Ultrafast coherent nonlinear dynamics of intersubband excitations in a quasi-two-dimensional electron gas

The ultrafast dynamics of coherent intersubband polarizations in n-type modulation-doped GaAs/AlGaAs quantum wells is studied by femtosecond time-integrated and time-resolved four-wave-mixing. At a low electron density of View the MathML source, intraband Coulomb scattering results in irreversible dephasing with a decay time of View the MathML source which is independent of excitation density and fully accounts for the View the MathML source linewidth of the intersubband transition. Nonlinear propagation of tailored mid-infrared field transients is studied using amplitude and phase-resolved detection. A coherent response corresponding to partial Rabi flops of up to 60° in the Bloch sphere is observed with excitation pulses of only View the MathML source energy.