# Talk:Anti-reflective coating

WikiProject Physics (Rated B-class, Mid-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.
Mid  This article has been rated as Mid-importance on the project's importance scale.

## Merge #1

Should this page be merged with Optical_coating#Antireflection_coatings? They seem to have extremely similar contents.

The contents of that section should be merged here, and then that section should be reduced to a summary, with the "main article" template linking to the broader description here. Antireflection coatings are an important enough special case to have their own article.--Srleffler 17:12, 30 April 2006 (UTC)

I agree with Srleffler on keeping the Anti-reflective coating article. myth 00:52, 7 January 2007 (UTC)

Merge complete--Srleffler 05:41, 18 January 2007 (UTC)

## Merge #2

I also think Anti-reflection lens should be merged here. An "anti-reflection lens" is just a lens with an anti-reflective coating. Besides this, though, that term is AFAIK not used at all in optics. From the content of the article, it is presumably used in the consumer eyewear industry. I don't see why opthalmic uses of antireflection coatings can't be covered in a section here instead.--Srleffler 00:36, 18 January 2007 (UTC)

Pro merge and redirect Dr Lind 11:44, 30 January 2007 (UTC)

Merge complete. --Srleffler 13:15, 30 January 2007 (UTC)

## Nanostructure?

I recall reading some time ago that certain insect eyes have a natural AR coating that works completely differently to the types described in the article. It was a type of nanostructure involving pillars of material on the surface. Scientists were studying the structure with an eye to using it for engineered coatings. Anybody know anything about this? It would make a good addition to the article.--Srleffler 05:41, 18 January 2007 (UTC)

I found some articles on it and added a section.--Srleffler 06:02, 18 January 2007 (UTC)

## One case where quantum mechanics makes things more intuitively understandable

The current text has:

If this is the case, the incident beam I, when reflected from the second interface will travel exactly half its own wavelength further than the beam reflected from the first surface. If the intensities of the two beams, R1 and R2, are exactly equal, then since they are exactly out of phase, they will destructively interfere and cancel each other. Therefore, there is no reflection from the surface, and all the energy of the beam must be in the transmitted ray, T.

This way of explaining things implies that part of the incident light is reflected and then "destroys" itself. The average well-informed reader may imagine two photons being reflected, one from each surfact, and then "canceling each other," resulting in the loss of two photons. An electrical analogy might be that pairs of electrons and protons would emerge from the two surfaces and that their electrical charges would balance each other so that their charges would not be detectable, but the original lens would thereafter be short the equivalent of a hydrogen atom.

As I understand it, it is a single quantum mechanical probability wave that propagates backwards from surfaces and also propagates forward through the lens. If there is no anti-reflective coating then there is a certain probability that the photon will be manifested on the reflected path, and another probability that it will be manifested on the forward part of its path(s). With the anti-reflective in place, the sum of the probabilities on the merged two reflected paths is zero or thereabouts, and the probability going forward through the lens is enhanced. (If a photon can't be manifested on the reflected path it will have to be manifested on the forward path.)

This kind of anti-reflectivity is correctly distinguished in the article from anti-reflective surfaces that just ensure that, e.g., the image of the sun is not reflected off a glass surface into the eyes of an observer at a certain point but is dispersed so widely that the glass surface is effectively very similar to the bark of a tree or some other such matte surface. P0M (talk) 03:14, 14 March 2008 (UTC)

I just noted an addition that was reverted. The person who added the misinformation probably did not understand the quantum mechanical explanation for why an extra coating actually increases transmission. If you think about light as a wave phenomenon, it's easy to imagine part of the waves of light heading back toward the source. If that happens it doesn't matter whether the reflections are visible to somebody looking at the lens from the front side. If you think about light as a particle phenomenon, it matters very much whether the particles go through or bounce off the first surface of the lens. If a particle is reflected from the first surface of the lens coating, or it is reflected from the second surface of the lens coating, it is in either case heading back toward the source. But the quantum mechanical explanation is that the waves both go forward and go back, but they are probability waves that determine the likelihood that a photon will be detected at one place or another. If they interfere with themselves so that the probability of a photon being detected in front of the lens goes to zero or thereabouts, the probability that it goes forward is increased. So more photons get through.
There may be a concise statement of this consequence of QM somewhere that could be cited. P0M (talk) 07:16, 21 April 2008 (UTC)
I suppose it could be done that way, but it also works with classical electromagnetic waves. The fun with quantum mechanics comes when you treat particles like electrons as waves, or classical waves like light, as particles. Gah4 (talk) 14:32, 10 January 2016 (UTC)

