Third-order Nonlinear Optical Absorption Coefficients Research Articles

The ultrafast tunable saturable absorption of metal complexes containing redox-active 1-(2-pyridylazo)-2-acenaphthequinol ligands

The extraordinary ultrafast tunable saturable absorption properties of metal complexes M(PAAL)2 (M = Co, Ni, Cu, Zn) containing redox-active 1-(2-pyridylazo)-2-acenaphthequinol ligands (PAAL) were investigated by Z-scan and pump-probe system. The obtained third-order nonlinear optical (NLO) absorption and refraction coefficient of each metal complex reach ∼10−2 cm/GW and ∼10−6 cm2/GW at 510 nm wavelength, respectively. Meanwhile, an ultrafast carrier relaxation process of approximately (200 ± 50) fs is observed for all of them. Furthermore, we found that the third-order nonlinear absorption coefficient of M(PAAL)2 is proportional to the central metal proton number. All the NLO properties indicate that those metal complexes posses potential applications for fabricating photonic devices.

Intense laser field effects on the intersubband optical absorption and refractive index change in the [formula omitted]-doped GaAs quantum wells

In this paper, we have investigated the effects of the non-resonant intense laser field on the electronic and optical properties such as linear, nonlinear and the total optical absorption coefficient and refractive index change for transitions between two lower-lying electronic states in the GaAs-based δ-doped quantum well. Within the effective mass approximation, we calculated the eigenvalues and corresponding eigenfunctions as a function of the intense laser parameter by solving the Schrödinger equation in the laser-dressed confinement potential. The analytical expressions of the linear and third-order non-linear optical absorption coefficients and refractive index changes are obtained by using the compact-density matrix formalism. The obtained results show that the separation between ground and first excited energy levels in the δ-doped quantum well decreases in energy by the increase of the laser field intensity and this effect leads to an optical red-shift in the intersubband transitions. This behavior gives us a new degree of freedom in tunability of different device applications based on the optical transitions.

Influence of image charge effect on impurity-related optical absorption coefficients and refractive index changes in a spherical quantum dot

We have investigated the influence of an image charge effect (ICE) on the energies of the ground and first few excited states of a hydrogen-like impurity in a spherical quantum dot (QD) in the presence of an external electric field. The oscillator strengths of transitions from the 1s-like state to excited states of 2px and 2pz symmetries are calculated as the functions of the strengths of the confinement potential and the electric field. Also, we have studied the effect of image charges on linear and third-order nonlinear optical absorption coefficients and refractive index changes (RICs). The results show that image charges lead to the decrease of energies for all the hydrogen-like states, to the significant enhancement of the oscillator strengths of transitions between the impurity states, and to comparatively large blue shifts in linear, nonlinear, and total absorption coefficients and refractive index changes. Our results indicate that the total optical characteristics can be controlled by the strength of the confinement and the electric field.

Intense laser field-induced nonlinear optical properties of Morse quantum well

Abstractauthoren This paper investigates the effects of an intense laser field and electric field on the optical properties of quantum well represented by Morse potential. The non-resonant, high-frequency intense laser effects upon the system are treated within the framework of non-perturbative approach, modifying the confinement potential associated to the heterostructure. The analytical expressions of the linear and third-order nonlinear optical absorption coefficients and refractive index changes are obtained by using the compact-density matrix formalism. The results for a typical GaAs quantum well correspond to several configurations of the structural parameter, the strengths of the intense laser radiation, and the static electric field. Numerical results reveal the striking influence of the external fields on the magnitude and resonant peak energy positions of the optical absorption coefficients and refractive index changes. Besides, the control of intersubband optical transitions by the structure parameter seems feasible.

Linear and nonlinear optical absorption coefficients and refractive index changes in Morse quantum wells under electric field

In this paper, we investigate theoretically the effects of electric field on the linear and nonlinear optical properties of Morse quantum wells considering a two-level system. The effective mass approximation and the envelope function approach are used to calculate the energy levels and wave functions. The analytical expressions of the optical properties are obtained by using the compact density-matrix approach. The linear and third-order nonlinear optical absorption coefficients and the refractive index changes are investigated as a function of the incident photon energy for several configurations of the structural parameter and the applied electric field. Numerical results, presented for a typical GaAs/AlGaAs quantum well, reveal that the electric field has a significant effect on the optical characteristics of these structures and intersubband transitions can be modified by tuning the structural range parameter of the potential.

