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Publications

This is the list of all peer-reviewed conference proceedings, journal articles, and book contributions of the TET group and pre-TET publications by Jens Förstner.

If something needs correction, or if you would like a reprint, please let us know. You can apply more/different filters in the RIS database interface.


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2018

Unveiling and Imaging Degenerate States in Plasmonic Nanoparticles with Nanometer Resolution

V. Myroshnychenko, N. Nishio, F.J. García de Abajo, J. Förstner, N. Yamamoto, ACS Nano (2018), pp. 8436-8446

DOI
Abstract

Metal nanoparticles host localized plasmon excitations that allow the manipulation of optical fields at the nanoscale. Despite the availability of several techniques for imaging plasmons, direct access into the symmetries of these excitations remains elusive, thus hindering progress in the development of applications. Here, we present a combination of angle-, polarization-, and space-resolved cathodoluminescence spectroscopy methods to selectively access the symmetry and degeneracy of plasmonic states in lithographically fabricated gold nanoprisms. We experimentally reveal and spatially map degenerate states of multipole plasmon modes with nanometer spatial resolution and further provide recipes for resolving optically dark and out-of-plane modes. Full-wave simulations in conjunction with a simple tight-binding model explain the complex plasmon structure in these particles and reveal intriguing mode-symmetry phenomena. Our approach introduces systematics for a comprehensive symmetry characterization of plasmonic states in high-symmetry nanostructures.


Ultrafast electric phase control of a single exciton qubit

A. Widhalm, A. Mukherjee, S. Krehs, N. Sharma, P. Kölling, A. Thiede, D. Reuter, J. Förstner, A. Zrenner, Applied Physics Letters (2018), pp. 111105

DOI
Abstract

We report on the coherent phase manipulation of quantum dot excitons by electric means. For our experiments, we use a low capacitance single quantum dot photodiode which is electrically controlled by a custom designed SiGe:C BiCMOS chip. The phase manipulation is performed and quantified in a Ramsey experiment, where ultrafast transient detuning of the exciton energy is performed synchronous to double pulse p/2 ps laser excitation. We are able to demonstrate electrically controlled phase manipulations with magnitudes up to 3p within 100 ps which is below the dephasing time of the quantum dot exciton.


Intensity surge and negative polarization of light from compact irregular particles

Y. Grynko, Y. Shkuratov, J. Förstner, Optics Letters (2018)

DOI
Abstract

We study the dependence of the intensity and linear polarization of light scattered by isolated particles with the compact irregular shape on their size using the discontinuous Galerkin time domain numerical method. The size parameter of particles varies in the range of X = 10 to 150, and the complex refractive index is m = 1.5 + 0i. Our results show that the backscattering negative polarization branch weakens monotonously, but does not disappear at large sizes, up to the geometrical optics regime, and can be simulated without accounting for wave effects. The intensity backscattering surge becomes narrower with increasing particle size. For X = 150, the surge width is several degrees.


Tailored UV Emission by Nonlinear IR Excitation from ZnO Photonic Crystal Nanocavities

S.P. Hoffmann, M. Albert, N. Weber, D. Sievers, J. Förstner, T. Zentgraf, C. Meier, ACS Photonics (2018), pp. 1933-1942

DOI

Solving Maxwell's Equations with Modern C++ and SYCL: A Case Study

A. Afzal, C. Schmitt, S. Alhaddad, Y. Grynko, J. Teich, J. Förstner, F. Hannig, in: Proceedings of the 29th Annual IEEE International Conference on Application-specific Systems, Architectures and Processors (ASAP), 2018, pp. 49-56

Abstract

In scientific computing, unstructured meshes are a crucial foundation for the simulation of real-world physical phenomena. Compared to regular grids, they allow resembling the computational domain with a much higher accuracy, which in turn leads to more efficient computations.<br />There exists a wealth of supporting libraries and frameworks that aid programmers with the implementation of applications working on such grids, each built on top of existing parallelization technologies. However, many approaches require the programmer to introduce a different programming paradigm into their application or provide different variants of the code. SYCL is a new programming standard providing a remedy to this dilemma by building on standard C ++17 with its so-called single-source approach: Programmers write standard C ++ code and expose parallelism using C++17 keywords. The application is<br />then transformed into a concrete implementation by the SYCL implementation. By encapsulating the OpenCL ecosystem, different SYCL implementations enable not only the programming of CPUs but also of heterogeneous platforms such as GPUs or other devices. For the first time, this paper showcases a SYCL-<br />based solver for the nodal Discontinuous Galerkin method for Maxwell’s equations on unstructured meshes. We compare our solution to a previous C-based implementation with respect to programmability and performance on heterogeneous platforms.<br


OpenCL-based FPGA Design to Accelerate the Nodal Discontinuous Galerkin Method for Unstructured Meshes

T. Kenter, G. Mahale, S. Alhaddad, Y. Grynko, C. Schmitt, A. Afzal, F. Hannig, J. Förstner, C. Plessl, in: Proc. Int. Symp. on Field-Programmable Custom Computing Machines (FCCM), IEEE, 2018


2017

Radar backscattering from a large-grain cometary coma: numerical simulation

S. Dogra, Y. Grynko, E. Zubko, J. Förstner, Astronomy & Astrophysics (2017)

DOI
Abstract

We numerically simulate the circular polarization ratio of the radar signal backscattered from a large-grain cometary coma and compare the simulation results with the radar measurements for seven comets. We apply the discrete dipole approximation method and a model of random irregular particles. Our results confirm water ice composition of the cm-sized chunks detected by the NASA Deep Impact space probe in the vicinity of the nucleus of Comet 103P/Hartley 2. The index of the power-law size distribution in this case can be constrained to the range n ≈ 3.3–4.3. For the other considered comets the circular polarization ratio can be reproduced with variations of the power index between 2 and 5.


Flexible FPGA design for FDTD using OpenCL

T. Kenter, J. Förstner, C. Plessl, in: Proc. Int. Conf. on Field Programmable Logic and Applications (FPL), IEEE, 2017

DOI

Hybrid coupled-mode modeling in 3D: perturbed and coupled channels, and waveguide crossings

M. Hammer, S. Alhaddad, J. Förstner, Journal of the Optical Society of America B (2017), pp. 613-624

DOI
Abstract

The 3D implementation of a hybrid analytical/numerical variant of the coupled-mode theory is discussed. Eigenmodes of the constituting dielectric channels are computed numerically. The frequency-domain coupled-mode models then combine these into fully vectorial approximations for the optical electromagnetic fields of the composite structure. Following a discretization of amplitude functions by 1D finite elements, pro- cedures from the realm of finite-element numerics are applied to establish systems of linear equations for the then- discrete modal amplitudes. Examples substantiate the functioning of the technique and allow for some numerical assessment. The full 3D simulations are highly efficient in memory consumption, moderately demanding in com- putational time, and, in regimes of low radiative losses, sufficiently accurate for practical design. Our results include the perturbation of guided modes by changes of the refractive indices, the interaction of waves in parallel, horizontally or vertically coupled straight waveguides, and a series of crossings of potentially overlapping channels with fairly arbitrary relative positions and orientations.


Spiral modes supported by circular dielectric tubes and tube segments

L. Ebers, M. Hammer, J. Förstner, Optical and Quantum Electronics (2017), pp. 49:176

DOI
Abstract

The modal properties of curved dielectric slab waveguides are investigated. We consider quasi-confined, attenuated modes that propagate at oblique angles with respect to the axis through the center of curvature. Our analytical model describes the transition from scalar 2-D TE/TM bend modes to lossless spiral waves at near-axis propagation angles, with a continuum of vectorial attenuated spiral modes in between. Modal solutions are characterized in terms of directional wavenumbers and attenuation constants. Examples for vectorial mode profiles illustrate the effects of oblique wave propagation along the curved slab segments. For the regime of lossless spiral waves, the relation with the guided modes of corresponding dielectric tubes is demonstrated.


Simulation of Second Harmonic Generation from Photonic Nanostructures Using the Discontinuous Galerkin Time Domain Method

Y. Grynko, J. Förstner, in: Recent Trends in Computational Photonics, Springer International Publishing, 2017, pp. 261-284

DOI
Abstract

We apply the Discontinuous Galerkin Time Domain (DGTD) method for numerical simulations of the second harmonic generation from various metallic nanostructures. A Maxwell–Vlasov hydrodynamic model is used to describe the nonlinear effects in the motion of the excited free electrons in a metal. The results are compared with the corresponding experimental measurements for split-ring resonators and plasmonic gap antennas.


Directional Emission from Dielectric Leaky-Wave Nanoantennas

M. Peter, A. Hildebrandt, C. Schlickriede, K. Gharib, T. Zentgraf, J. Förstner, S. Linden, Nano Letters (2017), pp. 4178-4183

DOI

Direction-tunable enhanced emission from a subwavelength metallic double-nanoslit structure

X. Song, N. Wang, M. Yan, C. Lin, J. Förstner, W. Yang, Optics Express (2017)

DOI
Abstract

Controlling light emission out of subwavelength nanoslit/aperture structures is of great important for highly integrated photonic circuits. Here we propose a new method to achieve direction-tunable emission based on a compact metallic microcavity with double nanoslit. Our method combines the principles of Young’s interference and surface plasmon polaritons interference. We show that the direction of the far-field beam can be controlled over a wide range of angles by manipulating the frequency and relative phase of light arriving at the two slits, which holds promise for applications in the ultracompact optoelectronic devices.


