Materials such as clouds, milk, candle wax, and even thick paint all have one thing in common; they consist of millions of tiny suspended particles which scatter light. A thick enough section of such a scattering material is opaque, with those suspended particles blocking the light entirely.
It's been a long-standing prediction of physics that visible light can actually pass through such "opaque" scattering mediums, using transparent channels known as eigenchannels. That theory has now been experimentally verified, thanks to a pair of researchers at the optical physics department of the University of Twente, Netherlands.
The two, Ivo Vellekoop and Allard Mosk, exploit the fact that such "disorded" mediums are fixed in time, and thus the seemingly random scattering process can be partially reversed. The process requires tuning relative phases of portions of a light beam so that they constructively interfere with each other.
Last year the same researchers demonstrated that this technique could be used to transmit a small portion of a beam through a scattering material, or optically focus it to a point within the material itself.
This year, with an improved test apparatus, Vellekoop and Mosk managed to pass as much as 44% more light through the material. They've also shown that a perfectly implemented version of their apparatus can transmit as much as two thirds of the incident light, no matter how thick the material is.
Such a technique could eventually be used to generate images of surfaces which have been painted, nondestructively test large vats of colloidal chemicals, or to allow navigational equipment to see though clouds or thick fog.
The results are being published in an upcoming issue of Physical Review Letters.