## odd term

What does the term used in the text, "light deep," mean? Is this a mistake? P0M (talk) 06:23, 28 March 2008 (UTC)

The whole phrase was "one-quarter of the wavelength of the light deep", i.e. "having depth equal to ¼ wavelength". Not a mistake, but it was very poorly phrased. I've rephrased it.--Srleffler (talk) 16:06, 28 March 2008 (UTC)

## Russian, Ukrainian, German inventions categories

Dear users. Unfortunately, many of us editors about inventions arent aware of an important category: Category:Inventions by country. This article fits Russian inventions, because Smakula was originaly from the Russian Empire, German inventions, because he have done it in Germany, and Ukrainian inventions, because even thought there was no Ukraine when he was bornm he was ethnicaly Ukrainian and today Kherson, where he was born, is Ukraine.

If you have the question of but wait a minute!!! Many people took part in thar invention, many theries. To who of them it goes?

To the one who is widely considered. For example. The Tank. Before the British made the tank that became commercialy succesful many people built models of it. Some succesful. But the British made it really famous, commercialy succesful. They made the model that counts, lets say it like that. Thats why the tank goes to British inventions.

Another point. If a man is of one nationality, but made the invention in another country, the invention fits both categories, and that is the case here. See the example of Rubber band. It enters the category of English inventions even though it was invented in Australia, why? It's inventor was English.

Please be aware of that type of categorising to. Kostan1 (talk) 10:30, 4 August 2008 (UTC)

## physics question

Such antireflective coating works only from one side, doesn't it? So why it shouldn't spontaneously create density gradient in photon containment, breaking 2nd law of thermodynamics? —Preceding unsigned comment added by 80.51.221.90 (talk) 15:26, 21 September 2008 (UTC)

Only works from one side? Not exactly true. That's like saying that a first-surface silvered glass mirror only works from one side. It "works" from both sides, but not in exactly the same way.
"Photon containment"? Where is anything said or implied about photon containment? The issue is not what happens to photons but what happens to the "delivery point" of photons when the probabilities for photon manifestation (or delivery or appearance or whatever you want to call it) are radically changed. P0M (talk) 17:31, 21 September 2008 (UTC)

If it would have slightest difference in reflectiveness from both side, it would be Maxwell's demon - for example in photon containment with dominant energy corresponding to wavelength of anti-reflective coating, it would spontaneously create density gradient - reduce entropy. Maybe there should be in the article a sentence or two why it has the same reflectiveness from both sides... I think we have to make such coatings from both side to make it work —Preceding unsigned comment added by 80.51.221.90 (talk) 20:27, 21 September 2008 (UTC)

There is no issue here. Antireflective coatings work equally well from both directions. If you want a mental exercise dealing with Maxwell's demon and the laws of thermodynamics, go look at Faraday isolator.--Srleffler (talk) 23:14, 21 September 2008 (UTC)

But if the coating would be only from one side, photon would reflect while going from high refractive index back to air. To prevent it we have to make coating from both sides. Maybe it should be mention in the article to prevent confusion. —Preceding unsigned comment added by 80.51.221.90 (talk) 06:07, 22 September 2008 (UTC)

