Large negative and positive delay of optical pulses in coherently prepared dense Rb vapor with buffer gas
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The study of the propagation of a weak probe pulse in an atomic cell filled with optically thick 87Rb vapor and Ne buffer gas for various one-photon detunings was discussed. It was observed that the pulse propagation underwent a transition from an ultraslow to a superluminal regime as the dark resonance line shape changed from a narrow transmission to a narrow absorption resonance. For large one-photon detuning, the contrast of the absorption resonance increased with laser intensity whereas the change in the resonance width was negligible. It was found that this process may be applied to precision instruments.