Nonlinear Optical Absorption Coefficients Research Articles

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.

Effect of Si δ-Doping on the Linear and Nonlinear Optical Absorptions and Refractive Index Changes in InAlN/GaN Single Quantum Wells**Supported by the Deanship of Scientific Research of University of Dammam under Grant No 2015134.

In the framework of effective mass approximation, we theoretically investigate the electronic structure of the Si δ-doped InAlN/GaN single quantum well by solving numerically the coupled equations Schrödinger–Poisson self-consistently. The linear, nonlinear optical absorption coefficients and relative refractive index changes are calculated as functions of the doping concentration and its thickness. The obtained results show that the position and the amplitude of the linear and total optical absorption coefficients and the refractive index changes can be modified by varying the doping concentration and its thickness. In addition, it is found that the maximum of the optical absorption can be red-shifted or blue-shifted by varying the doping concentration. The obtained results are important for the design of various electronic components such as high-power FETs and infrared photonic devices.

Third-order nonlinear optical investigations of the 1,1′-methylenedipyridinium tetrachloridocuprate(II) using Z-scan technique

We report here the third order nonlinear optical properties of the 1,1′-methylenedipyridinium tetrachloridocuprate(II) in chloroform (CHCl3) solution using Z-scan technique. Measurements were performed with a CW Diode laser at 635nm wavelength and 26mW power. The nonlinear optical absorption coefficient (β) and nonlinear refraction (n2) were of the order 4.46×10−4cm/W and 3.74×10−8cm2/W, respectively. The operating mechanism is reverse saturable absorption (RSA) as the excited-state absorption cross-section was found higher than ground state absorption cross-section. The magnitude of nonlinear absorption coefficient (β) was found decreasing with on-axis input intensity (I0). Our results suggest that this material is considered as a promising candidate for future optical devices applications.

Nonlinear optical response in a zincblende GaN cylindrical quantum dot with donor impurity center

We calculate the nonlinear optical absorption coefficient of a cylindrical zincblende GaN-based quantum dot. For this purpose, we consider Coulomb interactions between electrons and an impurity ionized donor atom. The electron-donor-impurity spectrum and the associated quantum states are calculated using the effective mass approximation with a parabolic potential energy model describing both the radial and axial electron confinement. We also include the effects of the hydrostatic pressure and external electrostatic fields. The energy spectrum is obtained through an expansion of the eigenstates as a linear combination of Gaussian-type functions which reduces the computational effort since all the matrix elements are obtained analytically. Therefore, the numerical problem is reduced to the direct diagonalization of the Hamiltonian. The obtained energies are used in the evaluation of the dielectric susceptibility and the nonlinear optical absorption coefficient within a modified two-level approach in a rotating wave approximation. This quantity is investigated as a function of the quantum dot dimensions, the impurity position, the external electric field intensity and the hydrostatic pressure. The results of this research could be important in the design and fabrication of zincblende GaN-quantum-dot-based electro-optical devices.

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.

Optical nonlinearity investigation of the tetracarbonyl(2,2′-bipyridyl)molybdenum(0) using Z-scan technique

Abstract The third order nonlinear optical properties of the Tetracarbonyl(2,2′-bipyridyl)molybdenum(0) in CHCl 3 solution have been studied using Z-scan technique. Measurements were performed with a CW Diode laser at 635 nm wavelength and 15 mW power. The nonlinear optical absorption coefficient ( β ) and nonlinear refraction ( n 2 ) were found at 2.86 × 10 −3 cm/W and 4.28 × 10 −7 cm 2 /W respectively. The nonlinear absorption coefficient β values decrease with increase in on-axis input intensity I 0 . The reverse saturable absorption (RSA) mechanism was responsible for the optical limiting effect. The results suggest that this material is considered as a promising candidate for future optical devices applications.

The effect of hydrostatic pressure, temperature and magnetic field on the nonlinear optical properties of asymmetrical Gaussian potential quantum wells

In this study, simultaneous effects of hydrostatic pressure, temperature and magnetic field on the linear and nonlinear intersubband optical absorption coefficients (OACs) and refractive index changes (RICs) in asymmetrical Gaussian potential quantum wells (QWs) are theoretically investigated within the framework of the compact-density-matrix approach and iterative method. The energy eigenvalues and their corresponding eigenfunctions of the system are calculated with the differential method. Our results show that the position and the magnitude of the resonant peaks of the nonlinear OACs and RICs depend strongly on the hydrostatic pressure, temperature and external magnetic field. This gives a new degree of freedom in various device applications based on the intersubband transitions of electrons.

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.

Investigation of optical nonlinearity of 8-hydroxyquinolinium 2-chloroacetate and 8-hydroxyquinolinium (Z)-3-carboxyacrylate salts by Z-scan technique

A novel two organic salts: 8-hydroxyquinolinium 2-chloroacetate and 8-hydroxyquinolinium (Z)-3-carboxyacrylate were synthesized and characterized using UV–visible, FTIR and NMR measurements. The characterization spectra confirm the expected molecular structure of the prepared salts. The Z-scan technique is used to achieve optical nonlinearity measurements with a CW Diode laser at 635nm wavelength and 14.5mW power. The nonlinear optical absorption coefficient (β) and nonlinear refraction (n2) of the two studied compounds were affected by Cl group more than OH. The reverse saturable absorption (RSA) mechanism was responsible for the optical limiting effect. The results suggest that this material considers as a promising candidate for future optical devices applications.