In a camera there is no real concern about reflections back into the camera from the inner surface of the (usually compound) lens. The main reason is that the inner surfaces are all a matte black except for the emulsion, and the emulsion is formulated to absorb light too. I would imagine that there might be some point in having anti-reflective coatings on the surfaces of lens elements within the compound lens. Maybe the cost gets to be a factor? P0M (talk) 16:23, 22 September 2008 (UTC)
Who says that there are no AR coatings inside camera lenses? Each non-coated surface causes about 4% reflection loss, which adds up in a 6-element camera lens with 12 surfaces. Moreover, reflected light can reflect again, either within other lens elements, or reflections from the image sensor could reflect from the any uncoated lens surface. Han-Kwang (t) 21:05, 22 September 2008 (UTC)
To 80.51.221.90: You seem to be talking about (and perhaps confusing) two unrelated issues in your messages above. Your first question, about the coating "working from only one side" and breaking the 2nd law of thermodynamics appeared to be considering whether a coating works the same when light is incident from the air side or from the substrate side. (It does in fact work the same either way.) Your later question appears to be about the unrelated issue of whether coatings should be applied to both sides of a lens. Of course they should. The loss at an uncoated surface is the same whether the light is incident from the air or from the glass. For the most common optical glass, the loss is about 4% per surface. A simple AR coating on both sides of the lens reduces this to about 1% per surface. More complicated coatings can reduce the loss per surface further.--Srleffler (talk) 22:26, 22 September 2008 (UTC)
This last part is interesting and might be useful to add to the article. On the other hand, the focus of the article is on the fact that there is such a thing as anti-reflective coating, how it works, etc., and only incidentally about things like multi-element lenses.
I just had a look at two lenses for my Nicomat camera, one by Nikon which clearly has anti-reflective coatings on both the outer side of the outer end of the compound lens and on the inner side (i.e., the one that is exposed to air inside the camera). A Vivitar telephoto lens for the same camera clearly has a coating on the outside end of the compound lens, but it is harder to be sure that there is a coating on the end that is inserted into the camera. But it is recessed quite a bit, so it is difficult to say for sure. Also, I don't know what corners are cut to make a lens that is 1/5 the price of one by Nikon. I don't have the specs for this lens anymore. P0M (talk) 01:32, 23 September 2008 (UTC)
I believe not mentioned in the article is the 180 degree phase shift on reflection from a higher index of refraction. It happens to both reflections, so cancels out. From the high index side, there is no 180 degree phase shift on either one, so antireflection still works. Also not considered are secondary reflections. As noted above, for thermodynamic reasons it has to work the same both ways. If you go through the math, including secondary reflections, it should do that. The diagram doesn't show the reflection back that is in phase with the transmitted ray, which adds to it, increasing the transmittance. There is no loss with dielectric reflection, so T=1-R. Gah4 (talk) 14:57, 10 January 2016 (UTC)

## German secrecy fact is dubious

The article uses this source to support the fact that anti-reflective coatings were a german secret until 1940. The fact that the Germans were using AR coatings for military uses may have been a secret, but the technology was not. In 1936, Dr. John Strong of Caltech published On a Method of Decreasing the Reflection From Non-Metallic Surfaces. According to this journal (published in 1941), Strong's paper described a vacuum deposition method for AR coatings. It would be handy if a copy of the paper could be found, but I'm having no luck. -Verdatum (talk) 22:06, 10 September 2009 (UTC)

It's not entirely a contradiction. The fact that something is a military secret does not prevent it from being independently discovered elsewhere. Also, it's clear that Strong's 1936 films were too fragile for production use, while the Zeiss article seems to imply that they were actually making binoculars with AR coated lenses. From the article you link, it wasn't until late in 1940 that the Americans were producing films that were durable enough to be practical. This is around the time that the German technology ceased to be a secret. Something about Strong's work should be added to the article, even if a copy of the paper can't be located.
I find it kind of amusing that the Germans were using their new technology for military hardware, while the Americans were using it for movie cameras and production equipment.--Srleffler (talk) 03:47, 11 September 2009 (UTC)

## Figure in "Interference in a quarter-wave anti-reflection coating"

I was wondering if the figure in the section "Interference in a quarter-wave anti-reflection coating" is misleading. It shows that the thickness of the coating is lambda/4 and the lambda is the wavelength of the incident wave in the air. However, the wavelength of the wave inside the coating is not lambda. It is less than lambda because the wave now is in a different medium than air. The thickness of the coating should have been (1/4) of the wavelength of the wave inside the coating. Am I right? I am not sure. Someone with knowledge of anti-reflective coating should check this. Thanks. — Preceding unsigned comment added by 165.91.183.249 (talk) 21:24, 28 May 2011 (UTC)

