# Talk:Polarization (waves)

WikiProject Physics (Rated B-class, High-importance)
This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
B  This article has been rated as B-Class on the project's quality scale.
High  This article has been rated as High-importance on the project's importance scale.

## merge

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)

Yes it was right to cut that out: Photons are spin one particles. Lasers would not work with spin 1/2 particles. The satement that photons have spin one is equivalent to the statement that the electric field is a vector field. The lack of a third spin direction has something to do with the photon's zero rest mass. Indevidual photons can have linear polarization. "Density matrix" is a statistical mechanics concept and does not appear in the description of pure quantum states. I don't know about the Bloch sphere, but I don't think it needs to be mentioned here. David R. Ingham 21:59, 9 March 2006 (UTC)

Polarization is the intensity or the intrinsic magnetic momentum(the spin)? statement like individual photon is linear polarized, any reference? Jackzhp (talk) 03:30, 21 October 2013 (UTC)
Your question is not clear. Individual photons are certainly not linearly polarized, however. They are circularly polarized.--Srleffler (talk) 05:58, 21 October 2013 (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)

The numbering of Pauli matrices also seems wrong (or non-standard). —Preceding unsigned comment added by 67.111.218.42 (talk) 23:56, 19 October 2010 (UTC)

Discrepancies like that usually turn out to be just notational differences between different authors or different fields. Arbitrary sign conventions and other types of convention can affect the appearance of expressions.--Srleffler (talk) 01:20, 20 October 2010 (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 metals 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 reflected from the silver layer remains clear. Can someone knowledgeable explain? --Georgius 16:55, 6 Jun 2005 (UTC)

Yes, except at normal incidence, reflections from metal are a little bit polarized, but maybe not enough to be included in the article. Metals tend to reflect both polarization well, except for oxides and surface irregularities. Dielectrics have a Brewster angle at which vertically (for a horizontal surface) polarized light is completely transmitted into the medium. A glance at that article looks as though the Brewster angle would be complex, and therefore not correspond to any plane wave, for a lossy material like a metal.

I think "circular polarizer on the camera" in the figure caption should read "linear" or perhaps vertical, but I am not entirely sure. If no-one is sure, maybe we should just delete the word "circular". I know that the sky tends to be linearly polarized and that my camera filter is linearly polarized, like my sun glasses, but I can't entirely rule out the possibility that the polarization could become elliptical somehow.

Circular polarizers used in photography start with a linear polarizer and then add a second birefringent layer to create circularly polarized light from the linear polarized light. This is done because many modern cameras have beam splitters (for focusing and metering) that don't work with linear polarized light. -Steve Pucci | talk 03:43, 16 May 2006 (UTC)

The blue sky is polarized because the scatterers are electric dipoles that are polarized (the charge is displaced) perpendicular the direction of the incident light. This is called Rayleigh scattering.

Stressed materials such as eyeglasses where they are held by the frames and tempered rear windows of cars rotate polarized light by transmitting the components differently, so one can see a pattern when looking with polarized glasses through the rear window at a reflection from a windshield, shiny paint or asphalt. David R. Ingham 22:49, 9 March 2006 (UTC)

## Satellite television

Can anybody add information about horizontal and vertical polarization in satellite television (for satellite channels)?. Thanks in advance.

Most satellites do not have a fixed orientation with respect to an earth observer, and spin as they revolve, and so are circularly polarized. A satellite would probably have to be geostationary (or at least geosynchronous) and non-spinning to have a linear polarization. Even then, it would only be a fixed orientation, and only coincidentally horizontally or vertically polarized. Also, usually a sat antenna points UP, making horizontal / vertical polarization kinda meaningless, as both would be in the wrong plane. --ssd 00:25, 29 December 2005 (UTC)

That is not exactly precise. If a satellite antenna were linearly polarized, the satellite's spinning would make the polarization change, not be circular. To reliably receive a rotating linear polarization with one receiver, one needs a circularly polarized antenna. I am not sure about the propagation or what satellites actually transmit. David R. Ingham 22:58, 9 March 2006 (UTC)

Current sattellites: Different signal in both linear polarizations. Old el cheapo rotating sattelites: Circular

Geosynchronous communication satellites use station keeping thrusters and gyroscopes to keep their orientation relative to earth fixed, thus a linearly polarized transmit antenna will always produce the same polarization at a given receiving location on earth. Current practice for most US domestic satellites is to use dual linear polarization, with odd numbered transponders having one polarization and even numbered transponders having the orthogonal polarization. This allows the reuse of frequencies on the same satellite with receive antenna polarization used to discriminate between two transponders operating on the same frequency. (Usually transponder frequency plans have transponders half overlapped. That is, the center frequency of one transponder falls at the edges of the two adjacent frequency transponders.)

The two polarizations do not necessarily correspond to vertical and horizontal relative to the earth. Indeed, a little thought to the geometry of the situation shows that for a fixed polarization orientation at the transmit antenna at the satellite, orientation of the polarization at the receive end will vary with geographical location. When describing the pointing parameters for a satellite receive antenna at any particular location on earth, in addition to providing the azimuth and elevation angles, you also have to provide a polarization angle which delineates the angle of one of the receive polarizations relative to level.

Many international satellite providers, such as Intelsat, use circularly polarized transmit antennas with adjacent transponders having opposite polarization senses.

Ooops - forgot to sign. 24.22.22.228 (talk) 01:36, 31 May 2014 (UTC)Gray

## imax passive polarized 3d glasses

Can someone explain how the imax passive polarized 3d glasses work here?

They are not like the old red-blue paper 3d glasses that give me a headache. They don't give me a headache at all and make things 3-d. Since they are called "passive polarized" I would think they should be listed here, or at least linked to here. I cannot seem to find them anywhere else.

• They're probably simply two orthoganally polarized lenses, with the movie being projected onto the screen twice, each channel being polarized so it's viewed by one eye. See stereoscopy and polarized glasses for more. --Bob Mellish 20:25, 11 November 2005 (UTC)

The screen has to be made with glass beads, not white material like paper or white paint. David R. Ingham 23:01, 9 March 2006 (UTC)

That's one way of doing it. The RealD system (Beowulf, etc, when in digital rather than Imax projection) uses two lenses of left and right hand circular polarisation. This is somewhat better as you don't have to maintain the glasses horizontal with the screen. Confusingly, the dichroic coatings on these glasses look red and green when viewed at about a 45-degree angle, leading people to incorrectly assume it's an anaglyptic method.—Preceding unsigned comment added by 68.123.239.154 (talk) 12:21, November 23, 2007

## unclear (transverse polarization)

I think this part of the article is confusing: "A plane wave is one where the direction of the magnetic and electric fields are confined to a plane perpendicular to the propagation direction."

I dug up a bit and found this on a previous version of the article: "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.". And in every physics book they only seem to take in account the electric field when describing polarization.

So, is the current version saying the same thing? I think it needs to either be reworded or further explained, because it can be confusing to people with few knowledge of electromagnetic waves.

nehalem 11:22, 15 January 2006 (UTC)

The sentence you quoted is not saying the same thing. It is defining what a "plane wave" is. Plane waves are usually assumed in elementary descriptions of polarization. Essentially a plane wave is a uniform light wave travelling in a single direction. All the wavefronts of the light are flat, and the electric and magnetic fields are therefore perpendicular both to each other and to the direction of propagation.

