Synthesis, <Emphasis Type="Italic">Spectrofluorometric</Emphasis> Studies,Micellization and non Linear Optical Properties of Blue Emitting Quinoline (AMQC) Dye

Blue emitting 2-amino-4-(3, 4, 5-tri methoxyphenyl)-9-methoxy-5,6 dihydrobenzo[f]isoquinoline-1-carbonitrile (AMQC) dye was synthesized by one-pot multicomponent reactions (MCRs) of 3,4,5-trimethoxybenzaldehyd, malononitrile, 6-methoxy-1,2,3,4-tetrahydro-naphthalin-1-one and ammonium acetate. Results obtained from spectroscopic and elemental analysis of synthesized AMQC was in good agreement with their chemical structures. Fluorescence polarity study demonstrated that AMQC was sensitive to the polarity of the microenvironment provided by different solvents. In addition, spectroscopic and physicochemical parameters, including electronic absorption, excitation coefficient, stokes shift, oscillator strength, transition dipole moment and fluorescence quantum yield were investigated in order to explore the analytical potential of AMQC. Dye undergoes solubilization in different micelles and may be used as a quencher and a probe to determine the critical micelle concentration (CMC) of SDS and CTAB. Nonlinear optical parameters of AMQC dye shows relatively lower nonlinear refractive index and nonlinear absorption coefficient at the power levels. Variation of n₂ with concentration is linear in the concentration range used in the present study.     

一种新型非晶态分子材料的非线性光学折射率和吸收特性

用单光束扫描法测量了在532nm处一种新型非晶态分子材料5,5′Bis(dimesitylboryl)2,2′bithiophene的非线性折射率和吸收系数样品非线性透射特性的分析表明,在靠近线性吸收区的532nm处有饱和吸收存在由三能级饱和模型和Zscan法确定了饱和强度、非线性折射率的实部和虚部研究结果表明:这种新型非晶态分子材料具有非常好的光子学应用前景.     

Investigation of third-order nonlinear optical properties of NNDC-doped PMMA thin films by Z-scan technique

A novel chalcone derivative, (2E)-1-(2,4-di- chloro-5-fluorophenyl)-3-[4-dimethylamino)phenyl]prop-2-en-1-one, abbreviated as NNDC, was prepared and characterized by elemental analyses, infrared (IR) and proton nuclear magnetic resonance (¹H NMR) spectrum, and thermal analyses. The NNDC-doped poly(methyl methacrylate) (PMMA) thin films with five different doping concentrations by weight were prepared by using a spin-coating method. Their linear optical properties were investigated by using a prism coupling measuring system. The third-order nonlinear optical properties of NNDC in 1,2-dichloroethane (NNDC/1,2-dichloroethane) solution and NNDC-doped PMMA (NNDC/PMMA) films were investigated by using the laser Z-scan technique with 20 ps pulses at 532 nm. A self-focusing effect was observed from the Z-scan curves for solution and thin films and the nonlinear refractive index of the film increases with the increase of the doping concentration. In addition, nonlinear absorption was negligible for all samples. The magnitude of third-order nonlinear refraction index n ₂ and the third-order nonlinear susceptibility χ ⁽³⁾ for thin films were 10⁻¹⁵ m²/W and 10⁻⁹ esu, respectively, which are about three orders larger than that of NNDC/1,2-dichloroethane solution. Some necessary analyses were presented. The results show that this material is a promising candidate for application in the nonlinear optical devices at 532 nm.     

Spherical polyelectrolyte block copolymer micelles: Structural change in presence of monovalent salt

Spherical polyelectrolyte block copolymer micelles were investigated as a function of added NaCl salt concentration using Small-Angle Neutron Scattering (SANS) and Light Scattering (LS). The micelles are formed by the self-association of charged-neutral copolymers made of a long deuterated polyelectrolyte moiety (NaPSS_d)₂₅₁ and a short hydrophobic moiety (PEP)₅₂. In presence of salt, the core shape and the aggregation number of the micelles are not affected. The hydrodynamic radius of the micelle is found to be identical to the radius of the whole micelle deduced from neutron scattering and thus the hydrodynamic radius is a valid measure of the corona thickness. At the lowest salt concentrations investigated the thickness of the corona, R_s, remains essentially constant and a contraction is observed above an added-salt concentration c_s of 2×10^-2 M where this crossover concentration corresponds to the average ionic strength of the free counterions in the corona. The contraction takes place while maintaining a rod-like behavior of the chains at short scale and obeys to: R_s c_s^-0.18. The exponent 0.18 suggests an electrostatic persistence length proportional to the Debye screening length.     

