The path length of light in opaque media
What happens when light passes through a glass of milk? It enters the liquid, is scattered unpredictably at countless tiny particles and exits the glass again. This effect makes milk appear white.http://www.dailysciencenow.tk/ The specific paths that the incident light beam takes depends, however, on the opacity of the liquid: A transparent substance will allow the light to travel through on a straight line, in a turbid substance the light will be scattered numerous times, travelling on more complicated zig-zag trajectories. But astonishingly, the average total distance covered by the light inside the substance is always the samehttp://www.dailysciencenow.tk/
Particles and Waves
"We can get a simplified idea of this phenomenon when we imagine light as a stream of tiny particles," says Stefan Rotter. "The trajectories of the photons in the liquid depend on the number of obstacles they encounter.
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Experiments in troubled water
The theoretical calculations describing this counterintuitive behaviour have already been published three years ago in a joint publication by Stefan Rotter's team and his colleagues from Paris. Now the same research groups managed to verify the remarkable result in an experiment. Test tubes were filled with water, which was then obfuscated with nanoparticles. As more nanoparticles are added, the light is scattered more strongly and the liquid appears more turbid.http://www.dailysciencenow.tk/