Optical and haptic properties of a surface are two prominent characteristics which are increasingly used to attribute the overall surface quality and functionality. For example, the surface of highly stressed ball bearings is micro-structured to increase their durability. The interior fittings of a car are mainly made of plastics, whose surfaces are designed to mimic certain natural (e.g. leather), or technical patterns.
Many optical and haptic properties are determined by the surface of the moulding tool which is used to recreate the surface. In case of, for example, a car´s dashboard, these moulds are meter-sized and contain a variety of different surface types. To structure such a tool's surface, laser ablation using ultrashort laser pulses is a promising technology. Laser ablations allows to create precise surface structures with features on a micrometer scale in a completely digitalized process.
In the currently implemented state of the art, structuring depths of laser ablation tool machining is limited to areas of less than 50 µm. This is insufficient for large tools and limits laser ablation to few surfaces. The goal of eVerest is to develop a machining technique to implement laser structuring for large-size moulding tools with micrometer-sized precision and ablation depths of several millimeters.
To achieve such a comparatively large depth, the focal position of the ablating laser must be constantly adjusted. A deformable mirror placed in the path of the laser beam could be used to adjust the focal position. An efficient process rate shall be maintained, hence the shift of the focal position, and thus the actuation rate of the deformable mirror, must take place on a time scale of a few milliseconds. The deformable mirror must allow a stroke of several micrometers on an aperture of a few millimeters to achieve the required focal shift. Deformable mirrors with large stroke often suffer from poor surface quality which hampers the required structuring precision, or they exhibit mechanical resonances which prohibit the required actuation rate of several kilohertz.
Development of a fast z-shifter based on piezo-controlled adaptive mirrors
The task of our lab is to develop a fast deformable mirror with high surface quality and sufficient stroke which allows for the required high actuation rate.
The project eVerest is funded by the German Federal Ministry of Education and Research (BMBF) under contract no. 02P14A140 ff.