The second order nonlinear optical response of two dipolar thiopheno-quinoid chromophores are calculated using extensive single and double-excitation configuration interaction. The (beta) values are found to be comparable in magnitude to those for the pheno-quinoid systems. The sign of the nonlinear response is, however, found to be positive in these systems, in contrast to the second-order nonlinear optical response of pheno-quinoid structures which are known to be negative.

Solvatochromy of fluorescence emission of new fluorine- containing chromophores with high second order hyperpolarizability (beta) is studied in solvents of different polarity. Together with UV/VIS-absorption spectra and electro-optical absorption experiments the result of the fluorescence experiments are used to calculate hyperpolarizabilities of chromophores using a simple two level model. Although the general shape of the investigated molecules was kept constant the chemical structure was varied by introduction of heteroatoms into the conjugated part of the molecules, and by partial fluorination of the molecule. The selected kind of substitution lead to different ground state geometries, and to different linear and nonlinear optical properties as well. The increase of fluorine content also leads to a reduction of refractive index which can be important to certain electro-optical applications. The investigated fluorine-containing chromophores show (beta) -values which are comparable with those of standard NLO-dyes like disperse red I but exhibit different linear optical properties.

Fullerene (C₆₀) was doped into porous Corning Vycor glass host while preserving its second order susceptibility. The range of loading factor is from 2 by 10E16 fullerene molecules/g of glass to 2 by 10E17 molecules/g. The susceptibility of the fullerene is substantially enhanced from the thin film value of 10E-15 esu, as reported in the literature. The observed second harmonic signal showed a broad spectrum similar to that of the thin film as the transition is vibration-assisted. The second harmonic signal was excited with the fundamental of a Q-switched Nd:YAG laser. Signals from those high loading factor samples that are oriented at a certain angle relative to the beam are comparable to that of powdered LiNbO₃. This geometry- related enhancement is interpret as a quasi phase-matching enhancement resulted from the observed birefringence. This birefringence originating from the C₆₀/Vycor interaction within the nanopores and nanochannels is enhanced over that of the glass alone. Loaded glass samples of 2-mm thickness showed a weak absorption in the visible region but good transmission in the IR. No thermal degradation was observed after irradiating the samples with the Nd:YAG laser for 2000 seconds at 1 kHz repetition rate pulses with a power input density of Mw/cm².

The linear and non-linear optical properties of two members of the S-5-nitro-N(1-phenyl ethyl)-2-pyridinamine (MBANP) family have been measured. These data have been analyzed together with previous work on MBANP itself and its racemate. There is strong evidence that neither Kleinman's conjecture nor the oriented gas model can be used to predict the second order non-linear properties of such materials. This contradicts the earlier indications based on partial determinations of (chi) ⁽²).

The present paper deals with the traditional and some new applications of the single crystal x-ray diffraction analysis of NLO materials. Traditionally, x-ray diffraction is used to prove molecular structure of a compound of interest, to establish crystal space group, packing array and features of the molecular geometry. This approach has been used in analysis of a large series of new organic NLO chromophores including substituted dicyanovinylaromatics, and some other NLO materials. Most of the compounds studied were found to demonstrate high molecular second-order optical susceptibilities. It was shown for the series of substituted dicyanovinylbenzenes what factors are responsible for the centric or acentric crystal structure of a given compound. Several new compounds of the series studied were found to exhibit a rather strong second harmonic generation signal in the solid state, in particular, 0-fluoro-dicyanovinylbenzene, p-dimethylamino- dicyanovinylbenzene, and 4-(4-methoxyphenyl)-1,1-dicyano- 1,3-butadiene, 4-MeO-C₆H₄-CHequalsCH-CHequalsC(CN)₂. Molecular and crystal structures of these compounds have been studied and analyzed. Another new application of the x- ray diffraction method in the study of NLO compounds is analysis of the electron density distributions in crystal and direct estimation of some of its characteristics responsible for NLO properties directly from the diffraction data. These opportunities of the method were demonstrated in the charge density study of crystals of DIVA and nMA. Second order optical susceptibilities were estimated from the diffraction data using a multiple model and were found to be close to the experimental values.

