| Research Abstract |
The purpose of this project is to clarify experimentally and theoretically the many body effects among excited electrons in confined exciton systems.
1. IR transient absorption spectra under resonant excitation and two-photon excitation spectra of confined excitons were measured in CuCl quantum dots. (1) Confinement effect on the exciton Rydberg excited states was different from the confinement of exciton translational motion and compared with the theory developed by Uozumi and Kayanuma. (2) The slow decay component of the transient absorption was closely related with the luminescence blinking and photo-ionization effects. (3) Coexistence of luminescence and light scattering under the exciton resonant excitation indicated the importance of non-Markovian process in the exciton transverse relaxation.
2. Single quantum dot spectroscopy was performed on GaAs isolated island structures. We studied (1) dynamics of multi-exciton luminescence and its excitation power dependence, (2) energy trans
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fer phenomena among quantum dots in an island structure through the continuum states, and (3) nonlinear anti-Stokes luminescence caused by the Auger process inherent to the quantum dots.
3. Energy level structures, optical spectra and resonant enhancement of internal electric field in excitons confined in spherical quantum dots were theoretically studied by taking exciton L-T splitting, bulk-like screening by background polarization and mirror image effect. Shape effect was also studied in cylindrically confined system.
4. For one-dimensional periodic structures, (1) spatial structures of the exciton wave functions, coupled modes with photons and the radiative shift and broadening of the coupled modes were studied as functions of exciton quantum numbers and sizes of the periodic structures. (2) Degenerate four wave mixing signal is enhanced by the giant nonlinear response induced by the exciton nonlocality. The comparison with the experimental results obtained for GaAs thin films confirmed the resonance enhancement of the internal electric field with the spatial structure different from dipole type. Less
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