On coherent mode-locking in a two-section laser

Currently existing lasers with passive mode-locking are two-section systems including an amplifier section and a saturable absorber section. The mechanism of generation of short pulses in them is based on the effects of saturation of the gain in the amplifier and absorption in the absorber, which prevent obtaining pulses with durations shorter than the relaxation time of the polarization in the amplifying and absorbing media. In this work, the new possibility of the generation of ultrashort pulses in a laser with passive mode-locking owing to the coherent character of the interaction of light with matter in the amplifying and absorbing media in ring and linear cavities has been theoretically analyzed. A practically interesting case where the amplifying and absorbing media are separated in the space of the cavity, rather than being homogeneously mixed in its volume, as was previously considered for such type of lasers, has been studied. It has been shown that the width of the spectrum of generated pulses can be much larger than the width of the amplification line and can vary depending on the parameters of the amplifying and absorbing media of the laser. The existence of nonsoliton scenarios of the regime of coherent passive mode synchronization, as well as the possibility of generation without injection of an auxiliary pulse, has been demonstrated.