Relative Refractive Index Change Research Articles

Non-resonant intense laser field effect on the nonlinear optical properties associated to the inter- and intra-band transitions in an anharmonic quantum well submitted to electric and magnetic field

Simultaneous effects of electric, magnetic, and non-resonant intense laser field on the nonlinear optical properties of a GaAs quantum well with an anharmonic confinement potential profile are theoretically investigated. Energy eigenvalues and eigenfunctions of the system are determined using the diagonalization method within the framework of the effective mass and parabolic band approximation. Nonlinear optical properties associated to the inter and intra band transitions are evaluated. Our numerical results for the intra-band response show that the resonance peak positions of the total optical absorption coefficients and relative refractive index changes shift towards higher energy levels (blueshift) by increasing the strength of the applied external electric, magnetic, and non-resonant intense laser field. The analysis of inter-band (electron-heavy hole) transitions reveals that the optical coefficients has a pronounced redshift induced by the electric field while a blueshift is caused by the magnetic and laser signals. It is seen that the nonlinear optical properties of such structures can be adjusted according to the purpose by changing the external perturbations and could be used in new optoelectronic device designs.

External fields controlling the nonlinear optical properties of quantum cascade laser based on staircase-like quantum wells

Abstract In this paper, we present a theoretical investigation of nonlinear optical properties of AlxGa1-x As-GaAs staircase-like quantum wells heterostructure under the effects of electric, magnetic, and intense laser fields. The electronic energy levels and their corresponding wave functions are computed numerically by solving the Schrodinger equation within the effective mass approximation. The obtained results show that the applied external fields have a huge impact on the intersubband transition between the ground and the first excited levels. The optical absorption coefficient and the relative refractive index changes can be blue shifted by increasing the electric field and red shifted by increasing the intense laser field parameter. However, we can obtain either the red or the blue shift by varying the intensity of an applied magnetic field. This interesting property of the applied magnetic field can be used in the design and fabrication of optoelectronic devices based on staircase-like quantum wells and operating in the red and blue domains.

Effect of intense laser and electric fields on nonlinear optical properties of cylindrical quantum dot with Morse potential

In this study, the influence of the external electric field on the nonlinear optical properties of a laser dressed cylindrical quantum dot with axial Morse potential are theoretically investigated using the total optical absorption coefficient as well as relative refractive index changes. The effect of the structural parameters on the structure's intraband optical properties is analyzed, optimizing the quantum dot in terms of the total optical absorption coefficient and the relative refractive index. Single-electron energies and wave functions of the system have been determined using analytical methods and the exact diagonalization technique. The quantities above mentioned are examined with the compact-density-matrix approach. The obtained results demonstrated that the system's intraband optical properties closely depend on both the applied external fields and the structural parameters. Such adequate tuning of the laser-dressed cylindrical quantum dots’ intraband optical properties gives us new possibilities in the regions of interest for optoelectronic device applications.

Theoretical investigation of linear and nonlinear optical properties in an heterostructure based on triple parabolic barriers: Effects of external fields

In this work, we have investigated theoretically the impact of intense laser, electric and magnetic fields on the linear and nonlinear optical properties of a quantum well heterostructure containing triple parabolic barriers (GaAs/AlGaAs). Within the framework of the effective-mass and parabolic band approximations, we have computed the confined lowest energy levels and their corresponding densities of probability, through the use of a finite difference technique to solve the corresponding differential equation. Besides, we evaluate the total optical absorption (TOACs) and relative refractive index change (RRICs) coefficients. The obtained findings show that an increase of the intensity of the intense laser field produces a blue shift at first and then a red shift of the TOACs and RRICs. A specific value of the laser field separating the two kinds of signal displacements is outlined. Contrarily to the intense laser field, an increment of the external static electric and magnetic fields induces only a blue shift in the variation of the TOACs and RRICs. In addition, we have discussed in detail the variation of diagonal and non-diagonal matrix elements which are responsible on the variation of the amplitudes of the TOACs and RRICs. We think that the obtained results can be useful in the design of new device's generation employed in optoelectronic domain.

Optical properties of a triple AlGaAs/GaAs quantum well purported for quantum cascade laser active region

A theoretical investigation on the conduction electron states in a triple inverse parabolic AlGaAs/GaAs quantum well, designed in the spirit of the active region for a quantum cascade laser, is performed. The study includes the influence of externally applied static electric and magnetic fields. The energy values and corresponding eigenfunctions are determined with the use of the effective mass approximation within the parabolic band description. The information on the allowed states is, then, used to evaluate some coefficients that represent the intraband nonlinear optical response of the structure. Numerical results are presented for the optical absorption and relative refractive index change coefficients as well as for those of nonlinear optical rectification and second harmonic generation. It is discussed that, in general, the amplitude and position of resonant peaks in the calculated quantities can be noticeably affected by the variation in the strength of the applied probe fields. Accordingly, the features of the investigated properties could suitably determine the application of this kind of structures for device proposals, as long as they can affect lasing regime in them.

