Talk:Polarizer

I'd like to store the underlying structure of the continuous text on this page, so that any discussion can point precisely.

Structure

Absorptive polarizers

The formulation "For practical use, the separation distance between the wires must be less than the wavelength of the radiation, and the wire width should be a small fraction of this distance." is pretty vague. It would be an improvement if the article could elaborate on this more numerically or give a criterion (like: a slotting of 1/xth wavelengths leads to y% polarization or something like that). —Preceding unsigned comment added by 134.95.22.221 (talk) 17:44, 14 November 2008 (UTC)

Absorptive vs reflective: the article explains (for the wire grid) the "riding" electrons induce a field that cancels the transmission (and produces the reflection). Could someone add an explanation of why transmission is still cancelled in absorptive poloroid film (where the electron movement is resistively dissipated, preventing induction of a reflection wave)? 150.203.48.127 (talk) —Preceding comment was added at 03:27, 26 November 2007 (UTC)

Is the image (Wire-grid-polarizer.svg) correct? The wire grid seems to be 90 degrees out-of-phase with the emergent wave.—The preceding unsigned comment was added by Schneeman (talk • contribs) .

• As it says in the article: "Note that the polarization direction is perpendicular to the wires; the naive concept of a wave "slipping through" the gaps between the wires is incorrect." --Bob Mellish 17:25, 28 June 2006 (UTC)
  • I just want to comment on this section. It is way to close to word for word from the book Optics by Eugene Hecht. Does anyone feel like rephrasing some of this?—The preceding unsigned comment was added by 67.189.113.62 (talk • contribs) .
• blush - thanks!—The preceding unsigned comment was added by Schneeman (talk • contribs) .
• It's easy to understand if you remember that a wire grid polarizer works because when the electric field of the wave is aligned with the wires, it makes the electrons in the wires move along their length, leading to absorption of the wave. If the e-field is perpendicular to the wires, the electrons can't move very far and there is much less absorption.--Srleffler 21:29, 28 June 2006 (UTC)

Can someone explain why there is no transmitted wave? As far as I can see, each wire acts as a dipole. When you sum the emitted waves from the dipole you get a wavefront that is reflected. But you also get one that is a mirror image, and which effectively continues the incident radiation.

Somehow the answer must be that (1) the dipoles emit in anti-phase to the incident radiation and (2) the incident radiation "continues" and "cancels out" the wave on the other side. But I see no intuitive way to understand why this happens.

200.120.169.43 19:21, 27 December 2006 (UTC) Andrew Cooke

Later. Ah. I think I understand now. What was confusing me was the idea that the electrons "absorb" the incoming wave and then re-emit it. That is a bad mental image. It is better to think the way you do the maths: there are various waves, with related amplitudes and phases, and electrons moving in a way consistent with them (and so can be ignored, since while they are "physically responsible" for what happens, they are completely described by the observed waves). And once you do the maths (conservation of energy, continuity of fields at boundaries) you will get "zero amplitude" in the transmitted region which, if you look at the terms in the maths, you can interpret as the "continued" wave being in exact antiphase with the "emitted wave" from the dipoles on that side.

Maybe this was a very personal problem. I do not know if it implies that the text should change. If someone else understand what I have said (which I suspect is not very clear), then perhaps they can clarify the text.

200.120.169.43 19:58, 27 December 2006 (UTC) Andrew

Well, I did add something. Maybe it simply confuses matters (although I like the image of electrons riding on waves). Incidentally, while I may write like a rambling madman, I do have a fairly decent degree in physics so please don't think this is just rubbish. I am describing a real issue; what worries me is whether or not it is helpful to other readers.

One final point - there's no real difference between absorptive and reflective polarizers (absorptive is a special case, where it's infinitely thick and has the same refractive index as the air). Are these engineering terms, or is the article wrong (ie there is little or no reflected wave; the energy is lost as heating in the wires)?

200.120.169.43 20:10, 27 December 2006 (UTC) Andrew

The difference between absorptive and reflective polarizers is both real, and practical. Practical reflective polarizers are not simply thin absorptive ones. Rather, they use a wavelength and polarization-dependent variation in material properties to produce a large difference in reflection of orthogonal polarizations of light. Calcite polarizers, for example, generally use birefringence to separate polarizations, and then arrange for one polarization to strike an interface at greater than the critical angle, producing total internal reflection. Reflecting thin-film polarizers use the sharp variation in reflectivity at the band edge of a multilayer dielectric coating (which also depends on the polarization) to produce high reflection for one polarization and low reflection for the other. Other effects are used in various types of polarizer.

By the way, be aware of the policy on original research. If you have to derive something yourself, you can't include it in an article. Only things that you can directly find written in some text or other source are suitable for inclusion in Wikipedia.--Srleffler 02:22, 28 December 2006 (UTC)

Wire grid polarizers are usually far more reflective than absorptive. They can be used as polarizing splitters quite effectively, and it's literally an off-the-shelf optical component, so I'm not sure why someone would classify them as absorptive. It's sometimes considered to be a type of form birefringence so there's little reason not to include it among the birefringent polarizers. You can make a low reflectivity WGP, but it takes some extra functionality. They absorb more than a typical MacNielle PBS for sure, but the fundamental mechanism is more reflective than absorptive (essentially an anisotropic metallic mirror), that is you can use them as decent splitters, which you can't do with a polaroid filter. It's also a little weird that the absorptive polarizer section starts with WGPs - I would think that the ubiquitous Polaroid filter is the canonical example rather than an "other".68.15.76.10 (talk) 22:05, 4 May 2017 (UTC)

Beam-splitting polarizers

Beam splitters can sorted according to their shape (cube or plate) or according to the phyisical principle:

Use of birefringence

Materials

• quartz
• calcite

Principle

Snell's law and refraction The rays experience differing refractive indices in the crystal, depending on their (linear) polarization. Snell's law holds, but now produced the ordinary or o-ray and the extraordinary or e-ray.

total internal reflection The critical angle is different for o-rays. than for e-rays.