Linear and nonlinear optical properties in an asymmetric double quantum well under intense laser field: Effects of applied electric and magnetic fields

In the present study, the effects of electric and magnetic fields on the linear and third-order nonlinear optical absorption coefficients and relative change of the refractive index in asymmetric GaAs/GaAlAs double quantum wells under intense laser fields are theoretically investigated. The electric field is oriented along the growth direction of the heterostructure while the magnetic field is taken in-plane. The intense laser field is linear polarization along the growth direction. Our calculations are made using the effective-mass approximation and the compact density-matrix approach. Intense laser effects on the system are investigated with the use of the Floquet method with the consequent change in the confinement potential of heterostructures. Our results show that the increase of the electric and magnetic fields blue-shifts the peak positions of the total absorption coefficient and of the total refractive index while the increase of the intense laser field firstly blue-shifts the peak positions and later results in their red-shifting.

Effect of impurity bound polaron on optical absorption in a GaAs modified Gaussian quantum dot

In the present work, the linear, third-order nonlinear and total optical absorption coefficients of a GaAs modified Gaussian quantum dot is investigated theoretically with considering electron longitudinal optical (LO) phonon and Coulomb impurity. We have employed the Lee–Low–Pines–Huybrecht variational method to calculate the ground and first excited states energy. The absorption coefficients calculations have also been performed by using the compact density matrix approach. Our calculations have been performed for different quantum dot sizes and various confinement potentials. The absorption coefficient resonance peaks shift toward higher energies when the LO phonon and the Coulomb potential are considered. The LO phonon interaction and the Coulomb potential have play key important in optical absorption coefficients.

Optical properties of spherical quantum dot with on-center hydrogen impurity in magnetic field

This paper studies linear and nonlinear optical properties of the GaAs spherical quantum dot (QD) with impenetrable walls, containing on-center hydrogen impurity, under the presence of the static magnetic field. Transition energy and electric dipole transition matrix element between the impurity electron ground and the first excited state with \(m = 0\) have been computed using the Lagrange mesh method within the effective mass approximation. The linear and the third-order nonlinear optical absorption coefficients (ACs) are obtained using the iterative procedure in the framework of the density matrix approach, and their behavior with respect to the incident photon energy is discussed. In addition, the dependence of these coefficients on the QD radius, magnetic field strength, intensity of the applied laser field and relaxation time is studied. It has been found that for large values of relaxation time, the nonlinear AC prevails over the linear one and the total AC becomes negative.

Rashba spin-orbit coupling effects on the optical properties of double quantum wire under magnetic field

We investigate the effects of Rashba spin-orbit interaction on the optical absorption coefficients and refractive index changes associated with transitions between the first two lower-lying electronic levels in double quantum wire. The wire system represented by a symmetric, double quartic-well confinement potential is subjected to a perpendicular magnetic field. The analytical expressions of the linear and third-order nonlinear optical absorption coefficients and refractive index changes are obtained by using the compact-density matrix formalism and iterative scheme. Optical properties are investigated as a function of structural parameter, magnetic field, Rashba spin-orbit interaction and photon energies. Numerical results reveal that competing effects between spin-orbit interaction and magnetic field modify strongly the optical properties and can be altered by these parameters.

Optical absorption coefficients and refractive index changes of an on-center hydrogenic impurity in a multi-layered spherical quantum dot: effects of external fields and geometrical size

Effects of an on-center hydrogenic impurity, external electric and magnetic fields on the electronic structure, optical absorption coefficients and refractive index changes of a multi-layered spherical quantum dot are investigated. To this end, the direct matrix diagonalization method and the compact density matrix approach are respectively, used to calculate energy eigenvalues and optical properties of the system. It is found that the geometrical size, hydrogenic impurity and external fields change the electronic structure of the system. Therefore, these parameters have a great influence on the linear and the third-order nonlinear optical absorption coefficients as well as the refractive index changes of the system.

