Search Results - (Author, Cooperation:S. W. Koch)

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  1. 1
    Staff View
    Publication Date:
    2018-03-27
    Publisher:
    American Physical Society (APS)
    Print ISSN:
    1098-0121
    Electronic ISSN:
    1095-3795
    Topics:
    Physics
    Keywords:
    Semiconductors II: surfaces, interfaces, microstructures, and related topics
    Published by:
    http://www.aps.org/

    Latest Papers from Table of Contents or Articles in Press
  2. 2
    L. Meckbach, T. Stroucken, and S. W. Koch
    American Physical Society (APS)
    Published 2018
    Staff View
    Publication Date:
    2018-01-19
    Publisher:
    American Physical Society (APS)
    Print ISSN:
    1098-0121
    Electronic ISSN:
    1095-3795
    Topics:
    Physics
    Keywords:
    Surface physics, nanoscale physics, low-dimensional systems
    Published by:
    http://www.aps.org/

    Latest Papers from Table of Contents or Articles in Press
  3. 3
    M. Hohenleutner ; F. Langer ; O. Schubert ; M. Knorr ; U. Huttner ; S. W. Koch ; M. Kira ; R. Huber
    Nature Publishing Group (NPG)
    Published 2015
    Staff View
    Publication Date:
    2015-08-01
    Publisher:
    Nature Publishing Group (NPG)
    Print ISSN:
    0028-0836
    Electronic ISSN:
    1476-4687
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Published by:
    http://www.nature.com/

    Latest Papers from Table of Contents or Articles in Press
  4. 4
    A. E. Almand-Hunter ; H. Li ; S. T. Cundiff ; M. Mootz ; M. Kira ; S. W. Koch
    Nature Publishing Group (NPG)
    Published 2014
    Staff View
    Publication Date:
    2014-02-28
    Publisher:
    Nature Publishing Group (NPG)
    Print ISSN:
    0028-0836
    Electronic ISSN:
    1476-4687
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Published by:
    http://www.nature.com/

    Latest Papers from Table of Contents or Articles in Press
  5. 5
    Staff View
    Publication Date:
    2018-05-15
    Publisher:
    Nature Publishing Group (NPG)
    Electronic ISSN:
    2045-2322
    Topics:
    Natural Sciences in General
    Published by:
    http://www.nature.com/

    Latest Papers from Table of Contents or Articles in Press
  6. 6
    Staff View
    Publication Date:
    2016-05-14
    Publisher:
    Nature Publishing Group (NPG)
    Print ISSN:
    0028-0836
    Electronic ISSN:
    1476-4687
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Published by:
    http://www.nature.com/

    Latest Papers from Table of Contents or Articles in Press
  7. 7
    Pollock, E. L. ; Koch, S. W.

    College Park, Md. : American Institute of Physics (AIP)
    Published 1991
    Staff View
    ISSN:
    1089-7690
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Chemistry and Pharmacology
    Notes:
    Computational path integral methods have been used to study the excitonic properties of an effective mass quantum dot model. The results are compared to those of variational calculations. The variational method, using a free particle basis, accurately gives the ground and low lying excited state properties for small radii dots where the kinetic energy dominates over the Coulomb interaction. The path integral approach, which is not restricted to small radii dots, gives a thermal average over states. One thermal effect noted for this model is an inversion of the surface charge layer with temperature due to the competition between thermal and Coulomb energies. At high temperature, where Coulomb effects are secondary, the thermal deBroglie wavelength sets the scale for the density variation near a surface and thus the heavier holes approach the surface more closely than the electrons. As the temperature is lowered the now more important Coulomb binding causes the holes to be cushioned away from the surface by the electron cloud. This inversion temperature decreases as the dot radius increases. Both calculations predict increasing biexciton binding energy with decreasing dot size.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.460254

    Articles: DFG German National Licenses
  8. 8
    Girndt, A. ; Knorr, A. ; Hofmann, M. ; Koch, S. W.

