Femtosecond midinfrared four-wave mixing is used to study the ultrafast dynamics of coherent intersubband polarizations in n-type modulation-doped GaAs/AlGaAs quantum wells. Time-integrated four-wave mixing yields a dephasing time of T2 = 320 fs, independent of excitation density. Time-resolved four-wave mixing unambiguously shows that the intersubband transition is purely homogeneously broadened by intraband Coulomb scattering within the low-density (n = 5 × 1010 cm-2) electron plasma. The nonlinear propagation of tailored midinfrared pulses is studied by electro-optic sampling, which allows direct time-resolved measurements of the electric field transients. Excitation pulses of only 1 pJ energy are needed to observe partial Rabi flops of up to 60° in the Bloch sphere.
- Coherent polarization
- Intersubband transitions
- Quantum wells
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Electrical and Electronic Engineering