Guided Wave Interaction in Photonic Integrated Circuits — A Hybrid Analytical/Numerical Approach to Coupled Mode Theory

M. Hammer, in: Recent Trends in Computational Photonics, 204th ed., Springer, 2017, pp. 77-105

Abstract

Frequently, optical integrated circuits combine elements (waveguide channels, cavities), the simulation of which is well established through mature numerical eigenproblem solvers. It remains to predict the interaction of these modes. We address this task by a general, “Hybrid” variant (HCMT) of Coupled Mode Theory. Using methods from finite-element numerics, the properties of a circuit are approximated by superpositions of eigen-solutions for its constituents, leading to quantitative, computationally cheap, and easily interpretable models.


2016

Wave interaction in photonic integrated circuits: Hybrid analytical / numerical coupled mode modeling

M. Hammer, in: Integrated Optics: Devices, Materials, and Technologies XX, SPIE, 2016, pp. 975018-975018-8

DOI
Abstract

Typical optical integrated circuits combine elements, like straight and curved waveguides, or cavities, the simulation and design of which is well established through numerical eigenproblem-solvers. It remains to predict the interaction of these modes. We address this task by a ”Hybrid” variant (HCMT) of Coupled Mode Theory. Using methods from finite-element numerics, the optical properties of a circuit are approximated by superpositions of eigen-solutions for its constituents, leading to quantitative, low-dimensional, and interpretable models in the frequency domain. Spectral scans are complemented by the direct computation of supermode properties (spectral positions and linewidths, coupling-induced phase shifts). This contribution outlines the theoretical background, and discusses briefly limitations and implementational details, with the help of an example of a 2-D coupled-resonator-optical-waveguide configuration.


Fabrication and characterization of two-dimensional cubic AlN photonic crystal membranes containing zincblende GaN quantum dots

S. Blumenthal, M. Bürger, A. Hildebrandt, J. Förstner, N. Weber, C. Meier, D. Reuter, D.J. As, physica status solidi (c) (2016), pp. 292-296

DOI
Abstract

We successfully developed a process to fabricate freestanding cubic aluminium nitride (c-AlN) membranes containing cubic gallium nitride (c-GaN) quantum dots (QDs). The samples were grown by plasma assisted molecular beam epitaxy (MBE). To realize the photonic crystal (PhC) membrane we have chosen a triangular array of holes. The array was fabricated by electron beam lithography and several steps of reactive ion etching (RIE) with the help of a hard mask and an undercut of the active layer. The r/a- ratio of 0.35 was deter- mined by numerical simulations to obtain a preferably wide photonic band gap. Micro-photoluminescence (μ-PL) measurements of the photonic crystals, in particular of a H1 and a L3 cavity, and the emission of the QD ensemble were performed to characterize the samples. The PhCs show high quality factors of 4400 for the H1 cavity and about 5000/3000 for two different modes of the L3 cavity, respectively. The energy of the fundamental modes is in good agreement to the numerical simulations.


Comparison between the physical-optics approximation and exact methods solving the problem of light scattering by ice crystals of cirrus clouds

A.V. Konoshonkin, N.V. Kustova, A.G. Borovoi, H. Okamoto, K. Sato, H. Ishimoto, Y. Grynko, J. Förstner, in: 22nd International Symposium on Atmospheric and Ocean Optics: Atmospheric Physics, SPIE, 2016

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Abstract

In the problem of light scattering by ice crystals of cirrus clouds, two exact methods (FDTD – finite difference time domain and DGTD – discontinuous Galerkin time domain) and the physical-optics approximation are used for numerical calculations of the Mueller matrix in the case of ice hexagonal plates and columns. It is shown that for the crystals larger than 10 μm at the wavelength of 0.532 μm the exact methods and physical-optics approximation closely agreed within three diffraction fringes about the centers of the diffraction patterns. As a result, in the case of random orientation of these crystals, the physical-optics approximation provides accuracy 95% for the averaged Mueller matrix.


Second harmonic generation spectroscopy on hybrid plasmonic/dielectric nanoantennas

H. Linnenbank, Y. Grynko, J. Förstner, S. Linden, Light: Science & Applications (2016)

DOI

Oblique incidence of semi-guided waves on step-like folds in planar dielectric slabs: Lossless vertical interconnects in 3D integrated photonic circuits

A. Hildebrandt, S. Alhaddad, M. Hammer, J. Förstner, in: Integrated Optics: Devices, Materials, and Technologies XX, SPIE, 2016

DOI

Phase sensitive properties and coherent manipulation of a photonic crystal microcavity

W. Quiring, B. Jonas, J. Förstner, A.K. Rai, D. Reuter, A.D. Wieck, A. Zrenner, Optics Express (2016)

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Abstract

We present phase sensitive cavity field measurements on photonic crystal microcavities. The experiments have been performed as autocorrelation measurements with ps double pulse laser excitation for resonant and detuned conditions. Measured E-field autocorrelation functions reveal a very strong detuning dependence of the phase shift between laser and cavity field and of the autocorrelation amplitude of the cavity field. The fully resolved phase information allows for a precise frequency discrimination and hence for a precise measurement of the detuning between laser and cavity. The behavior of the autocorrelation amplitude and phase and their detuning dependence can be fully described by an analytic model. Furthermore, coherent control of the cavity field is demonstrated by tailored laser excitation with phase and amplitude controlled pulses. The experimental proof and verification of the above described phenomena became possible by an electric detection scheme, which employs planar photonic crystal microcavity photo diodes with metallic Schottky contacts in the defect region of the resonator. The applied photo current detection was shown to work also efficiently at room temperature, which make electrically contacted microcavities attractive for real world applications.


Discrete plasmonic solitons in graphene-coated nanowire arrays

Y. Kou, J. Förstner, Optics Express (2016)

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Abstract

e study the discrete soliton formation in one- and two- dimensional arrays of nanowires coated with graphene monolayers. Highly confined solitons, including the fundamental and the higher-order modes, are found to be supported by the proposed structure with a low level of power flow. Numerical analysis reveals that, by tuning the input intensity and Fermi energy, the beam diffraction, soliton dimension and propagation loss can be fully controlled in a broad range, indicating potential values of the graphene-based solitons in nonlinear/active nanophotonic systems.


Light scattering by ice crystals of cirrus clouds: From exact numerical methods to physical-optics approximation

A. Konoshonkin, A. Borovoi, N. Kustova, H. Okamoto, H. Ishimoto, Y. Grynko, J. Förstner, Journal of Quantitative Spectroscopy and Radiative Transfer (2016), pp. 132-140

DOI
Abstract

The problem of light scattering by ice crystals of cirrus clouds is considered in the case of a hexagonal ice plate with different distributions over crystal orientations. The physical-optics approximation based on (E, M)-diffraction theory is compared with two exact numerical methods: the finite difference time domain (FDTD) and the discontinuous Galerkin time domain (DGTD) in order to estimate its accuracy and limits of applicability. It is shown that the accuracy of the physical-optics approximation is estimated as 95% for the averaged backscattering Mueller matrix for particles with size parameter more than 120. Furthermore, the simple expression that allows one to estimate the minimal number of particle orientations required for appropriate spatial averaging has been derived.


Simulations of high harmonic generation from plasmonic nanoparticles in the terahertz region

Y. Grynko, T. Zentgraf, T. Meier, J. Förstner, Applied Physics B (2016)

DOI

The role of electromagnetic interactions in second harmonic generation from plasmonic metamaterials

J. Alberti, H. Linnenbank, S. Linden, Y. Grynko, J. Förstner, Applied Physics B (2016), pp. 45-50

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Abstract

We report on second harmonic generation spectroscopy on a series of rectangular arrays of split-ring resonators. Within the sample series, the lattice constants are varied, but the area of the unit cell is kept fixed. The SHG signal intensity of the different arrays upon resonant excitation of the fundamental plasmonic mode strongly depends on the respective arrangement of the split-ring resonators. This finding can be explained by variations of the electromagnetic interactions between the split-ring resonators in the different arrays. The experimental results are in agreement with numerical calculations based on the discontinuous Galerkin time-domain method. (PDF) The role of electromagnetic interactions.... Available from: https://www.researchgate.net/publication/297612326_The_role_of_electromagnetic_interactions_in_second_harmonic_generation_from_plasmonic_metamaterials [accessed Aug 13 2018].


Light scattering by irregular particles much larger than the wavelength with wavelength-scale surface roughness

Y. Grynko, Y. Shkuratov, J. Förstner, Optics Letters (2016)

DOI
Abstract

We simulate light scattering by random irregular particles that have dimensions much larger than the wavelength of incident light at the size parameter of 𝑋=200 using the discontinuous Galerkin time domain method. A comparison of the DGTD solution for smoothly faceted particles with that obtained with a geometric optics model shows good agreement for the scattering angle curves of intensity and polarization. If a wavelength-scale surface roughness is introduced, diffuse scattering at rough interface results in smooth and featureless curves for all scattering matrix elements which is consistent with the laboratory measurements of real samples.


