Talk:Optical rotation

Untitled

Fixed: The discussion regarding invert sugar contains several errors. Levulose is another name for fructose, not sucrose. Sucrose, like glucose, is dextrorotatory (rotates the plane of polarization to the right). Fructose (levulose) is even more strongly levorotatory than glucose is dextrorotatory. Thus, an equal mixture of glucose and fructose (such as would be produced by hydrolysis of sucrose) will rotate polarization to the left. The term "invert sugar" for such a mixture does indeed derive from the change in rotation that accompanies the hydrolysis, but the change is from right to left, not left to right.

This article was not general enough (mainly giving a chemist's view of optical activity). I have edited it and added a physical explanation of the phenomenon.--J S Lundeen 19:00, 1 April 2006 (UTC)

Thanks for the expansion. Good to have this info! DMacks 16:40, 3 April 2006 (UTC)

Thanks for the correction. I am going to link to the invert sugar article, and link it here, to the benefit of both. --AJim (talk) 06:27, 2 January 2009 (UTC)

All individual molecules rotate plane poalrised light even non-chiral ones

I don't think that this is explained anywhere as far as I can see.

For non-chiral molecules the net effect cancels out the individual rotations thus no net rotation, just as is the case for a racemic mixture.

This info should be added somewhere. This is explained quite well in ("Organic Chemistry" by Morrison and Boyd) --Stolen Vehicle (talk) 17:31, 8 July 2013 (UTC)

Need to clarify - is Faraday effect a special case of optical activity, or distinct from it?

I have just edited the lead to distinguish optical activity from Faraday effect, however I am not sure this is valid.

I can gradually rotate plane polarized light using either a chiral material in zero field, or a nonchiral material in nonzero field. Are these both called "optical activity"?

Landau and Lifshitz refer to rotation in zero field as "natural optical activity". --Nanite (talk) 13:03, 6 December 2015 (UTC)

The terms are used separately for one or the other (so I think your edit was wrong, which I'll change), but they both result in circular birefringence (=rotation of plane of linear polarization) proportional to length of travel. From that alone you couldn't distinguish one black box from the other. But one distinction between the two black boxes is that optical activity will rotate the plane of polarization clockwise (or ccw) equally whether the beam is going to the left or right (or any direction actually) whereas the Faraday effect has opposite rotation between the two. Which is why it can be used for an optical isolator. Interferometrist (talk) 13:44, 11 December 2015 (UTC)

And I have never never heard the term "Natural optical activity" and will remove it. I appreciate that you read this terminology in a RS but it isn't a mainstream usage of the term. Interferometrist (talk) 13:53, 11 December 2015 (UTC)

Looking at this a bit futher, I now see that the name of the article is "Optical rotation" which is said to be synonymous with "Optical activity." But maybe not? I think the page should be named optical activity, the more common term, and then this would be clear. Unless someone finds usage of "Optical rotation" (in a RS!) different from optical activity, I will take them to be the same, and thus separate from Faraday rotation.Interferometrist (talk) 14:35, 11 December 2015 (UTC)

Thanks for checking my edit. Indeed there is also the term "circular birefringence" you mentioned. There should indeed be some reliable sources that clarify the distinction (is it true that circular birefringence == optical activity == optical rotation ?).

On a Google Books search for "optical activity" the first thing that came up was Barron's Molecular Light Scattering and Optical Activity. In the Preface, it seems he is saying:

• Faraday discovered something called "magnetic optical activity".
• A system is "optically active" if it can rotate the plane of linear polarization of light (if it can cause optical rotation), however,
• There are a wider class of "optical activity phenomena" that are all traced to a material treating left- and right-circular polarized light differently.
• If a substance is optically active without external influence (magnetic or electric fields) it is said to have "natural optical activity". Otherwise all materials are optically active in magnetic fields.
• In the book the term "circular birefringence" seems to be used only rarely.

In such a viewpoint, optical activity encompasses a wide class of effects: Faraday effect, chiral materials, circular dichroism, optical rotation, Cotton effect, etc....

Optical rotation is a then specific effect only for linearly polarized light, and I infer that he includes both reciprocal (chiral) and nonreciprocal (Faraday) rotation of polarization as "optical rotation".

