In gas lasers, it is common to put the end mirrors at Brewster angle to the optic axis.

The electromagnetic beam traveling between the mirrors of the laser, is reflected many times from these mirrors.

Since the mirrors are at Brewster angle, all the radiation that is polarized perpendicular to the beam plane is emitted out of the laser cavity at early stage.

In the gas tube remains only radiation polarized in the beam plane.

The advantage of this arrangement is that the beam have no reflection losses, since only the transmitted polarized beam is traveling between the mirrors.

The radiation out of these lasers is polarized as can be seen in figure 7.27.