Faster than light, light

Chuck Grimes cgrimes at tsoft.com
Thu Jul 20 22:51:26 PDT 2000


Gain-assisted superluminal light propagation

L. J. WANG, A. KUZMICH & A. DOGARIU

NEC Research Institute, 4 Independence Way, Princeton, New Jersey 08540, USA

Correspondence and requests for materials should be addressed to L.J.W. (e-mail: Lwan at research.nj.nec.com).

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 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 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.

see:

http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/ v406/n6793/full/406277a0_fs.html

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Comments?

Chuck Grimes



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