The mechanisms leading to a seemingly superluminal propagation of light indispersive media are examined. The anomalous dispersion near an absorptionline, involved in the first experiments displaying negative group velocitypropagation, is shown to be not only simpler but also more efficient than theso-called transparent dispersion used in the later experiments of Wang et al.(Nature (London) 406, 277 (2000)) and of Dogariu et al. (Phys.Rev.A 63, 053806(2001)). The modest pulse advances observed by these authors can in particularbe reproduced with a better overall transmittance of the medium and thesignificant advances attained with a single-line arrangement would probably beunattainable with their gain-doublet arrangement.
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