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  • Quantum Electronics and Laser Science Conference
  • OSA Technical Digest (Optica Publishing Group, 2001),
  • paper QMC2

Pulse propagation at negative group velocity in a transparent medium

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In a series of papers Chiao and coworkers 1-3 showed theoretically that anomalous dispersion can occur inside a transparent material, particularly on the DC side of a single gain line. It was predicted that by using a gain doublet,2 it is possible to obtain a transparent anomalous dispersion region where the group velocity of a light pulse exceeds c with almost no pulse distortion. Here we use gain-assisted linear anomalous dispersion to demonstrate superluminal light pulse propagation with a negative group velocity through a transparent atomic medium.4 We place two Raman gain peaks closely to obtain an essentially lossless anomalous dispersion region that results in a superluminal group velocity. The group velocity of a pulse in this region exceeds c and can even become negative, while the shape of the pulse is preserved. We measured a negative group velocity index of ng = -315( ± 5). Experimentally, a light pulse propagating through the spin-polarized atomic vapor cell exits from it earlier than propagating through the same distance in vacuum by a time difference that is 315 times of the vacuum light propagation time L/c = 0.2 ns.

© 2001 Optical Society of America

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