    [S.l.] : American Institute of Physics (AIP)
    Published 1995
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The ultrafast pump-probe signal of a two band semiconductor amplifier is theoretically analysed using Maxwell-Semiconductor-Bloch equations. It is shown that the coupling of the pump and probe pulse via the probe gain modification significantly contributes to the signal for short delay times between pump and probe. The probe signal exhibits dominant oscillatory interference-like structures which conceal intensity dependent ultrafast features. Despite the semiconductor is described with a two band model which does not include free carrier absorption and two photon absorption the results are qualitatively similar to those of recent experiments. © 1995 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.360040

    Articles: DFG German National Licenses
  9. 9
    Peyghambarian, N. ; Park, S. H. ; Koch, S. W. ; Jeffery, A. ; Potts, J. E. ; Cheng, H.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1988
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Large optical nonlinearities have been observed in molecular beam epitaxially grown thin films of ZnSe at room temperature and at T=150 K. A comparison with a plasma theory indicates that in both cases exciton screening is the dominating mechanism for the nonlinearity. The maximum nonlinear index per excited electron-hole pair at room temperature is comparable to that of bulk GaAs and GaAs-AlGaAs multiple quantum wells. The measured absorption and nonlinear index spectra agree quite well with our calculated values.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.99513

    Articles: DFG German National Licenses
  10. 10
    Wright, E. M. ; Koch, S. W. ; Ehrlich, J. E. ; Seaton, C. T. ; Stegeman, G. I.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1988
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    We present numerical calculations of the material figure of merit for a variety of bulk semiconductors at room temperature. For efficient switching to be possible in a half-beat-length nonlinear directional coupler, a minimum material requirement is that the figure of merit should exceed unity.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.99555

    Articles: DFG German National Licenses
  11. 11
    Jin, R. ; Chuang, C. L. ; Gibbs, H. M. ; Koch, S. W. ; Polky, J. N. ; Pubanz, G. A.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1988
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Room-temperature all-optical switching has been achieved in single-mode strip-loaded nonlinear directional couplers with a GaAs/AlGaAs multiple quantum well guiding layer. For low input intensities nearly complete (1:3–1:5) cross coupling occurs, while at high input intensities switching occurs so that most (〉3:1) of the light stays in the input guide. The effects of carrier diffusion are minimized by the use of picosecond pulses. The response time and the recovery time of the nonlinear directional couplers are measured with pump-probe experiments, and the origin of the nonlinearity is attributed to fast electronic effects.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.99782

    Articles: DFG German National Licenses
  12. 12
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    We present a systematic study of the dependence of the optical nonlinearities on quantum well thickness for GaAs/AlGaAs multiple quantum wells (MQW's) at room temperature and compare them with bulk GaAs. The maximum change in the refractive index is greatest for the MQW's with the smallest well size and decreases with increasing well size, reaching a minimum for bulk GaAs. The maximum index change per photoexcited carrier increases by a factor of 3 as the well size decreases from bulk to 76 A(ring) MQW.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.99157

    Articles: DFG German National Licenses
  13. 13
    Koch, S. W. ; Peyghambarian, N. ; Gibbs, H. M.

    [S.l.] : American Institute of Physics (AIP)
    Published 1988
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Nonlinear optical properties of laser-excited semiconductors are discussed, and the applications to optical bistability and optical logic are reviewed. The physical origin of the nonlinearities is analyzed in terms of the many-body interactions in the system of electron-hole pairs, causing effects such as plasma screening of the Coulomb interaction, band-gap renormalization, and band filling. Theoretical results for absorption and refractive-index spectra are compared to experimental data obtained for room-temperature GaAs and other semiconductors. The experimental and theoretical results for dispersive optical bistability in semiconductors are summarized, and recent experiments on optical logic gating and pattern recognition are discussed.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.340098

