Abstract: Arrangement for generating well-defined beam distribution over a surface or in a volume by means of a diffraction optical element (17). The arrangement includes at least one laser source (14), an optical filter means, preferably a mode-selective filter (16), a diffraction optical component (17) as well as possible coupling and focusing elements (15, 18). Said components, means and elements are positioned and fixed in a common unit and that the filter (16) is so developed that the beam from the source (14) after passage through said mode-selective filter (16) occurs essentially in one mode.