Types

The factual accuracy of this section is disputed.

A Nicol prism that consists of a crystal of calcite which has been split and rejoined with Canada balsam.

• Refraction takes place at the surface.
• Total internal reflection only of the o-ray occurs at the balsam interface, because the refractive index of refraction of Canada balsam lies between e and o.
• Advantage: Nicol prisms produce a very high purity of polarized light.

A Glan-Thompson prism consists of a crystal of calcite which has been split and rejoined with Canada balsam.

• no Refraction takes place at the surface, because the crystal axis lies in the surface and in the interface of the cut.
• Total internal reflection only of the o-ray occurs at the balsam interface, because the refractive index of refraction of Canada balsam lies between e and o.
• Advantage: produce a very high purity of polarized light.

A Glan-Foucault prism consists of a crystal of calcite which has been split and rejoined with Canada balsam.an air gap between the two halves. [[[User:Srleffler|Srleffler]] 21:07, 8 January 2006 (UTC)]

• nolittle refraction takes place at the surface, because the crystal axis is in the surface but not in the interface of the cut.the surface is typically perpendicular to the incident light.
• As the specific article states as least in the image, is that refraction takes only place upon the o-ray leaving the crystal--Arnero 20:45, 9 January 2006 (UTC)
  • This is true only if the light happens to be incident exactly perpendicular to the input surface. Polarizing prisms have some range of acceptance angle, however. They can accept an input beam that is not exactly perpendicular to the input face, and then of course there will be some refraction at the input surface. This is actually an important issue for this treatment, since one of the key practical differences between different types of polarizing prism is how large their acceptance angle is.--Srleffler 23:14, 9 January 2006 (UTC)
• Total internal reflection only of the o-ray occurs at the balsam interface, because the refractive index of refraction of Canada balsam lies between e and o.
• Advantage: produce a very high purity of polarized light.

A Glan-Taylor prism consists of a crystal of calcite which has been split and rejoined with an air gap between the two halves [ed. Srleffler 21:07, 8 January 2006 (UTC)].

• noLittle Refraction takes place at the surface, because the crystal axis is in the surface and in the interface of the cut.the surface is typically perpendicular to the incident light.
• As the image in the article shows that refraction only takes place upon the o-ray leaving the crystal
  • See above for why this is not exactly correct, in general--Srleffler 23:14, 9 January 2006 (UTC)
• Total internal reflection only of the o-ray occurs at the balsam interface, because the refractive index of refraction of Canada balsam lies between e and o.
• Advantage: Can be used at high laser powers
• Disadvantage: More losses at the air gap for the transmitted beam, may need AR-coating [?]

A Wollaston prism consists of a two crystals of calcite which have been split and re joined with Canada balsam or without nothing in between, with their optical axes perpendicular.

• no Refraction takes place at the surface, because the crystal axis lies in the surface and in the interface of the cut. But it takes place at the interface between the crystals.
• As one can see on the specific arcticle refraction takes place only at the rear surfaces. --Arnero 20:45, 9 January 2006 (UTC)
  • See above for why this is not exactly correct in general.--Srleffler 23:14, 9 January 2006 (UTC)
• no Total internal reflection takes place
• divergence angle: 15°-45°
• Advantage
  • low losses at cut
  • Polarization of both rays after separation is conserved

A Sénarmont prism consists of a two crystals of calcite which have been split and re joined with Canada balsam or without anything in between, with their optical axes perpendicular.--Srleffler 16:06, 10 January 2006 (UTC)

• no Refraction takes place at the surface, because the crystal axis lies in the surface but not in the interface of the cut. But it takes place at the interface between the crystals.
  • This is not true in general. See above.--Srleffler 23:14, 9 January 2006 (UTC)
• no Total internal reflection takes place
• Advantage
  • low losses at cut
  • Polarization of both rays after separation is conserved

A Rochon prism consists of a two crystals of calcite which have been split and re joined with Canada balsam or without anything in between, with their optical axes perpendicular.--Srleffler 16:06, 10 January 2006 (UTC)

• no Refraction takes place at the surface, because the crystal axis lies in the surface and in the interface of the cut. But it takes place at the interface between the crystals. The axis of the second crystal lies in the direction of the rays.
  • This is not true in general. See above.--Srleffler 23:14, 9 January 2006 (UTC)
• no Total internal reflection takes place
• Advantage: low losses at cut

A Foster prism is like a Glan-Thompson prism but adds another Total internal reflection to achieve:

• divergence angle: 90°
• Source

Some Glan-Thompson prism adds another Refraction to achieve:

• divergence angle: 90°
• disadvantage: dispersion

Some new design at a single surface use Total internal reflection to reflect both rays and then Refraction to split then.

