Brewster Angle
Definition and meaning of Brewster Angle in chemistry.
Brewster angle is the angle of incidence at which light reflected from a surface becomes completely plane-polarized, with the electric field vector oscillating only perpendicular to the plane of incidence.
In more detail
At this specific angle, the reflected and refracted rays are oriented exactly 90 degrees apart, which forces the component of light polarized parallel to the plane of incidence to vanish from the reflection entirely (it is fully transmitted instead). Only the perpendicular (s-polarized) component reflects, so the reflected beam is 100% polarized. The Brewster angle depends on the refractive indices of the two media and is used to characterize thin films, minimize glare, and align polarizing optics such as laser cavity windows.
Key facts
| Formula | tan θB = n2/n1 (Brewster's law) |
|---|---|
| Discoverer | Sir David Brewster (1815) |
| Key condition | Reflected and refracted rays are perpendicular to each other |
| Field | Physical Chemistry |
For light traveling from air (n1 = 1.00) onto glass (n2 = 1.50), the Brewster angle is θB = arctan(n2/n1) = arctan(1.50) ≈ 56.3°. Light striking the glass surface at this angle produces reflected light that is entirely polarized perpendicular to the plane of incidence.
Frequently asked questions
Why does reflected light become fully polarized at the Brewster angle?
At the Brewster angle, the reflected and refracted rays are perpendicular, meaning the oscillating dipoles in the second medium that would radiate the parallel-polarized reflected wave are aligned along the reflection direction and cannot emit light that way, so only the perpendicular polarization component reflects.
Does the Brewster angle depend on wavelength?
Yes, slightly, because it depends on the refractive indices n1 and n2, which vary with wavelength due to dispersion.