Linear and nonlinear optical properties in a disk-shaped quantum dot with a parabolic potential plus a hyperbolic potential in a static magnetic field

Linear and nonlinear optical properties in a disk-shaped quantum dot (DSQD) with a parabolic potential plus a hyperbolic potential in a static magnetic field are theoretically investigated within the framework of the compact-density-matrix approach and iterative method. The energy levels and the wave functions of an electron are obtained by three kinds of approximation methods. It is found that optical absorption coefficients and refractive index changes are not only by the characteristic parameters of the hyperbolic potential and the confinement frequency, but also by the magnetic field.     

Effect of laser radiation on optical properties of disk shaped quantum dot in magnetic fields

The optical absorption coefficients and changes in the refractive index in GaAs/AlGaAs, disk shaped quantum dots (DSQD) with simultaneously applied laser and magnetic field are studied in detail. The use of the density matrix formalism is made to study the variations in linear and non-linear polarizability with the frequency of the electric field. It is found that the absorption coefficient and the refractive index changes depend not only on the optical wave but also on the strength of the static magnetic field.     

Second harmonic generation in a disk shaped quantum dot in the presence of spin-orbit interaction

The second harmonic generation (SHG) coefficients for a disk shaped quantum dot (DSQD) in the magnetic field are studied in the presence of spin-orbit interactions (SOI). The spin-orbit terms we have used in our calculations are both Rashba and Dresselhaus. We have shown that the presence of SOI modifies the SHG terms. In addition, it has been shown that SOI coupling terms influence the spectrum of DSQD resulting in defined changes in the harmonic generation.     

Electronic and optical properties of a nanoring in the presence of external magnetic field

Optical properties of a nanoring with Winternitz–Smorodinsky confinement potential in the presence of an external magnetic field have been studied theoretically. Our results demonstrate that energy, oscillator strength and the linear, nonlinear and total absorption are strongly affected by size of the nanoring. Also, we found that magnetic field has little influence on energy difference, oscillator strength and optical absorption of the nanoring.     

Modified Debye screening potential in a magnetized quantum plasma

The effects of quantum mechanical influence and uniform static magnetic field on the Shukla-Nambu-Salimullah potential in an ultracold homogeneous electron-ion Fermi plasma have been examined in detail. It is noticed that the strong quantum effect arising through the Bohm potential and the ion polarization effect can give rise to a new oscillatory behavior of the screening potential beyond the shielding cloud which could explain a new type of possible robust ordered structure formation in the quantum magnetoplasma. However, the magnetic field enhances the Debye length perpendicular to the magnetic field in the weak quantum limit of the quantum plasma.     

Exciton optical absorption coefficients and refractive index changes in a strained InAs/GaAs quantum wire: The effect of the magnetic field

Magnetic field induced exciton binding energy is investigated in a strained InAs/GaAs quantum wire within the framework of single band effective mass approximation. The strain contribution to the potential is determined through deformation potentials. The interband emission energy of strained InAs/GaAs wire is investigated in the influence of magnetic field with the various structural parameters. Magnetic field induced photoionization cross section of the exciton is studied. The total optical absorption and the refractive index changes as a function of normalized photon energy between the ground and the first excited state in the presence of magnetic field are analyzed. The optical absorption coefficients and the refractive index changes strongly depend on the incident optical intensity and the magnetic field. The occurred blueshift of the resonant peak due to the magnetic field will give the information about the variation of two energy levels in the quantum well wire. The optical absorption coefficients and the refractive index changes are strongly dependent on the incident optical intensity and the magnetic field.     

Intersubband optical absorption coefficient changes and refractive index changes in a two-dimensional quantum pseudodot system

The optical absorption coefficient changes and refractive index changes associated with intersubband transitions in a two-dimensional quantum pseudodot system under the influence of a uniform magnetic field are theoretically investigated. In this regard, the electronic structure of the pseudodot system is studied using the one-band effective mass theory, and by means of the compact density matrix approach linear and nonlinear optical absorption coefficient and refractive index changes are calculated. The effects of an external magnetic field and the geometrical size of the pseudodot system on the optical absorption coefficient and refractive index changes are investigated. It is found that the absorption coefficient and refractive index changes are strongly affected not only by an external magnetic field but also by the geometrical size of the pseudodot system.     

