This PDF file contains the front matter associated with SPIE Proceedings Volume 9181, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

We exploit the strong spin-orbit coupling in iridium to modify the linear absorption spectrum of a novel iridium(III) complex so as to broaden the spectral region over which it exhibits reverse saturable absorption. We discuss the design of the new chromophore, present its ground-state absorption spectrum, and report values of its singlet excited-state lifetime and singlet and triplet excited-state absorption cross sections, determined from femtosecond transient difference absorption measurements and nanosecond and picosecond open-aperture Z scans.

Synthesis of several C₆₀-(antenna)_x conjugates was performed to demonstrate high flexibility in the design of organic nonlinear optical (NLO) nanostructures showing broadband characteristics with capability to absorb light over a wide range of wavelengths. It was achieved by covalent attachment of a hybrid combination of two types of light-harvesting fluorescent antenna chromophores on a C₆₀ cage. Ultrafast photoresponsive intramolecular Föster resonance energy-transfer among antenna units and shared excited energy-accepting C₆₀ cage is proposed as a plausible mechanism to enhance the broadband NLO ability. Characterization of the branched triad C₆₀(>DPAF-C₁₈)(>CPAF-C_2M) and the tetrad C₆₀(>DPAF-C₁₈)(>CPAF-C_2M)₂ was carried out by various spectroscopic techniques. These compounds showed approximately equal extinction coefficients of optical absorption over 400‒550 nm that corresponds to near-IR two-photon based excitation wavelengths at 780‒1100 nm. These nanomaterials may be utilized in NLO coatings for achieving efficient light-transmittance reduction at the same NIR wavelengths.

Singlet fission is a form of multiple exciton generation in which two triplet excitons are produced from the decay of a photoexcited singlet exciton. In a small number of organic materials, most notably pentacene, this conversion process has been shown to occur with unity quantum yield on sub-ps timescales. However, a poorly understood mechanism for fission along with strict energy and geometry requirements have so far limited the observation of this process to a few classes of organic materials, with only a subset of these (most notably the polyacenes) showing both efficient fission and long-lived triplets. Here, we utilize novel organic materials to investigate how the efficiency of the fission process depends on the coupling and the energetic driving force between chromophores in both intra- and intermolecular singlet fission materials. We demonstrate how the triplet yield can be accurately quantified using a combination of traditional transient spectroscopies and recently developed excited state saturable absorption techniques. These results allow us to gain mechanistic insight into the fission process and suggest general strategies for generating new materials that can undergo efficient fission.

For many optical semiconductor fields of study, the high photoconductivity of amorphous organic semiconductors has strongly been desired, because they make the manufacture of high-performance devices easy when controlling charge carrier transport and trapping is otherwise difficult. This study focuses on the correlation between photoconductivity and bulk state in amorphous organic photorefractive materials to probe the nature of the performance of photoconductivity and to enhance the response time and diffraction efficiency of photorefractivity. The general cooling processes of the quenching method achieved enhanced photoconductivity and a decreased filling rate for shallow traps. Therefore, sample processing, which was quenching in the present case, for photorefractive composites significantly relates to enhanced photorefractivity.

Recent research has focused on developing low-bandgap polymers for harvesting solar energy, fine-tuning desirable properties including power conversion efficiency, carrier mobilities and broad light absorption. However, little attention has been paid to their nonlinear optical properties. We characterized the optical second harmonic generation of corona poled films of poly(cyclopenta[2,1-b;3,4-b']dithiophen-4-ylidenedioctylmalonate). Despite being amorphous and lacking a typical donor-acceptor dye, these films display large nonlinear optical susceptibilities. Coupled with their stability and low absorption in the relevant wavelength region, these polymer films compare favorably to other materials. Our results show the promise of low-bandgap polymers for nonlinear optical applications.

The photorefractive effect in ferroelectric liquid crystalline mixtures containing photoconductive chiral compounds was investigated. Ter-thiophene compounds with chiral structures were chosen as the photoconductive chiral compounds, and they were mixed with an achiral smectic C liquid crystal. The mixtures exhibit the ferroelectric chiral smectic C phase. The photorefractivity of the mixtures was investigated by two-beam coupling experiments. It was found that the ferroelectric liquid crystals containing the photoconductive chiral compound exhibit a large gain coefficient of over 1200 cm^-1 and a fast response time of 1 ms. Real-time dynamic amplification of an optical image signal of over 30 fps using the photorefractive ferroelectric liquid crystal was demonstrated.