The electromechanical properties of ultrathin films of polyglutamates with either a preferential polar upright orientation of the helical chains or an orientation parallel to the substrate plane are compared. The electric field- induced change in film thickness as determined by an electromechanical interferometer is used to measure of the degree of polar order and the mechanical compliance. Following the approach by Whitesell and Chang monomolecular films of 15 nanometer thickness of the helical polypeptide poly((gamma) -benzyl-L-glutamate) (PBLG) were grown directly from a flat aluminum surface. The measured PBLG film polarization was found to be comparable to that of conventional ferroelectric materials. This result demonstrates that the polymerization starting from the surface forces the helical chains into a polar arrangement. A large mechanical plate modulus of the film of approximately 35 GPa as determined by electrostriction agreed with the theoretical prediction for a single PBLG molecule along the chain axis.In contrast to this, Langmuir- Blodgett layers of poly((gamma) -octadecyl-co-methyl-L- glutamate)s, bearing long flexible side chains, exhibited only negligible piezoelectric activities, as the helices are oriented parallel to the substrate surface.In this case the mechanical properties were almost entirely determined by the structure and packing of the flexible side chains.

This is a preliminary report on alternating polyelectrolyte deposition (APD) with the goal of making electro-optic films at room temperature. By means of the APD method, films were built up layer-by-layer at room temperature by a dipping process. APD requires two complementary polymers, one being negatively charged and the other being positively charged. The polymer in solution is attracted to the solid substrate by coulombic forces to form the next layer on the substrate. For the first time, second-order nonlinear optical (NLO) polymer films were prepared by APD in which both polymers were NLO-active. The cationic polymer contained a side-chain stilbazole chromophore, and the anionic polymer contained a main-chain cinnamoyl chromophore. The intensity of the second harmonic signal generated in the film increased quadratically with each layer for the first twenty layers.

The Langmuir-Blodgett (LB) films of tolan derivatives were studied by a new second-harmonic generation (SHG) phase measurement in terms of the directional sense of the net dipole moment and molecular structures. 4-Docosylamino-tolan derivatives with 4'-nitro group (ANT-22) or 4'-dicyano-vinyl (DCNANT-22) group were transferred by horizontal lifting. In rotational Maker-fringe, the envelope of ANT-22 LB film shows an in-plane polar anisotropy, and that of DCNANT-22 LB film shows a polar anisotropy perpendicular to the substrate. Nonlinear optical chromophore in ANT-22 is bound to lie almost flat upon the plane of the substrate, while DCNANT-22 molecules in thick multilayers tend to align perpendicular to the substrate. It was found by SHG phase measurement that the directional sense of the net dipole moment of ANT-22 was perpendicular to the compression direction.

The Langmuir-Blodgett (LB) film structure of E-4-[(N- octadecyl-6,7,8-trihydro-5-isoquinolylidene)methyl]-N,N- dibutylaniline octadecylsulfate is non-centrosymmetric when the dye is deposited on the up-stroke (Z-type) and when the layers are interleaved with poly(t-butyl methacrylate). The second-harmonic intensity increases as I_(N)^2(omega ) equals I₍₁)^2(omega )N², where N is the number of active layers, and the intensity is further enhanced when the dye is mixed in a 1 to 1 ratio with octadecanoic acid. The second-order susceptibility and repeat lattice spacing of the mixed LB films are as follows: (chi) _zzz⁽²) equals 76 pm V^-1 at 1.064 micrometers and l equals 3.15 nm layer^-1 when Z-type; (chi) _zzz⁽²) equals 52 pm V^-1 and l equals 4.13 nm bilayer^-1 when interleaved. The films are transparent at the fundamental wavelength and have a slight absorbance of ca. 5 X 10^-4 per dye layer at 532 nm. The second-harmonic intensity is the strongest to date from such a weakly absorbing LB film and this is attributed to the close proximity of the charge-transfer band and to an optimized packing arrangement.

