Order Nonlinear Optical Absorption Coefficients Research Articles

Consequences of dielectric mismatch on linear and third order nonlinear optical properties for CdS/ZnSe core/shell QD-matrix

In this work, we have performed a detailed investigation on optical properties for CdS/ZnSe spherical core/shell quantum dots surrounded by various dielectric matrices such as PVA, PMMA and SiO2. The wave functions and eigenenergies of confined electrons have been theoretically computed using the effective-mass formalism and the density matrix approach. The linear and third-order nonlinear optical properties have been evaluated for different matrices. Our results demonstrated that the linear, third order nonlinear optical absorption coefficients and refractive index changes are considerably sensitive to the geometrical parameters, the incident optical intensity and the dielectric environment.

Optical behaviour of nematic liquid crystal doped with carbon dot in the nonlinear optical regime

We delve into the effect of carbon dot (c-dot) doping at different concentrations (0.1, 0.2, 0.4, and 1 wt%) on the third order nonlinear optical properties of a nematic liquid crystal (NLC). C-dots were synthesized by the thermal decomposition of ammonium citrate salt. The size and morphology of prepared c-dots were confirmed by the TEM micrograph. Nonlinear optical properties of c-dot doped liquid crystal were investigated by the z-scan method using a Q-switched Nd: YAG laser delivering 7 ns pulse at 532 nm wavelength. A phenomenal increase in the nonlinear absorption coefficient, βeff, was observed for 0.2 wt% c-dot doped liquid crystal. There is an enhancement in the value of third order susceptibility, χ(3), of the order of 10 for the doped liquid crystal. An increase in the third order nonlinear optical absorption coefficient implies a better optical limiting characteristic than the pristine LC. The optical limiting threshold value of 0.2 wt% c-dot doped LC is found to be 1.23 J/cm2. We determine for the first time that c-dot doping in NLC leads to a significant improvement of the nonlinear optical properties compared to pure LC. The results indicate that the system under study could be a promising candidate for nonlinear photonic devices and optical limiters.

Studies on growth and characterization of (E)-N′-[4-(dimethylamino) benzylidene]-4-hydroxybenzohydrazide hemihydrate: a nonlinear optical material

Hydrazone compound (E)-N′-[4-(dimethylamino) benzylidene]-4-hydroxybenzohydrazide hemihydrate (DMABHBH) was synthesized and single crystals of DMABHBH were grown by solvent evaporation method at room temperature. Molecular structure of DMABHBH compound was confirmed by 1H and 13C nuclear magnetic resonance techniques. The presence of functional groups was confirmed by Fourier transform infrared and FT Raman spectral analyses. The X-ray crystal structure was elucidated at 173 K by single crystal X-ray diffraction and the results were compared with the corresponding values obtained at 298 K. The compound crystallizes in the chiral monoclinic space group P21. Mechanical stability of the grown crystals was estimated from the Vicker’s microhardness test. Powder second harmonic generation efficiency of DMABHBH is about 1.1 times that of potassium dihydrogen phosphate. DMABHBH is found to show optical limiting behavior at high input light intensities, the third order nonlinear optical absorption coefficient measured using open aperture Z-scan studies, is 0.95 × 10−11 m/W. Anti-bacterial activity was studied using the well and disc diffusion methods.

Optical absorption in a disk-shaped quantum dot in the presence of an impurity

The linear and third order nonlinear optical absorption coefficients have been calculated in a two dimensional disk quantum dot. The confinement potential has been taken to be a combination of a parabolic and inverse squared part. The study has been performed in the presence of a perpendicular static magnetic field and a central or off-central impurity. The resulting Schrödinger equation has been solved by applying the variational method. It has been found that the presence of impurity causes a huge increase in the square of the transition matrix and in the absorption coefficients, in particular in the third order coefficient. Moreover, the asymmetry which results in the case of off-central impurity has been dealt with carefully by taking into consideration the transition matrices which vanish in other cases.

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.

Polaron Effect of a Two Electron Parabolic Quantum Dot

Polaron induced double electron in a quantum dot is investigated using the exact diagonalization techniques and the compact density-matrix approach. The dependence of nonlinear optical processes on the incident photon energies and the polaronic effect are brought out. The linear, third order non-linear optical absorption coefficients and the refractive index changes of singlet and triplet states as a function of photon energy are obtained with and without the inclusion of polaronic effect. It is found that the geometrical confinement and the effect of polaron have great influence on the optical properties of dots.

Linear and nonlinear optical absorption coefficients and refractive index changes of a spherical quantum dot placed at the center of a cylindrical nano-wire: Effects of hydrostatic pressure and temperature

The combined effects of hydrostatic pressure and temperature on the optical absorption coefficients and refractive index changes of an InAs spherical quantum dot which is located at the center of a GaAs cylindrical nano-wire have been investigated. The wave functions and corresponding eigenvalues are calculated using finite element 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 the compact-density matrix formalism. The linear and third order nonlinear absorption coefficient and refractive index changes are presented as a function of the photon energy, dot radius, pressure, temperature, incident photon intensity and relaxation time. It is found from our calculations that the linear and third order nonlinear optical absorption coefficients, refractive index changes and resonance energy are quite sensitive to the dot size, applied hydrostatic pressure and temperature.

