing parameters. Using holographic interferometry, such a separated consideration of the different influences becomes possible. In comparison to other interferometric methods, the holographic interferonetry also allows not only the investigation of the optical component, e.g. a mirror, but also of the other components of the optical element. The results of this investigation lead to first conclusions about the operational behavior of the considered optical elements.