文档介绍：Gain-assisted superluminal light propagation
L. J. WANG, A. KUZMICH & A. DOGARIU
NEC Research Institute, 4 Independence Way, Princeton, New Jersey 08540, USA
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Einstein's theory of special relativity and the principle of causality1-4 imply that the speed of any moving object
cannot exceed that of light in a vacuum (c). Nevertheless, there exist various proposals5-18 for observing
faster-than- c propagation of light pulses, using anomalous dispersion near an absorption line4, 6-8, nonlinear9 and
linear gain lines10-18, or tunnelling barriers19. However, in all previous experimental demonstrations, the light
pulses experienced either very large absorption7 or severe reshaping9, 19, resulting in controversies over the
interpretation. Here we use gain-assisted linear anomalous dispersion to demonstrate superluminal light
propagation in atomic caesium gas. The group velocity of a laser pulse in this region exceeds c and can even
16, 17
e negative , while the shape of the pulse is preserved. We measure a group-velocity index of ng =
–310(±5); in practice, this means that a light pulse propagating through the atomic vapour cell appears at the exit
side so much earlier than if it had propagated the same distance in a vacuum that the peak of the pulse appears