We introduce a new method to make gradient index (GRIN) lenses in diffusive photopolymers with nearly arbitrary two-dimensional (2D) profiles. By modulating the 2D intensity pattern and power of the exposure with a deformable mirror device (DMD), the index profile of the GRIN lens can be controlled. Combined with the self-developing nature of the photophotopolymer, rapid on-demand printing of arbitrary micro-optics is enabled. We demonstrate the process by fabricating quadratic GRIN lenses, Zernike polynomials and multi-focal lenses.

We present a device for tunable spatial polarization shaping, based on a red light photo-addressable cell. Such a cell compartment is based on a bisazobenzene containing photoaligning layer and a rubbed PI aligning and is filled with the LC mixture E5. Switchable spatial addressing patterns are generated by a 200 channel micro optical addressing unit based on a red VCSEL array (λ = 650 nm) and diffractive beam shapers.

There is much interest in enhancement of the absorbance performance of nonlinear absorber solid-state filters. In this work we present an advanced reversible nonlinear filter based on a dye-doped sol-gel matrix. The absorbance enhancement was achieved by using a combination of two absorption mechanisms in the same molecule; a photochromic absorption which is induced by 2-photon absorption (2PA). The 2PA serves as the trigger for initiating the photochromism through Förster-resonance-energy-transfer (FRET) between the fluorescent donor and the photochromic acceptor. We synthesized a new bifunctional-chromophore that incorporated a carbazole-derived 2PA fluorescent donor and a chromene-derived photochromic acceptor, covalently linked together in a single molecule by a ~6 Å carboxyl group or oxygen bridge. The bifunctional-chromophore was doped in an inorganic-organic hybrid matrix prepared by the fast-sol-gel process. These materials solidify without shrinkage or formation of cracks and present promising properties as optical matrices for smart filters. The dye-doped sol-gel disc presents high transparency in the visible region ("colorless"), which under UV-irradiation (one-photon absorption in the photochromic part of the molecule), transforms into a strongly absorbing filter ("dark colored"), due to the conversion of the photochromic moiety to its "open" absorbing form. We have demonstrated that this ring-opening can also be induced by visible-light (620 nm) using the 2PA carbazole-derived moiety of the molecule. We have studied the fabrication routes and optical performance of these filters. We present studies of the 2PA mechanism of the carbazole derivative, FRET efficiency of the combined-molecule as well as in solutions of the individual moieties, and reversible dynamics of the photochromic moiety.

We report on recent studies of magneto-optic properties and Faraday rotation of polythiophenes and macrocycles of 3- alkylthiophenes. The hypothesis of the existence of persistent currents, analogous to the persistent currents in mesoscopic metal structures, is forwarded as a relevant mechanism basic to the large Faraday rotation in conjugated polymers as well as for the ferromagnetic transition in these polymers at cryogenic temperatures. Macrocycles of alkylthiophenes are presented and discussed as fundamental structures to investigate persistent currents in nanoscopic organic materials.

We report the use of Second Harmonic Generation (SHG) to investigate at the air-water interface molecular films of PL2(-) molecules, a chiral binaphthyl derivative. Under the compression of the monolayer film in a Langmuir trough, large fluctuations of the SHG intensity are observed. From the expressions of the SHG intensity with polarization control of the input fundamental and output harmonic beams, it appears that the intrinsic chirality of the PL2(-) molecule can be disentangled from the supramolecular chirality arising from PL2(-) molecular aggregates. With a careful polarization control of the input and output polarization configurations of the SHG optical set-up, it is then shown that the dominant origin of the observed SHG intensity fluctuations is the formation of PL2(-) molecular aggregates at the air-water interface. The proposed strategy is also suitable for the analysis of the fluctuations in the SHG intensity arising from molecular films at the air-water interface formed from achiral molecular compounds.

We report on the intensity dependent exciton dynamics in optically excited tris (8-hydroxyquinoline) aluminum (Alq₃) films grown by organic molecular beam epitaxy that show a strong quenching of light emission at low temperature. We further report on the mode properties in plasmonic Alq₃ waveguides and on the exciton emission in InP nanowires which are coated with a thin Alq₃ films and Mg:Ag metal cluster layers.

