Soliton regime of second harmonic generation in the presence of quasi-resonant impurities

We report a study of a soliton-like regime of second harmonic generation in a crystal containing impurity atoms with a quantum transition, which is quasi-resonant with respect to a laser pulse at the fundamental frequency. Mismatches of phase and group velocities are taken into account. It is shown that quasi-resonant impurities, on the one hand, lead to a decrease in the generation efficiency, and, on the other hand, they are capable of creating conditions for the implementation of a two-frequency soliton regime, which is impossible in their absence.