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Absorption (log of transmitted intensity/incident intensity) of the multiple QW structure at the and transitions (solid line). The pump pulse spectral intensity is shown as a dotted line. Inset (a): Scheme of the energy levels involved in the experiment and the optical selection rules. The two confined hole levels of lowest energy, and , of angular momentum , and the first confined electron level of spin , are given. The arrows represent the optical transitions involved for the pump pulse (solid arrow, circular polarization) or the probe pulse (dotted arrows, and circular polarizations). Inset (b): Scheme of the energy levels in a CdTe quantum well with a piezoelectric field. The arrows represent the allowed optical transitions.
Differential transmission spectra (a continuous signal, measured at negative delays, is subtracted from the data) for same (solid lines) and opposite (dotted lines) circular polarizations of the pump and probe pulses.
DT signal after spectral integration over the and transitions, as a function of the pump-probe delay. Solid lines correspond to the same circular polarization of the pump and probe pulses and dotted lines to opposite circular polarizations. Fits of data are shown as open circles. The inset show the level scheme of the excitons: is the exciton recombination time and and are the electron and hole spin-flip times.
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