The tricyanoquinodimethane group is one of the strongest (pi) -acceptors known to date. Yet it has not been employed as an acceptor in NLO chromophores with common aromatic (pi) -bridges. As an easily accessible example 7-(4-di-n- butylaminophenyl)-7,8,8-tricyanoquinodimethane is examined with respect to thermal/chemical stability and nonlinear optical efficiency. A derivative bearing an hydroxyethyl- spacer was synthesized and covalently attached to functionalized polyimides in a polymer analogous reaction. The second harmonic generation coefficients (d₃₃) of the resulting nonlinear optical polymers were measured using the Maker-fringes experiment.

In this study highly polarizable metallic complexes of Cu²⁺, Ni²⁺, and Cr³⁺ of Bis(salicylaldiminato) Schiff base have been synthesized. These nonlinear optical materials showed second harmonic generation (SHG) when they were pumped 1.06 micrometers Nd:YAG laser. The intensity of the SH signal varied between the metal complexes, being strongest for Ni-salen complex. An extensive study for these materials has been done to characterize their optical quality and chemical stability. We report here the synthesis, nonlinear optical characterization, electron paramagnetic resonance, FTIR, thermogravimetric measurements and the second order nonlinear response of thermally robust series of donor- acceptor substituted Bis(salicylaldiminato) Ni²⁺, Cu²⁺, and Cr³⁺ complexes.

A case study on the formation of electro-optic perhydrotriphenylene (PHTP) inclusion lattices is presented. Exploration of the capacity to include nonlinear optical (NLO) molecules shows for the first time that most linearly shaped and known NLO building blocks exhibit parallel alignment when co-crystallized with the PHTP host compound. Materials exhibiting macroscopic polar properties were obtained with a success rate of nearly 90%. A critical discussion on the possible real structures of polar PHTP inclusion lattices is given.

Electric Field Induced Second Harmonic GEneration (EFISH) and the electro-optic Kerr effect were applied to solutions of double stranded DNA, in which the average strand length varied from 2958 base pairs to 140 base pairs. This size range covers the transition from the `rod-like' model (which applies to samples < about 300 base pairs) to the `worm- like' model. In both these electro-optic measurements the electric dipole moment is primarily ionic in nature, and shows a saturating length dependence, although saturation occurred at different lengths. Saturation occurred at longer lengths for EFISH than for the Kerr effect.

The orientational order of amorphous or liquid crystalline polymers with azo or stilbene chromophores can be altered by polarized light. This photoorientation process is explained by a mechanism based on photosensitive trans-cis- isomerization cycles. Monte-Carlo simulations of the process in combination with quantum mechanical calculations show the time-evolution of the photoinduced refractive index change. The different dynamic behavior of various chromophores which is observed experimentally can be explained by the photochemical properties of the dyes. The application of the materials for optical storage and holographic optical elements is discussed.

Photoassisted poling of azo-dyes in polymer films is now well-known: it is a consequence of trans-cis photoisomerization. We report new experiments involving the photoisomerization of spiropyrans into merocyanines. With the help of a theoretical model, we discuss poling mechanisms. The study of the relaxation of electro-optical properties of photomerocyanine gives new results on the rotational mobility of dye molecules in polymers: in addition to the site-to-site variation, it is necessary to introduce a time variation of the mobility, after the end of the poling process.

We report on electrical conduction phenomena occurring during high electric field electrode poling of side chain (chi) ⁽²) polymers. Electric current and second harmonic intensity were measured simultaneously in poling experiments performed on samples with and without an additional inorganic poly-methyl-siloxane layer. Current densities appeared to be limited by a Bardeen-type potential barrier at the electrode/insulator interface. The field dependence of current density was found to be Schottky charge injection for medium field strengths (E_POL <EQ 100 V/micrometers ) whereas it was dominated by Fowler-Nordheim tunneling at higher poling fields. In the presence of the buffer layer, a significant suppression of tunneling was observed which leads to a reduced probability of singular breakdown events and shifted the limit of avalanche dielectric breakdown to higher internal effective poling fields.

