DEPHASING PROCESSES IN II-VI QUANTUM DOTS

The loss of phase coherence in II-VI quantum dots is investigated usin g experimental methods working both in the frequency and in the time d omain. Femtosecond differential absorption experiments reveal narrow r esonances at very early times after excitation and low excitation dens ities for CdSe quantum dots. A substructure is detected and explained by transitions from the series of confined hole states. By nondegenera te four-wave mixing experiments (NDFWM) the dephasing time is determin ed for CdS quantum dots with radii larger than the Bohr radius. Temper ature and excitation intensity dependent dephasing times between appro ximate to 20 fs and some 100 fs are measured and attributed to electro n-hole pair-phonon coupling and carrier-carrier scattering.