A laser utilizing a unique assembly for mounting a Brewster angle window. The mounting assembly includes an elongated annular member having a transverse slot at the appropriate Brewster angle to the plane perpendicular to the axis of the annular member. A rectangular window is held in place in the slot by the tension of a leaf spring. The mounting assembly may then be inserted in place at either the anode or cathode ends of the laser and permanently held in place without introducing any stresses in the window or affecting its alignment.

Laser device comprising a tube for gaseous or vaporous laser material, which tube is sealed at both ends by a window consisting of a plate of radiation-transmissive material. Each window plate rests directly on the associated end face of the tube and is held against this end face by a retaining frame surrounding the window plate and secured to the end face of the tube. The retaining frame has its surface remote from the end face provided with a flange extending inwardly to overlie the periphery of the window plate and has its surface facing the end face provided with a recess located at its inner edge surrounding the side edge of the window plate. An O-ring is received in the recess.