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

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. (C) 2000 Elsevier Science B.V. All rights reserved.