Linear Optical Absorption Coefficients Research Articles

The effect of hydrostatic pressure, temperature and magnetic field on the nonlinear optical properties of asymmetrical Gaussian potential quantum wells

In this study, simultaneous effects of hydrostatic pressure, temperature and magnetic field on the linear and nonlinear intersubband optical absorption coefficients (OACs) and refractive index changes (RICs) in asymmetrical Gaussian potential quantum wells (QWs) are theoretically investigated within the framework of the compact-density-matrix approach and iterative method. The energy eigenvalues and their corresponding eigenfunctions of the system are calculated with the differential method. Our results show that the position and the magnitude of the resonant peaks of the nonlinear OACs and RICs depend strongly on the hydrostatic pressure, temperature and external magnetic field. This gives a new degree of freedom in various device applications based on the intersubband transitions of electrons.

Linear and total intersubband transitions in the step-like GaAs/GaAlAs asymmetric quantum well as dependent on intense laser field

In this study, for a step-like GaAs- $Ga_{1-x}Al_{x}As$ asymmetric quantum well (AQW) the linear and total intersubband optical absorption coefficients and the refractive index changes are calculated as dependent on the intense laser field (ILF) and the right quantum well (RQW) width. Our results show that the location and the magnitude of all absorption coefficients and refractive index changes depend on ILF and the asymmetric parameter ( $ d=L_{R}/L_{L}$ ). Also, we showed that both ILF and d provide an important effect on the electronic and optical properties of step-like quantum well, and the changes of the energy levels, the dipole moment matrix elements and the resonant peak values of the absorption coefficients are dependent on the shape of the confinement potential. While for different asymmetric parameters the intersubband absorption spectrum shows blue shift up to the different critical ILF values, this spectrum shows red shift for ILF values greater than certain values. By considering the variation of the energy difference as dependent on the RQW width, for step-like QW the absorption spectrum shows blue or red shift. Especially, step-like QWs are used for producing terahertz radiation from intersubband transitions and they have more tunable structure parameters (the left (right) quantum well width, $ L_{L}(L_{R})$ , and the confinement potential in the left (right) hand side, $ V_{L} (V_{R})$ with respect to other asymmetric QWs (in the present study we used $ L_{R}=L_{L}/2$ , $ L_{L}$ , 3L L/2 and V R = 2V L/3 values). This case provides a new degree of freedom for controlling the optical properties in quantum wells (QWs). In addition, the nonlinear optics underlying the application of the ILF to asymmetric potential heterostructures becomes a subject of present-day interest. In conclusion: i) The electronic and optical properties of the step-like AQW vary by increasing ILF. ii) ILF leads to major modifications on the shape of the confining potential. iii) The position and the size of all absorption coefficients and refractive index changes depend on ILF and the asymmetric parameter values. iv) The absorption spectrum shows blue or red shift by increasing ILF.

Simultaneous effects of hydrostatic pressure, temperature and electric field on optical absorption in InAs/GaAs lens shape quantum dot

In this paper, we report the theoretical calculation of the linear, third-order nonlinear and total optical absorption coefficient in a lens shaped InAs/GaAs quantum dot. The simultaneous effects of QD radius, hydrostatic pressure, temperature and applied electric field on the total optical absorption coefficient in lens-shaped InAs quantum dots are investigated under the compact density matrix formalism and the effective mass approximation. From our calculation, it is found that the sub-band energies and total optical absorption coefficient are quite sensitive to the quantum dot radius, applied hydrostatic pressure, temperature and electric field. The results show that the total optical absorption peaks position and in magnitude change as quantum dot radius, hydrostatic pressure, temperature and electric field value varies.

