Nonlinear Refractive Index Changes Research Articles

Optical limiting properties of surface functionalized nanodiamonds probed by the Z-scan method

This work focuses on the optical limiting behavior of surface modified nanodiamonds (DNDs) namely, amino-terminated DNDs (DND-NH2) and hydrogen-terminated DNDs (DND-H). Their relevant nonlinear optical properties for optical limiting are compared to those of unfunctionalized DNDs. The optical limitation is characterized by means of nonlinear transmittance, Z-scan, and scattered intensity assessments when submitted to a nanosecond pulsed Nd:YAG laser operating at a wavelength of 532 nm. It is stated that the largest nonlinear attenuation is attributed to the DND-H system, whereas the exceedingly low threshold values for optical limiting for the DND-H and the DND-NH2 systems is attributed to their negative electron affinity character (NEA). Using Z-scan experiments, it is shown that nonlinear refraction combined with a significant nonlinear absorption predominates in the DND-H suspension, while the pure thermal origin of the nonlinear refractive index change is conjectured in the case of the DNDs. Besides, an amazing valley to peak profile was measured on DND - NH2indicating an unexpected positive sign of the nonlinear refraction coefficient. In addition, a stronger backscattered intensity signal is highlighted for the unfunctionalized DNDs through nonlinear scattering measurements.

Spherical quantum dot in Kratzer confining potential: study of linear and nonlinear optical absorption coefficients and refractive index changes

Linear and nonlinear optical absorption coefficients (ACs) and refractive index changes (RICs) between the ground and the excited states of the GaAs spherical quantum dot (QD) under the effect of Kratzer confining potential and laser field have been investigated theoretically. The electronic energy levels and their corresponding wave functions are obtained by solving Schrodinger equation using finite difference method within the effective mass approximation. The dependency of energies, probability densities, dipole matrix elements on the Kratzer potential parameters and on the size of QD are investigated. The use of density matrix formalism is made to study the variations in linear, nonlinear ACs and RICs with the energy and intensity of the laser field. Also the effect of variation of the QD size and Kratzer potential parameters on linear, nonlinear ACs and RICs are studied.

Far-field diffraction patterns and optical limiting properties of bisdemethoxycurcumin solution under CW laser illumination

In this work, nonlinear optical properties of bisdemethoxycurcumin solution were studied using diffraction ring patterns method. Multiple diffraction rings observed as a continuous wave (CW) laser beam passes through a bisdemethoxycurcumin solution. The nonlinear refractive index, n2, and change in refractive index, Δn, for sample were determined from the number of observed rings, and are found to be 0.8327 × 10−6 cm2/W and 0.00946 respectively. The evolution of the diffraction ring patterns are numerically studied using the Fresnel–Kirchhoff diffraction integral theory. The experimental findings are in good agreement with theoretical analysis. Also the optical limiting properties of the sample were measured at 473 nm. The obtained results proved that the sample bear good optical limiting property.

Pressure dependent optical properties of quantum dot with spin orbit interaction and magnetic field

In this paper, a detailed investigation of the effects of the interplay of temperature, hydrostatic pressure, Rashba spin orbit interaction, and external magnetic field on the optical properties for quantum dot is presented. We obtained the exact wavefunctions and energy levels of a harmonic potential quantum dots taking Rashba spin orbit interaction into account. We have obtained the linear and nonlinear absorption coefficients and relative refractive index change for varying incident photon energies using density matrix theory. Counter intuitive red shift in the absorption coefficient peaks with increase in hydrostatic pressure is demonstrated. The role of temperature and hydrostatic pressure on variation of effective charge carrier mass is investigated.

A theoretical evaluation of optical properties of InAs/InP quantum wire with a dome cross-section

In the present work, we have theoretically studied the optical properties of a InAs quantum wire with dome cross section. We have used a numerical method which is based on a combination of coordinate transformation and the finite difference method. For this purpose, we have used analytical expressions for optical properties obtained by the compact-density matrix formalism. We have evaluated the linear, non-linear and the total absorption coefficients between the ground state for electron and heavy hole as a function of photon energy. The linear, non-linear and total refractive index changes are also investigated. These optical properties are determined with varying the incident optical intensity and the height of the wire.

Polaron effects on nonlinear optical refractive index changes in semi-exponential quantum wells.

Nonlinear optical refractive index changes (RICs) with polaron effects are studied in this Letter. The energy levels and wave functions of the polaron Schrödinger equation are calculated and brought into the nonlinear RICs to analyze the difference between the effects of the presence and absence of polarons, as well as the specific representation of RICs with polarons.

