Study of the nonlinear optical properties of a crosslinkable chromophore for use in guest host polymer films

A guest/host material system in which the guest molecule is a functionalized, optically nonlinear, chromophore is described. A verification of the crosslinking process, an assessment of the nonlinear properties of the chromophore, using Solvatochromic methods, and an investigation of the electric field induced molecular orientation using second-harmonic generation are included.

Evidence of dispersion relations for the nonlinear response of the Lorenz 63 system

Along the lines of the nonlinear response theory developed by Ruelle, in a previous paper we have proved under rather general conditions that Kramers-Kronig dispersion relations and sum rules apply for a class of susceptibilities describing at any order of perturbation the response of Axiom A non equilibrium steady state systems to weak monochromatic forcings. We present here the first evidence of the validity of these integral relations for the linear and the second harmonic response for the perturbed Lorenz 63 system, by showing that numerical simulations agree up to high degree of accuracy with the theoretical predictions. Some new theoretical results, showing how to derive asymptotic behaviors and how to obtain recursively harmonic generation susceptibilities for general observables, are also presented. Our findings confirm the conceptual validity of the nonlinear response theory, suggest that the theory can be extended for more general non equilibrium steady state systems, and shed new light on the applicability of very general tools, based only upon the principle of causality, for diagnosing the behavior of perturbed chaotic systems and reconstructing their output signals, in situations where the fluctuation-dissipation relation is not of great help.

Surface modification and crystallization of the BaO-B2O3-SiO2 glassy system using CO2 laser irradiation

The surface modification and crystallization process of BaO-B2O3-SiO2 glass compositions when exposed to CO2 laser irradiation was evaluated as a function of the laser power, irradiation time and surface condition. The glass surface was modified by the application of laser power exceeding 0.40 W and an irradiation time of more than 300 s. Micro-Raman and X-ray diffraction measurements revealed at high laser power the formation of beta-BaB2O4 (beta-BBO) crystalline phase. The crystallization of the irradiated region was enhanced when beta-BBO micrometer sized particles were dispersed on the surface of the glass sample. The intensity of the second harmonic generation observed in the crystallized region was found to depend mainly on the condition of the glassy surface prior to glass irradiation. (C) 2007 Elsevier B.V. All rights reserved.

Avaliação do apêndice atrial esquerdo pela ecocardiografia transtorácica com imagem harmônica após evento neurológico agudo

Introdução: Embora a imagem com segunda harmônica esteja largamente disponível na maioria dos aparelhos de ultra-sonografia, sua acurácia para avaliar a morfologia e a função do apêndice atrial esquerdo (AAE) permanece precariamente caracterizada. Objetivos: Explorar o desempenho diagnóstico da ecocardiografia transtorácica com segunda harmônica (ETTsh) na avaliação do AAE após eventos neurológicos agudos. Métodos: Realizamos um estudo transversal em pacientes com eventos neurológicos isquêmicos agudos, encaminhados para realização de ETTsh e Ecocardiografia Transesofágica (ETE). As análises da área longitudinal máxima e do pico da velocidade de esvaziamento de fluxo do AAE foram realizadas por observadores cegos. Resultados: Foram avaliados 51 pacientes (49% femininas, 62 ± 12 anos) com eventos neurológicos isquêmicos agudos. Contraste ecocardiográfico espontâneo foi observado em 11 (22%) pacientes no AE, em 7(14%) no AAE e em 3 (6%) na aorta torácica descendente. Trombo no AAE foi identificado em apenas 2 (4%) pacientes. O mapeamento e a análise do AAE foi factível na maioria dos casos (98%), tanto para o estudo com Doppler quanto para avaliação da área do AAE. Observamos uma associação positiva e significativa entre o ETTsh e o ETE, tanto para a avaliação das velocidades máximas de esvaziamento do AAE (r=0,63; p<0,001) quanto para a área longitudinal máxima do AAE (r=0,73; p<0,001). Ademais, todos os pacientes com trombos no AAE ou contraste espontâneo (n=7) tiveram velocidade de esvaziamento inferior a 50 cm/s no mapeamento transtorácico (valor preditivo negativo de 100%). Na análise multivariada ajustada para diversos potenciais preditores transtorácicos de risco, a velocidade máxima de esvaziamento do AAE permaneceu independentemente associada com trombos no AAE ou contraste espontâneo. Conclusão: ETTsh pode fornecer informações relevantes a respeito da morfologia e dinâmica do AAE. Em particular, pacientes com velocidades altas de esvaziamento do AAE podem não necessitar de avaliação adicional com ETE.

