Within the Singles-CI approximation, the perturbation theory expression for γ (the non-resonant third-order nonlinear optical susceptibility) contains a class of terms which correspond to (i) the creation of an s-type exciton (ii) a transition to a p-type exciton, and (iii) a return to the ground state through an s-type exciton. The contribution of these terms to γ is considered in the limit of an infinite chain of polyacetylene. The infinite chain limit is obtained by considering a ring of polyacetylene and allowing the ring size to go to infinity. The limit is approached using three methods, each of which reveals a different characteristic length of the system. The form of the excitons is found to be independent of ring size for rings which are larger than the size of the exciton.

Using Floquet theory together with density matrix formalism, an exact, nonpertur-bative expression for the optical susceptibility of a three level system interacting with a single mode electric field is derived. By using a three state model that mimics a polymeric system, it is shown that in certain cases, using typical values for the intensity of the electric field, successive terms in the series χω=χ(1) + χ(3) E2… approach the same of order magnitude.

Experiments have shown that the third-order nonlinear spectrum of trans- polyacetylene has two peaks at 0.6 eV and 0.9 eV respectively. None of the existing theories can give a quantitatively satisfying interpretation. A new theory is proposed in this paper by considering the excitation-dependent damping, and the theoretical results agree with the observed spectrum very well.

Linear and nonlinear optical (NLO) polymeric materials with good processabilities are discussed. An azo-dye substituted copolymer (3RNO2, nitro-terminated diazo dye) are investigated. The polymer film was found to be transparent and attenuation loss was less than 2 dB/cm. The χ(3) of 3RNo2 reaches 5×10−11 esu in the near-resonant region. With polymers where the dye molecules are introduced into the polymer backbone (a main chain polymer), a χ(3) larger than 10−11 esu is obtained even in a monoazo dye introduced polymer. A new molecular crystal, symmetrically substituted benzylidene-aniline compound, SBAC for short, are also successfully polymerized (introduced into a polymer main chain) and their χ(3) values are revealed to be around 1010 esu in the near-resonant wavelength region. The optical transmission of these polymers is also investigated and revealed to be around 2 dB/cm. With poly(arylene vinylene), a certain population of χ-conjugation length will induce enhancement of the resonant χ(3) of the polymers. The polymer can be used to fabricate channel waveguides with the photo-bleaching technique.

The research described in part in this manuscript is a multi disciplinary effort to target key applications and material and processing requirements for these third order nonlinear optical polymers. It discusses the synthesis, characterization, and processing of nonlinear optical properties of polyimides which have been tailored for nonlinear optical activity.

This paper discusses the third-order nonlinear optical (NLO) properties of substituted phthalocyanines measured by time-resolved degenerate four-wave mixing at 1064 nm. The study explores optical pumping as a mechanism contributing to a large third-order optical nonlinearity in one member of this interesting class of NLO materials, PbPc(CP)4.

Dihydrogen, copper, platinum, and lead octakis(2-ethylhexyloxy)phthalocyanines (Pc's) were studied in polystyrene films at 532 nm and in chloroform solutions at 1064 nm by picosecond degenerate four wave mixing. Resonant χ(3) values of Pc's at 532 nm (a local minimum in the absorption spectrum) at a time coincident with the 20 psec pump pulses were as high as 104 times that of CS2 by extrapolation of the response from 1 wt % PtPc in polystyrene film to a value for pure PtPc. Delay of the probe pulse as long as 3 nsec revealed acoustic responses stronger than the fast electronic responses. The films showed the expected quadratic dependence of the instantaneous reflectivity on incident intensity only for a decade of magnitude of intensity, 100–1000 MW/cm2, with the output saturating at higher intensities. Excited state absorption at 532 nm was detected in the film samples by pulse-probe spectroscopy and was shown to be a factor in the saturation observed in the NLO signals. Nonresonant χ(3) values at 1064 nm were as high as 120 times that of CS2 from measured responses of 1 wt % chloroform solutions of Pc's. Time delay of the probe revealed both fast electronic and slower acoustic responses at 1064 nm too.

