This PDF file contains the front matter associated with SPIE Proceedings Volume 9564, including the Title Page, Copyright information, Table of Contents, Authors, and Conference Committee listing.

By placing an organic semiconductor material having a relatively narrow electronic transition into an optical microcavity, it is possible to 'mix' excitons with confined cavity photons, forming states termed 'cavity polaritons'. Here, I discuss the formation of polariton states in microcavities containing J-aggregates of two different molecular dyes (cyanine dyes), whose J-band electronic transitions are both coupled to the same cavity photon mode. Under such conditions, three polariton branches are formed, with the "middle" polariton branch composed of an admixture of the cavity photon and the two different exciton states. I show using both photoluminescence excitation spectroscopy and photoluminescence emission measurements that such "hybrid" polariton states effectively act as an energy transfer pathway, allowing energy to be transferred between the different exciton states. A model is presented that describes exciton scattering into polariton states, and the subsequent decay and energetic relaxation of polaritons. I argue that the transfer of middle-branch polaritons to the lower-lying excitonic states is an efficient process, that occurs in time-scale of less than 10 fs. I then discuss structures in which a single J-aggregated cyanine dye is placed into a microcavity in which the extended cavity path-length results in the formation of a series of closely spaced cavity photon modes. It is shown that excitons in the cavity can simultaneously undergo strong coupling with at least four cavity photon-modes, effectively forming a ladder of polariton states, with a significant polariton population found in 3 adjacent polariton branches.

In this talk we will discuss our recent work on the formation of organic-inorganic hybrid excitons in microcavities as well as the nonlinear optical response of hybrid excitonic systems. Using thin film 3,4,7,8-napthalenetetracarboxylic dianhydride (NTCDA) and ZnO nanocrystals/nanowires we demonstrate enhanced Rabi splitting of hybrid polaritons and improved third order nonlinear optical response. In the former case, the hybrid materials are embedded in an optical microcavity.

We discuss some optical properties of cellulose nanocrystals decorated with silver nanospheres. We give a short description of the discrete dipole interactions, and the broadening effects observed in the extinction spectrum. We also discuss some preliminary results for their use in organic photovoltaic devices.

In organic molecules, the strength of the linear and nonlinear optical response scales depends on the size of the structure. Power-laws that correlate the length of a structure and its nonlinear structure have been proposed by different researchers. These power-laws are described as function of the number of repeating units, and are derived from the experimental characterization of one set of homologue compounds. Typically, every set of homologues has been reported to obey a different power-law. We show how the sum rules allow to derive universal scaling power-laws that apply to all structures and are in agreement with the experimental data. Using the concept of universal scaling, we propose a classification of the scaling behavior that can be used to determine what are the best molecular paradigms for future nonlinear optical applications.

The maximization of the intrinsic optical nonlinearities of quantum structures for ultrafast applications requires a spectrum scaling as the square of the energy eigenstate number or faster. This is a necessary condition for an intrinsic response approaching the fundamental limits. A second condition is a design generating eigenstates whose ground and lowest excited state probability densities are spatially separated to produce large differences in dipole moments while maintaining a reasonable spatial overlap to produce large off-diagonal transition moments. A structure whose design meets both conditions will necessarily have large first or second hyperpolarizabilities. These two conditions are fundamental heuristics for the design of any nonlinear optical structure.

Electro-optic (EO) polymers are key materials for next generation optical communications not only in wide area network but also in local area and storage area network because EO polymer modulator can be operated at fast speed more than 100 GHz with low energy consumption and can be miniaturized in combination with silicon photonics. In practical applications, thermal stability is one of the important issues to be considered for developing EO polymers. Since EO activity of the polymer is proportional to dipole orientation factor of the EO moieties, electric field assisted poling around glass transition temperature (Tg) of the polymer is necessary. However, the poled order of the molecules relaxes gradually at finite temperature, and then EO activity decreases after long period of time. We have successfully developed thermally stable EO polymers that have high-Tg up to 180 °C. They show excellent thermal stability with the Telcordia thermal test. Thermal stability is also characterized by thermally stimulated depolarization current (TSDC) measurement. Analyzing the TSDC, we can estimate the activation energy and relaxation time of polarization at any temperature. We will discuss thermal stability of the high-Tg EO polymers and devices.

We used steady state and picosecond transient photoinduced absorption (PA), excitation dependence (EXPA(ω)) spectrum of the triplet exciton PA band, and its magneto-PA (MPA(B)) response to investigate singlet fission (SF) of hot-excitons into two separated triplet excitons in luminescent π-conjugated polymers. From the high energy step in the triplet EXPA(ω) spectrum of poly(dioctyloxy)-phenylenevinylene (DOO-PPV) films, we identified a hot-exciton SF (HE-SF) process having threshold energy at E≈2ET (=2.8 eV, where E_T is the energy of the lowest lying triplet exciton), which is about 0.8 eV above the lowest singlet exciton energy. The picosecond transient PA with 3.1 eV pump excitation shows that in DOO-PPV film a triplet exciton is generated at time, t<500 ps. However the ultrafast triplet generation is missing in DOO-PPV solution, indicating that the HE-SF is predominantly interchain in nature. The HE-SF process was confirmed by the triplet MPA(B) response for excitation at E>2E_T, which shows a typical SF response. Our work shows that the SF process in π-conjugated polymers is a much more general process than thought previously.

Detecting coherent anti-Stokes Raman scattering (CARS) signals from signal molecules is a longstanding experimental challenge. Driving the vibrational CARS response with surface plasmon fields has proven notoriously difficult due to strong background contributions, unfavorable heat dissipation and the phase dispersion of the plasmon modes in the ensemble. In this work we overcome previous experimental limitations and demonstrate time-resolved, vibrational CARS from molecules in the low copy number limit, down to the single molecule level. Our measurements, which are performed under ambient and non-electronic resonance conditions, establish that the coherent response from vibrational modes of individual molecules can be studied experimentally, opening up a new realm of molecular spectroscopic investigations.

Conjugated organic molecules effectively produce and harvest visible light and find utility in a variety of emergent optoelectronic technologies. There is currently interest in expanding the scope of these materials to extend functionality into the infrared (IR) spectral regions and endow functionality relevant in emergent technologies. Developing an understanding of the interplay between chemical and electronic structure in these systems will require control of the frontier orbital energetics (separation, position, and alignment), ground state electronic configurations, interchain arrangements, solid-state properties, and many other molecular features with synthetic precision that has yet to be demonstrated. Bridgehead imine substituted 4H-cyclopenta[2,1-b:3,4-b′]dithiophene (CPDT) structural units, in combination with strong acceptors with progressively delocalized π-systems, afford modular donor-acceptor copolymers with broad and long wavelength absorption that spans technologically relevant wavelength (λ) ranges from 0.7 < λ < 3.2 μm.1 Here we demonstrate that electronic and structural manipulation play a major role in influencing the energetics of these systems and ultimately controlling the band gap of the materials. These results bear implication in the development of very narrow band gap systems where precise control will be necessary for achieving desired properties such as interactions with longer wavelength light.

An all-optical switching device is demonstrated with a nonlinear waveguide structure filled with liquid crystal. The signal field coupled out the glass cladding has interesting intensity-depended property due to the coupling of two different nonlinear dynamics in the nonlinear optical layer. The device has an additional feature that the switching sign is controllable from positive to negative.

Soft-solids that retain the responsive optical anisotropy of liquid crystals (LC) can be used as mechano-optical, electro-optical and electro-mechanical elements. We use self-assembly of block copolymers to create reversible LC gels and elastomers that flow at elevated temperatures and physically cross link upon cooling. In the melt, they can be spun, coated or molded. Segregation of the end-blocks forms uniform and uniformly spaced crosslinks. Matched sets of block copolymers are synthesized from a single "prepolymer." Specifically, we begin with polymers having polystyrene (PS) end blocks and a poly(1,2-butadiene) midblock. The pendant vinyl groups along the backbone of the midblock are used to graft mesogens, converting it to a side-group LC polymer (SGLCP). In the present case, cyanobiphenyl groups are used as the nonphotoresponsive mesogens and azobenzene groups are used as photoresponsive mesogens. Here we show that matched pairs of block copolymers, with and without photo-responsive mesogens, provide model systems in which the optical density can be adjusted while holding other properties fixed (cross-link density, modulus, birefringence, isotropic-nematic transition temperature). For example, a triblock in which the SGLCP block has 95% cyanobiphenyl and 5% azo side groups is miscible with one having 100% cyanobiphenyl side groups. Simply blending the two gives a series of LC elastomers that have from 0 to 5% azo, while having all other physical properties matched. Results will be presented that show the outcomesof this approach to systematic and largely independent control of optical density and photo-mechanical sensitivity.