Nonlinear optical absorption of zinc-phthalocyanines in polymeric matrix

We realized and investigated films of zinc-phtalocyanines into poly(methylmethacrylate) (PMMA) for optical limiting applications. The ratio by weight of the compound to the host polymer was 0.083% and 0.15%. Linear optical characterization of films, performed by spectrophotometry, show a low degree of molecular aggregation of zinc-phtalocyanines in the polymeric matrix.Two different type of nonlinear optical investigation were performed separately on the obtained films. Measurements of nonlinear transmission were carried out using a ns Nd:Yag laser followed by OPO (532 nm) and a nonlinear response was observed. From the experimental data, the nonlinear absorption coefficient β was retrieved and found to be 29 and 43 cm/GW, respectively. The measurements of β was also performed via the z-scan technique on the same films, using 100 fs pulses at 800 nm. At this wavelength, the nonlinear absorption coefficient was evaluated to be 0.40 and 0.23 cm/GW.     

Ordering of a frustrated Josephson-coupled network system of sub-micron-scale grains

Ordering characteristics of a superconductive ceramic of YBa₂Cu₄O₈ are newly examined experimentally by analyzing the nonlinear magnetic responses, in order to discuss intergrain ordering of frustrated Josephson-coupled network system of sub-micron-scale grains below the superconductive critical temperature. The derived nonlinear magnetic susceptibility χ₂ shows a symmetric negative divergence at the temperature corresponding to the intergrain ordering point T_c2. The result indicates that the ordering of a 3D XY-type spin glass is associated with the same singularity of nonlinear chiral susceptibility at the temperature.     

Macroscopic and microscopic structural integrity in magnetic colloids—cationic micellar solution: Rheology, SANS and magneto-optical study

A stable mixture of two colloid system composed of double surfactant coated aqueous nanomagnetic fluid and aqueous micellar solution of cationic micelles of cetyletrymethyl ammonium bromide (CTABr) is prepared as a function of nanomagnetic fluid concentration. This mixed system is analyzed using three techniques such as zero field and field induced viscosity measurements, Small Angle Neutron Scattering technique and magneto-optical birefringence measurements. In field induced viscosity measurement it is observed that even 20% magnetic fluid concentration in CTABr aqueous solution shows 75% increase in viscosity compared to pure magnetic fluid. This suggests that in presence of CTABr micelles, a novel magneto rheological effect for low concentration of magnetic fluid is observed. From SANS measurements it is observed that aggregation number and a/b ratio increases with magnetic fluid concentration and magnetic birefringence reveals non-superimpose behavior of normalized field induced retardation. Results of these experiments are compared and indicate zero fields and field induced structural integrity between magnetic particles and soft micelles.     

Stability of the uniform alignment of lyotropic nematic liquid crystals doped with magnetic grains

The stability of the uniform alignment of lyotropic nematic liquid crystals doped with magnetic grains is theoretically analysed. The sample is assumed to be prepared in a uniformly magnetized state by means of an external magnetic field, which is switched off subsequently. We show that there is a critical concentration of magnetic grains above which the distorting effect of the magnetic interaction overcomes the stabilizing effect of the steric interactions among grains and micelles.     

Influence of the group-velocity on the pulse propagation in 1D silicon photonic crystal waveguides

We present a detailed analysis of the influence of the group velocity (GV) on the dynamics of optical pulses upon their propagation in one-dimensional photonic crystal waveguides (PhCW). The theoretical model used in our analysis incorporates the linear optical properties of the PhCW (GV dispersion and optical losses), free-carrier (FC) effects (FC dispersion and FC-induced optical losses) and nonlinear optical effects (Kerr nonlinearity and two-photon absorption). Our analysis shows that, unlike the case of uniform waveguides, the GV of the pulse, dispersion coefficients, and the waveguide nonlinear coefficient are periodic functions with respect to the propagation distance. We also demonstrate that linear and nonlinear effects depend on the group velocity, v _g , as v_g^-1v_{g}^{-1} and v_g^-2v_{g}^{-2}, respectively.     