Novel electrooptical effects in ferroelectric liquid crystals with high spontaneous polarization (Ps ) are observed. They are connected with the formation of a modulated distribution of the macroscopic dipole moments of smectic layers if going along the layer normal. The period (D) of this modulation (ferroelectric domains) near the electrode surfaces (DS) and in the bulk (DB) of a FLC-specimen can differ appreciably, depending on an applied external voltage. The main role of the value of the effective spontaneous polarization is established. A variuos number of domain structures and corresponding diffraction patterns are observed under variation of frequency and amplitude of the external electric field. A simple explanation of the new electrooptical responses is proposed on the basis of interference and incommensurability of bulk and surface domains.

Photoconductivity measurements on an epoxy-based photocrosslinkable second-order nonlinear optical (NLO) polymer - DGENC - NAC ( diglycidyl ether of nitrocatechol / nitroaniline prepolymer functionalized with cinnamoyl groups) are presented. Without introducing any sensitizer or charge carrier transport agents, large photoconductivity was obtained in this polymer system. Optical excitation of the NLO chromophores leads to photocarrier generation and it is conjectured that these NLO chromophores also play a role in the carrier transport. This polymer is one of the candidate materials for photorefraction.

Temperature and frequency dependent measurements are utilized to study the relaxation behavior of a photocrosslinking nonlinear optical (NLO) material based on a polyvinylcinnamate (PVCN) polymer matrix. 3-cinnamoyloxy-4-[4-(N, N-diethylamino)-2-cinnamoyloxy phenyl azo] nitrobenzene (CNNB-R) is used as a functionalized NLO active dye. Measurements of dielectric properties of PVCN doped with different levels of CNNB-R have been performed. NLO dye molecules were bonded to the host polymer by ultraviolet irradiation. Measurements were carried out from 50 to 200 °C and a frequency range of 30 Hz to 1 MHz. The effects of dye content and UV irradiation on the dielectric response are discussed.

An easily processable photocrosslinking guest-host system with stable second order nonlinear optical properties using polyvinylcinnamate as a host polymer has been developed1–2. Samples were made as free standing films from photo-crosslinkable polyvinylcinnamate and different concentration levels of 3-cinnamoyloxy-4-[4-(N, N'-diethylamino)-2-cinnamoyloxy phenyl azo] nitrobenzene. Photo-crosslinking was carried out by ultraviolet radiation at the major wavelengths viz. 297 and 313 nm subsequent to corona poling. Dynamic mechanical properties of these polymer films were investigated. The changes in the storage and loss moduli, as well as relaxation behavior of the system upon crosslinking and poling are discussed.

As an orientation control technique for organic materials, epitaxial growth on crystal substrates was studied for DBNA, a derivative of p-nitroani1 ine, and polydiacetylene(PDA)-3BCMU using Vacuum Deposition and Molecular Beam Epitaxy(MBE).

The thin film of DBNA was epitaxially grown on a KCl(001) surface by Vacuum Deposition. Molecular orientation to the substrate (parallel or normal) was controlled by MBE. PDA-3BCMTJ thin films were prepared by UV light irradiation of DA-3BCMU(monomer) thin films which were epitaxially grown on a KCl(001) surface, x(3) values of this oriented thin film were larger than those of unoriented spin-casted thin film.

THERMID, made of acetylene-terminated polyimide oligomers, was developed by National Starch & Chemical Co. It is capable of forming thicker deposits than conventional polyimides. It is a candidate for a broad array of electronic and optoelectronic applications, including passivation coating, alpha-particle barrier, interlayer dielectric, encapsulation of discrete devices and IC, optical waveguide, and multilayer dielectric for thin hybrids. The study and evaluation of electrical and optical properties of THERMID polyimide give more support to their application in the semiconductor industry.

The third-order nonlinear optical properties of a series of homopolymers and a random copolymer of conjugated aromatic Schiff base polymers have been investigated by picosecond third harmonic generation spectroscopy in the wavelength range 0.9–2.4 um. The off-resonant χ(3)(-3ω;ω, ω, ω) value at 2.4 μm was found to be 1.6×10−12esu for the parent polymer (PPI). 2, 5-Dimethoxy and 2, 5-dihydroxy substitutions or random colpolymerization was found to enhance the nonresonant optical nonlinearity of PPI by a factor of 1.5–4.5. 2-Methyl substitution lowered the χ(3) value. The three-photon resonance enhanced χ(3) of the polymers was in the range l.l×10−11 to 5.2×l0−11 esu. A three-level essential states model was found to describe the observed χ(3) spectra and the resulting fitting parameters were used to explain the observed trends in structure - χ(3) relationships.

