Theoretical studies on the optical absorption coefficients and refractive index changes in parabolic quantum dots in the presence of electric and magnetic fields

The optical absorption coefficients and the changes in the refractive index in GaAs/AlGaAs parabolic quantum dots(QDs) with applied electric and magnetic fields are studied in detail. Analytical expressions for the linear and nonlinear intersubband absorption coefficients and refractive index changes are obtained by using a compact density matrix approach and an iterative procedure. Finally, the calculated results show the incident optical intensity, the frequencies of the confined potential of the QDs and the applied electric and magnetic fields have a great influence on the optical absorption coefficients and refractive index changes in this system.     

Optical Conductivity of Impurity-Doped Parabolic Quantum Wells in an Applied Electric Field

The optical conductivity of impurity-doped parabolic quantum wells in an applied electric field is investigated with the memory-function approach, and the analytic expression for the optical conductivity is derived. With characteristic parameters pertaining to GaAs/Ga_1-xAl_xAs parabolic quantum wells, the numerical results are presented. It is shown that, the smaller the well width, the larger the peak intensity of the optical conductivity, and the more asymmetric the shape of the optical conductivity; the optical conductivity is more sensitive to the electric field, the electric field enhances the optical conductivity; when the dimension of the quantum well increases, the optical conductivity increases until it reaches a maximum value, and then decreases.     

A study of fatigue crack growth under random stresses in the aspect of statistics

A CCT experiment controlled by pseudo random signals generated by a white-noise generator with narrow-band filter has been done in the MTS-880 system to compare the effects of different K _char on d/dt. A fatigue crack growth life prediction formula which is only dependent on Power Spectrum Density (P. S. D.) of the history under Gaussian narrow-band history is derived. The theoretical results are in good agreement with the experimental ones.     

The second-harmonic generation in parabolic quantum dots in the presence of electric and magnetic fields

The second-harmonic generation (SHG) coefficient for parabolic quantum dots (QDs) subject to applied electric and magnetic fields is theoretically investigated, within the framework of the compact-density-matrix approach and an iterative method. Numerical results are presented for typical GaAs/AlGaAs parabolic QDs. These results show that the radius of QD and the magnitude of electric and magnetic fields have a great influence on the SHG coefficient. And the peak shifts to the aspect of high energy when considering the influence of electric and magnetic fields. Moreover, the SHG coefficient also depends sensitively on the relaxation rate of the spherical QD system.     

Polaron effects on the optical absorptions in cylindrical quantum dots with parabolic potential

The optical absorptions considering polaron effects in cylindrical quantum dots (QDs) with an applied electric field are theoretically studied. It is shown that pronounced optical absorptions dependence of the quantum dot parameters can be obtained. Moreover, the theoretical values of the optical absorptions obviously increase when considering the electron–LO–phonon interaction.     

Polaron effects on the optical rectification in a two-dimensional quantum pseudodot system

Using the compact density-matrix approach and the iterative method, the optical rectification in a two-dimensional quantum pseudodot system under the influence of a static magnetic field is theoretically investigated. The effects of an external magnetic field and the geometrical size of the pseudodot system on the optical rectification are presented. What’s more, we find that the polaron effect has an important influence on the optical rectification.     

Optical second harmonic generation in asymmetric double triangular quantum wells

The second harmonic generation (SHG) in the asymmetric double triangular quantum wells (DTQWs) is investigated theoretically. The dependence of the SHG coefficient on the right-well width of the DTQWs is studied, and the influence of the applied electric field on SHG coefficient is also taken into account. The analytical expression of the SHG coefficient is analyzed by using the compact density-matrix approach and the iterative method. Finally, the numerical calculations are presented for the typical GaAs/Al_xGa_1−xAs asymmetric DTQWs. The results show that the calculated SHG coefficient in this coupled system can reach the magnitude of 10⁻⁵ m/V, 1–2 orders of magnitude higher than that in step quantum well, and that in double square quantum wells. Moreover, the SHG coefficient is not a monotonic function of the right-well width, but has complex relationship with it. The calculated results also reveal that an applied electric field has a great influence on the SHG coefficient. Applying an appropriate electric field to a DTQW with a wider right well can induce a sharper peak of the SHG coefficient due to the double-resonant enhancement.     

Third-harmonic generation in cubical quantum dots

Third-harmonic generation (THG) for cubical quantum dots (CQDs) with an applied electric field is theoretically investigated in the framework of the compact-density-matrix approach and an iterative method. The confined wave functions and energies of electrons in the CQDs are calculated in the effective-mass approximation. Numerical calculations are presented for typical GaAs/AlAs CQDs. The results demonstrate that the THG strongly depends on the length of the CQDs and the magnitude of the electric field. Also, the peaks shift towards the higher energy region with increasing electric field.     

Polaron effects on the third-harmonic generations in a two-dimensional quantum pseudodot system

The third-harmonic generations (THG) considering polaron effects in the two-dimensional quantum pseudodot system with a uniform magnetic field are theoretically studied. It is found that the THG coefficient is strongly affected not only by an external magnetic field, but also by the geometrical size of the pseudodot system. Moreover, the theoretical values of the THG is obviously increased when considering the electron–LO–phonon interaction.     

Linear and nonlinear intersubband optical absorption in double triangular quantum wells

The linear and the third-order nonlinear optical absorptions in the asymmetric double triangular quantum wells (DTQWs) are investigated theoretically. The dependence of the optical absorption on the right-well width of the DTQWs is studied, and the influence of the applied electric field on the optical absorption is also taken into account. The analytical expressions of the linear and the nonlinear optical absorption coefficients are obtained by using the compact density-matrix approach and the iterative method. The numerical calculations are presented for the typical GaAs/Al_xGa_1?xAs asymmetric DTQWs. The results show that the linear as well as the nonlinear optical absorption coefficients are not a monotonous function of the right-well width, but have complex relationships with it. Moreover, the calculated results also reveal that applying an electric field to the DTQWs with a thinner right-well can enhance the linear optical absorption but has no prominent influence on the nonlinear optical absorption. In addition, the total optical absorption is strongly dependent on the incident optical intensity.