DE2442888

A laser is disclosed with a single, critical surface Brewster window. The Brewster window is formed by a Littrow prism having a first planar surface located along the principal optical axis of the laser and oriented at Brewster's angle with respect thereto, for admitting a refracted, plane polarized component of the laser beam. The Littrow prism has a second substantially planar face which does not require the conventional, high quality "laser polish." This second face intersects the first face along a line perpendicular to the principal axis, at an angle with respect to the first face such that the second face is substantially perpendicular to the refracted component of the laser beam. A planar mirror mounted by means of a layer of index matching optical cement, is mounted on the second face of the Littrow prism, perpendicular to the direction of propagation of the refracted, plane polarized component. This component is reflected back upon its self and out of the first planar face of the prism along the principal axis of the laser, whereby laser action is sustained. An alternate embodiment is disclosed where the laser path is folded upon itself and a 45 DEG -90 DEG triangular prism is employed for communicating the laser beam between the two legs of the system, via the Littrow prism. A third embodiment is disclosed of a folded path gaseous discharge laser having an improved optical efficiency and power output.