Localized modes in chi((2)) media with PT-symmetric localized potential

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Violet-blue emissions due to frequency up-conversion in Nd3+-doped fluoroindate glasses

We report the observation of intense frequency up-conversion in Nd3+-doped fluoroindate glasses pumped by the second harmonic of a cw mode-locked Nd: YAG laser. Mechanisms for generating the observed emissions are discussed.

Geração de segundo harmônico em vidros teluritos TeO2 – LiNbO3

Pós-graduação em Ciência dos Materiais - FEIS

Chromatic spatial contrast sensitivity estimated by visual evoked cortical potential and psychophysics

The purpose of the present study was to measure contrast sensitivity to equiluminant gratings using steady-state visual evoked cortical potential (ssVECP) and psychophysics. Six healthy volunteers were evaluated with ssVECPs and psychophysics. The visual stimuli were red-green or blue-yellow horizontal sinusoidal gratings, 5^° × 5^°, 34.3 cd/m2 mean luminance, presented at 6 Hz. Eight spatial frequencies from 0.2 to 8 cpd were used, each presented at 8 contrast levels. Contrast threshold was obtained by extrapolating second harmonic amplitude values to zero. Psychophysical contrast thresholds were measured using stimuli at 6 Hz and static presentation. Contrast sensitivity was calculated as the inverse function of the pooled cone contrast threshold. ssVECP and both psychophysical contrast sensitivity functions (CSFs) were low-pass functions for red-green gratings. For electrophysiology, the highest contrast sensitivity values were found at 0.4 cpd (1.95 ± 0.15). ssVECP CSF was similar to dynamic psychophysical CSF, while static CSF had higher values ranging from 0.4 to 6 cpd (P < 0.05, ANOVA). Blue-yellow chromatic functions showed no specific tuning shape; however, at high spatial frequencies the evoked potentials showed higher contrast sensitivity than the psychophysical methods (P < 0.05, ANOVA). Evoked potentials can be used reliably to evaluate chromatic red-green CSFs in agreement with psychophysical thresholds, mainly if the same temporal properties are applied to the stimulus. For blue-yellow CSF, correlation between electrophysiology and psychophysics was poor at high spatial frequency, possibly due to a greater effect of chromatic aberration on this kind of stimulus.

PT-symmetric coupler with chi((2)) nonlinearity

We introduce the notion of a PT-symmetric dimer with a chi((2)) nonlinearity. Similarly to the Kerr case, we argue that such a nonlinearity should be accessible in a pair of optical waveguides with quadratic nonlinearity and gain and loss, respectively. An interesting feature of the problem is that because of the two harmonics, there exist in general two distinct gain and loss parameters, different values of which are considered herein. We find a number of traits that appear to be absent in the more standard cubic case. For instance, bifurcations of nonlinear modes from the linear solutions occur in two different ways depending on whether the first-or the second-harmonic amplitude is vanishing in the underlying linear eigenvector. Moreover, a host of interesting bifurcation phenomena appear to occur, including saddle-center and pitchfork bifurcations which our parametric variations elucidate. The existence and stability analysis of the stationary solutions is corroborated by numerical time-evolution simulations exploring the evolution of the different configurations, when unstable.

