The polarization properties of time-integrated four-wave mixing (FWM) and pump-and-probe transmission (PPT) signal spectroscopy were investigated for a system of excitons confined in CdSSe quantum dots (QD's) embedded in a glass matrix. A strong FWM signal was observed by scattering σ- circularly polarized light on the population grating created by two σ+ pulses (forbidden geometry according to the noninteracting oscillator's model). A similar depolarization effect is observed in the PPT studies: the difference in the signals in the σ+ σ+ and σ+ σ- geometries decays for delay times of about 5 ps. No marked scattering is observed if the population grating is created by two pulses of opposite (σ+ and σ-) polarizations. We demonstrate that these facts are associated to a strong exciton-exciton coupling in the QD and to the inhomogeneous spin dephasing of the QD excitons due to a random exchange splitting of the J = 1 exciton state, originating from the lowered QD symmetry.
|Number of pages||4|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - Mar 2003|