We describe pulse propagation through a slab with periodic dielectric function ε(t), thus extending our previous investigation for monochromatic incidence [Phys. Rev. A 79, 053821 (2009)]. Based on the concepts of phase and group delays, we prove that, for an incident quasi-monochromatic pulse, the transmitted pulse can be expressed as a superposition of partial pulses that are exact replicas of the incident pulse and that exit the slab with a time delay. These partial pulses have harmonic carrier frequencies ω c - nΩ (n is an integer, ω c is the carrier frequency of the incident pulse, and Ω = 2π/T is the slab modulation frequency). We find numerically that these partial pulses can be fast (peak velocity vn > c or vn < 0) or slow (vn << c). Further, we investigate the peak velocity v p of the outcoming pulse for several cases. We find that this peak velocity v p and the partial peak velocities vn do not diverge--as occurs to the group velocity v g of the bulk dynamic-periodic medium when ω c = Ω/2. We expect that these results could be verified in the microwave regime [see Halevi et al., Proc. SPIE 8095, 80950I (2011)].

No abstract

No abstract

We study the possibility for ultrashort pulse generation from THz quantum cascade lasers via the colliding pulse mode locking technique. Our analysis shows that this approach could enable sub-ps pulses from QCLs, even in devices with carrier recovery times as short as ~ 10 ps.