Terahertz Laser Field Research Articles

Floquet engineering of electronic states and optical absorption in laterally-coupled quantum rings under a magnetic field

Tuning electronic and optical properties of low-dimensional quantum systems in a flexible way is of particular importance in designing semiconductor-based devices. Semiconductor quantum rings (QRs) are nanoscopic structures that have become promising systems for physical and technological applications due to their unique electronic and optical properties. Here, we explore the fundamental electronic and optical properties of laterally-coupled QRs by taking into account the combined effects of applied magnetic and non-resonant terahertz intense laser fields. The laser-dressed electronic states are solved using the Floquet theory of periodically driven quantum systems in high-frequency limits within the framework of effective mass approximation. We demonstrate that increasing the laser field parameter leads to reduced tunnel splitting in the energy spectrum and more pronounced Aharonov-Bohm oscillations for the ground state energy, due to the attenuation of the tunnel coupling. Furthermore, depending on the position of the avoided crossings in Aharonov-Bohm oscillations of laterally-coupled quantum rings, the evolution of the avoided crossings with increasing the laser field parameter can be elucidated as the attenuated tunnel coupling or the competition between the attenuated tunnel coupling and the strengthening anisotropy of the laser-dressed QR potential well. The intensity of the intraband optical transition of laterally-coupled QRs can be effectively tuned and reaches a larger value by manipulating the laser parameter and magnetic field. Optical Aharonov-Bohm oscillations in laterally-coupled QRs are still exhibited by changing laser field parameters. Our findings offer a novel approach to manipulate the electronic and optical performances as well as the Aharonov-Bohm oscillations based on the laterally-coupled QRs by using an intense terahertz laser field.

Entanglement control in a laser driven single layer graphene system

Abstract In this letter, we have proposed a new model for quantum control of atom photon entanglement in a single layer graphene via von Neumann reduced entropy of entanglement. We consider the effect of terahertz laser field intensity on the degree of entanglement (DEM) in the resonance and off-resonance condition of the applied fields. We also investigate the spatially dependent of the DEM when two applied light becomes standing wave pattern in x and y directions. Our results show that in different parametric conditions, the population of the different states can be controlled and this leads to modifying the DEM of the system.

Coherent enhancement of a frequency comb modulated by a terahertz laser field in high-order harmonic generation

Coherent enhancement of a frequency comb modulated by a terahertz laser field in high-order harmonic generation

Effects of external perturbations on light absorption by light/heavy hole excitons in a semi-parabolic quantum well

The effects of electric, magnetic, and intense terahertz laser fields on optoelectronic properties are investigated in a GaAs/AlxGa1-xAs semi-parabolic quantum well. The binding energy, exciton light absorption coefficients, interband transition energies, and dipole elements in the matrix are studied within the structure of the parabolic band and effective-mass approximations. The transition energy difference between the ground-state electron energy level and the ground-state heavy hole (light hole) energy level and matrix elements are carried out as functions of external perturbations with a constant well size. The results exhibit that the exciton binding energies of heavy and light holes reduce as long as the laser dressing parameter is larger. The optical absorption of light hole exciton in the system is stronger than the heavy hole exciton. And the excitonic energies, transition energies, and absorption coefficients are much more sensitive and controlled by changing the external perturbations.

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.

Intense terahertz laser field induced electro-magneto-donor impurity associated photoionization cross-section in Gaussian quantum wires

Using expressions derived within the compact density matrix approach, the peaks of optical absorption and the changes of refractive index of a hydrogenic impurity in a GaAs/GaAlAs Gaussian quantum well wire are calculated taking into account the influence of static electric, magnetic and intense laser fields. The photoionization cross section, with normalized photon energy, is computed for different values of static electric field, magnetic field, and laser dressing parameter. The dipole moment matrix elements and the transition energy between ground and first excited state energy levels are computed as functions of quantum wire width and confinement potential depth, with and without external perturbations. Donor impurity binding energy is investigated in presence of the aforementioned electromagnetic probes, using parabolic band and effective mass approximations. The results show that the absorption coefficients depend on the transition energy difference between initial and final states involved as well as on the corresponding polarization response via dipole matrix elements. Discussed optical properties are field-sensitive and they can be tuned within the desired energy ranges using these external perturbations. • Peaks of optical absorption and changes of refractive index of a hydrogenic impurity in a GaAs/GaAlAs Gaussian quantum well wire are calculated. • They have been computed taking into account the influence of static electric, magnetic and intense laser fields. • Photoionization cross section, with normalized photon energy, is computed. • Donor impurity binding energy is investigated in the presence of aforementioned electromagnetic-probes, using parabolic band and effective mass approximations. • Discussed optical properties are field-sensitive and they can be tuned within the desired energy ranges using these external perturbations.

