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First Picture of an Atom's Shadow (nationalgeographic.com)
70 points by loki_dx 1607 days ago | hide | past | web | 14 comments | favorite

This may be a dumb question but what does the shadow fall on for the scientists to take a picture of it? If is is landing on the 'lens' then wouldn't 'silhouette' be a more appropriate term?

As far as I understand all matter is made of atoms so at the atomic level there wouldn't really be matter (wall, ground etc.) for the shadow to be cast on.

Amazing nonetheless.

It took a little googling. Here's a potential answer.

The paper the article is based on talks about "absorption imaging". Googling that I found another paper [1] in ArXiV which describes the method a little bit: "absorption imaging, where the attenuation of a laser beam passing through an atom cloud is measured, is the workhorse of ultracold atom experiments. The shadow cast by the atom cloud onto the CCD allows an estimation of the atomic column density."

And if I understood correctly, a CCD is a "charge-coupled device" [2], sort of a digital camera. And that's where the shadow falls.

[1] http://arxiv.org/pdf/1101.4206v2.pdf [2] http://en.wikipedia.org/wiki/Charge-coupled_device

Actually, if you're curious, there's matter that isn't made of atoms, such as neutrinos.

The article uses 'shadow' in the sense of: region of less light behind an object. But actually, at this small scales the wave nature of light becomes quite important, since for an object smaller than the wavelength the distortion of the light wave is damped exponentially on an scale of the wavelength. So I think the word shadow is as appropriate as silhouette, since both somehow imply light rays ( and are therefore a rather loose usage on the meaning of the words).

The paper at arXiv: http://arxiv.org/abs/1201.5280

These are terrible, but really funny https://www.youtube.com/watch?v=KUFkb0d1kbU

So, what do we actually see on the photo? Is the black dot a shadow of the nucleus or a shadow of the electron shell? And these ripples are effects or the wave properties of light?

I'd also be curious about the effects of diffraction and whether the atom appears as a sphere. If so, can we expect to see a Poisson spot, which a bright spot in the middle of the shadow caused by constructive interference?

Actually it appears to be the spatial pattern of absorption of around 6 million photons. So technically it is a shadow, but it's not like you are flashing an atom from the right and taking a picture from above. I'd like to know more about Fresnel lens aberrations to have an opinion about the feasibility of such a measure.

Interesting. When I read the title, I was curious about the practical use of that photo until I read that this would lead to study DNA inside living cells.

I don't quite understand the how nor the consequences. How does this compare to crystallography?

You could use this for things that don't crystallize. It might even be easier to reproduce than crystallizing for things that can.

reminds me of Dune II

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