Recently, there has been much interest in doped polymeric materials owing to their suitability for optical device applications.[1] While most of this effort has been centered on poled polymers and their applications to electrooptics, doped polymers are beginning to emerge as a promising material class for all-optical device applications. In this contribution, we discuss the status of doped polymers as third-order optical materials. Particular attention is focused on those properties that make doped polymers attractive as device materials such as optical nonlinearity and loss and their suitability for nonlinear-optical fiber devices.

Third-order nonlinear optical properties of lyotropic liquid crystal poly(1,4-phenylene-2,6-benzobisthiazole), PBT, solutions are studied by third harmonic generation measurements. Besides the enhancement observed for this coefficient with respect to the pure PBT, coupling is observed between the mean filed nematic director n and the incident fundamental polarization B0. Different geometries, with respect to the relative orientation of B0 and n, provided different harmonic Maker Fringe Patterns. These data are compared using refractive index measurements, independently achieved on these materials, and necessary for Maker Fringe analysis.

Results are presented from third harmonic generation, (THG), experiments on a number of polysilane films. The polymers studied include poly(di-n-hexylsilylene) PDHS, and copoly(di-n-hexyl, hexylmethylsilylene) PDHS / PHMS. These polymers exhibit positive thermochromism, where the transition temperature and spectral properties are dependent on the copolymer ratio. The nonlinear susceptibility, , in the low temperature phase of the polymer increases by approximately 4 − 5 times that of the high temperature phase where the absorption maximum decreases by ∼ 60 nm. The polymers are prepared as neat, solid films on fused silica substrates. Thickness and refractive index measurements of these polymers were made by UV-VIS-NIR spectroscopy.

Soluble conjugated polymers, poly (3-alkylthiophene)s were prepared by chemically oxidative polymerization. The polymers had no absorption at wavelengths longer than 600 nm, indicating that the polymers were suitable for waveguide structures. Dispersion of refractive index (real and imaginary parts) was calculated from the reflectance data using the Kramers-Kronig relation. The dispersion agreed with the result obtained by ellipsometry. Third order optical nonlinearity, χ(3)(−3ω; ω, ω, ω), of the polymers was determined by optical third harmonic generation (THG). Enhancement of the χ(3) by three photon absorption was observed when a beam of 1.54 μm was used as a fundamental. Also, light propagation properties were investigated by using slab waveguides of the polymers.

The polydiacetylene having diacetylenic substituents has been prepared by γ-ray irradiated solid-state polymerization of 15, 17, 19, 21- hexatriacontatetrayne. It has been found that the polymer can be converted into the di(polydiacetylene), i.e., a new type of the fused-ring polymer of conjugated 10π-electron system, by the subsequent heat-treatment in the solid-state.

We report a novel method to obtain stable second order nonlinear optical (NLO) properties in polymeric thin films. Photocross-linking between the NLO active molecules and a photoreactive polymer is achieved by UV irradiation subsequent to poling. The thin film exhibits a nonlinear coefficient d33of 16.5 pm/V at a doping level of 20% by weight of NLO active molecules and possesses quite stable second order nonlinear optical properties

The second- and third-order nonlinear susceptibilities χ(2) and χ(3) of a polymer thin film are determined for three wavelengths (543.Snm, 632.8nm and 1523nm) using a method based on the linear and quadratic electro-optic effect. The frequency dependences of χ(2) and χ(3), deduced from a simple two-level electron-spring model, are consistent with our experimental results. Using this frequency dependence the intensitydependent refractive index, determined by nonlinear grating coupling, is transformed to a χ(3) value for the quadratic electro-optic effect. This value is in good agreement with our experiments. The layer structure used is simple and consists basically of a polymer layer sandwiched between thin metal electrodes.

Theoretical second hyperpolarizabilities for a series of iso-electronic conjugated inorganic systems, including polyphosphazenes, have been evaluated using electronic structure methods. The nonlinear optical properties of these molecules are controlled by the electronegativity difference along the backbone, which may be modulated by the electron donating/accepting properties of the ligands.

The third order nonlinear optical properties of thin films of polybenzimidazobenzophenanthroline ladder (BBL) and semi–ladder (BBB) polymers and their model compound cis–BBB were investigated by picosecond, third harmonic generation. The χ(3) (−3ω, ω ω, ω) spectrum of BBL, BBB, and cis-BBB was obtained in the wavelength range 1.0–2.4µm and shown to exhibit a three–photon peak at respectively 1.695, 1.695, and 1.50 µm. The magnitude of the three–photon enhanced χ(3) was 6.40×10−11, 3.15×10−11, and 0.77×10−11 esu, respectively, for BBL, BBB, and cis–BBB. The results show that the χ(3) of BBL and BBB is enhanced by a factor of 50 and 17, respectively, relative to the model compound cis–BBB at 1.05µm.

The temporal and thermal stability of second order nonlinear optical properties of polymers is an important issue in the development of poly meric electro-optic devices. This has been addressed by introducing interchain crosslinking. A number of crosslinked systems developed by photochemical reactions have been presented.

Planar waveguides from a photocross-linkable polymer have been fabricated on glass and Si0 2 on silicon using the spin coating process. The polymer has been cross-linked by exposure to UV radiation (λ = 254nm). Prism coupling technique has been used to couple a laser beam into the waveguide structure. The waveguiding parameters such as number of modes, loss, thickness, and index of refraction of the polymer have been determined before and after crosslinking. The refractive index of the polymer before cross-linking differs significantly from that after cross-linking. No anisotropy has been observed in the refractive indices for the uncross-linked or cross-linked samples. The refractive index and thickness of the polymer film before and after cross-linking have also been measured using an ellipsometer and found to be in very good agreement with those obtained by the prism coupling technique. Dye molecules with large second order hyperpolarizability were utilized as guests into the photocross-linkable polymer matrix for second order nonlinear optical applications. Electro-optic properties of this polymeric system are reported.

