@article{4120, abstract = {{The intensity dependence of optically-induced injection currents in unbiased GaAs semiconductor quantum wells grown in [110] direction is investigated theoretically for a number of well widths. Our microscopic analysis is based on a 14 x 14 band k . p method in combination with the multisubband semiconductor Bloch equations. An oscillatory dependence of the injection current transients as function of intensity and time is predicted and explained. It is demonstrated that optical excitations involving different subbands and Rabi flopping are responsible for this complex dynamics.}}, author = {{Pochwała, Michał and Duc, Huynh Thanh and Förstner, Jens and Meier, Torsten}}, issn = {{1862-6254}}, journal = {{physica status solidi (RRL) - Rapid Research Letters}}, keywords = {{tet_topic_qw}}, number = {{3}}, pages = {{119--121}}, publisher = {{Wiley}}, title = {{{Intensity-dependent ultrafast dynamics of injection currents in unbiased GaAs quantum wells}}}, doi = {{10.1002/pssr.201004529}}, volume = {{5}}, year = {{2011}}, } @article{4049, abstract = {{The injection of photocurrents by femtosecond laser pulses in (110)-orientedGaAs/AlGaAs quantum wells is investigated theoretically and experimentally. The roomtemperature measurements show an oscillatory dependence of the injection current amplitude and direction on the excitation photon energy. Microscopic calculations using the semiconductor Bloch equations that are set up on the basis of k.p band structure calculations provide a detailed understanding of the experimental findings.}}, author = {{Thanh Duc, Huynh and Förstner, Jens and Meier, Torsten and Priyadarshi, Shekhar and Racu, Ana Maria and Pierz, Klaus and Siegner, Uwe and Bieler, Mark}}, issn = {{1862-6351}}, journal = {{physica status solidi (c)}}, keywords = {{tet_topic_qw}}, number = {{4}}, pages = {{1137--1140}}, publisher = {{Wiley}}, title = {{{Oscillatory excitation energy dependence of injection currents in GaAs/AlGaAs quantum wells}}}, doi = {{10.1002/pssc.201000831}}, volume = {{8}}, year = {{2011}}, } @article{4118, abstract = {{We numerically investigate the coupling between circular resonators and study strong light‐matter coupling of single as well as multiple circular resonators to quantum‐mechanical resonators in two dimensional model simulations. For all cases, the computed resonances of the coupled system as function of the detuning show anti‐crossings. The obtained mode splittings of coupled optical resonators are strongly depending on distance and cluster in almost degenerate eigenstates for large distances, as is known from coupled resonator optical waveguides. Vacuum Rabi splitting is observed for a quantum dot strongly coupled to eigenmodes of single perfectly cylindrical resonators. }}, author = {{Declair, S. and Meier, Torsten and Förstner, Jens}}, issn = {{1862-6351}}, journal = {{physica status solidi (c)}}, keywords = {{tet_topic_phc, tet_topic_microdisk}}, number = {{4}}, pages = {{1254--1257}}, publisher = {{Wiley}}, title = {{{Numerical investigation of the coupling between microdisk modes and quantum dots}}}, doi = {{10.1002/pssc.201000869}}, volume = {{8}}, year = {{2011}}, } @article{4040, abstract = {{We numerically investigate the interaction dynamics of coupled cavities in planar photonic crystal slabs in different configurations. The single cavity is optimized for a long lifetime of the fundamental mode, reaching a Q-factor of ≈43, 000 using the method of gentle confinement. For pairs of cavities we consider several configurations and present a setup with strongest coupling observable as a line splitting of about 30 nm. Based on this configuration, setups with three cavities are investigated.