Coupling of gain materials to metallic nanostructures and thin films offers an avenue for amplification of plasmonic modes in both confined and extended geometries. In the past decade, a deeply sub-wavelength analogue to the laser, using surface plasmons instead of photons, has been proposed and demonstrated. Additionally, propagating surface plasmon polaritons on extended metallic films have been amplified using gain media to achieve chip-scale propagation lengths. Here, we investigate a core-shell nanoparticle structure amenable to amplification of resonant surface plasmon modes using a gold nanorod as the core and an organic polymer semiconductor gain medium as the shell. Organic semiconducting polymer gain media are of interest because, unlike laser dye molecules, they do not undergo significant concentration quenching in the solid-state and, therefore, can result in a high chromophore density in the optical near-field of the metal nanostructure. For investigations of resonant surface plasmon mode amplification, we fabricate gold nanorod-F8BT core-shell nanoparticles through a miniemulsion synthesis process. A more distinct threshold in emitted intensity as a function of optical pump energy is observed from these hybrid structures and neat F8BT nanoparticles compared to dissolved F8BT molecules. However, spectral narrowing is not observed from these structures, potentially due to the low heterostructure yield and poor spectral overlap between the absorption and emission bands of the F8BT with the pump laser and the longitudinal surface plasmon resonance of the nanorods, respectively. Future work will focus on increasing heterostructure yield, employing a red-emitting gain material such as MEH-PPV to couple to longitudinal surface plasmon modes and alternative thin-film geometries in which plasmonic mode-emitter interactions can be easier to control.

Nonlinear absorption was investigated in a poly (3-hexylthiophene) (P3HT) PCBM fullerene blend, one of the most popular organic solar cell’s materials. We observed three-photon absorption in the bulk hetero junction photodiode configuration. The output photocurrent of the photodiode was interpreted in terms of the three-photon absorption properties of the P3HT:PCBM blend at 1550 nm. Can the concept be extrapolated to high efficiency solar cells? We propose an optical antenna technology revisited with plasmonics and organic rectifiers that should permit the development of an ultra-high efficiency PV technology that is compatible with large-area fabrication (self assembling) and low-cost (plastic) technologies.

Optical sensors that are applied in conjunction with bright optical sources such as lasers typically have to be protected from damaging light exposure levels by the use of optical limiters. The principal aims for optical limiter materials are: (1) to block selectively the frequency of interest at high light levels and – at low light levels – exhibit high transmittance of optical frequencies in order to enable the fabrication of transparent yet protective windows; (2) a rapid response time when exposed to high light levels. Novel opportunities for the design of materials with dynamic switchable limiting properties are provided by optically transparent two-photon active polymer nanocomposites materials in which the scattering strength of embedded particle fillers can be dynamically modulated by the nonlinear absorption of a polymer host medium. In a first part this contribution will present recent results on the synthesis of silica nanoparticles that are index-matched to organic solvents by means of polymer functionalization. Effective medium theory will be shown to provide a valuable tool in predicting polymer-graft compositions that are index-matched to the embedding solvent thus resulting in dramatically reduced linear scattering cross section of the particle dispersant. The second part of this contribution will present preliminary results on the linear and nonlinear optical properties of particle dispersions in both solvent and solutions of two-photon active (TPA) dyes. For mixed solutions of TPA-dyes and index-matched particle fillers an increased limiting efficiency is observed while neat particles are found to be TPA inactive.

In organic molecules, the optical response originates from the motion of the pi-electrons, which are constrained to move along the molecule’s conjugated path. As an electron moves through the conjugated path, it interacts with the rest of the charges such that its motion is very dependent on the shape of the molecule. In this paper we introduce a simple model for that allows us to determine how the shape of the conjugated path affects the nonlinear optical response of the molecule. Our results apply to typical second-order dipolar structures: we have determined how the symmetry of the conjugated path affects the optical response, and we have found potential new strategies for making better molecules.

