Kinetics of four-wave mixing for a two-dimensional magnetoplasma in strongmagnetic fields

We investigate the femtosecond kinetics of an optically excited two-dimensi onal magnetoplasma at intermediate and high densities under a strong magnet ic field perpendicular to the quantum well (QW). We assume an additional we ak lateral confinement which lifts the degeneracy of the Landau levels part ially. We calculate the femtosecond dephasing and relaxation kinetics of th e laser pulse excited magnetoplasma due to bare Coulomb potential scatterin g, because screening is of minor importance under these conditions. In part icular, the time-resolved and time-integrated four-wave-mixing (FWM) signal s are calculated by taking into account three Landau subbands in both the v alance and the conduction band assuming an electron-hole symmetry. The FWM signals exhibit quantum beats mainly with twice the cyclotron frequency. Co ntrary to general expectations, we find no pronounced slowing down of the d ephasing with increasing magnetic field. On the contrary, one obtains a dec reasing dephasing time because of the increase of the Coulomb matrix elemen ts and the number of states in a given Landau subband. In the situation whe n the loss of scattering channels exceeds these increasing effects, one get s a slight increase at the dephasing time. However, details of the strongly modulated scattering kinetics depend sensitively on the detuning, the plas ma density, and the spectral pulse width relative to the cyclotron frequenc y. [S0163-1829(98)04143-5].