Light scattering by ice crystals of cirrus clouds: comparison of the physical optics methods

A.V. Konoshonkin, N.V. Kustova, A.G. Borovoi, Y. Grynko, J. Förstner, Journal of Quantitative Spectroscopy and Radiative Transfer (2016), pp. 12-23

DOI
Abstract

The physical optics approximations are derived from the Maxwell equations. The scattered field equations by Kirchhoff, Stratton-Chu, Kottler and Franz are compared and discussed. It is shown that in the case of faceted particles, these equations reduce to a sum of the diffraction integrals, where every diffraction integral is associated with one plane–parallel optical beam leaving a particle facet. In the far zone, these diffraction integrals correspond to the Fraunhofer diffraction patterns. The paper discusses the E-, M- and (E, M)-diffraction theories as applied to ice crystals of cirrus clouds. The comparison to the exact solution obtained by the discontinuous Galerkin time domain method shows that the Kirchhoff diffraction theory is preferable.


2015

Planar prism spectrometer based on adiabatically connected waveguiding slabs

F. Civitci, M. Hammer, H. Hoekstra, Optics Communications (2015), pp. 29-37

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Abstract

The device principle of a prism-based on-chip spectrometer for TE polarization is introduced. The spectrometer exploits the modal dispersion in planar waveguides in a layout with slab regions having two different thicknesses of the guiding layer. The set-up uses parabolic mirrors, for the collimation of light of the input waveguide and focusing of the light to the receiver waveguides, which relies on total internal reflection at the interface between two such regions. These regions are connected adiabatically to prevent unwanted mode conversion and loss at the edges of the prism. The structure can be fabricated with two wet etching steps. The paper presents basic theory and a general approach for device optimization. The latter is illustrated with a numerical example assuming SiON technology.


Coupling Mediated Coherent Control of Localized Surface Plasmon Polaritons

F. Zeuner, M. Muldarisnur, A. Hildebrandt, J. Förstner, T. Zentgraf, Nano Letters (2015), pp. 4189-4193

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Subwavelength binary plasmonic solitons

Y. Kou, J. Förstner, Optics Letters (2015)

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Abstract

We study the formation of subwavelength solitons in binary metal-dielectric lattices. We show that the transverse modulation of the lattice constant breaks the fundamental plasmonic band and suppresses the discrete diffraction of surface plasmon waves. New types of plasmonic solitons are found, and their characteristics are analyzed. We also demonstrate the existence of photonic-plasmonic vector solitons and elucidate their propagation properties.


Robust Population Inversion by Polarization Selective Pulsed Excitation

D. Mantei, J. Förstner, S. Gordon, Y.A. Leier, A.K. Rai, D. Reuter, A.D. Wieck, A. Zrenner, Scientific Reports (2015), pp. 10313

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Abstract

The coherent state preparation and control of single quantum systems is an important prerequisite for the implementation of functional quantum devices. Prominent examples for such systems are semiconductor quantum dots, which exhibit a fine structure split single exciton state and a V-type three level structure, given by a common ground state and two distinguishable and separately excitable transitions. In this work we introduce a novel concept for the preparation of a robust inversion by the sequential excitation in a V-type system via distinguishable paths.


Full Resonant Transmission of Semiguided Planar Waves Through Slab Waveguide Steps at Oblique Incidence

M. Hammer, A. Hildebrandt, J. Förstner, Journal of Lightwave Technology (2015), pp. 997-1005

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Abstract

Sheets of slab waveguides with sharp corners are investigated. By means of rigorous numerical experiments, we look at oblique incidence of semi-guided plane waves. Radiation losses vanish beyond a certain critical angle of incidence. One can thus realize lossless propagation through 90-degree corner configurations, where the remaining guided waves are still subject to pronounced reflection and polarization conversion. A system of two corners can be viewed as a structure akin to a Fabry-Perot-interferometer. By adjusting the distance between the two partial reflectors, here the 90-degree corners, one identifies step-like configurations that transmit the semi-guided plane waves without radiation losses, and virtually without reflections. Simulations of semi-guided beams with in-plane wide Gaussian profiles show that the effect survives in a true 3-D framework.


Unveiling Nanometer Scale Extinction and Scattering Phenomena through Combined Electron Energy Loss Spectroscopy and Cathodoluminescence Measurements

A. Losquin, L.F. Zagonel, V. Myroshnychenko, B. Rodríguez-González, M. Tencé, L. Scarabelli, J. Förstner, L.M. Liz-Marzán, F.J. García de Abajo, O. Stéphan, M. Kociak, Nano Letters (2015), pp. 1229-1237

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Abstract

Plasmon modes of the exact same individual gold nanoprisms are investigated through combined nanometer-resolved electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL) measurements. We show that CL only probes the radiative modes, in contrast to EELS, which additionally reveals dark modes. The combination of both techniques on the same particles thus provides complementary information and also demonstrates that although the radiative modes give rise to very similar spatial distributions when probed by EELS or CL, their resonant energies appear to be different. We trace this phenomenon back to plasmon dissipation, which affects in different ways the plasmon signatures probed by these techniques. Our experiments are in agreement with electromagnetic numerical simulations and can be further interpreted within the framework of a quasistatic analytical model. We therefore demonstrate that CL and EELS are closely related to optical scattering and extinction, respectively, with the addition of nanometer spatial resolution.


A process for the preparation of a population inversion in a quantum system using multi-pulse excitation

A. Zrenner, J. Förstner, D. Mantei. A process for the preparation of a population inversion in a quantum system using multi-pulse excitation. 2015.

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Abstract

Die Erfindung betrifft ein Verfahren zur Präparation einer Besetzungsinversion in einem Quantensystem (Q) mittels Mehrpulsanregung, wobei ein Quantensystem (Q) umfassend wenigstens einen Quantenpunkt mit zwei orthogonalen Zuständen (/X>, /Y>), insbesondere die mit zueinander orthogonalen Polarisationen (P1, P2) optisch anregbar sind, mit einem ersten Laserpuls (L1) beleuchtet wird, welcher zur resonanten Anregung des ersten (/Y>) der zwei Zustände (/X>, /Y>) eingestellt wird und zeitlich nachfolgend mit einem zweiten Laserpuls (L2) beleuchtet wird, der zur resonanten Anregung des zweiten (/X>) der zwei Zustände (/X>, /Y>) eingestellt wird.


Interference of surface plasmons and Smith-Purcell emission probed by angle-resolved cathodoluminescence spectroscopy

N. Yamamoto, F. Javier García de Abajo, V. Myroshnychenko, Physical Review B (2015)

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Abstract

We investigate the interplay between geometrical lattice resonances and surface plasmons mediating the emission of Smith-Purcell visible light via angle-resolved cathodoluminescence spectroscopy. We observe strong modulations in the dispersion curves of Smith-Purcell radiation (SPR) when they intersect the surface plasmons of silver gratings using a 200-kV transmission electron microscope. The decay of the plasmons away from the grating is directly probed by controlling the electron-beam position relative to the sample surface with nanometer precision. Our measurements are in excellent agreement with numerical simulations, clearly revealing the presence of characteristic Fano profiles resulting from the interference of the light continuum and the discrete plasmon states for each direction of emission. The intensity anomaly in the SPR emission pattern can be well explained from the geometrical consideration of the intersections between the dispersion planes of the SPR and surface plasmon polariton (SPP). A strong and directional SPR beam can be realized under the condition that the SPR dispersion plane comes in contact with the band edge of the SPP dispersion plane.


How planar optical waves can be made to climb dielectric steps

M. Hammer, A. Hildebrandt, J. Förstner, Optics Letters (2015)

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Abstract

We show how to optically connect guiding layers at different elevations in a 3-D integrated photonic circuit. Transfer of optical power carried by planar, semi-guided waves is possible without reflections or radiation losses, and over large vertical distances. This functionality is realized through simple step-like folds of high-contrast dielectric slab waveguides, in combination with oblique wave incidence, and fulfilling a resonance condition. Radiation losses vanish, and polarization conversion is suppressed for TE wave incidence beyond certain critical angles. This can be understood by fundamental arguments resting on a version of Snell’s law. The two 90° corners of a step act as identical partial reflectors in a Fabry–Perot-like resonator setup. By selecting the step height, i.e., the distance between the reflectors, one realizes resonant states with full transmission. Rigorous quasi-analytical simulations for typical silicon/silica parameters demonstrate the functioning. Combinations of several step junctions can lead to other types of optical on-chip connects, e.g., U-turn- or bridge-like configurations.


2014

Oblique incidence of semi-guided waves on rectangular slab waveguide discontinuities: A vectorial QUEP solver

M. Hammer, Optics Communications (2014), pp. 447-456

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Abstract

The incidenceofthin-film-guided, in-planeunguidedwavesatobliqueanglesonstraightdiscontinuities of dielectricslabwaveguides,anearlyproblemofintegratedoptics,isbeingre-considered.The3-D frequencydomainMaxwellequationsreducetoaparametrizedinhomogeneousvectorialproblemona 2-D computationaldomain,withtransparent-influx boundaryconditions.Weproposearigorousvec- torial solverbasedonsimultaneousexpansionsintopolarizedlocalslabeigenmodesalongthetwo orthogonal crosssectioncoordinates(quadridirectionaleigenmodepropagationQUEP).Thequasi-ana- lytical schemeisapplicabletoconfigurations with — in principle — arbitrary crosssectiongeometries. Examples forahigh-contrastfacetofanasymmetricslabwaveguide,forthelateralexcitationofa channel waveguide,andforastepdiscontinuitybetweenslabwaveguidesofdifferentthicknessesare discussed.


