Apparatus and method for laser welding in a controllably pure gaseous environment at sub-atmospheric as well as high pressures. A workpiece to be welded is contained within a vessel having a light transmitting means which allows passage of a laser beam into the vessel. A gas stream is introduced to the vessel through a gas inlet means and positioned so that the stream deflects ionized particles from impinging on the light transmitting means. The gas stream simultaneously serves to cool the light transmitting means. Weld debris and spent gas are exhausted through a gas exhaust means which preferably is located adjacent to the workpiece. The apparatus is particularly suited to the laser welding of oxide dispersion strengthened alloys.