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660 results on '"A. Seilmeier"'

1. Locating environmental charge impurities with confluent laser spectroscopy of multiple quantum dots

Author

Hauck, M., Seilmeier, F., Beavan, S. E., Badolato, A., Petroff, P. M., and Högele, A.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Optics
Abstract

We used resonant laser spectroscopy of multiple confocal InGaAs quantum dots to spatially locate charge fluctuators in the surrounding semiconductor matrix. By mapping out the resonance condition between a narrow-band laser and the neutral exciton transitions of individual dots in a field effect device, we identified spectral discontinuities as arising from charging and discharging events that take place within the volume adjacent to the quantum dots. Our analysis suggests that residual carbon dopants are a major source of charge-fluctuating traps in quantum dot heterostructures.

Published
2014
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2. Sub-Kelvin optical thermometry of an electron reservoir coupled to a self-assembled InGaAs quantum dot

Author

Seilmeier, F., Hauck, M., Schubert, E., Schinner, G. J., Beavan, S. E., and Högele, A.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Optics
Abstract

We show how resonant laser spectroscopy of the trion optical transitions in a self-assembled quantum dot can be used to determine the temperature of a nearby electron reservoir. At finite magnetic field the spin-state occupation of the Zeeman-split quantum dot electron ground states is governed by thermalization with the electron reservoir via co-tunneling. With resonant spectroscopy of the corresponding excited trion states we map out the spin occupation as a function of magnetic field to establish optical thermometry for the electron reservoir. We demonstrate the implementation of the technique in the sub-Kelvin temperature range where it is most sensitive, and where the electron temperature is not necessarily given by the cryostat base temperature., Comment: 5 pages, 4 figures

Published
2014
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3. Forming and confining of dipolar excitons by quantizing magnetic fields

Author

Kowalik-Seidl, K., Vögele, X. P., Seilmeier, F., Schuh, D., Wegscheider, W., Holleitner, A. W., and Kotthaus, J. P.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Optics
Abstract

We show that a magnetic field perpendicular to an AlGaAs/GaAs coupled quantum well efficiently traps dipolar excitons and leads to the stabilization of the excitonic formation and confinement in the illumination area. Hereby, the density of dipolar excitons is remarkably enhanced up to $\sim 10^{11} cm^{-2}$. By means of Landau level spectroscopy we study the density of excess holes in the illuminated region. Depending on the excitation power and the applied electric field, the hole density can be tuned over one order of magnitude up to $\sim 2.5$ $10^{11} cm^{-2}$ - a value comparable with typical carrier densities in modulation-doped structures., Comment: 4.3 Pages, 4 Figures

Published
2010
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21. Error Compensation in Initial Temperature Estimation of Electric Motors using a Kalman Filter

Author

Wilfried Hofmann, H. Joshi, Yves Burkhardt, and M. Seilmeier

Subjects
010302 applied physics, Electric motor, business.product_category, Computer science, 020208 electrical & electronic engineering, Compensation methods, 02 engineering and technology, Kalman filter, 01 natural sciences, Compensation (engineering), Control theory, Magnet, 0103 physical sciences, Electric vehicle, 0202 electrical engineering, electronic engineering, information engineering, Torque, Node (circuits), business
Abstract

To generate high accuracy torque by adapting the permanent magnet flux, it is vital to estimate the temperature of permanent magnets. These are nowadays extensively used in electric motors assembled in electric vehicle. In this paper, a short introduction on consequences of neglecting permanent magnet temperature estimation is explained followed by the existing research on permanent magnet temperature estimation methods. This paper focuses on the most ignored topic in majority of research articles based on thermal modelling of electric motor, i.e. initial temperature estimation of each thermal node, its algorithm and its error compensation methods. It is proposed that the error generated from incorrect reference temperature can be compensated with the help of a Kalman filter integrated in thermal network. The proposed method overcomes the challenges involved in an automotive application. Simulation results obtained using experimental data reveal that the proposed theory can be used for practical implementation.

Published
2020
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38. Infrared pulses of 1 picosecond duration tunable between 4 micrometer and 18 micrometer

Author

Dahinten, T., Plodereder, U., Seilmeier, A., Vodopyanov, K.L., Allakhverdiev, K.R., and Ibragimov, Z.A.

Subjects
Laser pulses, Ultrashort -- Research, Tunable lasers -- Usage, Nonlinear optics -- Observations, Business, Computers, Electronics, Electronics and electrical industries
Abstract

The difference frequency mixing of neodymium glass laser pulses and infrared dye laser pulses generates infrared pulses. Different combinations of laser dyes and nonlinear crystals such as AgGaS2 and GaSe are used in the determination of tuning between 4 and 18 micrometers. The midinfrared pulses have an energy of the order of microjoules, and the photon conversion efficiency is less than 2%.

Published
1993

44. Sensorless Control of PMSM for the Whole Speed Range Using Two-Degree-of-Freedom Current Control and HF Test Current Injection for Low-Speed Range

Author

Markus Seilmeier and Bernhard Piepenbreier

Subjects
Engineering, business.industry, Flatness (systems theory), Automatic frequency control, Feed forward, Estimator, Control engineering, Low speed, Control theory, Harmonics, Position error, Reference tracking, Electrical and Electronic Engineering, business
Abstract

In this paper, an innovative sensorless two-degree-of-freedom current control scheme for the whole speed range is proposed. It consists of a model-based dynamic feedforward control to set the reference response and model reference tracking controllers providing disturbance rejection and the position error signals needed for sensorless control. For low- and zero-speed operation, alternating test current injection is used to gain a position error signal. A flatness-based test signal precontrol provides compensation for secondary saliencies like cross-saturation and higher harmonics. For mid- and high-speed operation, it is shown how the model-based dynamic feedforward control can be modified to obtain a high-quality position error signal from the tracking controller. No additional model-based estimator evaluating back-EMF information is needed. The effectiveness of the proposed method is proven by experimental results.

Published
2015
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48. Intersubband carrier dynamics in a biased GaAs/AlGaAs quantum-well infrared photodetector.

Author

Schmidt, S. R., Seilmeier, A., and Liu, H. C.

Subjects
*DYNAMICS, *OPTICAL detectors, *ELECTRONS
Abstract

We present time and spectral resolved pump and probe studies of the intersubband dynamics in a bound to quasibound GaAs/AlGaAs quantum-well infrared photodetector dependent on the external electric field. Without bias, the excited electrons are scattered back to the ground subband with a time constant of about 2 ps. Subsequent intrasubband cooling is observed in the ground state, which gives rise to a relaxation component on a 50 ps time scale. With an applied electrical field, 35%–45% of the excited electrons escape to continuum states and are accelerated along the electrical field. Within time constants between 5 and 8 ps, the extended electrons are recaptured by wells in the low field bulk domain close to the collector contact. The redistribution of the carriers in the picosecond time regime and the screening of the external field due to the separation between electrons and donors leads to a change of the absorption spectrum for a time period shorter than the intrinsic response time of the electrical circuit.© 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2002
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