waves in the 23a are again refracted by the first face 12a of the second plate into ray 24a which is reflected from the second face 12d as the ray 24b and thereafter recombines with the wave 24 to degrade its polarization purity this comes about because the s type polarization which was reflected in ray 22a is transmitted through 22c 23a 24a and 24b to recombine with ray 24 furthermore the device is easily affected by temperature and the extinction ratio is not fixed placing the wire grid polarizer on the surface 14a of plate 14 which as shown is perpendicular to ray 25 rejects the dominant s polarization in wave 23a 24a 24b 24 and finally 25 by reflection this is indicated in the drawing by the dashed line rays 35 34 33 32 31 and their related rays for clarity of illustration these rays have been shown displaced from the single solid line incoming ray 25 but it will be undstood that in fact for each ray such as 25 there is a superposed reflected ray such as 35 ordinarily any reflection from a wire grid polarizer would pass back to the laser unless the polarizer was tilted however in this invention the reflected wave loses part of its energy at each.