In top-hat _Z scans that employ tunable sources such as optical parametric generators without line-narrowing gratings, the size of the aperture used to clip the beam may exceed the coherence length, and the variation with z of the transverse profile of the resulting partially coherent beam may differ significantly from that of a perfect top-hat beam. After a careful validation of our experimental set-up, we perform picosecond open-aperture Z scans with a top-hat beam at selected wavelengths in the visible and nanosecond open-aperture Z scans with a spatially Gaussian beam at 532-nm wavelength on a toluene solution of a particular platinum(II) 2,2′-bipyridyl complex bearing naphthalimidylethynyl-substituted fluorenylacetylide ligands. We report values of the singlet and triplet excited-state absorption cross sections of the complex.

Since the discovery of graphene in 2004 by Novoselov and Geim, a lot of research emphasis has been directed towards its characterization. Most of the important scientific breakthroughs have been obtained on exfoliated graphene (produced via the well known ‘scotch tape’ method), nowadays, different synthetic routes have been developed to obtain largescale graphene. Among several optical techniques, Raman spectroscopy is the one most often employed to characterize the defects, number of graphene layers and other properties of the graphitic films regardless of their fabrication method. In this work, we will report on the microscopic imaging of the two-photon fluorescence (2PF) properties and the second harmonic generation (SHG) in both single layer and few layer graphene.

We have been studying exciplex formation in nonlinear optical materials containing a high concentration of 2PA chromophores (AFX dyes) as a means to enhance the nonlinear optical properties. A number of dipolar AFX dyes having various electron-accepting moieties (π-excess and π-deficient examples) and three bisimide compounds having substituents with varying electron-withdrawing power were synthesized to study exciplex formation in their solid state blends. In substrate supported thin films of various equimolar blends containing an AFX dye and bisimide, the dye monomer emission was severely quenched, and a new emission, red-shifted by up to 110 nm, appeared. The emission energies were consistent with the charge recombination energy calculated from the energy levels of the donor and acceptor present in the blend, which confirmed the emission was from an exciplex. Time resolved emission measurements also indicated the presence of much longer lived transients in the blends, consistent with exciplex formation. Spectroelectrochemistry confirmed that the radical cations of these dyes had strong absorption in the NIR region, so exciplex formation is a means to enhance nonlinear optical absorption of the dyes in this spectral region.

Three series of new organic pyridinium salt chromphores with high nonlinearities and crystal growth characteristics have been designed and synthesized through modifying the cations and counteranions. The chromophores with strong coulomb interactions to surpass the intermolecular interaction have been adopted to induce the non-centrosymmetric packing of molecules which is advantage to high macroscopic second-order optical nonlinearities. At the same time, heterocycle was introduced to substitute phenyl group of the DAS (4-N, N-dimethylamino-4′-N′-methyl-pyridinium tosylate) cation, which can form a series of new pyridinium-based chromophores to extend the molecular structure of NLO materials. Kurtz powder tests revealed that out of these pyridinium salts, the maximum powder second harmonic generation (SHG) efficiency is 1300 times of urea standard at the non-resonant wavelength of λ=2109 nm. The effect of heterocycle on the nonlinear properties and crystal growth abilities of the new developed materials have been studied. Single crystals were successfully obtained from methanol by slow cooling and evaporation methods. The reasons for considerably different macroscopic nonlinearities of these compounds have been explored in terms of intermolecular interactions.

Recently we have formulated a simple Monte Carlo model¹ for the study of the photomechanical effect in polymeric fibers pumped with a linearly polarized laser beam.^2–4 The model fiber is a host - guest system consisting of the polymeric matrix and azodye chromophores, which undergo multiple trans - cis - trans cycles when illuminated by linearly polarized light. Current paper is focused on the topic so-far neglected in,¹ closely related to the hypothetical cooperative mechanism of stress relaxation^2–4 – on the characterization of local voids in computer-generated polymeric matrix. We study void-size distributions and void-void correlation functions.

We have developed a stochastic photon transport model in multilayer skin tissue in an effort to study normal and bruised skins. The model uses a detailed seven layer skin approximation allowing more biologically relevant input than previous models using one or three layers. Our model is improved with clinically obtained reactance spectra in an effort to develop time correlations of chromophore concentrations in developing bruises. This combination of modeling and spectroscopic measurements provides a new tool for detailed, non-invasive studies of human skin tissue.

