This PDF file contains the front matter associated with SPIE Proceedings Volume 7774, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Successfully predicting the frequency dispersion of electronic hyperpolarizabilities is an unresolved challenge in materials science and electronic structure theory. It has been shown1 that the generalized Thomas-Kuhn sum rules combined with linear absorption data and measured hyperpolarizabilities at one or two frequencies, may be used to predict the entire frequency-dependent electronic hyperpolarizability spectrum. This treatment includes two- and threelevel contributions that arise from the lowest two or three excited state manifolds, enabling us to describe the unusual observed frequency dispersion of the dynamic hyperpolarizability in high oscillator strength M-PZn chromophores, where (porphinato)zinc(II) (PZn) and metal(II)polypyridyl (M) units are connected via an ethyne unit that aligns the high oscillator strength transition dipoles of these components in a head-to-tail arrangement. Importantly, this approach provides a quantitative scheme to use linear optical absorption spectra and very few individual hyperpolarizability values to predict the entire frequency-dependent nonlinear optical response. In addition we provide here experimental dynamic hyperpolarizability values determined by hyper-Rayleigh scattering that underscore the validity of our approach.

We introduce a self-consistent theory for the description of the optical linear and nonlinear response of molecules that is based strictly on the results of the experimental characterization. We show how the Thomas-Kuhn sum-rules can be used to eliminate the dependence of the nonlinear response on parameters that are not directly measurable. Our approach leads to the successful modeling of the dispersion of the nonlinear response of complex molecular structures with different geometries (dipolar and octupolar), and can be used as a guide towards the modeling in terms of fundamental physical parameters.

Donor-acceptor biphenyl derivatives are particularly interesting model compounds presenting a charge transfer absorption band because the extent of conjugation, and therefore the amount of charge transfer between the substituents, may be varied by a controllable structural feature, namely the torsion angle between the two phenyl rings. This feature has become even more interesting since chromophores of strong zwitterionic character, synthesized with a twist of nearly 90°, have been shown to exhibit unprecedented quadratic responses [1], over an order of magnitude above that of the best conventional push-pull chromophores. In this context, we have investigated both experimentally and theoretically, two biphenyl based systems with varying inter-aryl angles: a nitro-piperidinyl series [2] of conventional push-pull character and a pyridinium-phenoxide series [3] of zwitterionic character. The results agree qualitatively with semiempirical simulations based on the AM1 Hamiltonian [4] used with the COSMO solvation model [5]. For the first series, the decrease in quadratic response with increasing dihedral angle indicates that oscillator strength loss is the dominant factor. In the second series, the corresponding increase in quadratic response points to the change in dipole moment upon excitation as the leading effect. Here, we will analyze to what extent the more ab initio electronic structure calculations based on the density functional theory may provide more quantitative results in spite of the problems they face in the description of charge transfer systems.

Conjugated polymers have been extensively studied and are implemented in devices such as transistors and lightemitting devices. We will present a solution-based study by linear and nonlinear optical characterization techniques in which we study the behavior of different substituted poly(thiophene)s. A profound hyper-Rayleigh scattering study has been performed in their neutral and oxidized oxidation state while continuously monitoring the transition.

Experimental investigations of two-photon absorption (TPA) cross-section using nonlinear transmission (NLT) and a new pump-probe mode-mismatched thermal lens (TL) scheme, in the picosecond regime are reported. Both methods are used in a prospect of comparison. Values of the TPA coefficient and cross-section in perylenediimide derivatives (PDI) at 532 nm and 1064 nm wavelengths are given.