}}, author = {{Declair, S. and Meier, Torsten and Zrenner, Artur and Förstner, Jens}}, issn = {{1569-4410}}, journal = {{Photonics and Nanostructures - Fundamentals and Applications}}, keywords = {{tet_topic_phc}}, number = {{4}}, pages = {{345--350}}, publisher = {{Elsevier BV}}, title = {{{Numerical analysis of coupled photonic crystal cavities}}}, doi = {{10.1016/j.photonics.2011.04.012}}, volume = {{9}}, year = {{2011}}, } @article{4044, abstract = {{A simulation environment for metallic nanostructures based on the Discontinuous Galerkin Time Domain method is presented. The model is used to compute the linear and nonlinear optical response of split ring resonators and to study physical mechanisms that contribute to second harmonic generation.}}, author = {{Grynko, Yevgen and Förstner, Jens and Meier, Torsten}}, issn = {{1825-1242}}, journal = {{AAPP | Atti della Accademia Peloritana dei Pericolanti}}, keywords = {{tet_topic_numerics, tet_topic_shg, tet_topic_meta}}, number = {{1}}, title = {{{Application of the discontinous Galerkin time domain method to the optics of metallic nanostructures}}}, doi = {{10.1478/C1V89S1P041}}, volume = {{89}}, year = {{2011}}, } @article{4091, abstract = {{We present a nonequilibrium ab initio method for calculating nonlinear and nonlocal optical effects in metallic slabs with a thickness of several nanometers. The numerical analysis is based on the full solution of the time‐dependent Kohn–Sham equations for a jellium system and allows to study the optical response of metal electrons subject to arbitrarily shaped intense light pulses. We find a strong localization of the generated second‐harmonic current in the surface regions of the slabs. }}, author = {{Wand, Mathias and Schindlmayr, Arno and Meier, Torsten and Förstner, Jens}}, issn = {{1521-3951}}, journal = {{Physica Status Solidi B}}, keywords = {{tet_topic_shg}}, number = {{4}}, pages = {{887--891}}, publisher = {{Wiley-VCH}}, title = {{{Simulation of the ultrafast nonlinear optical response of metal slabs}}}, doi = {{10.1002/pssb.201001219}}, volume = {{248}}, year = {{2011}}, } @inproceedings{4122, abstract = {{We experimentally and theoretically investigate injection currents generated by femtosecond single-color circularly-polarized laser pulses in (110)-oriented GaAs quantum wells. The current measurements are performed by detecting the emitted Terahertz radiation at room temperature. The microscopic theory is based on a 14 x 14 k • p band-structure calculation in combination with the multi-subband semiconductor Bloch equations. For symmetric GaAs quantum wells grown in (110) direction, an oscillatory dependence of the injection currents on the exciting photon energy is obtained. The results of the microscopic theory are in good agreement with the measurements. }}, author = {{Duc, H. T. and Pochwala, M. and Förstner, Jens and Meier, Torsten and Priyadarshi, S. and Racu, A. M. and Pierz, K. and Siegner, U. and Bieler, M.}}, booktitle = {{Ultrafast Phenomena in Semiconductors and Nanostructure Materials XV}}, editor = {{Tsen, Kong-Thon and Song, Jin-Joo and Betz, Markus and Elezzabi, Abdulhakem Y.}}, keywords = {{tet_topic_qw}}, publisher = {{SPIE}}, title = {{{Injection currents in (110)-oriented GaAs/AlGaAs quantum wells: recent progress in theory and experiment}}}, doi = {{10.1117/12.876972}}, volume = {{7937}}, year = {{2011}}, } @article{4046, abstract = {{We demonstrate by spin quantum beat spectroscopy that in undoped symmetric (110)-oriented GaAs/AlGaAs single quantum wells, even a symmetric spatial envelope wave function gives rise to an asymmetric in-plane electron Land´e g-factor. The anisotropy is neither a direct consequence of the asymmetric in-plane Dresselhaus splitting nor a direct consequence of the asymmetric Zeeman splitting of the hole bands, but rather it is a pure higher-order effect that exists as well for diamond-type lattices. The measurements for various well widths are very well described within 14 × 14 band k·p theory and illustrate that the electron spin is an excellent meter variable for mapping out the internal—otherwise hidden—symmetries in two-dimensional systems. Fourth-order perturbation theory yields an analytical expression for the strength of the g-factor anisotropy, providing a qualitative understanding of the observed effects.