Saturable Absorber, Coherent Population Oscillations, and "Slow Light"
  The paper presents a critical analysis of publications devoted to one of the methods for production of the so-called "slow light" (the light with an anomalously low group velocity) due to extremely high local steepness of the dispersion curve of the medium. The method in point employs for this purpose the effect of coherent population oscillations accompanied by burning of a narrow spectral hole in the homogeneously broadened absorption spectrum. Physical model of the effect proposed in the studies under consideration is based on analysis of response of a nonlinear medium to a low-frequency intensity modulation of the incident light beam. We show that all the observations described in these papers can be easily interpreted in the framework of the simplest model of saturable absorber and have nothing to do with the effects of hole burning and group velocity reduction. 
V.S.Zapasskii and G.G.Kozlov