An apparatus for connecting two workpiece parts to form a workpiece by through-transmission welding by means of weld seams running in a preselected weld seam pattern in regions of the workpiece parts having different characteristics is provided. The apparatus has a laser beam source with a plurality of individually controllable laser beam emitters of different power which are arranged adjacently in an X direction and a homogenizer arranged downstream. At least two reflection channels are provided in the homogenizer which run parallel to one another in a Y direction and completely penetrate the homogenizer in a Z direction by a channel depth.