When one considers polarization of a plane wave, it's convenient to just talk about what the electric field does, since for a plane wave the magnetic field is always perpendicular to the electric field, and is proportional to it. There is nothing fundamental in this—polarization is as much a magnetic field effect as an electric field one. It just makes for a simpler description to only deal with one of the fields. --Srleffler 15:02, 15 January 2006 (UTC)

$\vec H \perp \vec E \perp \vec k$ should hold for all waves, not just for plane waves. From the Maxwell equations we have $\vec H \perp \vec D \perp \vec k$ and in isotropic media $\vec D // \vec E$. I therefore see a point in nehalems comment and propose to change the articles definition of plane waves from "A plane wave is one where the directions of the magnetic and electric fields are perpendicular both to each other and to the propagation direction." to "A plane wave propagates everywhere in the same direction, and like all electromagnetic waves has the electric and magnetic fields perpendicular to the propagation direction." I will change it if I dont hear objections. --danh 02:33, 16 January 2006 (UTC)

It is not true that Maxwell equations require that $\vec H \perp \vec D \perp \vec k$. Only H must be perperndicular to D. For instance guided modes of a slab waveguide have longitudinal components (TE modes have a longitudal component for H, and TM modes have a longitudinal component for E). As Gnixon indicated on this page also polarizations in Fibers have longitudinal modes. The article intorduction is simply wrong to define polarization as perpendicular to the direction of propogation. Electric field Polarization (Usually simply called polarization, as via Maxwell equations it uniquely set the magnetic field polarization) is simply the direction of the electric field vector in space and time. All the polarizations of a system can be spanned by a basis of just two vectors because of the so called "transverse condition" of maxwell equations which puts a 1 dimensional constraint on three dimensional space. The name is misleading as the polarization is not always transverse to the direction of propogation.Eranus 14:36, 30 November 2007 (UTC)

I agree with you and Gnixon. --Danh 23:26, 2 December 2007 (UTC)

I agree that that was an improvement. To be even more picky than usual, I could suggest "propagating electromagnetic waves", because evanescent fields may be called waves but have no real direction of propagation. An example is the field on the outside of the dielectric, in total internal reflection. David R. Ingham 23:15, 9 March 2006 (UTC)

I agree with danh's edit of the sentence, except that E&M waves may generally have longitudinal components. An example is E&M fields confined to circular waveguide, for which either the electric or magnetic field may be longitudinal. (The description of polarization in this case is virtually identical to that of free space E&M waves.) The property of E and H being perpendicular to the direction of propagation holds for (infinite) free space or a uniform material. I'll make a slight change to the sentence. --Gnixon 17:15, 24 July 2006 (UTC)

The important point about a plane wave is that a plane is two-dimensional. Light is a transverse wave, the wave fields are orthogonal to the direction of propagation, but in general they have both x and y components (if propagation is in the z direction). Most descriptions, including the transverse wave article, talk as if light can be understood by exact analogy to a water wave. However, a water wave is transverse in only one dimension. Phenomena such as circular polarization can only arise when the transverse wave is two-dimensional.

AJim (talk) 03:23, 9 July 2008 (UTC)

Your comment about light compared to water is worthy. You, and the current article version (See former comments) are wrong in stating that polarization must be perpendicular to the direction of propagation. Polarization is a two dimentional space because of the transverse condition (One of Maxwell equations)
$\nabla \cdot \mathbf{H} = 0$
which is a 1D constraint on 3D space. This 2D space is not a necceseraly a plane. It is the plane perpendicular to propogation for plane waves, it is not for guided modes.Eranus (talk) 12:26, 23 July 2008 (UTC)
I'm familiar with the fact that guided electromagnetic waves can have longitudinal components. I think it is actually true that this cannot occur in free space or a homogeneous medium of infinite extent, but I'm relying on dim memory from a long time ago and don't have a reference handy. If true, this is an important fact to include. Plane waves don't actually exist. If we can say something about general waves in free space, we should.
Your first change to the intro is not technically correct, because the intro defines polarization (as discussed here) as a property of transverse waves. That definition does not limit the discussion to EM waves, but it does exclude guided modes with a longitudinal component. I'm not sure how best to deal with this.--Srleffler (talk) 04:21, 24 July 2008 (UTC)
I took a stab at reworking the intro. For transverse waves, it is true that polarization describes the orientation of oscillations in the plane transverse to the propagation direction. The intro now mentions that there exist waves that are neither transverse nor longitudinal, and that these have polarization too. The wording could be improved.--Srleffler (talk) 04:52, 24 July 2008 (UTC)
OK this is a matter of definition, I was willing to accept that all E&M waves are transverse becasue they obey one of Maxwell equations also called the transverality condition:
$\nabla \cdot \mathbf{H} = 0$
I always thought that this is a bad name because the condition does not require generally that the polarization be perpendicular to the propagation. So my thiking was to continue to call EM wave transverse, because :$\nabla \cdot \mathbf{H} = 0$ is an important quality of all E&M waves which means that the vectorial nature of light add only 2 dimentions rather than three. Maybe you are right that we should stick to the literal meaning of transverse and simply not call EM waves transverse in general. Then it is important to clearly state the 2D vectorial nature, somehow. I don't know how to write this well because this an issue of history, I believe initialy people thought that all EM waves are literaly transverse and the name stuck. I'm not sure how to write this well, as a first stage we must keep it correct.
I'm very curious about whether all bulk or free spacee modes are transverse in the way you mean, asyou say it is an important fact to state. Specifically I remember some journal club lecture of radially polarized light being purely longitudenal at the waist (focus). I think in general higher order Laguerre Gaussian Modes have longitudenal components, but I'm not sure. Anyway this should be better checked and stated, I'm glad you did not reinset the statement until we resolve this. —Preceding unsigned comment added by Eranus (talkcontribs) 08:07, 24 July 2008 (UTC)
I double checked and indeed realistic beams measured in experiments can have longitudinal components even in free space with no sources. This is true for instance for radially polarized beams near the focus where the longitudinal componenets can be larger than the transverse components.
• Dorn, R. and Quabis, S. and Leuchs, G. (dec 2003). "Sharper Focus for a Radially Polarized Light Beam". Physical Review Letters 91 (23,): 233901–+. Check date values in: |date=` (help)

We are rightfully trying to make polarization simple and correct in the intro but it is not so simple in reality.Eranus (talk) 08:48, 15 May 2009 (UTC)

## Introduction

I think this article's introduction needs expansion, and some clarification. It also (most importantly) needs to tie down the subject matter more specifically. If I gave you this piece of text on its own:

In electrodynamics, XXXXXXXXXXXX (also spelled XXXXXXXXXXXXXX) is a property of waves, such as light and other electromagnetic radiation. Unlike more familiar wave phenomena such as waves on water or sound waves, electromagnetic waves are three-dimensional, and it is their vector nature that gives rise to the phenomenon of XXXXXXXXXXXX.

You wouldn't know for certain what it was talking about, no matter how knowledgeable in the subject you were. However, if I instead gave you this:

XXXXXXXXXX is the economic theory holding that the prosperity of a nation depends upon its supply of capital, and that the global volume of trade is "unchangeable." The amount of capital, represented by bullion (amount of precious metal) held by the state, is best increased through a positive balance of trade with other nations, with large exports and low imports. XXXXXXXXXX suggests that the ruling government should advance these goals by playing a protectionist role in the economy, by encouraging exports and discouraging imports, especially through the use of tariffs.

If you knew enough about the subject, you could determine that this was the introduction to Mercantilism. As I understand it, this should be the primary goal of the introduction - to define in simple terms the subject of the article so that a) readers who were looking for something else don't get bogged down in the rest of the page; and b) readers wade into the very nasty maths which comes later on armed with some knowledge of the subject matter. Correct me if I'm wrong on this.

