Students at the University of Rochester have developed a clever optical system which allows for limited invisibility thanks to a bit of optic
Almost all invisibility technologies work by taking light and passing it around the object as if it were never there. The problem is, a lot of these methods are very expensive and not very practical — and don’t even work if you change your perspective from a head on view.
[Joseph Choi] figured out you can do the same thing with four standard achromatic lenses with two different focal lengths. The basic concept is each lens causes the light to converge to a tiny point in between itself and the next lens — at which point it begins to diverge again, filling the following lens. This means the cloaked area is effectively doughnut shaped around the tightest focal point — if you block the center point of the lens, it won’t work. But everything around the center point of the lens? Effectively invisible. Take a look at the following setup using lasers to show the various focal points and “invisibility zones”.
Pretty cool stuff — let’s see someone in our community make one! Any cool applications come to mind? It’d be quite fun with giant lenses, but we think that would probably get quite expensive pretty fast…. More info can be found in their paper on Paraxial Ray Optics Cloaking.