• divergence angle: 90°

This section is so badly flawed I'm not sure it is worth saving. It is riddled with factual errors. I've tried to mark them where I could, but there are more and I don't feel comfortable direct-editing it too much since this is a talk page. Beyond, that, though I'm not sure that this would be a good scheme for reorganizing the article. Right now, the article organizes the types of polarizers more or less chronologically by development. It would be useful to add a comparison of the merits of different types of polarizers, perhaps as a separate section, but I can't see replacing the nice explanation currently in the article with this ugly list of redundant bulleted points. --Srleffler 21:07, 8 January 2006 (UTC)

>redundant bulleted points

This is happening with the individual arcticles on the prisms. I wanted to prepare a merger.

I do not think you should attempt to merge these articles. The prism articles are very well written. The stuff above is a nightmare.

NB: Talk pages are not a good place to "hash out" text for a page, as you can see by what is happening. The conventions about never deleting other peoples' comments, and about signing every contribution on talk pages quickly reduce the proposed text to an unreadable mess. In the rare cases where it is necessary to hash out text "offline" from the real page, I have seen people create a "subpage" for the proposed text. I've never done this myself, though. --Srleffler 23:14, 9 January 2006 (UTC)

>chronologically

Absorptive polarizers is not chronologically nor is the separation into absorption and splitting nor is it standard. The history subsection may be better suited.

Nicol was first, followed by Brewseter's angle, says the 2nd edition of:

• Optics, Eugene Hecht, Addison Wesley, 4th edition 2002, hardcover, ISBN 0-8053-8566-5
• non chronological overview

>factual errors

Sorry, I should have carefully looked up the factual (as I did not write them) articels on the individual prisms, thank you that you helped me. And the article does not support memorizing. --Arnero 20:45, 9 January 2006 (UTC)

>direct-editing

Maybe only two turns.

History

Nicol was first

Application

and were extensively used in microscopy

Use of Fresnel equations

Principle

Beam overlap leads to Interference. This can be used as an advantage to increase the intensity of the s-beam or reducing the number of plates or films.

Some math collected from the linked wiki articles:

• Air. at 589.3 nm n= 1.0002926
• Magnesium Fluoride: Refractive index at 500 nm: no = 1.37397, ne = 1.3916.
• glass (typical) at 589.3 nm nn 1.5 to 1.9. BK7: 1.5164
• Critical angle. $\theta _{c}=\arcsin \left({\frac {n_{2}}{n_{1}}}\right)$ n1 is the refractive index of the denser medium. For Air-MgF this is 46°.
• Brewster's angle $\theta _{B}=\arctan \left({\frac {n_{2}}{n_{1}}}\right)$ n1 is the refractive index of the medium, were the angle is measured. For MgF-BK7 this is 47°. So it is just in the region of total internal reflection. For Air this angle is 36° inside the MgF.

Types

• Brewster's angle for interfaces between air and glass
• Brewster angle for interfaces between Magnesium Fluoride and glass fused into a cube using interference called a Thin film polarizer
• Combination: Thin film polarizer on a plate. The Fresnel equations changes sign for p-polarization when moving the angle across Brewster's angle.

When choosing an angle of 40° inside MgF, reflections from the Air-MgF interface and the MgF-BK7 interface will interfere destructivly for p-polarization and constructivly for s-polarization. --Arnero 18:34, 8 January 2006 (UTC)

NB: Not all thin films are MgF.--Srleffler 21:13, 8 January 2006 (UTC)

But MgF was given as a typical example to me, especially for AR-coating. And as MgF has a low index of refraction it seems also suitable for thin film polarizers. The trouble is, I do not know the second material to build the stack with, so I used BK7, which is more typlically a substrate. --Arnero 20:49, 9 January 2006 (UTC)

Yes, MgF is very commonly used for cheap single-layer AR coatings, because of its low index. It is typically not used for multilayer coatings. A much more common structure for multilayer stacks is alternating layers of SiO₂ and a higher index material. There are many choices for the high-index material. The coatings I order usually use tantala (Ta₂O₅) or hafnia (HfO₂) but other materials are used for other applications. Coating design is quite complicated. There is a lot of knowledge that goes into the choice of the materials, the deposition methods, etc. --Srleffler 23:32, 9 January 2006 (UTC)

History of the discussion

Comments moved out of article:

• Many more prisms have been invented, and it would be nice, if this arcticle would help the user to choose the right one for him : Fock Polarizer. User:Arnero 04:45, January 6, 2006
• The big question is: What is the difference between a thin-film polarizer and a beam splitting dielectric mirror? Are the thin films birefringent? Then maybe a single film is sufficient, kind of inverser Nicol prism. Anyone who used a beam splitting dielectric mirror has observed, that it works like a polarizer. A .5 beam splitter in 45° may transmitt .7 p-polarization. What is the prove, that the internal Brewster's angle does not play a role? With the right dieelectric materials, this angle becomes 45°. Polarizers who are optimized for having a small stack may have to be used with anoter angle. User:Arnero 04:45, January 6, 2006
• BIREFRINGENT THIN FILMS AND POLARIZING ELEMENTS The second part focuses on an emerging planar technology in which anisotropic microstructures are formed by oblique deposition in vacuum. User:Arnero 04:45, January 6, 2006

Discussion copied from Arnero's talk page

I think the comment about Brewster's angle in the context of thin film polarizers is at best confusing, and probably outright wrong. The response is mostly due to the variation in the interference in the film with angle of incidence rather than Brewster's angle. When you make a thin film polarizer, you aren't constrained to keep the angle at or even near Brewster's angle. Unlike Brewster's angle, the polarization can change dramatically with wavelength. Perhaps there are thin-film polarizers that do use an internal Brewster's angle reflection, but this certainly need not always be the case.--Srleffler 14:15, 30 December 2005 (UTC)

>variation in the interference in the film with angle of incidence
This does not distinguish between directions of polarization, only wavevector directions

>Perhaps there are thin-film polarizers that do use an internal Brewster's angle reflection, but this certainly need not always be the case
So why are you so certain?