Happy-melon 12:32, 30 May 2006 (UTC)

Actually, someone knowledgeable in the subject would immediately think of polarization. It's the most obvious distinction between electromagnetic waves and water or sound waves, which depends on the 3-dimensional (transverse) nature of the EM wave. I understand your point, though, and you're right: the introduction fails to give any sense of what polarization is.--Srleffler 14:23, 30 May 2006 (UTC)

I have omitted any reference to the fact the transverse waves must have the oscillation perpendicular to the direction of propagation. This is simply not true, my comments on the talk page about this have been ignored in the main text for the past year, thus I corrected it myself. I don't think I changed the intro especially well, and in general agree with happy-melons comments. I'll be glad if anyone rewrites the intro better, but please do not reintroduce the false concept of polarization always perpendicular to direction of propagation. This is true for plane waves and is stated in that section.Eranus (talk) 14:52, 23 July 2008 (UTC)

I reverted the intro to an older version (with minor revisions), July 24th. I don't understand why it is important to continue and write the misconception that polarization must be transverse to the direction of propagation. I don't understand what's wrong with the simple concept of polarization being the direction of the wave oscillation? Why do we need to say that the sound does not have polarization rather than saying that sound waves have longitudinal polarization. The important difference between sound and electro-magnetic waves, is that for sound waves the direction of oscillations is determined uniquely (It must be longitudinal)for any wave distribution, while for electro-magnetic waves the direction of oscillation is not unique, but limited to two dimensions by the transvesality condition div H=0.Eranus (talk) 12:37, 2 December 2008 (UTC)

Sorry Eranus. I was focused on trying to provide a simpler explanation, and didn't take the time to refresh my memory about this discussion. Your new text is better. I am still concerned about the intro though. Polarization is an important concept that comes up in everyday life and in high school (elementary school?) science classes. The intro to this article ought to be both technically correct and comprehensible to a smart 13-year old. At the least, the latter ought to be able to get an understanding of the typical case: a transverse EM wave in free space, which can have linear, circular, or elliptical polarization. That's not all there is to polarization, of course, but it is such an important special case that it needs to be handled prominently and in plain English. I'm not sure how we do that without losing accuracy, but I think we need to.--Srleffler (talk) 23:19, 2 December 2008 (UTC)

## Combining waves

Disclaimer: I am not a physicist.

I was just reading that you can take any light source, split it into two orthogonally-polarized beams, and combine them again to get the original source. This is news to me (I would have thought that you were putting in an infinite variation of polarizations, and only getting two out), but it makes sense. In the article, it says:

• Plane waves of any polarization can be described instead by combining waves of opposite circular polarization, for example.

If I am understanding correctly, would this be better worded:

• Plane waves of any polarization can be described by combining waves of opposite circular polarization, for example, or by combining waves of linear polarization rotated 90° from each other.

In other words, they're just like complex sinusoids, where $e^{ix} = \cos x + i\sin x \!$ and $\cos x = {e^{ix} + e^{-ix} \over 2}$ are two different valid ways of thinking about things. (A sinusoid is a sum of helices or a helix is a sum of sinusoids.) — Omegatron 02:20, 18 July 2006 (UTC)

That would not be better wording in the context, but it is true. You can decompose a beam of light of any polarization into any two polarization components that form a basis. There are many possible choices, of which perpendicularly polarized linear polarizations and counter-rotating circular polarizations are the most obvious. Your version is not better wording only because the preceding portion of the article describes light in terms of perpendicular linearly-polarized components, and the point of that statement is to indicate that this was an arbitrary choice, and that one can instead consider a pair of circularly-polarized components.--Srleffler 05:48, 18 July 2006 (UTC)
Oh.  :-) The article is worded a little poorly. Overly technical. — Omegatron 05:58, 18 July 2006 (UTC)
I thought it was very clear where it said: The "cartesian" decomposition of the electric field into x and y components is, of course, arbitrary. Plane waves of any polarization can be described instead by combining waves of opposite circular polarization, for example. It's a technical subject, so some skill in reading logical technical writing may be assumed. Dicklyon 06:40, 18 July 2006 (UTC)

## Mud flats

The only water in the picture is a trickle at the bottom of the river channel, and the sea (which is the dark brown patch just about visible at the top right hand side, above the bank of seaweed and below the headland). The tide was very far out (I think I'm right in saying it was spring tide, and the Severn estuary has one of the highest tidal ranges anywhere in the world), and the reflections are sunlight off the wet mud. Originals are at image:Mudflats-polariser-1.jpg and image:Mudflats-polariser-2.jpg. --ajn (talk) 20:37, 18 July 2006 (UTC)

OK, I yield that point. I still think it makes more sense to talk about reflection off water however, since that's the relevant ingredient of mud that is reflecting. Dicklyon 20:43, 18 July 2006 (UTC)

Just to make things clear, "In the first picture, the polarizer is rotated to minimize the effect; in the second it is rotated 90° to maximize it: almost all reflected sunlight is eliminated". "First", "Second"? How about left and right? It is a little confusing...

I hope now it is clearer. --danh 00:02, 12 January 2007 (UTC)

## eccentricity/ellipticity

I don't understand the preference for ellipticity over eccentricity in the description of the polarization ellipse. In terms of the Stokes parameters I, Q, U, V, with Ip=sqrt(Q^2+U^2+V^2), we have ellipticity = V/Ip and eccentricity = sqrt(Q^2+U^2)/Ip, so ellipticity represents the degree of circular polarization (0 for linear, 1 for circular), while eccentricity represents the degree of linear polarization (0 for circular, 1 for linear). (See, e.g., Stokes parameters.) As far as I can see, the physical interpretations of the two parameters are complementary. Is there some other motivation for preferring ellipticity?

[Sorry, those expressions are wrong. See below. Gnixon 14:26, 22 August 2006 (UTC)]

I'll hold off on an edit for awhile in case someone sets me straight.

Gnixon 21:35, 23 July 2006 (UTC)

I don't know the answer to your question, but policy forbids you from changing it on the grounds you describe. Per Wikipedia:No original research, Wikipedia documents what has been published (and to some extent what is done) elsewhere. The article asserts that ellipticity is used in preference to eccentricity. This is a statement of fact, about the practice in the optics community. You may not replace such a statement with an argument based on your thoughts about what the practice should be. That would be "original research" as Wikipedia defines it. There are good reasons for this strict rule, and the policy linked above explains them so I won't reiterate. The only grounds for altering the statement would be if you thought it was an incorrect description of the practice, in other words if you have evidence that optical engineers and scientists do not always use ellipicity in preference to eccentricity.--Srleffler 02:48, 16 August 2006 (UTC)

I believe the answer is what the text was trying to say by "limited physical meaning", meaning that eccentricity as a measure is not very good because it is undefined for linear polarization, and infinitly sensitive to small amounts of ellipticity near linear polarization. So I put that in the article. Dicklyon 03:51, 16 August 2006 (UTC)

Never mind. I take it back. Looks like I was wrong about eccentricity. Dicklyon 03:56, 16 August 2006 (UTC)

I think of eccentricity in problems like orbital mechanics, where the problem is centered on one of the two foci of the ellipse (off-center). Ellipticity is better for problems which are symmetrical about the center of the ellipse, which applies to light polarization, and covariance, and spheroids. Pqmos 21:00, 14 November 2006 (UTC)

### Discussion moved from srleffler's talk page

I seem to be interpreting the statement about ellipticity differently than you are. The article says "Ellipticity is used in preference to the more common geometrical concept of eccentricity, which is of limited physical meaning in the case of polarization."

"Ellipticity is used [by the field]."

"Ellipticity is to be preferred over eccentricity, which has limited physical meaning."