Meta-nitroaniline (mNA) and 2-cyclo-octylamino-5- nitropyridine (COANP) single crystal films with thickness of 5 to 20 micrometers were grown between two transparent fused quartz plates on which indium-tin-oxide layers were deposited. Both linear and quadratic electro-optic effects of the crystals were examined by an ac modulation method. The figures of merit for mNA and COANP are estimated to be 3.2 X 10^-2 m/V and 4.2 X 10^-12 m/V, respectively. The crystals were of high quality due to the excellent protection provided by the cells and the figure of merits of the crystals did not decrease with time. It is believed that the method adopted in the paper is applicable to electro-optic cell fabrication with other compounds if those crystals are grown from melt are feasible. It is suggested that the electro-optic cells have excellent potential use for device fabrication because of their durability and relative easy manipulation during crystal growth.

A challenging issue to design devices for photonic applications is to achieve a complete manipulation of the molecular order. Azo-dye aromatic polymers have been shown to offer interesting prospects for material engineering using light matter interactions. Dual-frequency irradiation using appropriate combinations of circular beams polarizations are demonstrated to enable full control of the molecular polar rotation. More recent results on photoinduced surface-relief gratings have also opened the way of molecular translation control using optical fields. Understanding of the relevant parameters of molecular translation processes is a key issue for optimization of such optomechanical effect: a simple model accounting qualitatively for the essential features of photoinduced surface-relief gratings is presented. It illustrates the application of optically powered molecular motors.

Femtosecond hyper-Rayleigh scattering (HRS) is used for the suppression of multi-photon fluorescence contributions to the apparent HRS signal. The intrinsic high harmonic content of the femtosecond pulse is used as a high frequency amplitude modulation source. Due to the nonzero fluorescence lifetime, a high amplitude modulation frequency will result in an amplitude demodulated and phase shifted fluorescence signal. At very high modulation frequencies, the fluorescence signal becomes completely demodulated and only the inherent HRS signal will remain. Experimental verification has been obtained by the fluorescence suppression for a well known centrosymmetric fluorophore, 9,10-diphenylanthracene, added to a solution of a well characterized nonlinear optical chromophore, crystal violet. A comparison has also been made between the first hyperpolarizability value (beta) of a nonfluorescent ionic hemicyanine dye and the (beta) value of the fluorescent inclusion complex of the dye incorporated in an amylose matrix. The inherent fluorescence-free (beta) value for the complex appeared to be twice the value for the dye itself.

Femtosecond hyper-Rayleigh scattering (HRS) has been used to prove the spatial orientational fluctuations between nonlinear optical chromophores as dopants in spincoated polymer films. The fluctuation in the second-order incoherently scattered light intensity upon micro- translating the solid sample is indicative of the degree of spatial correlation between the individual chromophores. The decay of the autocorrelation function of this fluctuating signal is characterized by a spatial correlation length. Electric-field poling of dipolar chromophores is shown to increase this correlation length. The longer correlation length after poling results from a higher degree of spatial orientational correlation between the individual chromophores. The temporal characteristics of this correlation length have been studied and compared with thermal relaxation times, obtained with coherent second- harmonic generation (SHG). A significant difference in relaxation time between coherent (SHG) and incoherent (HRS) measurements in electric-field poled thin polymeric films has been observed experimentally. Based on the intrinsic symmetry requirements for even-order nonlinear optical effects, rotational relaxation of the chromophore only was invoked in combination with translational diffusion of free volume in the polymer matrix over the coherence length for coherent second-harmonic generation and over the wavelength in the incoherent case.