>Unlike Brewster's angle, the polarization can change dramatically with wavelength
Yes thats a difference, but I think the only one. One usually uses thin film polarizers for narrow bandwidth lasers and there the compactness is of greater importance. --Arnero 16:07, 30 December 2005 (UTC)

Please don't put discussion or questions in the article pages. That kind of material belongs on the article's talk page.--Srleffler 13:47, 6 January 2006 (UTC)

According to Macleod's book (see ref. below), a MacNeille prism works the way I think you have in mind, with a thin-film stack designed such that light passes through a series of thin-film interfaces at Brewster's angle. These polarizers have a very wide spectral range, but limited angular range for obvious reasons. Plate polarizers cannot be made based on this principle, because "the Brewster angle for normal thin-film materials...is found to be greater than 90° referred to air as the incident medium. In other words, it is beyond the critical angle for the materials. [In the MacNeille prism] this is solved by building the multilayer filter into a glass prism so that the light can be incident on the multilayer at an angle greater than critical."

Plate polarizers, on the other hand, depend on the fact that the width of the high-reflectance zone of a quarter-wave stack is different for s and p polarization. There thus exists a region at the edge of the reflection band where the reflection is high for s-polarized light and low for p-polarized light. Further layers are used to smooth out ripples in the transmission spectrum, etc. The spectral range for these polarizers is narrow, and shifts with angle of incidence like any other bandpass coating.

While cube polarizers can be made based on the Brewster principle, they are often made using the same principle as plate polarizers. The latter tend to have a broader spectral range than plate polarizers, because of the higher angle of incidence of the light at the coating layer interfaces.

• Macleod, H Angus (2001). Thin-Film Optical Filters, 3rd ed. Institute of Physics. pp. 362–368. ISBN 0750306882.

--Srleffler 14:42, 6 January 2006 (UTC)

Beam splitters

The section on beam splitting polarizers may need to be broken up in two. I have just been reminded that the Glan-type polarizers are not truly polarizing beamsplitters, even though they are often called that. The transmitted beam is 100% polarized. The reflected beam is not. (qv. Talk:Glan-Foucault prism). The Wollaston-type prisms are true polarizing beamsplitters, as are the dielectric type (plate and cube).--Srleffler 23:17, 10 January 2006 (UTC)

Circular Polarisers

Circular Polarisers should be added too to the article. helohe (talk) 13:47, 20 March 2006 (UTC)

I agree, especially since circular polarizer redirects to this page. I can't find much information about them, though. I know what circular polarization is (see polarization), but I don't see how rotating a circular polarizer would make any difference. I've heard that you want to use a circular polarizer for any modern camera that does through-the-lense focus or metering. One site, [1], says that such metering uses semi-silvered mirrors to extract light from the optical path. Doesn't metallic reflection not change polarization? Don't digital non-SLR cameras do focus and metering by reading the CCD?

The thing that photographers call a "circular polarizer" seems to actually select a single linear polarization, and then make that circularly polarized. The effect you want for improving picture quality is linear polarization. The additional step of making the output of the filter circularly-polarized is just to make sure that the viewfinder and metering electronics in an SLR camera see the same thing as the film or CCD will. A semi-silvered mirror at an angle will reflect some polarizations more than others. With an SLR and a linear polarizer, this means that you (and the electronics) would see a brighter or dimmer image than the film will see. I wouldn't think that a non-SLR digital camera would be affected.

So:

1. Rotating it makes a difference because it's a linear polarizer with circular output
2. Metallic reflection does change polarization, because the (angled) mirror will reflect some polarizations more than others.
3. You might be right about digital non-SLR cameras.

I agree that it should be added to the article, but that needs to be done by someone who knows how it works. It sounds like a linear filter followed by a quarter-wave plate, but that would produce horrible chromatic aberration. I can't imagine how one would make one that is suitable for colour photography.--Srleffler 04:59, 13 November 2006 (UTC)

I think you are right (linear polarizer followed by quarter wave), but wrong to think that is a problem. The detector itself does not care about polarization. This is just to get some light (of some range of wavelengths) reflected into the autofocusing dohickey (although that doesn't explain metering, which would be messed up, I admit).200.120.169.43 20:34, 27 December 2006 (UTC) Andrew Cooke

Let me throw an oar in the water concurring that this stuff should get boiled down (by someone who's certain what they're talking about :-) and put in the page; I came looking for it, and didn't find anything at all.
--Baylink 00:03, 5 April 2007 (UTC)

One way to produce circular polarization is 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 (45°) between the fast and slow axes of the quarter wave plate. Think of the linear polarization as the vector sum of two orthogonal components of equal amplitude and phase, one parallel to the fast and one parallel to the slow axis of the plate. After passing through the plate their amplitudes are still equal but their relative phases have changed to be a quarter wavelength (90°) apart, so that their vector sum is now circularly polarized. If the axis of the linearly polarized light is rotated a quarter turn (90°) relative to the quarter wave plate, then the handedness of the circular polarization will be reversed, because the relative phases will be switched, that is, the fast component will now be the slow component. Also, the direction of passage through the circular polarizer matters; if the light enters the quarter wave plate and exits through the linear polarizer, the exiting light will be linearly polarized. That is, turning a circular polarizer around converts it into a linear polarizer. Someone, besides me, could help by adding an illustration. --AJim (talk) 22:06, 20 May 2009 (UTC)

Sunglasses use simple linear polarizers, e.g. sheets of Polaroid, not circular polarizers, to cut down glare. Light that has been reflected off a surface such as glass or water is partially linearly polarized, usually in the horizontal direction if the reflecting surface is horizontal. Sunglasses use vertical polarizers to eliminate most of this reflected light.