Accelerating Finite Difference Time Domain Simulations with Reconfigurable Dataflow Computers

H. Giefers, C. Plessl, J. Förstner, ACM SIGARCH Computer Architecture News (2014), pp. 65-70

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Simulation of Planar Photonic Resonators

S. Declair, J. Förstner, in: Handbook of Optical Microcavities, Pan Stanford Publishing Pte. Ltd., 2014


Engineering plasmonic and dielectric directional nanoantennas

A. Hildebrandt, M. Reichelt, T. Meier, J. Förstner, in: Ultrafast Phenomena and Nanophotonics XVIII, SPIE, 2014, pp. 89841G-8941G-6

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Abstract

Optical and infrared antennas provide a promising way to couple photons in and out of nanoscale structures. As counterpart to conventional radio antennas, they are able to increase optical felds in sub-wavelength volumes, to enhance excitation and emission of quantum emitters or to direct light, radiated by quantum emitters. The directed emission of these antennas has been mainly pursued by surface plasmon based devices, e.g. Yagi-Uda like antennas, which are rather complicated due to the coupling of several metallic particles. Also, like all metallic structures in optical or infrared regime, these devices are very sensitive to fabrication tolerances and are affected by strong losses. It has been shown recently, that such directed emission can be accomplished by dielectric materials as well. In this paper we present an optimization of nanoscopic antennas in the near infrared regime starting from a metallic Yagi-Uda structure. The optimization is done via a particle-swarm algorithm, using full time domain finite integration simulations to obtain the characteristics of the investigated structure, also taking into account substrates. Furthermore we present a dielectric antenna, which performs even better, due to the lack of losses by an appropriate choice of the dielectric material. These antennas are robust concerning fabrication tolerances and can be realized with different materials for both the antenna and the substrate, without using high index materials.


General relation for group delay and the relevance of group delay for refractometric sensing

H.J.W.M. Hoekstra, M. Hammer, Journal of the Optical Society of America B (2014)

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Abstract

The relevance of our definition for sensitivity in refractometric sensing, being the relative change in the transmittance of a certain output channel of an optical device over the change in the refractive index of the probed material, is discussed. It is compared to one based on spectral shift per refractive index unit change. Further, there is discussion on how group delay and sensitivity are interrelated and can be converted into each other and which physical quantities are relevant for high sensitivity. As a by-product of the theory presented, a general expression relating group delay and the ratio of the time-averaged optical energy and the input power is presented.


Light Scattering By Random Irregular Particles With Different Morphology

Y. Grynko, E. Zubko, 2014

Abstract

We simulate numerically light scattering by random irregular particles of two classes of shape: Gaussian random field particles and agglomerated debri particles. Comparison of the angular dependencies of the scattering matrix elements for the case of non-absorbing material shows qualitative similarity of optical properties of both types despite different morphology of scatterers. Absorbing particles result in the difference in linear polarization. However, a strong similarty remains for the intensity curves.


2013

Optical Experiments on Second-Harmonic Generation with Metamaterials Composed of Split-Ring Resonators

M.W. Klein, C. Enkrich, M. Wegener, J. Förstner, J.V. Moloney, W. Hoyer, T. Stroucken, T. Meier, S.W. Koch, S. Linden, in: Photonic Metamaterials: From Random to Periodic, OSA, 2013

DOI
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.


Optimal second-harmonic generation in split-ring resonator arrays

Y. Grynko, T. Meier, S. Linden, F.B.P. Niesler, M. Wegener, J. Förstner, in: Ultrafast Phenomena and Nanophotonics XVII, SPIE, 2013

DOI
Abstract

Previous experimental measurements and numerical simulations give evidence of strong electric and magnetic field interaction between split-ring resonators in dense arrays. One can expect that such interactions have an influence on the second harmonic generation. We apply the Discontinuous Galerkin Time Domain method and the hydrodynamic Maxwell-Vlasov model to simulate the linear and nonlinear optical response from SRR arrays. The simulations show that dense placement of the constituent building blocks appears not always optimal and collective effects can lead to a significant suppression of the near fields at the fundamental frequency and, consequently, to the decrease of the SHG intensity. We demonstrate also the great role of the symmetry degree of the array layout which results in the variation of the SHG efficiency in range of two orders of magnitude.


Cubic GaN quantum dots embedded in zinc-blende AlN microdisks

M. Bürger, R. Kemper, C. Bader, M. Ruth, S. Declair, C. Meier, J. Förstner, D. As, Journal of Crystal Growth (2013), pp. 287-290

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Abstract

Microresonators containing quantum dots find application in devices like single photon emitters for quantum information technology as well as low threshold laser devices. We demonstrate the fabrication of 60 nm thin zinc-blende AlN microdisks including cubic GaN quantum dots using dry chemical etching techniques. Scanning electron microscopy analysis reveals the morphology with smooth surfaces of the microdisks. Micro-photoluminescence measurements exhibit optically active quantum dots. Furthermore this is the first report of resonator modes in the emission spectrum of a cubic AlN microdisk.


Collective effects in second-harmonic generation from split-ring-resonator arrays

F.B. Niesler, S. Linden, J. Förstner, Y. Grynko, T. Meier, M. Wegener, in: Conference on Lasers and Electro-Optics 2012, OSA, 2013

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Abstract

We perform experiments on resonant second-harmonic generation from planar gold split-ring-resonator arrays under normal incidence of light as a function of the lattice constant. Optimum nonlinear conversion occurs at intermediate lattice constants.


Light scattering by randomly irregular dielectric particles larger than the wavelength

Y. Grynko, Y. Shkuratov, J. Förstner, Optical Letters (2013), pp. 5153-5156

DOI

Whispering gallery modes in zinc-blende AlN microdisks containing non-polar GaN quantum dots

M. Bürger, M. Ruth, S. Declair, J. Förstner, C. Meier, D.J. As, Applied Physics Letters (2013), pp. 081105

DOI
Abstract

Whispering gallery modes (WGMs) were observed in 60 nm thin cubic AlN microdisk resonators containing a single layer of non-polar cubic GaN quantum dots. Freestanding microdisks were patterned by means of electron beam lithography and a two step reactive ion etching process. Micro-photoluminescence spectroscopy investigations were performed for optical characterization. We analyzed the mode spacing for disk diameters ranging from 2-4 lm. Numerical investigations using three dimensional finite difference time domain calculations were in good agreement with the experimental data. Whispering gallery modes of the radial orders 1 and 2 were identified by means of simulated mode field distributions.


Cubic GaN quantum dots embedded in zinc-blende AlN microdisks

M. Bürger, R. Kemper, C. Bader, M. Ruth, S. Declair, C. Meier, J. Förstner, D. As, Journal of Crystal Growth (2013), pp. 287-290

DOI

2012

Photonic crystal waveguides intersection for resonant quantum dot optical spectroscopy detection

X. Song, S. Declair, T. Meier, A. Zrenner, J. Förstner, Optics Express (2012)

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Abstract

Using a finite-difference time-domain method, we theoretically investigate the optical spectra of crossing perpendicular photonic crystal waveguides with quantum dots embedded in the central rod. The waveguides are designed so that the light mainly propagates along one direction and the cross talk is greatly reduced in the transverse direction. It is shown that when a quantum dot (QD) is resonant with the cavity, strong coupling can be observed via both the transmission and crosstalk spectrum. If the cavity is far off-resonant from the QD, both the cavity mode and the QD signal can be detected in the transverse direction since the laser field is greatly suppressed in this direction. This structure could have strong implications for resonant excitation and in-plane detection of QD optical spectroscopy.


Optimization of the intensity enhancement in plasmonic nanoantennas

A. Hildebrandt, M. Reichelt, T. Meier, J. Förstner, AIP AIP Conference Proceedings 1475, 2012

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Abstract

We design the geometrical shape of plasmonic nanostructures to achieve field patterns with desired properties. For this, we combine Maxwell simulations and automatic optimization techniques. By allowing variations of the geometrical shape, which can be based on either boxes or arbitrary polygons, we maximize the desired objective.


Engineering high harmonic generation in semiconductors via pulse shaping

M. Reichelt, A. Hildebrandt, A. Walther, J. Förstner, T. Meier, in: Ultrafast Phenomena and Nanophotonics XVI, Proc. SPIE 8260, 2012, pp. 82601L

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Abstract

Paper Abstract High harmonic generation is investigated for a two-band model of a semiconductor nanostructure. Similar to an atomic two-level system, the semiconductor emits high harmonic radiation. We show how one can specifically enhance the emission for a given frequency by applying a non-trivially shaped laser pulse. Therefore, the semiconductor Bloch equations including the interband and additionally the intraband dynamics are solved numerically and the spectral shape of the input pulse is computed via an optimization algorithm. It is demonstrated that desired emission frequencies can be favored even though the overall input power is kept constant. We also suggest special metallic nano geometries to achieve enhanced localized optical fields. They are found by geometric optimization.


