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The American Institute of Physics Bulletin of Physics News Number 415 (Story #1)
February 18, 1999
by Phillip F. Schewe and Ben Stein

LIGHT HAS BEEN SLOWED TO A SPEED OF 17 METERS/SECOND by passing it through a Bose- Einstein condensate (BEC) of sodium atoms at nK temperatures. In general light is slowed in certain materials, a property exploited in making optical lenses. As the index of refraction of these materials gets higher, however, absorption increasingly takes its toll on the light beam. In an experiment at the Rowland Institute of Science, (Lene Vestergaard Hau,, physicists have used a BEC (and its enormous index of refraction) as the optical medium, but with the following important modification. They contrived a system of laser beams whose pattern of interference created an effect called electromagnetically induced transparency, allowing light to propagate unabsorbed but at greatly reduced speeds, in this case a factor of twenty million compared to the speed of light in vacuum; greater light-speed slow downs are expected, to as low as cm/sec. The researchers also observed unprecedentedly large intensity-dependent light transmission. Such an extreme nonlinear effect can perhaps be used in a number of opto-electronic components (switches, memory, delay lines) and in converting light from one wavelength to another. (Hau et al., Nature, 18 February 1999.)