Brewster's Angle
Definition
The special angle where reflected light becomes perfectly polarized — used in sunglasses and laser windows.
Symbol: · Unit: degrees
Technical definition
The angle of incidence θ_B where reflected and refracted rays are 90° apart, given by tanθ_B = n₂/n₁. At this angle, reflected light is fully s-polarized (electric field perpendicular to the plane of incidence).
Example
Polarized sunglasses exploit Brewster's angle: sunlight reflecting off water near ~53° is horizontally polarized, and the glasses' vertical polarizers block it — killing glare.
Common confusion
Brewster's angle polarizes the reflected beam, not the refracted one — the transmitted light is only partially polarized. It also only works for the specific n₂/n₁ pair; there is no universal Brewster angle.