Glasses for viewing many types of 3D movies also use simple linear polarizers. The two images are projected in linearly polarized light, polarized in perpendicular directions.

Circular polarizers usually use quarter-wave plates, and are therefore wavelength-dependent. It is difficult and expensive to circularly polarize white light.

DOwenWilliams (talk) 22:03, 26 February 2011 (UTC) David Williams

I would point out that RealD cinema uses circular polarization.Dave3457 (talk) 01:27, 5 March 2011 (UTC)

As has been pointed out (and I recently edited the http://en.wikipedia.org/wiki/Polarizing_filter_(photography) page to clarify) the "circular" polariser used in photography comprises a linear polariser (facing the scene you're photographing) and a quarter-wave plate behind it (facing into the camera) to "redistribute" the polarisation to avoid problems with metering or focussing systems that work using a fraction of the lens-light taken with an angled beamsplitter mirror. 3D cinema can be achieved using linearly polarized light (with the images for each eye polarised at right angles to each other), but suffers the problem that if you tilt your head then the left and right images start to mix. By using left- and right-hand circularly polarized light instead (and in this case the 3D glasses have the quarter-wave-plate side facing the cinema screen and the linear-polariser side facing the eye) tilting the head does not interfere with the polarizing action - giving a better image and less ghosting. Andrew Steer / techmind.org 217.33.180.66 (talk) 09:32, 11 September 2013 (UTC)

In the "Creating circularly polarized light" image, the text below it describes the Fast Axis as the vertical axis and the Slow Axis as the horizontal axis. Shouldn't this be the other way around for this image..? Because wouldn't the horizontal component of the linearly polarized light "linger" while the vertical component continues ahead by a phase of pi/2 which should lead to RHCP(according to the non-optics definition: looking parallel to the direction of propagation) or LHCP(according to the optics definition: looking antiparallel to the direction of propagation). This seems to be consistent with what I found in my textbooks (Pedrotti,Saleh&Teich), but is contradicted here. — Preceding unsigned comment added by Mdoughe1 (talk • contribs) 13:43, 30 September 2015 (UTC)

The lead

The lead should explain briefly why anyone would want to depolarize something such as light in the first place. JayKeaton (talk) 07:50, 26 October 2008 (UTC)

Malus' Law

"where

I₀ is the initial intensity,

and θ_i is the angle between the light's initial plane of polarization and the axis of the polarizer."

Shouldn't it be plane of vibration, rather than plane of polarization? Maybe i'm talking rubbish but my understanding was that θ_i was the angle between the axis of the polarizer and the plane containing the electric vector (plane of vibration) Jh39 (talk) 01:00, 26 February 2009 (UTC)

They are the same thing. The light's initial plane of polarization is the plane in which its electric fields vibrate.--Srleffler (talk) 03:14, 26 February 2009 (UTC)

Huh...according to Wheelan and Hodgson 'Essential Pre-University Physics', in polarized EM waves, the plane of vibration is the plane containing the oscillations of the electric feild, and the plane of polarization is the plane perpendicular to the plane of vibration, containing the oscillations of the magnetic feild. Jh39 (talk) 00:34, 27 February 2009 (UTC)

You're probably misreading them, or perhaps they are mistaken. The polarization of a light wave is always defined by the direction of the electric field. --Srleffler (talk) 03:51, 27 February 2009 (UTC)

These two extracts are from Essential Pre-University Physics:

'The plane of vibration is that which contains the electric vector and the direction of propogation'

'For historical reasons, the plane of polarization was chosen to be that perpendicular to the electric vector'

I also found this in 'Optics' by Michael Harold Freeman, C. C. Hull, W. N. Charman:

'The term "plane of polarization" was originally used to describe the orietation of the magnetic vector but (of course) it has sometimes been used referring to the electric vector. To avoid this confusion the term plane of vibration is now used and this refers to the electric vector, being that plane containing the electric vector and direction of propogation of the light. The term "plane of polarization" should not be used'

http://books.google.co.uk/books?id=lXNFnybj9wwC&pg=PA393&lpg=PA393&dq=%22plane+of+vibration%22+%22plane+of+polarization%22&source=bl&ots=P6ieh0DYeN&sig=y6_UFoaDHpuL6uqna8jpQHxrby0&hl=en&ei=YHenSdLjJ4S2jAf__pX0Dw&sa=X&oi=book_result&resnum=9&ct=result

Essential Pre-University Physics may not have been entirely up-to-date; my copy was printed in 1974, but 'Optics' was published in 2003 and it seems to agree. Jh39 (talk) 06:29, 27 February 2009 (UTC)

Some other references I glanced at online appear to agree. While polarization is always considered to be determined by the direction of the electric field, the specific phrase "plane of polarization" appears to have been defined historically before the underlying physics was understood. It's best therefore to simply avoid using that phrase, as Freeman et al. suggest.--Srleffler (talk) 22:45, 27 February 2009 (UTC)

All this discussion of the meaning of "plane of polarization" is interesting, but there is a bigger problem: The Pauli Lectues refer to a different law as "Malus's Law". In vol 2, "Optics and the Theory of electrons", he defines it as the differential equation grad[P]S_ = n(dx/ds), where 'S_' stands for 'S' with a bar over it in the text, [P] is a subscript (P the point at which variation is taken) and 'x' a vector., S_ = Indefinite Integral(nds), (n the refractive index).