We report on the first use of high-(Beta) micrometers nonlinear- optical chromophores in photorefractive polymer composites based on poly(N-vinylcarbazole). We demonstrate that the photorefractive effect in these materials originates mostly from the electrooptic effect whereas in high-performance materials known to date the photorefractive effect mostly originates from an orientational birefringence resulting from a nonuniform orientation of the electrooptically active chromophores.

Langmuir-Blodgett (LB) films of the amphiphilic, metal free, phthalocyanine 1,4-di(4-hydroxybutyl)-8,11,15,18,22,25- isopentyllphthalocyanine (A40iso5H₂) have been deposited onto a hydrophobically treated glass side. Extrapolation of the pressure-area isotherm shows the area per molecule to be approximately 161 angstroms², which is consistent with similar phthalocyanines. The relationship between absorption and film thickness was studied by measuring the absorption spectra of increasing numbers of monolayers. A mathematical program was used to fit the absorption peaks and hence allow calculation of the phthalocyanine molecule angle on the substrate surface in the characteristic herringbone structure. Measurement of the diffuse reflectance spectra enabled a calculation of the refractive index and extinction coefficient to be made across a range of wavelengths. The step structure of the films was analyzed using a scanning electron microscope to investigate film homogeneity at the boundary and across the film surface. The films were deposited onto a layer of gold in order to excite surface plasmons with a 632.8 nm He-Ne laser. The optical constants of the LB films were determined at this wavelength from the surface plasmon curves using a fitting procedure. The results obtained at 632.8 nm were compared with the values calculated from spectroscopic data, and found to be in good agreement.

Nonresonant photoinduced birefringence of an acceptor-donor azo dye doped in polymethyl methacrylate film was studied by degenerate four-wave mixing and Z-scan methods with a He-Ne laser. The sample has appreciable large third-order nonlinear susceptibility and polarization sensitivity. The nonlinear mechanism of the material originates from photoinduced birefringence of polar azo molecule.

Hyper-Rayleigh scattering is used to investigate the nonlinear optical properties of novel organometallic compounds. For a series of ruthenium and gold y-arylacetylides, including some bimetallic complexes, the influence of the organometallic donor group, chain length and type of acceptor on the quadratic hyperpolarizability is studied. The hyperpolañzabiities found are among the highest (1027 esu) known for organometallic compounds. Moreover, electric-field induced second-harmonic generation confirms these values and indicates that only one major tensor component is present. Keywords: hyper-Rayleigh scattering, nonlinear optics, second-harmonic generation, organometallic compounds

We address two experimental issues concerning the measurement of depolarized Hyper-Rayleigh scattering (HRS). The first issue concerns with the possibility of two-photon induced fluorescence (TPF). We observed that the depolarization of TPF from crystal violet, which is an octupolar molecule with a very short fluorescence lifetime, is identical to that expected theoretically for HRS. This makes distinguishing the two processes difficult. The second issue concerns with the way second harmonic light is collected in a HRS measurement. We developed a simple procedure to ensure the depolarization ratio measured would correspond to the ideal 90 degree(s) scattering from a point source. We measure the depolarized HRS of p-nitroaniline (PNA) using this improved technique. The result indicates that the hyperpolarizability tensor of PNA has essentially the characteristics of a rod-like structure, with a single nonvanishing diagonal component (beta) ₃₃₃, where the 3- axis corresponds to the polar direction. This is in contrast with previous-theoretical calculations, which predicted non- negligible values for some of the off-diagonal components. A plausible explanation of the experimental result is suggested based on a model of the local field correction factors.

Time-reversal symmetry property of the nonlinear optical hyperpolarizability is examined in terms of the Manley-Rowe power relation to find relationship to the overall permutation symmetry. An extended symmetry relation is discovered reducing the independent number of the hyperpolarizability tensor components describing the second- order nonlinear optical processes. Experimental implications are discussed.

