Mechanism of optical polarization dephasing in bulk GaAs and multiple quantum wells

The optical polarization dephasing times in bulk GaAs and GaAs/Al0.3Ga0.7As quantum wells at room temperature are measured using time-resolved degenerate-four-wave mixing (DFWM). Under the conditions of excitation pulse central wavelength of 785nm and carrier density of 1011cm-2, the dephasing times of 28 and 46 fs for bulk GaAs and multiple quantum wells, respectively, are measured. Because the carrier-carrier scattering rate in quantum wells is reduced due to the confinement of the carrier behavior，the dephasing time of the quantum wells is longer than that of bulk. The dependence of the DFWM signal on the intensity and the polarization of the incident pulses is evaluated by a theoretical model of third-order nonlinear density matrix.