I believe I'm competent to disagree with the latter statement (or at least its second clause) without "original research." My question might have been better posed as: Is there a tradition (perhaps well-justified) of using ellipticity in the field of optics, (and if so, why)? In any case, unless I'm missing some point, I think the sentence should be reworded on NPOV grounds. Would it have been more appropriate for me to add a "citation needed" tag instead of posting to the talk page and planning an edit? Gnixon 21:35, 21 August 2006 (UTC)

Posting it to the talk page was entirely appropriate, and probably better than just putting a citation needed tag on it. Yes, you're right that I read the statement differently, focusing more on the first part rather than the second. There are really two separate issues here: Is ellipticity used in optics in preference to eccentricity, and if so, is this because the latter "is of limited physical meaning", as opposed to merely being due to some historical convention etc. In principle, WP:NOR prescribes that both questions should be settled by reference to published literature; you aren't actually supposed to use your own personal expertise in editing Wikipedia, unless you are certain that your contribution is backed up by verifiable external sources.
In this case, I think the first question definitely would need to be settled by reference to published sources, if you dispute it. I have several books I could consult, but unfortunately they are all at work right now. The statement that eccentricity is of limited physical meaning could probably just be removed if you are sure it is wrong, but give it a few days. That claim was added by User:Russell E several years ago, separately from the claim that ellipticity is the preferred parameter. Russell is still around, and I left him a note to check out this discussion. He may well look at the issue and say that he made a bad call in writing that, or he may have some explanation or citation to back up his statement. --Srleffler 04:14, 22 August 2006 (UTC)

I don't really know what I was thinking when I wrote that phrase ("of limited physical meaning.."). I guess I was thinking that, seeing as the polarisation ellipse is a phantom concept (except in the unusual case of coherent monochromatic waves where the inequality I^2<=Q^2+U^2+V^2 becomes the equality Gnixon quotes above) then it makes sense to work with a parameter that is more closely tied to the Poincare sphere representation of statistical polarisation instead (since the ellipticity angle, the arctangent of the ellipticity, is equal to half the "latitude" of the QUV-vector). But in retrospect, saying as much doesn't seem necessary at that point. We could just remove the phrase. We still need to say that ellipticity is used in preference to eccentricity, but I don't see any ambiguity; to me it is clear that it is descriptive ("is preferred") and not prescriptive ("is to be preferred"). However I don't see the harm in changing it, to, say, "is commonly preferred". As to the issue of personal expertise versus familiarity with literature, I did consult literature extensively when I made my major edits to this article. Rather than cite every sentence, which is just too cumbersome and really mainly suited to controversial or cutting-edge topics, I listed them at the bottom. I will admit though that I cannot recall whether I drew the reason for the convention from a specific source or from my memory. If we really want to say why, we should indeed try to find it in the literature.. unfortunately I don't have access to any texts at the moment but if I did I'd start with Born & Wolf. --Russell E 04:29, 22 August 2006 (UTC)
I'm used to everyone just working either in the coherence matrix Ei*Ej or the Stokes parameters, which of course define the Poincare sphere and can be used to define a mean ellipse for the polarized component. I personally find it useful to visualize the ellipse. As for references, Hecht doesn't mention ellipticity and I don't think Jackson does, either. Tomorrow I'll flip through B&W and perhaps a couple others. Anyway, I can see the argument for using ellipticity since it's a coordinate of the Poincare sphere.
If there's someone who's familiar with the common practice in optics, I don't think a reference is necessary, but it would be nice if the sentence could briefly explain the reason. Can you take a shot at it, Russell? Gnixon 06:02, 22 August 2006 (UTC)
I wouldn't like to take a shot at it as I'm now feeling unsure of it myself! And I don't have any texts on hand to check... sorry.--Russell E 07:31, 22 August 2006 (UTC)

P.S. I think math above is incorrect. What messes this all up is the factor of two relating angles in physical space vs QUV space. It is indeed true that V/Ip = sqrt(1-(U^2+Q^2)/Ip^2) and also that eccentricity = sqrt(1-ellipticity^2), it isn't true that ellipticity = V/Ip... V/Ip is the sine of twice the ellipticity angle, the latter of which is the arctangent of the ellipticity. sin(atan(epsilon)/2) is not equal to epsilon. --Russell E 05:25, 22 August 2006 (UTC)

Yikes, I think you're right. I may have to retract any claims of competency. But it's late; I'll look at this again tomorrow. Gnixon 06:56, 22 August 2006 (UTC)
On the other hand, if eccentricity = sqrt(1-ellipticity^2) and eccentricity = sqrt((Q^2+U^2))/Ip (according to Stokes parameters), doesn't it then follow that ellipticity=V/Ip !? Gawd, it's not late here but I'm suffering children-induced sleep deprivation!--Russell E 07:34, 22 August 2006 (UTC)
Sorry, you're absolutely right (and my face is red). With L=sqrt(Q^2+U^2) I calculate ellipticity=V/(Ip+L) and eccentricity=sqrt(2L/(Ip+L)), so neither parameter has the simple relationship to Stokes parameters that I claimed. Stokes_parameters is no excuse for me since I put those statements there. I really have no idea what I was thinking---you're probably right that I made a 0.5 error in some angle. It would still be nice if that sentence explained why ellipticity (or ellipticity angle) is used. Can the Poincare sphere argument be put concisely enough? Gnixon 14:23, 22 August 2006 (UTC)
Ah good, glad I'm not going nuts. Those relations are at least a bit less ugly than mine with forward and inverse trig functions but you're right, they've no obvious geometric meaning in terms of the Poincare sphere. I've added words to this effect in the article... how's that?--Russell E 00:10, 23 August 2006 (UTC)
Thanks, I like it. Also thanks for catching my math error. Actually, I'd be fine with not mentioning eccentricity at all, but what you have makes a useful point. Gnixon 01:05, 24 August 2006 (UTC)

I wrote that sentence: "Ellipticity is used in preference to the more common geometrical concept of eccentricity, which is of limited physical meaning in the case of polarization."

I learned the concept of eccentricity in high school (part of analytic geometry, I think). I only encountered the much more esoteric concept of ellipticity when I began to work with circularly polarized light, over 20 years later. Circular Dichroism is, for instance, commonly reported in millidegrees of ellipticity. So I had to look it up. Once I compared them, it seemed obvious why the one that did not blow up would be preferred. The most important thing I wanted to accomplish was to help other people when they encountered ellipticity for the first time to realize that this was not the method they (most likely) already knew about for describing the shape of an ellipse. In other words, to raise a red flag for them, so that they would notice that this was something they did not already know about. --AJim (talk) 21:49, 19 March 2009 (UTC)

## incoherent / noncoherent

Is anyone alse bothered by the use of the term incoherent? I think that means without logical thought, and that the term we want here is noncoherent, or perhaps non-coherent. tim 14:21, 16 August 2006 (UTC)

Incoherent is the more common term here. It applies to light just as it does to your thoughts (sorry, I couldn't resist). Try googling "define:incoherent". Dicklyon 15:09, 16 August 2006 (UTC)
Yes, "incoherent" is the correct term for both thoughts and light: "incoherent: lacking cohesion, connection, or harmony;".--Srleffler 16:03, 16 August 2006 (UTC)

## Photographic Polarizers

The picture showing how a polarizer on a camera enhances the appearance of clouds and sky has an error in the caption below. <or not, read below - pqmos>

The caption claims that "... on circular polarizers because they emit circularly polarized light". This is wrong for two reasons. Most obviously, it can only "pass" or transmit any light, not "emit", or it would be a source. The other more important error is that these polarizers are never in my experience truly "circular" in the sense that they select one circular polarization. In my experience they are always linear polarizers, which can be rotated so the linear axis is at any orientation. They incorrectly advertise themselves as "circular" polarizers, but only because they are circular in shape and motion, but not in polarization.

I fixed this in the article, but then someone reverted it. So I am offering an explanation here. I'm a noob at Wikipedia, so correct my protocol if you can.

Discussion of circular polarization: Sunlight gets linearly polarized as it scatters from air and fine dust to make the blue color in the sky. So a linear polarizer can cut most of the blue from the sky and make it seem darker, so the clouds stand out. There wouldn't be any such effect from a circular polarizer: everything would appear as before, just darkened by 1/2 of the intensity or power. Of course reflected glare is often strongly linearly polarized, so a viewer or photographer can benefit from a linear filter.

