Computer generated beam shaping and focusing optical elements for laser material processing

The paper presents a theoretical investigation of computer generated optical elements having a microstructure on a planar substrate. The field of application is the beam shaping in laser material processing, especially the generation of various intensity distributions and figures in the focus domain. These optical elements match the wavefront phase not only at the Fresnel zone border, but also in the inner of the zones. The inverse task of focusing has been solved based on the rules of geometrical optics. As an example, the surface profile has been evaluated for the focusing of a Gaussian laser beam into a cross-shaped intensity profile. The Fresnel-Kirchhoff integral has been applied to these elements and the results of diffraction calculations have been discussed for C02 laser and NdYag laser applications. Furthermore, we have carried out a first experiment with a low power C02 laser and compared the results with the theory. The cross-shaped focus obtained during the experiment was f ully comparable with the theoretical result.