Near-field coupling and second-harmonic generation in split-ring resonator arrays

Y. Grynko, T. Meier, S. Linden, F.B.P. Niesler, M. Wegener, J. Förstner, AIP Conference Proceedings 1475, 2012, pp. 128-130

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Abstract

We simulate the linear and nonlinear optical response from split-ring resonator (SRR) arrays to study collective effects between the constituent SRRs that determine spectral properties of the second harmonic generation (SHG). We apply the Discontinuous Galerkin Time Domain (DGTD) method and the hydrodynamic Maxwell-Vlasov model to calculate the SHG emission. Our model is able to qualitatively reproduce and explain the non-monotonic dependence of the spectral SHG transmission measured experimentally for SRR arrays with different lattice constants


Cavity-assisted emission of polarization-entangled photons from biexcitons in quantum dots with fine-structure splitting

S. Schumacher, J. Förstner, A. Zrenner, M. Florian, C. Gies, P. Gartner, F. Jahnke, Optics Express (2012)

DOI
Abstract

We study the quantum properties and statistics of photons emitted by a quantum-dot biexciton inside a cavity. In the biexciton-exciton cascade, fine-structure splitting between exciton levels degrades polarization-entanglement for the emitted pair of photons. However, here we show that the polarization-entanglement can be preserved in such a system through simultaneous emission of two degenerate photons into cavity modes tuned to half the biexciton energy. Based on detailed theoretical calculations for realistic quantum-dot and cavity parameters, we quantify the degree of achievable entanglement.


Convey vector personalities - FPGA acceleration with an openmp-like programming effort?

B. Meyer, J. Schumacher, C. Plessl, J. Förstner, in: 22nd International Conference on Field Programmable Logic and Applications (FPL), IEEE, 2012, pp. 189-196

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Abstract

Although the benefits of FPGAs for accelerating scientific codes are widely acknowledged, the use of FPGA accelerators in scientific computing is not widespread because reaping these benefits requires knowledge of hardware design methods and tools that is typically not available with domain scientists. A promising but hardly investigated approach is to develop tool flows that keep the common languages for scientific code (C,C++, and Fortran) and allow the developer to augment the source code with OpenMPlike directives for instructing the compiler which parts of the application shall be offloaded the FPGA accelerator. In this work we study whether the promise of effective FPGA acceleration with an OpenMP-like programming effort can actually be held. Our target system is the Convey HC-1 reconfigurable computer for which an OpenMP-like programming environment exists. As case study we use an application from computational nanophotonics. Our results show that a developer without previous FPGA experience could create an FPGA-accelerated application that is competitive to an optimized OpenMP-parallelized CPU version running on a two socket quad-core server. Finally, we discuss our experiences with this tool flow and the Convey HC-1 from a productivity and economic point of view.


Collective Effects in Second-Harmonic Generation from Split-Ring-Resonator Arrays

S. Linden, F.B.P. Niesler, J. Förstner, Y. Grynko, T. Meier, M. Wegener, Physical Review Letters (2012), pp. 015502

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Abstract

Optical experiments on second-harmonic generation from split-ring-resonator square arrays show a nonmonotonic dependence of the conversion efficiency on the lattice constant. This finding is interpreted in terms of a competition between dilution effects and linewidth or near-field changes due to interactions among the individual elements in the array.


Convey Vector Personalities – FPGA Acceleration with an OpenMP-like Effort?

B. Meyer, J. Schumacher, C. Plessl, J. Förstner, in: Proc. Int. Conf. on Field Programmable Logic and Applications (FPL), IEEE, 2012, pp. 189-196

DOI

2011

Numerical analysis of coupled photonic crystal cavities

S. Declair, T. Meier, A. Zrenner, J. Förstner, Photonics and Nanostructures - Fundamentals and Applications (2011), pp. 345-350

DOI
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.


Injection currents in (110)-oriented GaAs/AlGaAs quantum wells: recent progress in theory and experiment

H.T. Duc, M. Pochwala, J. Förstner, T. Meier, S. Priyadarshi, A.M. Racu, K. Pierz, U. Siegner, M. Bieler, in: Ultrafast Phenomena in Semiconductors and Nanostructure Materials XV, SPIE, 2011

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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.


Intensity dependence of optically-induced injection currents in semiconductor quantum wells

M. Pochwala, H.T. Duc, J. Förstner, T. Meier, in: CLEO:2011 - Laser Applications to Photonic Applications, OSA, 2011

DOI
Abstract

The intensity dependence of optically-induced injection currents in semiconductor quantum wells is investigated numerically. Oscillatory behavior of the electron charge current transients as function of intensity and time is predicted and explained.


Phonon-assisted decoherence and tunneling in quantum dot molecules

A. Grodecka-Grad, J. Förstner, physica status solidi (c) (2011), pp. 1125-1128

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Abstract

We study the influence of the phonon environment on the electron dynamics in a doped quantum dot molecule. A non-perturbative quantumkinetic theory based on correlation expansion is used in order to describe both diagonal and off-diagonal electron-phonon couplings representing real and virtual processes with relevant acoustic phonons. We show that the relaxation is dominated by phononassisted electron tunneling between constituent quantum dots and occurs on a picosecond time scale. The dependence of the time evolution of the quantum dot occupation probabilities on the energy mismatch between the quantum dots is studied in detail.


Electrong-factor anisotropy in symmetric (110)-oriented GaAs quantum wells

J. Hübner, S. Kunz, S. Oertel, D. Schuh, M. Pochwała, H.T. Duc, J. Förstner, T. Meier, M. Oestreich, Physical Review B (2011), pp. 041301 (R)

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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.


Simulation of the ultrafast nonlinear optical response of metal slabs

M. Wand, A. Schindlmayr, T. Meier, J. Förstner, physica status solidi (b) (2011), pp. 887-891

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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.


Application of the Discontinuous Galerkin Time Domain Method to the Optics of Bi-Chiral Plasmonic Crystals

Y. Grynko, J. Förstner, T. Meier, A. Radke, T. Gissibl, P.V. Braun, H. Giessen, D.N. Chigrin, AIP, 2011, pp. 76-78

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Abstract

A simulation environment for metallic nanostructures based on the Discontinuous Galerkin Time Domain method is presented. It is used to model optical transmission by silver bi‐chiral plasmonic crystals. The results of simulations qualitatively and quantitavely agree with experimental measurements of transmitted circular polarization.


Theoretical approach to the ultrafast nonlinear optical response of metal slabs

M. Wand, A. Schindlmayr, T. Meier, J. Förstner, CLEO:2011 - Laser Applications to Photonic Applications (2011)

DOI
Abstract

We present an ab-initio method for calculating nonlinear and nonlocal optical effects in metallic slabs with sub-wavelength thickness. We find a strong localization of the second-harmonic current at the metal-vacuum interface.


Simulation of Mutual Coupling of Photonic Crystal Cavity Modes and Semiconductor Quantum Dots

S. Declair, X. Song, T. Meier, J. Förstner, D.N.. Chigrin, AIP, 2011, pp. 123-125


Intensity-dependent ultrafast dynamics of injection currents in unbiased GaAs quantum wells

M. Pochwała, H.T. Duc, J. Förstner, T. Meier, physica status solidi (RRL) - Rapid Research Letters (2011), pp. 119-121

DOI
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.


Numerical investigation of the coupling between microdisk modes and quantum dots

S. Declair, T. Meier, J. Förstner, physica status solidi (c) (2011), pp. 1254-1257

DOI
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.


Oscillatory excitation energy dependence of injection currents in GaAs/AlGaAs quantum wells

H. Thanh Duc, J. Förstner, T. Meier, S. Priyadarshi, A.M. Racu, K. Pierz, U. Siegner, M. Bieler, physica status solidi (c) (2011), pp. 1137-1140

DOI
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.


Application of the discontinous Galerkin time domain method to the optics of metallic nanostructures

Y. Grynko, J. Förstner, T. Meier, AAPP | Atti della Accademia Peloritana dei Pericolanti (2011)

DOI
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.


Transformation of scientific algorithms to parallel computing code: subdomain support in a MPI-multi-GPU backend

B. Meyer, C. Plessl, J. Förstner, in: Symp. on Application Accelerators in High Performance Computing (SAAHPC), IEEE Computer Society, 2011, pp. 60-63

DOI

Method for transmission of information about polarization state of photons to stationary system

J. Förstner, D. Mantei, S.M.. de Vasconcellos, A. Zrenner. Method for transmission of information about polarization state of photons to stationary system. 2011.

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Abstract

The method involves exciting a quantum system with photons in a polarization state. Two states of the quantum system are excited with linear horizontal and vertical polarizations that are orthogonal to each other, where the states exhibit an energetic gap smaller than energetic bandwidth of photons. The states are assigned based on the polarizations, where the quantum system is arranged in a superposition state. The quantum system is formed by a quantum bit that is formed as a two-level system.


2010

Microscopic analysis of charge and spin photocurrents injected by circularly polarized one-color laser pulses in GaAs quantum wells

H.T. Duc, J. Förstner, T. Meier, Physical Review B (2010), pp. 115316-1

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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.


Modeling excitonic line shapes in weakly disordered semiconductor nanostructures

I. Kuznetsova, N. Gőgh, J. Förstner, T. Meier, S.T. Cundiff, I. Varga, P. Thomas, Physical Review B (2010)

DOI
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.


Tuning quantum-dot based photonic devices with liquid crystals

K.A. Piegdon, S. Declair, J. Förstner, T. Meier, H. Matthias, M. Urbanski, H. Kitzerow, D. Reuter, A.D. Wieck, A. Lorke, C. Meier, Optics Express (2010)

DOI
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.


