Polarisation

Polarisation (British spelling) or polarization refers to the orientation of the oscillations of a transverse wave relative to its direction of travel. In optics, polarization describes the direction of the electric field of an electromagnetic wave, with the magnetic field oscillating perpendicular to both the direction of travel and the electric field.

Light can be linearly polarized, circularly polarized, or elliptically polarized. Linear polarization has the electric field oscillating along a fixed line. Circular polarization has the electric field rotating with constant magnitude, producing two orthogonal components that are 90 degrees out of phase; elliptical polarization is the general case.

Polarisation can be produced or modified by reflection, refraction, scattering, and passage through anisotropic materials such as birefringent crystals. Polarizing filters, such as Polaroid sheets, transmit only light with electric-field orientation within a chosen plane. Malus's law describes how transmitted intensity depends on the angle between the light's polarization and the filter axis.

Unpolarized light contains many randomly oriented polarizations and can become polarized by a polarizer; partially polarized light lies between these extremes. Polarization states can be described using Stokes parameters or the Poincaré sphere.

Applications include sunglasses and camera filters that reduce glare, liquid-crystal displays, and 3D cinema, as well as optical communications that use polarization-division multiplexing. Polarisation is also used in stress analysis with polarized light, and in astronomy and remote sensing to study scattering, magnetic fields, and material properties. In quantum contexts, the polarization state of individual photons is a common basis for quantum information experiments.