polarisasjonsellipse

Polarisasjonsellipse, or the polarization ellipse, is a geometric representation of the state of polarization of a monochromatic light wave. At a fixed point in space and time, the tip of the electric field vector traces an ellipse in the plane transverse to the direction of propagation. If the polarization is purely linear, the ellipse degenerates into a straight line; if it is circular, the ellipse has equal axes.

The ellipse is described by two angles: the orientation angle, denoted ψ, which is the angle between the major axis of the ellipse and a reference axis (often the x-axis), and the ellipticity angle, χ, defined so that tan χ = b/a, where a and b are the semi-major and semi-minor axes. The sign of χ indicates the handedness of the polarization (right-handed or left-handed). Special cases include χ = 0 for linear polarization and χ = ±π/4 for circular polarization.

A common time-domain description expresses the electric field as the sum of two orthogonal components with a phase difference: E(t) = Re{Ex0 e^{iωt} x̂ + Ey0 e^{i(ωt+δ)} ŷ}. The resulting trajectory depends on the relative amplitudes Ex0, Ey0 and the phase δ. In practice, polarization states are often described using Stokes parameters (I, Q, U, V) or Jones vectors, from which the ellipse parameters ψ and χ can be derived.

Polarization ellipses are studied with instruments such as polarimeters, waveplates, and polarizers. They have broad applications in optical communications, microscopy, remote sensing, and astronomy, where precise control and measurement of polarization provide diagnostic information about light sources and media.