Self-assembled quantum dots in a liquid-crystal-tunable microdisk resonator

K.A. Piegdon, M. Offer, A. Lorke, M. Urbanski, A. Hoischen, H. Kitzerow, S. Declair, J. Förstner, T. Meier, D. Reuter, A.D. Wieck, C. Meier, Physica E: Low-dimensional Systems and Nanostructures (2010), pp. 2552-2555

DOI
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.


Phonon-mediated relaxation in doped quantum dot molecules

A. Grodecka-Grad, J. Förstner, Journal of Physics: Conference Series (2010)

DOI
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.


Enhanced FDTD edge correction for nonlinear effects calculation

C. Classen, J. Förstner, T. Meier, R. Schuhmann, in: 2010 IEEE Antennas and Propagation Society International Symposium, IEEE, 2010

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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.


Theory of phonon-mediated relaxation in doped quantum dot molecules

A. Grodecka-Grad, J. Förstner, Physical Review B (2010)

DOI
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.


Anticrossing of Whispering Gallery Modes in microdisk resonators embedded in an anisotropic environment

S. Declair, C. Meier, T. Meier, J. Förstner, Photonics and Nanostructures - Fundamentals and Applications (2010), pp. 273-277

DOI
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.


Reversal of Coherently Controlled Ultrafast Photocurrents by Band Mixing in Undoped GaAs Quantum Wells

S. Priyadarshi, A.M. Racu, K. Pierz, U. Siegner, M. Bieler, H.T. Duc, J. Förstner, T. Meier, Physical Review Letters (2010)

DOI
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.


Microscopic theoretical analysis of optically generated injection currents in semiconductor quantum wells

H.T. Duc, J. Förstner, T. Meier, in: Ultrafast Phenomena in Semiconductors and Nanostructure Materials XIV, SPIE, 2010, pp. 76000S-76000S-9

DOI
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.


2009

Generation of injection currents in (110)-oriented GaAs quantum wells: experimental observation and development of a microscopic theory

M. Bieler, K. Pierz, U. Siegner, P. Dawson, H.T. Duc, J. Förstner, T. Meier, in: Ultrafast Phenomena in Semiconductors and Nanostructure Materials XIII, SPIE, 2009, pp. 721404-721404-13

DOI
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.


Indirect Dephasing Channel for Optically Controlled Spin in a Single Quantum Dot

A. Grodecka, P. Machnikowski, J. Förstner, in: Advances in Optical Sciences Congress, OSA Technical Digest (CD) (Optical Society of America, 2009), 2009

DOI
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.


Coupling Dynamics of Quantum Dots in a Liquid-Crystal-Tunable Microdisk Resonator

J. Förstner, C. Meier, K. Piegdon, S. Declair, A. Hoischen, M. Urbanski, T. Meier, H. Kitzerow, in: Advances in Optical Sciences Congress, OSA Technical Digest (CD) (Optical Society of America, 2009), paper NTuC2, 2009

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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.


Anticrossing of Whispering Gallery Modes in Microdisk Resonators Embedded in a Liquid Crystal

J. Förstner, S. Declair, C. Meier, T. Meier, in: AIP Conference Proceedings, AIP Conference Proceedings , 2009, pp. 60-62

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Abstract

We numerically investigate Whispering Gallery Modes (WGM) in a subwavelength microdisk resonator [1] embedded in an uniaxial anisotropic liquid crystal environment. It is shown that the WGMs have anticrossing behavior when modes of different radial mode order M or azimuthal order N approach each other spectrally.


Indirect spin dephasing via charge-state decoherence in optical control schemes in quantum dots

A. Grodecka, P. Machnikowski, J. Förstner, Physical Review A (2009)

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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.


2008

Theoretical study of phononassisted singlet-singlet relaxation in two-electron semiconductor quantum dot molecules

A. Grodecka, P. Machnikowski, J. Förstner, physica status solidi (c) (2008), pp. 474-478

DOI
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.


Transition between different coherent light–matter interaction regimes analyzed by phase-resolved pulse propagation

T.H. zu Siederdissen, N.C. Nielsen, J. Kuhl, M. Schaarschmidt, J. Förstner, A. Knorr, G. Khitrova, H.M. Gibbs, S.W. Koch, H. Giessen, Optics Letters (2008)

DOI
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.


Phonon-assisted tunneling between singlet states in two-electron quantum dot molecules

A. Grodecka, P. Machnikowski, J. Förstner, Physical Review B (2008)

DOI
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.


2007

Line narrowing and hole burning within the homogeneous linewidth: a new wave-mixing effect in two-level systems

J. Förstner, A. Knorr, M. Lindberg, S.W. Koch, Optics Letters (2007)

DOI
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.


2006

Interplay of electron-phonon and Coulomb interaction in semiconductor quantum dots

J. Förstner, A. Knorr, J.V. Moloney, physica status solidi (c) (2006), pp. 2389-2392

DOI
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.


Theory of ultrafast nonlinear optics of Coulomb-coupled semiconductor quantum dots: Rabi oscillations and pump-probe spectra

J. Danckwerts, K.J. Ahn, J. Förstner, A. Knorr, Physical Review B (2006), pp. 165318-165318-18

DOI
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.


Optical Experiments on Second-Harmonic Generation with Metamaterials Composed of Split-Ring Resonators

M.W. Klein, C. Enkrich, M. Wegener, J. Förstner, J.V. Moloney, W. Hoyer, T. Stroucken, T. Meier, S.W. Koch, S. Linden, in: Photonic Metamaterials: From Random to Periodic, OSA, 2006

DOI
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.


Optical experiments on second-harmonic generation from metamaterials consisting of split-ring resonators

M.W. Klein, C. Enkrich, M. Wegener, J. Förstner, J.V. Moloney, W. Hoyer, T. Stroucken, T. Meier, S.W. Koch, S. Linden, in: 2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, IEEE, 2006

DOI
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.


2005

Microscopic theory of electron dynamics and time-resolved two-color two-photon photoemission at semiconductor surfaces

A. Zeiser, N. Bücking, J. Förstner, A. Knorr, Physical Review B (2005)

DOI
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.


Normal Mode Coupling in Photonic Crystal Nanocavities

J. Förstner, C. Dineen, A. Zakharian, J.V. Moloney, S.W. Koch, in: Frontiers in Optics, OSA, 2005

DOI
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.


Ultrafast quantum kinetics of semiconductor intersubband transitions: polaron signatures and dephasing dynamics

S. Butscher, J. Förstner, I. Waldmuller, A. Knorr, in: 2005 Quantum Electronics and Laser Science Conference, IEEE, 2005, pp. 640-642

DOI
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.


Femtosecond Transfer Dynamics of Photogenerated Electrons at a Surface Resonance of Reconstructed InP(100)

L. Töben, L. Gundlach, R. Ernstorfer, R. Eichberger, T. Hannappel, F. Willig, A. Zeiser, J. Förstner, A. Knorr, P.H. Hahn, W.G. Schmidt, Physical Review Letters (2005)

DOI
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.


Quantum information processing using Coulomb-coupled quantum dots

J. Danckwerts, J. Förstner, A. Knorr, in: AIP Conference Proceedings, AIP, 2005

DOI
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.


Ultrafast electron-phonon interaction of intersubband transitions: Quantum kinetics from adiabatic following to Rabi-oscillations

S. Butscher, J. Förstner, I. Waldmüller, A. Knorr, Physical Review B (2005), pp. 045314-045314-4

DOI
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.


Phase Evolution of Solitonlike Optical Pulses during Excitonic Rabi Flopping in a Semiconductor

N.C. Nielsen, T.H. zu Siederdissen, J. Kuhl, M. Schaarschmidt, J. Förstner, A. Knorr, H. Giessen, Physical Review Letters (2005)

DOI
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.


Temporal and Spatial Pulse Compression in a Nonlinear Defocusing Material

N.C. Nielsen, T. zu Höner Siederdissen, J. Kuhl, M. Schaarschmidt, J. Förstner, A. Knorr, S.W. Koch, H. Giessen, in: Springer Series in Chemical Physics, Springer Berlin Heidelberg, 2005, pp. 19-21

DOI
Abstract

We investigate the spatiotemporal characteristics of subpicosecond pulse propagation in the nonlinear defocusing regime below the band edge of bulk GaAs. We observe temporal and spatial pulse compression and instabilities.


Electromagnetic field structure and normal mode coupling in photonic crystal nanocavities

C. Dineen, J. Förstner, A. Zakharian, J. Moloney, S. Koch, Optics Express (2005)

DOI
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.


Resonance fluorescence of semiconductor quantum dots: Signatures of the electron-phonon interaction

K.J. Ahn, J. Förstner, A. Knorr, Physical Review B (2005)

DOI
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.


Kinetic theory of the electron transport in the two photon photo emission at semiconductor surfaces

N. Bucking, A. Zeiser, J. Förstner, A. Knorr, in: 2005 Quantum Electronics and Laser Science Conference, IEEE, 2005, pp. 1929-1931

DOI
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.


2004

Temporal phase evolution during excitonic Rabi flopping in semiconductors

T. Höner zu Siederdissen, N.C. Nielsen, J. Kuhl, J. Förstner, A. Knorr, H. Giessen, in: International Quantum Electronics Conference and Photonic Applications Systems Technologies, OSA, 2004

DOI
Abstract

Theoretically and experimentally, we investigate temporal phase evolution during Rabi-flopping on the A-exciton resonance in CdSe using a novel fast-scanning XFROG method and observe phase changes smaller than π/2 compared to the slightly-chirped input pulse.


