State-filling and self-action processes at resonant excitation of excitons in colloidal quantum dots

Abstract

The anomalous nonlinear absorption of colloidal CdSe/ZnS quantum dots has been revealed in the case of resonant excitation of the basic exciton transition by powerful picosecond light pulses: bleaching at moderate input intensities is substituted by retardation of bleaching rate and even by increasing of absorption. The latter has been explained by saturation (state-filling) effect of two-level system with decreasing lifetime of the excited state at high excitation because of Auger recombination. The observed changes of output intensity cross-section profile versus exciting intensity were attributed to the creation of transparency channel in the cell with highly absorbing colloidal solution of quantum dots by laser beam due to state-filling, strip-effect and finally self-diffraction of Fresnel or Fraunhofer type by induced aperture.