Resonant saturation laser spectroscopy of a single self-assembled quantum dot

We performed high resolution resonant laser spectroscopy on a single self-assembled quantum dot (QD) at liquid He temperatures. We explore the two-level nature of the QD excitonic transition through the investigation of its behavior as a function of the laser power. The quantum ground state exciton absorption peak size diminishes with increasing power while its width increases. Fitting these dependencies to the predictions of a two-level atom model we extract unambiguously a radiative lifetime of 660 ps, a residual collisional broadening about 0.18 μ eV as well as the spectral fluctuation 1.3 μ eV. We find that at high power the line width of the exciton absorption is essentially given by the Rabi frequency.