Hyper-Rayleigh scattering has become the technique of choice for the determination of the first hyperpolarizabilities of non-linear optical (NLO) molecules. Moreover, by exploiting the sensitivity of this second-order NLO-technique to molecular and supra-molecular symmetry, this technique was upgraded to a powerful spectroscopic tool. We did this by probing the symmetry of NLO-functionalized dendrimers, measuring the first hyperpolarizability at different generations. These results are compared with measurements on side-chain NLO-functionalized linear co-polymers with different degrees of NLO-functionalized along the polymer backbone. The measurement show, in a unique way at the molecular level, that the dendrimers in solution form globular structures at generations with 32 and 64 end-groups with restricted mobility of the end-groups.

In this work, we have investigated theoretically the structure/hyperpolarizability correlations of push-pull molecules sing a two-form two-state model. For this, we have defined a parameter MIX characterizing the mixing between the two-limiting resonance forms and thus ruling the molecular structure and polarization. Also, we have analyzed the solvent effect on the structure and on the polarizabilities of push-pull molecules using the Onsager reaction field theory. We have shown that the dependences of the linear and nonlinear polarizabilities on the solvent dielectric constant look similar to the structure/(hyper)polarizability correlations. Finally, we have investigated experimentally the solvent effect on a series of push-pull polyenes of increasing length. In particular, we have determined the scalar (mu) _g(Beta) (0) product (where (mu) _g is the ground-state dipole and (Beta) (0) the vector part of static quadratic hyperpolarizability tensor) in different solvents using the electric-field-induced-second-harmonic generation technique. For the different chain lengths, we have obtained a mapping of the positive (mu) _g(Beta) (0) peak. This leads for the longest compound of the series to a record high value of (mu) _g(Beta) (0) product in chloroform.

A hyper-Rayleigh scattering, HRS, system constructed around an optical parametric power oscillator, allowing wide fundamental wavelength tunability is described. The benefits of this system are highlighted by out-of-resonance measurements of the octupolar molecular ion crystal violet at 1450 and 1500 nm. The static hyperpolarizability was found to be comparable with that of the dipolar dye Disperse Red 1 with the nonlinearity-transparency trade-off worse for the octupole. Multiphoton induced fluorescence is one of the major obstacles with HRS. With a tunable laser system this problem can be overcome for a lot of chromophores. This is demonstrated by HRS-measurements of two dicyanovinyl compounds at 1300 nm and a stilbazolium salt at 1500 nm.

This investigation explores the effect that aromatic subgroups have on the nonlinear optical properties of highly conjugated multi-dimensional molecules. In particular, carbon-cage fullerenes, porphyrins and phthalocyanines have been studied The optimized geometries were determined from all-electron ab-initio calculations. The nonlinear properties were obtained using the finite field approximation. Data of polarization versus static electric field was obtained from valence-electron semi-empirical calculations using the AMI Hamiltonian. The static electric fields were created using a variety of conditions. Polynomial fits were performed with 14 to 400 data points. The nonlinear properties were extracted from expansions of order four to sixteen. These last three conditions allowed estimation and minimization of the uncertainty in the results. Aromaticity was evaluated by analyzing the molecular geometry.

A way to control the bandgap in semi-conducting polymers is by preparing polymers with a partially conjugated backbone. In our laboratory, three conjugated copolymers containing PPV trimers as light emitting chromophores have been synthesized, which emit in the blue, green and orange wavelength region. The copolymers have a well defined conjugated backbone consisting of regularly alternating terphenylene and p-phenylene-vinylene blocks. The desired control of conjugation length is achieved through steric interaction induced by the side-chains in the terphenyl blocks of the copolymer. In this paper we evaluate the electrical and optical properties of LED devices based on these conjugated PPV block copolymers.