Frequency upconversion involving triads and quartets of ions in a Pr3+/Nd3+ codoped fluoroindate glass

Frequency upconversion (UC) processes involving energy transfer (ET) among Nd 3+ and Pr 3+ ions in a fluoroindate glass are reported. In a first experiment, the excitation of Pr 3+ [transition 3H 4→ 1D 2] and of Nd 3+ [transition 4I 9/2→( 2G 7/2+ 4G 5/2)] was achieved with a dye laser operating in the 575-590 nm range. In a second experiment, the Nd 3+ ions were excited with the second harmonic of a Nd: YAG laser at 532 nm. The ET processes leading to UC in both experiments were studied by monitoring the blue fluorescence decay at 480 nm due to the transition 3P 0→ 3H 4 in Pr 3+. In the more relevant UC process, quartets of ions (Nd-Nd-Pr-Pr) are excited due to absorption of three laser photons by two Nd 3+ ions which transfer their energy to two Pr 3+ ions. Each Pr 3+ ion promoted to the 3P 0 level decays to the ground state emitting one photon in the blue region. This conclusion was achieved investigating the dependence of the UC fluorescence intensity as a function of laser intensity, samples concentrations, and temporal behavior of the UC signal. Other UC processes involving nonisoionic groups of three ions are also reported. © 2002 American Institute of Physics.

Heterochromatic Flicker Electroretinograms Reflecting Luminance and Cone Opponent Activity in Glaucoma Patients

PURPOSE. To measure heterochromatic flicker electroretinograms (ERGs) at high (36 Hz) and intermediate (12 Hz) temporal frequencies to evaluate luminance and cone opponent responses, respectively, in glaucoma eyes with (perimetric) and without (preperimetric) visual field defects. METHODS. Flicker ERGs were recorded from one randomly chosen dilated eye of 32 patients (mean age, 61 +/- 11 years; 15 men, 17 women) from the Erlangen Glaucoma Registry and from 24 healthy volunteers (mean age, 43 +/- 11 years; 14 men, 10 women). Red and green light-emitting diodes in a Ganzfeld stimulator were sine wave-modulated in counterphase. The responses were measured at 36 Hz, the frequency at which ERGs reflect activity of the luminance pathway, and at 12 Hz, the frequency at which ERGs reflect chromatic activity. RESULTS. Response amplitudes were similar in glaucoma patients and controls. Phase differences were observed in patients with visual field defects (perimetric) compared with the control group at 36 and 12 Hz in the first harmonic and second harmonic responses. Patients without visual field defects (preperimetric) showed phase differences for the second harmonic component at 36 Hz. No age effect on response amplitudes and phases was found in any of the subject groups (controls and patients). CONCLUSIONS. The responses displayed phase differences but not amplitude differences in perimetric glaucoma patients at both 36 and 12 Hz, suggesting that both magnocellular and parvocellular pathways are affected. Preperimetric glaucoma patients also showed phase differences. The response phase may be sensitive to early dysfunction of the inner retina. (ClinicalTrials.gov number, NCT00494923.) (Invest Ophthalmol Vis Sci. 2011;52:6757-6765) DOI:10.1167/iovs.11-7538

Solar-Terrestrial Signal Record in Tree Ring Width Time Series from Brazil

This work investigates the behavior of the sunspot number and Southern Oscillation Index (SOI) signal recorded in the tree ring time series for three different locations in Brazil: Humaita in Amaznia State, Porto Ferreira in So Paulo State, and Passo Fundo in Rio Grande do Sul State, using wavelet and cross-wavelet analysis techniques. The wavelet spectra of tree ring time series showed signs of 11 and 22 years, possibly related to the solar activity, and periods of 2-8 years, possibly related to El Nio events. The cross-wavelet spectra for all tree ring time series from Brazil present a significant response to the 11-year solar cycle in the time interval between 1921 to after 1981. These tree ring time series still have a response to the second harmonic of the solar cycle (5.5 years), but in different time intervals. The cross-wavelet maps also showed that the relationship between the SOI x tree ring time series is more intense, for oscillation in the range of 4-8 years.

