Dynamics and origin of the optical Kerr effect in CdSe nanoparticles in the resonant regime

In the resonant regime, the optical Kerr effect of CdSe-doped glasses is due to photoexcitation of carriers whose presence modifies the optical properties of the CdSe quantum dots. The recovery time, which governs the repetition rate at which such devices could be operated, is equal to the recombination time of these carriers. At low laser intensity, the recombination time may be shortened by the photodarkening effect. At higher intensity, nonlinear processes such as Auger recombination may play a significant role as already suggested although the first data could not clearly make the difference between a cubic (Auger) process or a quadratic one. Using three different time-resolved techniques, optical phase conjugation, nonlinear absorption, and time-resolved luminescence, we clearly observed that, for a fresh sample, at high laser intensity and for not too long delay times, carrier recombination is dominated by Auger processes.