Compact-density Matrix Formalism Research Articles

Nonlinear optical properties of nanospherical layer in the presence of an electric field

The linear and nonlinear optical properties in a spherical nanolayer quantum system subjected to an uniform applied electric field directed with respect to the z-axis have been theoretically investigated within the compact-density matrix formalism and the iterative method. The dependence of the optical absorption coefficients (ACs) and refractive index (RI) changes on the core radius R1, on the inner radius of the clad R2, and on the applied electric field F has been investigated detailedly. The results show that the optical ACs and RI changes of the nanospherical layer have been strongly affected by these factors. Moreover, the outcome of the calculation also suggests that all the factors mentioned above can give rise to blue-shift or red-shift significantly.

Quantum wire with parallelogram cross section: optical properties

In the present work, the optical properties of a GaAs quantum wire with a parallelogram cross section are studied. In this regard, we have used the expressions for the optical properties obtained by the compact-density matrix formalism. Here, we have investigated the intersubband optical absorption coefficients and refractive index changes as a function of the structure parameter of the wire (side length) and the incident optical intensity. According to the obtained results, it is found that (1) the total refractive index changes increase and shift towards lower energies when the side length increases and that (2) the total absorption coefficient decreases as the side length increases. Also, the resonance peak shifts towards lower energies by increasing the side length.

Nonlinear optical properties of a three-dimensional anisotropic quantum dot

The linear and nonlinear optical properties in a three-dimensional anisotropic quantum dot subjected to a uniform magnetic field directed with respect to the z -axis have been investigated within the compact-density matrix formalism and the iterative method. The dependence of the linear and nonlinear optical properties on the characteristic frequency of the parabolic potential, on the magnetic field, and on the incident optical intensity is studied in detail. Moreover, taking into account the position-dependent effective mass, the dependence of the linear and nonlinear optical properties on the dot radius is investigated. The results show that the optical absorption coefficients (ACs) and refractive index (RI) changes of the anisotropic quantum dot (QD) are strongly affected by these factors, and the position effect also plays an important role in the optical ACs and RI changes of the anisotropic QD.

Biexcitonic absorption in a disk-shaped GaN quantum dot

The present work investigates the nonlinear optical properties of a GaN quantum dot in the disk limit via the exciton and biexciton states using the compact density matrix formalism. Based on this model, we calculate the ground state energy of the exciton and biexciton states by the variation method, within envelope function and effective mass approximations. Linear and nonlinear optical absorption (α (1), α (3)) and oscillator strengths attributed to the optical transitions are obtained. The details of the behaviour of α (1) and α (3) around the resonance frequencies and for different quantum dot geometries are presented. It is found that the size of quantum dot and the optical intensity have a remarkable effect on the optical absorption, and the biexcitonic two-photon absorption coefficient(K 2) has also been calculated in this system. The results show that this parameter is strongly affected by the size of the quantum dot.

Study of optical properties in a cubic quantum dot

In this paper, the effect of hydrostatic pressure on both the intersubband optical absorption coefficients and the refractive index changes is studied for typical GaAs/Al x Ga1−x As cubic quantum dot. We use analytical expressions for the linear and third-order nonlinear intersubband absorption coefficients and refractive index changes obtained by the compact-density matrix formalism. The linear, third-order nonlinear, and total intersubband absorption coefficients and refractive index changes are calculated at different pressures as a function of the photon energy with known values of box length (L), the incident optical intensity (I), and Al concentration (x). According to the results obtained from the present work, we have found that the pressure plays an important role in the intersubband optical absorption coefficient and refractive index changes in a cubic quantum dot.

Effects of the hydrostatic pressure and temperature on optical properties of a hydrogenic impurity in the disc-shaped quantum dot

The combined effects of hydrostatic pressure and temperature on the optical absorption coefficient and refractive index changes of a hydrogenic impurity in a disc-shaped quantum dot with parabolic confinement in the presence of an external electric field have been investigated by using the perturbation method within the effective-mass approximation. Analytical expressions for the linear and third-order nonlinear absorption coefficients and refractive index changes have been obtained by using the compact-density matrix formalism. We discussed the linear, third-order nonlinear, total absorption coefficients and refractive index changes as functions of photon energy, relaxation time, pressure, and temperature with I=1.5×10 4 W/cm 2, F=50 kV/cm, and ℏ ω 0 = 50 meV . Our results show that the pressure and temperature play an important role in the optical absorption coefficients and refractive index changes in a disc-shaped quantum dot.