The advantage of organic materials like polystyrene is their plasticity so that they can be made into any shape. Polystyrene has a rather large refractive index of 1.58 and can be easily doped with the required laser dye and also can be made into spheres of the required size. Fabrication of microspheres was basically carried out by J. Vanderhoff and his assistants at Lehigh University. The host material in all of these samples is polystyrene. Microspheres doped with Bis-MSB, PPO and alpha-NPO dyes were studied with suitable lasers like UV, N₂ and XeCl excimer. We have observed enhanced emission and lasing action at certain wavelengths which correspond to the whispering gallery modes of polystyrene spheres. Characterization of the lasing process in microspheres with respect to their sizes will be presented. The 2D crystalline structure on a periodic array thin films of polystyrene microspheres has been studied by both diffraction and microscopic techniques and will be presented as well.

We present efficient blue electroluminescence devices based on pure soluble poly(paraphenylene) polymers and poly(phenylene) oligomers. Highly efficient green and red emission light is produced with a new color conversion technique by pumping fluorescent dye layers with blue organic light-emitting diodes. The high intrachain order of the laddertype poly(paraphenylene) allows us to observe stimulated emission in the blue-green spectral regions, which does not compete with dissipative processes, like in other conjugated polymers. We discuss the state of the art situation to realize an optically pumped homopolymer solid state laser.

The considerably interest in the possibility of fabricating efficient optical limiters based on solid-state materials have led us to develop an easy method for producing RSA compound doped in PMMA. The chosen RSA dye was a soluble silicon phthalocyanine (SiPc(OC₇H₁₅)). By comparing the non linear absorption of this compound in solution in THF and in PMMA, we show that broadband solid-state limiters can be made with such a dye for visible nanosecond-pulse excitation. The importance of broadband criterion such as the photopic transmission to adjust the transmission at low incident energy in conjunction with the color neutrality are also stressed.

The transient absorption spectrum of a nonaggregated vanadylphthalocyanine solution has been measured by a subpicosecond pump-probe spectroscopy technique. A biexponential response with time constants of 4 ps and 800 ps has been observed. The dependence of the polarizations of pump and probe light has been investigated. The parallel-to- perpendicular ratio, i.e. the ratio of transient absorption change between configurations where pump and probe polarizations are parallel and perpendicular to each other, respectively, is 4:3. This is different from the ratio in ordinary 1D molecules, reflecting the 2D character of the vanadylphthalocyanine molecule.

The optical limiting response and excited-state absorption properties of a novel organic polymer (poly(5-2-methythio-4- methyl-5-pyrimidinyl)-2,4-pentadine-1-ol)-p-toluene sulfinate) in chloroform solvent have been investigated and its solutions almost have no absorption in visible spectral range. A Nd:YAG laser source with 8-ns/21-ps pulse width and 532-nm wavelength was employed. The pulse-width-dependent measurements indicated that the optical limiting mechanism is excited state absorption along with nonresonant two photon absorption. The open aperture Z-scan was also performed to measure the molecular excited state absorption coefficient. The nanosecond optical limiting behavior of the various concentration solution samples with nominal transmissions of 87%, 56% and 26% have been measured as a function of the beam fluence. The theoretical fitting result of excited state cross section can be fitted on the mode that excited-state absorption is the predominant mechanism causing the observed optical limiting behavior.

Using nonlinear polymer waveguides in integrated optics requires an adaptation of the device to the very special waveguiding characteristics of polymer films. We present in this paper new devices based on diffraction gratings for electro-optic modulation and potentially high efficient second-harmonic generation that are in general well suited to the use of polymers. We optimized the devices through numerical simulation to the use of PNA-PMMA films. We obtain experimentally 40% light modulation at (Delta) V equals 51.9 V (r₃₃ equals 4.3 pm/V) concerning electro-optic modulation and a conversion efficiency of (eta) equals 5.83 * 10^-6 1/W ((chi) ₃₃ equals 8 pm/V) for second-harmonic generation.

