COHERENT INTERSUBBAND POLARIZATIONS IN A QUASI-2-DIMENSIONAL ELECTRON-PLASMA STUDIED BY FEMTOSECOND 4-WAVE-MIXING IN THE MIDINFRARED

We present the first study Of the ultrafast dynamics of coherent inter subband polarizations in a two-dimensional electron plasma using femto second four-wave-mixing in the mid-infrared. Experi ments with modulat ion-doped GaInAs/AlInAs multiple-quantum-well samples of different dop ing concentrations show a fast decay of the coherent third-order inter subband polarization on a sub-500 fs time scale, depending strongly on carrier density and lattice temperature. Electron-electron scattering is identified as the main dephasing scattering mechanism.