We report the synthesis of azobenzene-containing coil-liquid crystal-coil triblock copolymers that form uniform and highly reproducible elastomers by self-assembly. To serve as actuators to (non-invasively) steer a fiber optic, for example in deep brain stimulation, the polymers are designed to become monodomain “single liquid crystal” elastomers during the fiber-draw process and to have a large stress/strain response to stimulation with either light or heat. A fundamental scientific question that we seek to answer is how the interplay between the concentration of photoresponsive mesogens and the proximity to the nematic-isotropic transition governs the sensitivity of the material to stimuli. Specifically, a matched pair of polymers, one with ~5% azobenzene-containing side groups (~95% cyanobiphenyl side groups) and the other with 100% cyanobiphenyl side groups were synthesized from identical triblock pre-polymers (with polystyerene end blocks and 1,2-polybutadiene midblocks). These can be blended in various ratios to prepare a series of elastomers that are precisely matched in terms of the backbone length between physical crosslinks (because each polymer is derived from the same pre-polymer), while differing in % azobenzene side groups, allowing the effect of concentration of photoresponsive groups to be unambiguously determined.

Photopolymers have been applied in many Additive Manufacturing (AM) systems and mostly are cured by UV light. Biodegradable photo-curable polymers are very limited and are not commercially available. DLP-projected maskless AM systems become more and more popular nowadays, but its working area is limited if the part resolution is required. For larger working envelope purpose, liquid crystal display (LCD) panel has great potentials, and LCD’s resolution has been improved significantly in the past few years due to the smart phone application. Therefore, in this research, LCD panel is used to replace DLP for a maskless AM system to cure biodegradable materials, Polycarprolactone (PCL) and Poly(ethylene glycol) diacrylate (PEG-DA). Due to the characteristics of LCD panel, the material systems should be sensitive and photo-polymerized in visible-light range, particularly in RGB. In this study, various percentages of visiblelight photoinitiator, Irgacure 784, in the material systems were investigated. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were utilized to characterize cured biomaterials. Because of the use of photoinitiator, the biocompatibility of the cured materials was also concerned, and hence, MTT assay tests were performed. The preliminary tests of fabrication, using the LCD-projected maskless AM system, cured grid patterns to illustrate the feasibility. The visible-light-curable PCL and PEG-DA will be able to be adopted in tissue engineering scaffold applications in the future.

The phenomenon of vector polyphotochromism within a wide spectral range is revealed in organic polarization-sensitive materials when material is illuminated with linearly polarized actinic light. The effect has a purely vector nature, while the transmission spectrum of the exposed material essentially changes in case of observing between crossed polarizers and the change in the spectrum unambiguously depends on the energy exposure. A significant dependence of the kinetic of the vector polyphotochromism induction on the power density of linearly polarized actinic light (445 nm) is shown for probing beam of 635 nm. It is also shown that the kinetics of the effect depends on the degree of integration of the component molecules of the material by the cohesion of both ways the electrostatic forces (by use mineral electrolytes and polyelectrolytes) and the covalent bonds (azopolymers based on different chromophores), as well as on the photosensitive layer thickness and the concentration of the chromophore. The mechanism of the phenomenon is discussed. Considering the fact that the change in the spectral characteristics occurs throughout the full visible range, this effect may be used for creating the spectrally selective dynamic polarization holographic gratings, displays based on new physical principles, and also for creating modulators and dynamic polarization spectral filters controlled by light.

Proton transfer is one of the most fundamental processes in nature. Metastable-state photoacids can reversibly generate a large proton concentration under visible light with moderate intensity. which provides a general approach to control various proton transfer processes. Several applications of mPAHs have been demonstrated recently including control of acid-catalyzed reactions, volume-change of hydrogels, polymer conductivity, bacteria killing, odorant release, and color change of materials. They have also been utilized to control supramolecular assemblies, molecular switches, microbial fuel cells and cationic sensors. In this talk, the mechanism, structure design, and applications of metastable-state photoacids are introduced. Recent development of different types of metastable-state photoacids is presented. Challenges and future work are also discussed.

