Talk:Orbital angular momentum of light

OAM and SAM

What absolutely bothers me to no end: Spin is something I attribute to fermions. Orbital angular momentum I attribute to bosons. In the context of quantum mechanics these words differentiate between half-integer and integer spins. What is, quantum mechanically speaking, the property that induces electron excitations? SAM or OAM???? It is entirely unclear from this article. "If {\displaystyle m=0} m=0, the mode is not helical and the wavefronts are multiple disconnected surfaces, for example, a sequence of parallel planes (from which the name "plane wave")." "Plane waves" as everyone understands them are a superposition of m=-1 and m=+1 (spin angular momentum) states; a transversal oscillation travelling in a single plane. These m=0 plane waves here, might also be called plane waves, but it is certainly not where the word "plane wave" comes from. That's a bold lie, confusing people for no good reason. — Preceding unsigned comment added by 129.69.48.75 (talk) 08:30, 19 August 2019 (UTC)

Proposed merge with Optical vortex and Vortex laser beam

See Talk:Optical vortex for discussion on this point. — Preceding unsigned comment added by Tyharvey313 (talk • contribs) 17:43, 2 July 2018 (UTC)

OAM: only a beam of light?

Is the opening statement of "The orbital angular momentum of light (OAM) is the component of angular momentum of a light beam that is dependent on the field spatial distribution, and not on the polarization", limiting in its definition? Doesn't a single photon have OAM (and also polarization) that could be independent of a collection of photons (beam) it's traveling with? The opening statement, and article in general, seems to suggest OAM is specific to a beam of multiple photons. PizzaAddict (talk) 23:49, 15 March 2015 (UTC)

How does one impart OAM on light?

...the answer to this is strangely missing from the article (or I can't easily find it through all the math). Maybe it deserves it's own section? --Osndok (talk) 17:03, 17 March 2014 (UTC)

Actually it is extremely simple. You can even do this experiment at home if you have two laser pointers!

First, in order to have "angular momentum" you need to define an origin, so call a point in your room "the origin." Now turn on one laser (assume its a nice 0,0 gaussian beam etc.) and aim it directly at that point. Of course your laser doesn't have any OAM (or spin, if it's linearly polarized). Now set up the other laser to the left of the first one and also aim it for the origin. It also doesn't have any OAM. Turn both lasers on together (so their beam centers cross at the origin) and you still have no AOM of course.

Now here is the highly technical part. You offset the left laser so it passes just above the origin, and the right laser so it passes just below the origin. To get "OAM" you take the bold step of calling all of that light "one beam". Voila! And as the article explains, all of the AOM (by symmetry) in this case is "internal".

Now that you've performed this cutting-edge experiment, I hope you (and the fans of this page) can appreciate just how banal the "discovery" of OAM was, and how you can use this revolutionary concept to apply for research funding :-) Interferometrist (talk) 15:18, 17 July 2014 (UTC)

Requested move

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

The result of the proposal was Move Mdann52 (talk) 18:04, 8 July 2012 (UTC) (non-admin)

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• Light orbital angular momentum → Orbital angular momentum of light
• Light spin angular momentum → Spin angular momentum of light

– Wording more clearly identifies concept hierarchy, avoids placing light as possible grammatical modifier rather than subject. Compare with wording in intros, as well as title of supertopic angular momentum of light. ENeville (talk) 17:56, 30 June 2012 (UTC)

• Support as it avoids the implication this is about a non-heavy angular momentum -- 70.49.127.65 (talk) 04:32, 2 July 2012 (UTC)

• Modification I don't know why I didn't think of this at first, but I suppose it would be more consistent with general naming patterns to have these articles plus angular momentum of light moved to "[X] momentum (light)", with the parenthetical. So that'd be:

• Angular momentum of light → Angular momentum (light)
• Light orbital angular momentum → Orbital angular momentum (light)
• Light spin angular momentum → Spin angular momentum (light)

I don't know what, if any, is the policy is for pulling in a third article for a different turn in naming, but I advance the proposal. ENeville (talk) 17:30, 2 July 2012 (UTC)

Comment I prefer the original proposal over this one. -- 70.49.127.65 (talk) 21:53, 2 July 2012 (UTC)

