Optics

Polarization of light

Polarization describes the orientation of the transverse electric field; an analyzer obeys Malus’s law, I = I₀ cos²θ, for linearly polarized light.

Polarization describes the orientation of the transverse electric field; an analyzer obeys Malus’s law, I = I₀ cos²θ, for linearly polarized light.

Model and quantities

An electromagnetic wave is transverse: its electric field E is perpendicular to propagation. Linearly polarized light has a fixed E orientation; a polarizer transmits the component parallel to its transmission axis. If θ is the angle between the analyzer axis and the incident polarization, an ideal analyzer gives I = I₀ cos²θ. Unpolarized light is reduced to I_b/2 by an ideal polarizer.

Quick check

Unpolarized light contains many electric-field vibration directions perpendicular to propagation; linearly polarized light vibrates along one defined direction. A second polarizer acts as an analyzer: Malus’s law gives transmitted intensity $I=I_0\cos^2 heta$, where $heta$ is the angle between transmission axes. For crossed axes, ideal transmission vanishes; at 45°, half the incident polarized intensity remains. Polarization is used in glare-reducing sunglasses, LCD screens, and stress analysis of transparent materials.