Abstract: It is profitable to oscillate a beam on objects when a high power CO.sub.2 laser beam or a high power YAG laser beam welds or anneals the objects. In order to let a laser beam scan, a device for reciprocating a lens or a device for rotating two mirrors synchronously has been proposed. These devices suffer from the difficulty of cooling. Prior devices are not applicable to a high power laser. A parallel laser beam is first reflected by a parabolic mirror. Then a mirror which is reciprocally swaying by a galvanometer reflects the beam toward the objects. A water inlet and an outlet are mounted on a rear surface of the swaying mirror. Cooling water is carried out through coiled tubes. Excellent heat diffusion prevents the galvanometer from malfunction.

Abstract: Metal sheets having different thicknesses are abutted and laser-welded. During laser welding, the laser beam weaves from side to side with respect to a weld line. As a result, the width of the weld bead is increased and the gradient of the weld bead surface is decreased whereby no sharp edge remains at the weld line. The resulting one-piece sheet can be used as a press material without any pre-pressing processing, such as grinding.