Functional photoactive and electroactive nanodevices

Most of current ultra-miniaturized devices are obtained by the top-down approach, in which nanoscale components are fabricated by cutting down larger precursors. Since this physical-engineering method is reaching its limits, especially for components below 30 nm in size, alternative strategies are necessary. Of particular appeal to chemists is the supramolecular bottom-up approach to nanotechnology, a methodology that utilizes the principles of molecular recognition to build materials and devices from molecular components. The subject of this thesis is the photophysical and electrochemical investigation of nanodevices obtained harnessing the principles of supramolecular chemistry. These systems operate in solution-based environments and are investigated at the ensemble level. The majority of the chemical systems discussed here are based on pseudorotaxanes and catenanes. Such supramolecular systems represent prototypes of molecular machines since they are capable of performing simple controlled mechanical movements. Their properties and operation are strictly related to the supramolecular interactions between molecular components (generally photoactive or electroactive molecules) and to the possibility of modulating such interactions by means of external stimuli. The main issues addressed throughout the thesis are: (i) the analysis of the factors that can affect the architecture and perturb the stability of supramolecular systems; (ii) the possibility of controlling the direction of supramolecular motions exploiting the molecular information content; (iii) the development of switchable supramolecular polymers starting from simple host-guest complexes; (iv) the capability of some molecular machines to process information at molecular level, thus behaving as logic devices; (v) the behaviour of molecular machine components in a biological-type environment; (vi) the study of chemically functionalized metal nanoparticles by second harmonic generation spectroscopy.

Nanoscopic studies of conjugated polymer blends by (electric) scanning probe microscopy

Conjugated polymers and conjugated polymer blends have attracted great interest due to their potential applications in biosensors and organic electronics. The sub-100 nm morphology of these materials is known to heavily influence their electromechanical properties and the performance of devices they are part of. Electromechanical properties include charge injection, transport, recombination, and trapping, the phase behavior and the mechanical robustness of polymers and blends. Electrical scanning probe microscopy techniques are ideal tools to measure simultaneously electric (conductivity and surface potential) and dielectric (dielectric constant) properties, surface morphology, and mechanical properties of thin films of conjugated polymers and their blends.rnIn this thesis, I first present a combined topography, Kelvin probe force microscopy (KPFM), and scanning conductive torsion mode microscopy (SCTMM) study on a gold/polystyrene model system. This system is a mimic for conjugated polymer blends where conductive domains (gold nanoparticles) are embedded in a non-conductive matrix (polystyrene film), like for polypyrrole:polystyrene sulfonate (PPy:PSS), and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). I controlled the nanoscale morphology of the model by varying the distribution of gold nanoparticles in the polystyrene films. I studied the influence of different morphologies on the surface potential measured by KPFM and on the conductivity measured by SCTMM. By the knowledge I gained from analyzing the data of the model system I was able to predict the nanostructure of a homemade PPy:PSS blend.rnThe morphologic, electric, and dielectric properties of water based conjugated polymer blends, e.g. PPy:PSS or PEDOT:PSS, are known to be influenced by their water content. These properties also influence the macroscopic performance when the polymer blends are employed in a device. In the second part I therefore present an in situ humidity-dependence study on PPy:PSS films spin-coated and drop-coated on hydrophobic highly ordered pyrolytic graphite substrates by KPFM. I additionally used a particular KPFM mode that detects the second harmonic electrostatic force. With this, I obtained images of dielectric constants of samples. Upon increasing relative humidity, the surface morphology and composition of the films changed. I also observed that relative humidity affected thermally unannealed and annealed PPy:PSS films differently. rnThe conductivity of a conjugated polymer may change once it is embedded in a non-conductive matrix, like for PPy embedded in PSS. To measure the conductivity of single conjugated polymer particles, in the third part, I present a direct method based on microscopic four-point probes. I started with metal core-shell and metal bulk particles as models, and measured their conductivities. The study could be extended to measure conductivity of single PPy particles (core-shell and bulk) with a diameter of a few micrometers.

