Nonlinear Optical Absorption Coefficients Research Articles

The electric and magnetic field effects on the optical absorption in double QWs with squared, U-shaped and V-shaped confinement potentials

ABSTRACT Through this paper, we exhibit the effects of electric and magnetic fields on the linear and third-order nonlinear optical absorption coefficients (OACs) in symmetric InGaN/GaN double QWs considering different confinement potential shapes (squared, U-shaped, V-shaped) under electric and magnetic fields are theoretically investigated. The magnetic field is taken in-plane while the electric field is oriented along the growth direction of the nanostructure. Our calculations have been performed within the effective-mass approximation and the compact density-matrix approach. We used the finite element method to solve numerically the Schrodinger equation considering various shaped confinement potentials. Our results reveal that the increase in the magnetic and electric fields blue-shifted the OAC's peak positions and improves their associated amplitudes. Furthermore, we have also found that the optical absorption coefficients are very important in squared-shape compared to than in U- and V-shape.

Electronic and nonlinear optical absorption of an off-center hydrogenic donor impurity in GaAs/GaAlAs hexagonal quantum dot under electric field

In this paper, the energy levels and nonlinear optical properties modulated by the applied electric field are analytically investigated where a hydrogenic impurity is confined in the GaAs/GaAlAs hexagonal quantum dot(QD). The linear and nonlinear optical absorption coefficients(OACs) have been obtained by using the compact density matrix and iterative approach. In the one electron approximation, an off-center hydrogenic donor impurity is considered, and the results show that the energy levels and nonlinear optical absorption of the dot depend strongly on the hydrogenic impurity. Especially, The overall results show that the geometric parameter and the magnitude of confinement potential of hexagonal QD, and the applied electric field act a very important role in the electronic and optical properties of hexagonal QD.

Investigation of linear and nonlinear optical absorption coefficients and refractive index changes of a zigzag quantum well with structure parameters and applied external fields

In this study, we have investigated some linear and nonlinear optical properties of GaAs/GaAlAs zigzag quantum well structures under different electric and magnetic field intensities. We also examined the effect of adjustable structural parameters as well as width on the optical response of the system. The diagonalization method has been the tool to numerically solve the effective mass approximation Schrödinger equation obtaining the energy levels and related wave functions needed to evaluate the expressions of linear, third-order nonlinear, and total optical absorption coefficients and relative refractive index changes derived within the compact density matrix method. Results show that the optical response becomes blue-shifted with the applied electric and magnetic fields’ increment.

Anisotropic photoelectric properties in GaN/AlN quantum dots under terahertz laser polarization

The linear and nonlinear anisotropic optical absorption coefficients(OACs) and refractive index changes(RICs) of GaN/AlN cubical quantum dots(CQDs) subjected to terahertz laser field(TLF) are investigated. The results show that under the polarization of TLF, with the increase of laser dressing parameters, the peak of OACs and RICs increases nonlinearly and have a redshift. More importantly, our work indicated that with the enhancement of TLF polarization, the redistribution of electron excited state wave function will lead to the “loss” of optical properties in the specific frequency band. The redistribution of electron ground state wave function has a significant modulation effect on the magnitude of OACs(RICs) peak. • The enhancement of the refractive index changes was observed at low frequencies. • The phenomenon of wave function exchange in laser field modulation is found. • The modulation of laser field on optical coefficient cannot cover the whole frequency band.

Optical Properties of Cylindrical Quantum Dots with Hyperbolic-Type Axial Potential under Applied Electric Field.

