Linear Optical Absorption Coefficients Research Articles

Optical properties of spherical quantum dot using screened Kratzer potential

Here we investigate the optical properties of a spherical quantum dot using the screened Kratzer potential. The density matrix formalism is employed to study refractive index changes, along with linear and nonlinear optical absorption coefficients. To this effect, the radial Schrödinger equation is solved using the Nikiforov-Uvarov functional analysis method, resulting in analytical expressions for the energy eigenvalues and the associated eigen functions. Effects of dot size, potential parameters, and screening length on these properties are analyzed in detail for a GaAs quantum dot. The obtained results reveal that the optical response of the system is highly sensitive to the dot size and potential parameters, and thus it can be tuned accordingly. The impact of external magnetic and Aharonov-Bohm flux fields on the optical properties of the GaAs quantum dot is also discussed. The findings of this study may provide useful insights in design and optimization of quantum dot-based optoelectronic devices.

Peculiar band geometry induced giant shift current in ferroelectric SnTe monolayer

The bulk photovoltaic effect (BPVE) occurs when homogeneous noncentrosymmetric materials generate photocurrent or photovoltage under illumination. The intrinsic contribution to this effect is known as the shift current effect. We calculate the shift current conductivities of the ferroelectric SnTe monolayer using first-principles methods. Our results reveal a giant shift-current conductivity near the valley points in the SnTe monolayer. More remarkably, the linear optical absorption coefficient at this energy is very small, resulting in an enormous Glass coefficient that is four orders of magnitude larger than that of BaTiO3. To understand these giant shift-current effects, we employ a three-band model and find that they arise from the nontrivial energy band geometries near the valley points, where the shift-vector diverges. This serves as a prominent example highlighting the crucial role of band geometry in determining the fundamental properties of solids.

Linear and nonlinear optical absorption coefficients in InGaN/GaN quantum wells: Interplay between intense laser field and higher-order anharmonic potentials

This computational investigation delves into the electronic and optical attributes of InGaN/GaN nanostructures subjected to both harmonic and anharmonic confinement potentials, coupled with the influence of a nonresonant intense laser field (ILF). The theoretical framework incorporates higher-order anharmonic terms, specifically quartic and sextic terms. The solutions to the Schrödinger equation have been computed employing the finite element method and the effective mass theory. Moreover, linear and third-order nonlinear optical absorption coefficients are derived via a density matrix expansion. Our analysis reveals the feasibility of manipulating electronic and optical properties by adjusting confinement potential parameters, system attributes, and laser field intensity. In addition, the ILF induces remarkable modifications, characterized by reduced resonance peak amplitudes and a blue shift in absorption coefficients. Intriguingly, regardless of potential harmonicity, the impact of incident electromagnetic intensity is notably more pronounced in the absence of the ILF. These findings hold significant promise for advancing theoretical predictions, providing valuable insights into the intricate interplay between confinement potentials, laser fields, and their effects on electronic and optical behaviors within nanostructures.

Measuring the linear optical absorption coefficient by interferometry and the thermal lensing effect: a numerical analysis

We report on a pump-probe thermal lensing method for measuring the linear absorption coefficient of liquids by using interferometry and numerical analysis. The method is based on interferograms generated when a localized photothermal effect is induced in the sample. The photothermal effect itself is induced by a pump beam impinging on a sample located on-axis of the probe beam, which is one of the paths of a Mach-Zehnder interferometer. A digital camera is employed as the acquisition device allowing the capture and storage of the experimental data. During the experiment, a total of three photographs are taken and stored on a personal computer, and by using an algorithm, the numerical analysis is done. Numerical analysis is subsequently used to calculate the photothermal phase difference and the normalized spatial distribution of the pump beam irradiance. Plotting the phase difference as a function of the spatial distribution of the pump beam produces a linear dependence from which the linear absorption coefficient is obtained. The sensitivity of the method (λ/1500) is validated using ethanol, methanol, and carbon disulfide.

