Indirect "Ghost imaging" of objects...?

[favalora]

According to Physical Review Focus, a paper in Phys. Rev. A reports:

Under special optical arrangements, physicists can create an image of an object using light that has never interacted with the object. This "ghost imaging" has been around for more than a decade, but it has yet to find much practical use. That could change now that researchers have generated a ghost image of an opaque object, as described in the April Physical Review A.

The paper abstract says,

A CCD array is placed facing a chaotic light source and gated by a photon counting detector that simply counts all randomly scattered and reflected photons from an object. A “ghost” image of the object is then observed in the gated CCD. Differing from all published ghost-imaging experiments, this setup captures ghosts from scattered and reflected light of an object, instead of the transmitted ones. This new feature is not only useful for practical applications, but is also important fundamentally. It further explores the nonclassical interference nature of thermal light ghost imaging.

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You can see an image here. Does anyone understand this?

By the way, I was directed to this by http://www.geekpress.com.

This seems to be a completely different thing than Stanford's Dual Photography, whose video (bottom) is worth a look if you've never seen it.

-g

[yuzirneym]

Hello,
Ghost imaging is a clever but very simple idea. If you take a spatially-incoherent beam and split it into two with a 50/50 beamsplitter, you'll get two individually incoherent, but strongly cross-correlated beams. Now if you detect them separately and correlate the photocurrents (it's called coincidence counting in quantum mechanics, but it's a photocurrent correlation), you can measure that cross-correlation. If the coherence length is narrow, then you can put a mask in one arm, and get a high resolution image of the mask from the cross correlation. Nonclassical light offers high contrast images (with classical light, the image is embedded in a prominent background, but with a pair of entangled photons you can essentially get backgroundless images).

As for the arguments about nonlocality and lack of a classical explanation for ghost image formation with thermal (chaotic) light, it is simply not true. Semiclassical photodetection theory and statistical optics is sufficient to explain ghost imaging with thermal light.

[favalora]

Hi -

Thank you for that thoughtful explanation! I am surprised that I hadn't heard about this a long time ago.

-Gregg

[Tom B.]

(Standard disclaimer) I claim no expertise on this topic but ...

It kind of reminds me of "Intensity interferometry" as first used in astronomy and later in quantum optics applications. Brief
intro here: http://en.wikipedia.org/wiki/Hanbury-Br ... iss_effect