Well, the lambda ${\displaystyle \lambda }$ symbol represents the wavelength of light, but doesn't neccessarily specify the wavelength as being in air, vacuum, or some other medium. The refractive index of the coating also has to be taken into account, and so does the angle of incidence and the color of the light. A ${\displaystyle \lambda }$/4 (wavelength/4 or 1/4 wavelength) coating means that the thickness of the coating is 1/4 of the wavelength of the light that the transmission is centered on, taking into account that the wavelength is shorter in a higher refractive material. For multiple coating stacks, the refractive index of each layer must also be taken into account, because the center-wavelength will shift in each of them. Not only that, but the desired angle of incidence must also be taken into account. For an AR coating with a 0 degree angle of incidence the coating will be thicker than a coating centered on the same wavelength but at a 45 degree angle. Zaereth (talk) 03:40, 29 May 2011 (UTC)

This point should be made clear in the article itself and not in the discussion section. — Preceding unsigned comment added by 128.227.117.247 (talk) 21:01, 3 February 2012 (UTC)

## history of multi-coating

I remember when Pentax (Asahi) introduced the first multi-coated lenses in the early '70s, under patents from an American firm (whose name I forget). (That alone is remarkable, that a Japanese firm would license American patents to manufacture someithing it hadn't invented.) There were people who said it couldn't possibly work. This bit of history ought to be included. WilliamSommerwerck (talk) 15:16, 25 August 2011 (UTC)

Well, according to the book Thin-film optical filters, W. Geffken created the first interference filters, using multi-layer stacks, back in 1939. The book says nothing about the first multi-layer stacks in AR coatings. (It does say that Joseph Fraunhofer created the first intentionally produced AR coatings back in 1817, but that was a single layer.) It seems to me that 30 years would be a long time between multi-layer filters and AR coatings, but stranger things have happened. While I don't doubt your memory, what we'd really need is a reliable source so Wikipedia can verify the information. I don't have time to research it right now, but if you can find something, I'm sure it would make a wonderful addition to the article. Zaereth (talk) 16:29, 25 August 2011 (UTC)
OK, I had a few minutes at break today to do a little research. It appears, according to Applied optics and optical engineering, that Geffken is indeed responsible for creating the first multi-layer stacked AR coarings back in Germany, during World War II. Geffken apparently based his work on Thelen's theoretical designs, coming up with the standard quarter-half-quarter design. I hope that helps. Zaereth (talk) 18:20, 26 August 2011 (UTC)

## Invention

Regarding the edit war today: if AR coatings were invented in Germany by a Ukrainian expatriot, that would be sufficient to list them as both a Ukrainian and a German invention. In fact, though, Rayleigh and Taylor predate Smakula by 30 years, so neither tag is appropriate. One could tag it as a British invention, but I think it is more appropriate not to tag it at all. This isn't an article on a single device with a single inventor. It's an article on a type of technology. Different versions of that technology were developed at different times. Ascribing the whole article as an "invention" attributable to a particular country is inaccurate and pointless.--Srleffler (talk) 11:58, 29 April 2013 (UTC)

