Effect Of Laser Field Research Articles

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.

Effect of the impurity on the Aharonov-Bohm oscillations and the intraband absorption in GaAs∕Ga1−xAlxAs quantum ring under intense THz laser field

The simultaneous effect of intense THz laser field and hydrogenic donor impurity on Aharonov-Bohm effect in a GaAs∕Ga1−xAlxAs single quantum ring is investigated using the non-perturbative Floquet theory in high-frequency limit and Ehlotzky approximation. It is shown that the intense THz laser field and donor impurity destroy the usual Aharonov-Bohm oscillations of the electron ground state. The Aharonov-Bohm-like oscillations of the excited energy levels, as well as the dipole, allowed optical transition energies can be effectively controlled by changing the laser field parameter and impurity position. Furthermore, an unusual oscillatory behavior is also observed for the dependence of optical transition intensity on magnetic field induction. The obtained results indicate the possibility of the prediction and effective control of electronic and optical properties of future devices on quantum rings.

Electromagnetically induced transparency in a GaAs/InAs/GaAs quantum well in the influence of laser field intensity

Effects of laser field on electromagnetically induced transparency is investigated in a GaAs/InAs/GaAs quantum well. The taken system is InAs sandwiched between GaAs semiconducting materials. The confinement potential and the well size of the quantum well are kept constant. The three atomic sub-levels are considered and the system is considered using a density matrix approach. Laser field induced intersubband electromagnetically induced transparency in the three level single quantum well is discussed theoretically. Laser field related optical susceptibilities, Rabi frequency and the detuning parameters are computed in the present work. The variation of real and imaginary parts of optical susceptibility as a function of normalized detuning, in the influence of laser field, is obtained. The refractive index and the group velocity of the probe light pulse are found in the presence of laser field intensity. The variation of group index as a function of probe field energy, with the application of laser field, is reported. For the five units of laser parameter, the reduction of Δp∕Ωc value is found to be 0.0762. The laser field dependence on the optical susceptibilities on the normalized detuning, refractive index and the group index is brought out.

Optical resonance near the edge of a photonic band gap (PBG): turning the effects of a PBG on/off using a resonant driving field

ABSTRACTWe studied the effects of a coherent monochromatic resonant laser field driving the transition of a two-level atom embedded in a photonic band gap (PBG) material on the emission dynamics of the atom. When the transition frequency of the atom lies outside a PBG and sufficiently far from the band edge that the emission dynamics of the atom is not normally affected by the gap, the dynamic stark splitting of the upper level of the atom into two dressed states by a sufficiently strong resonant driving field can bring the lower dressed state close enough to the band edge or even inside the gap so as to be affected by the gap, providing a switchable means of extending the novel effects of atom–photon interaction near the edge of a PBG for atomic transitions outside the gap and far from the band edge. The net effect is as if a sufficiently strong resonant field driving a transition of an atom embedded in a PBG actively shifts the PBG close enough to the transition so that the gap affects the emission dynamics associated with the transition.

Electron-related optical responses in triple δ-doped quantum wells

ABSTRACTA detailed theoretical study on the electron-related optical responses in triple δ-doped GaAs quantum wells in the presence of non-resonant, monochromatic intense laser field is presented. For this purpose, we first obtained the bound subband energy levels and their corresponding envelope wave functions of the structure for different central doping concentrations within the effective-mass approximation. Then, we calculate the effect of the non-resonant intense laser field on the optical properties of this structure using the compact-density-matrix approach via the iterative method. We found that the optical absorption coefficients and refractive index changes in the triple δ-doped GaAs quantum well can be modulated by changing the central doping concentration and the intensity of the non-resonant, monochromatic laser field. In addition, it is shown that a sufficiently intense laser field suppresses the multiple quantum well configuration towards a single potential well one and the optical response becomes practically independent of the δ-doping concentration.

Linear and nonlinear optical properties in the terahertz regime for multiple-step quantum wells under intense laser field: Electric and magnetic field effects

We present a theoretical study on the linear and nonlinear optical properties in AlrGa1-rAs/GaAs asymmetric multiple step quantum wells (AMSQW) under the effects of a non-resonant intense laser field (ILF), electric, and magnetic field. Calculations are for the linear optical absorption and refractive index relative changes combined with the second and third harmonic generation. The potential profile is constructed as a function of the Aluminum concentration, so that the heterostructure has four steps of different concentration, width and height. The energy levels and corresponding wavefunctions are obtained by solving the Schördinger equation, for an electron, in the envelope function approach, with parabolic bands, and the effective mass approximations. The results show that variations in ILF, electric field and magnetic field have significant influences on the magnitude and peak energy positions of the SHG and THG coefficients. Therefore, we can conclude that the effects of ILF, electric and magnetic fields can be used to tune and control the SHG and THG in the range of the terahertz electromagnetic spectrum.Keywords: Multiple-step quantum wells; Linear optical properties; Second and third harmonic generation; Terahertz radiation; Intense laser field; Electric and magnetic fields.