In this paper, we have researched the electronic and optical properties of cylindrical quantum dot structures by selecting four different hyperbolic-type potentials in the axial direction under an axially-applied electric field. We have considered a position-dependent effective mass model in which both the smooth variation of the effective mass in the axial direction adjusted to the way the confining potentials change and its abrupt change in the radial direction have been considered in solving the eigenvalue differential equation. The calculations of the eigenvalue equation have been implemented considering both the Dirichlet conditions (zero flux) and the open boundary conditions (non-zero flux) in the planes perpendicular to the direction of the applied electric field, which guarantees the validity of the results presented in this study for quasi-steady states with extremely high lifetimes. We have used the diagonalization method combined with the finite element method to find the eigenvalues and eigenfunction of the confined electron in the cylindrical quantum dots. The numerical strategies that have been used for the solution of the differential equations allowed us to overcome the multiple problems that the boundary conditions present in the region of intersection of the flat and cylindrical faces that form the boundary of the heterostructure. To calculate the linear and third-order nonlinear optical absorption coefficients and relative changes in the refractive index, a two-level approach in the density matrix expansion is used. Our results show that the electronic and, therefore, optical properties of the structures focused on can be adjusted to obtain a suitable response for specific studies or goals by changing structural parameters such as the widths and depths of the potentials in the axial direction, as well as the electric field intensity.

Spectral features and optical absorption of vertically stacked V-groove quantum wires

The spectral features and the linear, nonlinear, and total optical absorption coefficients of two realistic mathrm {GaAs/Ga}_{1-x}{mathrm{Al}}_x{mathrm{As}} vertically stacked V-groove quantum wires confining electronic states were theoretically studied. The compact density matrix formalism and the finite element method were used as solution frameworks. The influence of the barrier width, inter-sidewall angle, the crescent thickness of the stack, and the influence of a static electric field on the energy spectrum and the optical coefficients is addressed. Increasing the crescent thickness (inter-sidewall angle) leads to a reduction (non-monotonous increase) of the energy values, while the presence of a static electric field leads to controllable stark-like patterns. In all cases, anti-crossing points are reported. By increasing the crescent thickness, inter-sidewall angle, or barrier width, a non-monotonous blue-/red-shift of the resonant peaks of the optical absorption is observed. In addition, the results in asymmetric/symmetric vertically coupled V-groove quantum wire systems suggest that the quantum tunneling phenomenon can be linked to the enhancement of the total optical absorption due to the possibility of the generation of dipole moments by higher electron mobility. Thus, optical fields oriented along the growth direction enhance the optical absorption. Furthermore, the absorption coefficient maximum is drastically modified by varying the inter-sidewall angle, and even the evolution tendency can be inverted due to the anti-crossing points in the energy spectra. Since the obtained resonant peaks are located below 20 meV in the spectra, the analyzed system could be interesting for exploring and designing new Terahertz devices.

Influence of temperature and hydrostatic pressure on the nonlinear optical properties in a GaAs/GaAlAs Kratzer-Fues confined quantum well

The investigation of the comprehensive influence of temperature and hydrostatic pressure on the nonlinear optical absorption coefficients(OACs), optical rectification(OR), second harmonic generation(SHG) and third harmonic generation(THG) in a Kratzer-Fues confined quantum well(QW) is carried out by means of the effective-mass approximation and density matrix formalism. The findings indicate that the nonlinear optical properties(OACs, OR, SHG, THG) are significantly different in response to temperature and hydrostatic pressure. Simultaneously, we find that the effects of temperature and hydrostatic pressure on the nonlinear OACs, OR, SHG and THG in this system are more pronounced. So the magnitude and the red and blue shift in the position of the OACs, OR, SHG and THG can be adjusted by changing the strength of the temperature and hydrostatic pressure, thus promoting the development of the optical modulators and miscellaneous device applications based on the nonlinear properties. • The OACs, OR, SHG and THG in Kratzer-Fues QW are studied. • We obtain the energy eigenvalues and eigenfunctions via the fine difference method. • The effect of P and T on these important optical quantity are also studied. • Nanostructures possess considerably different behaviors under P and T.

Preparation and nonlinear optical characterization of Flourine-doped cadmium oxide thin films

Undoped CdO films and three different molarities of cadmium oxide (CdO) films were doped with fluorine on glass slides via a chemical spray pyrolysis method. The samples were analyzed using X-ray diffractometry (XRD), scanning electron microscopy (SEM), UV–VIS-NIR spectroscopy, electrical measurements, and Z-scan measurements. XRD measurement revealed better crystallinity with preferred orientation at [111] plane. Nanospheres of varying sizes were obtained from the surface micrographs. The direct band gap energy decreased as the fluorine concentration increased. The film resistivity recorded a decline with increased carrier mobility as the flourine concentration increased. The nonlinear optical absorption coefficient (β) gotten for 0.0003 M, 0.0004 M, and 0.0005 M at 632.8 nm wavelength are 3.83×10–3 m/W, 5.7 × 10–3 m/W and 5.48×10–3 m/W respectively. The deposited films find potential application in solar cell and optoelectronic devices.