But very few phenomena give rise to circular polarization. I have read that the light reflected from the carapace of certain scarab beetles is partially circularly polarized. You could only verify this if you had a circular-polarizing filter (not a linear filter cut in the shape of a circle). So I've been on the lookout for circular polarizers for years, but have yet to find one. I've read that you can make circular light from linear with a "Fresnel Rhomb", from which I think you could make a circular filter using that and a linear filter. But I have yet to do that. Pqmos 21:30, 14 November 2006 (UTC)

I reverted you. The way I interpret that caption and what I have read elsewhere, is that a so-called "circular polarizer" is neither a device that selects a single circular polarization, nor merely a linear polarizer cut in the shape of a circle. Rather, it looks like it is a device that selects a single linear polarization, and then converts that linearly polarized light to circular polarization. The polarizer thus emits, but does not pass circularly-polarized light, and it behaves when rotated the same as a linear polarizer, but the output, being circularly polarized, does not cause polarization-dependent changes in reflection off of the mirror in an SLR camera. One can make a device that does this for a single wavelength by combining a linear polarizer with a quarter-wave plate. I have no idea how they would make an achromatic version for photographic use.

Now, I am not 100% certain that my interpretation is correct, but I am pretty sure that a "circular polarizer" is not just a linear polarizer that can be rotated. There are lots of photography websites that discuss the choice between a linear polarizer and a circular polarizer for photographic use. The distinction seems to be that the latter is more expensive, but works with auto-exposure SLR cameras, while the former does not. This is consistent with my explanation, but not with yours. Hopefully someone else here can give us a more definitive explanation.--Srleffler 02:21, 15 November 2006 (UTC)

You are correct that a so-called circular polarizer is a linear polarizer sandwiched with a quarter-wave plate. It will select a linear polarization state from the scene just like a linear polarizer, but then mixes both linear states behind it so that the partially-reflective mirror will still direct about half the light to the AF sensor. As for things in nature making circular polarization, optically-active molecules have that property, don't they? If you really want to select a circular polarization state for the scene, like for the beetle, just hold the filter backwards, quarter-wave plate out. But I agree that "emit" is perhaps the wrong word. Dicklyon 02:55, 15 November 2006 (UTC)

Very exciting. It sounds like they did the same thing I wanted to do with the Fresnel Rhomb and linear analyzer, but in a compact plate. I'll go check it out in a store somewhere and get back to you here. Thanks!!

Optically active molecules are supposed to rotate the plane of plane-polarized light, not select one circular polarization over another. (Also see the Wiki on Optical Rotation.) It seems to me that chiral molecules should glow circular if they fluoresce, and absorb linear and emit circular for transmission. The first may happen in chirally pure samples; and the second is probably precluded by phase-matching problems over extinction distances. If I can buy a circular analyzer, I'll try to check that out too, but it may be tough to find chirally pure substances -- they'll have to be bio-molecules. 199.46.200.233 17:40, 17 November 2006 (UTC)

I checked out a camera "circular polarizer", and indeed it appears to be more than just a linear polarizer cut in a circular shape. Looking one way through it (proper for the camera) it works for the eye just like an ordinary linear polarizer, like polarized sunglasses. But turned around, it only changes the (apparent?) color of linear polarized light without blocking it. I say apparent color because the faint shades of blue and yellow I saw correspond to the appearance of linear polarized light to the human eye as a very faint blue-on-yellow hourglass (stare at a spot on a blank white lcd monitor, and slowly tilt your head, watching for a blue and yellow pattern about an inch in diameter).

I'm convinced this is not just a linear polarizer, and that the wiki article has no error regarding the circular polarizer as it is written. Should I delete this sub-discussion, or condense it for the benefit of others like me who may follow? Thanks to all who helped me get this right. 199.46.199.231 18:58, 2 January 2007 (UTC)

The word "emits" is probably not correct. See my description above. There's no need to remove complicated discussions that may be of value to someone who is trying to understand what's up to improve it. Dicklyon 20:06, 2 January 2007 (UTC)

In case you don't already know this, the blue and yellow pattern you describe is known as Haidinger's brush, and appears due to a weak polarization sensitivity in the human eye. As Dicklyon indicates, the discussion should remain as it is. Talk pages are a permanent record. When they get too long, we archive them.--Srleffler 23:41, 2 January 2007 (UTC)

The classical way to produce circular polarization is, indeed, to place a quarter wave plate after a linear polarizer. There is an additional requirement that they be in a particular relation to each other. The axis of linear polarization should be half way between the fast and slow axes of the quarter wave plate. Think of the linear polarization as the vector sum of two orthogonal components, one parallel to the fast and one parallel to the slow axis of the plate. After passing through the plate their relative phases have changed so that their vector sum is now circularly polarized. The direction of passage matters; if the light enters the quarter wave plate and exits through the linear polarizer, the exit light will be linearly polarized. That is, turning a circular polarizer around converts it into a linear polarizer. --AJim (talk) 01:58, 20 February 2009 (UTC)

## Poincaré sphere is a 3-manifold not a 2-manifold

Something is wrong in the discussion of a Poincaré sphere in the present version of this (polarization) article. Here the Poincaré sphere is presented as a 2-sphere, a 2-dimensional objected embedded in three-dimensional infinite Euclidean (flat) space. This is wrong. See Poincaré sphere.

i can believe that the genuine Poincaré sphere is useful for understanding polarisation and the Stokes parameters. However, describing it incorrectly is not going to help anyone to understand anything. If someone understands this, then please correct the text.

Boud 14:08, 9 February 2007 (UTC)

i put {{expert}} on the two sections where Poincaré sphere is discussed rather confusingly here. Feel free to remove them once the confusion is sorted out. If optics people use the term in a way totally different to the way mathematicians use it, then that would need disambiguation. Boud 14:21, 9 February 2007 (UTC)

## Careful - Instructor at work

I'm a student at the K.U.Leuven, Belgium. We're currently participating in a project concerning polarization in collaboration with another college. Apparently one of the instructors there has deliberately entered erroneous information in articles concerning polarization. There is no specific information available as to the precise identity of the instructor or to the nature of the information he has slipped in, but I thought people should be aware of this.—Preceding unsigned comment added by The Akulamatata (talkcontribs) 10:27, 17 May 2007

Did anybody notice this? It should be possible to look for IP addresses from Belgium and check out the edits made around the time this comment was posted. 140.247.79.217 (talk) 16:50, 18 September 2008 (UTC)
I noticed it at the time. I took it as likely a hoax, or an attempt to encourage students to check other sources and not treat Wikipedia as "gospel". Deliberate errors tend to get fixed pretty quickly, anyway. I don't see any sign of unreverted harmful edits in this article between 31 Dec 2006 and 23 May 2007, but of course the warning above doesn't say that the edits are in this article, but rather that they are in "articles concerning polarization".--Srleffler (talk) 23:41, 18 September 2008 (UTC)

## Wording

The discussion below is copied from User talk:Srleffler. It is in regard to this edit.--Srleffler (talk) 03:43, 14 December 2007 (UTC)

I admit that "movement" is not perfect, but the word "evolution" is simply wrong in this context. This is a scientific article, so when you use scientific words, they should be used properly. —Preceding unsigned comment added by 74.134.251.147 (talk) 03:35, 13 December 2007 (UTC)

I'm not sure if I missed your point, or if you just don't understand the meaning of the word "evolution". As far as I can see, the word is used properly.
Excerpt from dictionary.com:
ev·o·lu·tion, noun
...
4. a process of gradual, peaceful, progressive change or development, as in social or economic structure or institutions.
5. a motion incomplete in itself, but combining with coordinated motions to produce a single action, as in a machine.
6. a pattern formed by or as if by a series of movements: the evolutions of a figure skater.
--Srleffler (talk) 04:40, 13 December 2007 (UTC)

If somewhere in this article was a section about a "theory" involving polarization, but the word was used with the common meaning of "guess" instead of the scientific meaning, it would quickly be changed. "Evolution" has the same problem. It has an exact scientific definition as well as common definitions (like the definitions you would expect to find in a dictionary after the better, more scientific ones have been given). In a scientific sense to evolve means the gradual change due to a selective pressure, and only that. Your use matches the COMMON usage definitions, and would be fine to go with in a COMMON article. But this is a scientific article, and evolution is simply not the right word here. —Preceding unsigned comment added by 74.134.251.147 (talk) 06:27, 13 December 2007 (UTC)

If this were a biology article, I might agree with you. The usage seen here is not unusual in physics, however. Something that changes gradually and progressively from one state to another is properly described as "evolving" from the first state to the later one.
This discussion really should be at Talk:Polarization. I will copy it there. If you want to reply, please reply there. I'll see your response.--Srleffler (talk) 03:43, 14 December 2007 (UTC)

## SIMPLE ENGLISH!

There is a rough draft at simple:Polarization. But it needs more illustrations and other work. --68.0.124.33 (talk) 20:14, 3 November 2008 (UTC)
Thanks for the link to the simple English article. I think this article should either (a) have a tag on it saying it's too technical and has to be made easier to understand for the layperson and/or (b) should have a link AT THE TOP to the simple English version. I consider myself to be a fairly well educated person with an interest in science, but no physics background. Although I'm confident the introduction is a very accurate description, I basically understood nothing of it. At least, with the simple English version, I could get the gist, thanks to the metaphors.Star-lists (talk) 00:55, 28 January 2014 (UTC)

See discussion above, and the discussion of transverse polarization.

