Large negative and positive delay of optical pulses in coherently prepared dense Rb vapor with buffer gas RID B-9041-2008
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We experimentally study the group time delay for a light pulse propagating through hot Rb-87 vapor in the presence of a strong coupling field in a Lambda configuration. We demonstrate that the ultraslow pulse propagation is transformed into superluminal propagation as the one-photon detuning of the light increases due to the change in the transmission resonance line shape. Negative group velocity as low as -c/10(6)=-80 m/s is recorded. We also find that the advance time in the regime of the superluminal propagation grows linearly with increasing laser field power.
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