Passive mode-locking is one of the main methods for generation of ultra-short pulses in lasers [1]. The critical part of a passively mode-locked lasers is a nonlinear absorber placed in a cavity. It was shown to be possible [2, 3], in the coherent regime of light-matter interaction (in particular using self-induced-transparency (SIT) effects), to achieve a mode-locking (so called coherent or SIT mode-locking) with a pulse duration smaller than the polarization relaxation time T2 of the medium - the limit which can be not be conquered by other mode-locking approaches.