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Mikrostrukturierter Strahlformer für das Fügen von Glas und Keramik mit einem CO2-Laser
The paper presents an example of a computer-generated optical element having a microstructure on a planar substrate. The element transforms a Gaussian C02-laser beam into a special intensity distribution of the focus. There, in the focus region a part of the laser power is asymmetrically distributed around a sharp intensity peak. This special beam shaper has to be applied in order to join glasses or ceramics by glass solder using a C02 laser with a power of about 1 00 W. There, the problem of stress in the sample and in the joint arises if a conventional sharp focused laser beam is applied. The new focus shape minimizes the stress because the temperature distribution is optimized. The optical element used is a Fresnel zone plate with phase matching. The inverse task of focusing has been solved based on the rules of geometrical optics. The Fresnel-Kirchhoff integral has been applied to these elements to check-up and optimize the focusing result. There, a eight-level reflector wasrealiz ed by three mask electron-beam lithography and etching in a silicon substrate covered with an titan/gold layer at the end. The designed intensity distribution in the focus region was verified by a beam analyzer with a low-power C02 laser. Furthermore, a first experiment with a 100 W C02 laser was carried out. It has been shown that the beam shaper developed here reduces the stress in the joint region of the sample.