An approach to the measurement of the nonlinear refractive index of very short lengths of optical fibers

A method for the measurement of the nonlinear-refractive index coefficient in single-mode optical fibers is presented. It takes advantage of the high sensitivity of the acousto-optic interaction effect in optical fibers to the fiber properties. Direct measurement of the nonlinear-refractive index change resulting from cross-phase modulation between a probe and a pump signal is obtained from the fiber's acousto-optic interaction performance. It is a non-interferometric method in which a very short length of fiber (<0.25 m) is required.

Nonlinear optical properties of asymmetric double-graded quantum wells

ABSTRACTIn this work, the effects of the structure parameters, such as the central barrier thickness and the aluminium concentrations x, on the linear and nonlinear intersubband optical absorption coefficients and refractive index changes of the asymmetric double-graded quantum wells (ADGQWs) under the presence of an external static electric field are studied theoretically. The nonlinear optical properties of the ADGQWs are obtained using the compact-density matrix approach and iterative method. The numerical results obtained from the present work show that the external static electric field and the structure parameters play an important role in the optical properties of ADGQWs. Depending on the asymmetric nature of the confinement potential, in an electric field of kV/cm, the overlap between electronic wave functions decreases with increasing field whereas it increases for larger field values. The tunability of intersubband transitions can be applied to optical modulators and various device applications based on the optical transitions of electrons.

Impurity-related optical properties of a laser-driven quantum dot

In this paper, we explore theoretically the effect of an on-center Gaussian impurity on the optical properties of a laser-driven parabolic quantum dot system under uniform magnetic field. Laser radiation with circular polarization has been treated within the framework of high-frequency Floquet approach. The linear and third-order nonlinear optical absorption coefficients and refractive index changes have been examined by means of the compact-density matrix approach. Numerical results reveal that the position and magnitude of the resonant peaks of absorption coefficients and refractive index changes are sensitively affected by magnetic field, the depth and the range of the impurity potential. Besides, the presence of intense laser field causes a red-shift in the positions and reduction in the amplitudes of the resonant peaks of optical characteristics.

Vortex solitons produced in spatially modulated linear and nonlinear refractive index waveguides

We discuss analytical localized soliton solutions to the generalized nonautonomous nonlinear Schrodinger equation (NLSE) in waveguides featuring transverse modulation of both the linear and nonlinear refractive index changes. We utilize the similarity transformation technique to obtain these solutions. It turns out that the generalized nonautonomous NLSE with space-dependent coefficients can be reduced to the stationary NLSE, provided certain constraints are placed on the linear and nonlinear refractive indices. Various shapes of exact vortex soliton solutions are studied theoretically and analytically. Finally, the stability analysis of the solutions is discussed numerically. Our findings address an alternative way for the realization of stable vortex solitons with higher topological charges and the radial quantum numbers.

Study of plasmonic slot waveguides with a nonlinear metamaterial core: semi-analytical and numerical methods

Two distinct models are developed to investigate the transverse magnetic stationary solutions propagating in one-dimensional anisotropic nonlinear plasmonic structures made from a Kerr-type nonlinear metamaterial core embedded between two semi-infinite metal claddings. The first model is semi-analytical, in which we assume that the anisotropic nonlinearity depends only on the transverse component of the electric field and that the nonlinear refractive index modification is small compared to the linear one. This method allows us to derive analytically the field profiles and nonlinear dispersion relations in terms of the Jacobi elliptical functions. The second model is fully numerical and is based on the finite element method in which all the components of the electric field are considered in the Kerr-type nonlinearity, with no presumptions as to the nonlinear refractive index change. Our finite-element-based model is valid beyond the weak nonlinearity regime and generalizes the well-known single-component fixed power algorithm that is usually used. Examples of the main cases are investigated, including those with strong spatial nonlinear effects at low power. Loss issues are reduced through the use of a gain medium in the nonlinear metamaterial core. Using anisotropic nonlinear FDTD simulations, we provide some results for the properties of the main solution.

Linear and nonlinear optical properties of an off-center donor in GaAs/AlGaAs and AlGaAs/GaAs core-shell ellipsoidal quantum dots

In the present work, the linear and nonlinear absorption coefficients and refractive index changes of an off-center donor in both GaAs/Al0.3Ga0.7As and Al0.3Ga0.7As/GaAs core-shell ellipsoidal quantum dots have been studied, emphasizing on the influence of impurity position and the shapes of core and shell. The results show that the impurity position and the shape of core and shell have an important effect on the optical properties of the system, and the influence of core and shell shapes in such two core-shell structures is different. The physical reasons for the results have been discussed in detail.