Noise-driven optical absorption coefficients of impurity doped quantum dots

We make an extensive investigation of linear, third-order nonlinear, and total optical absorption coefficients (ACs) of impurity doped quantum dots (QDs) in presence and absence of noise. The noise invoked in the present study is a Gaussian white noise. The quantum dot is doped with repulsive Gaussian impurity. Noise has been introduced to the system additively and multiplicatively. A perpendicular magnetic field acts as a source of confinement and a static external electric field has been applied. The AC profiles have been studied as a function of incident photon energy when several important parameters such as optical intensity, electric field strength, magnetic field strength, confinement energy, dopant location, relaxation time, Al concentration, dopant potential, and noise strength take on different values. In addition, the role of mode of application of noise (additive/multiplicative) on the AC profiles has also been analyzed meticulously. The AC profiles often consist of a number of interesting observations such as one photon resonance enhancement, shift of AC peak position, variation of AC peak intensity, and bleaching of AC peak. However, presence of noise alters the features of AC profiles and leads to some interesting manifestations. Multiplicative noise brings about more complexity in the AC profiles than its additive counterpart. The observations indeed illuminate several useful aspects in the study of linear and nonlinear optical properties of doped QD systems, specially in presence of noise. The findings are expected to be quite relevant from a technological perspective.

Excitonic effects on linear and nonlinear optical absorption coefficients and refractive index changes in one-dimensional quantum dots with linear potential

Excitonic effects on linear and nonlinear optical absorption coefficients (OAC) and refractive index changes (RIC) in one-dimensional quantum dots with linear potential are theoretically investigated within the framework of the compact-density-matrix approach and iterative method. It is found that linear and nonlinear OAC and RIC with excitonic effects in one-dimensional quantum dots are larger than that without excitonic effects. Besides, when excitonic effects are considered, our results show a remarkable dependence of linear and nonlinear OAC and RIC on linear potential.

The effects of pressure and hydrogenic donor impurity on the linear and nonlinear optical properties of a GaAs/GaAlAs nanowire superlattice

The combined effects of hydrostatic pressure, presence and absence of hydrogenic donor impurity are investigated on the linear and nonlinear optical absorption coefficients and refractive index changes of a GaAs/Ga1−xAlxAs nanowire superlattice. The wave functions and corresponding eigenvalues are calculated using finite difference method in the framework of effective mass approximation. Analytical expressions for the linear and third order nonlinear optical absorption coefficients and refractive index changes are obtained by means of compact-density matrix formalism. The linear and third order nonlinear absorption coefficient and refractive index changes are presented as a function of photon energy for different values of hydrostatic pressure, incident photon intensity and relaxation time in the presence and absence of hydrogenic donor impurity. It is found that the linear and third order nonlinear absorption coefficients, refractive index changes and resonance energy are quite sensitive to the presence of impurity and applied hydrostatic pressure. Moreover, the saturation in optical spectrum and relaxation time can be adjusted by increasing pressure in presence of impurity whereas the effect of hydrostatic pressure is negligible in the case of absence of hydrogenic impurity.

Spin–orbit interaction effects on the optical properties of quantum wires under the influence of in-plane magnetic fields

In this work, we studied the effects of in-plane magnetic field and Rashba spin–orbit interaction on the intersubband optical absorption coefficients and changes in refractive index for transitions between the first two lower-lying electronic levels of quantum wire represented by a parabolic confining potential. The analytical expressions of the linear and third-order nonlinear optical absorption coefficients and refractive index changes are obtained by using the compact-density matrix formalism and iterative scheme. Optical properties are investigated as a function of quantum wire radius, strength and orientation of magnetic field, strength of Rashba spin–orbit interaction and photon energies. Numerical results reveal that the optical absorption coefficients and refractive index changes are strongly affected and thus can be controlled by these parameters.

Study of electron-related intersubband optical properties in three coupled quantum wells wires with triangular transversal section

This work concerns theoretical study of confined electrons in a low-dimensional structure consisting of three coupled triangular GaAs/AlxGa1−xAs quantum wires. Calculations have been made in the effective mass and parabolic band approximations. In the calculations a diagonalization method to find the eigenfunctions and eigenvalues of the Hamiltonian was used. A comparative analysis of linear and nonlinear optical absorption coefficients and the relative change in the refractive index was made, which is tied to the intersubband electron transitions.

Linear and nonlinear optical absorption coefficients of spherical dome shells

Linear and nonlinear optical absorption coefficients of spherical dome shells are theoretically investigated within analytical wave functions and numerical quantized energy levels. Our results show that the inner radius, the outer radius and the cut-off angle of spherical dome shells have great influences on linear and nonlinear optical absorption coefficients as well as the total optical absorption coefficients. It is found that with the increase of the inner radius and the outer radius, linear and nonlinear optical absorption coefficients exhibit a blueshift and a redshift, respectively. However, with the increase of the cut-off angle, linear and nonlinear optical absorption coefficients do not shift. Besides, the resonant peaks of linear and nonlinear optical absorption coefficients climb up and then decrease with increasing the cut-off angle. The influences of the incident optical intensity on the total optical absorption coefficients are studied. It is found that the bleaching effect occurs at higher incident optical intensity.

