Observation of homogeneous optical spectrum in CdSe quantum dots using femtosecond accumulated photon echo

Abstract

We performed heterodyne-detected accumulated photon echo experiments in CdSe quantum dots. The excitonic dephasing time T 2 was directly observed under very low excitation density of 10 −3 photons per dot. The echo signal consists of two exponential decays: the fast decay component is due to the confined acoustic phonon sideband, while the slow one to the zero–phonon line. The sharp zero–phonon line width increased linearly with the temperature rise, and its linear temperature coefficient was proportional to 1/ R 2. This feature agrees well with the theory based on the interaction between confined excitons and acoustic phonons through deformation potential. The 1/ R-dependent homogeneous broadening at the low temperature suggests the surface scattering.