Characterization of intensity-dependent optical rotation phenomena in chiral molecules in solution

The rotation of the plane of polarization of linearly polarized light by chiral molecules in solution is due to a forward scattering event. Ordinary optical rotation, a single-photon effect, is independent of intensity. As the light intensity is increased, other effects can appear, such as two-photon scattering or alignment of the molecule by one photon and scattering with a change of polarization by another. Both of these effects result in intensity-dependent (or nonlinear) optical rotation. A polarimeter was used to measure the nonlinear optical rotation of solutions in a heterodyne experiment. No nonlinear optical rotation was found in molecules lacking an absorption band near the laser frequency. In the three pyrimidine nucleosides studied, which do have such an absorption band, a nonlinear optical rotation was identified that was cumulative with each laser pulse. The effect persisted with a time constant that was on the order of seconds and characteristic of the molecule.     

Luminescence tuning and enhanced nonlinear optical properties of nanocomposites of ZnO-TiO2

In this article we present the spectral and nonlinear optical properties of ZnO-TiO(2) nanocomposites prepared by colloidal chemical synthesis. Emission peaks of ZnO-TiO(2) nanocomposites change from 340 nm to 385 nm almost in proportion to changes in E(g). The nanocomposites show self-defocusing nonlinearity and good nonlinear absorption behaviour. The nonlinear refractive index and the nonlinear absorption increase with increasing TiO(2) volume fraction at 532 nm and can be attributed to the enhancement of exciton oscillator strength. ZnO-TiO(2) is a potential nanocomposite material for the tunable light emission and for the development of nonlinear optical devices with a relatively small limiting threshold.     

Axially modified gallium phthalocyanines and naphthalocyanines for optical limiting

Phthalocyanines (Pcs) offer a high architectural flexibility in structure, which facilitates the tailoring of their physical, optoelectronic and chemical parameters over a very broad range. This tutorial review describes the recent advances in the synthesis of soluble axially substituted or bridged gallium phthalo- and naphthalocyanine compounds, and their photophysical and nonlinear optical properties. The exploitation of the chemical reactivity of the Ga-Cl bond can allow the preparation of a series of highly soluble axially substituted and bridged Pc complexes. Axial substituents in Pcs influence favourably nonlinear optical absorption for the presence of a dipole moment perpendicular to the macrocycle in the axially substituted phthalocyanines. All Z-scans performed exhibit a decrease of transmittance about the focus typical of an induced positive nonlinear absorption of incident light. Substitution and dimerization of the phthalocyanine monomer resulted in significant reductions in the saturation energy density of the material displaying clear evidence of the usefulness of structurally modifying the gallium phthalocyanine unit. Similar to indium phthalocyanines, gallium phthalocyanines are also among the most promising materials that have been investigated as limiters of intense light and the current series presents a selection of structural modifications useful for varying their nonlinear optical properties.     

Large third-order optical nonlinear effects of gold nanoparticles with unusual fluorescence enhancement

The third-order nonlinear optical properties of two solutions of gold nanoparticles protected by carbazolyldiacetylene derivatives were investigated using the Z-scan technique. Both gold nanoparticle colloid solutions in toluene show unusual fluorescent enhancement and large third-order nonlinear optical properties including nonlinear absorption and refractive effects. When extending the pi-conjugated length of the ligands, the third-order nonlinear properties of composite materials based on gold nanoparticles were enhanced accordingly.     

Syntheses, and optical, fluorescence, and nonlinear optical characterization of phosphine-substituted terthiophenes

Earlier studies of phosphine-substituted terthiophenes have demonstrated that some of these materials exhibit nonlinear absorption at 532 nm. However, this wavelength is significantly removed from the linear absorption maxima of the complexes, suggesting that better nonlinear absorption might be observed at wavelengths closer to the linear absorption maxima. To investigate this possibility, a library of compounds has been prepared either by varying the group attached to the nonbonding pair of electrons on the phosphorus atoms of 5,5'-bis(diphenylphosphino)-2,2':5',2'-terthiophene (PT(3)P), or by introducing additional substituents on the 5'-position of 5-(diphenylphosphino)-2,2':5',2'-terthiophene (PT(3)). All these compounds have been characterized using multinuclear NMR, UV-vis, and fluorescence spectroscopy. The compounds are strongly fluorescent, and both the fluorescence wavelength and the intensity depend upon the thiophene substituents. The nonlinear optical properties have also been evaluated at various wavelengths in the blue region. Each compound exhibits reverse saturable absorption, and the intensity of the reverse saturable absorption at a particular wavelength depends on the chemical structure of the compound.     

