Slowing it down
8 Aug 2011 by Evoluted New Media
For the first time, scientists in Glasgow have been able to drag light by slowing it down to the speed of sound and sending it through a rotating crystal. The work may be a potentially important step in optical storage and quantum information.
For the first time, scientists in Glasgow have been able to drag light by slowing it down to the speed of sound and sending it through a rotating crystal. The work may be a potentially important step in optical storage and quantum information.
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The green laser leaving the ruby crystal – it has been slowed down and rotated |
Many people think the speed of light is constant – 671 million miles per hour – but this is only the case in a vacuum. In other substances – such as water or solids – its speed is reduced, with different wavelengths travelling at different speeds. What’s more, light can also be dragged when it travels through a moving substance like glass, air or water.
“The speed of light is constant only in a vacuum. When light travels through glass, movement of the glass drags the light with it too,” said Professor Miles Padgett of the Optics Group in the school of physics and astronomy at the University of Glasgow.
“Spinning a window as fast as you could is predicted to rotate the image of the world behind it ever so slightly. This rotation would be about a millionth of a degree and imperceptible to the human eye.”
Padgett’s colleague, Dr Sonja Franke-Arnold came up with the idea of using slow light in a ruby to observe this photon drag. Together with Dr Graham Gibson from Glasgow and professor Robert Boyd from the Universities of Ottawa and Rochester, they shone a primitive image made up of the elliptical profile of a green laser through a ruby rod spinning on its axis at up to 3,000 rmp.
When the light entered the ruby, it slowed down to around the speed of sound – around 741mph. The spinning motion of the rod drags the light with it, resulting in the image being rotated by around 5° – a large enough difference to be visible with the naked eye.
“We mainly wanted to demonstrate a fundamental optical principle, but this work has possible applications too,” said Franke-Arnold.
“Images are information and the ability to store their intensity and phase is an important step to the optical storage and quantum information, potentially achieving what no classical computer can ever match.”
She said the option to rotate an image by a set arbitrary angle presents a new way to code information. The work is published in Science.