Effect of hydrogenic impurity on linear and nonlinear optical absorption coefficients and refractive index changes in a quantum dot

The analytical expressions of linear and nonlinear optical absorption coefficients and refractive index changes in a quantum dot with a hydrogenic impurity are obtained by using the compact-density-matrix approach and iterative method. The wave functions and the energy levels are obtained by using the variational method. Numerical results show that the optical absorption coefficients and refractive index changes are strongly affected by the hydrogenic impurity.

Comment on “Linear and nonlinear optical absorption coefficients and refractive index changes in asymmetrical Gaussian potential quantum wells with applied electric field”

Guo and Du (2013) reported theirs result for the linear and nonlinear optical absorption coefficients and refractive index changes in asymmetrical Gaussian potential quantum wells with applied electric field. We find both the energy and the corresponding wavefunction for the low-lying state are wrong to applied in their works. For the same set of parameters studied by Guo and Du, we obtain new and reliable results via the differential method.

Linear and nonlinear optical absorption coefficients and refractive index changes in GaN/AlxGa(1−x)N double quantum wells operating at 1.55 μm

In the present paper, the linear and nonlinear optical absorption coefficients and refractive index changes between the ground and the first excited states in double GaN/AlxGa(1−x)N quantum wells are studied theoretically. The electronic energy levels and their corresponding wave functions are obtained by solving Schrödinger-Poisson equations self-consistently within the effective mass approximation. The obtained results show that the optical absorption coefficients and refractive index changes can be red- and blue-shifted through varying the left quantum well width and the aluminum concentration xb2 of the central barrier, respectively. These structural parameters are found to present optimum values for carrying out the transition of 0.8 eV (1.55 μm). Furthermore, we show that the desired transition can also be achieved by replacing the GaN in the left quantum well with AlyGa(1−y)N and by varying the aluminum concentration yAl. The obtained results give a new degree of freedom in optoelectronic device applications such as optical fiber telecommunications operating at (1.55 μm).

Linear and nonlinear optical absorption coefficients and refractive index changes in double parabolic-square quantum well as dependent on intense laser field

In this study, for double parabolic-square quantum well (DPSQW) the linear and nonlinear intersubband optical absorption coefficients and the refractive index changes are calculated as dependent on the intense laser field (ILF). Our results show that the location and the size of all absorption coefficients and refractive index changes depend on ILF. Also, we show that ILF provides an important effect on the electronic and optical properties of DPSQW, and the changes of the energy levels and the dipole moment matrix elements are dependent on the shape of the confinement potential. Such effects can provide methods to drive tunable semiconductor lasers, which may be tailored by quantum potential well parameters and by ILF values.

Polaronic effect on linear and nonlinear optical properties of spherical quantum dots under electric field

The polaronic effect on the linear and nonlinear optical properties of spherical quantum dots with a shallow hydrogenic impurity under electric field are studied, taking into account the interactions with both confined and surface optical phonons. In addition, the interaction between impurity and phonons has also been considered. Numerical results on typical Zn1−xCdxSe/ZnSe material show that the polaronic effect or electric field redshifts the peak positions of linear and nonlinear optical absorption coefficients and refractive index changes, but does not significantly affect the peak values of them. The polaronic effect is enhanced with the decreasing quantum dot radius or Zn concentrations. Additionally, it is found that the electric field has an important influence on the polaronic effect especially on the surface optical phonons.

Impurity-Related Linear and Nonlinear Optical Absorption Coefficients of Unstrained (In,Ga)N-GaN Symmetric Coupled QWs

Linear, third-order nonlinear and total optical absorption coe cients associated with intra-conduction band in wurtzite unstrained (In,Ga)N-GaN coupled quantum wells are calculated. Based on the e ective-mass and the one-band parabolic approximations, the well and the barrier-widths e ects are investigated variationally under nite con nement potential barrier. The results indicate that the structure size have a great in uence on the optical properties. The results reveal also that larger optical absorption coe cients are obtained compared to single quantum well and a signi cant red-shift is obtained as the structure size increases. It is found that the modulation of the absorption coe cients can be easily obtained by adjusting the barrier and/or the well widths.

