Incident Optical Intensity Research Articles

Linear and nonlinear optical absorption coefficients in inverse parabolic quantum wells under static external electric field

In the present theoretical study, the linear and third-order nonlinear optical absorption coefficients have been calculated in GaAs/Ga1−xAlxAs inverse parabolic quantum wells (single and double) subjected to an external electric field. Our calculations are based on the potential morphing method in the effective mass approximation. The systematic theoretical investigation contains results with all possible combinations of the involved parameters, as quantum well width, quantum barrier width, Al concentration at each well center and magnitude of the external electric field. Our results indicate that in most cases investigated, the increase of the electric field blue-shifts the peak positions of the total absorption coefficient. In all cases studied it became apparent that the incident optical intensity considerably affects the total absorption coefficient.

Linear and nonlinear intersubband optical absorption coefficients and refractive index changes in symmetric double semi-V-shaped quantum wells

In this study, the changes in the refractive index and intersubband optical absorption coefficients in symmetric double semi-V-shaped quantum wells are investigated theoretically. The energy levels and the envelope wave functions of an electron confined in finite potential double semi-V-shaped quantum wells are calculated within the effective-mass approximation framework. The analytical expressions of the refractive index and intersubband optical absorption coefficients are obtained using the compact density matrix approach. The effects of the incident optical intensity and structure parameters, such as the barrier width, confinement potential and the well width, on the optical properties of the double semi-V-shaped quantum wells are investigated. The numerical results show that both the incident optical intensity and structure paremeters have a great effect on the optical characteristics of these structures.

Electric‐field‐induced optical absorption and refractive‐index changes of a shallow hydrogenic impurity in an InAs/GaAs quantum wire

AbstractThe effect of electric‐field strength on the binding energy of a hydrogenic impurity in an InAs/GaAs quantum wire is discussed. Calculations have been performed using Bessel functions as an orthonormal basis within a single‐band effective‐mass approximation. The electric‐field‐induced photoionization cross section of the hydrogenic impurity is investigated. The total optical absorption and the refractive‐index changes as a function of normalized photon energy between the ground and the first excited state under the influence of an electric field are analyzed. The optical absorption coefficients and the refractive‐index changes strongly depend on the incident optical intensity and the electric‐field intensity.

Pressure induced optical absorption and refractive index changes of a shallow hydrogenic impurity in a quantum wire

Pressure induced binding energy of a hydrogenic impurity in an InAs/GaAs quantum wire is investigated. Calculations are performed using Bessel functions as an orthonormal basis within a single band effective mass approximation using variational method. Photoionization cross-section of the hydrogenic impurity in the influence of pressure 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 pressure are analyzed. The optical absorption coefficients and the refractive index changes strongly depend on the incident optical intensity and pressure. The occurred blue shift of the resonant peak due to the pressure gives 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 pressure.

The linear and nonlinear intersubband optical absorption coefficients and refractive index changes in a V-shaped quantum well under the applied electric and magnetic fields

In this study, the changes in the optical absorption coefficients and the refractive index in a V-shaped quantum well have investigated theoretically. Within the effective mass approximation, the electronic structure of the V-shaped quantum well is calculated by numerical methods from the Schrödinger equation. Optical properties are obtained using the compact density-matrix approach. In the present work, the linear, third-order nonlinear and total absorption and refractive index changes investigated as a function of the quantum well width, the incident optical intensity, strengths of the magnetic and electric fields. Our results show that the magnetic and electric fields strengths, the quantum well width and incident optical intensity have a great effect on the optical characteristics of these structures.

Effect of position-dependent effective mass on linear and nonlinear optical properties of a cubic quantum dot

In this paper, we first obtain an analytic relation for studying the position-dependent effective mass in a GaAs/Al x Ga 1− x As cubic quantum dot. Then, the effect of position-dependent effective mass on the intersubband optical absorption coefficient and the refractive index change in the quantum dot are studied. Our numerical calculations are performed using both a constant effective mass and the position-dependent effective mass. We calculate the linear, nonlinear and total intersubband absorption coefficient and refractive index change as a function of the incident optical intensity and structural parameters such as dot length. The results obtained from the present work show that spatially varying electron effective mass plays an important role in the intersubband optical absorption coefficient and refractive index change in a cubic quantum dot.

