Pump-probe absorption/gain spectroscopy of strongly confined semiconductornanocrystals

The density matrix approach has been employed to analyze the pump-probe spe ctroscopic absorption spectra of small semiconductor nanocrystals popularly known as quantum dots (QDs) under the strong confinement regime (SCR) with sizes smaller than the bulk exciton Bohr radius such that the Coulombic in teraction energy becomes negligible in comparison with the confinement ener gy. The average time rate of absorption has been obtained by incorporating the radiative and nonradiative decay processes as well as the inhomogeneous broadening arising due to nonuniform QD sizes. The analytical results are obtained for QDs duly irradiated by a strong near-resonant pump and a broad band weak probe. Numerical estimations have been made for: (i) isolated QDs and (ii) QD-arrays of GaAs and CdS. The results agree very well with the a vailable experimental observations in CdS QDs. The results in the case of G aAs QDs can lead one to experimentally estimate absorption/gain spectra in the important III-V semiconducting microscopic structures. (C) 2001 Academi c Press.