Strahlformende und fokussierende Bauelemente für CO2-Laser in der Materialbearbeitung

The paper deals with the investigation of computer generated optical elements having a microstructure on a planar substrate.Our domain of interest is the application of phase elements to beam shaping for material processing.These elements allow the generation of nearly arbitrary intensity distributions in the focus domain without the usual scanning mirrors.Lateral phase jumps of higher order laser modes can be compensated by an appropriate element design.The optical elements presented here, are based on the idea to match the wavefront phase by a Fresnel zone plate not at the zone border only but also in the inner of the zones.A short description of the methods for the solution of the invers task of focusing is given on the base of geometrical optics.As an example the surface profile has been evaluated for the focusing of a gaussian laser beam into a cross.The Fresnel-Kirchhoff integral has been applied to these element and the result of diffraction calculations has been shown for C02 l aser application.Furthermore, we have carried out some experiments with a 10 Watt C02 laser and compared the result with the theory.The cross shape of the focus in the experiment was fullycomparable with the theoretical result.The cross dimension was 3.6 mm ineach direction.There, a eight level element was realized with a three mask electron beam lithography and etching in a system of copper layers on a glass substrate.The efficency, i.e. the power ratio contained within the focus domain with intensities higher 5% of the maximum focus intensity was 87% theoretically and 76% experimentally.