Excitonic effects on linear and nonlinear optical absorption coefficients and refractive index changes in one-dimensional quantum dots with linear potential

Excitonic effects on linear and nonlinear optical absorption coefficients (OAC) and refractive index changes (RIC) in one-dimensional quantum dots with linear potential are theoretically investigated within the framework of the compact-density-matrix approach and iterative method. It is found that linear and nonlinear OAC and RIC with excitonic effects in one-dimensional quantum dots are larger than that without excitonic effects. Besides, when excitonic effects are considered, our results show a remarkable dependence of linear and nonlinear OAC and RIC on linear potential.

The effects of pressure and hydrogenic donor impurity on the linear and nonlinear optical properties of a GaAs/GaAlAs nanowire superlattice

The combined effects of hydrostatic pressure, presence and absence of hydrogenic donor impurity are investigated on the linear and nonlinear optical absorption coefficients and refractive index changes of a GaAs/Ga1−xAlxAs nanowire superlattice. The wave functions and corresponding eigenvalues are calculated using finite difference method in the framework of effective mass approximation. Analytical expressions for the linear and third order nonlinear optical absorption coefficients and refractive index changes are obtained by means of compact-density matrix formalism. The linear and third order nonlinear absorption coefficient and refractive index changes are presented as a function of photon energy for different values of hydrostatic pressure, incident photon intensity and relaxation time in the presence and absence of hydrogenic donor impurity. It is found that the linear and third order nonlinear absorption coefficients, refractive index changes and resonance energy are quite sensitive to the presence of impurity and applied hydrostatic pressure. Moreover, the saturation in optical spectrum and relaxation time can be adjusted by increasing pressure in presence of impurity whereas the effect of hydrostatic pressure is negligible in the case of absence of hydrogenic impurity.

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.

Study of electron-related intersubband optical properties in three coupled quantum wells wires with triangular transversal section

This work concerns theoretical study of confined electrons in a low-dimensional structure consisting of three coupled triangular GaAs/AlxGa1−xAs quantum wires. Calculations have been made in the effective mass and parabolic band approximations. In the calculations a diagonalization method to find the eigenfunctions and eigenvalues of the Hamiltonian was used. A comparative analysis of linear and nonlinear optical absorption coefficients and the relative change in the refractive index was made, which is tied to the intersubband electron transitions.

Linear and nonlinear optical absorption coefficients of spherical dome shells

Linear and nonlinear optical absorption coefficients of spherical dome shells are theoretically investigated within analytical wave functions and numerical quantized energy levels. Our results show that the inner radius, the outer radius and the cut-off angle of spherical dome shells have great influences on linear and nonlinear optical absorption coefficients as well as the total optical absorption coefficients. It is found that with the increase of the inner radius and the outer radius, linear and nonlinear optical absorption coefficients exhibit a blueshift and a redshift, respectively. However, with the increase of the cut-off angle, linear and nonlinear optical absorption coefficients do not shift. Besides, the resonant peaks of linear and nonlinear optical absorption coefficients climb up and then decrease with increasing the cut-off angle. The influences of the incident optical intensity on the total optical absorption coefficients are studied. It is found that the bleaching effect occurs at higher incident optical intensity.

Absorption Spectra and Refractive Index Changes of an Exciton in a Core/Shell Quantum Dot

The absorption spectra and the refractive index changes are calculated theoretically for an exciton in a core/shell quantum dot. The advantage of our methodology is that one can investigate the influence of the repulsive core by varying two parameters in the confinement potential. The dimensionality effect of exciton quantum dots on the optical absorptions has been studied. It has been found that in the same regime, the optical absorption intensities of excitons are much smaller for the core/shell quantum dots than for the two-dimensional quantum rings. The linear and the nonlinear optical absorption coefficients and refractive index changes have been examined with the change of the confinement potential. The results show that the optical absorptions and the refractive index changes are strongly affected by the repulsive core of core/shell quantum dots. Moreover, the calculated results also reveal that as the inner radius increases, the peak values of the absorption coefficients and the refractive index changes of an exciton will show the optical Aharonov-Bohm oscillation in core/shell quantum dots.

Nonlinear optical absorption investigations of the novel organic–inorganic hybrid salt: Bis[1,1′-methylenedipyridinium] hexacyanidoferrate(II) octahydrate by Z-scan technique

The organic–inorganic hybrid salt: bis[1,1′-methylenedipyridinium] hexacyanidoferrate(II) octahydrate is synthesized and characterized by multinuclear NMR, IR and UV–Vis spectroscopies and elemental analysis. The third order nonlinear optical properties of the new complex in an aqueous solution have been studied using Z-scan technique. Measurements were performed with a CW diode laser at 635nm wavelength and 26mW power. The nonlinear optical absorption coefficient (β) and nonlinear refraction (n2) were found at 9.2×10−5m/W and 1.78×10−8cm2/W respectively. The mechanism responsible for the optical limiting is analyzed. The results suggest that this material considers as a promising candidate for future optical devices applications.

Effect of hydrogenic impurity on linear and nonlinear optical absorption coefficients and refractive index changes in a quantum dot

The analytical expressions of linear and nonlinear optical absorption coefficients and refractive index changes in a quantum dot with a hydrogenic impurity are obtained by using the compact-density-matrix approach and iterative method. The wave functions and the energy levels are obtained by using the variational method. Numerical results show that the optical absorption coefficients and refractive index changes are strongly affected by the hydrogenic impurity.

Comment on “Linear and nonlinear optical absorption coefficients and refractive index changes in asymmetrical Gaussian potential quantum wells with applied electric field”

Guo and Du (2013) reported theirs result for the linear and nonlinear optical absorption coefficients and refractive index changes in asymmetrical Gaussian potential quantum wells with applied electric field. We find both the energy and the corresponding wavefunction for the low-lying state are wrong to applied in their works. For the same set of parameters studied by Guo and Du, we obtain new and reliable results via the differential method.