Optical enhancement or decrease of the nonlinear optical (NLO) properties of organic compounds is expected at the excited state due to changes in dipole moments and oscillator strength caused by electron density distribution different from that at the ground state. It is necessary to evaluate NLO properties at the excited state in development and practical application of highly functional organic molecules. A novel excited state hyper-Rayleigh scattering (HRS) measurement system was constructed to evaluate hyperpolarizability (beta) at the excited state of molecules in solutions. The system is composed of a ns Nd:YAG probe laser of various intensities and a ns tunable pump laser for excitation. The HRS intensity at 2(omega) for p-nitoaniline in methanol solutions, proportional to the square of the incident laser power, increased upon excitation at 464nm and also depended on the delay time between a pump and a probe pulse. The (beta) value for p-nitroaniline at the excited triplet state was evaluated.

Electric field poling of nonlinear optical (NLO) polymer films at very high electric fields can lead to (chi) ⁽²)- distributions with poor spatial homogeneity, making such films unsuitable for optical devices. We report on further improvements of our scanning second harmonic microscopy using scanning near field optic techniques and on result on scanning optically poled films. Using a scanning Kelvin microprobe, a 2D image of the charge and polarization distribution inside the polymer films can be obtained. Similarities between the charge image and the second harmonic image are observed and allow to analyze the casus of the (chi) ⁽²)-fluctuations. By measuring poling currents through triple stack layers and simultaneously detecting the second harmonic response, the internal electric field inside the NLO-film can be determined. Amorphous SiC:H layers, which were obtained by plasma enhanced chemical vapor deposition, are shown to be suitable for optical buffer layers and for dielectric interface coatings.

Monitoring of electrical field poling processes by optical polarimetry (EFPOP) is presented as a simple alternative method for the study of induced noncentrosymmetry, related to nonlinear optical second-order effects in organic chromophore-doped sol-gel films. Dynamics of EFPOP has been closely followed in guest-host systems, consisting of porous sol-gel silicate film matrices doped with p-nitroaniline, as evidence of the EFPOP sensitivity to chromophore orientational order.

We present novel, fully functionalized, photorefractive (PR) polyesters. The chemical design and the material's glass transition temperature well above room temperature allows for permanent poling of these systems. The photorefractive properties were determined via degenerate four-wave mixing and two-beam coupling experiments as a function of the applied external electric field and the degree of permanent poling. Due to the restricted orientational mobility of the chromophores, the PR effect is reduced to an almost pure charge-generation and transport phenomenon. Consequently, the temporal response of the systems is limited by charge- generation or transport processes only. Degradation of the materials is substantially limited because of the covalent attachment of the photoconducting as well as the nonlinear optical moieties to the polymer backbone. No crystallization or phase separation was observed. The system show response times of about 200 ms with (Delta) n approximately equals 1.10^-3. To our knowledge, this work presents the first characterization of PR efficiencies for fully functionalized polymers as a function of the permanent Pockels coefficient (chi) ⁽²).

Linear conjugated, fluorine-containing chromophores are differing from conventional chromophores like disperse red one by a reduced linear refractive index. Second order nonlinear optical susceptibilities of asymmetrically substituted fluorine-containing dyes reach, however, values as high as those of DR I or of similar chromophores. This can be concluded from measurements of solvatochromy of absorption and fluorescence spectra, electroabsorption measurements, and from quantum chemical calculations carried out for a series of azomethine and azo dyes. The chemical constitution of the conjugated part of investigate chromophores has an important influence both on linear and non nonlinear optical properties. So azomethine dyes show a blue shifted absorption in comparison to the absorption of azo chromophores. This goes along with lower off-resonant second order susceptibility. Introduction of fluorine into the acceptor part of the molecule by attaching a CF₃- group does not lead to a significantly lower second order susceptibly in comparison to non-fluorinated chromophores. Perfluorination of the acceptor part result in case of the investigated molecules in an increased second order susceptibility as compared to the non-fluorinated chromophore. Polymers which contain these chromophores are either prepared by physical doping or by covalent bonding of the dyes to the polymeric main chain.In case of physically doped polymers the classes of thermally stable allylic polymers and of polyphenyl quinoxalines (PPQs) were used as matrix material. These polymers show miscibility with the investigated chromophores up to high concentrations and are haracterized by glass transition temperatures between 140 degrees C and 180 degrees C or 180 degrees C and 350 degrees C (PPQs) dependent on chemical structure and on dye concentration. Polymers which contain the active chromophores in side chains were prepared on basis of maleic acid anhydride or as novolak epoxy amine aduct polymer. The former can be utilized for preparation of waveguides by means of Langmuir-Blodgett technique while the later provide films of excellent quality by spin-coating and subsequent corona poling. Second order susceptibilities of the polymer films as determined by second harmonic generation reach values between 5 and 27 pm/V dependent on chromophore concentration and preparation conditions.