Off-centre impurity-related nonlinear optical absorption,second and third harmonic generation in a two-dimensional quantum ring under magnetic field

Abstract

The effects of an off-centre donor impurity on the non-linear optical absorption, second and third harmonic generation in a GaAs two-dimensional disc-shaped quantum ring under magnetic field are investigated within the compact density-matrix formalism and the effective mass approximation. The results reveal that: (i) the absorption spectra extend on larger energy intervals at the increment of the magnetic field; (ii) the possibility of generating second harmonic response from the system is demonstrated for an impurity placed on the repulsive part of the confining potential; (iii) both second harmonic and third harmonic coefficients are one order of magnitude larger for an impurity placed on the repulsive part of the potential and are blue-shifted by the increment of the magnetic field regardless the impurity position.     

Excitons and magnetoexcitons in coupled quantum nanostructures: the role of a dirty environment

The effect of a random field caused by impurities, interface roughness and so on, on the optical properties and superfluidity of a quasi-two-dimensional system of excitons is studied. The influence of a random field on the density of the superfluid component of excitonic systems at low temperatures is investigated. For quasi-two-dimensional excitonic systems in a random field the Kosterlitz–Thouless temperature in the superfluid state is calculated. The superfluidity and Bose–Einstein condensation of indirect excitons in coupled quantum dots are studied. Magnetoexciton light absorption in the disordered quantum wells is considered. The two-particle problem of the magnetoexciton motion in the external field depending on the external magnetic field is reduced to the one-particle motion with effective magnetic mass in some effective field. The energy and optical absorption of the magnetoexciton in a single and coupled quantum dots are studied using the effective-magnetic-mass Hamiltonian. In the coherent potential approximation the coefficient of magnetoexciton optical absorption in single and coupled quantum wells is calculated. In the strong magnetic fields the exciton peak decreases with magnetic field increasing in accordance with the experimental data. The localization of direct and indirect magnetoexcitons is investigated. Received: 14 April 2000 / Accepted: 17 April 2000 / Published online: 6 September 2000     

Linear and Nonlinear Optical Absorptions of a Hydrogenic Donor in a Quantum Dot Under a Magnetic Field

The linear and nonlinear optical properties of a hydrogenic donor in a disc-like parabolic quantum dot in the presence of an external magnetic field are studied. The calculations were performed within the effective mass approximation, using the matrix diagonalization method and the compact density-matrix approach. The linear and nonlinear optical absorption coefficients between the ground （L =0） and the first excited state （L = 1） have been examined based on the computed energies and wave functions. We find that the linear, nonlinear third-order, and total optical absorption coefficients are strongly affected by the confinement strength of QDs, the external magnetic field, and the incident optical intensity.     

Wideband magneto-optic modulation in a bismuth-substituted yttrium iron garnet waveguide

We present a tunable wideband bismuth-substituted yttrium iron garnet (Bi-YIG) waveguide magneto-optic (MO) modulator. High-speed current transients are used to switch the in-plane magnetization of the film, which modulates an 800 nm optical beam. Large bandwidth optical modulation is achieved by driving the device in a non-resonant mode that is well below the ferromagnetic resonance frequency of the film. The MO modulator has the potential of operating at bandwidths higher than 1 GHz by tuning the applied static magnetic field.     

Intersubband optical absorption in a quantum well under a tilted magnetic field

By using an appropriate coordinate transform we have calculated the intersubband optical absorption in the single square well under a tilted magnetic field. In this study the dependence of the intersubband transitions on the magnetic field strength and the direction of the magnetic field (tilt angle) is discussed. We show that intersubband optical absorption is sensitive to the tilt angle. This behaviour in the intersubband optical absorption gives a new degree of freedom in regions of interest device applications.     

Third-harmonic generation in cylindrical parabolic quantum wires with static magnetic fields

The third-harmonic generation (THG) and its conversion efficiency in Al_xGa_1-xAs/GaAs cylindrical parabolic quantum wires with static magnetic fields are studied in detail. The calculated results show that the parabolic confining potential and the static magnetic field have evident influence on the THG and its conversion efficiency. In addition, the conversion efficiency of the THG is also related to the input optical intensity. It is noted that very high conversion efficiency of the THG can be obtained by increasing properly the input optical intensity and choosing an optimized parabolic confining potential and applied static magnetic field.     