    Articles: DFG German National Licenses
  14. 14
    Lee, S. G. ; McGinnis, B. P. ; Jin, R. ; Yumoto, J. ; Khitrova, G. ; Gibbs, H. M. ; Binder, R. ; Koch, S. W. ; Peyghambarian, N.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1994
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    We have demonstrated ultrafast switching behavior in a current injected GaAs/AlGaAs multiple-quantum-well nonlinear directional coupler at room temperature. The results show low crossover pulse energy (10 pJ) and full recovery within 1 ps.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.111127

    Articles: DFG German National Licenses
  15. 15
    Pereira, M. F. ; Koch, S. W. ; Chow, W. W.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1991
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    A many-body theory for the optical susceptibility in highly excited strained-layer quantum wells is presented. Gain spectra are computed for the example of InxGa1−xAs/InP and different In concentrations, yielding zero, tensile, and compressive strain.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.105830

    Articles: DFG German National Licenses
  16. 16
    Kang, K. ; Kepner, A. D. ; Hu, Y. Z. ; Koch, S. W. ; Peyghambarian, N. ; Li, C.-Y. ; Takada, T. ; Kao, Y. ; Mackenzie, J. D.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1994
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Spectral hole burning at room temperature is used as a technique to compare optical nonlinearities of semiconductor quantum dot materials prepared by the sol-gel and glass fusion techniques. In an effort to understand the mechanism of photodarkening in quantum dots and assess its effect on optical nonlinearities, we prepared and characterized three representative samples with similar dot sizes. We found that photodarkening can be reduced substantially by controlling the media surrounding the dots. The sol-gel derived samples with 80 wt % SiO2 do not exhibit appreciable photodarkening while the melt-quenched glasses with 56 wt % SiO2 exhibit strong photodarkening effects at room temperature which results in reduction of their optical nonlinearity by a factor of (approximately-equal-to)20 compared with the sol-gel derived samples.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.111867

    Articles: DFG German National Licenses
  17. 17
    Jin, R. ; Boggavarapu, D. ; Khitrova, G. ; Gibbs, H. M. ; Hu, Y. Z. ; Koch, S. W. ; Peyghambarian, N.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1992
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The emission linewidth above threshold is measured in a GaAs/AlGaAs microcavity surface-emitting laser with a single cavity mode. The measured linewidth broadening factor is in good agreement with theoretical calculations that include the most important many-body Coulomb effects of the electron-hole plasma.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.108377

    Articles: DFG German National Licenses
  18. 18
    Jin, R. ; Okada, K. ; Khitrova, G. ; Gibbs, H. M. ; Pereira, M. ; Koch, S. W. ; Peyghambarian, N.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1992
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Optical nonlinearities in strained-layer InGaAs/GaAs multiple quantum wells (MQWs) are studied using pump-probe spectroscopy. It is found that the carrier density required for absorption saturation in a strained InGaAs/GaAs MQW is about a factor of two lower than that in an unstrained GaAs/AlGaAs MQW with similar structures, while the nonlinear index change per carrier is about the same for both samples. The decrease in the saturation density in the strained MQW is explained by the increase of the top valence-band curvature caused by the compressive strain in the quantum well.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.108414

    Articles: DFG German National Licenses
  19. 19
    Pereira, M. F. ; Binder, R. ; Koch, S. W.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1994
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Nonlinear optical absorption spectra and refractive index changes are computed for coupled-band semiconductor quantum wells by numerically solving the interband polarization equation. The theory combines band-structure engineering with many-body techniques and is applied to lattice-matched GaAs-AlGaAs and strained InGaAs-GaAs systems with carrier densities ranging from the excitonic to the gain regimes. Good agreement with recent experimental results is found.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.111180

    Articles: DFG German National Licenses
  20. 20
    Chow, W. W. ; Pereira, M. F. ; Koch, S. W.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 1992
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    The carrier density modulation response of a semiconductor laser medium is analyzed. The differential gain and linewidth enhancement factor are computed as functions of strain and threshold gain. The example of InGaAs/InP with different InAs content is used to illustrate the situations of zero, tensile and compressive strain.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.107789

    Articles: DFG German National Licenses