He then describes this as "Verbally, it states that if rays have at any time been normal to a surface F, then there always exist surfaces, namely those for which S_ is constant, which are normal to the rays".

Clearly this law is different. So how did this difference emerge? 99.170.187.117 (talk) 22:35, 31 May 2009 (UTC)

If I follow you, the equation is:

$\nabla _{P}{\bar {S}}=n{d{\vec {x}} \over ds}.$

It's hard to interpret this, since you haven't defined all the variables. It doesn't appear to be related. It's not uncommon for classical scientists to have more than one law named after them. Malus presumably did more than one thing in his career...--Srleffler (talk) 23:34, 31 May 2009 (UTC)

Étienne-Louis Malus died at the age of 37; his productive period was rather short, though he did make several important contributions to the understanding of light. However, when considering his (only) "law", you should keep in mind that at the time he formulated it there was no electromagnetic theory. In fact the notion that light was formed by two-dimensional transverse waves was only arrived at through attempts to explain his law by Fresnel, Young and their collaborators. --AJim (talk) 17:28, 6 July 2010 (UTC)

Polarizer/Analyzer

Perhaps the sentence "If two polarizers are placed one after another (the second polarizer is generally called an analyzer)" can somehow be linked to the 'analyzer' page? It took me forever to look up 'polarizer' when I was researching the word 'analyzer.' —Preceding unsigned comment added by 163.239.203.207 (talk) 05:01, 1 June 2009 (UTC)

I added a link at the top of Analyser.--Srleffler (talk) 01:31, 2 June 2009 (UTC)

Chiral-fiber polarizers

I deleted the following section from the article for now. The user who posted it appears to have a conflict of interest, and has been posting material promoting Chiral Photonics in many articles. This technology might merit a mention in this article, but perhaps someone else should write the text, and we should have a citation to a reliable source supporting it.--Srleffler (talk) 21:57, 18 June 2009 (UTC)

Utilizing its fiber twisting technology, Chiral Photonics has developed in-fiber polarizers. The polarizers are all based on twisting standard PANDA polarization maintaining fiber. A twist pitch of approximately 10 microns results in light of the same handedness, co-handed light, being scattered out into the cladding whereas light of the opposite handedness, cross-handed light, being transmitted.

Chiral Photonics has developed two types of linear in-fiber polarizers. In one approach, the PANDA fiber is twisted while in the other it is tapered. In addition, they have developed a circular in-fiber polarizer. Applications of these polarizers include pressure and current sensing as well as, in the case of the circular polarizer, biophotonic uses.

Theory and observation

Consider the intensity of the transmitted beam, this is measured at close to 0.5 of the incident beam. Not mentioned in the article is the matter of crossed polarizers which transmit the cosine of the angle between them. So the diagram showing a narrow angle of polarisation with an unchanged amplitude from that component when incident cannot be right as it represents a minute transmitted intensity. I know this diagram has long been in universal use, but it is wrong. If you take crossed polarisers the transmission is zero, then put a third polarizer between them and depending on the angle there can be significant transmission, about 0.25 of the incident beam when the middle polarizer is at 45° . So each component of the incident beam is converted to a tranmitted narrow beam by the cosine law. In quantum mechanics each photon is transmitted by chance according to the cosine. I think a diagram indicating that the emergent narrow component is almost infinitely high would help a lot. But I suggest discussion first. Reg nim (talk) 20:30, 5 September 2009 (UTC)

I don't follow what you are trying to say. Intensity is not a product of amplitude and polarization angle. An ideal polarizer transmits light with a single polarization angle, and the amplitude of the transmitted light is equal to that of the corresponding component in the incident beam. The transmitted intensity is not "minute". Real polarizers can quite well approximate the ideal. A good calcite or vanadate polarizing cube can transmit light with as high as a 10⁶ ratio of light in the correct polarization, to that in the perpendicular component. The transmission of the correctly-aligned component is not 100% due to losses in the polarizer, but can be quite high.--Srleffler (talk) 01:24, 6 September 2009 (UTC)

The diagram of the wire grid polarizer is a bit misleading, though, since it shows diagonally polarized light as well as vertical and horizontal components. The transmitted vertically-polarized beam will have contributions from all of the incident light except that which is exactly horizontal.--Srleffler (talk) 01:34, 6 September 2009 (UTC)

Could someone give a quantum-mechanical description of what happens when a photon goes through a linear polarizer? If it is not aligned with the polarizer, light in bulk comes through polarized with intensity proportional to the cosine of the angle between the incident light's polarization and the polarizer, but for a single photon, its wavelength determines its energy, so what happens? It has to come out polarized according to the filter, so does it get probabilistically rejected based on the cosine of the angle and otherwise get turned and pass through? In other words, in the case that it passes through, how does it wind up being repolarized? —Ben FrantzDale (talk) 12:57, 18 May 2012 (UTC)

Merging the present “Polarizing filter” article with this page

I have made a study of the relevant Wikipedia pages related to this issue and have found that for many people the term Polarizing filter is synonymous with term Polarizer. As a result there is certain amount of confusion taking place. I feel a search for Polarizing filter should lead to this Polarizer page, and the present Polarizer filter page should be renamed Polarizing filter (Photography) I don’t feel that the present Polarizing filter page should be merged with this one given that it is a specialized use of a polarizer and the article is quite lengthy. I would suggest a section on this Polarizer page which gives a quick introduction to their use in photography but then directs people to the Polarizing filter (Photography) article for more details.