Polaron signatures in the line shape of semiconductor ;intersubband transitions: quantum kinetics of the electron–phonon interaction

S. Butscher, J. Förstner, I. Waldmüller, A. Knorr, physica status solidi (b) (2004), pp. R49-R51

DOI
Abstract

We present a theory of the optical line shape of coherent intersubband transitions in a semiconductor quantum well, considering non-Markovian LO-phonon scattering as major broadening mechanism. We show that a quantum kinetic approach leads to additional polaron resonances and a resonance enhancement for gap energies close to the phonon energy.


Subpicosecond spatiotemporal pulse compression in a nonlinear defocusing material

N.C. Nielsen, T.H.z. Siederdissen, J. Kuhl, M. Schaarschmidt, J. Förstner, A. Knorr, S.W.. Koch, H.. Giessen, in: International Conference on Ultrafast Phenomena 2004, Technical Digest (CD) (Optical Society of America, 2004), 2004

Abstract

We demonstrate temporal and spatial pulse compression and modulational instabilities in the nonlinear defocusing regime near the band edge of bulk GaAs. Experiment and theory show that spatiotemporal coupling is responsible for these surprising phenomena.


Self-consistent Projection Operator Theory of Intersubband Absorbance in Semiconductor Quantum Wells

I. Waldmüller, J. Förstner, A.. Knorr, in: Nonequilibrium Physics at Short Time Scales, Springer Berlin Heidelberg, 2004

DOI
Abstract

Due to their many-particle character and their application in quantum cascade lasers, optical intersubband excitations in semiconductor quantum wells have become the focus of many recent publications [1,2]. In samples of high quality, intrinsic processes like electron-electron and electron-phonon many particle correlations determine the basic optical and transport properties such as lineshape and ultrafast dynamics. At the same time, intersubband excitations allow the direct investigation of dynamical properties of an important model system of many particle physics - the two-dimensional electron gas. We here present a microscopic theory for the intersubband dynamics and absorption. The calculation of absorption spectra of MQW systems is in principle composed of two parts: the determination of the polarization in a single quantum well within a density matrix approach as the source of electromagnetic radiation (Fig. 1a) and the calculation of the generated fields in the geometry of interest (Fig. 1b) within a Green's function approach [3,4]. We will here focus on the so-called single-pass geometry (cf. Fig. 1b, [5]).


Temporal and spatial compression of near-resonant pulses in a nonlinear defocusing semiconductor

N.C. Nielsen, J. Kuhl, M.. Schaarschmidt, J. Förstner, A. Knorr, S.W. Koch, H.. Giessen, in: Conference on Lasers and Electro-Optics/International Quantum Electronics Conference and Photonic Applications Systems Technologies, Technical Digest (CD) (Optical Society of America, 2004), 2004

Abstract

The coupled spatiotemporal characteristics of subpicosecond pulses propagating in the nonlinear defocusing regime near the band edge of bulk GaAs are investigated experimentally and theoretically. We demonstrate pulse compression both in time and transverse space.


Nonlinear light pulse propagation in Bragg-periodic multiple semiconductor quantum well samples: ultrafast switching of a resonant photonic band gap

M. Schaarschmidt, J. Förstner, A. Knorr, J.P. Prineas, N.C. Nielsen, J. Kuhl, G. Kithrova, H.M. Gibbs, H. Giessen, S.W. Koch, in: Conference on Lasers and Electro-Optics/International Quantum Electronics Conference and Photonic Applications Systems Technologies, OSA, 2004

DOI
Abstract

We investigate theoretically the ultrafast nonlinear suppression of the resonant photonic band gap by strong laser pulses in semiconductor multiple qnantum wells. We achieve good agreement with our measurements on reflection samples.


Light Propagation and Many-Particle Effects in Semiconductor Nanostructures

J. Förstner, 2004

Abstract

In dieser Arbeit wird eine Theorie vorgestellt, welche die quantenmechanische Vielteilchenphysik der Licht-Materie Wechselwirkung in Halbleiternanostrukturen beschreibt. Diese mikroskopische Beschreibung wird durch Kombination eines allgemeinen Dichtematrixansatzes mit speziellen Methoden zur Auswertung der Maxwellgleichungen wie der zeitaufgelösten Finite-Differenzen-Methode (FDTD) erreicht. Die Theorie wird auf verschiedene physikalische Situationen angewendet, wie z.B. Lichtausbreitung in Volumenhalbleitern, Interband- und Intersubbandübergänge in Quantenfilmstrukturen und optische Anregung von Quantenpunkten. Der Fokus liegt dabei auf der Beschreibung der linearen und nichtlinearen Antwort des Vielteilchensystems und seiner Ankopplung an das elektromagnetische Feld. In diesem Zusammenhang wird sowohl die Erzeugung als auch der Zerfall von optischen Anregungen untersucht, indem verschiedene Kopplungsmechanismen wie Elektron-Phonon-, Elektron-Photon- und Elektron-Elektron-Wechselwirkung berücksichtigt werden. Im Bereich der linearen Optik, also für Anregung mit geringer Intensität, ermöglicht die Theorie die Berechnung von Absorptionsspektren. Verschiedene Effekte in linearer Optik werden in dieser Arbeit untersucht und beschrieben: Linienaufspaltung durch Polaritonen im Volumenmaterial, Zunahme der Linienbreite bei Intersubbandübergängen verursacht durch Elektron-Elektron- und Elektron- Phonon-Streuung in einzelnen Quantenfilmen, Bildung einer optischen Bandlücke durch starke radiative Kopplung in Vielfilmstrukturen in Bragg-Geometrie, Phononenseitenbänder verursacht durch quantenkinetische Effekte in einzelnen Quantenpunkten und schliesslich Superradianz und Interferenzeffekte in Quantenpunktgittern. Bei nichtlinearer Anregung treten Dichte-Rabiflops als fundamentale Prozesse in allen betrachteten Systemen auf und können als kohärente Be- und Entvölkerung von quantenmechanischen Zuständen beobachtet werden. Der Einfluss von starker Lichtkopplung und verschiedenen Wechselwirkungen auf dynamische Größen wie die Besetzung wird untersucht. Bei nichtlinearer Propagation, bei der sich ein starker Lichtpuls über längere Strecken in einem System bewegt, wird selbstinduzierte Verstärkung der Transmission näher betrachtet. Des weiteren werden von der Coulombwechselwirkung verursachte nichtlineare Effekte wie exzitoninduziertes Dephasieren in Volumenmaterial und verschränkte Zustände in Quantenpunkten untersucht, die einen Zusammenbruch der Hartree-Fock- Näherung darstellen. Zusammenfassend werden in dieser Arbeit verschiedene lineare und nichtlineare optische Effekte in Halbleiternanostrukturen verschiedener Dimensionalität mit Hilfe einer allgemeinen Theorie, die einen Dichtematrixansatz mit den Maxwellschen Gleichungen kombiniert, untersucht.


Adiabatically driven electron dynamics in a resonant photonic band gap: Optical switching of a Bragg periodic semiconductor

M. Schaarschmidt, J. Förstner, A. Knorr, J.P. Prineas, N.C. Nielsen, J. Kuhl, G. Khitrova, H.M. Gibbs, H. Giessen, S.W. Koch, Physical Review B (2004)

DOI
Abstract

The adiabatic driving of the resonant electron dynamics in a one-dimensional resonant photonic band gap is proposed as an optical mechanism for nonlinear ultrafast switching. Pulsed excitation inside the photonic gap results in an ultrafast suppression and recovery of the gap. This behavior results from the adiabatic carrier dynamics due to rapid radiative damping inside the band gap.


Coherent Control of THz Coherent Transients of Molecular Rotational Transitions via Shaped THz Pulses

W. Hurlbut, N. Amer, Y. Lee, J. Förstner, A. Knorr, S. Koch, J. Nibler, American Physical Society , 2004

Abstract

We demonstrate coherent scattering effects when a narrow-band THz pulse tuned to a HCl rotational transition resonance propagates through optically thick vapor. The THz wave and the molecular polarization exchange energy mediated by coherent scattering. Two phase-locked single-cycle THz pulses coherently control free-induction-decay of gas-phase HCl rotational transitions. A single-cycle THz pulse impulsively excites 3 rotational transitions in HCl (nu = 0.625, 1.25, 1.875 THz). Following the excitation, the molecules reradiate via free induction decay (FID). A second identical pulse incident on the vapor of relative phase Deltaphi (Deltaphi = 2pinutau where tau = pulse temporal separation) coherently controls FID by adjusting the relative phase.


Dynamics of the phonon-induced electron transfer between semiconductor bulk and surface states

A. Zeiser, N. Bücking, J. Götte, J. Förstner, P. Hahn, W.G. Schmidt, A. Knorr, physica status solidi (b) (2004), pp. R60-R62

DOI
Abstract

The coupling of surface and bulk states at semiconductor surfaces through electron–phonon interaction is discussed. The governing equations are derived from a microscopic theory in the framework of the density matrix theory. To gain a first insight, model wave functions are used to simulate the dynamics of nonequilibrium electron distributions in three- and two-dimensional states, coupled by Fröhlich interaction. Typical time scales for the coupling are found to be in the order of few hundreds of femtoseconds.


