Power broadening of the exciton linewidth in a single InGaAs∕GaAs quantum dot

We use high-resolution photocurrent spectroscopy to investigate the ground state of a single quantum dot. In the limit of low optical excitation power, we observe a ground state linewidth down to 4μeV. With increasing excitation intensities, the linewidth shows a characteristic power broadening. This effect is a direct consequence of the saturation of the absorption in a two-level system under conditions of high excitation intensities. From a comparison of both effects, we conclude that power-dependent dephasing is negligible in our system.