The high-performance photorefractive polymer hybrid liquid crystal structures are investigated in detail by use of optical tow-wave mixing technique. In such structures an amplification of laser light can be realized by two-beam coupling mechanism. Photorefractive properties of the structures rely on the spatial light induced charge carrier density modulation in thin film of photoconducting polymer. The spatially modulated space-charge field induces efficient reorientations of molecules of adjacent to polymeric layer nematic liquid crystal forming, in this way, the refractive index grating. Efficient energy transfer between the incident and the higher-order diffracted beams has been observed in dynamic self-diffraction process on thin phase gratings at oblique light incidence. The phase shift between the light intensity pattern the light intensity pattern and the refractive index modulation grating, responsible for the energy exchange, can be controlled by the applied electric field enabling reversal of direction of energy flow. Energy transfer and diffraction efficiency are found to exhibit different response characteristics with fringe spacing, voltage, cell parameters and light modulation-depth. The net exponential gain coefficient reported for the structures amounted to (Gamma) approximately equals 2600 cm$_-1) and was obtained at driving voltages of the order of 1 V/micrometers .

Optical nonlinearity and multiplex holographic storage using azo side-chain polymer are studied by using degenerate four- wave mixing and polarized pump-probe laser method. The He-Ne excitation laser wavelength is located at the tail end of the absorption peak of the sample. This material shows high grating diffraction efficiency and promises information storage capability using weak absorption. The diffraction efficiency of the grating is up to the order of 10^-2. The effect of input beam polarization planes on grating is studied. The diffraction grating efficiency is lowest when the polarization of the redout beam is orthogonal to that of both writing beams. An angle multiplex holographic storage study is also performed in the sample. Information can be stored for a long time at room temperature. The information readout of this multiplex holographic storage system can be controlled by the polarization state of the readout beam. Dependence of grating diffraction efficiency on the sample temperature is studied. It is demonstrated that the higher the temperature under the melting temperature of the sample, the higher the diffraction efficiency and the faster the relaxation time of the grating. The grating is completely erased by increasing the temperature over the melting temperature of the sample. Reading the grating with a circularly polarized light does not erase the grating. When two recording beams are turned off, a large part of the grating remains for a long time and only a small part of the grating degrades. The results show that the azo side-chain polymer is a good information storage material. The anisotropic optical nonlinear refractive index of the sample is also measured. The relationship of the nonlinear refractive index of the samples, the different ratios of azo functional groups in the polymers, and the temperature of the sample are also studied. The highest nonlinear refractive index is up to the order of 10^-2. The optical nonlinearity of the samples increase with increasing sample temperature. No anisotropic nonlinearity appears when the temperature of the sample is over the melting temperature of the sample. The anisotropic nonlinearity levels of three samples with different azo side-group ratios in the polymer are compared.

Two stilbene derivatives, DANS and CNDS, were synthesized. The optical properties of organic doped PMMA poled polymer films were investigated with in situ second-harmonic generation (SHG) measurement and UV-visible absorption measurement. Optimum corona poling temperatures of the polymer films were studied. The second-order susceptibility (chi) ^(2_ of CNDS/PMMA is larger than that of DANS/PMMA, although CNDS molecules in PMMA is less ordered than DANS. The molecular second-order polarizability (beta) of the CNDS was estimated to be about 1.4 X 10^-28esu. The relaxation of SHG intensity of CNDS/PMMA was slower than that of DANS/PMMA. It is concluded that CNDS is a better dopant than DANS as second-order nonlinear-optical material.