Abstract: 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.