Polarization
of Electromagnetic Waves |

**In General **> see light; optics /
electromagnetism.

* __Remark__: Unpolarized light must be polychromatic!

* __Malus' law__: The intensity
of polarized light passing through a linear polarizer decreases by a factor
cos^{2}*α*; > s.a. hidden variables.

* __Of sky light__: The scattering
that causes the blue sky (mostly single scattering) also polarizes it; To first
approximation there are two 0-polarization
points, the Sun and the anti-Sun, but double scattering causes
them to split vertically into two closely spaced points (Brewster and Babinet
points, each of index 1/2).

* __Demonstration__: Black
light sandwich – a transparency foil between two polarizers, allows to
see two index-1/2 singularities in direction
space.

@ __General references__: Pye 00 [I]; Gamel & James PRA(12)-a1303 [degree of polarization, and degree of purity for two-level quantum systems]; Trippe JKAS(14)-a1401 [rev, and astronomy].

@ __Stokes polarization parameters__:
Schaefer et al AJP(07)feb;
> s.a. gravitational-wave background.

@ __Polarization of skylight__: Smith AJP(07)jan
[model]; Ropars et al CP(14) [and the sunstone as an ancient Viking navigational tool].

**Faraday Rotation** > s.a. cmb polarization.

* __Idea__:
The rotation of the plane of polarization of light going through a magnetic
field (or other medium); > s.a. electromagnetism
in curved spacetime.

* __Gravitational__: The rotation
of the plane of polarization of polarized electromagnetic radiation traveling
through a gravitational field; In the case of a gravitational wave, the effect
vanishes for localized (astrophysically generated) waves and is
non-zero but negligible for cosmological ones.

@ __General references__: Ganguly et
al PRD(99)
[degenerate relativistic]; Zavattini PRL(06)
+ pw(06)mar
[observation,
and axions]; Cornean & Nenciu JFA(09)-a0807 [thermodynamic
limit]; Melrose ApJ(10)-a1010 [effect of magnetic-field reversals]; Oppermann et al A&A(15)-a1404 [extragalactic].

@ __Gravitational__: Perlick & Hasse CQG(93);
Sereno PRD(04);
Halilsoy & Gurtug PRD(07),
Faraoni NA(07)-a0709 [due
to gravitational waves].

**Other Effects** > s.a. Coherence; earth [auroras].

* __Birefringence__: A polarization-dependent
doubling in photon propagation speed, or anisotropic index of refraction; It
happens in material media such as calcite, and in vacuum either as a quantum field theory effect in the presence of strong electromagnetic fields, or in modified gravity theories such as bi-metric
models and Poincaré gauge theory; A similar effect can occur for gravitational waves; > s.a. axions; finsler
geometry; modified
electromagnetism; non-commutative gauge theories; QCD phenomenology.

* __Dichroism__: Anisotropic
absorption of components of an electromagnetic wave; For example, by a grid of parallel conductors.

* __Optical activity__: The
rotation of the electric field of a plane wave traversing some materials (e.g., quartz).

@ __Optical activity__: Barbieri & Guadagnini NPB(04)
[gravitational]; Agulló et al a1705-GRF [in a curved spacetime geometry, for quantum radiation].

@ __Birefringence, material medium__:
Ghosh & Fischer PRL(06)
+ pw(06)nov
[in a chiral
liquid].

@ __Birefringence, vacuum__: Chen et al MPLA(07)he/06 [and
vacuum
dichroism, experimental searches]; Hattori & Itakura AP(13) [in strong magnetic fields]; Karbstein et al PRD(15)-a1507 [in strong inhomogeneous electromagnetic fields]; Mignani et al MNRAS(16)-a1610 + news sn(16)dec [in X-rays from neutron stars]; Karbstein a1611-ln [pedagogical]; Schneider et al a1708 [and gravitational dynamics]; Wang a1712 [of gravitational waves].

@ __Birefringence, cosmological__:
Exirifard PLB(11)-a1010 [theory]; di Serego Alighieri a1011-proc [methods, rev]; Yadav et al PRD(12)-a1207 [with cmb], Gruppuso et al JCAP(16)-a1509 [constraints from Planck and Bicep2/Keck data]; Duval & Schücker PRD(17)-a1610 [in Robertson-Walker cosmologies]; Whittaker et al a1702/MNRAS [using resolved radio sources].

@ __Experiments and examples__: Ouseph et al AJP(01)nov
[polarization by reflection]; Holleczek et al OE(11)-a1012 [cylindrically polarized states of light].

@ __Related topics__: Berry & Dennis PRS(01)
[polarization singularities in vector
waves]; news sn(10)mar ["superchiral" light]; Shukla & Prakash MPLB(16)-a1610 [polarization squeezing].

> __In gravitation and cosmology__:
see kaluza-klein
phenomenology; non-commutative physics; Non-Symmetric
Gravity; gravitational phenomenology; observational
cosmology; photon phenomenology in quantum
gravity; tests
of
general relativity
with
light; tests of the equivalence principle.

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jan 2018