RESUMEN
Lasers are widely used for structuring metallic surfaces by ablating material. An alternative approach for laser structuring is surface structuring by laser remelting (WaveShape), which is based onthe continuous remelting of a thin surface layer using laser radiation while simultaneously modulating the laser power. The structures are generated by redistribution of the molten material. The structure height and the structure wavelength of periodic structures created using WaveShape can be precisely adjusted by the adaption of various process parameters. However, the structures produced are mostly asymmetrical. An asymmetric structure refers to a structure that is not symmetrical and is inclined in or against the scanning direction. In the context of this work, the asymmetry of the structures was significantly reduced through two different process adaptations. As a first adaption, a compensation term is added to the laser power modulation, which is calculated from the difference profile between a target profile and a structured profile. With this adaption, the shape deviation of an asymmetrical structure could be decreased by 66 %. Asymmetry can be reduced efficiently, although the difference profile required must be determined from a preliminary process step. As a second adaption, a modulation of the scanning speed is investigated with which shape deviation can be decreased by 40 %. Asymmetry is not as effectively prevented as when using the first adaption, but the adaption can be performed without the difference profile. Another aim was to investigate the destructuring, i.e. the removal and therefore smoothing, of asymmetric structures. Using the inverse laser power modulation for destructuring, the structure height of a symmetrical structure can be reduced by 91 % while the structure height of an asymmetric structure can be reduced by 68 %. To increase the efficiency of destructuring of an asymmetrical structure, iterative destructuring was investigated. With two iterations of destructuring, the structure height was reduced by 90 %. As a second approach for more efficient destructuring of asymmetric structures an adaption of the laser power modulation via a compensation term was investigated. The structure height could be reduced by 86 %. In summary, results show that asymmetry can be prevented when structuring with WaveShape and that asymmetric structures can be destructured efficiently.
RESUMEN
Recent results of processing fused silica using a high-power Q-switched CO2 laser source with a maximum output power of 200 W are presented. Compared to the processing with continuous wave laser radiation, the main advantage of pulsed laser radiation is the influence of the light-matter interaction with high laser peak power at small average laser power. An application for the approach presented in this paper is the flexible manufacturing and form correction of optics. This laser-based process is nearly independent of the surface geometry and can even be enhanced by laser polishing and expanded to other glass materials. Hence, the high-power Q-switched CO2 laser source is used to ablate glass material with an ablation rate up to 2.35 mm3/s and also for ablating glass material locally in a vertical dimension down to 3 nm.
RESUMEN
Structuring by remelting is an innovative approach for structuring metallic surfaces with laser radiation, where no material is removed but reallocated while molten. Based on this remelting principle an innovative structuring technique is investigated, where laser beams are superposed. A melt pool is generated by a cw laser beam with constant feed rate. A pulsed laser is superposed onto the cw laser and evaporates a small amount of molten material and, therefore, generates vapour pressure, which shapes the melt pool surface. The solidification follows this newly shaped surface. For this process a new optical system was designed and built up, which allows the combination of cw and pulsed laser beams.