Resonant peaks of the linear optical absorption and rectification coefficients in GaAs/GaAlAs quantum well: Combined effects of intense laser, electric and magnetic fields

In this study, the resonant peaks of the linear optical absorption (OA) and rectification coefficients in GaAs/GaAlAs quantum well are calculated as dependent on the applied electric field (F), the magnetic field (B) and the laser field intensity parameter (α0). Our results show that the shape of confined potential profile, the energy levels and the dipole moment matrix elements are changed as dependent on the F, B and α0. Also, the resonant peaks of the OA and rectification coefficients depend on the applied external field effects. Therefore, the variation of the resonant peaks of these coefficients which can be appropriate for various optical modulators and infrared optical device applications can be smoothly obtained by the alteration electric, magnetic and intense laser field.

Influence of the shape of quantum dots on their optical absorptions

We have investigated the effects of the shape of quantum dots on their optical absorptions. Calculations are performed by using the matrix diagonalization method and the compact density-matrix approach within the effective-mass approximation. We have calculated the linear, third-order nonlinear and total optical absorption coefficients as a function of the incident photon energy in circular, elliptic, and triangular shaped quantum dots. Our results show that the shape of quantum dots has great influence on optical absorption coefficients.

The low-lying states and optical absorption properties of a hydrogenic impurity in a parabolic quantum dot modulation by applied electric field

Using the configuration-integration method, we investigated theoretically the low-lying states and optical absorption properties of a hydrogenic impurity in a parabolic quantum dot modulation by applied electric field. The low-lying states and optical absorption properties depend sensitively on the electric field F and the strength of the parabolic confinement ℏω0. We discuss the linear and third-order nonlinear optical absorption coefficients of the dot (i) with the impurity ion and (ii) without the impurity ion. In the first case, the increase of the parabolic confinement ℏω0 (or the electric field F) can induce the blueshift (or redshift) of the peak of the absorption coefficient. Also the optical intensity can induce the increase of the third-order nonlinear optical absorption coefficients to weaken and even bleach the total optical absorption coefficients. Similar behavior has also been observed in the second case, but there is no redshift of the peak positions of the absorption coefficient with the increase of the electric field F. Compared with the second case, it is easily seen that there are the blueshifts of the peak of the absorption coefficients, which can be used as a technical means for detecting impurities.

Nonlinear intersubband absorption and refractive index change in n-type δ-doped GaAs for different donor distributions

In this study, both the linear and nonlinear intersubband optical absorption coefficients and the refractive index changes are calculated for the uniform, triangular and Gaussian-like donor distribution. The Gaussian-like distribution differs from the Gaussian distribution other authors use. The electronic structure of n-type Si δ-doped GaAs has been theoretically calculated by solving the Schrodinger and Poisson equations self-consistently. Our results show that the location and the size of the linear and total absorption coefficients and refractive index changes depend on the donor distribution type. The shape of δ-effective potential profile and the subband properties are changed as dependent on the donor distribution model. Therefore, the variation of the absorption coefficients and refraction index changes, which can be appropriate for various optical modulators and infrared optical device applications can be smooth obtained by the alteration donor distribution model.

Linear and nonlinear optical absorption coefficients of two-electron spherical quantum dot with parabolic potential

Linear and nonlinear absorption coefficients of two-electron spherical quantum dot (QD) with parabolic potential are investigated in this paper. Wave functions and energy eigenvalues of the 1s2, 1s1p, 1s1d and 1s1f electronic states have been computed by using an optimization approach, which is a combination of Quantum Genetic Algorithm (QGA) and Hartree–Fock Roothaan (HFR) method. It is found that the strength of S→P transition is stronger than P→D and D→F transitions. Also the peak positions and amplitudes of the absorption coefficients are sensitive to the electron spin. It should be noted that the peak positions and amplitudes of absorption coefficients are strongly dependent on the parabolic potential. Additionally, dot radius, impurity charge, incident optical intensity and relaxation time have a great influence on the linear and nonlinear absorption coefficients.