Preparation of cold Mg + ion clouds for sympathetic cooling of highly charged ions at SPECTRAP

Die Elektronen in wasserstoff- und lithium-ähnlichen schweren Ionen sind den extrem starken elektrischen und magnetischen Feldern in der Umgebung des Kerns ausgesetzt. Die Laserspektroskopie der Hyperfeinaufspaltung im Grundzustand des Ions erlaubt daher einen sensitiven Test der Quantenelektrodynamik in starken Feldern insbesondere im magnetischen Sektor. Frühere Messungen an wasserstoffähnlichen Systemen die an einer Elektronenstrahl-Ionenfalle (EBIT) und am Experimentierspeicherring (ESR) der GSI Darmstadt durchgeführt wurden, waren in ihrer Genauigkeit durch zu geringe Statistik, einer starken Dopplerverbreiterung und der großen Unsicherheit in der Ionenenergie limitiert. Das ganze Potential des QED-Tests kann nur dann ausgeschöpft werden, wenn es gelingt sowohl wasserstoff- als auch lithium-ähnliche schwere Ionen mit einer um 2-3 Größenordnung gesteigerten Genauigkeit zu spektroskopieren. Um dies zu erreichen, wird gegenwärtig das neue Penningfallensystem SPECTRAP an der GSI aufgebaut und in Betrieb genommen. Es ist speziell für die Laserspektroskopie an gespeicherten hochgeladenen Ionen optimiert und wird in Zukunft von HITRAP mit nierderenergetischen hochgeladenen Ionen versorgt werden.rnrnSPECTRAP ist eine zylindrische Penningfalle mit axialem Zugang für die Injektion von Ionen und die Einkopplung eines Laserstrahls sowie einem radialen optischen Zugang für die Detektion der Fluoreszenz. Um letzteres zu realisieren ist der supraleitende Magnet als Helmholtz-Spulenpaar ausgelegt. Um die gewünschte Genauigkeit bei der Laserspektroskopie zu erreichen, muss ein effizienter und schneller Kühlprozess für die injizierten hochegeladenen Ionen realisiert werden. Dies kann mittels sympathetischer Kühlung in einer lasergekühlten Wolke leichter Ionen realisiert werden. Im Rahmen dieser Arbeit wurde ein Lasersystem und eine Ionenquelle für die Produktion einer solchen 24Mg+ Ionenwolke aufgebaut und erfolgreich an SPECTRAP in Betrieb genommen. Dazu wurde ein Festkörperlasersystem für die Erzeugung von Licht bei 279.6 nm entworfen und aufgebaut. Es besteht aus einem Faserlaser bei 1118 nm der in zwei aufeinanderfolgenden Frequenzverdopplungsstufen frequenzvervierfacht wird. Die Verdopplerstufen sind als aktiv stabilisierte Resonantoren mit nichtlinearen Kristallen ausgelegt. Das Lasersystem liefert unter optimalen Bedingeungen bis zu 15 mW bei der ultravioletten Wellenlänge und erwies sich während der Teststrahlzeiten an SPECTRAP als ausgesprochen zuverlässig. Desweiteren wurde eine Ionequelle für die gepulste Injektion von Mg+ Ionen in die SPECTRAP Falle entwickelt. Diese basiert auf der Elektronenstoßionisation eines thermischen Mg-Atomstrahls und liefert in der gepulsten Extraktion Ionenbündel mit einer kleinen Impuls- und Energieverteilung. Unter Nutzung des Lasersystems konnten damit an SPECTRAP erstmals Ionenwolken mit bis zu 2600 lasergekühlten Mg Ionen erzeugt werden. Der Nachweis erfolgte sowohl mittels Fluoreszenz als auch mit der FFT-ICR Technik. Aus der Analyse des Fluoreszenz-Linienprofils lässt sich sowohl die Sensitivität auf einzelne gespeicherte Ionen als auch eine erreichte Endtemperatur in der Größenordnung von ≈ 100 mK nach wenigen Sekunden Kühlzeit belegen.