}}, author = {{Hübner, J. and Kunz, S. and Oertel, S. and Schuh, D. and Pochwała, M. and Duc, H. T. and Förstner, Jens and Meier, Torsten and Oestreich, M.}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qw}}, number = {{4}}, pages = {{041301(R)}}, publisher = {{American Physical Society (APS)}}, title = {{{Electron g-factor anisotropy in symmetric (110)-oriented GaAs quantum wells}}}, doi = {{10.1103/physrevb.84.041301}}, volume = {{84}}, year = {{2011}}, } @article{4129, abstract = {{We study a single quantum dot molecule doped with one electron in the presence of electron-phonon coupling. Both diagonal and off-diagonal interactions representing real and virtual processes with acoustic phonons via deformation potential and piezoelectric coupling are taken into account. We employ a non-perturbative quantum kinetic theory and show that the phonon-mediated relaxation is dominated by an electron tunneling on a picosecond time scale.A dependence of the relaxation on the temperature and the strength of the tunneling coupling is analyzed.}}, author = {{Grodecka-Grad, Anna and Förstner, Jens}}, issn = {{1742-6596}}, journal = {{Journal of Physics: Conference Series}}, keywords = {{tet_topic_qd}}, publisher = {{IOP Publishing}}, title = {{{Phonon-mediated relaxation in doped quantum dot molecules}}}, doi = {{10.1088/1742-6596/245/1/012035}}, volume = {{245}}, year = {{2010}}, } @article{4174, abstract = {{A quantum dot molecule doped with a single electron in the presence of diagonal and off-diagonal carrierphonon couplings is studied by means of a nonperturbative quantum kinetic theory. The interaction with acoustic phonons by deformation potential and piezoelectric coupling is taken into account. We show that the phonon-mediated relaxation is fast on a picosecond time scale and is dominated by the usually neglected off-diagonal coupling to the lattice degrees of freedom leading to phonon-assisted electron tunneling. We show that in the parameter regime of current electrical and optical experiments, the microscopic non-Markovian theory has to be employed.}}, author = {{Grodecka-Grad, A. and Förstner, Jens}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qd}}, number = {{11}}, publisher = {{American Physical Society (APS)}}, title = {{{Theory of phonon-mediated relaxation in doped quantum dot molecules}}}, doi = {{10.1103/physrevb.81.115305}}, volume = {{81}}, year = {{2010}}, } @article{4127, abstract = {{The dynamics of charge and spin injection currents excited by circularly polarized, one-color laser beams in semiconductor quantum wells is analyzed. Our microscopic approach is based on a 14x14 k · p band-structure theory in combination with multisubband semiconductor Bloch equations which allows a detailed analysis of the photogenerated carrier distributions and coherences in k space. Charge and spin injection currents are numerically calculated for [110]- and [001]-grown GaAs quantum wells including dc population contributions and ac contributions that arise from intersubband coherences. The dependencies of the injection currents on the excitation conditions, in particular, the photon energy are computed and discussed.}}, author = {{Duc, Huynh Thanh and Förstner, Jens and Meier, Torsten}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qw}}, number = {{11}}, publisher = {{American Physical Society (APS)}}, title = {{{Microscopic analysis of charge and spin photocurrents injected by circularly polarized one-color laser pulses in GaAs quantum wells}}}, doi = {{10.1103/physrevb.82.115316}}, volume = {{82}}, year = {{2010}}, } @inproceedings{4176, abstract = {{A microscopic theory that describes injection currents in GaAs quantum wells is presented. 