Text: Light is Slowing Down Scientists put on the brakes SCIENTISTS have managed to slow down the speed of light so that it can be overtaken by a bicycle. By passing it through an illuminated atomic cloud, they have cut the speed of a pulse of yellow laser light from 186,000 miles per second to 0.01 mile per second and plan to reduce it further to a crawl of about half an inch a second. This puts the speed of light in the shade when compared with the world-record cyclist Bruce Bursford, who has clocked up 207 miles per hour or 0.057 miles per second. The feat is reported today by Dr Lene Hau of the Rowland Institute for Science, and Harvard University, Cambridge, Massachusetts, and colleagues. Light is already known to slow down a little when it enters a piece of glass, because glass has a refractive index which is larger than that of free space. Dr Hau said: "We are using a much more interesting mechanism to slow light down by a factor of 20 million." The trick is to use one light beam to alter the refractive index of an unusual medium - a cloud of sodium atoms cooled to ultra-low temperatures known as a "Bose-Einstein condensate" - in such a way that it can slow down a second pulse of light. The trick has a number of applications, Dr Hau said, such as converting infra-red light into blue light. "In the future, this could be of importance for laser light projectors - it is hard to generate blue light otherwise." Another possible use is in night vision. She said: "This technique can be used to convert infrared light to the visible spectrum (so we can see it) at low power cost." The technology could also help to reduce the noise in communications, and create switches that can control light. These may be useful in computers that work on light rather than electricity. Dr Hau said: "These possible applications are of course for the future - perhaps 10 years down the line if we get to work on it. Right now we have an experimental set-up where we are pushing technology to the outermost limit. We'll have to figure out how to make this into a practical instrument." The London Telegraph, Feb. 18, 1999

See Also:

Source: