Optical Refractive Index Changes Research Articles

Hydrogenic impurity effect on optical properties of Wannier-Mott exciton confined in a spherical quantum dot with Kratzer potential under magnetic field

Confinement effects of Kratzer potential on a Wannier-Mott Exciton(W-M) are studied in a spherical quantum dot(QD) in the presence of a static magnetic field. Time independent Schr$\ddot{o}$dinger equation is solved numerically to obtain the energy states. The excitonic transitions so realized have been used to explore the non-linear optical properties that are important for optical characterization of materials such as the optical absorption coefficients (ACs) and refractive index changes (RICs). Impact of magnetic field, strength of the laser field and transition parameters using familiar compact density matrix approach are also analyzed. It has been observed that optical properties get radically modified under confinement effects. Also, the shift of degeneracy of different excitonic energy levels with the magnetic field in confinement potential has been reported for the first time for W-M exciton in the spherical quantum dot, the study that may have crucial input to the literature and myriad of practical implications.

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.

Linear and nonlinear optical properties in wurtzite MgZnO/ZnO double quantum wells: Roles of external electric and magnetic fields

In this work, the modulation effects of external magnetic and electric fields on the inter-subband optical absorption coefficients and refractive index changes in asymmetric wurtzite MgZnO/ZnO double quantum wells are investigated considerably. The linear and nonlinear characteristics among the three lowest confined states are calculated here. The obtained results show that the optical properties of the structure are very sensitive to the external field. The optical characteristics related to higher energy levels which have been ignored in past works are as important as the transition related to the ground state. The transition from the ground state to the second excited state is the most sensitive to the external fields. The optical parameters can be risen by two orders of magnitude through the manipulation of the applied electric and magnetic fields.

Multiple polarization-selective and wideband enhanced optical properties of a cubic quantum dot realized by the multi-physical field.

The coupling of intense laser field and electric field serves as a new method to achieve the desired electronic states, optical absorption coefficients and refractive index changes of cubic quantum dot for the first time, to the best of our knowledge. The stationary Schrödinger equation was derived and calculated by means of the Kramers-Henneberger transformation, the non-perturbative Floquet method, and the finite difference method. The energy-level anticrossing is activated by multi-physical field to transform suitable quantum states, resulting in the multiple-polarization-selective absorption and refractive index changes. The results show that ultra-wideband frequency shift and resonance enhancement characteristics of optical absorption coefficients and refractive index changes strongly depend on the laser-dressed parameter, the amplitude of electric field, and the polarization directions of the intense laser field and electric 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

Nonlinear optical absorption and refractive index change in realistic [formula omitted] V-groove quantum wires

The intersubband optical absorption coefficient and refractive index change of a realistic single-electron GaAs/Ga1−xAlx V-groove quantum wire are calculated. Finite confinement potentials and analytic models capable of adapting to many V-groove quantum wire shapes reported in the literature are used in the calculations. This scheme allows analyzing the effect of the inter-sidewall angle and crescent thickness on the optical response. Additionally, the effects of external fields such as hydrostatic pressure and temperature are taken into account. The results show that the geometrical parameters have a principal role compared to the temperature and hydrostatic pressure. In addition, optical activity within the Terahertz band using the parameter values that fit the typically V-groove quantum wires reported in the literature was found.

Calculation of linear and nonlinear optical properties of spherical quantum dots with Hulthén plus Hellmann confining potential

The optical absorption coefficients (OACs) and refractive index changes (RICs) in the GaAs/Ga1−x AlxAs spherical quantum dots (QDs) under Hulthén plus Hellmann confining potential have been investigated by adjusting the structural parameters with the applied tuning elements. Energy levels and wavefunctions of this system have been determined by means of the Nikiforov–Uvarov (NU) method. Expressions for the OACs and RICs are derived by the density matrix method. We display that both the radius of QDs and the depth of the Hulthén plus Hellmann confining potential have a significant impact on OACs and RICs. Furthermore, we can draw conclusions that the applied tuning elements can manage the amplitudes and resonances frequency of the OACs and RICs.

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.

The effect of terahertz laser field on the optical absorption coefficients and refractive index changes of hyperbolic confinement quantum wells

In this paper, the potential profile with applying terahertz laser field is deduced by the Kramers-Henneberger transformation. In the frame of effective quality, the Schrödinger equation is solved to obtain the energy levels and the wave functions. Then, the variations of optical absorption coefficients (OACs) and the optical refraction index changes (ORICs) are deduced by the compact matrix approach and the iterative method. The results illustrate that the OACs and the ORICs are regulated by the terahertz laser field. The influence of the intensity of incident light on the OACs and the ORICs also are discussed.

Restorable, enhanced, and multifaceted tunable optical properties in a coaxial quantum well driven by the electric field and intense laser field.

A new method for regulating optical properties of a coaxial cylindrical quantum well using the electric field and intense laser field is investigated in the effective mass approximation. By means of the finite difference method and the correct dressing effect of the confinement potential, the results show that the enhancement and recovery of optical absorption and refractive index change strongly depend on the multifaceted-cooperative regulation of the laser parameter, the electric field strength, the angle between the electric field and polarization direction of laser, and the barrier width. This is promising for the design of a new generation of highly polarization sensitive devices, optical repair equipments and optical phase modulators by adopting the multistage combination of electric and intense laser fields.

Optical properties of a quantum well with Razavy confinement potential: Role of applied external fields

In this present work, the effect of applied external fields and well width on the optical absorption and refractive index change coefficient of a GaAs quantum well with Razavy confinement potential is theoretically presented. For this, firstly, the confined subband energy levels of the structure and the envelope wave functions corresponding to these states have been computed using the diagonalization method within the framework of effective mass and parabolic band approximation. Then, by using this information, the coefficients of total – linear plus nonlinear – intersubband optical absorption (TOAC) and relative refractive index changes (RRIC) of the structure are evaluated. The obtained numerical results show that the increase in the magnitude of the applied external fields creates a blue shift in TOAC and RRIC. Also, contrarily to the applied external fields, an increment of the quantum well width have induced a red shift in the TOAC and RRIC. We discuss in detail the variation of the diagonal matrix elements and the energy difference (E2–E1) which are responsible for the change of amplitudes of the calculated coefficients. We believe that the obtained numerical results can be useful in the design and application of the next generation devices used in the optoelectronics field. • The magnitude of the TOACs peak decrease with the static electric field. • The magnitude of the TOACs peak increase with the ILF. • The magnitude of the RRICs decrease with the ILF. • The increase of ILF leads to important effects on the optical properties of Razavy QW.

Nonlinear optical properties in a hybrid system composed of metal nanoparticles and Morse quantum wells

We investigate linear and nonlinear optical absorption coefficients (OACs) and refractive index changes(RICs) of a Morse quantum well when a quantum-sized metal nanoparticle is placed nearby. The exciton–plasmon coupling induces the modification of the energy interval and the relaxation rate of the Morse quantum well. The spontaneous decay rate of the Morse quantum well is also modified due to Purcell effect. These modification above reduce the magnitudes of the linear and nonlinear OACs and RICs of the Morse quantum well. More colorful results are demonstrated by controlling the size of the metal nanoparticle and the distance between the Morse quantum well and the metal nanoparticle. Our findings provide a way for manipulating the linear and nonlinear optical properties of the Morse quantum well.

Ultra-wide frequency tuning range for optical properties in coaxial quantum well driven by intense laser field

A new approach for controlling intersubband transitions and optical properties of coaxial cylindrical quantum well is proposed. Considering the correct dressing effect for the confinement potential, the new ultra-wide tuning mechanism is based on the variation of quasibound states with the intensity of long-wavelength laser field. By means of the finite difference method, the results provide a new explanation for the anticrossing of energy levels and exhibit great potential for ultra-wide frequency tunability (ranging from terahertz to the mid-infrared region) of the optical absorption coefficient and refractive index changes by modulating the laser parameters and barrier thickness.

Nanostructure wrinkle thin films on flexible substrate: Tunable optical properties

Nanostructure wrinkle created by amorphous diamond like carbon (a:DLC) thin films on a flexible Polyethylene Terephthalate (PET) substrate via chemical bath deposition technique was studied in detail. Atomic force microscopy (AFM) image revealed that the nanostructure wrinkle pattern with varying wavelengths from 350 nm to 170 nm are closely spaced and randomly oriented on the PET substrate. Raman spectra analysis showed that the chemical composition i.e., sp2/(sp2 + sp3) bonding ratio in the deposited a:DLC nanostructure wrinkle thin films was varied by changing the sucrose weight percentage in the precursor solution used for a:DLC thin film deposition. The optical band gap energy decreased from 3.17 eV to 2.04 eV for the a:DLC nanostructure wrinkle thin films due to increasethe sucrose weight percentage in the precursor solution from 5 to 30 respectively. The disorderness and defect density in the a:DLC nanostructure wrinkle thin films calculated from Raman spectra as well as from Urbach energy calculation. The change in optical transmittance, extinction coefficient, refractive index and optical band gap energy has been discussed in terms of composition and nanostructure wrinkle pattern of the a:DLC thin films.

Linear and nonlinear optical absorption coefficients and refractive index changes of zigzag quantum wells affected by terahertz laser field

This study introduces the influence of terahertz laser field on optical absorption coefficients (OACs) and refractive index changes (RICs) related to the quantum wells with zigzag confinement potential. The energy levels and wave functions of the system are obtained by solving the Schrödinger equation within the framework of the effective-mass. The OACs and RICs are inferred from the scheme of compact density-matrix formalism. The results show that the peak of OACs and RICs are modulated by terahertz laser field and the potential parameter of quantum wells.

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.

Nonlinear optical properties in AlGaAs/GaAs symmetric coupled quantum wells

Based on the density matrix approach and iterative method, we calculated the analytic forms of linear and third-order nonlinear optical absorption coefficients and refractive index changes for symmetric coupled quantum wells (SCQWs) considering a two-level system, and gave the corresponding numerical results. The calculated results show that the optical properties of SCQWs are significantly better than those of asymmetrically coupled quantum wells, and the optical absorption coefficient and refractive index change are affected by the structure parameters of the SCQWs and the incident optical intensity. Their physical mechanisms are elucidated.

Anisotropic optical properties in a square quantum well wire under different polarizations of intense laser fields

In this paper, the polarization angle of intense laser field and incident light effects on the intersubband optical absorption and refractive index change in the square quantum well wire are investigated theoretically by Kramers–Henneberger approximation. It is found that the polarization angle of the intense laser field can influence the energy gap and exchange electronic configuration by breaking symmetry. Hence, the incident light polarization angle should be considered. The variation of optical absorption and refractive index change are given with different polarization-intense laser fields and probe light, which provides the possibility of designing various polarization-sensitive devices.

Effect of terahertz laser field on anisotropic optical absorption and refractive index changes of coaxial square quantum well wires

The influence of terahertz laser field on nonlinear anisotropic optical properties, such as optical absorption and refractive index changes is studied. By solving the Schrödinger equation of the system in the framework of effective mass with the Kramers–Henneberger (KH) transformation, the eigenfunctions and energy eigenvalues of the system are obtained. The optical absorption and refractive index changes are deduced by the compact density matrix form and the scheme of iterative method. The results show that the polarization angle and intensity of terahertz laser field have a strongly influence on the peak of optical absorption and refractive index change in different directions respectively.