14 × 14 band k.p theory is used to compute the band structure including anisotropy and spin-orbit interaction. Transient injection currents are obtained via numerical solutions of the semiconductor Bloch equations. Depending on the growth direction of the considered quantum well system and the propagation and polarization directions of the incident light beam, it is possible to generate charge and/or spin photocurrents on ultrashort time scales. The dependence of the photocurrents on the excitation conditions is computed and discussed.}}, author = {{Duc, Huynh Thanh and Förstner, Jens and Meier, Torsten}}, booktitle = {{Ultrafast Phenomena in Semiconductors and Nanostructure Materials XIV}}, editor = {{Song, Jin-Joo and Tsen, Kong-Thon and Betz, Markus and Elezzabi, Abdulhakem Y.}}, keywords = {{tet_topic_qw}}, pages = {{76000S--76000S--9}}, publisher = {{SPIE}}, title = {{{Microscopic theoretical analysis of optically generated injection currents in semiconductor quantum wells}}}, doi = {{10.1117/12.840388}}, volume = {{7600}}, year = {{2010}}, } @article{4177, abstract = {{Excitonic spectra of weakly disordered semiconductor heterostructures are simulated on the basis of a one-dimensional tight-binding model. The influence of the length scale of weak disorder in quantum wells on the redshift of the excitonic peak and its linewidth is studied. By calculating two-dimensional Fouriertransform spectra we are able to determine the contribution of disorder to inhomogeneous and also to homogeneous broadenings separately. This disorder-induced dephasing is related to a Fano-type coupling and leads to contributions to the homogeneous linewidth that depends on energy within the inhomogeneously broadened line. The model includes heavy- and light-hole excitons and yields smaller inhomogeneous broadening for the light-hole exciton if compared to the heavy-hole exciton, which agrees qualitatively with the experiment.}}, author = {{Kuznetsova, I. and Gőgh, N. and Förstner, Jens and Meier, Torsten and Cundiff, S. T. and Varga, I. and Thomas, P.}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qw}}, number = {{7}}, publisher = {{American Physical Society (APS)}}, title = {{{Modeling excitonic line shapes in weakly disordered semiconductor nanostructures}}}, doi = {{10.1103/physrevb.81.075307}}, volume = {{81}}, year = {{2010}}, } @article{4125, abstract = {{We numerically investigate the behavior of Whispering Gallery Modes (WGMs) in circularly shaped resonators like microdisks, with diameters in the range of optical vacuum wavelengths. The microdisk is embedded in an uniaxial anisotropic dielectric environment. By changing the optical anisotropy, one obtains spectral tunability of the optical modes. The degree of tunability strongly depends on the radial (azimuthal) mode order M (N). As the modes approach each other spectrally, anticrossing is observed, leading to a rearrangement of the optical states.}}, author = {{Declair, S. and Meier, Cedrik and Meier, Torsten and Förstner, Jens}}, issn = {{1569-4410}}, journal = {{Photonics and Nanostructures - Fundamentals and Applications}}, keywords = {{tet_topic_microdisk}}, number = {{4}}, pages = {{273--277}}, publisher = {{Elsevier BV}}, title = {{{Anticrossing of Whispering Gallery Modes in microdisk resonators embedded in an anisotropic environment}}}, doi = {{10.1016/j.photonics.2010.03.002}}, volume = {{8}}, year = {{2010}}, } @article{4123, abstract = {{GaAs-based semiconductor microdisks with high quality whispering gallery modes (Q44000) have been fabricated.A layer of self-organized InAs quantumdots (QDs) served as a light source to feed the optical modes at room temperature. In order to achieve frequency tuning of the optical modes, the microdisk devices have been immersed in 4 – cyano – 4´-pentylbiphenyl (5CB), a liquid crystal(LC) with a nematic phase below the clearing temperature of TC≈34°C .We have studied the device performance in the temperature rangeof T=20-50°C, in order to investigate the influence of the nematic–isotropic phase transition on the optical modes. Moreover,we havea pplied an AC electric field to the device,which leads in the nematic phase to a reorientation of the anisotropic dielectric tensor of the liquid crystal.This electrical anisotropy can be used to achieve electrical tunability of the optical modes.Using the finite-difference time domain (FDTD) technique with an anisotropic material model, we are able to describe the influence of the liquid crystal qualitatively.