Nonlinear optical properties of a hydrogenic impurity in an ellipsoidal finite potential quantum dot

The linear and the third-order nonlinear optical absorption coefficient and refractive index changes of a hydrogenic impurity in an ellipsoidal quantum dot have been investigated, using the compact-density matrix formalism and an iterative method. In this regard, the effect of the size and geometry of the dot, aluminium concentration in GaAs/ Al xGa 1− x As structures, and optical intensity on the optical absorption coefficient and refractive index changes are investigated. It is found that the light intensity, size and geometry of the dot and aluminium concentration have a great influence on the absorption coefficient and refractive index changes of the dot.

INTERSUBBAND OPTICAL ABSORPTION COEFFICIENTS AND REFRACTIVE INDEX CHANGES OF AN ELLIPSOIDAL FINITE POTENTIAL QUANTUM DOT

Intersubband optical absorption coefficient and refractive index changes of a weakly prolate ellipsoidal quantum dot, using the compact-density matrix formalism and iterative method, are investigated. In this regard, the linear and nonlinear intersubband optical absorption coefficient and refractive index changes of a GaAs / Al x Ga 1-x As ellipsoidal quantum dot, as functions of the dot radius, ellipticity constant, stoichiometric ratio and incident light intensity are calculated. The results indicate that absorption coefficient and refractive index changes strongly depend on the light intensity, size and geometry of the dot and structure parameters such as aluminium concentration in GaAs / Al x Ga 1-x As structures.

Effect of pressure on intersubband optical absorption coefficients and refractive index changes in a V-groove quantum wire

In this paper, the effect of hydrostatic pressure on the intersubband optical absorption and the refractive index changes in a GaAs/Ga 1−xAl xAs ridge quantum wire are studied. We use analytical expressions for the linear and third-order nonlinear intersubband absorption coefficients and refractive index changes obtained by the compact-density matrix formalism. The linear, third-order nonlinear, and total intersubband absorption coefficients and refractive index changes are investigated at different pressures as a function of photon energy with known values of width wire ( b ), the incident optical intensity ( I ), and the angle θ . According to the results obtained from the present work, we have found that the pressure plays an important role in the intersubband optical absorption coefficients and refractive index changes in a V-groove quantum wire.

Nonlinear optical properties of a two-dimensional elliptic quantum dot

The linear and third order nonlinear optical absorption coefficient and refractive index changes of an elliptic quantum dot have been investigated, using the compact-density matrix formalism and an iterative method. In this regard, the effect of optical intensity, size and geometry of the dot on the optical absorption coefficient and refractive index changes are investigated. It is found that, not only the light intensity but also the size and the geometry of the dot have a great influence on the optical absorption coefficient and refractive index changes of the system.

Refractive index changes in AlGaN/GaN heterostructure field-effect transistors

Using the envelope wavefunction approximation and the compact density matrix formalism, we have investigated theoretically the linear and nonlinear refractive index changes in AlGaN/GaN quantum well heterostructures aimed for designing electro-optical modulators. The confining potential in the heterostructures is assumed to be semiparabolic. Simulated results reveal that the refractive index changes strongly depend on both the Al composition and the delta-doping concentration. On the other hand an applied electric field further enhances the refractive index changes. Compared with AlGaAs/GaAs heterostructures and quantum dots, the amount of the refractive index is larger in the AlGaN/GaN quantum well heterostructures studied. The fact to have a large refractive index change leads to the use of relatively weaker incident beam intensities.

Optical nonlinearities in delta-doped AlGaN/GaN quantum well heterostructures

The linear and nonlinear optical properties such as second-harmonic generation susceptibility, optical absorption and refractive index change associated with intersubband transitions in AlGaN/GaN quantum well heterostructures have been investigated theoretically. The electronic states of these structures are calculated using both the envelope wave function approximation and the compact-density matrix formalism. The confining potential has been assumed to be semiparabolic. The results obtained for typical AlGaN/GaN single-heterostructure field effect transistors reveal that these properties strongly depend on the Al composition and the doping concentration as well. Also calculated is the electric field effect on the susceptibility, the refractive index, and the absorption coefficient. It was thus found that the applied electric field can improve considerably the nonlinear optical behavior of the AlGaN/GaN heterostructures studied.

Interband optical absorptions in a parabolic quantum dot

The linear and nonlinear optical absorptions considering excitonic effect in a parabolic quantum dot are studied. Analytic forms of the linear and third-order nonlinear optical absorption coefficients are obtained for a symmetric parabolic quantum dot using the compact density matrix formalism. Based on this model, numerical results are presented for a typical CdS parabolic quantum dot. The calculated results show that the factors of the parabolic potential confinement and the incident optical intensity have great influence on the optical absorption coefficients. Furthermore, the optical absorption saturation intensity can be controlled by adopting a proper parabolic confinement potential.