Simultaneous effects of hydrostatic pressure, temperature and electric field on optical absorption in InAs/GaAs lens shape quantum dot

In this paper, we report the theoretical calculation of the linear, third-order nonlinear and total optical absorption coefficient in a lens shaped InAs/GaAs quantum dot. The simultaneous effects of QD radius, hydrostatic pressure, temperature and applied electric field on the total optical absorption coefficient in lens-shaped InAs quantum dots are investigated under the compact density matrix formalism and the effective mass approximation. From our calculation, it is found that the sub-band energies and total optical absorption coefficient are quite sensitive to the quantum dot radius, applied hydrostatic pressure, temperature and electric field. The results show that the total optical absorption peaks position and in magnitude change as quantum dot radius, hydrostatic pressure, temperature and electric field value varies.

Noise-driven optical absorption coefficients of impurity doped quantum dots

We make an extensive investigation of linear, third-order nonlinear, and total optical absorption coefficients (ACs) of impurity doped quantum dots (QDs) in presence and absence of noise. The noise invoked in the present study is a Gaussian white noise. The quantum dot is doped with repulsive Gaussian impurity. Noise has been introduced to the system additively and multiplicatively. A perpendicular magnetic field acts as a source of confinement and a static external electric field has been applied. The AC profiles have been studied as a function of incident photon energy when several important parameters such as optical intensity, electric field strength, magnetic field strength, confinement energy, dopant location, relaxation time, Al concentration, dopant potential, and noise strength take on different values. In addition, the role of mode of application of noise (additive/multiplicative) on the AC profiles has also been analyzed meticulously. The AC profiles often consist of a number of interesting observations such as one photon resonance enhancement, shift of AC peak position, variation of AC peak intensity, and bleaching of AC peak. However, presence of noise alters the features of AC profiles and leads to some interesting manifestations. Multiplicative noise brings about more complexity in the AC profiles than its additive counterpart. The observations indeed illuminate several useful aspects in the study of linear and nonlinear optical properties of doped QD systems, specially in presence of noise. The findings are expected to be quite relevant from a technological perspective.

Spin–orbit interaction effects on the optical properties of quantum wires under the influence of in-plane magnetic fields

In this work, we studied the effects of in-plane magnetic field and Rashba spin–orbit interaction on the intersubband optical absorption coefficients and changes in refractive index for transitions between the first two lower-lying electronic levels of quantum wire represented by a parabolic confining potential. The analytical expressions of the linear and third-order nonlinear optical absorption coefficients and refractive index changes are obtained by using the compact-density matrix formalism and iterative scheme. Optical properties are investigated as a function of quantum wire radius, strength and orientation of magnetic field, strength of Rashba spin–orbit interaction and photon energies. Numerical results reveal that the optical absorption coefficients and refractive index changes are strongly affected and thus can be controlled by these parameters.

Influence of the shape of quantum dots on their optical absorptions

We have investigated the effects of the shape of quantum dots on their optical absorptions. Calculations are performed by using the matrix diagonalization method and the compact density-matrix approach within the effective-mass approximation. We have calculated the linear, third-order nonlinear and total optical absorption coefficients as a function of the incident photon energy in circular, elliptic, and triangular shaped quantum dots. Our results show that the shape of quantum dots has great influence on optical absorption coefficients.

The low-lying states and optical absorption properties of a hydrogenic impurity in a parabolic quantum dot modulation by applied electric field

Using the configuration-integration method, we investigated theoretically the low-lying states and optical absorption properties of a hydrogenic impurity in a parabolic quantum dot modulation by applied electric field. The low-lying states and optical absorption properties depend sensitively on the electric field F and the strength of the parabolic confinement ℏω0. We discuss the linear and third-order nonlinear optical absorption coefficients of the dot (i) with the impurity ion and (ii) without the impurity ion. In the first case, the increase of the parabolic confinement ℏω0 (or the electric field F) can induce the blueshift (or redshift) of the peak of the absorption coefficient. Also the optical intensity can induce the increase of the third-order nonlinear optical absorption coefficients to weaken and even bleach the total optical absorption coefficients. Similar behavior has also been observed in the second case, but there is no redshift of the peak positions of the absorption coefficient with the increase of the electric field F. Compared with the second case, it is easily seen that there are the blueshifts of the peak of the absorption coefficients, which can be used as a technical means for detecting impurities.

