@inproceedings{4184, abstract = {{We have experimentally investigated injection currents generated by all-optical excitation of GaAs/AlGaAs quantum wells excited with 130 fs optical pulses. The currents have been detected via free-space THz experiments at room temperature. Our experiments prove that Coulomb effects strongly influence injection currents. This becomes most prominently visible when exciting light-hole exciton transitions. At this photon energy we observe a pronounced phase shift of the current transients which is due to oppositely oriented heavy-hole and light-hole type contributions. We are currently developing a microscopic theory based on a 14×14 k.p model in combination with the semiconductor Bloch equations to describe the observed features quantitatively. The combined theoretical and experimental approach will allow us to analyze the influence of the bandstructure and interaction effects on the injection current amplitude and current dynamics.}}, author = {{Bieler, M. and Pierz, K. and Siegner, U. and Dawson, P. and Duc, H. T. and Förstner, Jens and Meier, Torsten}}, booktitle = {{Ultrafast Phenomena in Semiconductors and Nanostructure Materials XIII}}, editor = {{Tsen, Kong-Thon and Song, Jin-Joo and Betz, Markus and Elezzabi, Abdulhakem Y.}}, keywords = {{tet_topic_qw}}, location = {{San Jose (California / USA)}}, pages = {{721404--721404--13}}, publisher = {{SPIE}}, title = {{{Generation of injection currents in (110)-oriented GaAs quantum wells: experimental observation and development of a microscopic theory}}}, doi = {{10.1117/12.811841}}, volume = {{7214}}, year = {{2009}}, } @inproceedings{4181, abstract = {{We experimentally and theoretically investigate microdisk resonators with embedded quantum dots immersed in a liquid crystal in its nematic phase, showing the tunabililty of the photonic modes via external parameters like temperature or electric field.}}, author = {{Förstner, Jens and Meier, Cedrik and Piegdon, Karoline and Declair, Stefan and Hoischen, Andreas and Urbanski, Mark and Meier, Torsten and Kitzerow, Heinz-Siegfried}}, booktitle = {{Advances in Optical Sciences Congress}}, isbn = {{9781557528735}}, keywords = {{tet_topic_microdisk}}, location = {{Honolulu, Hawaii United States}}, publisher = {{OSA Technical Digest (CD) (Optical Society of America, 2009), paper NTuC2}}, title = {{{Coupling Dynamics of Quantum Dots in a Liquid-Crystal-Tunable Microdisk Resonator}}}, doi = {{10.1364/nlo.2009.ntuc2}}, year = {{2009}}, } @article{4187, abstract = {{We study phonon-assisted electron tunneling in semiconductor quantum dot molecules. In particular, singletsinglet relaxation in a two-electron-doped structure is considered. The influence of Coulomb interaction is discussed via comparison with a single-electron system. We find that the relaxation rate reaches similar values in the two cases but the Coulomb interaction shifts the maximum rates toward larger separations between the dots. The difference in electron-phonon interaction between deformation potential and piezoelectric coupling is investigated. We show that the phonon-induced tunneling between two-electron singlet states is a fast process, taking place on the time scales of the order of a few tens of picoseconds.}}, author = {{Grodecka, A. and Machnikowski, P. and Förstner, Jens}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qd}}, number = {{8}}, publisher = {{American Physical Society (APS)}}, title = {{{Phonon-assisted tunneling between singlet states in two-electron quantum dot molecules}}}, doi = {{10.1103/physrevb.78.085302}}, volume = {{78}}, year = {{2008}}, } @article{4256, abstract = {{We present phase-resolved pulse propagation measurements that allow us to fully describe the transition between several light–matter interaction regimes. The complete range from linear excitation to the breakdown of the photonic bandgap on to self-induced transmission and self-phase modulation is studied on a high-quality multiple-quantum-well Bragg structure. An improved fast-scanning cross-correlation frequency-resolved optical gating setup is applied to retrieve the pulse phase with an excellent signal-tonoise ratio. Calculations using the semiconductor Maxwell–Bloch equations show qualitative agreement with the experimental findings. }}, author = {{zu Siederdissen, Tilman Höner and Nielsen, Nils C. and Kuhl, Jürgen and Schaarschmidt, Martin and Förstner, Jens and Knorr, Andreas and Khitrova, Galina and Gibbs, Hyatt M. and Koch, Stephan W. and Giessen, Harald}}, issn = {{0146-9592}}, journal = {{Optics Letters}}, keywords = {{tet_topic_polariton, tet_topic_qw}}, number = {{11}}, publisher = {{The Optical Society}}, title = {{{Transition between different coherent light–matter interaction regimes analyzed by phase-resolved pulse propagation}}}, doi = {{10.1364/ol.30.001384}}, volume = {{30}}, year = {{2008}}, } @article{4317, abstract = {{Phonon-assisted singlet-singlet relaxation in semiconductor quantum dot molecules is studied theoretically. Laterally coupled quantum dot structures doped with two electrons are considered. We take into account interaction with acoustic phonon modes via deformation potential and piezoelectric coupling. We show that piezoelectric mechanism for the considered system is of great importance and for some ranges of quantum dot molecule parameters is the dominant contribution to relaxation. It is shown that the phonon-assisted tunneling is much faster (down to ∼ 6 ps even at zero temperature) in comparison with other decoherence processes. The influence of Coulomb interaction is discussed and its consequences are indicated. We calculate the relaxation rates for GaAs quantum dot molecules and study the dependence on quantum dot size, distance and offset between the constituent quantum dots. In addition the temperature dependence of the tunneling rates is analyzed.}}, author = {{Grodecka, Anna and Machnikowski, Paweł and Förstner, Jens}}, issn = {{1610-1634}}, journal = {{physica status solidi (c)}}, keywords = {{tet_topic_qd}}, number = {{2}}, pages = {{474--478}}, publisher = {{Wiley}}, title = {{{Theoretical study of phononassisted singlet-singlet relaxation in two-electron semiconductor quantum dot molecules}}}, doi = {{10.1002/pssc.200880319}}, volume = {{6}}, year = {{2008}}, } @article{4303, abstract = {{The interaction of strong low-area pulses with two-level systems shows absorption line narrowing and hole burning within the homogeneous linewidth as a result of nonlinear wave mixing. The wave mixing results from the two-level electronic saturation nonlinearity and occurs, depending on the sign of the pulse area, as a strong absorption enhancement or gain at the transition frequency of the two-level system for resonant excitation.}}, author = {{Förstner, Jens and Knorr, A. and Lindberg, M. and Koch, S. W.}}, issn = {{0146-9592}}, journal = {{Optics Letters}}, keywords = {{tet_topic_polariton}}, number = {{20}}, publisher = {{The Optical Society}}, title = {{{Line narrowing and hole burning within the homogeneous linewidth: a new wave-mixing effect in two-level systems}}}, doi = {{10.1364/ol.27.001830}}, volume = {{27}}, year = {{2007}}, } @article{4189, abstract = {{We theoretically study the biexciton-phonon interaction in strongly confined semiconductor quantum dots. For spectrally narrow single-pulse excitation generation of biexcitonic occupations is only possible via a two-photon cascade, which exhibits renormalized Rabi oscillations and spectrally compressed phononsidebands.}}, author = {{Förstner, Jens and Knorr, A. and Moloney, J. V.}}, issn = {{1610-1634}}, journal = {{physica status solidi (c)}}, keywords = {{tet_topic_qd}}, number = {{7}}, pages = {{2389--2392}}, publisher = {{Wiley}}, title = {{{Interplay of electron-phonon and Coulomb interaction in semiconductor quantum dots}}}, doi = {{10.1002/pssc.200668111}}, volume = {{3}}, year = {{2006}}, } @inproceedings{4241, abstract = {{We discuss second-harmonic generation experiments on planar arrays of magnetic split-ring resonators, using 150 fs pulses at 1.5 mum wavelength. Lithographic tuning reveals by far the largest signals when exciting the magnetic-dipole resonance.}}, author = {{Klein, M. W. and Enkrich, C. and Wegener, M. and Förstner, Jens and Moloney, J. V. and Hoyer, W. and Stroucken, T. and Meier, Torsten and Koch, S. W. and Linden, S.}}, booktitle = {{2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference}}, isbn = {{9781557528131}}, issn = {{2160-9004 }}, keywords = {{tet_topic_meta}}, location = {{Long Beach, CA (USA)}}, publisher = {{IEEE}}, title = {{{Optical experiments on second-harmonic generation from metamaterials consisting of split-ring resonators}}}, doi = {{10.1109/cleo.2006.4629006}}, year = {{2006}}, } @article{4243, abstract = {{We investigate the optical properties of a Coulomb-coupled double-quantum dot system excited by coherent light pulses. Basic effects of Coulomb coupling regarding linear and nonlinear optical processes are discussed. By numerically solving the Heisenberg equation of motion we are able to present the temporal evolution of the system’s density matrix for a wide range of coupling parameters. The two main coupling effects in dipole approximation, biexcitonic shift and Förster energy transfer, are investigated and their qualitative and quantitative influence on absorption spectra, Rabi oscillations, and single- and two-pulse excitation is discussed. We present simulated differential transmission spectra to allow for comparison with recent experimental studies.}}, author = {{Danckwerts, J. and Ahn, K. J. and Förstner, Jens and Knorr, A.