Linear Optical Absorption Coefficients Research Articles

Nonlinear optical properties of a D− system in a spherical quantum dot

The nonlinear optical properties of a D− system confined in a spherical quantum dot represented by a Gaussian confining potential are studied. The great advantage of our methodology is that the model potential possesses the finite height and range. Calculations are carried out by using the method of numerical diagonalization of Hamiltonian matrix within the effective-mass approximation. We calculate the linear, third-order nonlinear and total optical absorption coefficients under the density matrix formalism. Numerical results for GaAs−Ga1−xAlxAs QDs are presented. Our results show that the optical absorption coefficients in a spherical QD are much larger than their values for GaAs quantum wells. It is found that optical absorptions are strongly affected not only the confinement barrier height, dot radius, the electron–impurity interaction but also the position of the impurity.

Effects of the Magnetic Field on the Linear and Nonlinear Optical Absorption Coefficients and the Refractive Index Changes in a Spherical Quantum Dot

The linear and third-order nonlinear optical absorption coefficients (ACs) and the refractive index change (RIC) for a spherical quantum dot, having a hydrogenic impurity under an applied magnetic field have been theoretically studied. In numerical calculations, a variational scheme is adopted within effective mass approximation to determine the energy eigenvalues for the impurtiy. The variations of impurity binding energy with the dot radius, the linear and nonlinear ACs and RIC with the photon energy are investigated and effect of homogeneous magnetic field strength is discussed on these optical properties. It has been found that the binding energy, ACs and RIC are sensitively dependent on the magnetic field strength. Moreover, the calculated results also indicate that the absorption peak energies move to higher energies with increasing magnetic field.

Linear and nonlinear optical absorption coefficients in an asymmetric graded ridge quantum wire

In this article, the optical absorption coefficients in an asymmetric ridge quantum wire within the framework of the density matrix formalism are studied. The energy spectrum and wave functions of a quantum wire with graded confinement potential using the effective mass approximation are analytically calculated. The results show that parameters such as the asymmetry and width of the potential well change the position and magnitude of the absorption peak and saturation intensity. The incident optical intensity also has a great effect on the total absorption.

Intersubband optical absorption coefficient changes and refractive index changes in a two-dimensional quantum pseudodot system

The optical absorption coefficient changes and refractive index changes associated with intersubband transitions in a two-dimensional quantum pseudodot system under the influence of a uniform magnetic field are theoretically investigated. In this regard, the electronic structure of the pseudodot system is studied using the one-band effective mass theory, and by means of the compact density matrix approach linear and nonlinear optical absorption coefficient and refractive index changes are calculated. The effects of an external magnetic field and the geometrical size of the pseudodot system on the optical absorption coefficient and refractive index changes are investigated. It is found that the absorption coefficient and refractive index changes are strongly affected not only by an external magnetic field but also by the geometrical size of the pseudodot system.

Effect of magnetic fields on the linear and nonlinear intersubband optical absorption coefficients and refractive index changes in square and graded quantum wells

In this study, both the intersubband optical absorption coefficients and the refractive index changes as dependent on the magnetic field are calculated in square and graded quantum wells. Our results show that the position and the magnitude of the linear and total absorption coefficients and refractive index changes depend on the magnetic field strength and the shape of potential. The incident optical intensity has a great effect on the total absorption and refractive index changes.

Linear and nonlinear optical absorptions of an exciton in a quantum ring

Optical absorptions of excitons have been studied in a quantum ring with parabolic confinement potential. Binding energies of the ground ( L=0) and the first excited ( L=1) states has been investigated as a function of the ring radius. Based on the computed energies and wave functions, the oscillator strengths have been examined, as well as the linear, third-order nonlinear and total optical absorption coefficients. The results are presented as a function of the incident photon energy. It is found that the electron–hole interaction and the ring radius have a great effect on the optical properties of excitons in a quantum ring.

Electronic and optical properties of GaN/AlN quantum dots with adjacent threading dislocations

We present a theory to simulate a coherent GaN QD with an adjacent pure edge threading dislocation by using a finite element method. The piezoelectric effects and the strain modified band edges are investigated in the framework of multi-band k · p theory to calculate the electron and the heavy hole energy levels. The linear optical absorption coefficients corresponding to the interband ground state transition are obtained via the density matrix approach and perturbation expansion method. The results indicate that the strain distribution of the threading dislocation affects the electronic structure. Moreover, the ground state transition behaviour is also influenced by the position of the adjacent threading dislocation.

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.

Linear and nonlinear optical absorption coefficients and binding energy of a spherical quantum dot

The binding energy and wavefunctions of the 1s, 1p, 1d and 1f energy states of a spherical quantum dot (QD) with parabolic potential were calculated by using a method which is a combination of the quantum genetic algorithm (QGA) and the Hartree–Fock–Roothaan (HFR) approach. In addition, the linear and the third-order nonlinear optical absorption coefficients based on optical transitions in QDs with and without impurity were calculated. The results show that the parabolic potential has a great effect not only on the binding energies and but also on the optical absorption coefficients. Moreover, the calculated results also reveal that the linear and nonlinear optical absorption coefficients are strongly affected by the existence of impurity and the incident optical intensity.

Calculation of linear and nonlinear optical absorption coefficients of a spherical quantum dot with parabolic potential

In the effective mass approximation, we calculated the binding energy and wave function for the 1s-, 1p-, 1d- and 1f-states of a spherical quantum dot (QD) with parabolic potential by using a combination of quantum genetic algorithm (QGA) and Hartree–Fock–Roothaan (HFR) method. In addition, we also investigated the linear and the third-order nonlinear optical absorption coefficients as a function of the incident photon energy for the 1s–1p, 1p–1d and 1d–1f transitions. Our results are shown that the existence of impurity has great influence on optical absorption coefficients. Moreover, the optical absorption coefficients are strongly affected by the incident optical intensity, relaxation time, parabolic potential and dot radius.

