Talk:Polarizer

message: ====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)
replies: text: 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)
thread_title: Use of [[Fresnel equations]]

message: * 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)
replies: text: 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)
thread_title: Types

message: ===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)
thread_title: History of the discussion

message: 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)
thread_title: Discussion copied from Arnero's talk page

message: 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)
thread_title: Beam splitters

message: 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)
thread_title:  The lead 

message: 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)
replies: text: I added a link at the top of Analyser.--Srleffler (talk) 01:31, 2 June 2009 (UTC)
thread_title:  Polarizer/Analyzer 

message: 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)
thread_title:  Chiral-fiber polarizers 

message: 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)
replies: text: 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)

text: 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)

text: 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)
thread_title:  Theory and observation 

message: 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)
replies: text: 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)
thread_title:  New Circular Polarizers Section 

message: 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)
thread_title:  Changing the structure of the sections. 

message: 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)
replies: text: 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)
thread_title:  interwiki links 

message: 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)
thread_title:  Illustrations 

message: 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)
thread_title:  Image on demonstrating Malus' Law