}}, author = {{Piegdon, Karoline A. and Offer, Matthias and Lorke, Axel and Urbanski, Martin and Hoischen, Andreas and Kitzerow, Heinz-Siegfried and Declair, Stefan and Förstner, Jens and Meier, Torsten and Reuter, Dirk and Wieck, Andreas D. and Meier, Cedrik}}, issn = {{1386-9477}}, journal = {{Physica E: Low-dimensional Systems and Nanostructures}}, keywords = {{tet_topic_qd, tet_topic_microdisk}}, number = {{10}}, pages = {{2552--2555}}, publisher = {{Elsevier BV}}, title = {{{Self-assembled quantum dots in a liquid-crystal-tunable microdisk resonator}}}, doi = {{10.1016/j.physe.2009.12.051}}, volume = {{42}}, year = {{2010}}, } @article{4169, abstract = {{It is demonstrated that valence-band mixing in GaAs quantum wells tremendously modifies electronic transport. A coherent control scheme in which ultrafast currents are optically injected into undoped GaAs quantum wells upon excitation with femtosecond laser pulses is employed. An oscillatory dependence of the injection current amplitude and direction on the excitation photon energy is observed. A microscopic theoretical analysis shows that this current reversal is caused by the coupling of the light- and heavy-hole bands and that the hole currents dominate the overall current response. These surprising consequences of band mixing illuminate fundamental physics as they are unique for experiments which are able to monitor electronic transport resulting from carriers with relatively large momenta.}}, author = {{Priyadarshi, S. and Racu, A. M. and Pierz, K. and Siegner, U. and Bieler, M. and Duc, H. T. and Förstner, Jens and Meier, Torsten}}, issn = {{0031-9007}}, journal = {{Physical Review Letters}}, keywords = {{tet_topic_qw}}, number = {{21}}, publisher = {{American Physical Society (APS)}}, title = {{{Reversal of Coherently Controlled Ultrafast Photocurrents by Band Mixing in Undoped GaAs Quantum Wells}}}, doi = {{10.1103/physrevlett.104.217401}}, volume = {{104}}, year = {{2010}}, } @inproceedings{4167, abstract = {{The electromagnetic field in the vicinity of sharp edges needs a special treatment in numeric calculation whenever accurate, fast converging results are necessary. One of the fundamental works concerning field singularities has been proposed in 1972 [1] and states that the electromagnetic energy density must be integrable over any finite domain, even if this domain contains singularities. It is shown, that the magnetic field H(, ϕ) and electric field E(, ϕ) are proportional to ∝ (t−1) for  → 0. The variable  is the distance to the edge and t has to fulfill the integrability condition and thus is restricted to 0 < t < 1. This result is often used to reduce the error corresponding to the singularity without increasing the numerical effort [2 - 5]. For this purpose, a correction factor K is estimated by inserting the proportionality into the wave equation. It is shown, that this method improves the accuracy of the result significantly, however the order of convergence is often not studied. In [4] a method to modify the material parameters in order to use analytic results to improve the numeric calculation is presented. In this contribution we will - inspired by the scheme given in [4] - develop a new method to estimate a correction factor for perfect conducting materials (PEC) and demonstrate the improvement of the results compared to the standard edge correction. Therefore analytic results (comparable to [1]) are consequently merged with the scheme in [4]. The main goal of this work is the calculation of the second harmonic generation (SHG) in the wave response of so-called metamaterials [6]. Frequently these structures contain sharp metallic edges with field singularities at the interfaces which have a strong impact on the SHG signals. Thus, an accurate simulation of singularities is highly important. However, the following approach can also be applied to many other setups, and one of them is shown in the example below.