The nonlinear optical properties of GaAs/GaAlAs triple quantum well: Role of the electromagnetic fields and structural parameters

Being relevant to the field of device applications, multiple semiconductor quantum wells are systems that exhibit remarkable optical and electronic properties. These can be properly tuned by suitably modifying the composition, structural parameters, and the application of external probes. Here, the electronic and optical properties of a GaAs/GaAlAs triple quantum well have been investigated under the influence of applied electric and magnetic fields, as well as the change of well and barrier widths. We have used the diagonalization method to numerically solve the Schrödinger equation under the effective mass approximation for obtaining the subband energy levels and related electronic wave functions. The expressions used for evaluating linear, third-order nonlinear, and total optical absorption coefficients (TOACs) and relative refractive index changes (RRICs) were previously derived within the compact density matrix method. According to our results, whilst an increment in the applied electric field causes a red shift in TOACs and RRICs, a blue shift of the optical responses occurs with increasing the applied magnetic field. Besides, a blue shift is observed as well by changing the width of the central well (LwL), whilst a red shift is noticed when changing left and right wells (LwL and LwR) and barrier (LbL and LbR) widths for zero fields. We believe that our study could make a contribution to designing new quantum-well-based optoelectronic devices.

Effects of Applied Magnetic Field on the Optical Properties and Binding Energies Spherical GaAs Quantum Dot with Donor Impurity.

The screened modified Kratzer potential (SMKP) model is utilized to scrutinize the impacts of an applied magnetic field (MF) on the binding energies and linear and nonlinear optical properties spherical GaAs quantum dot with donor impurity (DI). To accomplish this goal, we have used the diagonalization method to numerically solve the Schrödinger equation under the effective mass approximation for obtaining the electron energy levels and related electronic wave functions. The expressions used for evaluating linear, third-order nonlinear, and total optical absorption coefficients and relative refractive index changes were previously derived within the compact density matrix method. It has been shown here that the MF and DI impacts the characteristics of the absorption coefficients and the refractive index changes. This study’s results will find application in optoelectronics and related areas.

The ultrafast tunable saturable absorption of three azo-Schiff base ligands and related metal complexes

Three azo-Schiff base ligands with large conjugated systems and five related transition metal complexes were synthesized and investigated by femetosecond open-aperture Z-scan and pump-probe system. The ultrafast tunable saturable absorption of the ligands and their metal complexes were observed at 400 nm wavelength. The obtained third-order nonlinear optical (NLO) absorption coefficients of eight compounds are evaluated to be −8.49 ∼ −80.63 cm/GW. Meanwhile, the ultrafast carrier relaxation time (187–592 fs) of all compounds was observed in the pump-probe experiment. The modulated impacts of metal coordination on NLO responses are analyzed by a five-level energy system. We deem that the performance of metal complexes is determined by the number of shell electrons of central metal. All the results indicate that those compounds have potential applications for tunable saturable absorber in NLO field.

The impact of hydrostatic pressure and temperature on the binding energy, linear, third-order nonlinear, and total optical absorption coefficients and refractive index changes of a hydrogenic donor impurity confined in GaAs/AlxGa1−xAs double quantum dots

The impact of hydrostatic pressure and temperature on the binding energy, linear, third-order nonlinear, and total optical absorption coefficients and refractive index changes of a hydrogenic donor impurity confined in GaAs/AlxGa1−xAs double quantum dots

Optical properties of Al x Ga1−x As/GaAs Woods–Saxon quantum well in the presence of hydrostatic pressure and applied electric field