一种侧链共轭聚噻吩衍生物薄膜的三阶非线性光学响应

合成了一种侧链共轭的聚噻吩衍生物聚3-（5′辛基-噻吩乙烯基）噻吩（POTVTh）,并通过溶液旋涂制备了聚合物薄膜.吸收光谱显示该聚合物薄膜具有较小的禁带宽度和宽的光谱响应.采用Z扫描技术在800 nm下用飞秒激光器研究了该聚合物薄膜的三阶非线性光学特性,非线性吸收系数为5.63×10^-7cm/W,非线性折射率为-6.38×10^-11 cm²/W,三阶非线性极化率为4.21×10^-9esu,比侧链未共轭的 关键词： 聚噻吩衍生物 侧链共轭 三阶非线性极化率 非线性折射率     

Study of optical properties in a cubic quantum dot

In this paper, the effect of hydrostatic pressure on both the intersubband optical absorption coefficients and the refractive index changes is studied for typical GaAs/Al _x  Ga_1?x As cubic quantum dot. We use analytical expressions for the linear and third-order nonlinear intersubband absorption coefficients and refractive index changes obtained by the compact-density matrix formalism. The linear, third-order nonlinear, and total intersubband absorption coefficients and refractive index changes are calculated at different pressures as a function of the photon energy with known values of box length (L), the incident optical intensity (I), and Al concentration (x). According to the results obtained from the present work, we have found that the pressure plays an important role in the intersubband optical absorption coefficient and refractive index changes in a cubic quantum dot.     

Linear and nonlinear optical properties in a semiconductor quantum well under intense laser radiation: Effects of applied electromagnetic fields

In this work we are studying the intense laser effects on the electron-related linear and nonlinear optical properties in GaAs–Ga_1?xAl_xAs quantum wells under applied electric and magnetic fields. The calculated quantities include linear optical absorption coefficient and relative change of the refractive index, as well as their corresponding third-order nonlinear corrections. The nonlinear optical rectification and the second and third harmonic generation coefficients are also reported. The DC applied electric field is oriented along the hererostructure growth direction whereas the magnetic field is taken in-plane. The calculations make use of the density matrix formalism to express the different orders of the dielectric susceptibility. Additionally, the model includes the effective mass and parabolic band approximations. The intense laser effects upon the system enter through the Floquet method that modifies the confinement potential associated to the heterostructure. The results correspond to several configurations of the dimensions of the quantum well, the applied electric and magnetic fields, and the incident intense laser radiation. They suggest that the nonlinear optical absorption and optical rectification are nonmonotone functions of the dimensions of the heterostructure and of the external perturbations considered in this work.     

A Fluorescence Study of Novel Styrylindoles in Homogenous and Microhetrogeneous Media

In this paper are presented absorption and fluorescence emission properties of 3-styrylindoles viz. 3-(2-phenylethenyl-E)-NH-indole (1), 3-[2-(4-nitrophenyl)ethenyl-E)-NH-indole (2), 3-[2-(4-cyanophenyl)ethenyl-E]-N-ethylindole (3) and 3-[2-(4-cyanophenyl)ethenyl-E]-NH-indole (4) in organic solvents, 1,4-dioxane-water binary mixtures and micelles (SDS, CTAB and Triton-X-100). The fluorescence properties of 2-4 have been utilized to probe the microenvironment (binding constant, CMC, micropolarity and solubilization site) of the micelles.     

Biexcitonic absorption in a disk-shaped GaN quantum dot

The present work investigates the nonlinear optical properties of a GaN quantum dot in the disk limit via the exciton and biexciton states using the compact density matrix formalism. Based on this model, we calculate the ground state energy of the exciton and biexciton states by the variation method, within envelope function and effective mass approximations. Linear and nonlinear optical absorption (α ⁽¹⁾, α ⁽³⁾) and oscillator strengths attributed to the optical transitions are obtained. The details of the behaviour of α ⁽¹⁾ and α ⁽³⁾ around the resonance frequencies and for different quantum dot geometries are presented. It is found that the size of quantum dot and the optical intensity have a remarkable effect on the optical absorption, and the biexcitonic two-photon absorption coefficient(K ₂) has also been calculated in this system. The results show that this parameter is strongly affected by the size of the quantum dot.     

The influence of the structural characteristics of the substrate and the medium on the stability of triflusal and acetylsalicylic acid in micellar systems