Generation of High-Intensity Single Attosecond Pulse by Using Inhomogeneous Chirped Pulse

The generation of high-order harmonics and single attosecond pulses from $$ {H}_2^{+} $$ has been theoretically investigated beyond the Born–Oppenheimer approximations. It is found that with the introduction of the inhomogeneous effects of the laser field in frequency and space, not only the harmonic cutoff can be remarkably enhanced, but also the single short quantum path can be selected. Further, with the increase of the initial vibrational state and by properly adding a terahertz controlling field, the harmonic yield can be enhanced by 2.5 orders of magnitude, showing a highintensity supercontinuum with the bandwidth of 511 eV. As a result, four single attosecond pulses shorter than 28 as can be produced. Moreover, the present scheme can also be achieved in the multicycle pulse duration, which is much better for practical application.

Stability and coherence of strong-coupling magneto-bipolaron in asymmetric quantum dot under laser field effect

On the fundamental basis of the modified Lee Low Pines theoretical method, we study analytically the stability and coherence of magneto-bipolaron in asymmetric quantum dot (QD) under the laser field. It is observed that, the bipolaron stability strongly depends on the electron–phonon coupling constant, magnetic field, laser frequency and high laser field strength. It is shown that, the laser field can trap and cool the magneto-bipolaron under certain conditions. The laser and magnetic field strongly affect the coherence time of bipolaron. This study enables to construct superconducting materials.

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.

Electron-related optical responses in Gaussian potential quantum wells: Role of intense laser field

A theoretical study of the effects of non-resonant intense laser field on the optical response in a Gaussian potential quantum well is performed in the framework of the effective mass approximation. The obtained results indicate that, the depth and range of the considered confinement potential and intense laser field intensity has a significant effect on the optical properties in Gaussian potential quantum wells. Also it was found that the laser field is more effective on the optical response in Gaussian potential quantum wells with smaller range.

Kerr nonlinearity and nonlinear absorption coefficient in a four-level M-model cylindrical quantum dot under the phenomenon of electromagnetically induced transparency

The Kerr nonlinearity and the nonlinear absorption coefficient in a four-level M-model of a GaAs cylindrical quantum dot (QD) with parabolic potential under electromagnetically induced transparency are investigated. By solving the density matrix equations in the steady-state, the third order susceptibility is obtained. Then, by using the real and imaginary parts of third order susceptibility, the Kerr nonlinearity and the nonlinear absorption coefficient, respectively, for this system are computed. The effects of the radius and height of the cylindrical QD are then investigated. In addition, the effects of the control laser fields on the Kerr nonlinearity and the nonlinear absorption coefficient are investigated.

Impurity-related optical response in cylindrical quantum dots with a δ-doped axial potential under an intense laser field

A theoretical study of the effects of a nonresonant intense laser field on the absorption coefficients and refractive index changes for a two-level system associated with transitions from the 1S -like impurity state to the 2Pz -like impurity state in a cylindrical quantum dot with a δ-doped axial potential is performed in the framework of the effective mass approximation. It is found that the nonresonant intense laser field and axial impurity position have obvious effects on the transition matrix elements and also on the difference between the electron densities of the states in cylindrical quantum dots, which are related to the refractive index changes and optical absorption coefficients.

Third-harmonic generation of a laser-driven quantum dot with impurity

The third-harmonic generation (THG) coefficient for a laser-driven quantum dot with an on-center Gaussian impurity under static magnetic field is theoretically investigated. Laser field effect is treated within the high-frequency Floquet approach and the analytical expression of the THG coefficient is deduced from the compact density-matrix approach. The numerical results demonstrate that the application of intense laser field causes substantial changes on the behavior of THG. In addition the position and magnitude of the resonant peak of THG coefficient is significantly affected by the magnetic field, quantum dot size and the characteristic parameters of the impurity potential.

The effects of intense laser field on optical responses of n-type delta doped GaAs quantum well under applied electric and magnetic fields

This work presents the results of the theoretical study of the effects of non-resonant intense laser field, electric and magnetic fields on optical responses of GaAs n-type δ-doped quantum well associated to the electron transitions. Optical properties are obtained by using the compact-density matrix method. The numerical results show that the applied external fields have a significant effect on the optical characteristics of these structures, such as the optical absorption coefficient and refractive index. Thus, such futures can be use to tune the optical properties of doped semiconductor heterostructures.

