Nonlinear dynamics investigation in few-cycle laser seeding of quantum cascade lasers: role of permanent dipole moment

•Ultrafast dynamics in quantum cascade laser is numerically investigated.•The numerical simulation is based on the full wave Maxwell-Bloch model.•If including permanent dipole moment (PDM), a quasi-comb appears.•The underling mechanism is clarified.•Carrier-envelope-phase is locked to the QCL output.

The ultrafast dynamics in the few-cycle laser seeding of quantum cascade laser (QCL) is numerically investigated via the exact solution of the full-wave Maxwell-Bloch equations. It is found that, with or without taking permanent dipole moment (PDM) into account, the QCL emission is quite different: beyond the fundamental frequency band, additional high and low bands occur for that with PDM, which forms an ultra-broad quasi-comb. The origin for this is closely related to the generation of second order harmonic and direct-current components as a result of PDM breaking down the parity symmetry. Moreover, the carrier-envelope-phase (CEP) of laser seed is locked to the QCL output, no matter with or without PDM, and this phase controlled QCL maybe has more wide and convenient applications in related fields.