Linear and nonlinear pulse propagation in a multiple-quantum-well photonic crystal

N.C. Nielsen, J. Kuhl, M. Schaarschmidt, J. Förstner, A. Knorr, S.W. Koch, G. Khitrova, H.M. Gibbs, H. Giessen, Physical Review B (2004)

DOI
Abstract

We investigate the temporal and spectral properties of subpicosecond pulses transmitted on the heavy-hole exciton transition through a multiple-quantum-well Bragg structure, exhibiting a one-dimensional photonic band gap. At low light intensities, a temporal propagation beating is observed. This beating is strongly dependent on the optical dephasing time T2 which is dominated by the radiative interwell coupling. In an intermediate intensity regime, the Pauli-blocking nonlinearity leads to gradual suppression of the photonic band gap and vanishing of the linear propagation beating. For highly nonlinear excitation, we find signatures of selfinduced transmission due to Rabi flopping and adiabatic following of the carrier density. Numerical simulations using the semiconductor Maxwell-Bloch equations are in excellent agreement with the experimental data up to intensities for which higher many-particle correlations become more important and self-phase modulation occurs in the sample substrate.


Optical dephasing of coherent intersubband transitions in a quasi-two-dimensional electron gas

I. Waldmüller, J. Förstner, S. Lee, A. Knorr, M. Woerner, K. Reimann, R.A. Kaindl, T. Elsaesser, R. Hey, K.H. Ploog, Physical Review B (2004)

DOI

2003

Theory of the lineshape of quantum well intersubband transitions: optical dephasing and light propagation effects

I. Waldmüller, M. Woerner, J. Förstner, A. Knorr, physica status solidi (b) (2003), pp. 474-477

DOI
Abstract

We outline a theoretical description of the absorption linewidth of quantum well intersubband transitions by solving Maxwell’s equations for a non-local susceptibility including many particle effects. We show that the intersubband absorption results from a complex interplay between mean-field effects, dephasing contributions and light propagation effects, all being very sensitive to subband dispersion.


Correlated influence of carrier-carrier/carrier-phonon interaction and radiative damping on semiconductor intersubband transitions

I. Waldmuller, J. Förstner, A. Knorr, M. Woerner, K. Reimann, R. Kaindl, R. Hey, K. Ploog, in: Postconference Digest Quantum Electronics and Laser Science, 2003. QELS., IEEE, 2003

DOI
Abstract

The linewidth of intersubband transitions resulting from simultaneous action of many-body contributions and radiative damping is analyzed. The processes are non-additive and a self-consistent treatment is necessary to explain recent experiments.


Phonon-Assisted Damping of Rabi Oscillations in Semiconductor Quantum Dots

J. Förstner, C. Weber, J. Danckwerts, A. Knorr, Physical Review Letters (2003)

DOI

Phonon-induced damping of Rabi oscillations in semiconductor quantum dots

J. Förstner, C. Weber, J. Danckwerts, A. Knorr, physica status solidi (b) (2003), pp. 419-422

DOI
Abstract

The phonon-induced dephasing dynamics of semiconductor quantum dots during nonlinear optical excitation is studied using quantum kinetic equations. We find that despite the decoherence process Rabi oscillations occur even for relatively long pulse durations and that their signatures in pump-probe experiments only get suppressed for high input pulse areas.


Pulse propagation in Bragg-resonant multiple quantum wells: from pulse breakup to compression

N.C. Nielsen, J. Kuhl, M. Schaarschmidt, J. Förstner, A. Knorr, S.W. Koch, H.M. Gibbs, G. Khitrova, H. Giessen, physica status solidi (c) (2003), pp. 1484-1487

DOI
Abstract

The nonlinear propagation of subpicosecond pulses resonant to the hh 1s exciton in Bragg-periodic multiple quantum wells is investigated experimentally and theoretically. We show coherent pulse breakup and its suppression for increasing pulse intensity in good agreement with calculations based on the semiconductor Maxwell-Bloch equations. For highly nonlinear excitation, pulse compression is observed which is strongly enhanced by the additional contribution of self-phase modulation in the barrier and substrate material.


Self-induced transparency in InGaAs quantum dot waveguides

S. Schneider, P. Borri, W. Langbein, U. Woggon, J. Förstner, A. Knorr, R.L. Sellin, D. Ouyang, D. Bimberg, physica status solidi (c) (2003), pp. 1548-1551

DOI
Abstract

We present the experimental observation and the theoretical modelling of self-induced transparency signatures such as nonlinear transmission, pulse retardation and reshaping for subpicosecond pulse propagation in a 2 mm-long InGaAs quantum-dot ridge waveguide at 10 K. The measurements were obtained using a cross-correlation frequency resolved optical gating technique which allows us to retrieve the field amplitude of the propagating pulses.


Self-induced transparency in InGaAs quantum-dot waveguides

S. Schneider, P. Borri, W. Langbein, U. Woggon, J. Förstner, A. Knorr, R.L. Sellin, D. Ouyang, D. Bimberg, Applied Physics Letters (2003), pp. 3668-3670

DOI
Abstract

We report the experimental observation and the theoretical modeling of self-induced-transparency signatures such as nonlinear transmission, pulse retardation and reshaping, for subpicosecond pulse propagation in a 2-mm-long InGaAs quantum-dot ridge waveguide in resonance with the excitonic ground-state transition at 10 K. The measurements were obtained by using a cross-correlation frequency-resolved optical gating technique which allows us to retrieve the field amplitude of the propagating pulses.


Damping of electron density Rabi-oscillations and self-induced-transparency in semiconductor quantum dots

J. Förstner, C. Weber, J. Danckwerts, A. Knorr, in: Postconference Digest Quantum Electronics and Laser Science, 2003. QELS., IEEE, 2003

DOI
Abstract

A non-Markovian quantum kinetic theory of the coupled electron-phonon system in semiconductor quantum dots is used to analyze the nonlinear dipole decoherence and light propagation dynamics for arbitrary pulse strengths and lengths.


2002

Light Propagation- and Many-particle-induced Non-Lorentzian Lineshapes in Semiconductor Nanooptics

J. Förstner, K. Ahn, J. Danckwerts, M. Schaarschmidt, I. Waldmüller, C. Weber, A. Knorr, physica status solidi (b) (2002), pp. 155-165

DOI
Abstract

The occurrence of non-Lorentzian lineshapes is analyzed for a variety of nanooptical semiconductor systems such as quantum wells and quantum dots. Their origin is traced back to light–matter interaction (light propagation) and many-particle correlations (electron–electron and electron– phonon interaction).


Theory of ultrafast dynamics and lineshape of semiconductor quantum well intersubband emitters

I. Waldmüller, J. Förstner, A. Knorr, in: Nonlinear Optics: Materials, Fundamentals and Applications, OSA, 2002

DOI
Abstract

On the basis of a density matrix approach including electron-electron scattering, a detailed analysis of the temporal dynamics and the dephasing process after optical excitation in intersubband emitters is presented for a wide range of parameters.


Coherent nonlinear pulse propagation on a free-exciton resonance in a semiconductor

N.C. Nielsen, S. Linden, J. Kuhl, J. Förstner, A. Knorr, S.W. Koch, H. Giessen, Physical Review B (2002), pp. 245202-245202-10

DOI
Abstract

The coherent exciton-light coupling in pulse propagation experiments on the A-exciton resonance in bulk CdSe is investigated over a broad intensity range. At low light intensities, polariton propagation beats due to interference between excited states on both polariton branches are observed. In an intermediate intensity regime, the temporal polariton beating is suppressed in consequence of exciton-exciton interaction. At the highest light intensities, self-induced transmission and multiple pulse breakup are identified as a signature for carrier density Rabi flopping. Exciton-phonon scattering is shown to gradually eliminate coherent nonlinear propagation effects due to enhanced dephasing of the excitonic polarization. Calculations using the semiconductor Maxwell-Bloch equations are in qualitative agreement with the experimental data.


Nonlinear Pulse Propagation in Semiconductors: Hole Burning within a Homogeneous Line

J. Förstner, A. Knorr, S.W. Koch, Physical Review Letters (2002), pp. 476-479

DOI
Abstract

Features reminiscent of spectral hole burning in a homogeneous line are predicted to result from the interaction of small area pulses with the semiconductor exciton resonance. The small area pulses may be designed through pulse shaping or evolve naturally in bulk semiconductors via polaritonic effects. The spectral features exhibit signatures that are characteristic for the underlying material nonlinearity and should occur in any system with isolated spectral resonances and coherent nonlinearities.


Nonlinear Polariton Pulse Propagation in Bulk Semiconductors

J. Förstner, A. Knorr, S. Kuckenburg, T. Meier, S. Koch, H. Giessen, S. Linden, J. Kuhl, physica status solidi (b) (2002), pp. 453-457

DOI
Abstract

Nonlinear propagation of optical pulses through an extended bulk semiconductor is investigated using the coupled semiconductor Maxwell‐Bloch equations including excitation induced correlations. For short pulse excitation around the exciton resonance, the theory describes the development of polariton beats and their suppression at increasing input pulse intensities due to the coupling of single exciton states to the Coulomb‐correlated continuum of two‐exciton states. A comparison of the theoretical results with experimental observations for CdSe bulk material is presented.


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