'Darkness Ray' Beams Invisibility From a Distance

KentuckyFC writes "Optical engineers generally build imaging systems with the best possible resolving power. The basic idea is that an imaging system focuses light into a pattern known as a point spreading function. This consists of a central region of high intensity surrounded by a concentric lobe of lower intensity light. The trick to improving resolution is narrowing and intensifying this central region while suppressing the outer lobe. Now optical engineers have turned this approach on its head by suppressing the central region so that the field intensity here is zero while intensifying the lobe. The result is a three-dimensional beam of darkness that hides any object inside it. The engineers say this region can be huge — up to 8 orders of magnitude bigger than the wavelength of the imaging light. What's more, the optics required to create it are simple and cheap: a lens consisting of concentric dielectric grooves. The team has even tested a prototype capable of hiding a 40-micrometre object in visible laser light."

Babinet called, wants his principleback.

[goombah99]

I think they must have skipped the chapter in their basic handbook of optics called Babinet's principle. Because they just re-invented Babinet focusing.

Please move on. There is nothing to see here ;-)

[140Mandak262Jamuna]

It has been easy to make objects invisible from time immemorial. Even though till about 14th century people did not really understand vision, and they thought some kind of rays emanate from the eyes that allows them to perceive it, they knew how to make objects invisible. Just turn the light off. Put it in a dark room without light, and no one can see it!

The technique here is a marginal improvement for practical purposes. There is a light in the room, still you can't see the object, objects that could be as much as 8 wavelengths of that monochromatic light, placed at the correct location. If there is any other source of light, the objects would be plainly visible due to scattering of that light. So it would be impractical to make an invisibility cloak out of it. You need to make the object disappear from all sources of light from all directions.

Though the technique is not going to lead to invisibility cloak, it is probably a great achievement to hide an object when there is one light source. Though people would think is 1 is pretty close to zero, in reality, there is a huge difference between 1 light source and no light source. It is a good great achievement, collect your brownie points scientists.

For others, please move on there is nothing to see here.

references

[goombah99]

Here's some recent articles on the topic of shaping light beams so it curves or has extended focal range or dark spots

by the way the "lightning" redirection problem we originally of interest not as a weapon but to create virtual lightning rod arrays in the air to discharge destructive lightning harmlessly. Why? well back then there had been a few great arpanet outages and people realized how vulnerable we were ebcoming to lightning stikes as we depending on the ubiquitous internet to always be able to route around problems. turned out this was a weak point. I suspect it may have become less of one now in part because optical fiber now carries stuff. But I don't know. But it was the utility companies paying for the research at the time.

lightning weapon using self filamentation:
http://www.army.mil/article/82262/Picatinny_engineers_set_phasers_to__fry_/ [army.mil]

curving light "beams"
http://www.newscientist.com/article/dn16936-curved-laser-beams-could-help-tame-thunderclouds.html [newscientist.com]

forming a pseudo non-diffrating "beam" --- which is a totally wrong way to describe this.
http://www.mtu.de/en/technologies/engineering_news/others/Menges_Forming_non-diffracting_beams_en.pdf [www.mtu.de]

that too was applied to the lighning problem

even a slashdot articlee referencing that:
http://science.slashdot.org/story/09/04/15/0147234/curved-laser-beams-could-help-tame-lightning [slashdot.org]

a patent:
http://www.google.nl/patents/US6937791 [google.nl]

Re:references

[goombah99]

"forming a pseudo non-diffrating "beam" --- which is a totally wrong way to describe this."

Hum... Why?

Imagine you took a lens, bored out the center and put another lens in the middle with a different focal length. now you shine a beam of light through this. what happens in the far field is you get two focal spots. You might have been thinking one would be a donut, but as Babinet will tell you, that donut part disappears in the focal region.

  This is the crude, but easy to visualize, version of what these investigators did. One can do this more cleverly. Add more focal spots by adding concentric rings of different focii. in fact if you just make a really bad fresnel lens where you have constant curvature on each lenslet ( picture a triangle wave in glass) then you get an array of spots.

An axicon is just continuous limit of that discrete process.

it creats what looks like a beam that never difracts. but in reality is is just a bunch of separate focal spots that have merged in to a line giving that appearance.

why is this not a beam: None of the photon the form the first spot in the line actually pass through last spot. infact if you block the first spot in the "beam" it doens't stop the "beam" !