1. Zoran Ivić, University of Belgrade, Vinča Institute, PO Box 522, 11001 Belgrade, Serbia, National University of , Serbia
We study the effects of a dispersion of carrier wave on properties of a self-induced transparency solitons in two level media. We found that, in the absorbing (amplifying) media, soliton velocity gradually decreases (increases) as a function of its duration time. The degree of slowing down (accelerating) is determined by the ratio of the atomic transition frequency over the incoming pulse frequency. For example, an immediate pulse stopping is predicted for absorbing media when this ratio exceeds unity. For values less than one, velocity still decreases as a function of duration time, but now towards some finite value and can never be stopped. In the case of amplifying media super-luminal motion is predicted as well as in the case of resonance. However, in contrast to resonant case, there appear the lowest value of frequency ratio below which pulse velocity tends to sub-luminal region. This contradicts to fact that only super-luminal pulses should exist in amplifying media. For the intermediate values of frequency ratio velocity exhibits expecting behavior: increases with duration time until it reach critical value when the sudden drop is observed.
Our study reveals some new features of SIT phenomenon and opens novel ways how it may be exploited in the control of a propagation of electromagnetic radiation in two--level media. It may be achieved by varying frequency ratio. Convenient way of practical realization is the design of devices based on quantum metamaterials due to tunability of their parameters.