How about the following for the first paragraph?

Polarization (Brit. polarisation) is a property of waves that describes the direction of their oscillations. It is most commonly associated with light, which travels in free space as a transverse wave. For transverse waves, the polarization describes the orientation of the oscillations in the plane perpendicular to the wave's direction of travel. The oscillations may be oriented in a single direction (linear polarization), or the oscillation direction may rotate as the wave travels (circular or elliptical polarization). When light travels in a waveguide or optical fiber its waves can have both transverse and longitudinal oscillations. The polarization of these waves is more complex. For longitudinal waves such as sound waves in fluids, the direction of oscillation is by definition along the direction of travel.

I would really like to add "therefore longitudinal waves do not have polarization", but I don't think we have consensus for that.--Srleffler (talk) 04:01, 3 December 2008 (UTC)

## Mistake in introduction

It seems like there is a mistake in the Introduction to this page, when it has Real(Ax, Ay*e^i*phi,0)*e^(...). The real part of an exponential is the cosine, but the Real() operation is only shown operating on the other part of the equation. This looks like a typo. I apologize if this is not the proper place for this, I don't have time to read up on how to properly post this. -Richard

Fixed.--Srleffler (talk) 23:01, 4 December 2008 (UTC)

## Silmilarities?

I have at times wondered whether the polarization of Light and other electromagnetic radiations had ANYTHING to do with the polarization of electric charges separated in space (as for example between two electrodes). Considering that the phenomenon has the same name for both cases (i.e. Polarization); it would seem like they should be related at some level. It seems to me like the electric field component of the Poynting Vector (i.e. the direction of propagation) should force positive and negative charges apart in the direction of it's amplitude. Also, I seem to remember somewhere in Maxwell's equations the derived formula: Induced Electric Field Vector = [(Permitivity times Initial Electric Field Vector) + (Displacement Field Vector times Polarization Vector)]. The preceding equation makes me think that the polarization of the incoming radiation is caused by the movement of the electrical charges within the medium. Could someone please tell me if I am mistaken? Please excuse my non-Mathematical description of the formula which I seem to remember, as I do not know how to make bold, super, and subscripts (I suppose that I could have accessed the toolbar in MS Word but did not think of it). I wrote the word "times" in the equation instead of the letter "X" so as not to confuse it with vector (Cross Product) multiplication; as I remember it as scalar multiplication. Could someone please respond, thank you.JeepAssembler (talk) 21:57, 19 February 2009 (UTC)

Yes, when light propagates in a dielectric medium it creates a transient oscillating electric polarization. I believe this is why light propagates slower in media then it does in a vacuum. When light enters a conductive medium, the electrons are free to move, so they oscillate with the same frequency as the light wave's oscillating electric field. This efficiently extracts energy from the light wave. The oscillating electrons radiate, producing a new light wave. Interference causes the new wave to cancel except in the direction that satisfies the law of reflection. --Srleffler (talk) 04:01, 20 February 2009 (UTC)

## Image:Elliptical_polarization_schematic.png

Hello!

This bot has detected that this page contains an image, Image:Elliptical_polarization_schematic.png, in a raster format. A replacement is available as a Scalable vector graphic (SVG) at File:Polarisation (Elliptical).svg. If the replacement image is suitable please edit the article to use the vector version. Scalable vector graphics should be used in preference to raster for images that can easily represented in a vector graphic format. If this bot is in error, you may leave a bug report at its talk page Thanks SVnaGBot1 (talk) 10:33, 26 April 2009 (UTC)

## Recent changes

I've no quarrels with the content arguments but I have strong feelings as to the current fragmented structure[1] being, I believe, faulty and unencyclopedic. Would appreciate active members' participation with suggestions.
Warm regards, JaakobouChalk Talk 07:07, 1 May 2009 (UTC)

If no one steps up, I'd be forced to make a (second) attempt myself. JaakobouChalk Talk 15:00, 4 May 2009 (UTC)
I took a stab at it.--Srleffler (talk) 01:39, 5 May 2009 (UTC)
I like it. There is one more idea I would like to see included, although I do not know how best to do it right now. Polarization only becomes interesting when the waves are 3 dimensional, so that the oscillation can be decomposed into two orthogonal components. This keeps getting glossed over, and, I think, ignoring this makes it harder for people to understand polarization. I know the idea is introduced below, and is discussed in the transverse wave article, but I still think it deserves a brief mention here too. Maybe you can see a way to say that in the intro. --AJim (talk) 02:09, 5 May 2009 (UTC)
Are you thinking about water waves as examples of two-dimensional waves? Generally, I think introducing an abstract concept like dimensionality is more likely to be confusing than enlightening to a general audience. Water waves don't have meaningful polarization because the water only oscillates up and down, not side to side. If it could oscillate side to side as well, there would be two polarizations.--Srleffler (talk) 04:10, 5 May 2009 (UTC)
I agree the water example is a problem. Because the waves are confined to a surface, polarization is not an interesting concept; all waves are linearly polarized in the same direction. It is only when the second dimension of transverse motion is possible that you get interesting polarization. At that point it is not a case of "two polarizations", it is the full phenomenon; it hinges on having the second dimension. I started the plane wave description a few years ago; the plane wave approximation was the way I was taught. But now I wonder if using a ray might make an easier introduction, that is not bother about the infinite extent, etc., and just focus on the two dimensions of wave motion along the ray. There was no transverse wave article when I started to work on this; those concepts are critical. I extended the waves on a string introduction to transverse wave recently, and it seemed to work well to explain the idea to people new to the concept of polarization. I guess I would be satisfied if the introduction said something like "two dimensional transverse wave" instead of just "transverse wave". A few years ago the polarization intro did say something like that. It was changed from "two dimensional" to "vector", which I think is less clear, and was then lost entirely. --AJim (talk) 15:03, 5 May 2009 (UTC)

The "Incoherent radiation" section seems to be deeply flawed. While there is a connection between incoherent emission and lack of polarization, it is more complicated than the section indicates. Incoherent light can be fully polarized, and coherent light from a laser can be completely unpolarized. --Srleffler (talk) 03:13, 31 May 2009 (UTC)

## Sunglasses and eye protection

My optometrist said that for optimal protection, sunglasses should have both UV protection and polarization. I wouldn't assume that I know more than an optometrist, but I can think of no reason why polarization would protect one's eyes better. Thoughts? 98.141.72.165 (talk) 18:23, 7 June 2009 (UTC)

I'm not sure they provide much extra protection, but I wouldn't buy a pair of non-polarized sunglasses. Polarized ones just work better, since they cut reflections from ground and water dramatically. I guess they protect your eyes better, since they cut out these sources of glare. I think it's more about effectiveness than protection, though.--Srleffler (talk) 04:26, 8 June 2009 (UTC)

