High Power Direct Diode Laser (HPDDL) systems with output powers greater than 4.0kW in a compact robust package are now available. These industrial semiconductor (diode, solid state) lasers are a new type of heat source, which are beginning to replace conventional lasers for seam welding applications. The beam shape of the HPDDL systems are rectangular or a line source. This beam profile does not key-hole, thus yielding higher quality seam welding process. Due to their high efficiency, these HPDDL are very compact and can be mounted directly on a tube mill or robot enabling high speed and high quality welding of both ferrous and nonferrous metals. These all solid state laser systems inherently provide the ability to control the output laser energy with a degree that is unmatched by conventional Nd:YAG and CO(sub2) lasers.