Single-beam Z-scan measurement of the third-order optical nonlinearities of azo dyes

Organic dyes are very attractive optical materials for photonics and biophotonic applications. To quantitatively characterize their third-order nonlinear coefficients we have performed the experiments on two different azo dyes using a diode-pumped Nd:YAG laser at 532 nm. The |chi(3)| is of the order of 10(-6) esu. The relative contributions from nonlinear absorption (NLA) and nonlinear refraction (NLR) are dependent on the chemical structure and linear absorption of the dyes.     

Nonlinear optical properties of tetrapyrazinoporphyrazinato indium chloride complexes due to excited-state absorption processes

The multiphoton absorption properties of the axially substituted tetrapyrazinotetraazaporphyrinato complex Pyz(4)TAPInCl (1) are reported and interpreted. In particular, the nonlinear optical transmission of the complex and the excited states involved in the nonlinear absorption have been determined at the frequency of the second harmonic generation of a Nd:YAG laser in the nanosecond time regime. Pyz(4)TAPInCl has an excited-state absorption cross section larger than its ground state in the 460-540 nm spectral region, and it shows an optical limiting (OL) behavior at 532 nm, which derives from a sequential two-photon absorption with a larger absorption cross section of the excited triplet state with respect to the ground state. It results that the absorption cross section of 1 in the excited triplet state is 7.8 x 10(-18) cm(2) vs 0.9 x 10(-18) cm(2) of the ground state at the wavelength of OL analysis.     

Refractive index and nonlinear optical properties of polyaniline derivatives

An investigation of the refractive index and third-order nonlinear optical susceptibility χ⁽³⁾ of two polypernigraniline derivatives, poly (4,4'-diphenylimine methine) (PDPIM) and poly (4,4'-diphenylimine p-heptyloxybenzylidene) (PDPIHB) reveals effects of molecular structure on the linear optical and nonlinear optical properties of conjugated polymers. The χ⁽³⁾ (?3ωω,ω,ω) of PDPIM was found to decrease relative to polypernigraniline, reflecting the observed decrease of the oscillator strength of the 2.2 eV absorption band when a methine carbon replaces one of the nitrogen atoms of pernigraniline repeat unti. The alkoxyphenylene side group substitution at the methine carbon in PDPIHB, however, significantly enhances the nonlinear optical response of PDPIHB while reducing the refractive index compared to PDPIM and polypernigraniline. The present results suggest that structural changes in conjugated polymers can be made in such a way as to enhance the nonlinear optical properties while modulating the linear optical properties. © 1994 John Wiley & Sons, Inc.     

Electronic interactions in a branched chromophore investigated by nonlinear optical and time-resolved spectroscopy

The third order nonlinear optical properties of a trimer branched chromophore system and its linear molecule analog are investigated. Two-photon absorption and degenerate four wave mixing measurements were carried out on both systems. An enhancement in the nonlinear optical effect is observed for the branched trimer molecule in comparison to the linear chromophore system. Ultrafast time-resolved measurements were carried out to probe the excited state dynamics in the branched structures. The time-resolved measurements suggest that the two important processes affecting the nonlinear optical properties in the trimer system, charge transfer stabilization and initial electronic delocalization, occur on two different time scales.     

两个二茂铁基查尔酮衍生物的合成及超快三阶非线性光学响应

合成两种新颖的含二茂铁基团的查尔酮衍生物：1-二茂铁基-3-(4-叔丁基苯基)丙烯酮(a)和1-二茂铁基-3-联苯基丙烯酮(b),经₁H NMR、₁₃C NMR、HR-MS对其结构进行了表征;测定了该两化合物的热力学性质;采用量子化学方法计算了它们的分子轨道能量和极化率,给出了轨道电子云图;采用紫外-可见吸收光谱和Z-扫描技术测定了其线性和非线性光学性质。结果表明：与原料相比,化合物a和b的紫外吸收明显增加,且b的吸收波长更长;化合物a和b均存在分子内电荷转移现象,表现出超快三阶非线性光学响应。     

Synthesis and nonlinear optical absorption properties of two new conjugated ferrocene-bridge-pyridinium compounds

Two electron donor-π-acceptor (D-π-A) chromospheres, with ferrocene as the electron donor and pyridinium as the electron acceptor, were synthesized. The nonlinear optical absorption (NOA) properties in the solution state were investigated by the Z-scan technique. Both compounds exhibited reverse saturable absorption (RSA) and optical limiting effect under nanosecond pulse irradiation.     