Third-order nonlinear absorption spectra of an impurity in a spherical quantum dot with different confining potential

In this study, the linear and third-order nonlinear optical absorption coefficients of intersublevel transitions have been calculated for a spherical CdS/SiO2 quantum dot (QD) with infinite and different finite confining potential by using the density matrix formalism. The electron eigenenergies and the corresponding wavefunctions have been determined by the variational method under the effective mass approximation. We have investigated the effects of the incident optical intensity, QD radius, and confinement potential on the intersublevel optical absorption coefficients. It is found that the size of the dot and depth of the confinement have a great effect on the linear, the nonlinear, and the total absorption coefficients. Also, the total optical absorption saturation intensity is controlled by the strength of the confinement or the incident optical intensity.

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.

Intersubband optical absorption coefficients and refractive index changes in a parabolic cylinder quantum dot

Optical absorption coefficients and refractive index changes associated with intersubband transition in a parabolic cylinder quantum dot are theoretically investigated. In this regard, the electronic structure of the dot is studied using the one band effective mass theory, and by means of the compact-density matrix approach the linear and nonlinear optical absorption coefficients and refractive index changes are calculated. The effects of the size of the dot, optical intensity and electromagnetic field polarization on the optical absorption coefficient and refractive index changes are investigated. It is found that absorption and refractive index changes are strongly affected not only by the size of the dot but also by optical intensity and the electromagnetic field polarization.

Linear and Nonlinear Optical Absorptions of a Hydrogenic Donor in a Quantum Dot Under a Magnetic Field

The linear and nonlinear optical properties of a hydrogenic donor in a disc-like parabolic quantum dot in the presence of an external magnetic field are studied. The calculations were performed within the effective mass approximation, using the matrix diagonalization method and the compact density-matrix approach. The linear and nonlinear optical absorption coefficients between the ground (L = 0) and the first excited state (L = 1) have been examined based on the computed energies and wave functions. We find that the linear, nonlinear third-order, and total optical absorption coefficients are strongly affected by the confinement strength of QDs, the external magnetic field, and the incident optical intensity.

Linear and nonlinear optical absorption coefficients and refractive index changes in strained GaN/AlN quantum dots

The strain distribution and the piezoelectric potential are investigated in GaN/AlN cylinder quantum dot system. The effects of deformation and piezoelectric potential on the conduction band edge are included to investigate the electronic energy levels and the corresponding wave functions in effective-mass approximation. The results indicate that the degenerate energies are separated into two different energies. Based on the energy levels and wave functions, the linear and the third-order nonlinear optical absorption coefficients as well as refractive index changes have been calculated for intraband transition. The total absorption coefficients and refractive index changes will decrease with an increase in the incident optical intensity.

Electric field effects of hydrogenic impurity states in a disc-like quantum dot

Using the perturbation method and the effective mass approximation, we calculated the binding energies and the absorption spectra of hydrogenic impurity states of a disc-like quantum dot subject to an electric field. Both the electric field and the confinement effects on the binding energy were investigated in detail. Based on the computed energies and wave functions, the linear optical absorption coefficient was also calculated. We found that the optical properties of hydrogenic impurity states in a disc-like quantum dot are strongly affected by the confinement strength and the electric field.

Realization and characterization of tetra(tert-butyl) zinc phtalocyanine poly(methyl methacrylate) films for optical limiting applications

We investigated optical limiting effects in films of tetra(tert-butyl) zinc phtalocyanine dissolved into poly(methyl methacrylate) within a 0.15% maximum weight ratio. Spectroscopic analysis was performed on the realized films in order to retrieve the corresponding linear optical absorption coefficient, whose interpolation according to a model including a set of three Lorentzian oscillators enabled the evaluation of the degrees of monomer and dimer concentrations. Thereafter, nonlinear transmission measurements were carried out at two different wavelengths, 532 and 634 nm. All the investigated films showed a nonlinear optical response, which was found to increase as the resonant condition was approached.

Negative-donor centers and absorption spectra of quantum dots

Negative-donor centers in quantum dots with parabolic confinement potential havebeen studied for the case with the presence of a perpendicular magnetic field.Calculations are carried out by using the method of numerical diagonalization of theHamiltonian matrix within the effective-mass approximation. The ground-stateelectron structures and angular momentum transitions are investigated. Thebinding energies of the ground and some bound excited states are obtained as afunction of the applied magnetic field strength. As the magnetic field strengthB is increased, there may appear more bound states. On the basis of the computed energies andwavefunctions, the linear optical absorption coefficients have been examined, for between the1P and 1S states. The results are presented as a function of the incident photon energy for thedifferent values of the confinement strength and the magnetic field strength. It is foundthat the optical properties of the negative-donor centers in quantum dots arestrongly affected by the confinement strength and the magnetic field strength.

Polaron Effects on the Intersubband Optical Absorption Coefficient and Refractive Index Changes of an Infinite Confining Potential Quantum Box

In this work, The effects of electron-phonon interaction on the linear and nonlinear optical absorption coefficients and refractive index changes are investigated theoretically. In this regard the compact-density matrix approach and iterative methods are employed and the optical absorption coefficients and refractive index changes of a GaAs quantum box are obtained. The results show that the magnitude of these quantities are enhanced, the peaks are shifted to the higher energies and the width of the peaks becomes larger as the influence of electron-phonon interaction is considered.

Linear and nonlinear optical absorption coefficients and refractive index changes in spherical quantum dots: Effects of impurities, electric field, size, and optical intensity

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.