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In electrodynamics, the strength and direction of an electric field is defined by its electric field vector. In the case of a circularly polarized wave, as seen in the accompanying animation, the tip of the electric field [[Euclidean vector|vector]], at a given point in space, relates to the phase of the light as it travels through time and space. At any instant of time, the electric field vector of the wave indicates a point on a [[helix]] oriented along the direction of propagation. A circularly polarized wave can rotate in one of two possible senses: clockwise or ''right-handed circular polarization (RHCP)'' in which the electric field vector rotates in a [[Right-hand rule|right-hand]] sense with respect to the direction of propagation, and counter-clockwise or ''left-handed circular polarization (LHCP)'' in which the vector rotates in a [[left hand rule|left-hand]] sense.
''Circular polarization'' is a [[speciallimiting case (mathematics)|limiting case]] of ''[[elliptical polarization]]''. (alongThe withother [[linearspecial polarizationcase]]). Theis termsthe easier-to-understand ''circular'',[[linear polarization]]''elliptical'',. andAll ''linearthree polarization''terms were coined in 1822 by [[Augustin-Jean Fresnel]],<ref name=fresnel-1822z>A. Fresnel, "Mémoire sur la double réfraction que les rayons lumineux éprouvent en traversant les aiguilles de cristal de roche suivant les directions parallèles à l'axe", read 9 December 1822; printed in H. de Senarmont, E. Verdet, and L. Fresnel (eds.), ''Oeuvres complètes d'Augustin Fresnel'', vol. 1 (1866), pp.{{nnbsp}}731–51; translated as "Memoir on the double refraction that light rays undergo in traversing the needles of quartz in the directions parallel to the axis", {{Zenodo|4745976}}, 2021 (open access); §§9–10.</ref> who first detailedreported the case of circular polarization (without yet naming it) in 1821.<ref name=fresnel-1821a>A. Fresnel, "Note sur le calcul des teintes que la polarisation développe dans les lames cristallisées" et seq., ''Annales de Chimie et de Physique'', Ser. 2, vol. 17, pp. 102–11 (May 1821), 167–96 (June 1821), 312–15 ("Postscript", July 1821); reprinted (with added section nos.) in H. de Senarmont, E. Verdet, and L. Fresnel (eds.), ''Oeuvres complètes d'Augustin Fresnel'', vol. 1 (1866), pp. 609–48; translated as "On the calculation of the tints that polarization develops in crystalline plates, & postscript", {{Zenodo|4058004}} (Creative Commons), 2021; author's footnote to §16.</ref>
The phenomenon of polarization arises as a consequence of the fact that [[light]] behaves as a two-dimensional [[Transverse wave#Explanation|transverse wave]].
Circular polarization occurs when the two orthogonal electric field component vectors are of equal magnitude and are out of phase by exactly 90°, or one-quarter wavelength.
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