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Je crée ce fil destiné à recevoir tout ce qui concerne les sciences sans pour autant rentrer dans un des fils existants : articles à partager, anecdotes, curiosités, expériences, images, animations, conseils de lecture... Si un sujet venait à s'enrichir, il sera toujours possible de le déplacer ou de créér un nouveau fil.


Le titre de ce fil fait référence à la taverne du forum (pour l'aspect fourre-tout) et au site éponyme, qui agrège des contenus divers : blogs, podcasts, etc.

  • Yea 3

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J'ouvre le bal avec ce thread de John Baez :


An "optical vortex" is a beam of light that turns like a corkscrew as it moves. It's dark at the center. There's one type of optical vortex for each integer m.

You can use an optical vortex to trap atoms! They move along the dark tube at the center of the vortex.

(1/n) EQBco65UcAA6kIt.jpg
Photons have spin angular momentum, and in circularly polarized light this equals +1 or -1. An optical vortex is different: it exploits the fact that photons can also have orbital angular momentum!

So, some hotheads call an optical vortex a "photonic quantum vortex".

But you can study optical vortices without quantum mechanics, using the classical Maxwell equations!

The electromagnetic field is described using a complex function that in cylindrical coordinates is exp(imθ) times some function that vanishes at r = 0: the dark center.

(3/n) EQBilzhUUAA5Ilo.jpg
The phase of the electromagnetic field, exp(imθ), is undefined at the center of the optical vortex. It turns around m times as you go around the vortex. So this number m has to be an integer. It's a simple example of a "topological charge".

People make optical vortices using many different technologies, including spiral-shaped pieces of plastic, "computer-generated holograms", and computer-controlled liquid crystal gadgets called "spatial light modulators".

(5/n) EQBnCobU4AAtkaS.jpg
For more, try this:


The scary formula came from a nice article on Gaussian beams of light:


All pictures came from Wikicommons!

(6/n, n = 6)


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Ca fait moins flipper que Jurassic Park, en tous cas.

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