THE THIRD ORDER NONLINEAR SUSCEPTIBILITY OF INTERACTING ONE-DIMENSIONAL FRENKEL EXCITONS

An analytical expression of the third order nonlinear susceptibility χ(3) has been derived rigorously for a system of interacting Frenkel excitons in a one-dimensional chain of size N with the periodic boundary conditions. It has been clarified that the magnitude of interacting potential between excitons strongly influences the size dependence of χ(3) in the long wavelength approximation, which is well explained in terms of the cancellation effect between the contributions from [ground state] - [one-exciton] transitions and those from [one-exciton] - [two-exciton state] transitions.

Multiplex coherent anti-stokes Raman scattering (M-CARS) and second harmonic generation (SHG) techniques are used to map the real part of the nonresonant third order nonlinear optical susceptibility and the second order nonlinear optical susceptibility of a thermally microimprinted niobium borophosphate glass. In particular, such bimodal nonlinear imaging is employed in order to precisely evaluate how thermal poling can modify the amplitude of the nonresonant third-order nonlinearity of the sample. A systematic decrease of the M-CARS intensity is found in the poled areas with respect to the unpoled ones, suggesting therefore a reduction of the real part of the nonresonant third order nonlinear susceptibility within these regions. Such a reduction in the M-CARS intensity can be explained by sodium depletion in the subanodic zone and is mostly linked to the reduction of both the matter density and the linear refractive index, in agreement with earlier works on thermal poling on the same family of glasses.

In this paper, a detailed study on the third order nonlinear optical susceptibility for quadratic electro-optic effects for CdS/ZnS/CdS/ZnS core/shell/well/shell spherical quantum dots is realized. Electron energies and corresponding functions are investigated under the frame work of the effective-mass approximation. Then, the third order nonlinear susceptibility is determined using the density matrix method. The dot size effect on this susceptibility is also examined. Numerical calculations confirm that both position and intensity of the peaks can be controlled by varying shell thickness. In addition, by increasing the width of inner or outer shell, the peaks of susceptibility is redshifted and the intensities are increased. Moreover, the ‘inverted’ structure, ZnS/CdS/ZnS/CdS has shown better nonlinear optical properties.

Structure dependent third order nonlinear susceptibility in the presence of impurity and magnetic field in CdS/ZnS core/shell quantum dot

We theoretically analyze the optical response from an ultrathin film built up of oriented molecular aggregates, the operating states of which are represented by Frenkel exciton states. A four-level model, involving transitions between the ground, one-exciton and two-exciton states, exciton-exciton annihilation from the two-exciton state as well as relaxation from the annihilation level back to the one-exciton and ground states, is used for describing the film optical response. It is proved that the exciton-exciton annihilation may act not as a destructive but, on the contrary, as a constructive factor tending towards the occurrence of bistability. In particular, the effect of inhomogeneous broadening of the exciton optical transition, preventing the bistable behavior, may be suppressed considerably due to a fast exciton-exciton annihilation.

In the present theoretical work we have studied the optical properties such as optical electronegativity, refractive index, third order nonlinear optical susceptibility and nonlinear refractive index by varying composition of Bi2O3 for 60 TeO2-(30-x) B2O3-xBi2O3-10ZnO (where x=0, 5, 10, 15 and 20) glass samples. There is hardly any information in the literature on the evaluation of optical electronegativity using the optical energy gap values for the glass samples under reference. The glasses possess high value of refractive index (2.248-2.332), high values of third order non linear susceptibility in the 1.33-2.43×10−12esu range and high values of non linear refractive index (2.21-3.92 ×10−11) and the value of all these parameters increase with increasing Bi2O3 content.

Analytical solutions for heat conduction problems with three kinds of periodic boundary conditions and their applications

The authors report room-temperature measurements of the third order nonlinear susceptibility modulus ∣χ(3)∣ of thick (∼600nm) InN layers. Transmission measurements provide a room-temperature value for the optical band gap of the samples slightly above 1500nm. Third order nonlinear optical susceptibility has been measured using degenerate four wave mixing experiments at wavelengths near and above band gap. ∣χ(3)∣ values of (4.2–10)×10−10esu were measured at this wavelength range. The associated relaxation time of the generated population grating at 1500nm was measured. The obtained value of 4.8ps is consistent with a nonradiative recombination mechanism.