Dielectric confinement on exciton binding energy and nonlinear optical properties in a strained Zn1−xinMgxinSe/Zn1−xoutMgxoutSe quantum well

The band offsets for a Zn1−xinMgxinSe/Zn1−xoutMgxoutSe quantum well heterostructure are determined using the model solid theory. The heavy hole exciton binding energies are investigated with various Mg alloy contents. The effect of mismatch between the dielectric constants between the well and the barrier is taken into account. The dependence of the excitonic transition energies on the geometrical confinement and the Mg alloy is discussed. Non-linear optical properties are determined using the compact density matrix approach. The linear, third order non-linear optical absorption coefficient values and the refractive index changes of the exciton are calculated for different concentrations of magnesium. The results show that the occurred blue shifts of the resonant peak due to the Mg incorporation give the information about the variation of two energy levels in the quantum well width.

Size dependent effective band gap, optical absorption coefficients and refractive index changes in a wide ZnS/Zn1−xMgxS strained quantum well

Exciton binding energy of a confined heavy hole exciton is investigated in a Zn1−xMgxS/ZnS/Zn1−xMgxS single strained quantum well with the inclusion of size dependent dielectric function for various Mg content. The effects of interaction between the exciton and the longitudinal optical phonon are brought out. The effect of exciton is described by the effective potential between the electron and hole. The interband emission energy as a function of well width is calculated for various Mg concentration with and without the inclusion of dielectric confinement. Non-linear optical properties are carried out using the compact density matrix approach. The dependence of nonlinear optical processes on the well width is investigated for different Mg concentration. The linear, third order non-linear optical absorption coefficients values and the refractive index changes of the exciton are calculated for different concentration of magnesium content. The results show that the exciton binding energy is found to exceed LO phonon energy of ZnS for x>0.2 and the incorporation of magnesium ions and the effect of phonon have great influence on the optical properties of ZnS/Zn1−xMgxS quantum wells.

Numerical simulation of electronic structure, linear and third order nonlinear optical absorption coefficients in the polymeric nanoheterostructure using imaginary time propagation method

In the effective mass approximation, the charge density, the potential profile, the wavefunctions, and the corresponding energy states for zinc sulfide spherical quantum dot have been self-consistently solved, which is embedded in the polymeric media (PVP) by the imaginary time propagation method. Moreover, for the first time, the oscillator strength, linear, third order nonlinear, and total optical absorption coefficients for the transition between intersubbands 1s-1p, 1p-1d, 1d-1f, 1f-1g, 1g-1h, and 1h-1i are investigated with respect to photon energy and the saturation strength has been calculated for every transition too. Calculated result shows that the oscillator strength and the magnitude of optical absorption coefficients are enhanced for transition between intersubbands with higher energies. Also, calculations show that the total absorption coefficient depends on the strength of incident optical intensity and relaxation time.

Electric field induced exciton binding energy and its non-linear optical properties in a narrow InSb/InGaxSb1−x quantum dot

The effect of electric field on the binding energy, interband emission energy and the non-linear optical properties of exciton as a function of dot radius in an InSb/InGaxSb1−x quantum dot are investigated. Numerical calculations are carried out using single band effective mass approximation variationally to compute the exciton binding energy and optical properties are obtained using the compact density matrix approach. The dependence of the nonlinear optical processes on the dot sizes is investigated for various electric field strength. The linear, third order non-linear optical absorption coefficients, susceptibility values and the refractive index changes of electric field induced exciton as a function of photon energy are obtained. It is found that electric field and the geometrical confinement have great influence on the optical properties of dots.

Electronic states and the resonant optical non-linearity of exciton in a narrow band InSb quantum dot

Binding energy, interband emission energy and the non-linear optical properties of exciton in an InSb/InGa x Sb 1− x quantum dot are computed as functions of dot radius and the Ga content. Optical properties are obtained using the compact density matrix approach. The dependence of non-linear optical processes on the dot sizes is investigated for different Ga concentrations. The linear, third order non-linear optical absorption coefficients, susceptibility values and the refractive index changes of the exciton are calculated for different concentrations of gallium content. It is found that gallium concentration has great influence on the optical properties of InSb/InGa x Sb 1− x dots.

Design, synthesis, growth and characterization of 4-methoxy-4′-dimethylamino-benzylidene aniline (MDMABA): A novel third order nonlinear optical material

Synthesis, growth, X-ray crystal structure and characterization of a novel third order nonlinear optical material, 4-methoxy-4′-dimethylamino-benzylidene aniline (MDMABA), are reported for the first time. The asymmetric unit of MDMABA compound contains two crystallographically independent molecules (A and B), and they exist in the E-configuration. The structural perfection of the grown crystal is analyzed by high-resolution X-ray diffraction rocking curve analysis. The functional groups present in MDMABA are investigated by FTIR and FT-Raman spectral analyses. The placement of the protons is determined using HNMR spectrum. The range and percentage of optical transmission were ascertained by recording UV–vis–NIR spectrum. Thermal and mechanical properties are reported. Dielectric study shows that the dielectric constant of the crystal varies with frequency and temperature. The third order nonlinear optical absorption coefficient of the MDMABA crystal is determined by the Z-scan technique.

Nonlinear optical properties of a two-dimensional elliptic quantum dot

The linear and third order nonlinear optical absorption coefficient and refractive index changes of an elliptic quantum dot have been investigated, using the compact-density matrix formalism and an iterative method. In this regard, the effect of optical intensity, size and geometry of the dot on the optical absorption coefficient and refractive index changes are investigated. It is found that, not only the light intensity but also the size and the geometry of the dot have a great influence on the optical absorption coefficient and refractive index changes of the system.