Mid-IR refractive index sensor for detecting proteins employing an external cavity quantum cascade laser-based Mach-Zehnder interferometer.

Novel laser light sources in the mid-infrared region enable new spectroscopy schemes beyond classical absorption spectroscopy. Herein, we introduce a refractive index sensor based on a Mach-Zehnder interferometer and an external-cavity quantum cascade laser that allows rapid acquisition of high-resolution spectra of liquid-phase samples, sensitive to relative refractive index changes down to 10-7. Dispersion spectra of three model proteins in deuterated solution were recorded at concentrations as low as 0.25 mg mL-1. Comparison with Kramers-Kronig-transformed Fourier transform infrared absorbance spectra revealed high conformance, and obtained figures of merit compare well with conventional high-end FTIR spectroscopy. Finally, we performed partial least squares-based multivariate analysis of a complex ternary protein mixture to showcase the potential of dispersion spectroscopy utilizing the developed sensor to tackle complex analytical problems. The results indicate that laser-based dispersion sensing can be successfully used for qualitative and quantitative analysis of proteins.

Influence of applied external fields on the nonlinear optical properties of a semi-infinite asymmetric AlxGa1−xAs/GaAs quantum well

The asymmetric potential profiles are of great interest from the nonlinear optical properties point of view for semiconductor devices. The reason for this statement is because the existing theories on nonlinear optical properties obviously depends on the dipole matrix element for the involved transitions and an complete characterization for asymmetric potential profiles enables to the semiconductor device designers to have possible ranges of implementation and because the dipole matrix elements strongly depends on the asymmetry of the potential profile. Once the potential profile is well defined, with the desired range on operation, the external factors play also an important role on the optical properties tuning. In particular, in this paper we reported the absorption coefficient and the relative refractive index changes for semi-infinite inverse Gaussian-like profile for an AlxGa1−xAs/GaAs quantum well when is subjected to a z-directed electric field, to an in-plane x-directed magnetic field and finally to a non-resonant intense laser field effect, being the Al concentration the parameter that allows to shape the potential profile. In general, we conclude that the external factor are an efficient way to tune the optical properties that are in the range of the THz spectrum, at least for the intersubband transitions reported here.

Electron-related nonlinear optical properties of cylindrical quantum dot with the Rosen–Morse axial potential

We present a theoretical study on the effects of intense laser field (ILF) and static electric field on the linear and nonlinear optical properties of a cylindrical quantum dot with Rosen–Morse axial potential under the framework of effective mass and parabolic band approximations. This study also takes into account the effects of the structure parameters (η, V1, and R). The analytical expressions of the linear, third-order nonlinear and total optical absorption coefficients (TOACs) and the relative refractive index changes (RRICs) are obtained by using the compact-density-matrix approach. The results of numerical calculations show that the resonant peak position of the TOACs and RRICs shifts towards lower energies and the magnitude of the peak increases with the effect of the static electric field and ILF. In addition, it is observed that while the resonant energies of the TOACs and RRICs of system shift towards the higher (lower) energies with the enhancement of η, V1, they decrease with the augmentation of R. Thus, the findings of this study show that the optical properties of the structure can be adjusted by changing the magnitude of structure parameters and applied external fields.

Linear and nonlinear optical properties of a single dopant in GaN conical quantum dot with spherical cap

ABSTRACT The states of a single dopant centre in zinc-blende GaN-based conical quantum dots with spherical cap are theoretically investigated by analytically solving the corresponding effective mass equation taking advantage of the localisation of the ionised impurity at the cone apex. Nonlinear optical response is analysed through the calculation of the coefficients of optical absorption, relative refractive index change, and second and third harmonic generation, for the chosen set of allowed electron-donor states. The behaviour of the calculated optical quantities under changes in the geometry of the system due to variations in apical width and quantum dot radius is analysed and discussed.

Pyramidal core-shell quantum dot under applied electric and magnetic fields

We have theoretically investigated the electronic states in a core/shell pyramidal quantum dot with GaAs core embedded in AlGaAs matrix. This system has a quite similar recent experimental realization through a cone/shell structure [Phys. Status Solidi-RRL 13, 1800245 (2018)]. The research has been performed within the effective mass approximation taking into account position-dependent effective masses and the presence of external electric and magnetic fields. For the numerical solution of the resulting three-dimensional partial differential equation we have used a finite element method. A detailed study of the conduction band states wave functions and their associated energy levels is presented, with the analysis of the effect of the geometry and the external probes. The calculation of the non-permanent electric polarization via the off-diagonal intraband dipole moment matrix elements allows to consider the related optical response by evaluating the coefficients of light absorption and relative refractive index changes, under different applied magnetic field configurations.