But I am not sure if this is universal, so it's worth checking out more RSes. I imagine one problem is that there are two communities with only a little overlap. Semiconductor physicists will mainly talk about Faraday effects and chemists will mainly talk about optical rotation of their chiral compounds.--Nanite (talk) 16:04, 11 December 2015 (UTC)

Well thank you very much for your research and finding this! Indeed if this is standard usage, then my edit to the lede was somewhat in error and we need to correct the use of terminology (though there is a separate article on the Faraday effect so I think the topics should still be divided rather than overlapping beyond mentioning the common aspects). And yes, I will look further in our optics library. But I am quite sure that "Natural optical activity" is not really in use (though there should be such a term if "optical activity" is indeed so broad). We can both look further and get back to the matter of symantics  :-) Interferometrist (talk) 18:12, 11 December 2015 (UTC)

Update: I randomly grabbed several general optics books in our library and looked up optical activity in the index. 5 had an entry. Of those, I was surprised to see one also include the Faraday effect within the section and even used the phrase "Natural optical activity". The other discussed Faraday rotation separately or not at all and didn't use that surprising phrase. This isn't enough to get a good handle on the usage patterns. I do not believe that "optical activity" includes Faraday rotation according to general usage. But I'd say that if we find additional usage of that sort, then these terminologies should be mentioned as a linguistic note. But not if it's only in obscure instances (that was a very old book).

Thanks for doing the research. :) Indeed there are two usage patterns. In one camp you'll see sentences like "In contrast to optical activity the Faraday rotation is a non-reciprocal ...", and in the other camp you'll see things like "Unlike natural optical activity, the Faraday effect is ...". In any case, the phrase "natural optical activity" is far less used (7500 google hits) than the term "optical activity" (435000 hits) or "faraday effect" (160000 hits). OTOH, the searches do reveal what I suspected, which is that most discussion about optical activity is by chemists, whereas discussion about faraday effect is primarily done by physicists. And discussion of both is not common -- a google search for both "optical activity" and "faraday effect" yields 10000 hits. --Nanite (talk) 13:35, 17 December 2015 (UTC)

Also, on a different subject, it occurred to me that there is one other important case of optical activity that isn't currently even mentioned: liquid crystals. Even though I spend at least 12 hours a day starring at a computer monitor whose every pixel is controlled by the degree of polarization rotation in a liquid crystal! I suppose chiral liquid crystals should be added to this article as they DO appear to conform to the definition of optical activity (which excludes Faraday rotation, according to my current understanding of the terms). Interferometrist (talk) 17:18, 15 December 2015 (UTC)

There seems to me to be something missing here. Please correct me if I am wrong. Putting aside induced optical activity, there are other sources of optical activity than you seem to be discussing. The chirality article, for instance, seems to focus on chemical enantiomers, that is the intrinsic optical activity which occurs wherever molecules have mirror images. It is a bit more obscure, but there is another way to get optical rotation. You touch upon it when you mention liquid crystals, above. Secondary structure, most notably helical structures, will produce optical activity because the helices can be right or left handed. Look at the circular dichroism article, for instance. CD has biochemical relevance because of the helical structures that occur in proteins and nucleic acids. Do you agree that there is more to be said? AJim (talk) 02:52, 16 December 2015 (UTC)

That's very true. My guess is that the criterion is that the material only has to be chiral at a sub-wavelength level, and this need not be at the molecular level. Another example, lately there is a trend in the metamaterials research community to produce optical activity in artificial structures. If you shine light through a bag full of drywall screws, we wouldn't call it optically active for visible light, but doubtless it is optically active for microwaves. --Nanite (talk) 12:41, 17 December 2015 (UTC)

Relation to Waveplate

Is any relation between Optical rotation and Waveplate? Anyway, it is similar and must be noted each other. --Nashev (talk) 10:11, 16 November 2017 (UTC)

LCD and modern tv/monitor

"used in most modern televisions and computer monitors" or maybe not (see LED/OLED/Plasma/etc.) — Preceding unsigned comment added by 62.1.209.51 (talk) 11:52, 1 November 2020 (UTC)

Proposed merge of Dextrorotation and levorotation into Optical rotation

significant overlap fgnievinski (talk) 03:39, 13 April 2021 (UTC)