Recent activity in the development of nonlinear optical (NLO) materials with high second order susceptibilities has prompted the development of a wide variety of pendant polymers which possess desirable properties for device development, including high Tg minimal relaxation of the poled matrix, and high laser damage threshold. Ideal candidates for such systems are asymmetrically substituted oligomers of polyacetylenes such as dimethylaminonitrostilbene (DANS) and corresponding higher order oligomers. We report here a preliminary study of the synthesis of asymmetrically substituted donor/acceptor diphenyl-capped polyenes and thienylene vinylene oligomers attached as pendant moieties on polyvinylphenol (PVP) for second harmonic generation.

The optimum processing condition for a photocrosslinking Nonlinear Optical(NLO) polymeric system was established. Parameters such as change in heat capacity at glass transition temperature, rate of decrease of absorbance of residual uncrosslinked chromophores, and measurement of mass loss upon heating were used to set up the optimum condition. Poly(vinyl cinnamate) was used as the photocrosslinkable polymer and 3- cinnamoyloxy-4-[4-(N, N-diethylamino)-2-cinnamoyloxy phenyl azo] nitrobenzene was used as the NLO molecule. Poling at 70°C for 5 minutes followed by photocrosslinking with a dose of 2.5 mW/cm 2 for 10 minutes results in a stable second order nonlinear optical material.

The recently developed coherent microwave transient spectroscopy (COMITS) technique is capable of determining the complex dielectric properties of materials over a broad frequency range (15–140 GHz), in a single experiment. COMITS is based on the radiation and detection of picosecond duration electromagnetic transients by optoelectronically pulsed antennas. The essential features of the COMITS technique are described and representative results on dielectric and conducting polymers are presented.

It has been shown that the electrical conductivity of polymer blends filled with carbon black (CB) can be much higher than that of each constituent for the same level of loading. It is very difficult to understand this phenomenon due to the complexity of the three phases system. In particular it has been argued that the results could not be explained if the morphology of the blend was independent of the amount of CB. Indeed, an image analysis of the TEM and SEM micrographs of polymer blends filled with Ketjenblack (KB), reveals that the size distribution of the polystyrene component of the blend changes with the concentration of KB. One observes that an increase of 5% in KB results in a reduction of the average size of the PS component by 50% Since the KB dispersion seems to be linked to the dispersion of the polystyrene component our findings could explain why the dispersion is improved in the blend and gives rise to a lower percolation threshold.

The semicrystalline polyimide studied here has been developed by NASA Langley Research Center and film processed by Foster Miller Inc. Aromatic polyimides posess a unique property combination. The outstanding thermal stability (Tg above 230 C and Tm above 355 C) in addition to such other properties such as excellent radiation and solvent resistance is supported by excellent mechanical and electrical properties. For instance the tensile modulus of LARC-CPI is 513 ksi at 25 C and 206 ksi at 232 C, G1c=37.8 in lb/cm2 [1].

Molecularly doped polymer films have shown potential for applications in electrophotography and molecular electronics. The electrooptical and magnetic properties as well as conductivities are enhanced significantly by doping chargetransfer(CT) complexes or dye into a polymeric matrix, by comparison with nondoped polymer films.

Polycarbonate films doped with CT complexes based on 7,7′,8,8′- tetracyanoquinodimethane( TCNQ) were studied from 100K to 450K. Crystallization and formation of ‘nearly’ spaced aggregates within the polymer matrix were observed. These phenomena were affected by several factors such as the film thickness, evaporation process, temperature and concentration within the polymer matrix. Discontinuities in magnetic properties at 200K, possibly due to solvent encapsulation in the matrix, and at about 385K due to glass transition of the polymer were observed.

Characterization, conductivity measurements in comparison with pristine complexes, and photoirradiation studies on these doped films are presented.

Filled polymers containing conductive inclusions possess a number of unique microwave properties. The effective values of real ε1 and imaginary ε2 parts of complex dielectric permittivity ε=ε1 + εz of these materials may be easily changed by variation of their composition. The values of ε1 may have high (up to several hundreds) as well as negative meanings [1]. Besides, the filled polymers containing conductive inclusions may possess strong frequency dispersion of the effective dielectric permittivity at wavelengths λ∼1, where 1 is a size of inclusion. The investigation of dielectric properties of these materials at microwaves is of great interest as from the physical point of view as for technical applications.

A set of methods for measure complex dielectric permittivity of layer materials at microwaves is suggested. These methods allow one to measure dielectric permittivity of composite materials in with the mean size of inhomogeneities is comparable with the wavelength and materials with high dielectric permittivity.

Ab-initio STO-3G* geometry optimizations have been carried out on the first two oligomers of poly (p-phenylene sulfide) (PPS), namely diphenyl sulfide (I) (neutral species, radical cation and dication) and 1, 4-bis(phenylthio)benzene (II) (neutral species and radical cation). Aim of the work is to obtain a first theoretical insight into the geometry relaxation effects occurring in the doping of PPS. The results show that i) geometry changes in the radical cation of I are rather small, being much more pronounced in the dication, and ii) in the radical cation of II a strong geometry modification occurs, the central phenyl ring now lying in the plane of the C-S bonds with a clear quinoid-type structure. These findings are in agreement with our experimental results on the same two oligomers.