Possibilities to determine chromophore distribution in skin by spectral imaging were explored. Simple RGB sensor devices were used for image acquisition. Totally 200 images of 40 different bruises of 20 people were obtained in order to map chromophores bilirubin and haemoglobin. Possibilities to detect water in vitro and in vivo were estimated by using silicon photodetectors and narrow band LEDs. The results show that it is possible to obtain bilirubin and haemoglobin distribution maps and observe changes of chromophore parameter values over time by using a simple RGB imaging device. Water in vitro was detected by using differences in absorption at 450 nm and 950 nm, and 650 nm and 950 nm.

Sum rules are used to develop a broad understanding of light-matter interactions through investigations of universal properties and are applied to specific phenomena to gain insights into the underlying fundamental processes. We discuss universal properties associated with the third-order nonlinear-optical response and show how microscopic cascading – where two molecules interact through their hyperpolarizabilities to yield a second hyperpolarizability – must obey these same universal properties. In addition, we discuss how the sum rules imply more exotic classes of Hamiltonians and their consistency with physical laws, which may partially explain the difference between the sum-rule-derived fundamental limits and observations.

Quantum graphs are graphical networks comprised of edges supporting Hamiltonian dynamics and vertices conserving probability flux. Lateral confinement of particle motion on every edge results in a quasi one-dimensional quantum-confined system for which nonlinear optical effects may be calculated. Our ongoing research program is the first to investigate the nonlinear optical properties of quantum graphs. We seek to discover configurations with intrinsic first and second hyperpolarizabilities approaching their respective fundamental limits, to explore the NLO variation with the geometry and topology of the graphs, and to develop scaling laws for more complex graphs with self-similar properties. This paper describes a new methodology for calculating the hyperpolarizabilities of a class of graphs comprised of sequentially-connected edges. Such graphs include closed-loop topologies and their geometrically-similar but topologically-different open loop cousins, as well as other bent wire graphs and their combinations.

We study the effect of geometry on the nonlinear response of a network of quantum wires that form loops. Exploiting the fact that a loop’s transition moment matrix and energies are exactly solvable for each wire segment, they can be pieced together to determine a loop’s properties. A Monte Carlo method is used to sample the configuration space of all possible geometries to determine the shape that optimizes the intrinsic hyperpolarizability. We suggest that a combination of wire geometry and confinement effects can lead to artificial systems with ultra-large nonlinear response, which can be potentially made using known nanofabrication techniques.

The photorefractive effect in photoconductive ferroelectric liquid crystals (FLCs) that contain photoconductive chiral compounds was investigated. A series of novel photoconductive chiral compounds were synthesized. Terthiophene compounds with four chiral structures were chosen as the photoconductive chiral compounds and 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 FLCs containing the photoconductive chiral compound exhibit a large gain coefficient of over 800 cm^-1 and a fast response time of 8 ms.

We present here the optimized photorefractive polymeric composite (PPC) film based on simple materials of poly(N-vinylcarbazole) (PVCz)/4-azacycloheptylbenzylidenemalononitrile (7-DCST)/N-ethylcarbazole (ECz)/2,4,7-trinitro-9- fluorenone (TNF). The-simple-materials-based PPC was optimized from the photorefractive characteristics of PPCs with PVCz/7-DCST/ECz/TNF (the best ratio: 44/35/20/1 wt %) that changed molecular weights of PVCz: 23,000, 100,000, 290,000, 370,000, 520,000, 780,000, 860,000, and < 1,000,000 g mol^-1. Diffraction efficiency and photorefractive response time of the PPC film with M_w: 860,000 of PVCz/7-DCST/ECz/TNF (44/35/20/1 wt %) showed an appropriate photorefractive performance, which was determined as the optimized PPC. It is notable that the optimized PPC could be easily obtained from relatively inexpensive materials; furthermore, the required nonlinear optical dye 7-DCST could be synthesized in high-yield. We believe that the PPCs based on PVCz or other polyvinylcarbazole derivatives will be the potential composite for creating holographic displays because of low fabrication costs, and be of benefit to developing technologies.