Studies on the nonlinear optical properties of two-step GaAs/Ga1−xAlxAs quantum well

In this paper, the numerical computation for the absorption coefficient and the relative refractive index change, considering the third order correction nonlinear optical properties, is reported. This study was performed for a symmetric two-step GaAs/Ga1−xAlxAs quantum well, subjected to a constant electric field applied along the growth direction z, and an in-plane constant magnetic field B. We also consider the intense laser field effect, characterized through the laser-dressing parameter α0. The electronic structure computation was obtained by working under the effective mass approximation and the Schödinger equation was solved by diagonalization procedure. The optical properties are calculated by using the well-established compact density matrix formalism expressions for the nonlinear optical properties of interest. In general, we found that the structural parameters, as the step-like potential or the central barrier, permit the resonant peak and the amplitude design. We also found that the system becomes more sensitive to electric than to magnetic field, and finally that the intense, non-resonant, laser field can strongly change the optical properties of interest. Our results indicate that the implementation of the step-like potential profile, experimentally feasible, enhance the optical properties of interest, that falls within the THz electromagnetic range, and can be used to design a photodetector, or even can be used for quantum cascade lasers design.

Interlayer distance effects on absorption coefficient and refraction index change in p-type double-δ-doped GaAs quantum wells**Project supported by PISA 2016–1 UJAT and PRODEP Folio UJAT-245 of México.

In the framework of the Thomas–Fermi (TF) approach, a model for the p-type double-δ-doped (DDD) system in GaAs is presented. This model, unlike other works in the literature, takes into account that the Poisson equation associated with the system is nonlinear. The electronic structure is calculated for heavy and light holes. The changes in the electronic structure result of the distance d between the doped layers are studied. In particular, the relative absorption coefficient as well as the relative refractive index change is calculated as a function of the incident photon energy for heavy holes. The effect of the interlayer distance exhibits, in the absorption coefficient, a red shift of the peak position and a decrease in amplitude when the distance increases. In addition, the relative refractive index change node has a red shift as well as the interlayer distance increases. The calculations show that the effect of the separation between layers has a greater influence on the linear terms. These results are very important for theoretical calculations and engineering of optical and electronic devices based in δ-doped GaAs.

Tailoring the optical properties of quantum ring irradiated by THz laser

ABSTRACTThis study set out to introduce the optical nonlinearities of a intense laser-driven two-dimensional quantum ring subjected to external uniform magnetic field. Inclusion of the effect of non-resonant, high-frequency THz laser radiation is realised by the laser-dressed potential, whereas the total optical absorption coefficients, total relative refractive index changes and third-harmonic generation (THG) coefficient are inferred from the scheme of compact density-matrix formalism and iterative method. Our results reveal that the laser field smoothens the antidot region of the ring that consequences with remarkable modifications in the electronic structure and correspondingly the optical response of the system. We have found that the height and location of the resonant peaks of total optical absorption coefficient, total relative refractive index changes and THG coefficient can be controlled by the externally applied fields and system parameters. The tunability of the intersubband transitions could be beneficial for practical device application relying on the electronic optical transitions.

A theoretical study on the optical properties of a quantum well with short-range bottomless exponential potential

The effects of external applied fields on the electron-related optical nonlinear properties in a short-range bottomless exponential potential quantum well are investigated. The potential profile behaves as inverse square root in the vicinity of the origin and vanishes exponentially toward infinity, supporting a finite number of bound states whose energies and wave functions are determined within the effective-mass approximation. The linear, third-order nonlinear and total optical absorption coefficients (TOACs) as well as the coefficient of relative refractive index changes (RRICs) of the system are calculated from the expressions derived in the framework of the compact density matrix approach. The results obtained after numerical calculations show that with the effect of the static electric and magnetic fields (high-frequency THz laser field), the resonant peak position of the optical response shifts toward higher (lower) energies and the magnitude of the peak increases.

Intersubband optical properties of a laser-dressed asymmetric triple quantum well nanostructure

The simultaneous effect of static electric and magnetic fields as well as the intense THz laser field on the intersubband nonlinear optical properties of n-type asymmetric triple δ-doped quantum well is theoretically investigated. The calculations are carried out within the framework of the effective-mass and parabolic-band approximations, with the use of a diagonalization technique to determine the electron energies and the wave functions. The analytical expression of the total absorption coefficient and the relative refractive change of the structure have been found by using the compact-density-matrix approach via an iterative method. The obtained results show that the strengthening of the electric and the magnetic fields, as well as the increment of laser field parameter, lead to a blue shift of the resonant peaks of the intersubband optical absorption and the relative refractive index change spectrum. Additionally, the strengthening of the external fields leads to the reinforcement of the total absorption spectrum intensity. Finally, we have found that with the decrease in the number of the well, by keeping the effective width of the structure constant, the blue shift can be observed in the total absorption spectrum. Therefore, the obtained results give an additional possibility to tune the performance of new devices, based on the quantum wells nanostructures.

