1,721,055 research outputs found
Stresses in the plantar region for long- and short-range throws in women basketball players
No full textExcitonic resonant self-electro-optic-device configuration in polytype double-quantum-well structures
No full textWe consider a generic polytype double-quantum-well structure where it is possible to achieve a resonance between a spatially direct exciton (both the electron and hole are confined in the same well) and a spatially indirect exciton that has the hole in the same Valence subband, but the electron localized in the other quantum well. Since the two excitons are coupled through electron tunneling, the true excitonic eigenstates are direct-indirect hybrids. We have calculated the nonlinear optical susceptibility of such a system, including both charge-transfer and many-body effects. We have applied our model to the polytype AlSb/InAs/AlSb/GaSb/AlSb structure. The hybrid excitons show enhanced optical nonlinearities because of the charge-transfer character of the indirect exciton and the large oscillator strength of the direct one
A polariton condensate in a photonic crystal potential landscape
Full text linkThis work has been supported by the State of Bavaria and the Australian Research Council (ARC). The authors thank M D Fraser, N Y Kim, Y Yamamoto, and V D Kulakovskii for fruitful discussions. This publication was funded by the German Research Foundation (DFG) and the University of Wuerzburg in the funding programme Open Access Publishing.The possibility of investigating macroscopic coherent quantum states in polariton condensates and of engineering polariton landscapes in semiconductors has triggered interest in using polaritonic systems to simulate complex many-body phenomena. However, advanced experiments require superior trapping techniques that allow for the engineering of periodic and arbitrary potentials with strong on-site localization, clean condensate formation, and nearest-neighbor coupling. Here we establish a technology that meets these demands and enables strong, potentially tunable trapping without affecting the favorable polariton characteristics. The traps are based on a locally elongated microcavity which can be formed by standard lithography. We observe polariton condensation with non-resonant pumping in single traps and photonic crystal square lattice arrays. In the latter structures, we observe pronounced energy bands, complete band gaps, and spontaneous condensation at the M-point of the Brillouin zone.Peer reviewe
Temperature dependence of pulsed polariton lasing in a GaAs microcavity
No full textThe second-order correlation function g((2))(tau = 0), input-output curves and pulse duration of the emission from a microcavity exciton-polariton system subsequent to picosecond-pulsed excitation are measured for different temperatures. At low temperatures a two-threshold behaviour emerges, which has been attributed to the onset of polariton lasing and conventional lasing at the first and the second threshold, respectively. We observe that polariton lasing is stable up to temperatures comparable with the exciton binding energy. At higher temperatures a single threshold displays the direct transition from thermal emission to photon lasing.Peer reviewe
Polariton Dynamics and Bose-Einstein Condensation in semiconductor microcavities
No full textWe present a theoretical model that allows us to describe the polariton dynamics in a semiconductor microcavity at large densities, for the case of nonresonant excitation. Exciton-polariton scattering from a thermalized exciton reservoir is identified as the main mechanism for relaxation into the lower polariton states. A maximum in the polariton distribution that shifts towards lower energies with increasing pump power or temperature is shown, in agreement with recent experiments. Above a critical pump power, macroscopic occupancies (5x10(4)) can be achieved in the lowest-energy polariton state. Our model predicts the possibility of Bose-Einstein condensation of polaritons, driven by exciton-polariton interaction, at densities well below the saturation density for CdTe microcavities
Femtosecond dynamics and non-linearities of exciton-photon coupling in semiconductor microstructures
No full textWe have studied the femtosecond dynamics of excitonic resonances in quantum well microcavities under strong excitation. Very strong non-linearities are observed, which bear clear resemblance to the non-linearities of an atomic two-level system. The fact that the excitonic system undergoes Rabi flopping and AC Stark splitting is clearly evidenced in a number of cases. Excitation induced dephasing shows an effect much stronger than the light dressing and prevents the observation of the Rabi flopping only when exciting in the continuum. Most of the experimental findings are well reproduced by a dynamical solution of the Maxwell-Bloch equations for an ensemble of two-level systems. This allows in particular understanding of the occurrence of strong coherent gain in microcavitics. An exhaustive description of the experiments is given within the framework of semiconductor Maxwell-Bloch optical equations at the Hartree-Fock level. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS
Towards a room-temperature polariton amplifier
No full textMicrocavity exciton polaritons, the fundamental optical excitations of semiconductor microcavities with quantum wells inside, have been proposed as promising candidates for observing stimulated scattering, condensation and other phenomena related to the bosonic nature of excitons. Having a light mass, quantum degeneracy of polaritons can be reached at low densities and high temperatures. But the radiative time of polaritons is very short (in the picosecond range) and usually prevents an efficient thermalization and cooling of the excited cloud of polaritons. A 'coherently driven condensate', not corresponding to a thermal equilibrium, but featuring multiple occupation of single-particle states, can however be created by an external laser source resonantly exciting polaritons. Under this condition, stimulated parametric scattering of polaritons can provide huge optical gain on a weak probe pulse shined on the sample. In this work we demonstrate that this phenomenon can survive at temperatures close to room temperature and could be achieved in the future even above this limit. Clever sample designs favour the thermal robustness of polariton parametric amplification, but from the experimental data it turns out that the parameter that ultimately limits the highest temperature for polariton parametric scattering is the exciton binding energy
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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