ULTRAFAST DEPHASING OF COHERENT INTERSUBBAND POLARIZATIONS IN A QUASI-2-DIMENSIONAL ELECTRON-PLASMA

We present the first study of coherent intersubband polarizations in a pure electron plasma by femtosecond four-wave mixing in the midinfrar ed. Resonantly excited polarizations between consecutive conduction su bbands of narrow GaInAs/AlInAs quantum wells decay within about 500 fs , much faster than intersubband relaxation of electrons. The relation between the decay rate of the signals and the dephasing rate is analyz ed by solving the time-dependent Hartree-Fock equations for the single -particle density matrix. Electron-electron scattering is identified a s the main dephasing mechanism.