A Mach-Zehnder interferometer (MZI) is used to decouple the electro-optic (EO) and piezoelectric tensor components for a poled polymer film. In the past those using the MZI method failed to take into account the piezoelectric contribution in the polymer which can lead to erroneous EO coefficient data. The typical poled sample of polymer sandwiched between ITO glass and gold that was developed for the popular Teng-Man reflection ellipsometry method is used, providing for easy comparison with that method. The sample serves as a mirror in one arm of the interferometer with the gold side facing the beam for measuring the piezoelectric modulation and the glass side facing the beam to measure the coupled piezoelectric and EO modulation. Optical biasing in the reference arm allows for the baseline and modulated contrast of the system to be measured from which the tensor components are calculated. This method has the advantage over the reflection ellipsometry method of allowing for the independent determination of the Pockel's coefficients r₁₃ and r₃₃ and the piezoelectric coefficient d₃₃. The r₃₃ value of a guest host polymer that consists of AJLZ53/amorphous polycarbonate (APC) was found to be 122.7 pm/V and 123.0 pm/V for the MZI and reflection ellipsometry method respectively. The r₃₃ data fits well to the dispersion of the second order susceptibility tensor χ ₃₃₃ ⁽²⁾ based on the two-level model approximation. Measurements were done from 100 Hz to 100 kHz with the results showing that at higher frequencies the mechanical effects in the sample are negligible and modulation is almost entirely due to the EO effect, as expected.

Size- and concentration-dependent of Rayleigh scattering properties of transparent TiO₂ nanohybrid polymer have been systematically investigated. By utilizing the Rayleigh scattering technique, we can obtain the Rayleigh ratio of TiO₂ nanohybrid polymer prepared with different concentrations of TiO₂. We observed that these Rayleigh ratios are strongly dependent on the size and concentration of the nanoparticles. The larger the size and concentration of nanoparticles is, the larger the Rayleigh scattering is. Furthermore, this technique can be used to examine the saturation effect of Rayleigh scattering observed at high input power, and evaluate the size uniformity of nanoparticles in nanohybrid polymer.

Theoretical calculations have demonstrated that the ratio of second and third degree order parameters can define lattice dimensionality and furthermore, that an increased ratio of second to third degree order parameters represents reduced lattice dimensionality. As a result, the third degree order parameter (i.e. acentric order parameter) is increased, causing an increase in electro-optic activity with reduced lattice dimensionality. Experimentally, specific spatially-anisotropic interactions associated with coumarin moieties and Frechet-type (arene/perfluoroarene) dendrons have been incorporated into chromophore systems and have been shown to lead to lattices of reduced dimensionality, resulting in increased values of the acentric order parameter and therefore, electro-optic activity. Reductions in lattice dimensionality can also arise from guest chromophore-host chromophore interactions in binary chromophore organic glasses and from laserinduced ordering of host lattice chromophores observed in the laser-assisted electric field poling of azo-dye-containing host lattices. These interactions in various chromophore systems including investigation of EO and order properties are discussed.

Mesoscopic structures are important for photonics applications. Here we describe the preparation of (sub)micrometer droplet or line patterns of organic semiconductors by a simple casting process. Dewetting during the solvent evaporation leads to the formation of regular structures that are caused by the so-called dissipative structures that develop during nonequilibrium conditions. Controlling the casting conditions (concentration, speed, etc) we were able to tailor the resulting patterns. Examples for the patterns are luminescent or conducting aggregates that can be used as organic transistors. Coating the self-organized structures with metals is an easy process to produce patterend metal surfaces, which can be sued in plasmonics.

Whereas structure-properties relationships have been widely investigated at the molecular level, supramolecular structure-property relationships have been somewhat overlooked. In many cases, interchromophoric interactions are found to be detrimental (in particular in second-order NLO) and a lot of efforts have been devoted to circumvent and control these effects to achieve efficient NLO materials for electrooptics. At opposite, we have implemented a countermainstream route based on the confinement of push-pull chromophores in close proximity within organic nanodots where both their number and relative position/distance are controlled by covalent attachment onto appropriate organic scaffolds. In such multichromophoric organic superstructures (namely covalent nanoclusters), dipole-dipole interactions can be tuned by playing on the internal architecture (topology, number of chromophoric subunits, length of the covalent linkers) and on the nature and properties (polarity, polarizability) of the chromophoric subunits. Following this strategy, we present the investigation of two series of such organic nanoclusters built from push-pull chromophores where through-space interactions are shown to modify both one-photon (OPA) and two-photon absorption (TPA) of each chromophoric subunits leading to cooperative enhancement of TPA properties and improved transparency.