Intersubband optical absorption coefficients and refractive index changes in modulation-doped asymmetric double quantum well

The linear and the third-order nonlinear optical absorption coefficients and refractive index changes in a modulation-doped asymmetric double quantum well are studied theoretically. The electron energy levels and the envelope wave functions in this structure are calculated by the Schrödinger and Poisson equations self-consistently in the effective mass approximation. The analytical expressions of optical properties are obtained by using the compact density-matrix approach. In this regard, the linear, nonlinear and total intersubband absorption coefficients and refractive index changes are investigated as a function of right-well width ( L w 2 ) of asymmetric double quantum well. Our results show that the total absorption coefficients and refractive index changes shift toward higher energies as the right-well width decreases. In addition, the total optical absorption coefficients and refractive index changes is strongly dependent on the incident optical intensity.

Study of optical properties in a cubic quantum dot

In this paper, the effect of hydrostatic pressure on both the intersubband optical absorption coefficients and the refractive index changes is studied for typical GaAs/Al x Ga1−x As cubic quantum dot. We use analytical expressions for the linear and third-order nonlinear intersubband absorption coefficients and refractive index changes obtained by the compact-density matrix formalism. The linear, third-order nonlinear, and total intersubband absorption coefficients and refractive index changes are calculated at different pressures as a function of the photon energy with known values of box length (L), the incident optical intensity (I), and Al concentration (x). According to the results obtained from the present work, we have found that the pressure plays an important role in the intersubband optical absorption coefficient and refractive index changes in a cubic quantum dot.

Intensity-dependent nonlinear optical properties in a modulation-doped single quantum well

In the present work, the changes in the intersubband optical absorption coefficients and the refractive index in a modulation-doped quantum well have been investigated theoretically. Within the envelope function approach and the effective mass approximation, the electronic structure of the quantum well is calculated from the self-consistent numerical solution of the coupled Schrödinger–Poisson equations. The analytical expressions of optical properties are obtained by using the compact density-matrix approach. The numerical results GaAs/Al x Ga 1− x As are presented for typical modulation-doped quantum well system. The linear, third-order nonlinear and total absorption and refractive index changes depending on the doping concentration are investigated as a function of the incident optical intensity and structure parameters, such as quantum well width and stoichiometric ratio. The results show that the doping concentration, the structure parameters and the incident optical intensity have a great effect on the optical characteristics of these structures.

Exciton effects on the refractive index and optical absorption in wurtzite quantum wells via a fractional-dimensional space approach

The optical refractive index changes and absorption coefficients of quantum wells (QWs) are theoretically investigated with considering exciton effects within the framework of the fractional-dimensional space approach. The exciton wave functions and bound energies are obtained as a function of spatial dimensionality, and the dimension increases with the well width increasing. Then optical properties are obtained by using the compact-density matrix approach and an iterative method. Numerical results are presented for wurtzite ZnO/MgxZn1−xO QWs. The calculated results show that the changes of refractive index and absorption coefficients are greatly enhanced due to the quantum confinement of exciton. And the smaller the QW width (dimension) is, the larger influence of exciton on the optical properties will be. Furthermore, the exciton effects make the resonant peaks move to a lower energy. In addition, the optical properties are related to the QW width, the incident optical intensity and carrier density.

Highly flexible all-optical metamaterial absorption switching assisted by Kerr-nonlinear effect

A three-dimensional metamaterial nanostructure for realizing all-optical absorption switching is proposed and investigated. The structure consists of dual metallic layers for allowing near-perfect absorption due to electric and magnetic resonances, and a nonlinear Kerr-dielectric layer for actively manipulating the nanostructure absorption. The finite-difference time-domain simulation results demonstrate that, by adjusting the incident optical intensity, the metamaterial absorption can be flexibly tuned from near unity to zero. The all-optical absorption switching structure can find potential applications in actively integrated photonic circuits for thermal sensing, photo detecting, and optical imaging.

Nonlinear optical properties of an off-center donor in a quantum dot under applied magnetic field

The nonlinear optical properties of an off-center hydrogenic donor in a two-dimensional quantum dot under applied magnetic field are investigated in detail by using the matrix diagonalization method. Based on the computed energies and wave functions, the linear, third-order and total optical absorption coefficients as well as the refractive index changes have been examined between the ground state ( L = 0 ) and the first excited state ( L = 1 ) . The results show that the ion position, the applied magnetic field, the confinement frequency, and the incident optical intensity have an important influence on the nonlinear optical properties of off-center donors.