Symmetry in circularly polarized molecular high-order harmonic generation with intense bicircular laser pulses

We present symmetry effects of laser fields and molecular geometries in circularly polarized high-order harmonic generation by bichromatic counter-rotating circularly polarized laser pulses. Simulations are performed on oriented molecules by numerically solving time-dependent Schr\odinger equations. We discuss how electron recollision trajectories by the orthogonal laser field polarizations influence the harmonic polarization by using a time-frequency analysis of harmonics. It is found that orientation-dependent asymmetric ionization in linear molecules due to Coulomb potentials gives rise to a dependence of the polarization on the harmonic frequency. Effects of Coriolis forces are also presented on harmonic generation. Electron recollision trajectories illustrate the effects of the relative symmetry of the field and the molecule, thus paving a method for circularly polarized attosecond pulse generation and molecular orbital imaging in more complex systems.

Controllable population dynamics in Landau-quantized graphene

In this paper, we carry out a theoretical investigation on the population dynamics of graphene system under continuous-wave (cw) laser and chirped pulse excitation. Results of our numerical simulations reveal that complete population transfer from an initially occupied ground state to the initially unoccupied excited states can be achieved by choosing appropriate values of the chirp rate, the laser field intensity and frequency, as well as other system parameters. Also, we observe coherent Rabi-like population oscillations between the initial ground state and the excited final state. It is induced by the combined effect of cw and chirped-pulse laser fields. These results will contribute to the understanding of carrier-carrier and carrier-phonon interactions in graphene system, and may find applications in graphene-based high-speed electronic and optoelectronic devices.

Nonlinear optical properties of asymmetric n-type double δ-doped GaAs quantum well under intense laser field

The effect of non-resonant intense laser field on the intersubband-related optical absorption coefficient and refractive index change in the asymmetric n-type double δ-doped GaAs quantum well is theoretically investigated. The confined energy levels and corresponding wave functions of this structure are calculated by solving the Schrodinger equation in the laser-dressed confinement potential within the framework of effective mass approximation. The optical responses are reported as a function of the δ-doped impurities density and the applied non-resonant intense laser field. Additionally, the calculated results also reveal that the non-resonant intense laser field can be used as a way to control the electronic and optical properties of the low dimensional semiconductor nano-structures.

Effect of intense terahertz laser and magnetic fields on the binding energy and the transition energy of shallow impurity in a bulk semiconductor

The influences of intense terahertz laser and magnetic fields on shallow-donor states in GaAs bulk semiconductors in the Faraday geometry are studied theoretically in the framework of the effective-mass approximation. The interaction between the laser field and the semiconductor is treated nonperturbatively by solving analytically the time-dependent Schrödinger equation in which the two external fields are included exactly. In the nonresonant region, we have found that the binding and transition energies decrease with increasing laser-field intensity or decreasing laser-field frequency, and the binding energy increases with magnetic field. For relatively low radiation levels, the transition energy first slowly decreases with increasing magnetic field, but after a critical value, it rapidly increases with increasing magnetic field. However, it slowly decreases with magnetic field when the laser-field intensity is strong enough. Furthermore, in the vicinity of the resonant regime, the oscillatory behaviours of the binding and transition energies with laser-field frequency and magnetic field are observed. These results obtained indicate the possibility of manipulating the shallow impurity states in semiconductor by changing the intense laser-field frequency and intensity and the magnetic field, which gives a new degree of freedom in semiconductor device application.

Intense laser field effects on the third-harmonic generation in a quantum pseudodot system

In this research, we present the effects of high-frequency intense laser field on the third-harmonic generation associated with intersubband transitions in a two-dimensional quantum pseudodot system subjected to an uniform external magnetic field. Non-resonant monochromatic laser radiation with circular polarization is considered within the framework of high-frequency Floquet approach. On the basis of the compact-density matrix approach and an iterative method, the third-harmonic generation coefficient is calculated. The results presented for a GaAs quantum dot show that: (i) the position and magnitude of the resonant peak of third-harmonic generation depend strongly on magnetic field, the chemical potential and zero-point of pseudoharmonic potential; (ii) the strength of intense laser field modifies the confinement potential which results in considerable changes in the nonlinear optical response of the system.

Free Scattering Theory in Circularly Polarized Laser Field

<p class="Default">In the present study, we have investigated scattering of an electron by hydrogen atoms in the presence of the Circularly Polarized (CP) laser field. We have discussed the polarization effect of laser field on hydrogen atom and effect of the resulted polarized potential on differential scattering cross section is studied. We assumed the scattered electrons having kinetic energy 100 eV because it permitted to treat the scattering process in first order Born Approximation. The scattering electron was described by Volkov wave function. We found the differential scattering cross section decreases with the increase in scattering angle, for a fixed value of a laser parameters and kinetic energy of an incident electron. From this study we found that, the differential scattering cross section for the electric field perpendicular to the direction of momentum transfer depends on the elastic scattering amplitude. Finally, we concluded that the differential scattering cross section greatly depends upon the polarization of the laser field.</p><p><strong>Journal of Nepal Physical Society</strong><br />Volume 4, Issue 1, February 2017, Page: 78-87</p>