• Tags: Brewster, reflection, polarization
• Difficulty: Moderate

When unpolarized light hits a surface at Brewster's angle $i_B$, the reflected light is completely plane-polarized with the electric field perpendicular to the plane of incidence. Brewster's law: tan $i_B$ = $n_{2}$/$n_{1}$ = n (for air to medium). At Brewster's angle, the reflected and refracted rays are perpendicular: $i_B$ + r = 90°. For glass (n = 1.5): $i_B$ = t$an^{-1}$(1.5) = 56.3°. The refracted ray is partially polarized. Since only a small fraction of light is reflected (about 4-8% at Brewster's angle), multiple surfaces (pile of plates) are used to get appreciable polarized light by reflection.