Intersubband optical absorption coefficients and refractive index changes in a V‐groove quantum wire

AbstractIn this paper, the intersubband optical absorption coefficients and the refractive index changes are studied in a V‐groove quantum wire. We use analytical expressions for these properties obtained by the compact‐density matrix formalism. In this regard, the linear, nonlinear and total intersubband absorption coefficients and refractive index changes are investigated as a function of the bend width wire (b), the incident optical intensity (I), and the angle θ. According to the results obtained from the present work, it is deduced that: (i) The linear terms in the refractive index changes and absorption coefficients dose not change with incident optical intensity whereas nonlinear terms depend on incident optical intensity; (ii) The total refractive index changes and the absorption coefficients reduce as the incident optical intensity increases; (iii) The total absorption coefficient and refractive index changes increase and also shift toward higher energies as the bend width wire increases; and (iv) The total refractive index changes and absorption coefficients shift toward higher energies as the angle θ increases.

Nonlinear absorption spectra for intersubband transitions of CdSe/ZnS spherical quantum dots

The electronic structure and optical properties of a one-electron quantum dot (QD) were investigated by assuming a spherically symmetric confining potential of finite depth. In this particular case CdSe is surrounded by ZnS. The energy eigenvalues and wave functions dependence on QD dimension were calculated by using effective mass approximation. We also calculated energies of s, p, and d states, oscillator strengths, and the linear and third-order nonlinear intersubband optical absorption coefficients as a function of the QD dimension, incident photon energy, and incident optical intensity for the 1s-1p, 1p-1d, and 1p-2s transitions. Even in a simple composition, QD correct calculation of oscillator strength differs from the simplified approach in the most sensitive QD radius region below one Bohr radius.

Multistability at arbitrary low optical intensities in a metal-dielectric layered structure

We show that a nonlinear metal-dielectric layered slab of subwavelength thickness and very small average dielectric permittivity displays optical multistable behavior at arbitrary low optical intensities. This is due to the fact that, in the presence of the small linear permittivity, one of the multiple electromagnetic slab states exists no matter how small is the transmitted optical intensity. We prove that multiple states at ultra-low optical intensities can be reached only by simultaneously operating on the incident optical intensity and incidence angle. By performing full wave simulations, we prove that the predicted phenomenology is feasible and very robust.

Linear and nonlinear optical absorption coefficients in an asymmetric graded ridge quantum wire

In this article, the optical absorption coefficients in an asymmetric ridge quantum wire within the framework of the density matrix formalism are studied. The energy spectrum and wave functions of a quantum wire with graded confinement potential using the effective mass approximation are analytically calculated. The results show that parameters such as the asymmetry and width of the potential well change the position and magnitude of the absorption peak and saturation intensity. The incident optical intensity also has a great effect on the total absorption.

Linear and nonlinear optical properties of strained GaN/AlN quantum dots: Effects of impurities, radii of QDs, and the incident optical intensity

The linear and nonlinear optical properties of cylinder GaN/AlN quantum dots with strain effects and impurity are investigated by taking into account the effects of the deformation potential and piezoelectric potential on the conduction band edge. The results are presented as a function of photon energies and QD radii. The optical absorption spectrum and refractive index changes have a blueshift in the presence of the impurity. With increasing distance of the impurity’s position along the growth direction, the peak values of the refractive index changes decrease and shift to higher photon energy. When the sizes of the QDs increase, redshift effects are observed and the relative amplitudes diminish. It can be found that the nonlinear effect becomes obvious with increase of the incident optical intensity. Then there is a “hole-burning” in the absorption coefficient spectra and two new peaks will appear in the total refractive index change spectrum when the optical intensity becomes larger enough. Finally it can be concluded that the intensity of the incident light and the position of the impurity play an important role in the linear and nonlinear optical properties.

Nonlinear optical absorption coefficients and refractive index changes in a two-dimensional system

The nonlinear optical absorption coefficients and refractive index changes in a two-dimensional system are theoretically investigated. It is shown that the factors of the incident optical intensity, the relaxation time and the carrier density of the system have important influences on the optical absorption coefficients and refractive index changes. Moreover, the optical absorption coefficients are strongly bleached with the incident optical intensity and the relaxation time increasing.

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.

Nanostructure-enhanced laser tweezers for efficient trapping and alignment of particles.

We propose and demonstrate a purely optical approach to trap and align particles using the interaction of polarized light with periodic nanostructures to generate enhanced trapping force. With a weakly focused laser beam, we observed efficient trapping and transportation of polystyrene beads with sizes ranging from 10 μm down to 190 nm as well as cancer cell nuclei. In addition, alignment of non-spherical dielectric particles to a 1-D periodic nanostructure was achieved with low laser intensity without attachment to birefringent crystals. Bacterial cells were trapped and aligned with incident optical intensity as low as 17 μW/μm2.