The third harmonic generation (THG), linear and nonlinear optical absorption coefficients (OACs), and refractive index changes (RICs) are investigated in a Woods–Saxon quantum well (QW) modulated by the hydrostatic pressure and applied electric field. The effect of non-uniform aluminum doping (position-dependent effective mass (PDEM)) on the mass of the system is discussed, and further to explore the influence of PDEM on the nonlinear THG, OACs, and RICs of the Woods–Saxon QW. These nonlinear optical properties above are obtained using the compact-density matrix formalism. The electron states in a Woods–Saxon QW under the constant effective mass (CEM) and PDEM are calculated by solving the Schrödinger equation via the finite difference technique. The contributions from competing effects of the hydrostatic pressure and applied electric field to the nonlinear optical properties with CEM and PDEM are reported, as well as the comparison with each other. The observations reveal that the regulation of external fields and the influence of PDEM play an important role in the photoelectric properties of QW.

Optical absorption coefficients of spherical quantum dots system with inversely quadratic Yukawa-Hellmann potential

In this paper, the effects of hydrostatic pressure, temperature, Al-concentration and other structural parameters on the optical absorption coefficients (OACs) in inversely quadratic Yukawa-Herman potential (IQYHP) GaAs/AlηGa1−ηAs spherical quantum dots are studied theoretically. The Nikiforov-Uvarov (N–U) solution is used to solve the Schrödinger equation corresponding to this structure, and the energy levels and wave functions can be obtained. We also get nonlinear optical absorption coefficients by using compact density matrix theory and iterative method. The results show that various parameters play an essential role in OACs, including the red shift (blue shift) of OACs resonance peaks and the change of peaks size.

Effects of Intense Laser Field on Electronic and Optical Properties of Harmonic and Variable Degree Anharmonic Oscillators

In this paper, we calculated the electronic and optical properties of the harmonic oscillator and single and double anharmonic oscillators, including higher-order anharmonic terms such as the quartic and sextic under the non-resonant intense laser field. Calculations are made within the effective mass and parabolic band approximations. We have used the diagonalization method by choosing a wave function based on the trigonometric orthonormal functions to find eigenvalues and eigenfunctions of the electron confined within the harmonic and anharmonic oscillator potentials under the non-resonant intense laser field. A two-level approach in the density matrix expansion is used to calculate the linear and third-order nonlinear optical absorption coefficients. Our results show that the electronic and optical properties of the structures we focus on can be adjusted to obtain a suitable response to specific studies or aims by changing the structural parameters such as width, depth, coupling between the wells, and applied field intensity.

Optical absorption in core-shell quantum antidot under applied co-directed electric and magnetic fields

Using the matrix diagonalization method within the effective mass approximation and the rectangular potential profile, we investigate optical absorption coefficients (OAC) in the core-shell quantum antidot (QAD) Al0.3Ga0.7 As/GaAs/Al0.3Ga0.7 As in the presence of applied co-directed electrical and magnetic fields. The electric field effect on the electron wave functions, energy spectrum, oscillator strength of the intersubband electronic transitions is calculated for different size of QAD core and different value of the magnetic field induction. The total, linear and nonlinear optical absorption coefficients in QAD are obtained by considering 1 s-1p and 1p-1d electron quantum transitions as functions of the incident photon energy.

Study of ultrafast nonlinear optical response and transient dynamics of pyrene derivatives with intramolecular charge transfer characteristics

Two pyrene derivatives 1906 and 1936 with typical charge transfer characteristics were designed and synthesized to study the influence of intramolecular charge transfer (ICT) on the ultrafast nonlinear optical (NLO) absorption. Frontier molecular orbital distribution and hole-electron analysis show that compound 1906 has stronger ICT characteristics than 1936 by introducing the halogen effect. Intense ESA signals in the green region of these pyrene derivatives were observed in the transient absorption spectrum (TAS). The excited state dynamics clearly show singlet-based electronic transitions and relaxation processes. Femtosecond Z-scan experiment at 480 nm indicates the ultrafast NLO absorption performance of these pyrene derivatives can be significantly improved by enhancing the ICT characteristics. The photophysical mechanism is one-photon absorption (OPA) induced excited-state absorption (ESA). As the input intensity is 46.8 GW cm−2, the effective NLO absorption coefficient of 1906 is 7.6 × 10−13 W m−1 which is 6.3 times that of 1936. Our results indicate that these pyrene derivatives are promising potential candidates for ultrafast laser protection applications.