Photothermal beam deflection spectroscopy (PTBDS) is used together with waveguide loss measurements to distinguish between intrinsic, absorptive and scattering losses in polymeric waveguide materials. Overtones of vibrational modes of organic waveguide materials in the near infrared spectral regime can be distinguished very precisely with PTBDS. In an example of different polythiophens, we demonstrate the influence of the sidechains (CH_2- and CH₃-vibrations) and the conformation of the mainchain on the absorption spectrum in the spectral regime of optical telecommunications. The photothermal beam deflection method is also used for imaging waveguide structures and to investigate order parameters of dyes within a polymeric matrix.

The fabrication and characterization of high speed polymeric modulators are summarized in this paper. Electro-optic polymer modulators, made of a thermally crosslinked polyurethane with Disperse Red 19 side groups, have been fabricated, packaged, and tested for fiber-optic transmission applications. Two waveguide structures, straight channel waveguides and integrated Mach-Zehnder interferometers, were defined by reactive ion etching on corona poled polymer thin films. Microstrip line electrodes were used for wideband frequency response. The modulators have been fiber pigtailed, connectorized, and packaged with single mode optical fibers and wideband RF connectors, and packaged in rugged cases. Modulator performance and stability characteristics including halfwave voltage, frequency response, insertion loss, long term halfwave voltage stability, DC bias stability, and optical power handling capability at 1.3 micrometers wavelength were tested. Applications of the packaged polymer modulators in analog and digital transmission systems were also demonstrated.

We describe the applications, fabrication, and performance of thermo-optic polymer waveguide 1 X N switches.

Large photovoltaic responses have been recently observed in devices based on conjugated polymer-C₆₀ blends. Their enhanced performance, which relies on the formation of a bicontinuous network of donor-acceptor heterojunctions, is very sensitive to the morphology of the blend. In this paper, we propose sexithiophene-C₆₀ blends, prepared by coevaporation, as a model system for the study of these devices. Preliminary results suggest a microphase-separated morphology with a domain size comparable to the exciton diffusion length. A photovoltaic device with quantum efficiency of 1% is demonstrated.

Dc drift phenomenon in electro-optic polymer modulators has been analyzed. It is found that the dc drift originates from the difference between the dielectric relaxation times of the guiding and cladding layers. The dc drift is accelerated as the intensity of the guided light increases. Furthermore, when exposed to visible light, it becomes faster and the transmittance of the guided light decreases. The effect of the guided light and visible light on the dc drift is interpreted in terms of the photoconductivity of guiding layer.

We show, using AMPAC (Semichem, Inc.) AMI calculations of extended cyclophane structures that the third order polarization displays significant large magnitude negative Finite-Field (gamma) (0)s. Magnitudes as large as -85,000 X 10^-36 esu are calculated. Anticipated significant linear loss issues are not addressed, though no effort has yet been made to optimize ether for maximum magnitude (gamma) or minimum magnitude linear loss structure. It is expected that such a systematic theoretical and experimental optimization of molecules should lead to materials possessing unprecedented magnitudes of (gamma) , and possibly with sufficiently low loss to be practical.

Progress on second-order nonlinear optical polymers for high speed optical signal modulation is reported. New accordion polymers containing head-to-head backbone chromophores extended with a styryl-thienyl-vinyl linkage are described. The maximum absorption of the electronic transition (ground state yields excited state) for these polymers occurs at a wavelength of 494 nm. A corona-poled film of the ortho-xylyl bridged accordion polymer has a resonance-enhanced second- order nonlinear optical coefficient of 120 pm/V measured at 1.06 microns, and a glass transition temperature of about 187 degree(s)C. Along with linear polymer, polar cyclic dimers were formed during the polymerization. An extraction process was developed to remove the cyclic dimers from the polymer.