Unequal dependence of the dephasing rates for inhomogeneously broadened excitons on the intensities of the exciting beams in four-wave-mixing measurements - art. no. 033301

摘要

We study exciton dephasing in 8 nm GaAs quantum wells (QW) at 8 K by resonantly exciting the excitons at low densities. For this, we perform femtosecond degenerate four-wave mixing (DFWM) measurements using two laser beams. The exciton in the QWs are inhomogeneously broadened, with a photoluminescence linewidth of 1.8 meV. We investigate how the time integrated DFWM signal and its decay rate eta change as the average intensity of either of the two exciting beams is varied separately. We find that the dependence of eta on the intensity of the first pulse is about twice as that for the delayed pulse. We compare the results with a theory based on optical Bloch equations and relaxation rate approximation, accounting phenomenologically far dephasing due to exciton-exciton scattering. [References: 7]