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.

Terahertz laser field manipulation on the electronic and nonlinear optical properties of laterally-coupled quantum well wires.

An intense terahertz laser field is shown to actively manipulate the electronic states, as well as the linear and nonlinear optical absorption coefficients, of the laterally-coupled quantum well wires (LCQWWs). The laser-dressed quantum states of the LCQWWs are achieved using the non-perturbative Floquet method and the two-dimensional diagonalization technique under the effective mass approximation. We have demonstrated that the intense terahertz laser field induces a strong deformation of the confinement potential configuration of the LCQWWs, thus pronouncedly dressing the energy levels and wave functions. An unambiguous picture is depicted for the evolution of the laser-dressed quantum states with the increase of the laser-dressed parameter characterizing the strength of the laser-dressed effect. On this basis, the resonant peak positions of the linear and nonlinear optical absorption coefficients feature a blue shift followed by a red shift with an increase of the laser-dressed parameter. Furthermore, the evolution of the peak values for the linear and third-order nonlinear optical absorption coefficients as a function of the laser-dressed parameter is comprehensively discussed. Moreover, in contrast to the case without intense terahertz laser field, the peak values of the linear, third-order nonlinear, and total optical absorption coefficients can be obviously enhanced at the same frequency position by manipulating the appropriate laser-dressed parameter. A similar feature can be found in the linear, third-order nonlinear, and total refractive index changes. Our findings are conducive to the implementation of the expected quantum states and nonlinear optical effects in the LCQWWs, paving the way for new designs in tunable optical switches, infrared photo-detectors and infrared modulators.

Electronic and optical properties of cubic quantum dots subjected to terahertz laser field

This study introduces the influence of linearly polarized terahertz laser field (TLF) on electronic and anisotropic optical absorption coefficients (OACs) related to the cubical quantum dots (CQDs). 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 are inferred from the scheme of compact density-matrix formalism. The results show that the laser correction parameters and polarization angle of TLF have a significant influence on the optical properties. As a key result, the modulation of anisotropic OACs of CQDs by terahertz laser field with different parameters is given.

Combined effects of electric, magnetic, and intense terahertz laser fields on the nonlinear optical properties in GaAs/GaAlAs quantum well with exponentially confinement potential

Combined effects of electric, magnetic, and intense terahertz laser fields on the nonlinear optical properties in GaAs/GaAlAs quantum well with exponentially confinement potential

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.

Influence of hydrostatic pressure, temperature, and terahertz laser field on the electron-related optical responses in an asymmetric double quantum well

Influence of hydrostatic pressure, temperature, and terahertz laser field on the electron-related optical responses in an asymmetric double quantum well

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.

Intense-terahertz-laser modulated photoionization cross section of shallow-donor impurity in semiconductors in a magnetic field

The effects of intense terahertz laser and magnetic fields on the photoionization cross section (PICS) of shallow-donor impurity in semiconductors are investigated within the Faraday configuration. The donor ground-state energy level and its wave function are calculated using a combination of nonperturbative and variational methods where radiation field is exactly included through a laser-dressed Coulomb potential (LdCP). We find that a competition between donor ground-state binding energy and optical integrals in tailoring the magnitudes and peak positions of PICS is achieved by external fields via the LdCP. In this way, the magnitudes and peak positions of PICS can be decreased or increased and effectively tuned with an appropriate choice of external fields. The overall shape of PICS is optically anisotropic, which is more pronounced in the z-polarization direction for large laser field intensity or low magnetic field. In the vicinity of ωc, the overall shape of PICS in the z-polarization direction changes into that of PICS in the x-polarization direction. Our theoretical findings hold promising applications in designing and developing new efficient impurity-based devices manipulated by external fields.

The effects of hydrostatic pressure and temperature on photoionization cross section of impurities in semiconductors under magnetic and intense terahertz laser fields

Abstract We have presented a theoretical study on shallow-donor-related photoionization cross section (PICS) in semiconductors subjected to hydrostatic pressure, magnetic field, and intense laser field within the Vogit configuration. Calculations are performed for the donor ground state using a combination of nonperturbative and variational methods in which intense laser field is exactly taken into account via a laser-dressed Coulomb potential (LdCP). We find that the overall shape of shallow-donor-related PICS depends upon the incident optical field polarization, which is more significant when the incident optical field polarization is parallel to the magnetic field. The donor ground-state binding energy and the optical integrals act in an opposite manner to tailor the magnitudes and peak positions of shallow-donor-related PICS by changing radiation field through the LdCP or by changing magnetic field, hydrostatic pressure, and temperature, leading to a blueshift or redshift of shallow-donor-related PICS spectrum and to a decrease or increase of shallow-donor-related PICS magnitude manipulated by these factors. Thus, we can control the properties of shallow-donor-related PICS with an appropriate choice of two external applied fields, hydrostatic pressure, and temperature to meet some special needs in designing and developing new efficient optoelectronic devices.

