Wednesday, August 31, 2005

Light at any Speed

Stoping light in quantum leap "...researchers have slowed the speed of light down from 300,000 kilometres per second to a few hundred metres per second.

“To store the light in there, we turn the second laser beam off. The signal from the first laser beam is trapped inside the crystal. To get the signal out again, we turn the coupling beam on again. We can now store light for seconds, and potentially quite a bit longer,” Dr Sellars said. "

Euro boffins increase speed of light "Luc Thévenaz and his fellow researchers in the Nanophotonics and Metrology laboratory at EPFL said they were able not only to slow light down by a factor of three from its usual speed of 300 million metres per second in a vacuum, but they have also accomplished the considerable feat of speeding it up – effectively making light go faster than the speed of light."

They have "...demonstrated the first all-optical technique to slow light in off-the-shelf optical fibres."

A previous article explaining how superluminal speeds are achieved: "...a pulse of light can have more than one speed because it is made up of light of different wavelengths. The individual waves travel at their own phase velocity, while the pulse itself travels with the group velocity. In a vacuum all the phase velocities and the group velocity are the same. In a dispersive medium, however, they are different because the refractive index is a function of wavelength, which means that the different wavelengths travel at different speeds. Wang and colleagues report evidence for a negative group velocity of -310c, where c (=300 million metres per second) is the speed of light in vacuum."
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