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Dogariu A; Kuzmich A; Wang LJ
Title: Transparent anomalous dispersion and superluminal light-pulse propagation at a negative group velocity

Source: PHYSICAL REVIEW A 2001, Vol 6305, Iss 5, pp 3806-+

Abstract: Anomalous dispersion cannot occur in a transparent passive medium where electromagnetic radiation is being absorbed at all frequencies, as pointed out by Landau and Lifshitz. Here we show, both theoretically and experimentally, that transparent linear anomalous dispersion can occur when a gain doublet is present. Therefore, a superluminal light-pulse propagation can be observed (*) even at a negative group velocity through a transparent medium with almost no pulse distortion. Consequently, a negative transit time (**) is experimentally observed resulting in the peak of the incident light pulse to exit the medium even before entering it. This counterintuitive effect is a direct result of the rephasing process owing to the wave nature of light and is not at odds with either causality or Einstein's theory of special relativity.

Jackson AD; Lande A; Lautrup B
Title: Apparent superluminal behavior in wave propagation

Source: PHYSICAL REVIEW A 2001, Vol 6404, Iss 4, pp 4101-+

Abstract: The apparent superluminal propagation of electromagnetic signals seen in recent experiments is shown to be theresult of simple and robust properties of relativistic field equations. Although the wave front of a signal passing through a classically forbidden region can never move faster than light, an attenuated replica of the signal is reproduced ''instantaneously'' on the other side of the barrier. The reconstructed signal, causally connected to the forerunner rather than the bulk of the input signal, appears to move through the barrier faster than light.