Editing Polarization (waves) (section)

=== Specular reflection ===
In addition to birefringence and dichroism in extended media, polarization effects describable using Jones matrices can also occur at (reflective) interface between two materials of different [[refractive index]]. These effects are treated by the [[Fresnel equations]]. Part of the wave is transmitted and part is reflected; for a given material those proportions (and also the phase of reflection) are dependent on the [[angle of incidence (optics)|angle of incidence]] and are different for the ''s''- and ''p''-polarizations. Therefore, the polarization state of reflected light (even if initially unpolarized) is generally changed.

[[File:Brewster-polarizer.svg|class=skin-invert-image|right|thumb|upright=1.25|A stack of plates at Brewster's angle to a beam reflects off a fraction of the ''s''-polarized light at each surface, leaving (after many such plates) a mainly ''p''-polarized beam.]]
Any light striking a surface at a special angle of incidence known as [[Brewster's angle]], where the reflection coefficient for ''p''-polarization is zero, will be reflected with only the ''s''-polarization remaining. This principle is employed in the so-called "pile of plates polarizer" (see figure) in which part of the ''s''-polarization is removed by reflection at each Brewster angle surface, leaving only the ''p''-polarization after transmission through many such surfaces. The generally smaller reflection coefficient of the ''p''-polarization is also the basis of [[polarized sunglasses]]; by blocking the ''s''- (horizontal) polarization, most of the glare due to reflection from a wet street, for instance, is removed.<ref name=Hecht2002 />{{rp|348–350}}

In the important special case of reflection at normal incidence (not involving anisotropic materials) there is no particular ''s''- or ''p''-polarization. Both the {{mvar|x}} and {{mvar|y}} polarization components are reflected identically, and therefore the polarization of the reflected wave is identical to that of the incident wave. However, in the case of circular (or elliptical) polarization, the handedness of the polarization state is thereby reversed, since by [[Circular polarization#Left/Right|convention]] this is specified relative to the direction of propagation. The circular rotation of the electric field around the {{mvar|''x-y''}} axes called "right-handed" for a wave in the {{math|+''z''}} direction is "left-handed" for a wave in the {{math|−''z''}} direction. But in the general case of reflection at a nonzero angle of incidence, no such generalization can be made. For instance, right-circularly polarized light reflected from a dielectric surface at a grazing angle, will still be right-handed (but elliptically) polarized. Linear polarized light reflected from a metal at non-normal incidence will generally become elliptically polarized. These cases are handled using Jones vectors acted upon by the different Fresnel coefficients for the ''s''- and ''p''-polarization components.