This needs to be raised at Category talk:Inventions by country and WP:CAT so that we can sort it out for good. These nationalistic invention categories are a POV nightmare and beyond WP's ability to maintain in a neutral and accurate manner. Despite that, I doubt that we can get rid of them. Andy Dingley (talk) 12:13, 29 April 2013 (UTC)
Variations of a single invention that exist in parallel to each-other would properly be categorized on their separate pages (or redirect pages), but I see no reason why standard-setting inventions should be overshadowed by the original (and outdated) idea. I think it is more appropriate not to tag it at all. This isn't an article on a single device with a single inventor. It's an article on a type of technology. Of which every advancement must be acknowledged. G_PViB (talk) 12:26, 29 April 2013 (UTC)
Raised at WP:Categories_for_discussion/Log/2013_April_29#Category:Inventions_by_country Andy Dingley (talk) 12:43, 29 April 2013 (UTC)
I completely agree with Sreffler and Andy Dingley. Have to run now, but here's my preliminary suggestion: All content needs to be verifiable, including category assignments. Thus any challenged categorization requires to be backed up by the article text, with a citation to a reliable, secondary source that explicitly states that XX is a YY invention. See also here and here. — HHHIPPO 16:43, 29 April 2013 (UTC)
This is unnecessary even for cases like this one. G_PViB (talk) 18:38, 29 April 2013 (UTC)
I wouldn't call Wikipedia's core content policies "unnecessary". — HHHIPPO 19:09, 29 April 2013 (UTC)
This is a liberal interpretation of Wikipedia's policies by you. G_PViB (talk) 19:29, 29 April 2013 (UTC)
My exact wording might be a sub-optimal, since hasty, summary. I don't see though how the essence, any challenged statement needs a source, can be interpreted as not imperatively following from WP:V. — HHHIPPO 20:21, 29 April 2013 (UTC)
I tend to agree with Srleffler's assessment. AR coatings were known as far back as the 1700s, although they weren't understood until the early 1900s. In my opinion, if anyone should be listed as the "inventor" of the first process for making one artificially, it should be Fraunhofer, back in 1817. However, it's kind of like trying to pinpoint who invented the car. Was it the person who invented the carriage, the person who added a steam engine, the person who added a gasoline engine, or the person who invented the assembly line. (Many people will say the latter.) It's very difficult to say who "invented" the car as an object, and by which definition of "invent." I think a section detailing the evolution of AR coating would be helpful. Zaereth (talk) 18:56, 29 April 2013 (UTC)
G PViB: Category tags on an article about an area of technology are a poor way to acknowledge every advancement in the field.--Srleffler (talk) 23:19, 29 April 2013 (UTC)
I disagree. G_PViB (talk) 10:25, 2 May 2013 (UTC)
• I see at least three main problems here, neither of which are particularly about verification. They're issues that affect all of these national invention categories, for which we still don't have clear policy.
• What is an "invention"? Is it:
• Discovery? (i.e. empirical observation of the natural effect)
• Theoretical understanding of the principle?
• Invention of a mechanism or device?
• Construction of a practical device?
• Production of a commercial version?
• Can we have one, or more, "invention by country" cats? The scope of the "act of invention" (see above) could be narrower than that of the article, so especially if we permit several "acts" from the list above, we might have several.
• How is nationality defined? Particularly for expatriates (cf. bakelite), is this invention in the country in which it's invented (as I'd suggest) or is it also claimed by the birth country of the inventor, or their claimed citizenship at the time. This seems to be the worst offender for these categories turning into petty nationalism. Andy Dingley (talk) 19:50, 29 April 2013 (UTC)
My personal opinion is that catagorization and nationalism go hand-in-hand. Categories can be great for objects. A category of non-ferrous metals is an awesome thing to find. However, categories should be used very carefully for people, or the next thing you know (and history indicates it always happens), the categories themselves become weapons to label and classify entire groups of individuals for one insideous purpose or another. Zaereth (talk) 20:04, 29 April 2013 (UTC)
Yes, this is one of the severe problems with those categories. Another one: even if we can find and agree on answers to all of Andy's questions, and properly define those categories, the problem remains that the name of each category can't possibly convey such sophisticated definitions, and most readers will not look up the definition but just assume something. Thus, even after adding an exact definition, the categories will be useless at best, and misleading and inviting nationalism at worst.
P.S.: My favorite solution is getting rid of the categories, the above proposal to strictly follow policy is a second best choice while they are there. — HHHIPPO 20:32, 29 April 2013 (UTC)
To Andy Dingley: You've raised a lot of important issues about the definition of invention. I actually don't see the nationality issue as a big problem. I have no issue with saying that an invention by a Ukrainian citizen of Polish birth, working in Germany is attributable to all three nationalities. My objection in this article is that the article is not on the specific invention for which it was categorized, and that invention was not the first one discussed in the article.--Srleffler (talk) 23:19, 29 April 2013 (UTC)
Typically, an "invention" is defined as being a new, completely novel process or device. Using the example of the car again, each new addition along the path of creation was an invention, from the original chariot to the Lamborghini. Many times the same process or device can be invented by different people, independently, without having knowledge of each other. So by modern standards, the inventor is often the person who gets to the patent office first. AR coatings are no different, because there is an entire history behind it, which I actually find fascinating. I think that greatly expanding the history section could help. Then we could include the contributions of people like J. Strong, W. H. Geffcken, A. F. Turner, C. H. Cartwrite, or interesting stuff like the first commercial application in 1939, for the showing of Gone with the wind. I may do this at some point, but don't have time to gather up all my sources today. Perhaps in the near furture... Zaereth (talk) 01:48, 30 April 2013 (UTC)
