Polarization of Light
Polarization describes the orientation of the oscillating electric field of light, a consequence of its transverse wave nature with wide practical use.
Definition
The property of a transverse electromagnetic wave that specifies the orientation and rotation of its electric-field vector, ranging from linear through elliptical to circular states.
Scope
This area treats the vector nature of light: the direction in which its electric field oscillates. It covers linear, circular, and elliptical states of polarization and their mathematical description by Jones and Stokes-Mueller formalisms; the production and analysis of polarized light by polarizers and wave plates; the interaction of polarized light with anisotropic (birefringent) and optically active media; and the polarization changes that accompany reflection and refraction as described by the Fresnel equations. It explains optical phenomena that depend on field orientation and underlies a wide range of devices and measurements.
Sub-topics
Core questions
- What does it mean for light to be linearly, circularly, or elliptically polarized?
- How is polarized light produced, transformed, and analysed?
- How do anisotropic media alter the polarization of light?
- How does reflection change the polarization of light?
Key concepts
- linear polarization
- circular polarization
- elliptical polarization
- Jones vector
- Stokes parameters
- birefringence
- Brewster's angle
- optical activity
Key theories
- Polarization states and the Jones calculus
- The transverse electric field of fully polarized light is described by a two-component Jones vector, and optical elements act as Jones matrices, providing a compact algebra for predicting how polarization is transformed.
- Stokes-Mueller description of partial polarization
- Partially polarized and unpolarized light is described by four measurable Stokes parameters, with optical elements represented by Mueller matrices, extending polarization analysis to incoherent and depolarizing situations.
- Fresnel equations for reflection
- The amplitudes of the reflected and transmitted waves depend on polarization and angle of incidence through the Fresnel equations, predicting effects such as Brewster's angle at which reflected light is fully polarized.
Clinical relevance
Polarization is exploited in polarized-light microscopy for identifying birefringent crystals such as urate in gout, in polarimetry for measuring glucose and other optically active solutes, and in liquid-crystal displays and polarization-sensitive optical coherence tomography of tissue.
History
Malus discovered the polarization of light by reflection in 1808, and Brewster identified the angle at which reflected light is completely polarized. Fresnel's transverse-wave theory in the 1820s explained polarization and birefringence, while Stokes introduced his parameters in 1852 to describe partially polarized light.
Key figures
- Étienne-Louis Malus
- Augustin-Jean Fresnel
- David Brewster
- George Gabriel Stokes
Related topics
Seminal works
- hecht2017
- bornwolf1999
Frequently asked questions
- Why can polarizing sunglasses reduce glare?
- Light reflected from horizontal surfaces such as water or roads is partially horizontally polarized; sunglasses with a vertical transmission axis block much of that polarized glare while passing other light.
- Is ordinary light from the sun or a lamp polarized?
- No; thermal sources emit light with rapidly varying, randomly oriented field directions, so the light is unpolarized until it is filtered, reflected, or scattered in a way that selects a particular orientation.