Materials such as milk, paper, white paint and tissue are opaque because they scatter light, not because they absorb it, but no matter how great the scattering, light was always able to get through the material in question, went the theory.
Researchers Ivo Vellekoop and Allard Mosk of the University of Twente have now shaped the waveform of light and confirmed this with experiments. By doing so they have found the predicted ‘open channels’ in material along which the light is able to move.
In materials that have a disordered structure, incident light is scattered in every direction possible. In an opaque layer, so much scattering takes place that barely any light comes out ‘at the back.’ However, even a material that causes a great deal of light scattering has channels along which light can propagate. This is only possible if the light meets strict preconditions so that the scattered light waves can reinforce one another on the way to the exit.