Polarized sun glasses can play havoc on being able to read LCD displays found on some auto dashes, since the LCD displays use polarized light to operate. 24.22.22.228 (talk) 02:24, 31 May 2014 (UTC)Gray

## Axial Ratio

The discussion of axial ratio under the heading "Parameterization" is not correct. The axial ratio is defined as the ratio of the major axis to the minor axis, and thus it is always greater than unity. For linear polarization the AR is infinity, not zero as stated. Also, in the figure defining the angles, the angle Chi should be related to the axial ratio as cot(Chi) = AR. —Preceding unsigned comment added by 129.7.206.76 (talk) 01:32, 23 October 2009 (UTC)

Yes, it looks like the text was confused between conflicting definitions of "ellipticity". Some authors define it as minor over major axis rather than major over minor. I adjusted the text.--Srleffler (talk) 03:11, 23 October 2009 (UTC)
The error was introduced in July—the article formerly used the minor-over-major definition. An editor changed the definition, but did not check that the new definition was consistent with the text immediately below it.--Srleffler (talk) 03:19, 23 October 2009 (UTC)

## Sigma

σ+ and σ- refer to the two directions in which the E-field in circularly polarized light rotates. Is it therefore sensible to say that s-polarized light is also referred to as sigma polarization? I'm not convinced I've seen sigma used like this before, and using it here may be confusing.Mattyp9999 (talk) 16:23, 23 October 2009 (UTC)

We have to document actual uses of terms, even if there are different sets of terminology that are not consistent with one another. Of course, we should document usage in a way that is clear and does not confuse the reader. It doesn't matter whether it is "sensible" to call s-polarized light "sigma polarized". It only matters whether reliable sources actually do refer to s-polarized light that way.--Srleffler (talk) 16:49, 23 October 2009 (UTC)

## Requested move

The following discussion is an archived discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the move request was superseded by Talk:Polarization#Requested_move.  Skomorokh  07:20, 27 December 2009 (UTC)

Polarization (waves)Polarization — Page was moved without any discussion. Propose moving it back. --Srleffler (talk) 05:12, 7 December 2009 (UTC) This page should not have been moved without some discussion. The move has also not been completely implemented; there are broken links. I'm not sure whether it would be best to fix the links, or move the page back. We should discuss it.--Srleffler (talk) 19:57, 6 December 2009 (UTC)

I redirected Polarization to here for now, since the links to that page are intended to point to this article. If there is consensus that Polarization should redirect to the dab page, someone will have to fix every current link to Polarization to point here instead. Before we do that, though, we should make sure that there is actually consensus for this move. --Srleffler (talk) 20:02, 6 December 2009 (UTC)

• Strong oppose I think political polarization would have atleast equal footing with this. 70.29.211.163 (talk) 08:53, 22 December 2009 (UTC)
The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

## "It"

(In the intro) I replaced the word "it" with "polarization", because, otherwise the sentence comes across as saying that light propagates as a transverse wave. I think that is not the intended meaning. Hopefully this makes sense (see diff). In addition, this is not about whether or not polarization is perpendicular. I guess that is a topic for discussion. Thanks. Steve Quinn (formerly Ti-30X) (talk) 02:19, 24 December 2009 (UTC)

I undid your change. The sentence was carefully worded, and correct as written: in most cases, light in free space propagates as a transverse wave.--Srleffler (talk) 23:18, 31 December 2009 (UTC)

## relationship between Jones vector and axial ratio/tilt angle formulation

There is an equivalence between the Jones vector description (based on R and L circular polarizations) and the axial ratio/tilt angle description of polarization. It would be really great if this could be made explicit, with transformations being shown for both directions. This would help to unify the discussion of the two descriptions. I can supply two of the four relevant equations:

axial ratio= (abs(R) + abs(L)) / (abs(R) - abs(L))

tilt angle= 0.5 * arg(R/L)= 0.5 * (arg(R) - arg(L))

Dr. Phillip M. Feldman —Preceding unsigned comment added by Pfeldman (talkcontribs) 00:27, 18 January 2010 (UTC)

Can you also provide a reference for this material? One of our goals is to have citations to reliable sources for everything we can. Such citations are also useful for catching errors (typos, conflicts in variable definitions or sign conventions, etc.)--Srleffler (talk) 05:47, 18 January 2010 (UTC)

## new diagram

Ive created a new diagram related to polarisation, i leave it here for someone to inlude in a relevant place if it is up to par.

## Adding Axis to polarization diagram

I would really recommend adding axis to the polarization diagrams, it got me confused studying for this personally. And its not really scientific not including the axis. I never contributed to wikicommons before, so I am not sure how to add this myself, moreover it seems I am not auto-confirmed. Here are the suggested images: [2] GuySoft (talk) 15:26, 14 May 2010 (UTC)

## s and p polarization

The "Parametrization" section concerning the meaning of the "parallel" and "perpendicular" components is really off. The direction of the components has nothing to do with the surface or whatever of any Earth or what is used as directions in Astronomy, but is *only* related to the plane of incidence. Sure, if the mirror train is all horizontal (as what is found on a standard laboratory table), then it happens that the plane of incidence of the beam (which stays horizontal for all reflections) is the same for the entire setup, but this is simply convenience not to climb ladders. But if you are looking at some optical astronomical telescopes which points roughly to the zenit, light falls in vertically, and the s and p polarizations are just defined arbitrarily until the first mirror is hit that breaks that symmetry and pushes the beam sideways. Basically, the s-or-p definition make only sense if it's related to either the previous or the next surface. If someone is building a folded instrument with vertical "layers" of mirrors etc to keep the housing small, there may be as many different directions of s and p as there are mirrors.

Also note that the *magnetic*, not the *electric* component defines the s- and p-polarization, for historical reasons (see a text book like Born for example), although this is (for standard reasons) the worse choice of the two.

The section "Unpolarized light" mingles "correlation" and "polarization". Correlation is defined in time, space and with respect to polarization, Unpolarized light may very well be completely correlated in phase: a camera will still work even in standard daylight situations, because interference needs correlation in only one of the two polarization states. R. J. Mathar (talk) 21:54, 12 June 2010 (UTC)

I'm not sure, but it looks like you may have misread what the "Parameterization" section says. The designation of light as s- or p-polarized is, as you say, always done with reference to the plane of incidence. The article does not assert otherwise. You may have been confused by the fact that the article referred to a diagram showing the geometry, which is no longer present (the file was deleted).
Describing polarization of light in terms of s and p polarization works great if one is describing the interaction of light with a single surface. If one wants to describe the propagation of light through a more complicated optical system, however, one typically chooses a fixed coordinate system in which to represent the light's polarization state. For the common case of light propagating horizontally, a common choice is to consider polarization components that are vertical and horizontal. When the light intersects a surface, one must calculate the s- and p-components from the known vertical and horizontal polarization components in the incident light. Modern optical software automates this process.--Srleffler (talk) 03:15, 13 June 2010 (UTC)

### Diagram needed

--Srleffler (talk) 03:15, 13 June 2010 (UTC)

## citation for S and P Polarization section

If I am interpretting the article text correctly, an example of " and certain authors do refer to light with p-like electric field as TE and light with s-like electric field as TM" which is marked citation required is the Dover book "Modern Optics" by Fowles (section 2.7). Somebody else more familiar with the subject should probably verify. Peeter.joot (talk) 04:14, 14 August 2012 (UTC)

## Malus and the discover of polarization

In the section "In nature and photography" it says that Malus discovered polarization of light. This is certainly not true. He discovered polarization by reflection. --AJim (talk) 06:55, 25 November 2013 (UTC)

### History section needed

So who did discover polarization of light, or at least first observe phenomena now known to be due to polarized light? And who first understood the essential nature of plane polarized light? And of circularly polarized light? This article needs a section called History to answer these questions. Now we just have a few hints buried in various application sections. Dirac66 (talk) 03:26, 1 February 2015 (UTC)

I see that some of the answers are at Optical rotation#History, although without sources. Should we copy some of that section here? Dirac66 (talk) 03:31, 1 February 2015 (UTC)
I don't see much history of polarization itself in that article, just history of the discovery of rotation of polarization by certain materials. I agree, though, that this article needs a history section.--Srleffler (talk) 22:04, 1 February 2015 (UTC)

To clarify a bit about transmission polarization in broadcasting, especially US domestic practice.