The electron-related optical responses for the square tangent quantum well: Role of applied external fields

In the present work, a detailed investigation of the influence of external perturbations, in particular intense terahertz radiation, static electric and magnetic fields on the electron-related optical responses such as total optical absorption coefficients and relative refractive index changes for a quantum well with the square tangent potential is presented. The subband energy levels and their corresponding wave functions are obtained by solving the one-electron Hamiltonian of the system under the framework of the effective-mass and parabolic band approximations. Optical coefficients are reported for varying incident photon energies. The numerical results show that the optical response is shifted towards the blue with the increase in the magnitude of the applied external fields. These results can provide an input for use in optoelectronic device applications.

Computation of the nonlinear optical properties of n-type asymmetric triple δ-doped GaAs quantum well

Abstract In the present study, we present numerical results for the influence of non-resonant intense THz laser radiation as well as the structure parameters, such as well width and central doping concentrations, on the total optical absorption coefficients (TOACs) and relative refractive index changes (RRICs) in n-type asymmetric triple δ-doped G a A s quantum well (QW) by using the compact-density-matrix formalism via iterative method. In order to obtain these numerical results, we have first obtained the subband energy spectrum and the electronic wave functions of the structure by using the effective-mass and parabolic band approximation. We have then calculated the nonlinear optical (NLO) properties of the system, by employing these energy eigenvalues and eigenfunctions. The numerical results for these calculations show that; (i) the magnitude of the resonant peak of TOACs decreases and the peak position shifts towards the lower energies when the central doping concentration and the well width are increased; (ii) due to the intense laser field effect, the magnitude of the TOACs resonant peak initially increases and its position shifts towards higher energies and then it decreases, shifting towards lower energies; (iii) by increasing the central doping concentration (well width), the magnitude of the resonant peak of RRICs increases (decreases), and the resonant peak position shifts towards the lower energies; and finally (iv) because of the increase in the intensity of the laser field applied to the structure, the magnitude of the resonant peak of RRICs increases, and the resonant peak position initially shifts towards the higher energies and then shifting towards the lower energies.

The nonlinear optical properties of GaAs-based quantum wells with Kratzer–Fues confining potential: Role of applied static fields and non-resonant laser radiation

In the present paper, we report a theoretical investigations on the linear and nonlinear optical properties of a GaAs-based quantum well with the Kratzer-Fues confining potential, including the effects of external applied static electric, magnetic, and intense THz laser fields. The electronic structure of this system is obtained by using the effective-mass and envelope wave function approaches. Then, the coefficients of linear, third-order nonlinear, and total optical absorption (OACs) and relative refractive index changes (RICs) are calculated by using the iterative solutions of the compact-density matrix approach (CDMA). The obtained numerical results are reported as functions of the incident photon energy taking into account several values of static electric, static magnetic, and intense THz laser fields. These results show that the nonlinear optical properties of this structure are significantly affected by the magnitude of the external applied fields.

Nonlinear optical properties of a semi-exponential quantum wells: Effect of high-frequency intense laser field

In this present work, the effect of non-resonant, mono-chromatic intense laser field (ILF) on the linear and nonlinear optical properties of a semi-exponential quantum well (SEQW) is investigated theoretically within the effective-mass and envelope wave function approach. The bound subband energy levels and their envelope wave functions of the structure are calculated by using the diagonalization method. The optical properties of the system are obtained by using the compact-density matrix approach. The obtained numerical results show that the applied ILF and structure parameters have a significant impact on the optical properties of these structures, such as the linear, third-order nonlinear and total absorption coefficients and relative refractive index changes. Furthermore, from the findings of this study, it has been concluded that the linear and nonlinear optical properties in a SEQW under the ILF can be tuned by changing structure parameters, such as the effective range and depth of the system.

Strain effects in the absorption coefficient and relative refractive index change in double asymmetric AlxGa1−xN/GaN quantum wells

We theoretically investigate the optical absorption and the relative change in the index of refraction in asymmetric double zinc-blende AlxGa1−xN/GaN quantum wells. Particular emphasis is put in revealing the influence of lattice strain on these properties. For that purpose, the electronic energy structure is determined in the framework of the effective mass and parabolic band approximations whilst the strain effects are incorporated with the use of the model solid theory. The corresponding optical coefficients are then computed through the expressions obtained within the compact matrix density formulation. Linear and nonlinear contributions are reported as functions of the widths of both the separating central potential barrier and the left-hand quantum well.