We learned in polarization by reflection that the transmitted radiation is partially polarized.

The reflected wave is polarized parallel to the surface of the material, so the transmitted wave contains less radiation polarized parallel to the surface.

When several plates (such as microscope slides) are arranged as in figure 7.29, most of radiation polarized parallel to the surface is reflected, and the transmitted wave is polarized.

Figure 7.29: Polarization by transmission through several surfaces.

If the incident beam is at Brewster angle (q_B), the polarization of the transmitted beam is perpendicular to the boundary surface.

This is the same application as described in Brewster windows at the ends of a gas laser, where instead of many surfaces, the beam is transmitted again and again through the same two plates (Brewster windows).