Yazar "Karabulut, Ibrahim" seçeneğine göre listele

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    Effect of Coulomb interaction on nonlinear (intensity-dependent) optical processes and intrinsic bistability in a quantum well under the electric and magnetic fields
    (AMER INST PHYSICS, 2011) Karabulut, Ibrahim
    The effect of the electrostatic Coulomb interaction on the line shape related to the intensity-dependent intersubband optical processes in a Si delta-doped quantum well is studied using the density matrix formalism. The electronic structure of the quantum well is calculated from the self-consistent numerical solution of the coupled Schrodinger-Poisson equations. The line shape function is considerably modified by the optical intensity and the electric and magnetic fields. Moreover, we demonstrate the existence of the optical bistability for appropriate values of the optical intensity and also the control of the optical bistability with the electric and magnetic fields. It is also found that the intersubband relaxation time plays an important role in determining the optical bistability region. (C) 2011 American Institute of Physics. [doi:10.1063/1.3553641]
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    Intersubband resonant enhancement of the nonlinear optical properties in compositionally asymmetric and interdiffused quantum wells
    (AMER INST PHYSICS, 2008) Karabulut, Ibrahim; Safak, Haluk; Tomak, Mehmet
    We report the resonant enhancement of the second- and third-order optical nonlinearities in compositionally asymmetric quantum wells with finite confining potential and interdiffused quantum wells. The energy levels and the envelope wave functions in quantum wells are obtained by solving numerically the Schrodinger equation. The optical rectification, second and third harmonic generation coefficients are calculated within the framework of the density matrix formalism. The effect of the structure parameters such as the well width and the barrier height on the nonlinear optical properties is investigated in detail. The resulting nonlinear susceptibilities obtained in both quantum wells are considerably larger than those of bulk GaAs. (C) 2008 American Institute of Physics.
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    Linear and nonlinear optical absorption coefficients and refractive index changes in spherical quantum dots: Effects of impurities, electric field, size, and optical intensity
    (AMER INST PHYSICS, 2008) Karabulut, Ibrahim; Baskoutas, Sotirios
    In the present work, the case of a spherical quantum dot with parabolic confinement subjected to an external electric field with the presence of an impurity, the linear and third-order nonlinear optical absorption coefficients as well as refractive index changes have been calculated. The numerical method we are using for the calculation of the energy levels and the corresponding wave functions is the potential morphing method in the effective mass approximation. As our results indicate an increase of the electric field and/or the position of the impurity and/or the quantum dot radius redshifts the peak positions of the total absorption coefficient and total refractive index changes. Additionally, an increase of the position of the impurity and/or the quantum dot radius decreases the total absorption coefficient and increases the total refractive index changes. An increase also of the electric field decreases the total absorption coefficient but does not significantly affect the peak values of the total refractive index changes. Finally, an increase of the optical intensity considerably changes the total absorption coefficient as well as the total refractive index changes. (C) 2008 American Institute of Physics.
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    Nonlinear optical response in intersubband transitions of a symmetric quantum well: Role of electron-electron interactions
    (ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2017) Karabulut, Ibrahim
    We investigate theoretically the saturation problem of the nonlinear intersubband response in a symmetric quantum well. We first obtain the analytical expressions for the absorption/dispersion spectra from the steady-state solutions of the nonlinear density matrix equations. This expressions include the depolarization effect that results from the electron-electron interactions and also depends on the population difference between the first two subbands. We calculate the line shape of the dispersion spectrum and show that the dispersion spectrum becomes non-antisymetric as the intensity of the radiation increases. For larger values of the electron sheet density, this distortion becomes more apparent. We also find that the optical bistability can be obtained for appropriate values of the electron sheet density and the intensity of the optical radiation. Our results also show that the electron redistribution among the subbands by additional external factor has a dramatic effect on the nonlinear intersubband response. (C) 2017 Elsevier Ltd. All rights reserved.