High intensity laser stimulation induces stress in dye-doped photomechanical elastomers, causing a length change. Using principles of nonlinear optics and continuum mechanics, we develop a theoretical model quantifying how these elastomers react to laser stimulation. The model evaluates the quality of the response using a photomechanical coefficient, such that a larger coefficient means a larger stress, and hence a more highly photoresponsive material. We are able to determine the photoresponsiveness as a function of pre-strain, laser intensity, strain his- tory, and other properties. Furthermore, we test our model with various types of elastomers, as well as different dyes and doping agents.

We report on the modeling of fiber Bragg grating (FBG) networks in poly(methyl methacrylate) (PMMA) polymer fibers doped with azo dyes. Our target is the development of Photomechanical Optical Devices (PODs), comprised of two FBGs in series, separated by a Fabry-Perot cavity of photomechanical material. PODs exhibit photomechanical multi-stability, with the capacity to access multiple length states for a fixed input intensity when a mechanical shock is applied.

Using finite-difference time-domain (FDTD) numerical methods, we modeled the photomechanical response of both Fabry-Perot and Bragg-type PODs in a single polymer optical fiber. The polymer fiber was modeled as an instantaneous Kerr-type nonlinear χ⁽³⁾ material. Our model correctly predicts the essential optical features of FBGs as well as the photomechanical multi-stability of nonlinear Fabry-Perot cavity-based PODs.

Networks of PODs may provide a framework for smart shape-shifting materials and fast optical computation where the decision process is distributed over the entire network. In addition, a POD can act as memory, and its response can depend on input history. Our models inform and will accelerate targeted development of novel Bragg grating-based polymer fiber device networks for a variety of applications in optical computing and smart materials.

Existent photonic systems are highly integrated with the active component being completely isolated from the environment as a result of their complex format. There are almost no example for periodic photonic materials, which can interact with their environment by being sensitive to external stimuli while providing the corresponding photonic response. Due to this lack of interaction with the outside world, smart optical components, which are self-healing or adaptable, are almost impossible to achieve. I am going to present an aqueous colloidal system, consisting of core-shell particles with a solid core and a soft shell, bearing both negatively and positively charged groups. The described soft colloids exhibit like charges over a broad range of pH, where they repel each other resulting in a pefect and defect-free photonic crystal. In the absence of a net charge the colloids acquire the arrangement of an amorphous photonic glass. We showcase the applicability of our colloidal system for photonic applications by temporal programming of the photonic system and dynamic switching between ordered and amorphous particle arrangements. We can decrease the pH slowly allowing the particles to transit from negative through neutral to positive, and have them arrange accordingly from crystalline to amorphous and back to crystalline. Thus, we achieve a pre-programmable and autonomous dynamic modulation of the crystallinity of the colloidal arrays and their photonic response. References [1] Go, D., Kodger, T. E., Sprakel, J., and Kuehne, A. J.C. Soft matter. 2014, 10(40), 8060-8065.

Photorefractive (PR) polymers change their index of refraction upon illumination through a series of electronic phenomena that makes these materials one of the most complex organic systems known. The refractive index change is dynamic and fully reversible, making PR materials very interesting for a large variety of applications such as holography and 3D display. In order to improve the recording speed and achieve videorate for our stereographic display application, we have introduced a new type of electrode geometry where the anode and cathode are in the same plane and are shaped as interpenetrating combs. This type of electrode geometry does not require the sample to be tilted with respect to the writing beams to record the hologram, which is a significant advantage. To monitor the highly non-homogeneous field resulting from this configuration, we used a multiphoton microscope to directly observe the chromophore orientation in situ upon the application of an electric field. Most recently, we developed a fast repetition rate laser (10kHz) where the pulse width can be adjusted from microseconds to milliseconds so that, in conjunction with a ns Q-switched Nd:YAG laser and an externally chopped CW laser, the diffraction efficiency of the material could be measured over 9 orders of magnitude. This measurement helps us better understand the mechanism of grating buildup inside photorefractive polymers.

With submicrometer thick photoconducting, semiconductor ZnSe thin films as interlayers between ITO glass and thin film of C₆₀ doped mixture of polymer poly[N-vinylcarbazole] (PVK) and nematic liquid crystal (LC) 4,4’-npentylcyanobiphenyl (5CB), an updatable holographic recording medium was fabricated. When two laser beams were overlapped in the holographic recording medium, 2D diffraction patterns were seen, along with several interesting observations. The frequent sign changing of energy transferring between the two transmitted laser beams and large dynamic change in different diffraction orders implied complex processes of electric charge generation, transportation and compensation in the interfaces and within composite polymer film. Electrostatic modification based surface grating formation was proposed to explain all the findings.

