Mode-locking based on a zero-area pulse formation in a laser with a coherent absorber

We observe experimentally a mode-locking in a continuous narrow-band tunable dye laser with molecular iodine absorber cells, which transitions have large phase relaxation time T2. We show that the mode-locking arises due to coherent interaction of light with the absorbing medium leading to Rabi oscillations, so that zero-area (0{\pi}-) pulses in the absorber are formed. Such mode-locking regime is different to most typical passive modelocking mechanisms where saturation plays the main role.