Gain-assisted superluminal light propagation
Gain-assisted superluminal light propagation
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DOI：
10.1038/35018520
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发表时间：
2000-07-20
期刊：
影响因子：
64.8
通讯作者：
Dogariu, A
中科院分区：
文献类型：
--
作者：
Wang, LJ;Kuzmich, A;Dogariu, A
爱因斯坦的狭义相对论和因果原理(1-4)意味着任何运动物体的速度都不能超过真空中的光速(c)。然而，存在各种建议（5-18）来观察光脉冲的快于 c 的传播，使用吸收线（4,6-8）附近的反常色散、非线性（9）和线性增益线（10-18）或隧道势垒（19）。然而，在之前的所有实验演示中，光脉冲要么经历了非常大的吸收(7)，要么经历了严重的重塑(9,19)，导致了对解释的争议。在这里，我们使用增益辅助线性反常色散来演示原子铯气体中的超光速光传播。该区域中激光脉冲的群速度超过 c，甚至可以变为负值(16,17)，同时脉冲的形状保持不变。我们测量的群速度指数为 n(g) = -310(+/-5)；实际上，这意味着传播通过原子蒸气室的光脉冲出现在出口侧的时间比在真空中传播相同距离的光脉冲要早得多，以至于脉冲的峰值似乎在进入室之前就离开了室。观察到的超光速光脉冲传播与因果关系并不矛盾，是反常色散区域中不同频率分量之间经典干涉的直接结果。
Einstein's theory of special relativity and the principle of causality(1-4) imply that the speed of any moving object cannot exceed that of light in a vacuum (c). Nevertheless, there exist various proposals(5-18) for observing faster-than-c propagation of light pulses, using anomalous dispersion near an absorption line(4,6-8), nonlinear(9) and linear gain lines(10-18), or tunnelling barriers(19). However, in all previous experimental demonstrations, the light pulses experienced either very large absorption(7) or severe reshaping(9,19), 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 become negative(16,17), while the shape of the pulse is preserved. We measure a group-velocity index of n(g) = -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 to leave the cell before entering it. The observed superluminal light pulse propagation is not at odds with causality, being a direct consequence of classical interference between its different frequency components in an anomalous dispersion region.