Extended π-conjugated ruthenium zinc-porphyrin complexes with enhanced nonlinear-optical properties.

Zinc porphyrin dimers and trimers, in which the porphyrins are connected via a ruthenium metal core, exhibit large third-order nonlinear optical absorption coefficients and refractive indices. These properties are a result of the presence of multiple porphyrins, which lead to an extension of the π-conjugated system and the octupolar effect.

Optical properties of hydrogenic impurity in an inhomogeneous infinite spherical quantum dot

In the present work, using the effective mass approximation, the Schrödinger equation of system is solved in terms of Whittaker functions. The linear and third-order nonlinear optical absorption coefficient (AC) as well as refractive index (RI) changes associated with two intersubbund transitions (1s–2p and 2p–3d) in the case of a GaAs inhomogeneous infinite spherical quantum dot are investigated at different inner radii of shell and shell thicknesses. Regarding this, the optical properties of hydrogenic system are studied by means of compact density approach and dipole approximation. The results show that the system under study is strongly affected by inner radius of shell and shell thickness changes. Also it was found that the transition between orbital with bigger l value shift to higher photon energy region.

Linear and nonlinear intra-conduction band optical absorption in (In,Ga)N/GaN spherical QD under hydrostatic pressure

Linear, third-order nonlinear and total optical absorption coefficients of intra-conduction band 1s–1p transition with hydrogenic shallow-donor impurity in wurtzite (In,Ga)N/GaN spherical quantum dot are reported. Hydrostatic pressure effect is investigated within the framework of single band effective-mass approximation using a combination of Quantum Genetic Algorithm (QGA) and Hartree–Fock–Roothaan (HFR) method. The results show that the pressure has a great influence on optical absorption coefficients of QDs. A blue-shift of the resonant peak is observed while the maximum of the amplitude of optical absorption coefficients decreases under hydrostatic pressure effect. A good agreement is shown compared with results of the finding.

Simultaneous Effects of External Electric Field and Conduction Band Nonparabolicity on Optical Properties of a GaAs Quantum Dot Embedded at the Center of a GaAlAs Nano-Wire

An investigation of the optical properties of a GaAs spherical quantum dot which is located at the center of a Ga1−xAlxAs cylindrical nano-wire has been performed in the presence of an external electric held. The band nonparabolicity effect is also considered using the energy dependent effective mass approximation. The energy eigenvalues and corresponding wave functions are calculated by finite difference approximation and the reliability of calculated wave functions is checked by computing orthogonality. Using computed energy eigenvalues and wave functions, the linear, third-order nonlinear and total optical absorption coefficients and refractive index changes are examined in detail. It is found that (i) Presence of electric field causes both blue and red shifts in absorption spectrum; (ii) The absorption coefficients shift toward lower energies by taking into account the conduction band nonparabolicity; (iii) For large values of electric field the effect of conduction band nonparabolicity is less dominant and parabolic band is estimated correctly; (iv) In the presence of electric field and conduction band nonparabolicity the nonlinear term of absorption coefficient rapidly increases by increasing incident optical intensity. In other words, the saturation in optical spectrum occurs at lower incident optical intensities.

Nonlinear intersubband optical absorption in semiparabolic quantum wells

The linear and third-order nonlinear optical absorptions in semiparabolic quantum wells are studied in detail. Analytic formulas for the linear and third-order nonlinear optical absorption coefficients are obtained using the compact density matrix approach. Based on this model, numerical results are presented for typical GaAs/AlGaAs semiparabolic quantum wells. The results show that the factors of the incident optical intensity and the semiparabolic confinement frequency have great influences on the total optical absorption coefficients.