An azo-carbazole dye, 3-[(4-Nitrophenyl)azo]-9H-carbazole-9-ethanol (NACzEtOH), and its relatives doped in polyacrylate films have been known to show ‘photorefractive’ effect without external electric field even in symmetric optical alignment. We have already observed strong energy transfer due to phase-shifted grating by two-beam coupling experiments made for NACzEtOH doped PMMA films. Although the operation mechanism is still unknown, the high efficiency of diffraction is very promising for the application to real-time holography. For the convenience of analysis, we modified Kogelnik’s theory for thick grating by correcting the constraint condition and applied it to evaluate refractive index modulation and other parameters quantitatively. In order to clarify the operation mechanism, we conducted the writing and erasing of gratings by using red and green laser beams and analyzed the diffraction magnitude and response dynamics, showing that the response time strongly depended on the writing wavelength, and that the grating formation and its phase shift were not always synchronized.

The synthesis of new small-molecule amine compounds is presented. The triamino derivative with ethyl substituents possesses better processability in alcoholic solvent and was utilized as an electron-injection layer in organic light-emitting diodes (OLEDs) in order to avoid interlayer mixing. The performance of the resulting OLEDs that consisted of an Al cathode and a solution-processed molecular green-emitting layer is shown to depend on the thickness of the small-molecule electron-injection interlayer and is preliminarily discussed.

Several organic dyes have been shown to self heal when doped in a polymer matrix. Most measurements to date use optical absorbance, amplified spontaneous emission, or digital imaging as a probe. Each method determines a subset of the relevant parameters. We have constructed a white light interferometric microscope, which measures the absorption spectrum and change in refractive index during decay and recovery simultaneously at multiple points in the material. We report on preliminary measurements and results concerning the microscopes spatial resolution.

We present here the enhanced photorefractive performance and dynamic holographic image of poly(4-diphenylamino)styrene (PDAS)-based photorefractive polymeric composites (PPCs). PDAS and FDCST were synthesized as a photoconductive polymer and a nonlinear optical (NLO) dye, respectively. PPC films including PDAS, TPA (or ECZ), FDCST, and PCBM were investigated. The photorefractive quantities of the PDAS-based PPCs were measured by a degenerate four-wave mixing (DFWM) technique. Additionally, the dynamic holographic images were recorded through an appropriate PDAS-based PPC. Those dynamic holographic images clearly duplicate the original motion with high-speed quality. The present approach provides a promising candidate for the future application of dynamic holographic displays.

A new class of photorefractive (PR) composite based on a fully functionalized polymer with high phase-stability is reported. The polymer containing nonlinear optical (NLO) chromophore and charge-transporting carbazole moieties is synthesized by a polymer analogous reaction. The polymer is doped with plasticizer, NLO dye and sensitizer to fabricate the PR composite. The NLO dye is the same as the NLO chromophore moiety in the polymer side chain. PR performance of the composite is evaluated by degenerated four wave mixing and two-beam coupling measurements. Diffraction efficiency of 30% at relatively low applied electric field of 45 Vμm^-1 is achieved. Despite a high concentration of NLO dye, the composites show good stability for a long period without phase separation.

Polyethylene-glycol (PEG) exhibited bistable transmission characteristics (transparent or opaque) in heating (melting) and cooling (freezing) processes. The bistable temperature range depended on the molecular weight and extended when different types of PEGs were mixed. For example, when PEGs with molecular weights of 300 and 2000 were mixed, the bistability took place in the 2–38 °C range. This phenomenon was used to fabricate a bistable optical fiber switch in which the mixed PEG was put in the gap between the ends of two polymer fibers. The bistable transmission property was demonstrated by controlling the device temperature with a Peltier element.