Comment Those names would suggest that the titles are disambiguated from angular momentum. Since these are rather special cases of the general concept, the first suggestion was more appropriate. (And also the common name by which these concepts are referred to in the literature.)TR 13:38, 3 July 2012 (UTC)

It's worth noting that they are (also) disambiguated from the quantum mechanics meanings, and that the spin and orbital senses are perhaps the primary meanings (per WP:PRIMARYTOPIC) within those terms' namespaces, with the two dab pages showing them as the only actual article titles in occupation of such. (Note, I created one of them, mirroring an existing one). ENeville (talk) 15:43, 6 July 2012 (UTC)

• Support per WP:COMMONNAME.TR 13:38, 3 July 2012 (UTC)

The above discussion is preserved as an archive of the proposal. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Do the Photons with their Orbital Angular Momentum Radiate gravitational Waves?

Can anyone explain to me, that: Do the Photons with their Orbital Angular Momentum Radiate gravitational Waves? From the Wikipedia pages we find that: 1. “ Systems that have nonzero energy but zero rest mass, such as photons moving in a single direction, do not have ‘center-of-mass’ frames, because there is no frame in which they have zero net momentum. They always possess a net momentum magnitude that is equal to their energy divided by the speed of light. 2. The angular momentum of light is a vector quantity that expresses the amount of dynamical rotation present in the electromagnetic field of the light. Indeed, a beam of light, while traveling approximately in a straight line, can also be rotating (or “spinning”, or “twisting”) around its own axis. This rotation, while not visible to the naked eye, can be revealed by the interaction of the light beam with matter, as shown in the figure below: The total angular momentum of light and matter is conserved in time. But there are actually two distinct forms of rotation of a light beam, one involving its polarization and the other its wave-front shape. These two forms of rotation are hence associated with two distinct forms of angular momentum, respectively named (i) light spin angular momentum (SAM) and (ii) light orbital angular momentum (OAM).” From the above statements it appears that a photon moving in straight line with an orbital angular momentum, as shown in a picture in the Wikipedia page, is likely to radiate gravitational waves. What is the opinion of the expert editors? Question from: Hasmukh K. Tank — Preceding unsigned comment added by 117.228.55.242 (talk) 17:19, 6 March 2016 (UTC)

Holograms

Didn't want to add separate section but is this a typo (colored white and the remainder colored white): (from article), pasted under.

These holograms are the phase of the product of the vortex term and a phase-ramp term filtered such that points whose phase is in the lower half of all possible phase values are colored white, and the remainder are colored white. — Preceding unsigned comment added by 95.155.0.6 (talk) 20:29, 27 March 2016 (UTC)

Ohanian

There is a now-classic paper What is spin? Hans C. Ohanian. Citation: Am. J. Phys. 54, 500 (1986); doi: 10.1119/1.14580. that looks at the Poynting vector for both electromagnetism and for Dirac spinors. It shows that the "angular momentum" of both are located in/carried by the region of the beam where the intensity is falling off from the central maximum. I imagine that if one redoes his calculations with OAM, one would find the same results. Is this the case? The point of the Ohanian paper is that the spin of light (SAM) is not some "magical quantity" inherent in photons, but has an actual location where the gradient of the light field is changing. Showing that OAM works exactly the same way might help to demystify both of them. 67.198.37.16 (talk) 18:09, 17 November 2020 (UTC)

Animation of Laguerre-Gaussian beam

The article highlights that a focused Laguerre-Gaussian beam is a common example of orbital angular momentum. Still images sometimes struggle to communicate to the reader the helical nature of the wavefronts. To aid with this, researchers at King's College London have generated a rendered animation of an LG10 mode's intensity profile. We wish to add this to the article and would welcome any comments from the community/editors before introducing this edit.--J.Kingsley-Smith (talk) 18:14, 3 February 2022 (UTC)

https://en.wikipedia.org/wiki/Wikipedia:Be_bold

Be bold! — Preceding unsigned comment added by 49.199.247.57 (talk) 09:44, 20 April 2022 (UTC)

A focused Laguerre-Gaussian beam exhibiting orbital angular momentum through its helical wavefronts. The red/blue color indicates the positive/negative electric field.

— Preceding unsigned comment added by J.Kingsley-Smith (talk • contribs) 18:14, 3 February 2022 (UTC)