Polarizedlight

Polarized light is light in which the electric field vector oscillates in a defined orientation, or in which the components of the electric field have a fixed phase relationship. In ordinary light from most sources, the directions of the electric field are random, so the light is unpolarized. Polarization describes the geometry of the electric field, independent of intensity.

Polarization can arise when light is emitted by anisotropic materials, reflected from a surface, or scattered by particles. Reflection at certain angles, notably the Brewster angle, preferentially transmits one polarization, producing linearly polarized light. Scattering by atmospheric molecules (Rayleigh scattering) and by other small particles also yields partial linear polarization. Transmission through birefringent or dichroic materials can alter the polarization state, and addition of a phase delay between orthogonal components can produce circular or elliptical polarization.

Types and representations: Linear polarization has electric field oscillating along a single direction. Circular polarization has equal amplitudes with a 90-degree phase shift between orthogonal components, causing the vector to rotate at constant speed. Elliptical polarization is the general case, with unequal amplitudes and phase difference.

Measurement and notation: The polarization state can be described by Stokes parameters. The effect of a polarizer on intensity follows Malus's law: I_out = I_in cos^2 theta for linear polarization. Polarimetry uses specialized instruments to determine the polarization state.

Applications: Polarized filters are used in sunglasses and camera lenses to reduce glare; liquid-crystal displays control light polarization; polarization is used in 3D cinema, photography, and microscopy. In science, polarization methods diagnose material stress (photoelasticity), characterize thin films (ellipsometry), or enable polarization-division multiplexing in optical communications. In astronomy and atmospheric science, polarization reveals magnetic fields, scattering properties, and geometries of celestial and atmospheric processes.

Natural polarization: The sky often exhibits partial linear polarization perpendicular to the sun due to Rayleigh scattering; some animals navigate by sky polarization patterns.