We show that some experimental observations on ‘slow’ and ‘fast’ light can be interpreted in terms of simple models of classical nonlinear optics without attracting the idea of steep-dispersion-based modification of group velocity of light.
The slow-light effect, which implies reduction of the group velocity of light by many orders of magnitude, is considered to be one of the most exciting discoveries in quantum optics of the last decade. The physics underlying the effect is related to an extremely steep dispersion of the medium in a very narrow region of its transparency, while all the manifestations of the effect are usually reduced just to a small pulse delay. Perhaps this is the reason why, after the discovery of the slow-light effect, some of the simplest nonlinear phenomena associated with a retarded optical response have been implicitly revised and assigned to reduction of the light group velocity. In this lecture, a few examples of common inconsistencies in the area of the slow-light physics will be presented.
A critical review of experimental studies of the so-called 'slow light' arising due to anomalously high steepness of the refractive index dispersion under conditions of electromagnetically induced transparency or coherent population oscillations is presented. It is shown that a considerable amount of experimental evidence for observation of the 'slow light' is not related to the low group velocity of light and can be easily interpreted in terms of a standard model of interaction of light with a saturable absorber.