Abstract: A sealed laser plasma tube for use in a gas laser system. A Brewster window seals one end of the tube (the cathode end, in a preferred embodiment), and an end mirror which seals the opposite tube end (the anode end, in a preferred embodiment). In a laser system embodying the invention, a second end mirror is positioned adjacent to, but spaced from, the Brewster window. Intra-cavity elements may conveniently be inserted and replaced in the region between the sealed Brewster window and the second end mirror. The sealed mirror which seals the tube end opposite the window is preferably coated with at least an outermost layer of Hafnium oxide, to protect it from hard UV radiation originating within the plasma tube. The inventors have recognized that the problem of sealed window degradation is substantially less severe at the cathode end of an ion laser plasma tube, and that the sealed window should be attached at the tube end at which the window degradation problem is less severe.