Crosslinkable polymer with side-chain system was investigated to increase the content of NLO chromophores and improve the stability of oriented chromophores. In this work, a series of crosslinkable copolymers which beared different concentrations of chromophores with the tricyanofurane (TCF) acceptor and a kind of crosslinkable copolymers beared chromophores with dendritic tricyanopyrroline (TCP) acceptor were successfully synthesized and characterized. The crosslinked EO polymers which beared chromophores with the tricyanofurane (TCF) acceptor revealed the highest EO coefficient (r₃₃) of 47.0 pm/V at 1310 nm, which was similar with the r33 of uncrosslinked systems. Compared to the uncrosslinked EO polymer systems, the crosslinked ones exhibited significantly enhanced temporal stability. Keywords: Nonlinear optics; Crosslinkable system; Chromophore-containing copolymers; Side-chain; Crosslinking reaction; Thermally stable polymer

In order to minimize the intermolecular electrostatic interactions and effectively translate high value of chromophore into macroscopic electro-optical (EO) coeffcient (r33), the shape-modification of aniline-pyrroline (TCP) chromophore by combining three kinds of dendritic groups respectively to the N atom of pyrroline acceptor produced three kinds of dendritic chromophores. Their spherical structures can minimize intermolecular electrostatic interactions, and thus the poling efficience was higher than the chromophores without dendritic groups when chromophores as a guest in the host polymer APC. A large electro-optical (EO) coefficient was achieved as high as 75 pm/V at 1315 nm with 9% chromophores loading in APC film. On the basis of the above TCP chromophores, two kinds of novel molecular glasses based on self-assembly dendritic chromophores are also designed and synthesized as second-order nonlinear optical (NLO) materials, which named ETO and ETF. The NLO chromophore glasses ETO and ETF showed excellent filmforming ability by themselves. Their glass transition temperatures (T_g) were determined at 41℃ and 39 ℃, respectively. The in-situ second harmonic generation (SHG) measurement revealed the resonant electro-optical (EO) coefficient (d33) values of 38 and 32 pm/V for the poled films of ETO and ETF, respectively. The results indicate molecular glasses provide a new possible way different from the conventional polymer approach to prepare second-order NLO materials.

In this study, a series of acryloyloxy-substituted azobenzene derivatives, 3-(tert-butyl)-4,4’-bisacryoloxy-azobenzene (tBu-Azo-AO), 3-(tert-butyl)-4,4’-bis[3-(acryoloxy)propoxy]-azobenzene (tBu-Azo-AO3) and 3-(tert-butyl)-4,4’-bis[6-(acryoloxy)hexyloxy]-azobenzene (tBu-Azo-AO6) were synthesized and employed as monomers to prepare polymer films by copolymerizing dipentaerythritol hexaacrylate (DPE-6A) and methyl methacrylate (MMA), respectively. When exposed to a nanosecond laser beam at the wavelength of 355 nm, ultraviolet-visible (UV-Vis) absorption spectra of the resultant polymer films with different irradiation time were monitored. On the basis of the absorbance of the π-π* electronic transition, the kinetics of trans-to-cis photoisomerization of three kinds of azobenzene moieties were demonstrated and found to be influenced by both the pump energy and azobenzene concentration.

Two-photon excitation for creating 3D structure has widely been studied because this technique can be applied for various fields, for example creating of optoelectronic device and micro-optics. This technique was first used for photoresist. However it was used as method to create metal structure which has functionality like enhancement of electromagnetic field. We have already reported the 3D microstructures with submicron scale linewidth fabricated through two-photon photo-reduction of silver ions in poly(N-vinylpyrrolidone) (PVP) matrix using a femtosecond laser system. We studied the morphological behavior of two-dimensional silver structures fabricated by two-photon excitation of silver nitrate in PVP matrix to further analyze. The silver structure near the cover slip was fabricated on a microscope stage. Obtained structure was investigated using an atomic force microscopy (AFM), a scanning electron microscopy (SEM), an energy dispersive X-ray spectrometry (EDX), and an X-ray photoelectron spectroscopy (XPS). AFM measurement showed the photo-induced structure on a cover slip. EDX and XPS measurements showed that the silver ion was photo-reduced and the photo-reduced silver was interacted with PVP, respectively. We assume that the silver makes a cluster and the cluster is covered by PVP chain.

The photodegradation and recovery process in anthraquinone chromophores have been characterized using am­ plified spontaneous emission (ASE) in several Anthraquinone derivatives doped in poly(methyl methacrylate) (PMMA). To understand the mechanisms of self healing in disperse orange 11 (DOll) doped in PMMA and the role of the host polymer, we investigated reversible photodegradation in DOll doped in copolymer composed of different percentages of methyl methacrylate (MMA) and Styrene. The results suggest that the host polymer is an important factor in determining the distribution of domain sizes of dye molecules.