AM broadcasting (though we should probably say, medium wave broadcasting, since the polarization used is not a function of modulation but of frequency) is universally vertically polarized, both in the US and internationally. Generally the tower itself is the radiator, most being insulated from ground.

Television broadcasting in the US, both VHF and UHF, is overwhelmingly horizontally polarized, though some stations employ circular polarization. Other than certain classes of low power television stations, television stations in the US are not permitted to broadcast using vertical polarization only. The classic outdoor television receiving antenna is horizontally polarized log periodic dipole array or Yagi-Uda.

FM broadcast stations in the US are overwhelmingly circularly polarized, though horizontal polarization only was standard up until the late 60's, when circular polarization was first permitted. In the US, other than certain classes of low power FM stations and some stations operating in the band between 88.1 and 91.9 MHz to protect near by Channel 6 television stations, vertical polarization only is not permitted.

Practice outside of the US varies from country to country, with some jurisdictions unconcerned with polarization, some specifying horizontal only and some specifying vertical polarization only. 24.22.22.228 (talk) 02:21, 31 May 2014 (UTC)Gray

If you don't edit the article, this talk will soon be lost and gone.Fgnievinski (talk) 20:31, 14 July 2014 (UTC)

## bloated

this subject is important. the article needs rescue. it's too big. I'll ignore the measurements & applications sections. the theory section is bloated almost beyond repair. it absolutely has to be made leaner, or else it'll collapse under its own weight. that means moving portions into child articles. the only hope is for the theory section to be written as an overview. the vision is: let each topic article discuss its own polarization aspects instead of having this monstrous article talking about every topic's polarization aspects. please help. Fgnievinski (talk) 21:21, 14 July 2014 (UTC)

You're right that it's bloated, but I would go after the sections that don't have much to do with polarization per se, such as section 1.1.1. And there is more than a bit of duplication, but that is typical in Wikipedia where multiple authors have rewritten the same thing and it's a lot of work to consolidate them without either losing material or clarity. I'd get rid of some of the esoteric stuff, section 1.2.4.3 Coherency matrix (which indeed should be its own page) and 1.2.4.4.1 Pauli matrices. But I don't think splitting the material off into other pages (especially when they don't exist yet, or contain no useful content) is a solution. It's OK and expected that this page should mention everything having mainly to do with polarization or which have to do with polarization and aren't going to be covered elsewhere.
Thanks to Fgnievinski for your efforts, and let us try to further improve the page. But not just through slash and burn ;-) Interferometrist (talk) 22:38, 14 July 2014 (UTC)
P.S. Sorry about deletion of anchors etc.!Interferometrist (talk) 22:40, 14 July 2014 (UTC)
I'll take some time off. Right now I can only think that we've inherited a white elephant. Maybe starting a Template:Talkspace draft of an outline-type article would help (Wikipedia:Delete the junk#Why starting from scratch can be an advantage). Thanks for the consideration. Fgnievinski (talk) 01:55, 15 July 2014 (UTC)
But let me take the time to point out a fundamental difference that hopefully can be reconciled. What is it that you offer as an alternative to splitting the material off into other pages? In my view that is the only option currently on the table, even if that means creating a new polarization section in the target articles. It's NOT OK to have this page mentioning everything about polarization. For example, if dichroism doesn't care to mention polarization, the reverse must be true. The focus here should be on cross-cutting issues. Otherwise it'll never reach a manageable size. Again, any alternatives? Fgnievinski (talk) 03:10, 15 July 2014 (UTC)
Well I'm quite busy and need to take time off as well. If someone was getting paid to create this article, I'm sure s/he could rewrite the article, making it half as long (even without relegating material to separate pages) without compromising any information of importance, and much more readable. But unless you have that kind of time to devote to it (I certainly don't!) it isn't an option, so just starting from scratch isn't realistic. I would start with the current structure (more or less) which I DO think is logical (and you improved it) but make some of the sections more concise, remove some of the more esoteric material (but hopefully finding a place elsewhere on Wikipedia for it), and separate out some material which indeed deserves its own article. But just moving material to a different page doesn't really help if it means someone trying to learn the material needs to go off-page for essential aspects of the presentation, especially if that page doesn't already exist, and even more so when most of the traffic reading the child article would only have found it from the main page. Otherwise it's just as easy for someone to skip a section which they don't want to go into. That works best if it's something way down in the article, but if it's earlier in the article, you don't want someone giving up when they run into some heavy math when they just wanted a layperson's description, for instance. So that's the challenge.
Looking at the article as if I were a layperson, the biggest problem I see is that someone has to wade through section 1 (supposedly an "introduction") before getting to section 2 (and beyond) where polarization is really discussed. It was laid out more like a textbook where you lay out the basic math and definitions before talking about the subject at hand.
Your thoughts? Interferometrist (talk) 17:28, 15 July 2014 (UTC)

──────────────────────────────────────────────────────────────────────────────────────────────────── Hi. Let me offer a good counter-example which I recently came across: circular dichroism. Can you imagine if we were to try to incorporate that level of detail here or even in circular polarization? Well, that's how I see most of the present sections. There doesn't need to be more than a sentence or a paragraph about polarization in dichroism, polarization in reflection, polarizatin in birefringence. That's because someone who is interested in any of these is hardly interested in all of them. The guideline is clear: WP:Summary style applies here. Fgnievinski (talk) 22:51, 12 November 2014 (UTC)

Let me know if there persists any contention in disfavor of WP:Summary style; if I don't hear anything, I'll start dumping these specific sections into their respective main articles -- or else the present article will remain unmanageable. Thanks. Fgnievinski (talk) 01:19, 20 November 2014 (UTC)

## Gravity is an electromagnetic wave?

Since when did these fundamental forces merge? Also gravitational waves remain theoretical, not having been observed directly yet. — Preceding unsigned comment added by 12.71.77.109 (talk) 21:28, 30 July 2014 (UTC)

It isn't. The sentence was poorly phrased.--Srleffler (talk) 01:25, 31 July 2014 (UTC)
Whoops, apologies to Srleffler.... I saw this on the talk page first and edited the lede even though you had already resolved the ambiguity complained about here. Interferometrist (talk) 18:38, 31 July 2014 (UTC)

## Splitting Poincaré sphere

Poincaré sphere can be used for both polarized and unpolarized light, e.g., poles are circularly polarized, equator is linearly polarized. Jones vectors can be mapped to a point on the sphere just just Stokes vectors. Fgnievinski (talk) 16:30, 23 November 2014 (UTC)

## The other meaning of polarization in physics

Polarity is often used in physics to describe binary distinctions such as the north and south poles of a magnet or the positive and negative terminals of an electrical source. No such binary distinction exists for the notion in optics however, where it refers instead to asymmetries in the plane normal to the ray (though a binary distinction exists in the case of the chirality of circularly polarized light).

I mention this because the New York Times Magazine has an April 7 article by Mark Leibovich on polarization in politics which says "Polarization is an idea from physics. In 1808, the French engineer Étienne-Louis Malus noticed that a calcite crystal could block or transmit various kinds of light, depending on the angle by which you viewed it." Perhaps something more than just the hat note to "other uses" is needed in order to steer people to the proper connection in physics, namely those situations in which binary distinctions are made. Vaughan Pratt (talk) 16:05, 9 April 2015 (UTC)

Even in optics, "polarization" refers to a binary distinction. In the simple case of a linearly polarized plane wave, for example, you can describe the light as a mixture of vertically and horizontally polarized light. Two "orthogonal" states. --Srleffler (talk) 05:15, 11 April 2015 (UTC)