Synthesis and nonlinear optical properties of chromophores for photorefractive polymer materials

The synthesis and nonlinear optical (NLO) properties of a series of nitrostilbene-, dinitrostilbene-, and dicyanomethylenedihydrofuran-based chromophores potentially useful in photorefractive multifunctional polymers are reported. Electronic absorption spectra have been measured in different solvents. Electric field induced second harmonic (EFISH) generation results show that the 2-dicyanomethylen-3-cyano-5,5-dimethyl-2,5-dihydrofuran moieties lead to the best NLO performances. Dinitrophenyl-based chromophores have shown a reduced nonlinear response as compared with the mononitro analogues. Nonlinear optical properties of a selected nitro-dinitro couple have been also determined theoretically.     

Evaluation of nonlinear optical polymers for second-harmonic generation: toward the balance of absorption and nonlinearity against intrinsic trade-off

Despite many advantages toward nonlinear optical (NLO) waveguide devices, NLO polymers have not been adopted successfully into practical wavelength converters due to their high absorption losses. Empirical and theoretical understandings about NLO susceptibility imply the fundamental trade-off between optical absorption and nonlinearity. Our theoretical analysis elucidates the effect of absorption losses on second-harmonic generation (SHG). We compare analytically maximum conversion efficiencies for several NLO polymers and found a convincing approach for the development of NLO polymers with the optimum combination of high optical nonlinearity and low material absorption, which leads us to realize efficient polymeric SHG devices.     

Core-modified expanded porphyrins with large third-order nonlinear optical response

The third-order nonlinear optical response through measurement of two-photon absorption cross-sections (TPACS) for aromatic core-modified expanded porphyrin analogues by a femtosecond open aperture Z-scan method is reported. The values reported here are among the largest known so far in the literature for any organic molecules.     

Growth,optical, thermal,dielectric and mechanical studies of sodium hydrogen succinate single crystal

Sodium hydrogen succinate, an alkali metallo-organic third-order nonlinear optical crystal, had been grown successfully using aqueous solution by slow evaporation technique at room temperature. Transparent single crystals were selected and subjected to single-crystal X-ray diffraction analysis to identify lattice parameters, space group and morphology. The grown crystal was further subjected to powder X-ray diffraction to analyze the crystalline quality, UV–Vis–NIR spectral analysis to reveal optical transparency, FTIR spectroscopy for confirmation of the functional group analysis and TG–DTG/DSC analysis to determine the thermal stability. The dielectric constant and dielectric loss were studied as a function of frequency at different temperatures, and the results were discussed. The mechanical properties were calculated by Vickers microhardness test, and the third-order nonlinear optical parameters such as nonlinear refractive index, nonlinear absorption coefficient and real and imaginary parts of the third-order nonlinear optical susceptibility were determined by Z-scan technique.     

Heterogeneous exciton dynamics revealed by two-dimensional optical spectroscopy

We show that optical two-dimensional (2D) spectroscopy can recover ultrafast heterogeneous dynamics of closely spaced delocalized exciton states from a molecular exciton manifold characterized by a single absorption band. The complete experimental third-order nonlinear optical response from room-temperature J-aggregates in liquid phase is reproduced for the first time with self-consistent Frenkel exciton theory combined with modified Redfield theory. We show that exciton relaxation between the exciton states and nuclear-motion-induced exchange-narrowed energy fluctuations of individual delocalized exciton states can be distinguished because these two processes lead to a distinctively different evolution of the absolute 2D spectrum. Our technique also allows recovery of the variation of the exciton relaxation rates as well as the degree of exciton delocalization across the absorption band.     