An invention is anything that would give an advantage over a competitor. I would throw out art movements and recipes, but keep musical instruments, special kinds of brushes (i. e. tools to create new products) and everyday necessities and their regional variations. Sometimes an inventor didn't realize the entire potential of his invention - these kinds of inventions should be treated as discoveries. G_PViB (talk) 10:25, 2 May 2013 (UTC)
As per my usual convention, I will refer to a dictionary everytime when it comes to the actual usage of words, because these are absolutely the most reliabe sources on the words themselves. I do not feel that is incumbent upon us to redefine the words based on what we feel they should mean. Zaereth (talk) 08:56, 3 May 2013 (UTC)
I have found that the definitions given by specialists in their field are often more accurate, than the definitions in a dictionary. G_PViB (talk) 09:39, 3 May 2013 (UTC)
That all depends on whether you're writing for a specialized audience or a general one. Zaereth (talk) 09:45, 3 May 2013 (UTC)
Yes, however, "Invention" is a technical term and I would not trust the dictionary definition of technical terms if there are grounds for a debate about its precise meaning. G_PViB (talk) 09:52, 3 May 2013 (UTC)
Well, I love a challenge of sources, so from Funk and Wagnall's: "Invention (n.) 1 The act or process of inventing. 2 That which is invented: a useful invention. 3 Skill or ingenuity in contriving. 4 Mental fabrication or concoction. 5 In literature or art, creation by the exercise of imaginative powers: poetic invention. 6 In rhetoric, the finding out and selection of topics to be treated, or arguments to be used [like we're doing now]. 7 Archaic A finding: discovery. 8 Law" a The process of devising and producing and independent investigation of something not previously known or existing. b The article, device, or composition thus created."
From Webster's: invention (n.) 1. the act of inventing. 2. U.S. Patent Law. a new process, machine, improvement, etc., that is recognized as the product of some unique intuition or genius. 3. anything invented or devised. 4. the power or faculty of inventing or originating. 5. an act or instance of creating by exercise of the imagination, esp. in art, music, etc. 6. something fabricated, as a false statement. 7. a short contrapuntal musical composition for keyboard instrument.
From US Patent Law: "The definition for inventorship can be simply stated: “The threshold question in determining inventorship is who conceived the invention. Unless a person contributes to the conception of the invention, he is not an inventor."
As a general encyclopedia, we are writing for a general audience, so I believe that the words should be sourceable to the general definitions. However, if you have better sources, which contradict thee one, I'll be happy to review them tomorrow. Zaereth (talk) 10:44, 3 May 2013 (UTC)
See Talk:Nicolaus Copernicus. Sources that do not provide references to the studies that deal with the nuances of an existing debate can be safely ignored. G_PViB (talk) 13:08, 3 May 2013 (UTC)
Wikipedia is not a reliable source, nor do I see the definition you're speaking of on that talk page. I'm asking you to provide a reliable source which defines "invention" under your terms. Zaereth (talk) 16:24, 3 May 2013 (UTC)
However, if you have better sources, which contradict thee one, I'll be happy to review them tomorrow. To me that sounded like a primitive self-defense mechanism, so I've ignored it as well. P.S.: I'm referring to the omission of Nicolaus Copernicus nationality. G_PViB (talk) 16:49, 3 May 2013 (UTC)
Personal attacks will do little to unnerve me. Those usually reveal far more about the attacker than anything else. You issued the challenge and I have met it. Now I'm challenging you to back up your own assertions. Are you able or unable to do that? Zaereth (talk) 16:57, 3 May 2013 (UTC)
It's not a personal attack, it's an observation. [If it isn't so, I apologize.] But, seeing how you had to resort to logical fallacies to win the argument, I was probably correct. G_PViB (talk) 17:57, 3 May 2013 (UTC)
Claiming I'm primitive and resorting to logical fallacies to win an argument constitutes a personal attack. As an observation, your answers have all avoided the question, containing many words like "should" and "probably." I'm still asking for a definite definition. You brought up the idea of the defintion as provided by specialized sources, and I'm still waiting for you to produce those sources. Zaereth (talk) 18:16, 3 May 2013 (UTC)
Once again, have my heartfelt apology if that was a false impression. and "resorting to logical fallacies to win an argument" constitutes a personal attack That - most certainly doesn't. On the fallacy itself - you don't see the fallacy in first requesting a source to invalidate your sources (and failing to understand that it could be invalidated without a source), then requesting me to provide a source as if it is the same thing? You brought up the idea of the defintion as provided by specialized sources Which is justified by us having this debate. G_PViB (talk) 19:56, 3 May 2013 (UTC)
No, I am asking for a source that confirms the definition you originally provided so that I can verify with my own eyes that you're not making it up. (Not accusing, I just prefer verification.) Does that sound like too much to ask? Linguistics is something that really interests me, so if you have other definitions, please let us see them. (On a side note, dictionaries don't just make this stuff up. When working on a dictionary, you have to study the word in every field and every form of its usage. Then you must provide a definition for each usage in terms of syntax and context. by contrast, writing an encyclopedia is a piece of cake.) Zaereth (talk) 20:05, 3 May 2013 (UTC)
My definition was merely a vote. G_PViB (talk) 20:45, 3 May 2013 (UTC)
Oh, ok then, that satisfies my curiosity. Sorry about the misunderstanding. My main concern is that you were introducing a term which has a very specific meaning within a particular field, which would not normally be found in a dictionary (optics and metallurgy are full of these), making it difficult for the average reader to follow the article. Such terms are perfectly valid, and are called "jargon," but these need to be defined within the article for the general reader; the curious layman; etc... Zaereth (talk) 22:08, 3 May 2013 (UTC)