We report on the volume holographic grating formation in photopolymerizable polymer nanocomposites that incorporate new hyperbranched polymers (HBPs) acting as transporting organic nanoparticles. Since HBPs are easily dispersed to acrylate monomer without any aggregation and possesses ultrahigh index of refraction of the order of 1.8 in the green due to the inclusion of triazine and aromatic ring units, volume gratings with good optical quality and refractive index changes as large as 2.2 × 10⁻² can be recorded. It is also shown that the out-of-plane thickness change due to polymerization shrinkage is reduced to 2% or lower by the HBP dispersion.

Ferroelectric liquid crystal blends composed of a smectic liquid crystalline mixture, a photoconductive chiral dopant, and an electron trap reagent exhibit significant photorefractivity together with rapid responses. As such, they allow the dynamic amplification of moving optical signals. In the present work, the durability of a photorefractive ferroelectric liquid crystal blend was investigated. A series of photoconductive chiral dopants was prepared and the durability of blends incorporating these dopants during laser irradiation was examined. In addition, the effect of the conduction of photogenerated ionic species on the photorefractivity decay was clarified.

A new nonlinear optical organic material, 2,4,6-trimethylacetanilide (246TMAA), also known as N-[2,4,6- trimethylphenyl]acetamide, has been synthesized and grown as a single crystal by the slow evaporation technique by organic solvents. The grown crystals have been characterized by morphology study. The crystals are prismatic. Surface examination shows granular dendritic pattern in optical micrograph. The Scanning Electron Micrograph shows the layered growth of the crystal. The Differential Scanning Calorimeter plot shows no phase change until melting point (219°C). The density of the crystals is 1.1g/cc and the crystals are soft. The crystals are transparent in the visible region and in the ultra-violet region till 280 nm. 246TMAA crystallizes with 2 molecules in a monoclinic unit cell in the noncentrosymmetric point group m, space group Pn. Refractive indices of this optically biaxial crystal along the three crystallophysical axes have been measured at 633 nm. The optical second harmonic generation efficiency of the crystal at 1064 nm is about half that of the urea crystal, measured by powder method using Nd:YAG laser. The results show that the 246TMAA crystal can efficiently be used for up-conversion of infrared radiation into visible green light. The powder X-ray diffraction spectrum of the crystal has been obtained.

High intensities electromagnetic energy interacting with organic media gives rise to nonlinear optical effects. Hibiscus Sabdariffa is a flower whose concentrated solution presents interesting nonlinear optical properties. This organic material shows an important self-phase modulation with changes bigger than 2π. We present a diffraction ring patterns study of the Hibiscus Sabdariffa solution. Numerical results of transmittance, with refraction and simultaneous absorption, are shown.

photorefractive (PR) application because of a fast hole mobility. In most of the previous studies, phenyl-C61-butyric acid methyl ester (PCBM) was used as a sensitizer. In this study, a high-performance charge generator perylene bisimide (PBI) is synthesized and added into the composite. PBI derivatives owning a large core of π-conjugated rings provide a high electron affinity and high charge carrier mobility. These features are promising to improve PR properties. To the best of our knowledge, it is the first time for using a combine of PCBM and PBI to improve the PR performance of PDAA-based composites. 2-(4-(azepan-1-yl)benzylidene)malononitrile (7-DCST) is used as a nonlinear optical chromophore. (4-diphenylamino)phenyl)methanol (TPAOH) is used as a plasticizer. Consequently, a diffraction efficiency of 76 % and a response time of 8 ms were obtained with 532 nm green laser under the electric field of 55 V μm^-1. As a conclusion, the introduction of PBI is a promising approach for the photorefractive composite owning the video rate response.

Realization of energy efficient and cost effective electroluminescence applications of conjugated polymers, like organic light emitting diodes (OLEDs), requires a complete understanding of photo-chemical processes at metal-polymer interfaces. Therefore it is useful to study the effects of metal films on the photoluminescence of emissive organic layer fabricated on it. While investigating these processes we observed an interesting and unexpected phenomenon that, when conjugated polymer is deposited on thin gold film substrates, it exhibits remarkable photo-stability relative to that deposited on glass, even in the presence of molecular oxygen. This paper addresses the photo-stability enhancement by thin Au films and explores the photochemical mechanism behind it.