}}, author = {{Classen, C and Förstner, Jens and Meier, Torsten and Schuhmann, R}}, booktitle = {{2010 IEEE Antennas and Propagation Society International Symposium}}, isbn = {{9781424449675}}, keywords = {{tet_topic_numerics}}, location = {{Toronto, ON, Canada}}, publisher = {{IEEE}}, title = {{{Enhanced FDTD edge correction for nonlinear effects calculation}}}, doi = {{10.1109/aps.2010.5562017}}, year = {{2010}}, } @article{4172, abstract = {{Microdisks made from GaAs with embedded InAs quantum dots are immersed in the liquid crystal 4-cyano-4’-pentylbiphenyl (5CB). The quantum dots serve as emitters feeding the optical modes of the photonic cavity. By changing temperature, the liquid crystal undergoes a phase transition from the isotropic to the nematic state, which can be used as an effective tuning mechanism of the photonic modes of the cavity. In the nematic state, the uniaxial electrical anisotropy of the liquid crystal molecules can be exploited for orienting the material in an electric field, thus externally controlling the birefringence of the material. Using this effect, an electric field induced tuning of the modes is achieved. Numerical simulations using the finite-differences time-domain (FDTD) technique employing an anisotropic dielectric medium allow to understand the alignment of the liquid crystal molecules on the surface of the microdisk resonator.}}, author = {{Piegdon, Karoline A. and Declair, Stefan and Förstner, Jens and Meier, Torsten and Matthias, Heiner and Urbanski, Martin and Kitzerow, Heinz-Siegfried and Reuter, Dirk and Wieck, Andreas D. and Lorke, Axel and Meier, Cedrik}}, issn = {{1094-4087}}, journal = {{Optics Express}}, keywords = {{tet_topic_qd, tet_topic_microdisk}}, number = {{8}}, publisher = {{The Optical Society}}, title = {{{Tuning quantum-dot based photonic devices with liquid crystals}}}, doi = {{10.1364/oe.18.007946}}, volume = {{18}}, year = {{2010}}, } @inproceedings{4180, abstract = {{We show that an optically driven carrier spin undergoes indirect dephasing even in the absence of spin-reservoir coupling and illustrate it for phonon-induced decoherence during optical spin rotation in a single quantum dot.}}, author = {{Grodecka, Anna and Machnikowski, Pawel and Förstner, Jens}}, booktitle = {{Advances in Optical Sciences Congress}}, isbn = {{9781557528735}}, keywords = {{tet_topic_qd}}, publisher = {{OSA Technical Digest (CD) (Optical Society of America, 2009)}}, title = {{{Indirect Dephasing Channel for Optically Controlled Spin in a Single Quantum Dot}}}, doi = {{10.1364/nlo.2009.nma1}}, year = {{2009}}, } @article{4182, abstract = {{We demonstrate that an optically driven spin of a carrier in a quantum dot undergoes indirect dephasing via conditional optically induced charge evolution even in the absence of any direct interaction between the spin and its environment. A generic model for the indirect dephasing with a three-component system with spin, charge, and reservoir is proposed. This indirect decoherence channel is studied for the optical spin manipulation in a quantum dot with a microscopic description of the charge-phonon interaction taking into account its non-Markovian nature.}}, author = {{Grodecka, A. and Machnikowski, P. and Förstner, Jens}}, issn = {{1050-2947}}, journal = {{Physical Review A}}, keywords = {{tet_topic_qd}}, number = {{4}}, publisher = {{American Physical Society (APS)}}, title = {{{Indirect spin dephasing via charge-state decoherence in optical control schemes in quantum dots}}}, doi = {{10.1103/physreva.79.042331}}, volume = {{79}}, year = {{2009}}, }