Presently about 20 pages link to that page and about 3 of the links, given their context, should actually be directed to this Polarizer article. (This miss-linking is a result of the present confusion). I would be happy to take care of the re-linking.
After taking care of the articles that link to Polarizing filter I would then #redirect Polarizing filter to this Polarizer page.

For me this seems like a very viable solution to the present confusion.

Please comment. Dave 2346 (talk) 09:13, 16 February 2010 (UTC)

I think this is a much better idea than a merge - although the phenomenon is the same and the hardware may be similar, the 2 articles are quite different in approach and IMO should be. If there's a general consensus that there's a problem that needs fixing, this could be the way forward, although to be honest with a hatnote pointing to the other use I don't see a major need for a change (except for some link checking).

ChrisHodgesUK (talk) 09:34, 16 February 2010 (UTC)

Thanks for the feedback. This issue is of concern to me because I am about to put forth an extensive Circular polarizers section for this article and a Photographic polarizer is a circular polarizer. While there might be “easier” fixes, I feel the one I’m proposing is not problematic and fair to all. Again when people use the term Polarizing filter they often mean a general polarizer and not a circular polarizer being used for a specific purpose. It would be best if they could just quickly highlight the words “polarizing filter” and create an internal link. Those who mean a Photographic polarizer will be able to quickly recognize the link they want. Unless there are objections, I will go ahead with it after I post my Circular polarizers section.

Note: I have just posted my suggestion on the empty Polarizing filters talk page.

Dave 2346 (talk) 03:30, 17 February 2010 (UTC)

New Circular Polarizers Section

I appreciate that the circular polarizer section I’ve created is wordier than most articles on Wikipedia but with the advent of 3D cinemas using circular polarization now, the subject of how the glasses work is of interest to many people who don’t have a physics background.
Presently I have just stuck it on the end of this article and have not worked its inclusion into the introductory paragraph which is more or less devoted to linear polarization. By all means take a shot at it.

Once it is agreed that this is the place for it I will change the Circular polarizer #redirect

I welcome any feedback including critical.

Dave 2346 (talk) 19:04, 18 February 2010 (UTC)

I like what you are doing. Perhaps it would be useful to explicitly state that turning a circular polarizer around makes it into a linear polarizer. I wonder if you should include a reference to the Fresnel rhomb. As far as I can understand, Fresnel's device was the first way to produce circular polarization. Its invention coincides with the understanding that light is a two-dimensional transverse wave and that therefore circular polarization is possible. Fresnel and associates and their correspondent Thomas Young were trying to understand the implications of Malus' Law. Apparently, up until that time, the proponents of the "vibratory" theory of light only considered longitudinal motion. Circular polarization requires two-dimensional waves and the demonstration of circular polarization confirmed the value of what became known as the wave theory of light. It also nicely explains what Malus observed. --AJim (talk) 01:18, 19 February 2010 (UTC)

I don't have time to contribute to this article right now, but I wanted to point out that you need to be careful not to confuse two very different things: a true circular polarizer is a filter that blocks one circular polarization (left-handed, for example) and transmits the other (e.g. right-handed). This is not what photographic "circular polarizers" do. The latter are filters that pass a single linear polarization, but convert it to circular polarization after the filtering takes place. --Srleffler (talk) 02:35, 19 February 2010 (UTC)

+++++++++++++++++++++++++
AJim and Srleffler . I first should mention something. My knowledge of circular polarizers only really began several months ago when I went to see the movie Bolt in 3D. I don’t have any degrees and only a few years of engineering. So my potential for depth of contribution is limited. That being said I have been studying physics all of my life. This is my first major contribution and I only took it up because when I went to research circular polarizers on Wikipedia, I found nothing. That also being said I have enjoyed the experience and would love to contribute more. At this point I am just glad that the whole thing didn’t need to be trashed. I failed English the first time in high school so grammar is not my strong point, you have no idea how many rewrites I made.

Srleffler, my main concern is to be accurate and it would kill me if I posted something that wasn’t true and it stayed posted for any length of time. I am very appreciative that you ended up “looking over my shoulder”. Your comment is a good case in point. I'm guessing then that I should relabel the section "Polarizing Filters". On the other hand I am not sure to what extent people are going around calling Polarizing filters, circular filters. If almost everyone is doing it then the below might be appropriate.

I could leave what is already there more or less intact and just put something like the below in the introductory section.

- - Circular Polarizers - -

A circular polarizer is a filter that blocks one handedness of circular polarization and transmits the other much as a linear polarizer is a filter that fully blocks one ?????? of linear polarization and transmits the polarization that is orthogonal.

++ Something more should be inserted here. I would also try to avoid the word orthogonal as the audience I'm writing for may not have heard the word before. ++

It is however useful to first study the polarizing filter which is often confused with the true circular polarizer.

and then basically pick up from there.

Would the true nature of a circular polarizer need to be referenced or is it just common knowledge?

The name “polarizing filter” suggests linear or circular polarization, but is the name only used in the context of circular polarization combined with linear polarization? Unless you stop me I will go ahead and convert any use of the term “circular polarizer” to “polarizing filter” and/or “circular polarizing filter” in what I have written.

Is a possible construction of a true circular polarizer a linear polarizer laminated between to two quarter wave plates? If so I could "seed" the circular polarization section describing its operation. It would be better than nothing.