新型双重电荷转移分子的二阶非线性光学性质的 理论研究

以INDO/SCI方法为基础,按完全态求和(SOS)公式编制了计算分子二阶非线性光学系数β~i~j~k和β~μ的程序。研究了1,2-二氨基-4,5-二硝基苯1和其异构体1,3-二氨基-4,6-二硝基苯2的电子光谱和二阶非线性光学性质。计算表明分子1具有与分子2几乎相等的二阶非线性极化率。但由于分子1的偶极矩明显大于分子2的,故分子1的μβ值比分子2的μβ值大的多。在此基础上,研究了2,3-二(β-苯乙烯基)-5,6-二氰基吡嗪和2,3-二(β-噻吩乙烯基)-5,6-二氰基吡嗪和2,3-二(β-噻吩乙烯基)-5,6二氰基吡嗪衍生物的电子光谱和二阶非线性光学性质。结果表明,这些化合物均具有两个相距很近的强吸收峰,它们对β值的呈加和模式。由于这类化合物特征吸收峰均位于413nm以下且具有大的μβ值,所以,它们是一类很有前途的二阶非线性光学候选材料。     

Synthesis, growth, spectral, thermal, mechanical and optical properties of 4-chloro-4′dimethylamino-benzylidene aniline crystal: A third order nonlinear optical material

An organic nonlinear optical material, 4-chloro-4′dimethylamino-benzylidene aniline (CDMABA), was synthesized by the condensation of the p-chloroaniline and p-dimethylaminobenzaldehyde. Solubility of CDMABA was determined in acetone at different temperatures. Single crystals were grown by the solvent evaporation method from acetone solution at room temperature. Grown crystal was subjected to FTIR, FT-Raman and ¹H NMR spectral analyses to confirm the synthesized compound. The range and percentage of optical transmission was ascertained by recording UV–vis–NIR spectrum. Thermal properties were investigated by Thermo Gravimetric, Differential Thermal and Differential Scanning Calorimetric analyses. High Resolution X-ray Diffractometry (HRXRD) was employed to evaluate the perfection of the grown crystal. The third order nonlinear optical parameters (nonlinear refractive index and nonlinear absorption coefficient) were derived by the Z-scan technique.     

Nonlinear optical properties of polyvinylcarbazole composites with graphene

The study has focused on polyvinylcarbazole (PVK) composites with graphene. It has been shown that there is a noticeable nonadditive shoulder on the long-wavelength edge of the optical absorption of PVK in these samples, which can be attributed to the formation of a charge-transfer complex between PVK as a donor and graphene as an acceptor. The formation of the complex causes a significant nonlinear optical effect in the PVK/graphene composite. The revealed increase in both the nonlinearity coefficient with increasing laser intensity and the cross section with increasing incident energy density is due to the formation of the graphene^?· radical anion, an additional species contributing to nonlinear absorption, with an increase in the radiation energy density. Nonlinear optical properties of PVK composites with graphene isolated from a solution in tetrachloroethane after 1.5-h centrifugation (sample 1) have been considered. It has been suggested that a significant decrease in optical transmission of laser radiation by the composite T _OA = 0.4 at an energy density at focus of 502 J/cm² is due to the formation of the PVK/graphene charge-transfer complex responsible for the nonadditive shoulder on the long-wavelength optical absorption edge of PVK. During photoexcitation of graphene in the PVK/graphene composites at a laser wavelength of 1064 nm, mobile holes are generated in PVK, indicating the formation of graphene^?· radical anions as a result of charge transfer from PVK to photoexcited graphene. The observed increase in both β with an increase in the laser radiation intensity and the cross section (σ_exc — σ₀) with an increase in the incident energy density may be due to either the contribution of nonlinear transitions (S ₀ → S ₂, S ₀ → S ₁ → S ₂, T ₁ → T ₂) or the formation of the additional species, the graphene-· radical anions, participating in nonlinear absorption by increasing the energy density at the focus (F _foc, J/cm²).     

Synthesis and crystal structure of 21,23-dithiaporphyrins and their nonlinear optical activities

A series of novel 21,23-dithiaporphyrins have been synthesized and determination of their optical nonlinearities demonstrated that they have much larger nonlinear refractive cross section than normal porphyrins and exhibit reverse saturable absorption.