A spectrophotometric study of the alkaline hydrolysis of two salicylic acid (SA) derived drugs, performed on acetylsalicylic acid (ASA) and triflusal, both in the absence and presence of cationic micelles. In the absence of micelles, a catalytic effect is produced by the favoured OH⁻ ion in the molecule of triflusal, due to the presence of the trifluoromethyl group. The surfactants used were: hexadecyltrimethylammonium hydroxide (HDTAOH), hexadecyltrimethylammonium chloride (HDTACl), hexadecyltrimethylammonium bromide (HDTABr), hexadecylethyldimethylammonium bromide (HDEDABr) and tetradecyltrimethylammonium bromide (TDTABr). In micelles with reactive counterions, the pseudo-first-order rate constant (k_obs) increases with the increase in surfactant concentration, while in micelles with non-reactive counterions, the rate constant increased with surfactant concentration at low concentration, reaching a maximum, and decreased at high surfactant concentration, even to below the value found in the absence of micelle. The micellar binding constant of both drugs (K_S), the micellar rate constant (k_M) and the ion-exchange constant (K_X^OH) were determined according to variation in k_obs in relation to surfactant concentration, through the application of the pseudophase ion-exchange model (PPIE) proposed. The empirical parameters obtained were found to depend on the substrate and the surfactant structure, these parameters were: the counterion of the micelle, the size of the headgroup and the chain length of the hydrophobic tail of the surfactant.     

A theory of the magnetic susceptibility of composites

The absorption of ac magnetic field energy by nonconducting composites made with fillers consisting of microscopic magnetic inclusions with various shapes is investigated over a wide range of frequencies and temperatures. It is predicted that the temperature dependence of the susceptibility χ(ω,T) of these structures is nonstandard only when the interaction between particles of the finely dispersed phase is included. The effect of the magnetic particles is taken into account by introducing a stochastic force into the Boltzmann equation, and using the resulting equation to calculate the susceptibility χ, which is a complicated function of the concentration p of the added dispersed phase. It is shown that the susceptibility should have a singularity near the point p=p _cr. Fiz. Tverd. Tela (St. Petersburg) 39, 1622–1627 (September 1997)     

金属Fe薄膜的PLD制备及其非线性光学性质研究

采用脉冲激光沉积（PLD）技术在MgO基片上制备了金属Fe薄膜.利用原子力显微镜研究了不同制备温度对薄膜表面形貌的影响.x射线衍射分析表明沉积温度大于500℃时，Fe薄膜在MgO基片上有很好的结晶性，并有单一取向.通过z扫描方法测量了超薄Fe膜的光学非线性，得到了Fe薄膜的非线性折射率n₂＝709×10^-5cm²/ kW，非线性吸收系数 β＝-552×10^-3cm/W. 关键词： Fe薄膜 非线性 脉冲激光沉积     

Linear and nonlinear optical absorption coefficients in inverse parabolic quantum wells under static external electric field

In the present theoretical study, the linear and third-order nonlinear optical absorption coefficients have been calculated in GaAs/Ga_1−x Al _x As inverse parabolic quantum wells (single and double) subjected to an external electric field. Our calculations are based on the potential morphing method in the effective mass approximation. The systematic theoretical investigation contains results with all possible combinations of the involved parameters, as quantum well width, quantum barrier width, Al concentration at each well center and magnitude of the external electric field. Our results indicate that in most cases investigated, the increase of the electric field blue-shifts the peak positions of the total absorption coefficient. In all cases studied it became apparent that the incident optical intensity considerably affects the total absorption coefficient.     

Methods of measuring the nonlinear-optical coefficients of the refractive index of nonlinear media

A cousistent analysis of a method of measuring the coefficient n ₂ of the Kerr nonlinearity and the two-photon absorption coefficient in presented. The method is based on the study of the dependence of the nonlinear transmittance with respect to the far-field axial intensity of the laser beam on the position of the layer of the nonlinear medium on the z (longitudinal) coordinate of this beam (z scanning). The possibility for the measurement of n ₂ and the two-photon (multiphoton) absorption coefficient based on the study of the far-field variations in the spatial profile of the beam having passed through the nonlinear medium is also analyzed. The calculations prove the efficiency of the new method for measuring n ₂ and the two-photon (multiphoton) absorption coefficient.     

Rheological behaviour and shear thickening exhibited by aqueous CTAB micellar solutions

In this experimental work we carefully investigate the rheological behaviour and in particular the shear thickening exhibited by aqueous micellar solutions of CTAB with NaSal as added counterion. We are particularly interested in the evolution of the critical shear rate (at which shear thickening occurs) versus C _D , the surfactant concentration. We show that , at fixed salt concentration C _S , increases with C _D following a power law evolution with a positive exponent of + 5.8. On the other hand we show that if the ratio C _D / C _S is fixed, decreases with C _D with a negative exponent of -2.0. Nevertheless investigations of the zero shear viscosity indicate that in all situations (implying variation of the surfactant concentration C _D , or the salt concentration C _S or the temperature) is a decreasing function of the length of the micelles. All these evolutions are compatible with a gelation mechanism which could possibly be associated with entanglement effects of large interacting flowing structures. Received: 3 March 1998 / Revised: 16 June 1998 / Accepted: 3 July 1998