Self-induced transparency in a heterogeneous isotopic mixture

Self-induced transparency is theoretically studied in the system of quantum transitions whose frequencies differ due to the isotope shift caused by differences in the mass, shape, and shell structure of atomic nuclei. In the case of good mutual resolution of the spectral lines of different isotopes, only one component of the mixture is in resonance with the pulse field, while the rest of the components interact with the pulse under quasi-resonance conditions. This circumstance determines the specific features of the effect in heterogeneous media. The conditions for realisation of self-focusing and quasi-channeling are found taking into account transverse perturbations. The latter regime is characterised by a change in the shape of the propagating pulse whose transverse size remains invariable.