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    The role of permanent dipoles on the intensity-dependent nonlinear optical properties in asymmetric coupled quantum wells under a static electric field
    (ELSEVIER, 2016) Karabulut, Ibrahim; Paspalakis, Emmanuel
    We study theoretically the intensity-dependent nonlinear optical properties of an asymmetric coupled quantum well under a static electric field. Effects such as nonlinear absorption, optical rectification and refractive index are investigated theoretically by using the density matrix equations including the permanent dipole terms. Our results show that the effects of the permanent dipoles on the corresponding optical processes depend crucially on the direction and strength of the static electric field, especially for large optical intensities. Another interesting result of this work is that the nonlinear optical spectra studied here saturate with an increasing optical intensity and specifically the optical spectra in the case that the permanent dipoles are considered reach saturation for lower intensities than when the permanent dipoles are not considered. (C) 2016 Elsevier B.V. All rights reserved.
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    Second and Third Harmonic Generation Susceptibilities of Spherical Quantum Dots: Effects of Impurities, Electric Field and Size
    (AMER SCIENTIFIC PUBLISHERS, 2009) Karabulut, Ibrahim; Baskoutas, Sotirios
    Studying the case of spherical quantum dot with parabolic confinement subjected to an external electric field with the presence of an impurity, the second and third harmonic generation susceptibilities have been calculated. The numerical method we are using for the calculation of the energy levels and the corresponding wavefunctions, is the potential morphing method in the effective mass approximation. As our results indicate an increase of the electric field and/or the position of the impurity and/or the quantum dot radius enhances the peak values of the second
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    Second harmonic generation in an asymmetric rectangular quantum well under hydrostatic pressure
    (ELSEVIER SCIENCE BV, 2007) Karabulut, Ibrahim; Atav, Ulfet; Safak, Haluk; Tomak, Mehmet
    The effects of structure parameters and hydrostatic pressure oil the electronic states and the second harmonic generation (SHG) susceptibility of asymmetric rectangular quantum Well (ARQW) are studied. The asymmetry of the potential can be controlled by changing the structural parameters and this adjustable asymmetry is important for optimizing the SHG susceptibility. We have calculated analytically the electronic states in ARQW within the framework of the envelope function approach. Numerical results for Al-x/Ga1-x/As/GaAs/AlxrGa1-xr. As quantum well are presented. The results obtained show that the hydrostatic pressure and the structure parameters of ARQW significantly influence the SHG susceptibility. This behavior in the SHG susceptibility gives a new degree of freedom in regions of interest for device applications. (c) 2007 Elsevier B.V. All rights reserved.
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    Theoretical investigation of intersubband nonlinear optical rectification in AlxlGa1-xlAs/GaAs/AlxrGa1-xrAs asymmetric rectangular quantum wells
    (WILEY-V C H VERLAG GMBH, 2007) Karabulut, Ibrahim; Atav, Uelfet; Safak, Haluk; Tomak, Mehmet
    In this study, a theoretical investigation of intersubband nonlinear optical rectification in Alx1Ga1-x1As/ GaAs/AlxrGa1-xrAs asymmetric rectangular quantum wells is presented. The electronic states in the asymmetric rectangular quantum well are described within the framework of the envelope function approach including the effects of band nonparabolicity and the effective mass mismatch. The nonlinear optical rectification is calculated using the density matrix formalism. It is found that the nonlinear optical rectification in the asymmetric rectangular quantum well depends sensitively on the parameters such as the width and the asymmetry of the potential well. The adjustable parameters allow for tuning of the asymmetric rectangular quantum well system to the desired wavelength while retaining a large optical rectification coefficient. This gives a new degree of freedom in various device applications based on nonlinear optical properties. Band nonparabolicity is found to significantly influence both electronic states and nonlinear optical rectification. Moreover the resulting optical rectification coefficient is much larger than the ones for bulk GaAs and some other theoretical studies in literature. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.