102,336 research outputs found
Data for Optical bistability under non-resonant excitation in spinor polariton condensates
No full textExperimental data and numerical simulation results used to create the figures in the paper Pickup, L., Kalinin, K., Askitopoulos, A. M., Hatzopoulos, Z., Savvidis, P. G., Berloff, N. G., & Lagoudakis, P. (2018). Optical bistability under nonresonant excitation in spinor polariton condensates. Physical Review Letters.
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Polarition Dynamics in Semiconductor Microcavities
No full textThis thesis presents experimental analysis of polariton dynamics in semiconductor microcavities, by means of ultrafast laser spectroscopy. Polaritons resulting from strong mixing of quantum well excitons with photons trapped inside a cavity, possess integer spin and are expected to obey Bose-Einstein statistics at low densities. It is shown here how the new modified dispersion relation for these quasiparticles gives rise to entirely new properties.By constructing a prototype femtosecond goniometer we directly probe these quasiparticles and examine the angular properties of their dispersion relation. We identify ultrafast stimulated scattering of polaritons that results in huge amplification of the incident probe beam which relies on the bosonic property of polaritons to accumulate in a single quantum state. A microcavity working as an amplifier is the first of its kind to amplify massive quasiparticles in solid state system in contrast to amplification of light.A full theoretical analysis of the parametric scattering of polaritons above the amplification threshold when one or more modes on the dispersion are macroscopically and coherently occupied is developed explaining peculiar microcavity emission.Continuous wave excitation experiments reveal the formation from noise of a macroscopically coherent state, which has a well-defined phase. Strong nonlinear increase of the final state population with the increasing excitation density corresponds to condensation into a single polariton mode with macroscopic occupancy. This phenomenon possesses a number of similarities to Bose-Einstein condensation of atoms, but now realized in solids attracting much recent interest.</p
Teaching polaritons new tricks
No full textSemiconductor microcavities have attracted much recent interest because they utilize simultaneously 2D confinement of both excitons and photons in the same heterostructure. Strong coupling of these two states produces unique dynamics that can be well described in a quasiparticle state, the cavity polaritons. Their dispersion relation is dramatically modified with an apparent trap in k-space offering exciting new possibilities for tailoring nonlinear optical properties in microcavities. The reduced density of states inside the trap allows the macroscopic occupancy of polaritons producing much of the new physics. This paper describes recent work on nonlinear effects in semiconductor microcavities including stimulated scattering, parametric oscillation and non-equilibrium phase transition. By teaching polaritons new tricks, both fundamental questions about their bosonic nature can be answered and practical applications in a variety of optoelectronic and interferometric devices can be found
Polariton condensation in an optically induced two-dimensional potential
No full textWe demonstrate experimentally the condensation of exciton polaritons through optical trapping. The nonresonant pump profile is shaped into a ring and projected to a high quality factor microcavity where it forms a two-dimensional repulsive optical potential originating from the interactions of polaritons with the excitonic reservoir. Increasing the population of particles in the trap eventually leads to the emergence of a confined polariton condensate that is spatially decoupled from the decoherence inducing reservoir, before any buildup of coherence on the excitation region. In a reference experiment, where the trapping mechanism is switched off by changing the excitation intensity profile, polariton condensation takes place for excitation densities more than two times higher and the resulting condensate is subject to much stronger dephasing and depletion processes
Ultrafast polariton population build-up mediated by molecular phonons in organic microcavities
No full textA key prerequisite for low-threshold polariton lasing in organic or inorganic microcavity systems is the efficient population of the lower polariton ground state. Here, we report the observation of a resonant phonon-mediated relaxation process which gives rise to nonthermal polariton population with sub 100 fs build-up times. This mechanism is manifested by discrete maxima of the angular-resolved photoluminescence intensity, with corresponding shortening of the photoluminescence rise time at respective phonon resonances. The realization of enhanced relaxation rates in disordered J-aggregate systems is important for developing room temperature organic laser sources with less fabrication complexity than their crystalline counterparts
Ultrafast polariton dynamics in strongly coupled zinc porphyrin microcavities at room temperature
No full textTime and angle-resolved measurements reveal ultrafast dynamics of excitations in organic microcavities leading to dramatic modulation of probe transmission (~30%). We find that the induced changes have both fast and long-lived components. Fast response times are defined by vibronic relaxation and intersystem crossing (S1 ? T1), whereas long-lived changes are attributed to a build up of carriers in the nonradiative triplet state whose lifetime is longer than the repetition rate of the laser pulses, resulting thus in incomplete recovery of the ground state. Blueshifts of the lower polariton branch in the presence of the pump pulse indicate the presence of nonlinear interactions in the sample. However, there is no evidence yet for the pair-type scattering processes in porphyrin microcavities
An exciton-polariton bolometer for terahertz radiation detection
No full textWe experimentally investigate the feasibility of a bolometric device based on exciton-polaritons. Initial measurements presented in this work show that heating - via thermal expansion and bandgap renormalization - modifies the exciton-polariton propagation wavevector making exciton-polaritons propagation remarkably sensitive to thermal variations. By theoretical simulations we predict that using a single layer graphene absorbing layer, a THz bolometric sensor can be realized by a simple exciton-polariton ring interferometer device. The predicted sensitivity is comparable to presently existing THz bolometric devices with the convenience of being a device that inherently produces an optical signal output.</p
Bibliographie Hilarion G. Petzold 1958 – 2009 mit Anhang als Einführung
No full textDieses Archiv enthält die Gesamtbibliographie der Werke des Autors nebst einiger Texte „Über H. G. Petzold“ im Schlussteil der Bibliographie sowie einen Anhang mit einer Einführung in die Architektur des Werkes in seinem wissenslogischen Aufbau als Ausarbeitung seines „Tree of Science Modells“ (2007).This archive contains the complete bibliography of the author and some texts about H. G. Petzold, moreover an epilogue with an introduction to the architecture of the works in its epistemological structure and composition and as an elaborations of Petzold’s „Tree of Science Modell (2007).https://www.fpi-publikation.de/polyloge/01-2009-petzold-h-g-gesamtbibliographie-h-g-petzold-1958-2009-updating-november2009/peerReviewedpublishedVersio
Characterizing the electroluminescence emission from a strongly coupled organic semiconductor microcavity LED
No full textThe fabrication of a strongly coupled organic semiconductor light emitting diode (OLED) is described. The device is characterised through angle‐resolved photoluminescence and electroluminescence spectroscopy, with the efficiency of the polariton OLED being compared to that of an equivalent weakly coupled device. The external emission efficiency of the polariton OLED is approximately 6 times smaller than that of the OLED; an effect that is attributed to the relatively slow scattering of excitons towards states at the bottom of the lower polariton branch. The temporal responses of the polariton and standard OLED devices are measured under pulsed voltage excitation, and device dynamics are found to be limited by charge transport and recombination
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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