}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qd}}, number = {{16}}, pages = {{165318--165318--18}}, publisher = {{American Physical Society (APS)}}, title = {{{Theory of ultrafast nonlinear optics of Coulomb-coupled semiconductor quantum dots: Rabi oscillations and pump-probe spectra}}}, doi = {{10.1103/physrevb.73.165318}}, volume = {{73}}, year = {{2006}}, } @inproceedings{4191, abstract = {{We study optical second-harmonic generation from planar arrays of magnetic split-ring resonators at 1.5 microns resonance wavelength. We obtain by far the largest signals when exciting the magnetic-dipole resonance. }}, author = {{Klein, Matthias W. and Enkrich, Christian and Wegener, Martin and Förstner, Jens and Moloney, Jerome V. and Hoyer, Walter and Stroucken, Tineke and Meier, Torsten and Koch, Stephan W. and Linden, Stefan}}, booktitle = {{Photonic Metamaterials: From Random to Periodic}}, isbn = {{155752808X}}, keywords = {{tet_topic_meta}}, publisher = {{OSA}}, title = {{{Optical Experiments on Second-Harmonic Generation with Metamaterials Composed of Split-Ring Resonators}}}, doi = {{10.1364/meta.2006.tuc5}}, year = {{2006}}, } @inproceedings{4247, abstract = {{We numerically investigate strong light-matter interaction and normal mode coupling/splitting in a system composed of a single two-level atom and the localized mode of a small mode volume photonic crystal nanocavity.}}, author = {{Förstner, Jens and Dineen, Colm and Zakharian, A.R. and Moloney, Jerome V. and Koch, Stephan W.}}, booktitle = {{Frontiers in Optics}}, isbn = {{1557527970}}, publisher = {{OSA}}, title = {{{Normal Mode Coupling in Photonic Crystal Nanocavities}}}, doi = {{10.1364/fio.2005.fwc2}}, year = {{2005}}, } @article{4249, abstract = {{The interaction of electrons with LO phonons provides an important mechanism of optical dephasing and carrier scattering for the two-dimensional electron gas in semiconductor quantum wells. In this paper, the corresponding ultrafast nonlinearities for off-resonant and resonant intersubband excitations are investigated. Quantum kinetic effects of the electron-phonon interaction and the corresponding violation of the microscopic energy conservation yield a qualitative different picture compared to the standard Markovian theory, if the phonon energy is larger than the intersubband-gap energy.}}, author = {{Butscher, Stefan and Förstner, Jens and Waldmüller, Inès and Knorr, Andreas}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qw}}, number = {{4}}, pages = {{045314--045314--4}}, publisher = {{American Physical Society (APS)}}, title = {{{Ultrafast electron-phonon interaction of intersubband transitions: Quantum kinetics from adiabatic following to Rabi-oscillations}}}, doi = {{10.1103/physrevb.72.045314}}, volume = {{72}}, year = {{2005}}, } @inproceedings{4251, abstract = {{A system of two quantum dots coupled by dipole‐dipole interaction is investigated within a density matrix approach. We compute the temporal evolution of the system in the linear and nonlinear optical regime and discuss the possibility of performing basic quantum information gates. The influence of the Förster energy transfer on Rabi oscillations is discussed.}}, author = {{Danckwerts, J. and Förstner, Jens and Knorr, A.}}, booktitle = {{AIP Conference Proceedings}}, issn = {{0094-243X}}, keywords = {{tet_topic_qd}}, publisher = {{AIP}}, title = {{{Quantum information processing using Coulomb-coupled quantum dots}}}, doi = {{10.1063/1.1994668}}, volume = {{772}}, year = {{2005}}, } @article{4252, abstract = {{The electromagnetic field of a high-quality photonic crystal nanocavity is computed using the finite difference time domain method. It is shown that a separatrix occurs in the local energy flux discriminating between predominantly near and far field components. Placing a two-level atom into the cavity leads to characteristic field modifications and normalmode splitting in the transmission spectra.}}, author = {{Dineen, C. and Förstner, Jens and Zakharian, A.R. and Moloney, J.V. and Koch, S.W.}}, issn = {{1094-4087}}, journal = {{Optics Express}}, keywords = {{tet_topic_phc}}, number = {{13}}, publisher = {{The Optical Society}}, title = {{{Electromagnetic field structure and normal mode coupling in photonic crystal nanocavities}}}, doi = {{10.1364/opex.13.004980}}, volume = {{13}}, year = {{2005}}, } @article{4254, abstract = {{A microscopic description based on the density matrix formalism is developed to describe the dynamics of photoemission of hot electrons at semiconductor surfaces, including the interaction of bulk and surface states. The equations of motion for the electronic occupations and transitions include the interaction with arbitrary optical fields as well as the electron-phonon coupling. Model wave functions are used to qualitatively describe the bulk-surface dynamics and the subsequent time resolved two-photon photoemission s2PPEd spectra. Our results suggest that it is possible to extract energetic and temporal information of the underlying dynamical occupations of the intermediate states from the 2PPE spectra.