The third order nonlinear optical susceptibilities χ(3) of PbO-SiO2 and PbO-B2O3 glasses have been measured by the third harmonic generation (THG) method using silica glass as reference. It is found that the third order nonlinear susceptibilities χ(3) of each series of glasses increase with increasing lead content, corresponding to the increase in the polarizability per unit volume and the decrease in the energy gap of the glasses. The largest χ(3) values obtained are 31.1×10-14esu for a 66PbO⋅34SiO2 glass and 31.2×10-14esu for a 70PbO⋅30B2O3 glass, about 11 times larger than that of pure silica glass.

Zinc oxide (ZnO) and erbium doped zinc oxide (ZnO:Er) thin films, were deposited on heated glass substrates using spray pyrolysis technique. Third-order nonlinear-optical properties of ZnO and ZnO:Er have been investigated by the third harmonic generation (THG) method at the wavelength of 1064 nm using nanosecond Nd <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> :YAG laser radiation. The dependence of third order nonlinear susceptibility and transmission characteristics on the thin film roughness has been measured. Third order nonlinear optical susceptibility ( chi <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(3)</sup> ) values of the studied materials were in the remarkable range of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> esu. The deposited films have been analyzed using X-ray diffraction (XRD) and atomic force microscopy (AFM).

Nonlinear optical (NLO) polymers and their applications have been studied for long decades. The fundamental structures of the NLO polymers consist of the host-guest structures; the guest chromophores play a role of nonlinear mixing of multiple waves, while the host polymers fix the positions of the guest. The symmetry of the materials is closely associated with the nonlinear optical susceptibilities. The second order nonlinearity requires the materials to break the centro-symmetry. In general, the NLO polymers exhibit the centro-symmetry in as-prepared conditions, because the guest chromophores are randomly distributed in the host. So-called poling procedure, the procedure applying the DC electric fields, is conducted so as to align the chromophores in the polar order and break the symmetry. In our previous study, we successfully obtain the second order nonlinear susceptibility by using the NLO polymers with the amorphous ferroelectric polymers as host without the conventional poling procedure [1]. Taking advantage of the polarization self-organization behaviors specific to the amorphous ferroelectric polymers, the noncentro-symmetry of the guest chromophores was induced just by annealing the materials at the temperatures higher than the glass transition points (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ) of the polymers. In the present study, we will report that the nonelectrical poling is available even for the host-guest polymers with poly (methyl methacrylate) (PMMA), one of the most popular host materials for the NLO polymers.

Third order nonlinear optical susceptibility of fluorescein-containing polymers determined by electro-absorption spectroscopy

Periodic boundary condition is commonly used in the FE homogenization method for predicting the thermo-mechanical properties of composites. However, its existing numerical algorithms are generally inefficient. Linear displacement boundary condition is much easier and more efficient to implement for the Representative Volume Elements (RVEs) with conformal and nonconformal surface meshes. Aiming at replacing the periodic boundary condition by the linear displacement boundary condition to easily and efficiently predict the thermo-mechanical properties of composites, this paper compares the implementation efficiency and prediction accuracy of the periodic and linear displacement boundary conditions. Regarding the prediction of the elastic properties of composites, the balance of micro-energy and macro-energy of the RVEs imposed the periodic and linear displacement boundary conditions is checked, and the results demonstrate that these two boundary conditions guarantee the Hill lemma (i.e. the balance of micro-energy and macro-energy of the RVEs). Moreover, comparing with the experimental test and the multi-step micro-mechanical method, the effectiveness of the periodic and linear displacement boundary conditions to predict the elastic properties of composites is validated.

We study an ultracold and dilute superfluid Bose-Fermi mixture confined in a strictly one-dimensional (1D) atomic waveguide by using a set of coupled nonlinear mean-field equations obtained from the Lieb-Liniger energy density for bosons and the Gaudin-Yang energy density for fermions. We consider a finite Bose-Fermi interatomic strength g{sub bf} and both periodic and open boundary conditions. We find that with periodic boundary conditions--i.e., in a quasi-1D ring - a uniform Bose-Fermi mixture is stable only with a large fermionic density. We predict that at small fermionic densities the ground state of the system displays demixing if g{sub bf}>0 and may become a localized Bose-Fermi bright soliton for g{sub bf}<0. Finally, we show, using variational and numerical solutions of the mean-field equations, that with open boundary conditions--i.e., in a quasi-1D cylinder--the Bose-Fermi bright soliton is the unique ground state of the system with a finite number of particles, which could exhibit a partial mixing-demixing transition. In this case the bright solitons are demonstrated to be dynamically stable. The experimental realization of these Bose-Fermi bright solitons seems possible with present setups.

Considering computational speed vs. accuracy: Choosing appropriate mesoscale RVE boundary conditions