In this letter we demonstrate broadband electro-optic modulation with frequencies up to 40 GHz in slotted photonic crystal waveguides based on silicon-on-insulator substrates covered and infiltrated with a nonlinear optical polymer. Two dimensional photonic crystal waveguides in silicon enable integrated optical devices with an extremely small geometrical footprint on the scale of micrometers. The slotted waveguide design optimizes the overlap of the optical and electric field in the second order nonlinear optical medium and hence the interaction of the optical and electric wave.

We have fabricated organic electro-optic single crystalline thin films on various inorganic substrates. A high refractive index contrast of up to Δn = +0.6 at 1.55 μm with respect to glass substrates and up to Δn = -1.9 at 1.55 μm with respect to silicon substrates has been achieved. The single crystalline films can be grown quasi-epitaxially without lattice matching and also on amorphous substrates providing appropriate interface interactions and solid-liquid phase equilibrium conditions. The thickness of the single-crystalline films can vary between less than 30 nm and above 5000 nm; they are therefore appropriate for optical waveguiding structures, as well as nano-size electro-optic structures needed for future nanophotonics. Several organic electro-optic crystalline materials have been employed using solution or melt-based processing. The techniques are suitable for the fabrication of conventional wire electro-optic waveguides, silicon-organic hybrid electro-optic waveguides, as well as more complex organic-inorganic structures such as single-crystalline electro-optic microring resonators.

Dendrimers have recently been shown to be excellent templates for synthesizing nanoparticles in view of their unique structural features. The present study, we report on nonlinear absorption and optical limiting properties of dendrimer-embedded silver nanoclusters and their linear and nonlinear optical (NLO) properties. Optical absorption spectroscopy reveals prominent plasmon peaks indicating quantum confinement. Z-scan experiments using pulsed laser excitation within the tail region of Plasmon absorption in the nanosecond regimes reveal evidence of strong nonlinear absorption involving two photo absorption followed by saturation absorption. The third ordered susceptibility (χ⁽³⁾) measured using four wave degenarated four wave mixing tecnquie (FWDM).

In order to obtain high optical gain medium for low-threshold and compact polymeric lasers, a tert-butyl substitutional rhodamine B (t-Bu-RhB) was synthesized and doped in PMMA film. The optical properties were investigated and the results showed that the concentration of t-Bu-RhB in PMMA could be increased to 6.9 wt % without decrease of photoluminescence efficiency. Polystyrene (PS) PCs with bandgap of 595nm were fabricated by vertical-deposition method. Resonator cavity was constructed by sandwiching t-Bu RhB doped films with two PS PCs. When excited by a Nd:YAG laser beam(532nm,10Hz,8ns), single-mode laser emission was observed from the cavities with dye concentration of 3, 5, 6.9, 10 wt %. Lasing emission is located at 592nm, with the full-width at half-maximum (FWHM) of 1nm. Lasing threshold of the cavities dramatically decreased from 49.56 to 0.70 μJ/Pulse when the concentration of t-Bu RhB increased from 3 to 6.9 wt%. Through enhancing the dye concentration to decrease lasing threshold will save pump energy, which is not only important for economy of energy, but also in favor of extending the life of such laser devices.

Polymers incorporating photochromic molecules are promising materials for flexible optical switches and optical data storage devices. A study on reversible photoswitching of azobenzene incorporated polydimethylsiloxane is carried out using transmittance and UV-VIS absorption measurements. The influence of light intensity on the photoswitching behavior is also investigated. The transmittance measurements are correlated with the change in the intensity of the corresponding bands in the UV-VIS absorption spectra. It is shown that the photoswitching occurs reversibly and that the switching time scale decreases with increase in intensity.

Organic conjugated nonlinear optical (NLO) macromolecules have been shown to successfully absorb and detect entangled photons generated by the process of spontaneous parametric down-conversion (SPDC). Entangled photon pairs produced by SPDC are used in our laboratory to investigate entangled two-photon absorption (ETPA) at extremely low excitation fluxes in these materials. In this proceeding we show that with novel 2-D multi-annulene macromolecules we are able to demonstrate a strong ETPA cross-section which is also sensitive to the spatial orientation of the SPDC emission pattern.