Yazar "Karabulut, I." seçeneğine göre listele

Listeleniyor 1 - 5 / 5
  • Küçük Resim Yok
    Öğe
    Excitonic effects on the nonlinear optical properties of small quantum dots
    (IOP PUBLISHING LTD, 2008) Karabulut, I.; Safak, H.; Tomak, M.
    The excitonic effects on the nonlinear optical properties of small quantum dots with a semiparabolic confining potential are studied under the density matrix formalism. First, within the framework of the strong confinement approximation, we present the excitonic states and then calculate the excitonic effects on the nonlinear optical properties, such as second harmonic generation, third harmonic generation, nonlinear absorption coefficient and refractive index changes. We find the explicit analytical expressions between the corresponding nonlinear optical properties with and without considering the excitonic effects. It is seen that these analytical expressions are related only to ratios of the effective masses of electron and hole. These explicit expressions indicate that the excitonic effects on the corresponding nonlinear optical properties become more important with increasing orders of the optical susceptibilities. In addition, we suggest a scaling rule for the nth-order susceptibility as gamma((n+1)/2). The effect of the confining potential frequency on the corresponding nonlinear optical properties is also studied. Our results show a remarkable dependence of nonlinear optical properties on both the excitonic effects and the confining potential frequency.
  • Küçük Resim Yok
    Öğe
    Linear and nonlinear intersubband optical absorption coefficients and refractive index changes in a quantum box with finite confining potential
    (ELSEVIER, 2006) Unlu, S.; Karabulut, I.; Safak, H.
    In this work, both the intersubband optical absorption coefficients and the refractive index changes are calculated exactly in a quantum box. Analytical expressions for the linear and nonlinear intersubband absorption coefficients and refractive index changes are obtained by using the compact-density matrix approach. Numerical results are presented for typical GaAs/AlxGa1-xAs quantum box system. The linear, third-order nonlinear and total absorption and refractive index changes are investigated as a function of the incident optical intensity and structure parameters such as box-edge length and stoichiometric ratio. Our results show that both the incident optical intensity and the structure parameters have a great effect on the total absorption and refractive index changes. (c) 2006 Elsevier B.V. All rights reserved.
  • Küçük Resim Yok
    Öğe
    Linear and nonlinear intersubband optical absorptions in an asymmetric rectangular quantum well
    (SPRINGER, 2007) Karabulut, I.; Atav, U.; Safak, H.; Tomak, M.
    The linear and nonlinear intersubband optical absorptions in AlxlGa1-xlAs/GaAs/AlxrGa1-xrAs asymmetric rectangular quantum well are studied within the framework of the density matrix formalism. We have calculated the electron energy levels and the envelope wave functions using the effective mass approach. In addition, we have obtained an expression for saturation intensity. It is shown that the parameters such as asymmetry and width of potential well not only shift the peak positions in absorption spectrum but also considerably modify their height. These results suggest that the absorption process can be easily controlled by the structure parameters of an asymmetric rectangular quantum well. Also, the incident optical intensity has a great effect on the total absorption spectrum. We have seen that the absorption peak is reduced by half when the optical intensity is approximately 0.8 MW/cm(2) for well width L = 90 angstrom and beta = 0.5. Moreover, it is seen that the saturation intensity is quite sensitive to the structure parameters of an asymmetric rectangular quantum well. Thus, the results presented here can be useful for electro-optical modulators and photodetectors in the infrared region.
  • Küçük Resim Yok
    Öğe
    Nonlinear optical rectification and optical absorption in GaAs-Ga1-xAlxAs asymmetric double quantum wells: Combined effects of applied electric and magnetic fields and hydrostatic pressure
    (ELSEVIER SCIENCE BV, 2011) Karabulut, I.; Mora-Ramos, M. E.; Duque, C. A.
    The intersubband electron-related nonlinear optical absorption and nonlinear optical rectification in GaAs-Ga(1-x)AL(x)As asymmetric double quantum wells are studied, under the influence of combined or independent applied electric and magnetic fields as well as hydrostatic pressure. The outcome of the density matrix formalism and the effective mass, and parabolic-band approximations have been considered as main theoretical tools for the description. It is obtained that under particular geometrical conditions, with or without electric and/or magnetic field strength, the optical rectification is null and, simultaneously, in such circumstances the optical absorption has a relative maximum. It is also detected that the influence of the hydrostatic pressure leads to increasing or decreasing behaviors of the nonlinear optical absorption in dependence of the particular regime of pressure values considered, with significant distinction of the cases of opposite electric field orientations. (C) 2011 Elsevier B.V. All rights reserved.
  • Küçük Resim Yok
    Öğe
    Nonlinear optical rectification and optical absorption in GaAs-Ga1-xAlxAs double quantum wells under applied electric and magnetic fields
    (ELSEVIER SCIENCE BV, 2011) Karabulut, I.; Duque, C. A.
    In this work are studied the electron-related nonlinear optical absorption and nonlinear optical rectification in GaAs-Ga1-xAlxAs asymmetric double quantum wells under applied electric and magnetic field. The density matrix formalism and the effective mass and parabolic band approximations have been considered. The main findings show that in asymmetrical heterostructures under an appropriate strength of the electric field it is possible that the optical rectification is zero and in such circumstances the optical absorption has a relative maximum; similar behavior is observed in these optical properties as a function of the length of one of the two quantum wells and without applied electric field. Also, the results suggest that in asymmetric double quantum wells the optical absorption is a nonmonotonic increasing (decreasing) function of the applied magnetic field (width of the central barrier) and that particularly when the optical absorption has an inflection point the optical absorption has an absolute maximum. Finally we found that the resonant peaks in the nonlinear optical rectification and nonlinear optical absorption can be red-shifted to low photon energies or blue-shifted to large photon energies depending on the energy difference of the two lowest confined states in the heterostructure, and this condition can be controlled by changes in the external proofs such us applied electric and magnetic fields or by changes in the structural dimensions of the coupled quantum well system. (C) 2011 Elsevier B.V. All rights reserved.