A transparent plate which retards the phase of one plane of vibration of light relative to the plane at right angles; also known as a retardation plate. The retardation is usually a quarter of a wavelength (a quarter-wave plate) or half a wavelength (a half-wave plate). A quarter-wave plate converts elliptically or circularly polarized light into linear polarized light, or vice versa, while a half-wave plate rotates the direction of the plane of polarization of linearly polarized light. Wave plates are used in polarimeters.
Subjects: Astronomy and Astrophysics.