Polaron effects on the optical rectification in a two-dimensional quantum pseudodot system

Using the compact density-matrix approach and the iterative method, the optical rectification in a two-dimensional quantum pseudodot system under the influence of a static magnetic field is theoretically investigated. The effects of an external magnetic field and the geometrical size of the pseudodot system on the optical rectification are presented. What’s more, we find that the polaron effect has an important influence on the optical rectification.     

Cyclotron dynamics of neutral atoms in optical lattices with additional magnetic field and harmonic trap potential

We analytically and numerically discuss the stability and dynamics of neutral atoms in a two-dimensional optical lattice subjected to an additional harmonic trap potential and artificial magnetic field. The harmonic trap potential plays a key role in modifying the equilibrium state properties of the system and stabilizing the cyclotron orbits of the condensate.Meanwhile, the presence of the harmonic trap potential and lattice potential results in rich cyclotron dynamics of the condensate. The coupling effects of lattice potential, artificial magnetic field, and harmonic trap potential lead to single periodic, multi-periodic or quasi-periodic cyclotron orbits of the condensate. So we can control the cyclotron dynamics of neutral atoms in optical lattice by manipulating the strength of harmonic confinement, artificial magnetic field, and initial conditions. Our results provide a direct theoretical evidence for the cyclotron dynamics of neutral atoms in optical lattices exposed to the artificial gauge magnetic field and harmonic trap potential.     

Superfluid and dissipative dynamics of a Bose-Einstein condensate in a periodic optical potential

We create Bose-Einstein condensates of 87Rb in a static magnetic trap with a superimposed blue-detuned 1D optical lattice. By displacing the magnetic trap center we are able to control the condensate evolution. We observe a change in the frequency of the center-of-mass oscillation in the harmonic trapping potential, in analogy with an increase in effective mass. For fluid velocities greater than a local speed of sound, we observe the onset of dissipative processes up to full removal of the superfluid component. A parallel simulation study visualizes the dynamics of the Bose-Einstein condensate and accounts for the main features of the observed behavior.     

Exciton related optical absorption in a spherical quantum dot

An exciton in a spherical quantum dot is studied analytically within the effective mass approximation. A parabolic confinement under an electric field is considered. The linear and nonlinear optical absorption coefficients are calculated within the density matrix formalism. No assumptions are made about the strength of the confinement. It is shown how the competing mechanisms of the Coulomb interaction, the confinement and the applied static electric field affect the optical absorption.     

Effect of magnetic fields on the linear and nonlinear intersubband optical absorption coefficients and refractive index changes in square and graded quantum wells

In this study, both the intersubband optical absorption coefficients and the refractive index changes as dependent on the magnetic field are calculated in square and graded quantum wells. Our results show that the position and the magnitude of the linear and total absorption coefficients and refractive index changes depend on the magnetic field strength and the shape of potential. The incident optical intensity has a great effect on the total absorption and refractive index changes.     

Brownian particle in an optical potential of the washboard type

Experimental observations of the fluctuation-driven net transport of silica microspheres are presented in a two-dimensional optical potential of circular symmetry created by a Bessel light beam. The optical field is tailored to break symmetry and create a static tilted periodic (washboard) potential. As the tilt of potential exceeds a threshold, a transition between locked and running modes is observed. The running mode manifests itself by the rapid accumulation of particles at the beam center.     

Optical properties of a donor impurity in a two-dimensional quantum pseudodot

We investigate the linear and nonlinear optical properties of a donor impurity confined by a two-dimensional pseudoharmonic potential both including harmonic dot and antidot potentials in the presence of a strong magnetic field. Calculations are made by using the perturbation method and the compact density-matrix approach within the effective-mass approximation. Based on the computed energies and wave functions, the linear, third-order nonlinear and total optical absorption coefficients as well as the refractive index changes have been examined. The results are presented as a function of the incident photon energy for the different values of the chemical potential of the electron gas and the zero point of the pseudoharmonic potential. The results show that the optical properties of a donor impurity in a two-dimensional pseudoharmonic QD are strongly affected by the zero point of the pseudoharmonic potential, the chemical potential of the electron gas and the Coulomb interaction.