}}, author = {{Zeiser, A. and Bücking, N. and Förstner, Jens and Knorr, A.}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, number = {{24}}, publisher = {{American Physical Society (APS)}}, title = {{{Microscopic theory of electron dynamics and time-resolved two-color two-photon photoemission at semiconductor surfaces}}}, doi = {{10.1103/physrevb.71.245309}}, volume = {{71}}, year = {{2005}}, } @inproceedings{4258, abstract = {{A theoretical description of ultrafast phonon induced electronic transport between surface and bulk states after optical excitation is presented. In particular, the influence of the electron transfer processes on two photon photo emission is evaluated. }}, author = {{Bucking, N. and Zeiser, A. and Förstner, Jens and Knorr, A.}}, booktitle = {{2005 Quantum Electronics and Laser Science Conference}}, isbn = {{1557527962}}, pages = {{1929--1931}}, publisher = {{IEEE}}, title = {{{Kinetic theory of the electron transport in the two photon photo emission at semiconductor surfaces}}}, doi = {{10.1109/qels.2005.1549331}}, year = {{2005}}, } @inproceedings{4259, abstract = {{The ultrafast intersubband dynamics in a semiconductor quantum well subband system is investigated theoretically. Non-Markovian electron-phonon interaction leads to polaron formation and enhanced dephasing. }}, author = {{Butscher, S. and Förstner, Jens and Waldmuller, I. and Knorr, A.}}, booktitle = {{2005 Quantum Electronics and Laser Science Conference}}, isbn = {{1557527962}}, pages = {{640--642}}, publisher = {{IEEE}}, title = {{{Ultrafast quantum kinetics of semiconductor intersubband transitions: polaron signatures and dephasing dynamics}}}, doi = {{10.1109/qels.2005.1548881}}, year = {{2005}}, } @article{4260, abstract = {{Using a fully quantized description of strongly confined electrons interacting with acoustic phonons and the photon field, the nonstationary resonance-fluorescence spectra of a semiconductor quantum dot are investigated. For excitation pulses with durations approaching typical electron-phonon scattering times, the virtual quantum processes yield an observable electron-phonon sideband broadening.}}, author = {{Ahn, K. J. and Förstner, Jens and Knorr, A.}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qd}}, number = {{15}}, publisher = {{American Physical Society (APS)}}, title = {{{Resonance fluorescence of semiconductor quantum dots: Signatures of the electron-phonon interaction}}}, doi = {{10.1103/physrevb.71.153309}}, volume = {{71}}, year = {{2005}}, } @article{4262, abstract = {{Time-dependent two-photon photoemission spectra are used to resolve the femtosecond dynamics of hot electrons at the energetically lowest surface resonance of reconstructed InP(100). Two different cases are studied, where electrons either are lifted into the surface resonance via a direct optical transition or are captured from bulk states. These data are the first of this kind recorded with a time resolution below 70 fs. The microscopic analysis shows that electron-phonon scattering is a major mechanism for electron transfer between surface and bulk states.}}, author = {{Töben, L. and Gundlach, L. and Ernstorfer, R. and Eichberger, R. and Hannappel, T. and Willig, F. and Zeiser, A. and Förstner, Jens and Knorr, A. and Hahn, P. H. and Schmidt, W. G.}}, issn = {{0031-9007}}, journal = {{Physical Review Letters}}, number = {{6}}, publisher = {{American Physical Society (APS)}}, title = {{{Femtosecond Transfer Dynamics of Photogenerated Electrons at a Surface Resonance of Reconstructed InP(100)}}}, doi = {{10.1103/physrevlett.94.067601}}, volume = {{94}}, year = {{2005}}, } @article{4264, abstract = {{We demonstrate that the temporal pulse phase remains essentially unaltered before separate phase characteristics are developed when propagating high-intensity pulses coherently on the exciton resonance of an optically thick semiconductor. This behavior is a clear manifestation of self-induced transmission and pulse breakup into solitonlike pulses due to Rabi flopping of the carrier density. Experiments using a novel fast-scan cross-correlation frequency-resolved optical gating (XFROG) method are in good agreement with numerical calculations based on the semiconductor Bloch equations.}}, author = {{Nielsen, N. C. and zu Siederdissen, T. Höner and Kuhl, J. and Schaarschmidt, M. and Förstner, Jens and Knorr, A. and Giessen, H.}}, issn = {{0031-9007}}, journal = {{Physical Review Letters}}, keywords = {{tet_topic_qd}}, number = {{5}}, publisher = {{American Physical Society (APS)}}, title = {{{Phase Evolution of Solitonlike Optical Pulses during Excitonic Rabi Flopping in a Semiconductor}}}, doi = {{10.1103/physrevlett.94.057406}}, volume = {{94}}, year = {{2005}}, }