It’s been known for a long time that the speed of light can be slowed slightly as it travels through glass or water, but this is the first time that it’s been shown it can altered unimpeded by interactions with any materials in free space.

The team of collaborators from University of Glasgow and Heriot-Watt University in effect built a racetrack to race a pair of photons – one in its normal state alongside one that had a special mask applied that gave the photon shape.

Scientists show how they can slow the speed of light - University of Glasgow

Professor Padgett who leads the University of Glasgow’s Optics Group said, “It might seem surprising that light can be made to travel more slowly like this, but the effect has a solid theoretical foundation and we’re confident that our observations are correct.

“The results give us a new way to think about the properties of light and we’re keen to continue exploring the potential of this discovery in future applications. We expect that the effect will be applicable to any wave theory, so a similar slowing could well be created in sound waves, for example.”

The team’s paper, titled ‘Spatially Structured Photons that Travel in Free Space Slower than the Speed of Light’, is published in Science Express, which provides electronic publication of selected papers in advance of print in the journal Science.



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Heriot-Watt University