Linearpolarisation

Linear polarisation describes electromagnetic waves in which the electric field vector oscillates in a single plane as the wave propagates. The plane in which the electric field lies is called the plane of polarisation, and its orientation is specified by an angle relative to a reference axis. In contrast to unpolarised light, linear polarisation shows a fixed orientation of the field; the wave can be described as a superposition of two orthogonal components with a fixed phase relation.

Linear polarisation can be produced by a linear polariser that transmits only the component of the electric field along its transmission axis. It can also arise from reflection at a specific angle (Brewster's angle) or from scattering by particles or surfaces. Some light sources emit partially linearly polarised radiation, while birefringent media and wave plates can transform polarisation states.

Detection and analysis typically use polarimetry. A rotating linear polariser or a pair of orthogonal polarisers measures the intensity as a function of angle, yielding a cos^2 fit and the polarisation angle. Linear polarisation is conveniently described by Stokes parameters Q and U; the degree of linear polarisation is sqrt(Q^2+U^2)/I. Polarisation-maintaining optics preserve polarisation along propagation.

Applications include glare reduction in sunglasses and photography, liquid-crystal displays that rely on aligned polarisers, and radio and optical communications where the polarisation state affects antenna and fibre coupling. Linear polarisation is a baseline concept in optics, radio physics, and remote sensing, and it serves as a reference state for describing other polarisation forms such as circular and elliptical polarisation.