Manifestation of Exciton Coherence in Resonant Quantum Well Emission

Coherent Control of Optical Emission from a Conjugated Polymer

“…This is close to the energy shown previously to divide the upper levels, among which exciton migration is more rapid than radiation, from the lower, among which the converse applies [15][16][17]. Previous work [18,19] indicates that the longer lifetime of the RRS corresponds to longer phase coherence of the excited state. This picture agrees with the description of the relative suppression of migration before recombination, and indicates that energy relaxation due to migration dominates dephasing of the excitons created in PPV just above the energy threshold.…”

“…This is evidence that, under these conditions, dephasing is dominated by phonon interaction rather than exciton-exciton scattering, which would lead to strong density dependence in the decay of the secondary emission, as seen for GaAs quantum wells [18]. The intensity of the peak emission was linear with power, ruling out phenomena such as amplified spontaneous emission or superfluorescence [21] and confirming that the behavior observed here is different from the spectrally narrowed emission observed in many conjugated polymers [22].…”

“…As a result, the angle-integrated intensity shows little variation with interpulse delay beyond 200 fs. This is an example of the complication of coherent control by inhomogeneous broadening: excitons with different energies have phases which evolve at different rates during the time between pulses and hence at longer delays the second pulse will interfere constructively with some excitons but destructively with others [18,24]. By discriminating between emission in different directions we reduce the averaging of the excited ensemble, permitting us to observe the coherent manipulation of the quantum states generated in PPV.…”

Simple model for laser-induced electron dynamics

“…This kind of processes is nowadays the target of many research groups, and many interesting results have already been obtained, showing the importance of the relative phases of the quantum system, the pulse shape, and the time delay betwen pulses. [22][23][24][25][26][27] To explore the possibility of coherent control by ultrashort laser pulses within a simple model, well known in molecular physics but prototypic for surfaces and gap states in solids, we start with the electron dynamics of two-level and threelevel systems. The interaction of a system with a strong, rapidly varying electromagnetic pulse, during a very short time, requires a full nonadiabatic treatment of the problem.…”