Per BrownHairedGirl's advice, I suggest we continue the general discussion at Category talk:Inventions by country, and put notices on the talk pages where Andy earlier linked to CfD, plus Wikipedia talk:WikiProject Technology. Is that ok? — HHHIPPO 21:45, 29 April 2013 (UTC)

The discussion above is great, but has drifted quite far from what I see as the central issue for this article. That issue is that Alexander Smakula did not invent the antireflection coating, so it is nonsense to tag the article Anti-reflective coating with either the "Ukrainian inventions" or the "German inventions" tags. The presence of these tags on this article implies that anti-reflective coatings were first invented in either Ukraine or Germany, which is false. I propose to remove these tags from the article, and welcome any discussion on that subject. The "British invention" tag is also open to discussion.--Srleffler (talk) 01:00, 3 May 2013 (UTC)

• I agree, as per my above reasoning. It is impossible to pin this technology onto just one inventor, and there is no point listing a category for every country involved. Zaereth (talk) 08:50, 3 May 2013 (UTC)

## Calculus details

I'm going to remove the new "calculus details" section, for the following reasons:

• The article has a theory section, and this material belongs there.
• The new section is partly redundant with the existing theory section.
• To the extent that the new material is not redundant, I don't see an easy way to work it into the existing theory section.
• The new section treats interference without considering or even mentioning the phase of the waves.
• Wikipedia is not a textbook

--Srleffler (talk) 07:23, 27 November 2014 (UTC)

### Copy of removed section

If the name ${\displaystyle n_{o}}$ is given to the incident index, ${\displaystyle n_{g}}$ to the index of the glass to be covered, and ${\displaystyle n_{l}}$ to the index of the layer used, to have optimal destructive interferences, the 2 reflection coefficients are calculated as:

• for the reflection on the layer surface:

${\displaystyle r_{1}={\frac {n_{o}-n_{l}}{n_{o}+n_{l}}}}$

• for the reflection, on the glass, the coefficient is:

${\displaystyle r_{t}=\left({\frac {2*n_{o}}{n_{o}+n_{l}}}\right)*\left({\frac {n_{l}-n_{g}}{n_{l}+n_{g}}}\right)*\left({\frac {2*n_{l}}{n_{o}+n_{l}}}\right)}$ which takes into account the 2 transmissions and 1 reflection.

To completly destroy the reflected beam, the 2 coefficients must be equal: ${\displaystyle r_{1}=r_{t}}$ which leads to ${\displaystyle n_{l}^{3}+(4*n_{o}+n_{g})*n_{l}^{2}-(4*n_{o}*n_{g}+n_{o}^{2})*n_{l}-n_{o}^{2}*n_{g}=0}$

A simpler way to treat the problem is to neglect the transmissions, which leads to: ${\displaystyle {\frac {n_{o}-n_{l}}{n_{o}+n_{l}}}={\frac {n_{l}-n_{g}}{n_{l}+n_{g}}}}$ which is solved in ${\displaystyle n_{l}={\sqrt {n_{o}*n_{g}}}}$