Computational investgation of the optical properties of GaAs/Ga0.7Al0.3 Core/Shell Thin Film for optoelectronic Applications: under tuned external field and impurity effects

This study provides valuable insights into the optical properties of GaAs/Ga0.7Al0.3As core/shell quantum disks, including optical transitions, oscillator strength, linear optical absorption coefficient, and refractive index. We investigate these properties by employing the finite difference method. The Schrödinger equation has been solved within the effective-mass theory. However, our results reveal that adjustments in core/shell radii and electric field direction induce red-shifted resonance peaks, accompanied by improved magnitudes. Furthermore, strategically placing impurities within the core–shell region substantially enhances these optical properties. These discoveries carry the potential to catalyze groundbreaking progress and unveil fresh opportunities for technological innovation in the realm of nanostructured semiconductor devices.

Optical absorption coefficients of a single electron in a multilayer spherical quantum dot with a Kratzer-like confinement potential

The current study looks at how the Kratzer confinement potential affects the linear, third-order nonlinear, and total optical absorption coefficients (ACs) of a single electron in a multilayered spherical quantum dot (MSQD) by using the finite element method within the effective mass approximation. The variation of the transition energy has been investigated for two allowed transitions, 1p-2s and 2s-2p. Furthermore, we investigated the variation of the linear, third-order nonlinear, and total optical absorption coefficients as a function of the incident photon energy for several transitions while accounting for the effect of the Kratzer confinement potential. The findings show that the optical ACs and transition energy are strongly influenced by the Kratzer confinement potential.

Plasmon enhancement of third-order nonlinear optical absorption of gold nanoparticles dispersed in planar oriented nematic liquid crystals

We report structural and nonlinear optical properties of 20 nm gold (Au) nanoparticles (NPs) that are dispersed in planar degenerate (non-oriented) and planar oriented nematic liquid crystals (LCs) (4′-Pentyl-4-biphenylcarbonitrile-5CB). Taking advantage of elastic forces in the planar oriented nematic LC, we aligned AuNPs parallel to the 5CB director axis. In the case of planar degenerate, 5CB is not aligned and has no preferred orientation, forcing the AuNPs to disperse randomly. Results show that the linear optical absorption coefficient for the planar oriented 5CB/AuNPs mixture is larger than the corresponding planar degenerate sample. The nonlinear absorption coefficients are greatly enhanced in planar oriented samples at relatively high concentrations which can be attributed to plasmon coupling between the aligned AuNPs. This study demonstrates the utility of LCs for developing the assembly of NPs with enhanced optical properties which may offer important insight and technological advancement for novel applications, including photonic nanomaterials and optoelectronic devices.

Linear and nonlinear optical absorption coefficients and refractive index changes of GaAs/GaAsSb/GaAs V-shaped quantum wells affected by intense laser fields

Linear and nonlinear optical absorption coefficients and refractive index changes of GaAs/GaAsSb/GaAs V-shaped quantum wells affected by intense laser fields

Harmonic-Gaussian Symmetric and Asymmetric Double Quantum Wells: Magnetic Field Effects

In this study, we considered the linear and non-linear optical properties of an electron in both symmetrical and asymmetrical double quantum wells, which consist of the sum of an internal Gaussian barrier and a harmonic potential under an applied magnetic field. Calculations are in the effective mass and parabolic band approximations. We have used the diagonalization method to find eigenvalues and eigenfunctions of the electron confined within the symmetric and asymmetric double well formed by the sum of a parabolic and Gaussian potential. A two-level approach is used in the density matrix expansion to calculate the linear and third-order non-linear optical absorption and refractive index coefficients. The potential model proposed in this study is useful for simulating and manipulating the optical and electronic properties of symmetric and asymmetric double quantum heterostructures, such as double quantum wells and double quantum dots, with controllable coupling and subjected to externally applied magnetic fields.

