What Determines the Direction of Twist in Helical Wavefronts?

[jby]

Have you guys heard of this:

http://www.sciam.com/article.cfm?chanID=sa006&colID=5&articleID=0001A73A-45BC-1F7F-82D883414B7F0000

 

[jcsd]

No, I hadn't, I know light has spin angular momentum, but I never realized it had orbital angualr momentum too.

 

[Jonathan]

Yes! I just got that, I had never heard of it before. I'm planning to do as the article says and go get the diffraction grating from that website one of these days. Edit: I just went to the page and see that it doens't have the whole aricle, I just assumed it did...

 

[quantumdude]

The entire article was not available, but here are some info sites on the subject:

http://www.aias.us/pub/OAMLight/oamlight.html

It also has links to 2 research groups.

Here are some articles from the Los Alamos arXiv:

http://arxiv.org/PS_cache/quant-ph/pdf/0308/0308093.pdf
http://arxiv.org/PS_cache/quant-ph/pdf/0111/0111112.pdf
http://arxiv.org/PS_cache/astro-ph/pdf/0307/0307430.pdf

 

[bdkeenan00]

so the photon as linear momentum(P=E/c),spin(intrinsic angular momentum),and now we find out it has orbital angular momentum. Is there any other momenta associated with a photon?

P.S.
What does intrinsic mean anyway?

 

[jcsd]

Originally posted by bdkeenan00
so the photon as linear momentum(P=E/c),spin(intrinsic angular momentum),and now we find out it has orbital angular momentum. Is there any other momenta associated with a photon?

P.S.
What does intrinsic mean anyway?

Instrinsic means that it is a fundmanetal property of the photon, i.e. all photons have a spin quantum number(s) of 1 which is related to the spin angular momentum by:

√s(s+1)h/2π

As far as I'm aware, there are no other sorts of angular momentum other than those described associated with the photon (excpet for things like total angualr momentum which is the sum of spin and orbital angular momentum).

 

[eigenguy]

Where are you guys getting the idea that we didn't know that light has orbital angular momentum?

 

[jcsd]

Originally posted by eigenguy
Where are you guys getting the idea that we didn't know that light has orbital angular momentum?

No, it was just that I didn't know light had orbital momentum.

 

[bdkeenan00]

Originally posted by jcsd
Instrinsic means that it is a fundmanetal property of the photon, i.e. all photons have a spin quantum number(s) of 1 which is related to the spin angular momentum by:

√s(s+1)h/2π

As far as I'm aware, there are no other sorts of angular momentum other than those described associated with the photon (excpet for things like total angualr momentum which is the sum of spin and orbital angular momentum).

Thank you

 

[Swamp Thing]

The forked grating at http://departments.colgate.edu/physics/research/optics/oamgp/gp.htm

does not seem to have any assymmetry that would decide the direction of twist. What then determines whether the helical wavefront is right or left handed?

[Edit: The Sci Am article referred to in the original post contains a link to the site mentioned here. The page contains a grating pattern that let's anyone create "twisted" light using a laser pointer.]

 

[dlgoff]

does not seem to have any assymmetry that would decide the direction of twist. What then determines whether the helical wavefront is right or left handed?

quote from paper:

If we calculate the interference pattern generated by combining LG00 and LG0+1...

What would the pattern look like if it is generated with the left handed LG0-1? It must be something like a negative image.