Magnetic field effect on the electronic states and the intraband optical absorption spectrum of a laser dressed double quantum dot molecule

The simultaneous effects of intense terahertz (THz) laser, a homogeneous magnetic fields, and the modification of the structural parameters on the electronic states, and the intraband optical absorption spectrum in a two-dimensional double quantum dot molecule are theoretically investigated. The crossing and anticrossing are observed in the energy dependence on the magnetic field induction between the third and the fourth energy levels. Additionally, it is shown that an intense THz laser field always shifts the energy spectrum to higher values. The variation of the structural parameters leads to the change of the positions of the energy levels and the anticrossing point. Finally, we have found that the intraband optical absorption spectrum, particularly the absorption intensity and the peak position, can be effectively regulated by an intense THz laser and a magnetic fields, as well as by the variation of the structural parameters of the double quantum dot molecule.

Non-perturbative multiphoton excitation studies in an excitonic coupled quantum well system using high-intensity THz laser fields

Multiphoton excitations and nonlinear optical properties of exciton states in GaAs/AlxGa1−xAs coupled quantum well structure have been theoretically investigated under the influence of a time-varying high-intensity terahertz (THz) laser field. Non-perturbative Floquet theory is employed to solve the time-dependent equation of motion for the laser-driven excitonic quantum well system. The response to the field parameters, such as intensity and frequency of the laser electric field on the state populations, can be used in various optical semiconductor device applications, such as photodetectors, sensors, all-optical switches, and terahertz emitters.

Hydrostatic Pressure and Temperature Effect on the Electron-Related Optical Responses in Symmetric and Asymmetric n-Type Double Delta-Doped GaAs Quantum Well Under Terahertz Laser Field

The effects of non-resonant intense laser fields on the intersubband-related light absorption and relative refractive index change coefficients in symmetric and asymmetric n-type double $$\delta$$ -doped GaAs quantum wells are investigated. Systems are assumed to be also under the influence of hydrostatic pressure and the change of temperature. The single band effective-mass and envelope function approximations, together with analytical expressions for the linear and third-order nonlinear optical coefficients are used as theoretical tools. According to the numerical outcome, the nonlinear optical response is significantly affected by the intense non-resonant laser radiation, as a result of the associated distortion of conduction band energy profiles. For instance, it is revealed there is a laser-induced transition of the confining potential from double-delta geometry to single-triangular-like shape. Given the additional variations associated with the application of hydrostatic pressure and temperature, all these external probes could be used to control and suitablly tune the electronic and optical properties of GaAs n-type double $$\delta$$ -doped GaAs quantum wells.

Nonlinear optical properties of triple δ-doped quantum wells: The impact of the applied external fields

In the present paper, we theoretically investigate the effect of applied external fields, such as electric, magnetic, and intense terahertz laser fields on the optical absorption and the relative refractive index change coefficients of triple δ-doped quantum well structures. To investigate the applied external field effects, we perform the calculation of the allowed subband energy levels and their corresponding eigen-functions using the diagonalization method within the framework of the effective-mass approximation. The effects of the applied external fields on the nonlinear optical properties of the quantum well structure are treated within the compact-density-matrix approach via the iterative method. The numerical results obtained are presented for two different values of electric, magnetic, and intense terahertz laser fields. These results show that changing the intensity of the external electric, magnetic, and intense terahertz laser field. It is concluded that the nonlinear optical response of the triple δ-doped structure can be significantly changed through the changes in the configuration of the external probes.

The Effects of Intense Terahertz Laser and Magnetic Fields on Optical Properties of a Shallow Impurity in Semiconductors in the Faraday Configuration

The influence of intense terahertz laser and magnetic fields on the total optical absorption coefficient for the transitions between shallow‐impurity states 1s and in semiconductors within the Faraday configuration is studied by using the compact density‐matrix approach, where the energy levels and wave functions of shallow‐impurity states are obtained by using a combination of time‐dependent nonperturbative approach and variational method. We find that the transition energy of shallow‐impurity states and the dipole matrix element can be not only increased but also decreased by varying the external fields via laser‐dressed Coulomb potential. In this way, the saturable absorption and the resonant peak position and magnitude of the total optical absorption coefficient can be effectively tuned with an appropriate choice of the external fields. Moreover, an appreciable effect of cyclotron motion on the total optical absorption coefficient is observed. This gives new degree of freedom in various device applications based on the intradonor transition of electrons.