The third-order nonlinear optical properties of thin films of two series of conjugated rigid-rod polyquinolines, exemplified by poly(2, 2'-(l, 4-phenylene)-6, 6'-bis(4-phenyl quinoline)) (PPPQ, 2d) and poly(2, 7-(l, 4-phenylene)-4, 9-diphenyl-l, 6-anthrazoline) (PPDA, 3d), were investigated by third harmonic generation spectroscopy. Of the nine polyquinolines with diverse backbone structures, PPPQ has the largest optical nonlinearity with a χ(3) (-3ω; ω, ω, ω) value of 3.2 × 10−12 esu and 3.3 × 10−11 esu in the off-resonant and three-photon resonant regions, respectively. A comparison of the nonresonant χ(3) of the series of nine systematically derived polyquinolines showed that a scaling law of the form χ(3) ∼ (λmax)v ∼ Eg -v does not hold; in fact, the nonresonant χ(3) was essentially independent of the optical bandgap. These results suggest that structure-χ(3) propeny relationships in polymers cannot be inferred from those of oligomers and model compounds.

The molecule 2-(2-benzthiazolyl)-1-(2-thienyl)ethene has been studied by x-ray crystallography and has been found to be in the planar conformation with the double bonds in the trans configuration (from the N=C of the benzthiazole to the first double bond in the thiophene). Semi-empirical calculations show this configuration to be the least stable one by 1.5 Kcal/mole. To determine whether this discrepancy is due to crystal packing forces or a deficiency in the semi-empirical methodologies employed, ab initio Hartree-Fock calculations at the RHF/6–31G* level were performed on the four possible planar conformations. A comparison of the AM1 and the Hartree-Fock calculations indicates that while AM1 reproduces the trend in the energy components well, the trend in the total energy is not reproduced well. Comparisons with the experimental structure are also made. Analysis of the second hyperpolarizability indicates an enhancement of the NLO properties of this molecule over that of the uncapped polyenes.

This paper reports a potential new organic crystal materials MHBA whose cut-off wavelength is 370nm and powder SHG intensity is 30 times higher than that of Urea. The crystal structure, single crystal growth, linear and nonlinear optical properties of MHBA are reported in detail. MHBA crystal belongs to monoclinic system; space group is P21, and the unit cell parameters are: a=14.057Å, b=7.875Å, c=15.037Å and β=115.45°. The nonlinear susceptibilities are: d11=25.0d36KDP, d12=10d36KDP, d13=33.3d36KDP and d14=8.3d36KDP.

The third order nonlinear optical (NLO) response of metal free tetrakis(cumylphenoxy)-phthalocyanine, (H2Pc(CP)4) was investigated at 597 nm, near resonance with the strong Q band. The second hyperpolarizability, γ, and the figure of merit, χ(3)/α, measured with a 1.2 ps pulse. was approximately independent of concentration between a 4.6×10−4 M solution and a neat thin film. The decay of the nonlinear response, however, depended substantially on the concentration and physical state of the material.

Time-resolved degenerate four-wave-mixing studies have been conducted on solutions of transition-metal complexes of benzenedithiol using a 35 ps Nd:YAG laser operating at 1.064 μm. The nonlinear optical properties of the first-row Co(d7), Ni(d8), and Cu(d9) and the d8 group Ni and P t transition metal complexes are discussed.

we outline three methods for the preparation of fullerols as polyhydroxylated fullerene derivatives through the reaction of fullerenes with electrophilic reagents. The synthetic methodology includes a sequence of reactions using an aqueous acid chemistry, the epoxidation reaction, or the interesting nitronium chemistry as an key approach for the conversion of fullerenes to fullerols. The structure of fullerols was characterized and proposed to consist of at least 13 hydroxy functional moieties incorporating both hydroxy and hemi-ketal as parts of the structural components.