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Revista cubana de física

Second-Harmonic and Third-Harmonic Generation in Nanostructures with Asymmetric Confinement Potential: The Role of Two-level Atom Approximation

Dairo A. Causil, M. P. Urango Baquero, Alfonso A. Portacio

Published Dec 15, 2018• 0 citations

Abstract

The second harmonic generation (SHG) and third harmonic generation (THG) into a cylindrical quantum dot (CQD) with asymmetric confinement potential is studied theoretically within the framework the two-level atom approximation, by using the matrix density formalism. The energy levels and waves functions of an electron into CQD they were obtained by solving the time-independent Schrodinger equation. The numerical calculations make for a CQD of GaAs/GaAlAs. It was found that the increase in the confinement of the charge carriers produced by the increase of the magnetic field and/or the dimensions of the nanostructure generates a shift to blue in the transition energies of the electrons. Also a multiple resonances in the two-level atom approximation was found. These were associated with transition between excited state and ground state and a second transition getting a change permanent dipole moment.For the English version of the abstract, please be careful with the language.

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The second harmonic generation (SHG) and third harmonic generation (THG) into a cylindrical quantum dot (CQD) with asymmetric confinement potential is studied theoretically within the framework the two-level atom approximation, by using the matrix density formalism. The energy levels and waves functions of an electron into CQD they were obtained by solving the time-independent Schrodinger equation. The numerical calculations make for a CQD of GaAs/GaAlAs. It was found that the increase in the confinement of the charge carriers produced by the increase of the magnetic field and/or the dimensions of the nanostructure generates a shift to blue in the transition energies of the electrons. Also a multiple resonances in the two-level atom approximation was found. These were associated with transition between excited state and ground state and a second transition getting a change permanent dipole moment.For the English version of the abstract, please be careful with the language.

In the present work, we have studied numerically the second harmonic generation (SHG) and third harmonic generation (THG) in a cone-like quantum dot. For this purpose, we firstly obtained the energy levels and wave functions of this system. Then, we have used an expression for the SHG and THG by a compact density matrix approach and an iterative procedure. The SHG and THG enhance and shift toward lower energy by increasing the height h and vertex angle α. According to the results it is found that the structural parameters have great influence on the THG in this system.

Abstract In the current work, we have studied the second and third harmonic generation in asymmetrical Gaussian potential quantum dot subjected to the applied electric field. To do this, confined wave function together with energies of electron in an effective mass approximation framework were obtained. Apply these, the analytic expression for the second- and third harmonic generation are determined using a compact density matrix approach and an iterative procedure. According to the results, it is found that applying an electric field, enhances the peak values of the second- and third harmonic generation and redshifts the peak position of their spectrum. Our calculations indicate that increases the radius of quantum dot causes enhances the values of -harmonic generation and redshifts the peak positions of photon energy. It means by optimizing the confinement potential, the maximum –harmonic generation can be obtained. It should be noted that the structural parameters have a significant effect on the –harmonic generation in the considered system.

In the present work, we have studied the second-harmonic generation (SHG) and third-harmonic generation (THG) in a pyramid quantum dot. For this purpose, we first obtain the energy levels and wavefunctions of this system. Then, we have used an analytic expression for the SHG and THG by a compact density matrix approach and an iterative procedure. The SHG and THG enhance and shift to lower energies by increasing the height (h) and vertex angle (φ). According to the results, it is found that the structural parameters have great influence on the SHG and THG of a pyramid quantum dot.

The third-harmonic generation (THG) in

\mathrm{GaAs}∕\mathrm{AlGaAs}

cylindrical parabolic quantum wires with an applied static-electric field is studied in detail. An analytic formula for the THG susceptibility in the model is obtained by a compact density matrix approach and an iterative procedure. Finally, the calculated results show the parabolic confinement potential and the applied electric field have great influence on the THG susceptibilities in the system. Another important point is that the maximum THG susceptibility over ${10}^{\ensuremath{-}9}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{2}∕{\mathrm{V}}^{2}$ can be obtained by optimizing the parabolic confinement potential and the applied electric field, which is over ten orders of magnitude greater than in bulk GaAs. The contributors to the very giant three-order nonlinear include the very large dipole transition matrixes and the triple resonant condition.

Abstract In this theoretical work, we investigate how external fields like as electric, magnetic, and intense laser fields, as well as structural factors, affect the third harmonic generation (THG) coefficient of an AlGaAs/GaAs Manning-like double quantum well heterostructure. To achieve our goals, we numerically solve the time-independent Schrödinger equation using the diagonalization approach with the effective mass approximation and then derive the subband energy levels and corresponding wave functions of the structure. After that, we derive the mathematical expression of the THG coefficient by using the compact density matrix method. According to our results, the resonance peaks of the THG coefficient show shifting to the high-energy region with an increase in the field’s magnitude in cases where external fields (electric, magnetic, and intense laser) are applied separately. At the same time, increasing the depth (width) of the quantum well structure causes the THG peaks to shift to the high (low) energy region. We believe that the findings from this search will have a substantial impact on existing experimental device designs and applications.