AJim, you may or may not have noticed that a couple of sentences were directly lifted from your early comment about circular polarizers. :-) This section started with me only going to reword your paragraph and it grew.

I will definitely add something about how the polarizing filter used in photography is just a linear filter with a twist. (Pun intended)

Yes a Fresnel rhomb should be mentioned in passing somewhere. I noticed that, according to Srleffler, (and I’m taking his word for it :-) ) it is not a true circular polarizer either. I will just put it in the compiled links section for now. The Fresnel rhomb article is in need of an image, maybe I’ll make one since I went to all the trouble of learning Inkscape to create the two images here and to manipulate the others. Your historical note should be added there also but there are two issues for me. First it takes a lot more work to talk about something I haven’t already explored (and potentially troublesome for others) and second, or third if your counting, my main course of action is to flesh out a link path on Wikipedia that someone who has just watched a RealD movie could follow if they, like me, wanted learn about the physics behind the experience. I have two projects in mind, a short article about the Zscreen, and an article or section about the details of RealD glasses. I’ve begun reading the patents on both.

By the way, while I’m sure that a short article about the basics of the Zscreen would pass the Wikipedia inclusion test I’m not sure whether something specifically about RealD glasses would. Would it be alright if before embarking on the 3D glasses thing, I give one or the two of you a kind of proposal and you could tell me how and where you think it could fit in, if at all. I will do that after I tie up the loose ends here and finish something I’m doing on handedness conventions.

Quite frankly I would feel much more comfortable if one or both of you looked over any rather significant contributions I was about to make before they went to primetime. I just don’t feel right taking the risk of putting something out there that is either poorly written or just plain wrong. I was a little nervous pushing the Save Page button on the Circular Polarizer section the other day, as I was pushing the limits of my mental and linguist capabilities.

Would it be too much to ask if I directed you(s) to my sandbox before transferring something that I was not too sure about before putting it to mainspace? I know and like the idea of this encyclopedia being a large group effort but there is a fine line between being bold and being reckless.

Srleffler, I noticed you removed the Merge Discussion tags, I will take that as a go ahead. However strictly speaking, if I understand you right, since a Polarizing filter isn’t a circular polarizer, it should be on a separate page. With that in mind so that someone doesn’t have to do alot of re-linking again in the future I will direct the pages to either Polarizing filter or Polarizing filter (Photography) and redirect Polarizing filter here.

I have several more questions but I will save them for another time.

Well thanks for the direction, and please don't be worried about my ego.

Dave 2346 (talk) 01:21, 20 February 2010 (UTC)

.

Srleffler: I could find no evidence for your view that a “true” circular polarizer transmits one polarization (without altering it) and blocks the other. All the commercial sites I found selling circular polarizers called their linear polarizers that were laminated with quarter wave plates, circular polarizers. Eg http://www.lamdapacific.com/Webupdate/upload/2009424174727734.pdf

Also the textbook “Handbook of Optics 2 edition vol2, Bass M at http://heartfeltemotion.com/Handbook_of_Optics_2_edition_vol2_Bass_M.pdf (Section 22.19 ) refers to linear polarizers that are laminated with quarter wave plates as Circular Polarizers and refers to the device that you are talking about as a “homogeneous” circular polarizer. There is an extensive quote here Talk:Polarizer/Lengthy_quotes
Dave3 (talk) 15:48, 13 March 2010 (UTC)

Changing the structure of the sections.

Because of the recent creation of the circular polarizer section, I added a sentence in the introduction to reflect the new structure. (Note: Before the creation of the circular polarizer section, the article dealt exclusively with linear polarization.)
Although I did not change the order of the sections, I changed their hierarchy by introducing a new heading Linear polarizers and then changed the heading levels of the relevant lower sections. I also moved a sentence out of the main introduction and made it the Linear polarizers introduction.
I also added the word “linear” at strategic locations in the Linear polarizers section to emphasize the type of polarizer which is being discussed. (Six times in all) Dave3457 (talk) 16:46, 6 July 2010 (UTC)

interwiki links

Somebody has to check the interwiki links.. some of them should be linking to the article actually to the article: Polarizing filter (photography) and not to this general article about polarizers.. Ggia (talk) 07:35, 21 September 2010 (UTC)

A while ago a new Circular Polarizer section was created. I think the problem may be that while I sorted through the pages that linked to “Polarizing filter” I may not have gone through all of the pages that linked to “Circular Polarizer”. (Although, I suspect I did). Anyway, I will set myself a dead line of Oct 1st to go through the pages that link to both “Circular Polarizer” and “Polarizing filter”. As it happens I have something related to sort out. I won’t be going through those that link to just “Polarizer” however, I suspect there would be to many. If a page sent you to the general link “Polarizer”. I would urge you to change that specific page so that others don’t follow you here. Dave3457 (talk) 06:30, 24 September 2010 (UTC)

Illustrations

This article has many fine illustrations. Some of them are very prominent and even repeated in several places. In spite of this, communicating the idea of the circular polarizer is difficult.

There is, however, an excellent and simple animated illustration available in Commons. Unfortunately the graphics quality of this illustration is not the best, so I have asked the originator if there might be a possibility to improve or update that illustration. Bengt Nyman (talk) 10:06, 22 March 2014 (UTC)

Image on demonstrating Malus' Law

I see that you already have many images, but use the image to the left if you want to. I made it for v:Bell's theorem. It's an activity using three filters to demonstrate Malus' Law (a and b are for left and right handed people, respectively)--Guy vandegrift (talk) 17:51, 13 September 2015 (UTC)