Traditionally, liquid crystal display (LCD) systems employ color filters that are fabricated using organic dye and pigment based colorants. As a result, conventional color filters can lower the system performance by removing substantial amount of incident light through absorption. Also, the transmission bandwidth can be unacceptably large. Furthermore, there is a need to combine functions of multiple optical elements on one, facilitating miniaturization and compactness. Metal-insulator- metal (MIM) nanoresonators that can combine the functions of color filtering and polarizing can provide a useful solution to some of these issues. An MIM nanoresonator structure is proposed for use as color filters. However, the proposed structure uses high refractive index, inorganic materials in the insulator layer. Also, the bandwidth of transmission is not narrow enough to generate saturated color. Here, we simulated some MIM nanoresonator structures that might be realized using relatively low refractive index, polymeric materials and can function as polarizing, color filters in transmission mode. These structures might also yield narrower bandwidths of transmission. The simulations are carried out using a monochromatic version of RC-FDTD. This algorithm uses the 1st order Drude model to evaluate the convolution operation needed to make FDTD stable for metals for which the real part of permittivity is negative. Unlike the conventional RC-FDTD [3], the Drude parameters are computed at each wavelength of the incident light using the corresponding handbook value of permittivity. Hence, this version of RC-FDTD allows us to use the handbook permittivity values at all wavelengths of operation.

Deoxyribonucleic acid (DNA) has been a remarkable material in the development of optoelectronic devices for granted these days. In this research, we report on an optical phenomenon of DNA structures grown by a self-assembly process. Discrete 2D nanocrystal structures of DNA were prepared on a light-guiding substrate. The high evanescent field interaction between the guided light supplied via D-shaped optical fiber and DNA monolayers enabled the systematic investigating of the optical properties of DNA nanocrystal structures. In particular, light guided down the fiber and received by an optical spectrum analyzer enabled spectral analysis, while morphology studies of the self-assembly DNA were performed by atomic force microscopy.

We design and demonstrate a compact, low-power, low-dispersion and broadband optical modulator based on electro-optic (EO) polymer refilled silicon slot photonic crystal waveguide (PCW). The EO polymer is engineered for large EO activity and near-infrared transparency. The half-wave switching-voltage is measured to be V_π=0.97±0.02V over optical spectrum range of 8nm, corresponding to a record-high effective in-device r₃₃ of 1190pm/V and V_π×L of 0.291±0.006V×mm in a push-pull configuration. Excluding the slow-light effect, we estimate the EO polymer is poled with an ultra-high efficiency of 89pm/V in the slot. In addition, to achieve high-speed modulation, silicon PCW is selectively doped to reduce RC time delay. The 3-dB RF bandwidth of the modulator is measured to be 11GHz, and a modulation response up to 40GHz is observed.

In the attempt to improve optical limiting of cw lasers by exploiting the thermo-optic effect exhibited by gold nanostructures, we investigated two coupled systems consisting of either gold nanoparticles (AuNPs) or gold-silica core-shell (AuNSs), both functionalized with a thiolated-fulleropyrrolidine (C₆₀Py). We measured the optical limiting behavior under cw illumination at 514 and 647 nm, resonant with the surface plasmon resonance at around 520 of AuNPs and at 650 nm of AuNSs, respectively. Temporal response analysis shows the variation of transmitted irradiance in a 300 milliseconds time interval, corresponding to the blinking time of the human eye. Comparing the present results we those previously obtained for AuNPs1 we demonstrate an improvement of the response of functionalized nanoparticles (AuNPs- C₆₀Py) with respect to bare AuNPs.

The optical properties of sulforhodamine B (SRH) impregnated in photonic crystal by two step synthetic processes including a urethane bond formation between a 3-isocyanatopropyl triethoxysilane (ICPTES, -N=C=O) and a SRH with elevated temperature in pyridine and hydrolysis-condensation reactions between synthesized ICPTES/SRH (ICPSRH) and tetraethoxyorthosilicate (TEOS) in NH4OH. The monodisperse silica spheres impregnated the ICPSRH (ICPSRHS) are fabricated. The reduction of the absorption peak at 2270 cm^-1 representing asymmetric stretching vibration of –N=C=O indicates the progress of the reaction and new absorption peak at 1712 cm^-1 characterizing –C=O stretching vibration indicates the formation of urethane bond. The UV-visible absorption spectra show the broadened spectral line width by intermolecular interaction. The photoluminescence (PL) peak of the SRH in methanol shows a hypsochromic shift with the increase the excitation wavelength. However, the PL peak for the ICPSRH exhibits a bathochromic shift as the excitation wavelength increases. The PL peak for the ICPSRH shows no hypsochromic or bathochromic shift. The PL peaks for SRH in methanol, ICPSRH and ICPSRHS are at 568, 598 and 572 nm, respectively. The main cause of the PL peak shift is due to the intermolecular interaction.