Eur. Phys. J. D 23, 125-141 (2003)
https://doi.org/10.1140/epjd/e2003-00022-0

Propagation of light-pulses at a negative group-velocity

Laboratoire de Physique des Lasers, Atomes et Molécules (Unité Mixte de Recherche de l'Université et du CNRS (UMR 8523)) , Centre d'Études et de Recherches Lasers et Applications (Fédération de Recherches du CNRS (FR 2416)) , Bâtiment P5, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq, France

Corresponding author: ^a bruno.macke@univ-lille1.fr

Received: 4 July 2002
Revised: 8 November 2002
Published online: 4 February 2003

Abstract

This paper deals with the apparent superluminal propagation of electromagnetic pulses in a linear dispersive medium. One specifically examines the possibility that the pulse leaving the medium may be nearly identical to the incident one (low distortion) and in significant advance of it (strongly negative group-delays). Favourable conditions are obtained in a dilute medium where the required anomalous dispersion originates in an ensemble of narrow absorption or gain lines. Analytical expressions of the advancement of the pulse centre-of-gravity and of the lowest order distortion are established from the transfer-function of the medium. The experiments already achieved with arrangements involving a single absorption-line or a gain-doublet are analysed in detail and compared. The considerable difficulties to overcome in order to attain advancements comparable to the pulse width without important distortion are pointed out. New and promising schemes involving a narrow dip in a gain profile or absorption-doublets are proposed.