Coherent mode locking in a two-section laser with fast gain and absorber

Abstract Coherent mode locking is based on the formation of 2π pulses of self-induced transparency in the absorbing medium and π pulses in the amplifying medium. In this regime it becomes possible to generate ultrashort laser pulses down to one oscillation cycle with a pulse duration being much shorter than the polarization relaxation time T₂ of the amplifying and absorbing medium. In this article a two-section laser model with a ring resonator based on absorbing and amplifying medium with short relaxation times has been applied. We have demonstrated a self-starting regime of coherent mode locking with picosecond and femtosecond laser pulses using numerical simulations for the given model. In addition, we have shown that there is a significant influence of generation frequency detuning on laser pulse duration and intensity. Moreover, we have compared our numerical results with an analytical model of a coherent mode-locked laser based on the area theorem. We believe that the findings of this work can open a pathway towards the practical application of mode locking in mid-IR and THz quantum cascade lasers.