Linear and nonlinear magneto-optical absorption coefficients and refractive index changes in graphene

In this work, we study the magneto-optical absorption coefficients (MOACs) and refractive index changes (RICs) in monolayer graphene under a perpendicular magnetic field using the compact density matrix approach. The results are presented as functions of photon energy and external magnetic field. Our results show that there are three groups of the possible transitions: the intra-band, the mixed, and the inter-band transitions; in which the MOACs and the RICs appear as a series of peaks in both intra-band and inter-band transitions between the Landau levels. With an increase magnetic field, the resonant peaks give a blue-shift and reduce in their amplitudes. These results suggest a potential application of monolayer graphene in nanoscale electronic and magneto-optical devices.

Combined effects of the intense laser field, electric and magnetic fields on the optical properties of n-type double δ-doped GaAs quantum well

In the present work, the effects of the non-resonant intense laser field, electric and magnetic fields on the optical properties, such as linear, third order nonlinear and the total optical absorption coefficient and refractive index changes associated with the intersubband transitions between the ground and the first excited states in the n-type double δ-doped GaAs quantum well is theoretically studied by solving the Schrödinger equation in the laser-dressed confinement potential within the framework of effective mass approximation. 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. Our numerical results show that the optical absorption coefficient and refractive index change are quite sensitive to the applied external fields, such as non-resonant intense laser field, electric and magnetic fields. The obtained results can be applied for the design of various optoelectronic devices based on the intersubband transitions of electrons.

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.

Effects of electron–phonon interaction and impurity on optical properties of hexagonal-shaped quantum wires

We have investigated the influence of electron–phonon (e–p) interaction and hydrogenic donor impurity simultaneously on energy difference, binding energy, the linear, nonlinear and total refractive index changes and absorption coefficients of a hexagonal-shaped quantum wire. For this goal, we have used finite-element method (FEM), a compact density matrix approach and an iterative procedure. It is deduced that energy difference and binding energy decrease by changing the impurity position with and without e–p interaction. The dipole matrix elements have complex behaviours in the presence of impurity with and without e–p interaction. The refractive index changes and absorption coefficients increase and shift towards lower energies by enhancing a 1 with central impurity. In the presence of central impurity, the absorption coefficients and refractive index changes enhance and shift toward higher energies when e–p interaction is considered.

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.

Linear and nonlinear magneto-optical properties of monolayer phosphorene

We theoretically study the magneto-optical properties of monolayer phosphorene under a perpendicular magnetic field. We evaluate linear, third-order nonlinear, and total absorption coefficients and relative refractive index changes as functions of the photon energy and the magnetic field, and show that they are strongly influenced by the magnetic field. The magneto-optical absorption coefficients and relative refractive index changes appear in two different regimes: the microwave to THz and the visible frequency. The amplitude of intra-band transition peaks is larger than that of the inter-band transitions. The resonant peaks are blue-shifted with the magnetic field. Our results demonstrate the potential of monolayer phosphorene as a new two-dimensional material for applications in nano-electronic and optical devices as a promising alternative to graphene.

The effect of position-dependent mass on nonlinear optical absorption coefficients and refractive index changes in a quantum well

The influence of position-dependent mass (PDM) on nonlinear optical absorption (OA) coefficients and refractive index changes (RICs) is theoretically studied, within the framework of the iterative method and the compact-density-matrix approach. Through solving Schrödinger equation, the eigenfunctions and energy eigenvalues are obtained. The analytic expressions of the optical absorption coefficients and the refraction index changes are derived theoretically. The results reveal that the OA coefficients and the RICs are strongly affected by PDM, and both the peaks of them increase when considering PDM.

Multicomposition EPSR: Toward Transferable Potentials To Model Chalcogenide Glass Structures.

The structure of xAs40Se60-(1 - x)As40S60 glasses, where x = 1.000, 0.667, 0.500, 0.333, 0.250, and 0.000, is investigated using a combination of neutron and X-ray diffraction coupled with computational modeling using multicomposition empirical potential structure refinement (MC-EPSR). Traditional EPSR (T-EPSR) produces a set of empirical potentials that drive a structural model of a particular composition to agreement with diffraction experiments. The work presented here establishes the shortcomings in generating such a model for a ternary chalcogenide glass composition. In an enhancement to T-EPSR, MC-EPSR produces a set of pair potentials that generate robust structural models across a range of glass compositions. The structures obtained vary with composition in a much more systematic way than those taken from T-EPSR. For example, the average arsenic-sulfur bonding distances vary between 2.28 and 2.46 Å in T-EPSR but are 2.29 ± 0.02 Å in MC-EPSR. Similarly, the arsenic-selenium bond lengths from T-EPSR vary between 2.28 and 2.43 Å but are consistently 2.40 ± 0.02 Å in the MC-EPSR results. Analysis of these models suggests that the average separation of the chalcogen (S or Se) atoms is the structural origin of the changes in nonlinear refractive index with glass composition.