Optical manipulation of electron spin coherence in colloidal CdS quantum dots

We report experimental studies of optical manipulation of electron spin coherence by linearly or circularly polarized short laser pulses at room temperature, in an ensemble of colloidal CdS quantum dots. In addition to a conventional pump-probe configuration, a linearly polarized prepump pulse before the pump could significantly enhance the amplitude of pump-induced electron spin coherence, owing to the fact that prepump pulses produce more resident electrons. And a linearly or circularly polarized control pulse after the pump will efficiently suppress the spin coherence, because of the re-excitation of spin-polarized electrons to trion states by the absorption of control photons.