'Darkness Ray' Beams Invisibility From a Distance 86
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."
Re: Babinet called, wants his principleback. (Score:4, Insightful)
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.
By the way, an insightful thing to ponder here is, what happens to the light rays that were aiming for the center? (yes you can use a ray-optic basis set and still have interferrence). Well they were not in the beam! In a plane wave basis set, you would say, well all the plane waves with that K-vector were missing. Thus it's really simple to figure out how to create a dark spot. Just take an axiconically focused beam. Delete all parts of the axicon which focus in the dark region and replace them with any part of the axicon that focuses outside the dark region. Bam. that's it.
Did this myself a decade ago when I wanted arrays of dark spots in focused light. Why would I want that? I was trying to get the same effect as self fillamentation. but without non-linear effects in the media. That way I could create long arrays of ionized spots in the air, and use this to direct lighting beams.
Recently the military created a lightning weapon based on this.
But axicons and babinets prininciple this has been known for centuries.
Re:Invisibility cloak! (Score:4, Insightful)
Re:references (Score:4, Insightful)