| Summary: | We theoretically and experimentally investigate the non-linear optical properties of undoped
and n-doped quantum wells (QW's) in the presence of intense infrared lasers.
These lasers are polarized along the QW growth directions and near resonance with the
transitions between the conduction subbands. In n-doped QW's by inclusion of electronelectron
scattering and dynamic screening we study for the first time: (i) the effects of
the frequencies and intensities of the infrared fields on the dephasing rates associated
with the intersubband transitions, (ii) the generation of various nonlinear gain processes,
and (iii) coherent and optical processes such as coherent population trapping, dark line
and laser induced transparency effects. In undoped QW's by presenting a consistent
theory we show how one can use infrared coupling of the conduction subbands of a QW
to coherently manipulate absorption and emission spectra of excitons. We discuss these
effects in.terms of multi-photon coupling of the excitons or electrons, quantum interferences,
and by presenting a new model to treat laser-matter interaction. Following these
developments we put some of our own results to test by observing the emission dynamics
of excitons in the presence of an intense CO2 laser. We report the first observations of
infrared enhancement of the effective non-radiative decay rates of excitons and the effects
of multi-level transition processes in the emission of QW's. This thesis also includes an
extensive analysis of nonlinear effects in atomic systems. While the primary motivation
for this analysis was to understand and design nonlinear optics of QW's, in the process
some original contributions were made to the study of nonlinear optics of atomic systems. === Science, Faculty of === Physics and Astronomy, Department of === Graduate
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