Talk:Polarization
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This is three articles banged together -- can someone copyedit this?
- Done. Excised text:
Polarization in telecommunications: Of an electromagnetic wave, the property that describes the orientation, i.e., time-varying direction and amplitude, of the electric field vector.
Note 1: States of polarization are described in terms of the figures traced as a function of time by the projection of the extremity of a representation of the electric vector onto a fixed plane in space, which plane is perpendicular to the direction of propagation. In general, the figure, i.e., polarization, is elliptical and is traced in a clockwise or counterclockwise sense, as viewed in the direction of propagation. If the major and minor axes of the ellipse are equal, the polarization is said to be circular . If the minor axis of the ellipse is zero, the polarization is said to be linear . Rotation of the electric vector in a clockwise sense is designated right-hand polarization , and rotation in a counterclockwise sense is designated left-hand polarization .
Note 2: Mathematically, an elliptically polarized wave may be described as the vector sum of two waves of equal wavelength but unequal amplitude, and in quadrature (having their respective electric vectors at right angles and π/2 radians out of phase).
Source: from Federal Standard 1037C and from MIL-STD-188
From the article:
- Individual photons are inherently circularly polarized; this is related to the concept of spin in particle physics.
Can someone fact-check this?
- I think I just answered my own question: http://cse.unl.edu/~reyes/CPE.html
I have made a major overhaul of this entry, because it was somewhat incoherent and repetitive (presumably due to merges of several sources), missed some important points, and probably left a lot of people scratching their heads trying to visualize things without any diagrams. I hope my attempt is an improvement. I have tried to retain material from the previous version, or adapt it somewhat to fit in better. Some parts I omitted completely because they seem too specialized or they probably belong in other entries. The completely removed text appears below. Possibly some of the stuff I have added should also be ripped out and put into other more specific entries but it will take a little thinking over as to what is the best way to do that without reducing the article to a series of facts and links presented without explanation or continuity... so for now I've just put it all in here. Hacked out text:
For circular polarization, it is also useful to consider how the direction of the electric vector varies along the direction of propagation at a single instant of time. While in the plane the vector rotates in a circle (as time advances), along the propagation axis (at one instant) the tip of the electric vector describes a helix. The pitch of the helix is one wavelength, and the helix screw sense is either right handed or left handed. Visualizing this spatial variation in the direction of the electric field is useful in understanding how circularly polarized light can interact differently with helical molecular conformations, depending on whether the electric field and the molecule helix sense are the same or opposite. This is part of the phenomenon of circular dichroism.
[...]
As described by Maxwell's equations, light is a transverse wave made up of an interacting electric field E and a magnetic field B. The oscillations of these two interacting fields cause the fields to self-propagate in a certain direction, at the speed of light. In most cases, the directions of the electric field, the magnetic field, and the direction of propagation of the light are all mutually perpendicular. That is, both the E and B fields oscillate in a direction at right angles to the direction that the light is moving, and also at right angles to each other.
(In optics, it is usual to define the polarization in terms of the direction of the electric field, and disregard the magnetic field since it is almost always perpendicular to the electric field.)
[...]
A quarter-wave plate is constructed from a birefringent material, that is, in the plane of the plate there are two orthogonal axes and light passing through it propagates at a different speed along one axis than on the other. The thickness of the plate is adjusted so that the net difference in propagation speed is one quarter of a wavelength. If this plate is oriented so that the fast axis is forty five degrees to the direction of linear polarization then the light emerging from the other side will have two components of equal amplitude and a ninety degree phase difference, creating circular polarization. Rotating the quarter wave plate ninety degrees in the plane will reverse the sense of circular polarization.
Birefringence can be created by straining a normally uniform material. A properly arranged and controlled mechanical oscillator coupled to a strain-free window can convert linearly polarized light of a single color impinging on the window into alternating left and right hand circularly polarized light emerging from the other side. That is, the window can operate as an oscillating quarter wave plate. If this light is then passed through a material which has a circular dichroism at that color, the emerging light will have an amplitude modulation that varies with the frequency of the oscillator driving the quarter wave plate. This amplitude variation can be detected and used to measure the amount of circular dichroism exhibited. This amplitude will depend on the intrinsic property of the material, and upon the amount of material the light passed through, which in turn depends on the concentration of the absorbing substance and its thickness. Although the phenomenon measured this way is delta-absorption, the results are customarily reported in degrees of ellipticity through a simple algebraic conversion.
- Theorie mathematique de la lumiere, Henri Poincaré, Gauthiers-Villars, Paris, 1892. The original description of the Poincaré Sphere.
Rkundalini 15:11, 2 Jun 2004 (UTC)
Quantum?
MattSzy pointed out an error in the following text, in User talk:Rkundalini. I have cut it out and put it here until someone can correct it (or until I get around to reading up on the topic)... excised text follows
Since photons are spin-1/2 particles, mathematical descriptions of polarization states are closely related to spinors. Individual photons are inherently circularly polarized, and the coherency matrix is equivalent to the density matrix of quantum mechanics, if expressed using a circular basis. The quantum mechanics version of the Poincaré sphere is the Bloch sphere.
Rkundalini 15:07, 25 Jun 2004 (UTC)
mistake in definition of stokes parameters
there is a mistake in the definition of the stokes parameters.
S1 should be S1=Ip cos2psi cos2chi
S2 should be S2=Ip sin2psi cos2chi
- argh I'm sure I've fixed that before ... anyway, fixed now! -- Rkundalini 00:56, 25 Jan 2005 (UTC)
Polarization in elastic waves
Since elastic waves may have transverse components, they may be polarized. They also exhibit many of the properties of electromagnetic waves (e.g. birefringence, aka "shear-wave splitting"). But I don't know offhand how to incorporate that into this article. It's definitely related, but the structure of this article would make it hard to add. Gwimpey 06:02, Mar 5, 2005 (UTC)
- Are they mathematically equivalent to electromagnetic waves? If not I'd suggest a separate article, which refers to this one for concepts that are related. Something similar should probably done for gravitational wave polarization and any other types of waves with transverse components. -- Rkundalini 06:37, 10 Mar 2005 (UTC)
=== Observing polarization effects in everyday life ===
"All light which reflects off a flat surface is at least partially polarized."
I do not have any knowledge of the physical principles involved, but from my photographing days I seem to remember that a polarizing filter has a dramatic effect in suppressing light reflected from water or polished non-metallic surfaces, while the effect on light reflected from metalls seems insignificant.I have used this effect for taking pictures from a mirror - a polarizing filter removes doubled contours caused by reflection in the glass, while the image relected from the silver layer remains clear. Can someone knowledgable explain? --Georgius 16:55, 6 Jun 2005 (UTC)