## Figure

The figure titled "Interference in a quarter-wave anti-reflection coating" appears to not show the correct phase change upon reflection. The phase flips 180 deg when reflecting from low to high index. This occurs in both reflections here, so both reflected waves appear 180 deg off. [1] 199.46.200.230 (talk) 16:59, 6 January 2016 (UTC) TJ

The figure is correct. Both reflected waves cannot be 180 degrees out of phase. One must be 180 degrees out of phase with the other, which is what the figure depicts. If they were both 180 out, they would both in fact be in phase, and, thus, reflection would be doubled instead of eliminated. To achieve that you need a half-wave coating. Zaereth (talk) 22:03, 7 January 2016 (UTC)

I believe is right. Both R1 and R2 should be 180 degree phase shifted, such that they still cancel. This is the case when the left material has a lower index of refraction. The diagram would be right if the left material had the higher index of refraction, but then it would not normally be ${\displaystyle n_{0}}$. Also, it is usual to use r and t for amplitudes, R and T for intensities. Gah4 (talk) 07:12, 1 August 2017 (UTC)

Hello fellow Wikipedians,

I have just modified 3 external links on Anti-reflective coating. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

As of February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required regarding these talk page notices, other than regular verification using the archive tool instructions below. Editors have permission to delete the "External links modified" sections if they want, but see the RfC before doing mass systematic removals. This message is updated dynamically through the template {{sourcecheck}} (last update: 15 July 2018).

• If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
• If you found an error with any archives or the URLs themselves, you can fix them with this tool.

Cheers.—InternetArchiveBot 08:19, 7 July 2017 (UTC)

## Air

There is a revert concerning the use of AR coatings other than interfaces with air. It would seem that they could be used with water-glass or oil-glass interfaces with immersion microscopy, but I don't see any evidence of the use. Even more, in confocal microscopy, where light is coming in through the same lens, and the reflection could be more problematic. As I have no evidence of such use, I won't change it, but it would be interesting to know if there were some uses other than air. Water at 1.33 is probably different enough from glass to make a reasonable reflection. Gah4 (talk) 07:17, 1 August 2017 (UTC)

I've never heard of it, but that doesn't mean they don't exist. Most dye lasers use Brewster's angle rather than coatings to reduce reflections. Some microscopes use index-matching fluids, that equal the refractive index of the glass, to eliminate reflections. Liquids generally have a refractive index close to, or sometimes greater than glass or plastic substrates, so the normal reflection is usually much lower tan the air-to-glass interface. (Cassia oil has probably the highest refractive index of any natural liquid, of 1.62, nearly matching that of lead glass, but most oils are in that 1.4--1.5 range.) For these reasons it is unlikely tat the benefits of such a coating would outweigh the cost. Zaereth (talk) 08:40, 1 August 2017 (UTC)
Reminds me of some year ago when I was trying to find high index liquids. The ones I remember are iodized hydrocarbons. It seems that diiodomethane is 1.741, tri and quad might be higher. But I suppose that isn't natural. It might be that sometimes there is a need for water, but otherwise it does seem that coatings are usually used with air interfaces. Gah4 (talk) 09:29, 1 August 2017 (UTC)
Yeah, the refractive index is linked to the polarizability of the substrate, and that is also linked to the cohesive forces that turn a liquid into a solid. I've seen artificial liquids that go above 1.8. For relatively low-cost, natural liquids, though, it's mostly the essential oils that go higher than 1.5. (Cedar oil is 1.52, clove oil is 1.53, anise oil is 1.56, cinnamon oil is 1.58, etc...) The drawback is that they often leave whatever you're testing with a very strong odor, but the difference is typically a few hundred dollars per ounce. On the other and, most solvents, like ethanol, methanol, isopropyl, hexane, cyclohexane, etc., have indices very close to that of water. These are often used in dye lasers, yet I've never seen specialized coatings for them. Zaereth (talk) 09:52, 1 August 2017 (UTC)
Hi Gah. I reverted it. My main concern was to keep the explanation of the simplest interference coating simple and clear, for readers new to the concept. I don't doubt that glass-liquid AR coatings exist, but this is at best an uncommon application. The text now does mention that the described coating is for use in air.--Srleffler (talk) 11:56, 1 August 2017 (UTC)