Optical nonlinearities and ultrafast carrier dynamics in semiconductor quantum dots

The femtosecond (fs) studies of ultrafast optical nonlinearities, energy relaxation and trapping dynamics in three types of quantum dots are reported. High sensitivity fs nonlinear transmission experiments in the new chirp-free configuration were applied to measure pump-induced absorption changes for optical transitions involving the lowest and the first excited electron states in CdSe nanocrystallines of different radii. The Coulomb interaction influences all transitions, resulting in transition shifts which are seen as derivative-like features in transient absorption (TA). The pump intensity-dependent TA indicate a change in carrier relaxation channels at high pump levels, manifested as a distinct difference in the nonlinear optical response.