Optical 'watermills' control direction of light

Scientists at King's have built on research they conducted last year to achieve previously unseen levels of control over the travelling direction of electromagnetic wave in waveguides and proved that the process works equally well in reverse, opening up the way for the development of technologies that could revolutionise secure communications as well as high speed computing. In a paper published today the team demonstrates that light waves propagating along a surface will induce the spinning of electrons in a nearby nanoparticle. When speaking of spin in optics, one can think of the spinning wheel of a watermill as an illustration of the rotating 'motion' of the electric field vector representing the light field. Assuming the 'water wheel' analogy, the team's discovery is equivalent to demonstrating that a flow of water in the canal will cause the 'water wheel' to spin, thus acting as a 'water mill'. The team showed that the direction of propagation of the original wave determined the spinning sense of the electrons. This is only possible thanks to a very specific property of light waves guided along a surface which does not generally exist in free space, paving the way to a new understanding and new applications of spin on these guided light waves. Dr Francisco Rodríguez-Fortuño, from the Department of Physics and one of the study's authors, said: 'It has been very encouraging for us to experimentally confirm that this optical 'watermill' was working just as we expected.