Investigation on nonlinear optical properties of symmetric and asymmetric double V-shaped AlxGa1-xAs/GaAs potential wells with structural parameters and external electromagnetic fields

ABSTRACT Linear, nonlinear and total optical absorption coefficients and relative refractive index changes for symmetric and asymmetric double V-shaped quantum well configurations formed within AlxGa1-xAs/GaAs heterostructure have been theoretically investigated. Responses of these coefficients to well widths, barrier widths and aluminium concentrations within the barrier as well as applied external electromagnetic fields were the subject of this study. The electronic spectra of the structures are obtained as a solution to the Schrödinger equation with relevant potential and external agents in the framework of effective mass and envelope wave function approximations. The optical properties are calculated by the analytical expressions obtained by iterative solutions within the compact density matrix approach. Although increasing barrier width and aluminium concentration act similarly significant red shifting on the referred coefficients for both symmetric and asymmetric double V-shaped wells, the varying well widths act differently for each configuration. Strengthening electric and magnetic fields shift the resonance peaks to blue for both symmetric and asymmetric wells. The results show that optical properties can be controlled by structural parameters, external probes and asymmetry of double V-shaped wells.

First experiments with carbon black pigment dispersion acting as a Janus ultrasound contrast agent

Abstract Background: Theranostic ultrasound contrast agents comprise a therapeutic component whose controlled release is triggered by an ultrasound pulse. However, once the therapeutic component has been released from an ultrasound contrast agent microbubble, its intended uptake cannot be monitored, as its acoustically active host has been destroyed. Acoustic Janus particles, whose hydrophobic and hydrophilic properties depend on the external acoustic regime, are of potential use as contrast agents and drug-delivery tracers. The purpose of this study was to evaluate the hypothesis that submicron particles with Janus properties may act as ultrasound contrast agents whose hydrophobicity changes over time. Methods: Fifty samples of carbon black were subjected to 5-minute sonication with pulses with a center frequency of 10 MHz and a 1% duty cycle, after which the optical absorption coefficients were measured in n-octanol and water. These coefficients were compared with those of unsonicated samples. Results: Our preliminary results show that the difference between the linear absorption coefficients of sonicated and unsonicated samples was Δα = 80 ± 13 m−1 immediately after sonication, indicating that the carbon black particles were less hydrophobic after sonication than prior to it. Forty-eight hours after sonication, the difference in linear optical absorption coefficients had lessened to Δα = 16 ± 9 m−1, indicating that the carbon black particles had become more hydrophobic over time, but not equal to the hydrophobicity situation prior to sonication. Conclusion: The experiments confirmed that submicron carbon black particles have acoustic Janus properties.

Effects of the confinement potential parameters and optical intensity on the linear and nonlinear optical properties of spherical quantum dots

We study the linear and nonlinear optical properties of a spherical GaAs quantum dot with screened modified Kratzer potential (SMKP) by solving the time-independent Schrödinger wave equation using the diagonalization method. The obtained electronic properties of the system alongside the compact density formalism are used to evaluate the linear, third-order nonlinear and total optical absorption coefficients and change in the relative refractive index of the system. We show that the confinement potential parameters and optical intensity significantly affects the behaviour of absorption coefficients and refractive index changes. It is important to note that the findings of this study will find application in optoelectronics and related areas.

Hydrogenic impurity effect on the optical properties of Ga1-xAlxAs quantum wire under terahertz field

In this study, the effect of impurity factor on the optical absorption coefficients, refractive index changes, second harmonic generation, and third-harmonic generation for the intersubband transitions is explored between the electronic states of Ga1-xAlxAs quantum wire initiated by the symmetric parabolic potential. The system is conquered by the presence of an intense electric field, magnetic field, and Rashba spin-orbit interaction. For the linear and non-linear optical absorption coefficients, refractive index, second harmonic generation, and third harmonic generation coefficient, the analytical expressions are obtained with the assistance of the compact density-matrix approach. The arithmetical outcomes illustrate the optical properties are significantly intuitive to the concentration of impurity and can be controlled by this parameter. The variation in the magnitude and position of peaks via impurity factor indicates the opportunity in the mechanism of optical non-linearity in the quantum wire and also, helps in the optical non-linearity tuning which has device application.

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.

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.