Theoretical study of electronic and optical properties in doped quantum structures with Razavy confining potential: effects of external fields

We investigate the energy states of confined electrons in doped quantum structures with Razavy-like confining potentials. The theoretical investigation is performed within the effective mass and parabolic band approximations, including the influence of externally applied electric and magnetic fields. First, we analyze the case of a Razavy quantum well and determine its conduction subband spectrum, focusing on the lowest energy levels and their probability densities. These properties have been numerically determined by self-consistently solving the coupled system of Schrödinger, Poisson, and charge neutrality equations. Doping is introduced via an on-center $$\delta$$ -like layer. In order to evaluate the associated total (linear plus nonlinear) optical absorption coefficient (TOAC), we have calculated the corresponding diagonal and off-diagonal electric dipole matrix elements, the main energy separation, and the occupancy ratio which are the main factors governing the variation in this optical response. A detailed discussion is given about the influence of doping concentration as well as electric and magnetic fields, which can produce shifts in the light absorption signal, toward either lower or higher frequencies. As an extension of the self-consistent method to a two-dimensional problem, the energy states of quantum wire system of circular cross section, with internal doping and Razavy potential, have been calculated. The response of eigenvalues, self-consistent potentials and electron densities is studied with the variation in $$\delta$$ -doping layer width and of the donor density. Finally, the origin of Friedel-like oscillations, that arise in the density profile, generated by the occupation of internal and surface electronic states has been explained.

The effects of temperature and pressure on the optical properties of a donor impurity in [formula omitted] multilayer cylindrical quantum dots

This paper examines the variation of the linear, third-order nonlinear and total intersubband optical absorption (refractive index changes) coefficients of a donor impurity in multilayer cylindrical quantum dots (MCQDs), under the effect of temperature T and hydrostatic pressure P. Moreover, in this study, we also examined the effect of structure parameters on the optical absorption coefficients of the system. The Schrödinger equation describing the system is solved numerically by the finite element method (FEM) within the effective mass approximation. In our calculations, the confinement potential is modeled by a parabolic form in the radial direction and a square one in the z-direction. The optical absorption coefficients and refractive index changes have been investigated versus the quantum dot radius, indium composition and intensity of the incident electromagnetic for three allowed transitions: 1s - 1p, 2s - 1p and 1p - 1d. Our essential outcomes exhibit that the optical absorption coefficients and refractive index changes are strongly sensitive to the variation of quantum dot sizes, which enhance and blueshift as the quantum confinement is strong. On the contrary, the optical absorption coefficients and refractive index changes diminish and redshift as the quantum confinement reduces.

Regulation of optical properties by applied external fields for a quantum well with Hulthen potential

In this present study, the effects of electric, magnetic, and non-resonant intense laser field (ILF) on the linear, third-order nonlinear, and total optical absorption coefficients (TOACs) and relative refractive index changes (RRICs) of GaAs quantum well, having Hulthen confinement potential, were theoretically investigated. In addition, the dependence of the nonlinear optical properties in the structure on the optical intensity of incident photon and the inverse relaxation time was also calculated. To do this research, firstly the energy eigenvalues and eigenfunctions of the structure were calculated by using the effective mass and envelope function approaches. By using these calculated subband energy levels and wave functions belonging to these levels, the nonlinear optical properties of the system were obtained via the iterative method, within the compact density matrix approach framework. The obtained numerical results show that the optical properties of the considered system depend on the externally applied fields. With the applied external electric and magnetic field, the peak positions of TOACs and RRICs shift to higher energies, and the peak magnitudes increase. The high-frequency ILF applied to the structure shifts the peak positions of TOACs and RRICs initially towards higher energies and then towards lower energies and their peak sizes increase. These results show that the optical properties of the system can be adjusted purposively by changing the magnitude of applied external fields.